This collection includes power supplies suitable for almost any HeNe tube or laser head with an optical output power from .5 to 35 mW - and beyond. See the section: HeNe Laser Power Supply Selection Guide to identify the one (or more!) that may be most suitable for your collection of HeNe tubes as-is or with minor modifications. And, most of these circuits can be easily modified for your specific needs: For example, a very high power HeNe tube or a weird laser requiring multiple power supply feeds and separate starters
CAUTION: Although not explicitly shown in some schematics, accessible parts of the power supply and laser head should be connected to earth ground via a three-prong power cord. This protects against a dangerous shock hazard should there be a fault condition and also eliminates any possibility of even a slight tingle due to capacitive coupling of high voltages. Where such a problem is detected with an existing power supply, there is likely an insulation or wiring problem in either the supply or laser head which should be corrected. If a ground is simply added to the laser head case, the power supply may fail due to a problem elsewhere.
CAUTION: Where a ground was not shown on some of the commercial HeNe laser power supplies, its schematic may show one in the logical place assuming an Alden-type (2 wire) connection to the laser head. However, a few commercial power supplies used 3 wires with a separate ground.
WARNING: There are so many complete HeNe laser power supply schematics in this one document that their combined mass may cause a singularity to form inside your computer. :-) The lawyers made me include this statement - honest. ;-)
Note: For an explanation of the meanings of various designations like X, Y, HV+, Tube-, etc., used in these schematics, see the section: Notation used in HeNe Laser Power Power Supply Diagrams and Schematics.
Desig- Power Regu- Modu- <-- Tube Output Power (mW) -->
nation Input lation lation - .5 1 2 3 5 7 10 15 25 35 +
-----------------------------------------------------------------
ES-HL1 AC - - ********
LS-220 AC L - ******
ML-360 AC - - ********
ML-420 AC - - ******
ML-620 AC L - ******
ML-660 AC L - *******
ML-920 AC L - ****
SP-130 AC - - ****
SP-155 AC L - ******
SP-132 AC - - *****
SP-132M AC - - *****
SP-233 AC - - *****
SP-233M AC - - *****
SP-234 AC - - *****
SP-235 AC - - *****
SP-247 AC L - ********
SP-248 AC L - ****
SP-249 AC L - ****
SC-760 AC L - ***
JD-PS1 AC L - *****
AT-PS0 AC L - ***
AT-PS1 AC L - ***
AT-PS2B AC L - *******
AT-PS2A-X AC L V *****
SP-255 AC L - *******
SP-256 AC L - ********
SP-207 AC L - *********
SP-261 AC S - ****
LP-HL1 AC L - *****
LP-HL2 AC L - *****
HK-HI1 AC - V *****
SG-HL1 AC - - *********
SG-HL2 AC - - ********
SG-HL3 AC - - ***********
KC-HL1 AC - - ************
TF-HL1 AC L - *********
IC-HI1 DC S P ******
IC-HI2 AC S P ******
IC-HI3 DC S - ******
EG-LPS1 DC - - ******
ML-600 AC D - ******
ML-800 AC D - ******
ML-811 DC S - ******
ML-855 AC D - *****
ML-869 AC D/L V ****
HU-HL1 DC D - ****
YA-234 DC S - ***
LD-BS1 DC S - *******
SG-HI1 DC - - ********
SG-HI2 DC - - ********
SG-HI3 DC S - ********
SG-HI4 DC - - ********
SG-HM1 DC S - **************
SG-HM2 DC S - ********
DP-HI4 DC - - ********
KC-HI1 DC - - ********
YA-HI1 DC - - ******
Notes:
Many of these designs are quite old since modern commercial units tend toward inverter designs since they can be more compact and have higher efficiency. Unfortunately, modern inverter types are nearly always potted in Epoxy and impossible to disassemble and analyze. However, AC Line operated power supplies will drive HeNe tubes just as well as fancy inverters and are somewhat easier to construct and troubleshoot (especially for high power designs).
The line side circuitry is not shown for any of these. See the section: AC Input Circuitry for HeNe Laser Power Supplies for details.
Those with "Sam's" in the title were built using mostly scrounged parts like tube type TV power transformers that had been minding their own business in various storage cabinets often for many many years. My total cost for the remaining components for each power supply was generally not over $5.
They are presented in approximate order of output capability which is why the sequence of manufacturer and model number may appear somewhat random. :)
Estimated specifications (ES-HL1):
This is the power supply I traced out and measured which is in an Edmund Scientific 0.5 mw. Laser circa probably around 1975. I bought a 1 mW. tube (1986) when the old one broke. It is still running just fine. I think it is a rather clever design and I don't think they come any simpler.
X C5 C7
+-------------------||-----------+----------||-----------+---o HV+
| D7 D8 | D9 D10 D11 D12 | R5
| +--|>|-|>|--+--|>|-|>|--+--|>|-|>|--+--/\/\--+
| D1 D2 D3 Y | C6 | 18K |
+---+--|>|-|>|-|>|--+----+----------||-----------+ 1W / R6
||( | | | \ 33K
||( | C1 +_|_ / R1 / 1W
||( | 4.7uF --- \ 1M |
||( | 450V - | / / R7
||( | | | \ 33K
||( | +----+ W Transformer: 650 VRMS, 20 mA / 1W
||( | | | (primary not shown) |
||( | C2 +_|_ / R2 / R8
||( | 4.7uF --- \ 1M \ 33K
||( | 450V - | / / 1W
||( T | | | D1-D7: 1N4007 or similar |
+-------------------+----+ / R9
| | | \ 33K
| C3 +_|_ / R3 C1-C4: 4.7uF, 450V / 1W
| 4.7uF --- \ 1M C5-C7: .001uF, 2kV |Tube+
| 450V - | / .-|-.
| | | R1-R4: 1M, 1W | | |
| +----+ Z R5-R9: (ballast, 18K+4x33K, 1W) | |
| | | LT1 | |
| C4 +_|_ \ R4 | |
| 4.7uF --- / 1M ||_||
| 450V - | \ '-|-'
| | | |Tube-
+--|<|-|<|-|<|--+----+--------------------------------------------+---o
D4 D5 D6 HV-
Note that there are no equalizing resistors across the 1N4007s. While I have
been building similar supplies without them, the use of 10M resistors across
each diode to equalize the voltage drops is recommended.
The 650 V transformer output feeds a voltage doubler (D1 and D2 and C8 to C11) resulting in about 1,750 V across all the electrolytics. (Slightly less than 2 times the peak value of 650 VRMS.) The voltage multiplier consisting of D7 to D12 and C5 through C7 generates up to 6 times the transformer's peak voltage or around 5,300 V (the actual value will depend on various factors including stray capacitance and other losses). See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
The 150K ballast resistor is actually constructed from 4 - 33K resistors and one 18K resistor in series. It doesn't have to be, but this is convenient and allows the ballast to be changed easily (or just tap off the appropriate point for your tube. My notes show 600 V across the ballast resistor-combo.
The ballast resistor should be located close to the tube with as short a lead as possible and as little capacitance to surroundings as possible. The tube needs to see a high impedance source. This isn't super critical, but keep the wire down to 1 to 3 inches and the first few resistors away from any case or ground material.
Since there is no active regulator, the tube current will depend on the power line voltage and other factors like temperature. However, the relatively large ballast resistor in this power supply should minimize excessive variation.
There is also a GAMMEX HeNe laser power supply that appears virtually identical to this one. I don't have a sample but from a photo of the circuit board, the only obvious difference would appear to be the use of 6, 27K, 2 W resistors for the ballast. All the other parts and even the part values appear identical. So GAMMEX probably copied the circuit and adjusted the value of the ballast resistance until the desired current was obtained. :)
This diagram is not yet complete in the area of the control circuit in the lower right corner since it is difficult to trace it without removing the PCB. In particular, there are at least two tantalum caps and other components which contribute to the low noise performance.
The secondary voltage of T1 was guessed. :) There were no part numbers on the PCB so these are arbitrary.
The HeNe laser tube and its ballast resistor are not shown here. The ballast is a single 7 or 10 W resistor mounted on standoffs in the laser head. But there is also a thermal regulator in series with the anode of the tube. It implements a closed-loop feedback scheme using only the anode current with no other connections to stabilize the temperature of the OC mirror.
X C7 C8 C9
+------------||----------------+------||-------+------||-------+ HV+ o
| CR3 | CR4 CR5 | CR6 CR7 | CR8 |
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+
T1 | CR1 Y R7 55 | C10 | C11 | C12 |
+--+--|>|---+----+--/\/\--+------||-------+------||-------+------||-------+
||( | | |
||( | C1 +_|_ / R1 +---------+----+---o Tube-
||( | 10uF --- \ 499K T1: 1,200 VRMS, 20mA _|_ | |
||( | 500V - | / (primary not shown) _V_ CR9 / |
||( | | | | R7 \ |
||( | +----+ CR1-CR6: 6kV + 120K / |
||( | | | _|_ | |/ C Q1
||( | C2 +_|_ / R2 C1-C6: 10uF, 500V _V_ CR10 +--| D40V4
||( | 10uF --- \ 499K C7-C9: 470pF, 6kV _|_ | |\ E
||( | 500V - | / C10-C12: 6800 pF, 6kV //// R8 / |
||( | | | 1N4007 120K \ |
||( | +----+ (x2) 2W / |
||( | | | | |/ C Q2
||( | C3 +_|_ / R3 +--| D40V4
||( | 10uF --- \ 499K | |\ E
||( | 500V - | / R9 / |
||( | | | 120K \ |
+--|--------+----+ 2W / |
| | | | |/ C Q3
| C4 +_|_ / R4 +--| D40V4
| 10uF --- \ 499K | |\ E
| 500V - | / R10 / |
| | | 120K \ |
| +----+ R11 27.2K | |/ C Q4
| | | +---/\/\----+--| D40V4
| C5 +_|_ / R5 | | |\ E
| 10uF --- \ 499K | |/ E |
| 500V - | / +--------+---------| |
| | | | +---+ Q5 |\ C |
| +----+ ZD1 _|_, | | ZD2 PNP | |
| | | 1N4099 '/_\ | _|_, +----+
| C6 +_|_ / R6 6.8V | | '/_\ R12 |
| 10uF --- \ 499K (x2) +---+ | 5K 1W |
| 500V - | / Adjust +---/\/\----------+
| | | | |
+--|<|---+----+-----------------------------+----+
CR2
Estimated specifications (ML-360):
This power supply is almost identical to the ES-HL1, above, and may indeed just be a variation on it since Edmund Scientific very likely sold Metrologic lasers or clones under their own brand name.
I replaced the original quite dead soft-seal HeNe tube with a Uniphase 098-2 which is rated at 2 mW so the output is probably twice that of the original laser. No changes were required to satisfy the 4.5 to 5 mA current recommended for the 098-2. The set of ballast resistors is way overdesigned, power-wise, so there should be no problem with overheating. The only thing marginal may be the starting voltage but the 098-2 starts instantly.
HV+ o
X C5 C7 |
+-------------------||---------------+--------------||---------------+
| D7 D8 D9 | D10 D11 D12 D13 D14 D15 |
| +--|>|-|>|-|>|--+--|>|-|>|-|>|--+--|>|-|>|-|>|--+
| D1 D2 D3 Y | C6 | |
+--+--|>|-|>|-|>|--+----+----+---------||---------------+ R5 /
||( | | | | 3.9M \
||( | C1 +_|_ / R1 | /
||( | 5uF --- \ 1M | R6 R7 R8 R9 D16 D17 D18 |
||( | 450V - | / +---/\/\--/\/\--/\/\--/\/\---|>|-|>|-|>|---+
||( | | | |
||( | +----+ Transformer: 700 VRMS, 20 mA |
||( | | | (primary not shown) |
||( | C2 +_|_ / R2 |
||( | 5uF --- \ 1M Tube+|
||( | 450V - | / .-|-.
||( T | | | D1-D18: 1N4007 | | |
+------------------+----+ | |
| | | | |
| C3 +_|_ / R3 C1-C4: 5uF, 450V LT1 | |
| 5uF --- \ 1M C5-C7: .001uF, 2kV | |
| 450V - | / | |
| | | R1-R4: 1M, 1/2W ||_||
| +----+ Z R6-R9: (ballast, 18K+3x33K, 2W) '-|-'
| | | Tube-|
| C4 +_|_ \ R4 |
| 5uF --- / 1M |
| 450V - | \ HV- o--+
| | | |
+--|<|-|<|-|<|--+----+-----------------------------------------------+
D4 D5 D6
Note that there are no equalizing resistors across the 1N4007s. While I have been building similar supplies without them, the use of 10M resistors across each diode to equalize the voltage drops is recommended.
Also, the measured voltage across the filter capacitors exceeds their 450 VDC ratings until the laser tube starts, and then drops down a bit. But that is still beyond marginal in my book. Slight differences in the equalizing resistor values and/or leakage of the caps could result in a mess. Having said that, I haven't seen any of these with blown caps.
The only notable difference between ML-360 and ES-HL1 is that the starting voltage is fed to the anode of the HeNe tube via a set of blocking diodes in parallel rather than the more common series arrangement.
I was given another nearly identical power supply with the only difference being that there were only 2 diodes in series instead of 3 diodes for each stage of the voltage multiplier. I do not know what laser this came from.
Estimated specifications (ML-620):
I haven't been able to locate cross references for the ITT992 diodes and M639 transistors but would expext that 1N4007s and MJE3439s would be satisfactory substitutes.
The factory setting for HeNe tube current is about 4.5 mA. However, this can be adjusted by changing the value of R5 or R6. It works nicely with the typical 6" long 0.5 to 1.5 mW barcode scanner HeNe laser tube as a replacement since in all likelihood the original soft-seal tube will be very dead in any sample you acquire. However, the value of R5 or R6 may need to be changed to set the current at the optimal value for the replacement tube to maximize output power and tube life. Typical 6" tubes only require 3 to 3.5 mA.
X C5 C7 HV+
+---------------||---------------+----------||-----------+ o
| D7 D8 | D9 D10 D11 D12 | D13 D14 |
| +--|>|-|>|--+--|>|-|>|--+--|>|-|>|--+--|>|-|>|--+
| D1 D2 D3 Y | C6 | C8 |
+--+--|>|-|>|-|>|--+----+----------||-----------+----------||-----------+
||( | | | R12 R11 R10 |
||( | C1 +_|_ / R1 +----/\/\---/\/\---/\/\----+
||( | 4.7uF --- \ 1M |
||( | 450V - | / | +------------+ Tube-
||( | | | +---|- ]-|----+----+
||( | +----+ Tube+ +------------+ | |
||( | | | LT1 R9 / |
||( | C2 +_|_ / R2 56K \ |
||( | 4.7uF --- \ 1M T1: 700 VRMS, 25mA R8 2W / |
||( | 450V - | / (Primary not shown) 56K 2W | |/ C
||( T | | | +-----+--/\/\--+--| Q1
+------------------+----+ D1-D14: 1N4007 | | |\ E
| | | R10-R12: 12K,2W R7 / _|_.D16 |
| C3 +_|_ / R3 27K \ '/_\ 1N758 |
| 4.7uF --- \ 1M Q1,Q2: MJE3439 / | |
| 450V - | / | | |/ C
| | | +-----|-----------| Q2
| +----+ Z | | |\ E
| | | | | |
| C4 +_|_ \ R4 D15 _|_. +-------------+
| 4.7uF --- / 1M 1N758'/_\ |
| 450V - | \ | +---+ R6 |
| | | | | v 1.2K |
+--|<|-|<|-|<|--+----+---------------------------+----+-/\/\---/\/\--+
D4 D5 D6 R5 600 |
HV- o
Estimated specifications (ML-920):
X C9 C10 C11
+---------||------+-------||------+-------||------+
| CR3 | CR4 CR5 | CR6 CR7 | CR8
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--o HV+
| | | | |
| | +----||----+-------||------+-------||------+
T1 | CR1 |Y | C12 C13 C14 |
+--+---|>|---+----+ 33K /
||( | | | T1: 900 VRMS, 15mA 2W \ Rb1
||( | C1 +_|_ / R1 (primary not shown) /
||( | 4.7uF --- \ 510K | Rb2
||( | 450V - | / 1/2W CR1-CR9: 3x1N4007 +--/\/\--+
||( | | | 33K 2W |
||( | +----+ C1-C8: 4.7uF, 450V Rb3 |
||( | | | C9-C14: 1nF, 3kV +--/\/\--+
||( | C2 +_|_ / R2 | 33K 2W
||( | 4.7uF --- \ 510K R1-R8: 510K,1/2W |Tube+
||( | 450V - | / 1/2W R9-R11: 68K, 1W .-|-.
||( | | | | |
||( | +----+ Q1-Q3: MJE340T | |
||( | | | | |
||( | C3 +_|_ / R3 LT1 | |
||( | 4.7uF --- \ 510K 2-3 mW | |
||( | 450V - | / 1/2W | |
||( | | | | |
||( | +----+ ||_||
||( | | | '-|-'
||( | C4 +_|_ / R4 |Tube-
||( | 4.7uF --- \ 510K +----+
||( | 450V - | / 1/2W | |
||( | | | R10 / |
+--|---------+----+-----------------------------+ 68K \ |
| | | | 1W / |
| C5 +_|_ / R5 | | |/ C Q1
| 4.7uF --- \ 510K | +--| MJE340T
| 450V - | / 1/2W | | |\ E (NPN)
| | | | R11 / |
| +----+ | 68K \ |
| | | | 1W / |
| C6 +_|_ / R6 R9 / | |/ C Q2
| 4.7uF --- \ 510K 560K \ +--| MJE340T
| 450V - | / 1/2W 2W / | |\ E (NPN)
| | | | R12 / |
| +----+ | 68K \ |
| | | | 1W / |
| C7 +_|_ / R7 | | |/ C Q3
| 4.7uF --- \ 510K +-------|--| MJE340T
| 450V - | / 1/2W | | |\ E (NPN)
| | | | | |
| +----+ | +----+
| | | | |
| C8 +_|_ / R8 ZD1 _|_. R13 /
| 4.7uF --- \ 510K 1N749A '/_\ 910 \
| 450V - | / 1/2W 4.3V | 1/2W /
| | | | |
+---|<|---+----+-----------------------------+------------+--o HV-
CR2
On some versions of this power supply, the HV rectifiers may be single higher voltage diodes rather than multiple 1N4007s. Other component differences are also possible.
A transformer feeds a voltage doubler with a CRC filter, ballast resistors, and not much else except a power rheostat in the primary to adjust tube current.
T101 CR1 R102 R104 R105 R106
R101 +---+--|>|--+--/\/\--/\/\--+---+--/\/\--/\/\--+
_ S101 80,50W ||( | 7.5KV | 25K 25K | | 25K 25K |+
H o--_ ---/ ---/\/\-+--+ ||( | _|_ | | .-|-.
F101 Power ^ | )||( | ---.1uF | \ R106 | | |
1.5A +--+ )||( | C101 | 4KV C102 _|_ / 30M | |
Current )||( +---------+ .25uF --- \ 3W LT1 | |
115VAC Adjust )||( | | C103 | .1uF 5KV | / 10KV | |
)||( | | _|_ 4KV | | ||_||
N o--------------------+ ||( | | --- | | '-|-'
||( | | CR2 | R107 R108 | | R109 R110 |-
All 25K ohm resistors +-+ +--|<|--+--/\/\--/\/\--+---+--/\/\--/\/\--+
are rated 10W. 7.5KV 25K 25K 25K 25K
You're probably wondering about the lack of starting circuitry. Well, there
is none! The power transformer (T101) is probably similar to a neon sign or
oil burner ignition type with a quasi-constant current/high droop output. The
open circuit doubled/filtered output voltage is about 5,000 VDC which is
sufficient to start the wide bore (2.5 mm) HeNe tube. When the tube starts
and draws current, the output voltage drops down to about 1,500 VDC. T101,
in conjunction with R101 (Current Adjust) in the primary, the Rs in the CRC
filter, and large ballast resistance, limits the current to between 6 and 11
mA (depending on the setting of the R101).
The laser could be jumpered for either 115 VAC or 230 VAC using dual primaries on T101 (not shown). The only other change would be to use a 0.75 A fuse instead of the 1.5 A fuse.
It appears as though the original SP-130 used a hot cathode powered from a filament transformer (T102, 2.5 VAC, 6 A - not shown). However, the SP-130B tube had a more modern hollow aluminum cathode. Where the tube was replaced in an SP-130 (quite likely as they didn't last as long as modern ones), the newer style was probably installed. Samples of the SP-130B I've seen appear to still include T102 and its wiring even though they didn't have the hot cathode type tube.
T101 and all the HV circuitry are in separate potted blocks - there is no chance of disassembly should something fail. However, these appear to be extremely reliable (which is more than can be said of the laser tube!). Everything else (F101, S101, R101, T102, etc.) are accessible. The SP-233 exciter for the SP-133 laser head may be similar as it also has potted blocks for the power transformer and HV circuitry (but lacks T102 and R101).
Note that the starting voltage of 5 KV is marginal for all but the smallest modern narrow bore HeNe tubes. I have tested it with the SP-084-1 HeNe tube as well as other lower power barcode scanner HeNe tubes. While these did start and run reliably, 200K or more additional ballast resistance was required to reduce the current to their optimum operating range of 4 to 6.5 mA. I expect that the SP-130 power supply would not be able to start larger HeNe tubes (or hard-to-start smaller ones) at all even though its operating voltage and current might be adequate. Therefore, with so many more capable alternatives, it's probably not a good choice to build unless you happen to have an SP-130 laser tube laying around the house. :)
I have tried a few modern HeNe laser tubes in place of the original. Long (i.e., 10") 1 to 2 mW tubes seem to start reliably but tend to run at higher than desirable operating current at normal line voltage. For example, a Uniphase 098 that should get 3.7 mA runs at 6.5 mA and the 098-2 runs at 5.5 mA. So, additional ballast resistance would need to be added to use a replacement tube, probably better to do it in the cathode return. Very roughly, 100K ohms will reduce the current by 1 to 2 mA. On a Variac, the current could be set to the proper value. For unknown reasons, some shorter tubes would not start reliably at all, possibly related to the very high power supply ballast resistance and relatively long wire length to the tube anode.
The only reason the diagram looks a bit different than the others is that I didn't want to wasts a lot of page space with not much stuff. :)
T101
+-------+
_ ||( |
H o----- _------/ ---+ ||( |
F101 S101 )||( |
115VAC 0.5A Power )||( |
)||( |
N o------------------+ ||( |
||( | C111
+--+ +---------------------||------------+
CR101 | | CR102 |
+---------------|>|----------------|----+----------|>|----------------+ |
| | | |
| C110 C109 C108 C107 C106 | C105 C104 C103 C102 C101 |CR103|
+--)|--+--)|--+--)|--+--)|--+--)|--+--)|--+--)|--+--)|--+--)|--+--)|--+-|>|-+
| R110 | R109 | R108 | R107 | R106 | R105 | R104 | R103 | R102 | R101 | |
+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+ |
| C112 _|_ |
| C101-C110: 10uF, 450V C111-C113: 4.7nF, 6KV --- |
| CR101-CR105: 6KV R101-R110: 680K R111-R114: 68K, 5W CR105 |CR104|
| +-|<|-+-|<|-+
| Tube- +--------------+ Tube+ R114 R113 R112 R111 | C113 |
+----------|-| -|---------/\/\---/\/\---/\/\---/\/\---+----||-----+
+--------------+
LT1
There is also an SP-132M, which is mutli-spatial mode with a lower tube voltage and higher tube current. The only difference in the power supply is that R114 is not present.
Note that other manufacturers sell (or have sold) lasers identical in appearance to the SP-155. For example, there is a Uniphase model 155ASL-1 and a Liconix L-388 (even though it is made by Uniphase). However, these use a hard-seal Uniphase barcode scanner HeNe tube (similar to a model 098 with a tiny collimating lens glued to its OC to reduce divergence) rather than the fancy Spectra-Physics side-arm tube we know and love. But their power supplies are similar or identical to that used in the SP-155 and what follows should still apply. (There is also a Spectra-Physics model 155ASL which is physically identical to the Uniphase and Liconix lasers except for the name on the front. I assume it has the same construction though I haven't seen the insides of one up close and personal.)
The power supply is a simple line operated design and includes a current regulator which can easily be modified for any typical tube requirement. It can also be converted to a modulator in a number of ways.
High voltage diodes and capacitors are used in this design. An alternative is to use inexpensive 6 - 1,000 V diodes for each 6 kV diode shown here, and to use 6 - 0.003 uF, 1 kV capacitors in series for each 6 kV capacitor. I would recommend 10 M ohm equalizing resistors across each lower voltage device though for the diodes at least, this appears not to be essential.
I include two schematics below. The first one is from an unidentified source and the second is directly from an early SP-155 operation and service manual. The specs should be identical but the component changes indicate possible improvements in reliability and stability.
Estimated specifications (SP-155, circuit 1):
X C107
+--------------||-------------+
| C100 | C101
+--------------||-------------+--------||---------+---o HV+
| CR101 | CR102 CR103 | R107 (Rbp)
| +---|>|---+---|>|---+---|>|---+---/\/\---+
T100 | CR100 Y | C102 | 33K |
+---+-----|>|-----+-----+---------||--------+ 2W /
||( | | \ Rba
||( C103 +_|_ / R100 /
||( 10uF --- \ 470K T100: 1,245 VRMS, 10mA \
||( 450V - | / 1W (primary not shown) |
||( | | |Tube+
||( +-----+ W CR100-CR103: LMS60 (6kV) .-|-.
||( | | | |
||( C104 +_|_ / R101 C100-C102,C107: 560pF, 6kV | |
||( 10uF --- \ 470K C103-C106: 10uF, 450V | | LT100
||( 450V - | / 1W | |
||( T | | R100-R102: 470K, 1W | |
+---+ +-----+ R107 (ballast): 33K, 2W ||_||
| | | '-|-'
| C105 +_|_ / R102 |Tube-
| 10uF --- \ 470K +------------------+
| 450V - | / 1W |
| | | R103 |/ C Q100
| +-----+----/\/\------+----| MJE3439
| | Z 430K | |\ E
| | 1W | |
| C106 +_|_ _|_, /
| 10uF --- CR104 '/_\ \ R106
| 450V - | 1N5241B | / 2.74K
| | | \
| | | |
+-------------+--------------------+------+---o HV-
Note: Some versions of this unit may have only 3 main filter caps and slightly different components values but are otherwise similar.
The 1,245 V transformer output feeds a half wave rectifier (CR100) and filter resulting in about 1,700 V across all the electrolytics. (Slightly less than the peak value of 1,245 VRMS.) The voltage multiplier consisting of CR101 to CR103 and C100 through C103 generates up to 3 times the transformer's peak voltage or around 5,100 V (the actual value will depend on various factors including stray capacitance and other losses). See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
Q100, CR104, and R106 form a constant current regulator which will attempt to maintain the tube current at (Vz - .7)/R106 or about 3.75 mA in this case. Its compliance range is about 300 V. This can easily be adapted to your requirements by either changing CR104 or R106 appropriately.
The anode ballast resistor, Rba, needs to be large enough to maintain stability (usuall this means at least 75K-33K=42K or so in this case) and should be as close to the HeNe tube as possible. (The original schematic doesn't have anything for Rba though.) Commercial laser heads generally include an internal 75K ballast resister. See the section: Ballast Resistors, Function, Selecting for more information.
This one is from a SP-155 manual, dated 1977, and is apperently an earlier revision but matches the circuit in an SP-155 laser and replacement PCB I have:
Estimated specifications (SP-155, circuit 2):
X C100 C101
+--------------||-------------+--------||---------+---o HV+
| CR101 | CR102 CR103 | R104 (Rbp)
| +---|>|---+---|>|---+---|>|---+---/\/\---+
T100 | CR100 Y | C102 | 33K |
+---+-----|>|-----+-----+---------||--------+ 2W /
||( | | \ Rba
||( C103 +_|_ / R100 /
||( 10uF --- \ 330K T100: 975 VRMS, 10mA \
||( 500V - | / 1W (primary not shown) |
||( | | |Tube+
||( +-----+ W CR100-CR103: 6kV .-|-.
||( | | | |
||( C104 +_|_ / R101 C100-C102: 500pF, 6kV | |
||( 10uF --- \ 330K C103-C105: 10uF, 500V | | LT100
||( 500V - | / 1W | |
||( T | | R100,R101: 330K, 1W | |
+---+ +-----+ ||_||
| | '-|-'
| | |Tube-
| | +------------------+
| | |
| | R102 |/ C Q100
| +----------/\/\------+----| MJE3439
| |Z 300K | |\ E
| | 1W | |
| C105 +_|_ / /
| 10uF --- R103 \ \ R105
| 500V - | 33K / / 6.8K
| | \ \
| | | |
+-------------+--------------------+------+---o HV-
Instead of a zener diode, a resistor is used for setting the current. However, this doesn't any line regulation. Cost cutting? The operating current is also much higher than in the previous circuit - 6 mA instead of 3.7 mA (I measured it to confirm - approximately 42 V across R105!). So, perhaps this version of the SP-155 uses a higher current HeNe laser tube.
Also, if theres a problem with the circuit and/or the tube doesn't start, it would appear that the voltage on the filter capacitors (C103-C105) may exceed 1,500 V since the transformer will be lightly loaded. Even if perfectly balanced, the voltages on each could then exceed 500 V. Not good. So, someone redesigned the circuit and eliminated one of the filter capacitors but forgot about their voltage ratings. Apparently, the filter capacitorss in these things have been known to blow up. :)
In neither schematic is Tube- tied to ground which is fine since the tube is enclosed in the grounded metal case and both connections are fully insulated.
There is also an SP-133M, which is mutli-spatial mode with a lower tube voltage and higher tube current. The only difference in the power supply is that R113 is 30K instead of 50K for the SP-133M.
The resistors are probably all that differ as the additional 100K for the four resistors in the SP-233 would result in the voltage to the tube being about 600 V lower at 6 mA, which is consistent with a 2 mW versus a 5 mW laser.
Note that the SP-235 and SP-233 exciters for the SP-135 and SP-133 lasers are physically identical and both have a transformer feeding a potted module with 4 ballast resistors in glass tubes but the part numbers of the transformers are not the same and the values of the resistors in the glass tubes differ as well. The potted module has no part number so I have no idea of whether it's the same. See the previous section for what is known, which isn't much. :)
There are two interesting things that differentiate this otherwise relatively boring circuit and other typical power supplies in its class:
Estimated specifications (SP-235):
|
C111 SP-235 Exciter | SP-135 Laser Head
+------||-------+ |
| CR103 | CR104 R112 R113 HV+ | R116 R117
| +--|>|--+--|>|--+---/\/\---/\/\--------->>---/\/\--/\/\--+
| | C112 | | |
| +------||-------+ | /
T101 | CR102 | C101 C102 C103 C104 C105 | R118 \
+--+-+--|>|--+-+--|(--+--|(--+--|(--+--|(--+--|(--+ | /
||( | | + - | + - | + - | + - | + = | | \
||( | +-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+ | |Tube+
||( | R101 R102 R103 R104 R105 | | .-|-.
+--|----------------------------------------------+ | | | |
| R110 R109 R108 R107 R106 | | | |
| +-/\/\-+-/\/\-+-/\/\-+-/\/\-+-/\/\-+ | LT101 | |
| | - + | - + | - + | - + | - + | | | |
+-+--|<|--+-+--)|--+--)|--+--)|--+--)|--+--)|--+ | | |
| CR101 | C110 C109 C108 C107 C106 | ||_||
| +------||-------+ | '-|-'
| | C114 | HV- | |Tube-
| +--|<|--+--|<|--+---/\/\--/\/\---------->>---------------+
| CR105 | CR106 R115 R114 |
+------||-------+ |
C113 |
T101: 1,400 VRMS, 20 mA (primary not shown),
SP part number: 0406-7330-4 114-P-7 23316
CR101-CR106: 6kV
C101-C110: 10uF, 450V C111-C114: 4.7nf, 6kV
R101-R110: 680K R112-R115: 35K, 7W R116-R118: 30K, 5W
Note: Assuming the secondary components are isolated, the circuit is safe as drawn but I have heard there may be some slight sensation of shock when touching the laser head. Thus, it would probably be a good idea to connect the laser head case to earth ground via a three-prong power cord if this is not already present. However, it's also possible the shock is due to insulation breakdown inside the head so check for this first as it could damage the power supply with the additional ground connection (aside from being a serious shock hazard).
With minor modifications, it should be possible to use this design for somewhat larger HeNe tubes - possibly up to 7 to 10 mW - by removing one or more of the in-board ballast resistors, R112 to R115.
Estimated specifications (SP-247):
X R1 C1 C11
+---/\/\------||----------+---------||--------+
| 680K CR3 | CR4 CR5 | CR6
| +---|>|----+---|>|---+---|>|---+---|>|---+
T1 | CR1 Y | C10 | C12 |
+---+---|>|---+----+---------||---------+-----||-----+------+----+---o HV+
||( | | | | | |
||( | C2 +_|_ / R2 | R11 / |
||( | 10uF --- \ 680K T1: 1,200 VRMS, 20mA | 120K \ |
||( | 500V - | / 1W (primary not shown) | 2W / |
||( | | | | | |/ C Q1
||( | +----+ W CR1-CR6: 6kV | +--| MJE3439
||( | | | | | |\ E
||( | C3 +_|_ / R3 C2-C9: 10uF, 500V | R12 / |
||( | 10uF --- \ 680K C1, C10-C13: 500pF, 6kV | 120K \ |
||( | 500V - | / 1W | 2W / |
||( | | | R2-R9: 680K, 1W | | |/ C Q2
||( | +----+ R11-R14: 120K, 2W | +--| MJE3439
||( | | | | | |\ E
||( | C4 +_|_ / R4 Q1-Q4: MJE3439 | R13 / |
||( | 10uF --- \ 680K | 120K \ |
||( | 500V - | / 1W | 2W / |
||( | | | | | |/ C Q3
||( | +----+ +------------------+ +--| MJE3439
||( | | | | | |\ E
||( | C5 +_|_ / R5 | R14 / |
||( | 10uF --- \ 680K | 110K \ |
||( | 500V - | / 1 W | 2W / |
||( T | | | | R10 47K | |/ C Q4
+---|---------+----+ | +----/\/\----+--| MJE3439
| | | | | | |\ E
| C6 +_|_ / R6 | | |/ E |
| 10uF --- \ 680K | +----------| |
| 500V - | / 1W | | Q5 |\ C |
| | | | ZD1 _|_, 2N5086 | |
| +----+ C16 _|_ 1N5245A '/_\ +----+
| | | .047uF --- 15V | R17 |
| C7 +_|_ / R7 6kV | | 5K 1W R16 |
| 10uF --- \ 680K | Adjust +---/\/\---/\/\---+
| 500V - | / 1W | | | 1.5K
| | | | +--------+----+
| +----+ | | R15 R18 Rba
| | | | +---/\/\---/\/\---+--/\/\--+
| C8 +_|_ / R8 | 20K 20K |Tube+
| 10uF --- \ 680K | 2W 2W .-|-.
| 500V - | / 1W | <------ Rbp ------> | | |
| | | | | |
| +----+ Z C15 _|_ | | LT1
| | | .047uF --- | |
| C9 +_|_ / R9 6kV | | |
| 10uF --- \ 680K | ||_||
| 500V - | / 1W | '-|-'
| | | | |Tube-
+---|<|---+----+--------------+------------------------------+---o HV-
CR2 _|_
-
(Note: I originally had R14 and R10 being 120K and 48K, respectively. But inspecting an actual SP-247 shows 110K and 47K. The difference isn't critical in any case.)
The 1,200 V transformer output feeds a voltage doubler consisting of rectifiers CR1 and CR2 and filter capacitors C2 through C9 resulting in about 3,200 V across all the electrolytics. (Slightly less than 2 times the peak value of 1,200 VRMS.) The voltage multiplier consisting of CR3 to CR6 and C1 through C10 generates slightly less than 6 times the transformer's peak voltage or around 10,200 V. See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
C15 and C16 provide some additional filtering to the output so unlike the previous supplies whose outputs include the last multiplier diodes without filtering, this one is more pure DC. This would be better for laser communications, for example, as the tube current will have less ripple. However, it may not matter for a basic power supply so you could probably get away without having to find/construct this high voltage capacitor.
Q1 through Q5, their associated resistors, and ZD1 (15 V zener) maintains a constant voltage of 15 V across the combination of R16 + R17 so the tube current will be 15/(R16 + R17). For example, with the R17 set for 1.5 K, the tube current will be 5 mA. The adjustment range is approximately 2.3 to 10 mA. The voltage compliance range of this power supply should be over 1,000 V.
Keep in mind that if you include this high side regulator, it must be insulated to handle the full starting voltage. An alternative that might be easier to construct would be use this operating/starting voltage design but to substitute a similar compliance low-side regulator.
The anode ballast resistor, Rba, needs to be large enough to maintain stability (at least 75K - 40K = 35K or so in this case) and should be as close to the HeNe tube as possible. Commercial laser heads generally include an internal 75K ballast resister. See the section: Ballast Resistors, Function, Selecting for more information.
Estimated specifications (SP-248):
X R1 C1 C11
+---/\/\------||----------+---------||--------+
| 560K CR3 | CR4 CR5 | CR6
| +---|>|----+---|>|---+---|>|---+---|>|---+
T1 | CR1 Y | C10 | C12 |
+---+---|>|---+----+---------||---------+-----||-----+------+----+---o HV+
||( | | | | | |
||( | C2 +_|_ / R2 | R11 / |
||( | 10uF --- \ 560K T1: 1,000 VRMS, 20mA | 82K \ |
||( | 500V - | / 1W (primary not shown) | 2W / |
||( | | | | | |/ C Q1
||( | +----+ W CR1-CR6: DL800 (8kV?) | +--| MJE3439
||( | | | | | |\ E
||( | C3 +_|_ / R3 C2-C9: 10uF, 500V | R12 / |
||( | 10uF --- \ 560K C1, C10-C13: 500pF, 6kV | 82K \ |
||( | 500V - | / 1W | 2W / |
||( | | | R2-R9: 560K, 1W | | |/ C Q2
||( | +----+ R11-R14: 82K, 2W | +--| MJE3439
||( | | | | | |\ E
||( | C4 +_|_ / R4 Q1-Q4: MJE3439 | R13 / |
||( | 10uF --- \ 560K | 82K \ |
||( | 500V - | / 1W | 2W / |
||( | | | | | |/ C Q3
||( | +----+ +------------------+ +--| MJE3439
||( | | | | | |\ E
||( | C5 +_|_ / R5 | R14 / |
||( | 10uF --- \ 560K | 82K \ |
||( | 500V - | / 1 W | 2W / |
||( T | | | | R10 43K | |/ C Q4
+---|---------+----+ | +----/\/\----+--| MJE3439
| | | | | | |\ E
| C6 +_|_ / R6 | | |/ E |
| 10uF --- \ 560K | +----------| | R18
| 500V - | / 1W | | Q5 |\ C +--/\/\--+
| | | | ZD1 _|_, 2N5086 | | 1k |
| +----+ | 1N5245A '/_\ +----+ |
| | | | 15V | R17 | C18 _|_ +
| C7 +_|_ / R7 | | 5K R16 | 2uF ---
| 10uF --- \ 560K | Adjust +---/\/\---/\/\---+ 25V | -
| 500V - | / 1W | | | 1.5K |
| | | | +----+ +---------------+
| +----+ C16 _|_ | R15 | Rba
| | | .047uF --- +--/\/\--+-+--/\/\--+
| C8 +_|_ / R8 6kV | 82K | |Tube+
| 10uF --- \ 560K | 5W | .-|-.
| 500V - | / 1W | Rbp | | | |
| | | | | | |
| +----+ Z C15 _|_ C17 _|_ | | LT1
| | | .047uF --- 500pF --- | |
| C9 +_|_ / R9 6kV | 6kV | | |
| 10uF --- \ 560K | | ||_||
| 500V - | / 1W | | '-|-'
| | | | | |Tube-
+---|<|---+----+--------------+---------------------+-----+----+---o HV-
CR2 _|_
-
Note: Primary side interlock in laser head cable prevents power from being applied unless HeNe laser tube is connected. I guess the assumption is that the tube will start at less than 6 kV or else C17 may go BOOM!
However, based on tests I've run with one sample, C17 doesn't seem to be bothered by a tube that doesn't start or is disconnected.
See the SP-247 info, above, for description of operation.
Estimated specifications (SP-249):
See the SP-247 info, above, for the schematic and description of operation.
Estimated specifications (SC-760):
Estimated specifications (JD-PS1):
The main difference between the SP-247 and JD-PS1 is with respect to the location of the regulator: The SP-247 puts it in the anode circuit while the JD-PS1 puts it in the cathode return. The driver circuit for the cascade is also slightly modified. Note that either the anode nor cathode of the HeNe tube is earth/safety ground in this supply!
Please refer to Spectra-Physics Model 247 HeNe Power Supply (SP-247) for a description of circuit operation (making appropriate adjustments for the minor differences design and part labeling).
(Model number PS0 is arbitrary.)
Estimated specifications (AT-PS0):
(Schematic provided by: Wes Ellison.)
X R1 C1 C2 C3 C4
+---/\/\----||----+-------||------+-------||------+-------||------+
| 100K, 1 W D3 | D4 D5 | D6 D7 | D8 D9 | HV+
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--o
T1 | D1 |Y | | | |
+---+---|>|---+----+----||----+-------||------+-------||------+ R8 /
||( | | | C5 C6 C7 62K \
||( | C8 +_|_ / R2 2W /
||( | 10uF --- \ 4.7M T1: 700 VRMS, 10 mA \
||( | 450V - | / 1W (primary not shown) |
||( | | | .-|-.
||( | +----+ D1-D9: 3kV | | |
||( | | | | |
||( | C9 +_|_ / R3 C8-C11: 10uF, 450V LT1 | |
||( | 10uF --- \ 4.7M C1-C7: .005uF, 3kV | |
||( | 450V - | / 1W ||_||
||( T | | | '-|-'
+---|---------+----+ |
| | | +----+
| C10 +_|_ / R4 MJE2360T | |
| 10uF --- \ 510K |/ C / R7
| 450V - | / 1W +-----------| Q1 \ 68K
| | | R5 | |\ E / 2W
| +----+----------------/\/\-----------+ | |
| | Z 510K | +----+
| C11 +_|_ 1W ZD1 _|_, |
| 10uF --- 1N4744A '/_\ R8 /
| 450V - | 15V | 3.6K \
| | | /
| | | |
+---|<|---+------------------------------------+-------------+---o HV-
D2
The 700 V transformer output feeds a voltage doubler consisting of rectifiers D1 and D2 and filter capacitors C8 through C11 resulting in about 1,800 V across all the electrolytics. (Slightly less than 2 times the peak value of 700 VRMS.) The voltage multiplier consisting of D3 to D9 and C1 through C8 generates up to 5 times the transformer's peak voltage or around 9,000 V (the actual value will depend on various factors including stray capacitance and other losses). See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
Q1, ZD1, R7, and R8 form the low-side current regulator. The tube current will be (15-.7)/R8 or just about 4 mA. So, for a different current, select R11 to be 14.3/I. R7 reduces the power dissipation in Q1 over the useful voltage compliance range but will not prevent Q1 from blowing due to a short circuit.
Since the voltage compliance range of this power supply is only around 250 V, the ballast resistor will still need to be selected carefully to achieve stable regulation for your particular tube. See the sections beginning with: Selecting the Ballast Resistor for further info.
I acquired an Aerotech self-contained laser with a very similar power supply. Aside from part numbering (which I bet Wes assigned arbitrarily), the filter caps were 4.7 uF instead of 10 uF, and there were some other minor differences in resistor values, including the total ballast resistance, which was about 78K made up of 3 resistors in series. Amazingly, the very old soft-seal HeNe laser tube still outputs over 1.1 mW after a tune-up, which is probably near original condition. It has Epoxy sealed mirrors at both ends - to the glass stem at the HR-end and a Hughes-style mini mirror adjuster for the OC mirror. But it still has a nice mostly shiny getter and probably was never run very much. The model/date sticker is missing so I don't know exactly how old this laser is, but it's probably pre-1980.
(Model number PS1 is arbitrary - supply was unmarked).
Estimated specifications (AT-PS1):
X R9 C9 C11 C13 C15
+---/\/\----||----+-------||------+-------||------+-------||------+
| 100K, 1 W CR3 | CR4 CR5 | CR6 CR7 | CR8 CR9 | HV+
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--o
T1 | CR1 |Y | | | |
+---+---|>|---+----+----||----+-------||------+-------||------+ |
||( | | | C10 C12 C14 |
||( | C1 +_|_ / R1 R10 /
||( | 10uF --- \ 510K T1: 750 VRMS, 20 mA (Rbp) \
||( | 450V - | / 1W (primary not shown) 47K /
||( | | | 5W \
||( | +----+ CR1-CR9: 3kV |
||( | | | |
||( | C2 +_|_ / R2 C1-C8: 10uF, 450V +--+
||( | 10uF --- \ 510K C9-C15: .005uF, 3kV |
||( | 450V - | / 1W |
||( | | | R1-R8: 510K /
||( | +----+ Rb \
||( | | | /
||( | C3 +_|_ / R3 \
||( | 10uF --- \ 510K |
||( | 450V - | / 1W |Tube+
||( | | | .-|-.
||( | +----+ | | |
||( | | | | |
||( | C4 +_|_ / R4 | |
||( | 10uF --- \ 510K | | LT1
||( | 450V - | / 1W | |
||( T | | | | |
+---|---------+----+ | |
| | | ||_||
| C5 +_|_ / R5 '-|-'
| 10uF --- \ 510K |Tube-
| 450V - | / 1W |
| | | +----+
| +----+ | _|_
| | | | -
| C6 +_|_ / R6 |
| 10uF --- \ 510K |
| 450V - | / 1W |
| | | |
| +----+ |
| | | +----+
| C7 +_|_ / R7 MJE2360T | |
| 10uF --- \ 510K |/ C |
| 450V - | / 1W +-----------| Q1 |
| | | R8 | |\ E |
| +----+-------------/\/\-----------+ | |
| | Z 470K | / / R12
| C8 +_|_ 1W ZD1 _|_, R11 \ \ 375K
| 10uF --- 1N4744 '/_\ 3.6K / / 2W
| 450V - | 15V | \ \
| | | | |
+---|<|---+---------------------------------+-------------+----+---o HV-
CR2
Note: the laser head itself may have an additional ballast resistor (not shown).
The 750 V transformer output feeds a voltage doubler consisting of rectifiers CR1 and CR2 and filter capacitors C1 through C8 resulting in about 2,000 V across all the electrolytics. (Slightly less than 2 times the peak value of 750 VRMS.) The voltage multiplier consisting of CR3 to CR9 and C9 through C15 generates slightly less than 10 times the transformer's peak voltage or around 10,000 V. See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
Q1, ZD1, R8, and R11 form the low-side current regulator. The tube current will be (15-.7)/R11 or just about 4 mA. So, for a different current, select R11 to be 14.3/I.
Since the voltage compliance range of this power supply is only around 500 V, the ballast resistor will still need to be selected carefully to achieve stable regulation for your particular tube. See the sections beginning with: Selecting the Ballast Resistor for further info.
The anode ballast resistor, Rba, needs to be large enough to maintain stability (at least 75K-47K=38K or so in this case) and should be as close to the HeNe tube as possible. Commercial laser heads generally include an internal 75K ballast resister. See the section: Ballast Resistors, Function, Selecting for more information.
The modified circuit provides a current adjustment control, modulation input, 'Beam On' indicator, and tube current sense test points. I have implemented these changes to the Aerotech PS1 and installed the current adjust pot, jacks for Ground/Test+, Test-, Signal in, and Signal ground, and the Beam On LED on the power supply case.
| (Remainder of circuit |Tube-
| identical to Aerotech PS1) +----+-----------+-------+---o +
| | _|_ | |
| | | | - ZD2 _|_ R13 / Test
| +----+ | 1N4742 /_\ 1K \ 1 V/mA
| | | | 12V | /
| C6 +_|_ / R6 | | |
| 10uF --- \ 510K | +-------+---o -
| 450V - | / 1W | __|__ IL2
| | | | _\_/_ Beam
| +----+ | | On
| | | | +---+
| C7 +_|_ / R7 | MJE2360T | |
| 10uF --- \ 510K | |/ C |
| 450V - | / 1W | +---/\/\---| Q1 |
| | | | T2 | R15 |\ E |
| +----+ Z +--+ + 15K | |
| | | )||( | |
| | / R8 )||( | / R12
| | \ 470K )||( | \ 375 K
| C8 +_|_ / 1 W Signal in o----+ + / / 2W
| 10uF --- | 1:1 | R11 \ |
| 450V - | +------------------------------+ 1.5K / |
| | | | |
| | ZD1 _|_, R14 / |
| | 1N4744 '/_\ 5K +->\ |
| | 15V | Adjust | / |
| | | | | |
+---|<|---+-----------------------------------+---------+--+---+---o HV-
CR2
Each of the new and improved features is described below:
The phone line coupling transformer from a long forgotten 2400 baud modem served nicely for this application resulting in a useful frequency response from about 100 and 10,000 Hz.
Stay tuned for exciting future developments!
A similar approach can be used with any of the other HeNe laser power supply designs described in this document which use low-side regulation or which do not have any regulation.
CAUTION: Don't try this with power supplies using high-side regulation either by modifying the regulator (you would need a 15 kV coupling capacitor or 15 kV opto-isolator to hold off the starting pulse) or adding an additional low-side modulator (the two circuits will be fighting each other).
There may have been several versions of this model as I have two slightly different samples using the same circuit board. The one described below which designate model PS2B uses the higher voltage tap on the transformer. A nearly identical design - model PS3A - runs with a transformer secondary of 1,150 VRMS yielding 3,000 VDC operating, 12,000 VDC starting, and uses only 8 electrolytic filter capacitors.
See the section: Aerotech Model PS2A-X HeNe Laser Power Supply (AT-PS2A-X) for its circuit diagram with my modifications.
It appears as though Aerotech may have relabeled this supply the PS7 at some point since I have one of those that appears virtually identical both physically and electrically, or possibly at most, jumpered for the higher output voltage tap on the transformer. That would make sense since it is suitable for HeNe laser heads of around 7 mW.
Estimated specifications (AT-PS2B):
X R11 C11 C13 C15 C17
+---/\/\----||----+-------||------+-------||------+-------||------+
| 10M, 5 W CR3 | CR4 CR5 | CR6 CR7 | CR8 CR9 | HV+
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--o
| | | | | |
| | +----||----+-------||------+-------||------+ |
T1 | CR1 |Y | C12 C14 C16 |
+---+---|>|---+----+ +----+-------+
||( | | | | |
||( | C1 +_|_ / R1 R12 / |
||( | 10uF --- \ 510K T1: 1,380 VRMS, 20mA 62K \ |
||( | 500V - | / 1W (primary not shown) 2W / |
||( | | | | |/ C Q1
||( | +----+ CR1-CR9: 5kV +--| MJE2360T
||( | | | | |\ E
||( | C2 +_|_ / R2 C1-C10: 10uF, 500V R13 / |
||( | 10uF --- \ 510K C11-C17: .005uF, 5kV 62K \ |
||( | 500V - | / 1W 2W / |
||( | | | R1-R10: 510K | |/ C Q2
||( | +----+ R11-R14: 62K, 2W +--| MJE2360T
||( | | | | |\ E
||( | C3 +_|_ / R3 Q1-Q3: MJE2360T R14 / |
||( | 10uF --- \ 510K 62K \ |
||( | 500V - | / 1W U1: LM723 2W / |
||( | | | R24 | |/ C Q3
||( | +----+ +---/\/\---+--| MJE2360T
||( | | | | 3.3K | |\ E
||( | C4 +_|_ / R4 | |/ E |
||( | 10uF --- \ 510K +--------| Q4 | 2N4126
||( | 500V - | / 1W | |\ C | (PNP)
||( | | | | C18 | |
||( | +----+ +--------------+-+----||----+----+
||( | | | | | .005 uF
||( | C5 +_|_ / R5 _|_, ZD1 |
||( | 10uF --- \ 510K '/_\ 1N4744 +------------------------+
||( | 500V - | / 1W | 15 V, 1W |
||( T | | | | |
+---|---------+----+ | R15 15K 1N4148 |\ | C
| | | | +--/\/\--+----------|+ \* |/*
| C6 +_|_ / R6 | +-----+ |R14 15K | D1 |Err >--|
| 10uF --- \ 510K | |Vref*|-+--/\/\--|---+---+--|- / |\ E
| 500V - | / 1W | +-----+ 7.15V | | | |/ |
| | | | | | | R21 /
| +----+ | +---+ | \ R16 10K \
| | | | | | _|_ / 82K /
| C7 +_|_ / R7 | C19 _|_ / /_\ \ ZD2 |
| 10uF --- \ 510K | .1uF --- \ | | 1M4733 _|_,
| 500V - | / 1W | | / | | 5.1V '/_\
| | | | | | | | |
| +----+ +--------------+---+---+----------------+
| | | | R17 15K | R25 (Rbp)
| C8 +_|_ / R8 | R20 R19 | 47K 5W
| 10uF --- \ 510K +-+-/\/\-----/\/\----------+---/\/\---+
| 500V - | / 1W | | 1.5K 1.8K |
| | | +---+ /
| +----+ Current Adjust Rb \
| | | (6 to 11 mA) /
| C9 +_|_ / R9 |Tube+
| 10uF --- \ 510K Note: Components marked .-|-.
| 500V - | / 1W with '*' are part of | | |
| | | U1, LM723. (Compensation | |
| +----+ Z not shown.) | | LT1
| | | | |
| C10 +_|_ / R10 | |
| 10uF --- \ 510K ||_||
| 500V - | / 1 W '-|-'
| | | R23 |Tube-
+---|<|---+----+-------------+--/\/\--+------------------------+---o HV-
CR2 | 1K | _|_
- o Test o + -
1 V/mA
The 1,380 V transformer output feeds a voltage doubler consisting of rectifiers
CR1 and CR2 and filter capacitors C1 through C10 resulting in about 3,600 V
across all the electrolytics. (Slightly less than 2 times the peak value of
1,380 VRMS.) The voltage multiplier consisting of CR3 to CR9 and C11 through
C17 generates slightly less than 10 times the transformer's peak voltage or
around 18,000 V. See the section: Voltage
Multiplier Starting Circuits for a description of its design and operation.
Q1 through Q4, their associated resistors, and U1 (LM723) maintain a constant voltage of 22 V across the combination of R19 + R20 so the tube current will be 22/(R16 + R17). For example, with the R17 set for 750 ohms, the tube current will be 6.3 mA. The adjustment range is approximately 5 to 9 mA. The voltage compliance range of this power supply is about 800 V at 5 mA (possibly a couple hundred volts greater at higher currents).
The anode ballast resistor, Rba, needs to be large enough to maintain stability (at least 75K-47K=38K or so in this case) and should be as close to the HeNe tube as possible. Commercial laser heads generally include an internal 75K ballast resister. See the section: Ballast Resistors, Function, Selecting for more information.
I use an Aerotech PS2B which has had it regulator bypassed for general testing of HeNe laser tubes and heads from 0.5 mW to greater than 12 mW output power. See the section: Ballast Resistor Selector and Meter Box.
Estimated specifications (AT-PS2A-X):
X R11 C11 C13 C15 C17
+---/\/\----||----+-------||------+-------||------+-------||------+
| 10M, 5 W CR3 | CR4 CR5 | CR6 CR7 | CR8 CR9 | HV+
| +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--o
| | | | | |
| | +----||----+-------||------+-------||------+ /
T1 | CR1 |Y | C12 C14 C16 \ Rb
+--+---|>|---+----+ /
||( | | | T1: 1,150 VRMS, 20mA |Tube+
||( | C1 +_|_ / R1 (primary not shown) .-|-.
||( | 10uF --- \ 510K | |
||( | 500V - | / 1W CR1-CR9: 5kV | |
||( | | | | |
||( | +----+ C1-C4, C6-C9: 10uF, 500V LT1 | |
||( | | | C11-C17: .005uF, 5kV | |
||( | C2 +_|_ / R2 ||_||
||( | 10uF --- \ 510K R1-R4, R6-R9: 510K '-|-'
||( | 500V - | / 1W RX1-RX3: 100K, 2W |Tube-
||( | | | |
||( | +----+ QX1-QX3: MPSU60 +---------+-------+-+--o +
||( | | | _|_ | |
||( | C3 +_|_ / R3 - ZD2 _|_, R12 / Test
||( | 10uF --- \ 510K 1N4742 '/_\ 1K \ 1 V/mA
||( | 500V - | / 1W 12V | /
||( | | | Beam On | |
||( | +----+ +-----------+---|<|--------+-------+----o -
||( | | | | | IL2 LED R13 R14
||( | C4 +_|_ / R4 | | +---/\/\---/\/\---+
||( | 10uF --- \ 510K | | | | 5K 1.5K |
||( | 500V - | / 1W | +----+----+ Range |
||( | | | | | | |
+--|---------+----+ | | | Q1 +----+
| | | | | | 2N3904 | |
| C6 +_|_ / R6 | ZD1 _|_, \ (NPN) |/ C |
| 10uF --- \ 510K | 1N4744 '/_\ /<---------| |
| 500V - | / 1W | 15V | \ R15 |\ E |
| | | | | | 500K | |/ E QX1
| +----+ | | | Adjust +--| MPSU60
| | | | | | | |\ C (PNP)
| C7 +_|_ / R7 | +----+----/\/\----+ |
| 10uF --- \ 510K | | R16 10K |
| 500V - | / 1W / R17 | |
| | | \ 100K | RX1 |/ E QX2
| +----+ / +----/\/\----+--| MPSU60
| | | | 100K | |\ C (PNP)
| C8 +_|_ / R8 | 2W RX2 / |
| 10uF --- \ 510K | 100K \ |
| 500V - | / 1W | 2W / |
| | | | | |/ E QX3
| +----+ _|_ C18 +--| MPSU60
| | | --- 100pF | |\ C
| C9 +_|_ / R9 | RX3 \ |
| 10uF --- \ 510K | 100K / |
| 500V - | / 1W | 2W \ |
| | | | | |
+---|<|---+----+-------------+-----------------------------+----+--o HV-
CR2
Note: The total ballast resistance, Rb, should be 75K or more to maintain
stability. It is desirable for there to be at laest 20K in the power supply
itself (Rbp) to provide short circuit protection. The remainder (Rba) should
be as close to the HeNe tube anode as possible. Commercial laser heads
generally include an internal 75K ballast resister. See the section:
Ballast Resistors, Function, Selecting for
more information.
The 1,150 V transformer output feeds a voltage doubler consisting of rectifiers CR1 and CR2 and filter capacitors C1 to C4 and C6 to C9 resulting in about 3,000 V across all the electrolytics. (Slightly less than 2 times the peak value of 1,150 VRMS.) The voltage multiplier consisting of CR3 to CR9 and C11 through C17 generates up to 10 times the transformer's peak voltage or around 15,000 V (the actual value will depend on various factors including stray capacitance and other losses). See the section: Voltage Multiplier Starting Circuits for a description of its design and operation.
Current adjust (R15) and current range (R13) pots have been added, the latter being set by a screwdriver. This allows fairly linear control of tube current up to the set limit from the front panel. The minimum current is determined by what bypasses the transistors and passes through the base resistors. This will be up to 3 mA depending on operating conditions.
As desribed in the section: Enhancements to AT-PS1, a current test point and 'Beam-On' indicator have also been added.
The NPN transistor (Q1) buffers the reference voltage so that the very low current source from R15 can drive the base of the pass transistor cascade.
The base resistors, RX1 through RX3 equally distribute the voltage across the 3 PNP pass transistor, QX1 to QX3. The respective transistors act as emitter followers and maintain approximately the same voltages across their C-E terminals. Within the compliance range, the voltage across R13+R14 will be nearly equal to the voltage on the wiper of R15.
R17 and C18 act as a snubber to protect the transistor cascade from the initial over voltage when the tube fires but before the regulator can turn on. I do not know whether this is needed or how much if any it would protect the pass transistors when operating near their maximum ratings.
Three pass transistors are shown here only because that particular number fit conveniently into the drawing. :-) A greater or fewer number could be used with their associated base resistors. I will probably use 4 to provide a greater compliance and permit the same supply to drive a wider range of tubes. If only one particular tube is to be driven, a single stage in conjunction with a ballast resistor selected to set the operating current at the mid point of the range may be adequate.
The SP-255 exciter was designed to drive medium-to-large frame HeNe lasers like the Spectra-Physics model SP-124B. Although only rated at 15 mW, the SP-124B may produce more than 36 mW when new. :-) (See the sections starting with: Spectra-Physics 124 and 125 HeNe Laser Specifications.)
The SP-255 can easily be adapted for use with other lasers of similar size. Except for the whimpy starter (see below), it would easily drive HeNe tubes with power outputs of up to 35 mW (which with their longer bores, may need more starting voltage than the SP-124B). These include the Spectra-Physics 127 (and the similar OEM 107 and 907) Siemens LGK7676 (and its varients). Also see the section: Interesting and Strange HeNe Lasers for other examples of HeNe tubes that may be compatible with this power supply
For this model, I have both an original schematic and an actual sample unit. My only complaint is that the laser head (LT1 and Rb) attaches via a high quality HV BNC connector rather than the more common Alden type. Well, I guess you can't have everything!
Estimated specifications (SP-255):
Note: I suspect that the actual specs on compliance range are considerably lower, perhaps only 1,000 V (e.g., 4,500 to 5,500 V) but the value above might be possible at lower tube currents (less ripple).
This power supply will easily drive common HeNe tubes up to about 20 mW at the low end of its current range. The only thing possibly preventing it from powering larger 25 to 35 mW HeNe tubes is its somewhat anemic starting voltage (considering its exceptional 6,000 V maximum operating voltage and much more than adequate maximum current). The starting voltage is also not fully rectified so it pulses at 60 Hz and any capacitance in the cable and tube will greatly reduce its peak value. For high power or hard-to-start HeNe tubes, a small external boost starter may be needed. Alternatively, if you are willing to modify the power supply itself, additional stages can easily be added to the internal voltage multiplier if starting turns out to be a problem with your HeNe tube(s). See the section: Enhancements to Spectra-Physics Model 255 Exciter.
The schematic is available in ASCII (below) as well as in PDF format (link further below). For the ASCII version and the accompanying description, I have changed the part numbers to be more logically organized on the diagram.
Thus, if you are attempting to repair one of these supplies, they will not match the Spectra-Physics schematic (but there were no circuit board markings on mine anyhow). Also, the schematic and actual hardware differed in some component values but not anything that appears to be critical except that if your unit only has one capacitor for C3/C4, check its voltage rating - the use of two caps may have been an 'improvement'. :) Resistor values may also differ in various revisions. For example, another version used 56K, 3W for R10-R15 instead of the 30K, 5W resistors shown below.
X C3 C4
+-------||-----------||-------+--o HV+
| | LT1 R9
T1 | CR1 CR2 Y CR5 CR6 | Tube+ +-------+ Tube- 25K, 10W
+--+--|>|--|>|--+---+--|>|--|>|--+--/\/\------|- |-|---+-----/\/\---+
||( | | | Rb +-------+ _|_ R10 |
||( | | \ R1 - +--/\/\---+
||( | | / 6.8M T1: 2,200 VRMS, 50 mA | 30K, 5W |
||( | | \ 2W (primary not shown) | Q1 |/ C
||( | C1 _|_ | x--+-------|
||( | .5uF --- | CR1-CR6: 6kV | MJE3439 |\ E
||( | 5kV | \ R2 Rx / (Repeat |
||( | | / 6.8M C1-C2: .5uF, 5kV 30K \ Qx & Rx x
||( | | \ 2W C3-C4: 4.7nF, 5kV 5W / 5 times) |
||( T | | | | Qx |/ C
+---------------+---+ Qx (Q2-Q6): MJE3439 +-----x----------|
| | | Rx (R11-R15): 30K, 5W | MJE3439 |\ E
| | \ R3 \ R17 |
| | / 820K (Rb is in laser head) / 25K x
| | \ 2W \ |
| C2 _|_ | | Q7 |/ C
| .5uF --- | +----------|----------------|
| 5kV | \ R4 | | MJE3439 |\ E
| | / 820K | | R18 |
| | \ 2W | +----/\/\---+------+
| CR3 CR4 | | R5 R6 | ZD2 _|_, 1.47K | |
+--|<|--|<|--+ +---/\/\---/\/\------+ 1N970B '/_\ | R19 /
| 820K 820K | 24V | Q8 |/ C 330 \
| 2W 2W | +---------| /
| ZD1 _|_, | 2N3569 |\ E R20 |
| 1N753A '/_\ / | 500 /
| 6V | \ R21 | +->\
| | / 10K | | /
| | | | | | HV-
+------------------------+----------+-----------+---+--+--o
Current Adjust
Primary-side components consist of a fuse, power switch, neon power-on indicator, line voltage select switch, and interlock jack (for Jones plug jumper, some versions).
Here are the winding specs for the power transformer, T1 (from someone who had to disassemble one because they pushed their luck too far):
The basic circuit consisting of T1, CR1-CR4, and C1-C2, is a standard voltage doubler. R1-R8 provide a bleeder resistance as well as biasing the series regulator voltage reference. A single stage boost multiplier consisting of CR5-CR6 and C3-C4, provides a peak starting voltage approximately twice the no-load operating voltage - nearly 4 * V(peak) or 4 * 1.414 * VRMS of T1.
The series regulator is in the low side of the power supply and consists of a cascade of MJE3439 NPN transistors - a total of 7 in all (Q1-Q7). The combination of the MJE3439s and their associated base resistors labeled as Qx (Q2-Q6) and Rx (R11-R15) (the network denoted by the 'x's) are repeated 5 times (total) stacked one on top of the other to complete the diagram - I was lazy!).
Operating current is set by the Current Adjust pot (R20) and will be equal to: Io = 5.3 V / (R19 + R20) within the voltage compliance range of the regulator. The current range is about 6.5 to 15 mA. This could easily be extended to a lower current by increasing the R19 or R20 though it would seem like a waste of a nice piece of hardware to power a 0.5 mW HeNe tube! However, it could be used for this purpose if run from a Variac though the starting voltage would be proportionally lower and possibly inadequate unless the Variac were turned up until the tube started (but with way excessive current) and then quickly reduced - hard on both the tube and exciter though.
With 7 MJE3439s, the compliance range may be greater than 2,500 V. (However, usable compliance range is reduced at higher tube currents due to ripple.) ZD2 provides protection to limit the voltage across the regulator to a safe value for the transistors (approximately 2,600 V total, 370 V across each) should the compliance range be exceeded due to an accidental short circuit, defective laser head, or a HeNe tube which is too small. However, this allows more current to flow into the load which may then not be very happy :-(.
There are taps on the two primaries of T1 for 100, 117, and 125 VAC (primaries in parallel), and 200, 234, and 250 VAC (primaries in series). These would also provide additional options for the output voltage range when used without a Variac. The actual power supply has an externally accessible switch to select 115 or 230 VAC operation. However, changing the taps requires going inside and doing some minor soldering.
These schematics were drawn using the original Spectra-Physics part numbers for at least one version. It has obviously undergone some revisions as a couple of the part values are not sequential.
Newer versions of the SP-255 also have a two pin socket for a primary-side interlock, a circuit to implement the CDRH delay (4 seconds minimum, not shown on the schematics, but appears to be a thermal delay and power relay), a keyswitch for power, an incandescent power indicator (replaceable) instead of a neon lamp, and a detachable power cord with standard IEC connector. Note that the delay time of the time delay circuit will increase a