There are also brief descriptions of the Lexel-95 PSU, Spectra-Physics 265 exciter with a 165-3 argon head, and a few other systems. Schematics for these may be added in the future.
Also see the Laser Equipment Gallery for
for multiple detailed photos of several argon/krypton ion lasers and power
supplies.
It can drive a variety of small Ar/Kr ion tubes requiring up to 10 A or so
continuous current at 100 to 110 VDC. This covers the types of air-cooled
tubes you are most likely to acquire.
The Laser Equipment Gallery has detailed
views of various argon/krypton ion lasers including examples of the very
popular 60 series from American Laser Corporation. However, note that the ALC
and Omni models are plug compatible, the ALC power supply is NOT electrically
or physically the same as the Omni-150R described below.
The diagrams are available in both PDF and GIF format. There are three (3)
separate sheets:
Due to some inconsistencies between the '150R' and '532' schematics that I
used, some signal names and/or connectors identification may not match. I
have attempted to correct these discrepancies where possible. However, this
may have resulted in using names that were different than the 'official' ones
in some cases.
Note that ALC's own power supplies are entirely different electrically from
those from Omni. Only the heads and electrical interfaces are identical as
per Xerox standards. Thus, these schematics (150/155) do not at all apply to
an similar American product. Newer supplies have RS232 controls options and
are power factor corrected.
The basic operation of the each of the major functional blocks are summarized
below. For a more detailed discussion of the operation of the individual
circuits, see the chapter: Ar/Kr Ion Laser Power Supplies.
RLY1 also enables the power supply fan and the igniter circuitry. (The fan
in the laser head runs as long as SW2 is in the ON position.)
WARNING: This and ALL control circuitry is line-connected!
Configuration on older units is done on the 22 pin remote connector (P1 on the
Omnichrome 532 laser head).
Usually you ground the current input if using light and vice-versa. The 150
and 150R can be configured each way. You also have a choice of using the head
pot or the pot on the side of the supply, the supply pot is brought out on the
remote connector, and if your not using the remote, you have to put a plug on
the remote connector with jumpers. The CDRH requires a remote interlock jumper
on Class IIIa and up so they use the 22 pin connector for that as well.
But most 150s only run light, and wiring them for current as per the book
results in oscillation despite the book saying it can do either.
However some of the wires require special attention:
Unlike many other ion laser power supplies, these seem to always fail the same
way. The difficulty comes from the way their case and PCB are made. When you
have a dead one, my bet is that both MOSFETs, the fast recovery diode, one
capacitor, and the +15 V regulator are dead. Replace these and you are off
and running. 90% of the fail from 3 causes: MOSFET failure, miswiring, or a
loose heatsink that breaks off of the MOSFET leads where the cooling fan
vibrates the poorly mounted heatsink.
The particular model shown in the schematics uses a MASSIVE linear regulator
running off of a 220 VAC front-end for higher power Ar/Kr ion tubes requiring
more than 200 VDC at up to 35 AMPS! You better be able to afford the electric
and (cooling) water utility bills!
However, since the circuitry is quite simple - especially the feedback loops,
it can provide the ideal basis for a scaled down design of your own. By
substituting a 110 VAC front-end and using fewer transistors in the regulator
pass-bank, this basic approach would be suitable for a driving typical small
Ar/Kr ion tubes (e.g., 60X or Cyonics). See the section:
Sam's Linear Ar/Kr Ion Laser Power Supply
(SG-IL1) for the exciting details.
Also see the Laser Equipment Gallery for
for multiple detailed photos of several detailed views of the Lexel-75, a
smaller air-cooled cousin to the Lexel-88 as well as a power supply which
should be similar or identical to the one described below.
Lexel model 65 and 75 laser tubes require approximately 120 VDC across the
discharge while the model 88 tube requires around 220 VDC. It might start on
power supply running off of a 110 VAC line, but won't really run on it unless
it is three-phase.
I guess there is some confusion in Lexel's use of the 88 model designation for
more then one configuration. Most 2 to 5 watt ion lasers will run off 220 VAC
single-phase at low power, but not 110 VAC.
The 110 VAC 88D version of the Lexel-88 PSU will drive Lexel Model 65 and 75
tubes from single phase power (our schematics are for the 8A but they are
mostly similar except for the AC line front-end). The 88D may ignite and
barely run 88 tubes but not drive them to full current. Three-phase power is
really required for an 88 head and even then I imagine it won't take them all
the way up. Lexel-88 systems really need 220 VAC power.
The real common Lexel-88A runs off 220 VAC. The buck/boost transformer in the
front-end has 5 taps that can be configured as a autotransformer for stepup or
stepdown as much as 40 V, at currents to 25 A continuous. Selecting the
transformer taps will also aid you in getting the regulator pass-bank to
operate in the correct range (10 to 70 V for the Lexel-88) for a given tube
and is the first thing you check when you fire it up the laser.
The same transformer also provides a 110 VAC split tap in the primary for the
control relays.
The majority of the Lexel-88s are the "A" configuration, only a few 'Ds' were
made before an SCR (switchmode) version was released.
The Lexel-88 PSU has 12 RCA 2N6259 NPN transistors as the pass-bank, and these
are scarce/no longer made. The ECG sub is an ECG388, an inferior transistor
that is stressed badly in this application. I'm told high grade 2N3055s work
in a pinch, but have yet to try it for fear of popping the whole string.
It uses a water cooled 1/8th inch copper plate requiring 2.2 gpm of flow
through a 3/8th inch copper tube brazed to the plate. The plate is 14" x 4"
with one turn of water around the outside, with the 12 transistors and good
cooling, it's rated at 40 amps for 30 seconds at 250V DC, so you should be
able to adapt it to a air cooled heat sink for 10 amp service. All of the
transistors are isolated from the heat sink with BeO washers. That's not on
the schematics (Note caution about BeO dust!).
The Lexel-88 PSU was designed for industrial ion lasers and was used in argon
coagulators, so it has a lot of reserve kick that is not needed. It can
go all day at 30 amps or idle down at 10 mW and punch up to 5 watts for
sealing off arteries.
The 6 mH, 50 A choke used as part of the L-C smoothing network is a real back
breaker too, and that's millihenry, not microhenry.
The PSU gets its low voltages via a string of zeners - who needs a transformer
when you have 250 to 270 DC hanging around. It uses a good old 2 transistor
multivibrator to drive a doubler to get the -15 V for the op-amp. Regulation
is a surprising 2% at 25 A in current mode, and not much better in light mode.
Crude but very reliable, and you can diagnose any problem with just an ohm
meter and the diagnostic jacks on the front which give you current, tube drop,
and the amount of reserve voltage the pass-bank is dissipating; you add your
tube drop and the reserve, it should equal the rectified line volts, if not
the regulator is shorted, in which case it will limit itself to about 12 A.
The diagrams are available in both PDF and GIF format. There are
three (3) separate sheets:
Get LEXEL-88-PWR: 88psch.pdf or 88psch.gif.
Get LEXEL-88-CTL: 88csch.pdf or 88csch.gif.
Get LEXEL-88-HEAD: 88hsch.pdf or 88hsch.gif.
The .gifs are quite legible for on-line inspection. However, if you have
Adobe AcroRead or Acroexchange or the corresponding plugin for your browser,
the .pdf versions will permit more flexibility in viewing and should result in
nicer looking hard-copy when printed.
Note: Due to lack of complete documentation (schematics from different
versions of the Lexel-88 as well as some totally missing pieces), I have
interpolated in some cases and renamed signals to create a more consistent set
of drawings. So, these will give you the general idea but should not be
thought of as exact schematics of any specific model.
The basic operation of the each of the major functional blocks are summarized
below. For a more detailed discussion of the operation of the individual
circuits, see the chapter: Ar/Kr Ion Laser Power Supplies.
The schematics show the Lexel-88 wired for 220 VAC, 40 A input for use with
an Ar/Kr ion tube requiring about 200 VDC across the discharge. However,
selecting different taps on the buck/boost transformer (part of T2) and/or
rewiring the front-end for 110 VAC input or even modifying it for 240/208 VAC
three-phase would be a simple matter.
WARNING: For these line connected designs with a bridge rectifier, NO part of
the circuit can be tied to earth ground (as is possible with a HeNe supply)
for safety. Therefore, troubleshooting must be done with extreme care
especially if no isolation transformer is used. Connecting the ground lead of
a properly grounded scope to any part of the circuit will result in smoke or
worse!
WARNING: This is even more instantly deadly at 220 VAC!
WARNING: This and ALL of the associated control circuitry is line-connected!
The Lexel-88 may operate in either current or light control modes determined
by the setting of the Control Selector switch, S7.
Current Control PCB:
Interestingly, the light sensor in the laser head is on the low side so an
interface is needed to pass its error/control signal to the main error amp
which is controlling the pass-bank. This is accomplished using a PWM chip!
The error signal controls the duty cycle of a digital pulse train which is
coupled via an opto-isolator to a simple RC averaging circuit thus providing
the actual control signal!
(From: Steven Roberts (osteven@akrobiz.com)).
Lexel starters are a large coil and core series igniter transformer that has
a relay built into the starter magnetic path. The relay is initially closed
by the start signal, passing current through the igniter coil from a 6 uF
capacitor. It is then opened by the tube current passing through the
transformer core and nulling out the magnetic field caused by the relay's 2K
ohm coil. Kind of weird. If you didn't have one to look at you'd never
believe it works. A fully magnetic relaxation oscillator. How they ever get
it balanced is beyond me, there are no adjustments, so somebody was really
good at transformer core design.
For this reason, there is also no way I would recommend the use of such a
supply for anything but very initial testing and NEVER for unattended
continuous operation.
However, it enables something to be constructed reasonably quickly to give you
a taste of what is to come - or to be used for testing of Ar/Kr ion tubes in
unknown condition since there is virtually nothing to fail. You can short it
out without fear of blowing expensive parts. Since this is a subset of "Sam's
linear Ar/Kr laser power supply", the addition of regulator and control
circuitry in the future is straightforward.
WARNING: Everything is directly line connected. Great care (even more than
just considering the 1,500 W or so of raw power we are dealing with!) must be
taken in the basic construction, testing, and strict adherence to ALL safety
precautions during testing, use, and troubleshooting. See section: SAFETY
when Dealing with Ar/Kr Ion Laser Power Supplies and the document: Safety
Guidelines for High Voltage and/or Line Powered Equipment.
This is a simple AC line-connected AC to DC power supply. Note: Essential
safety and protection components not shown. See the section:
Required Safety/Protection Features.
Note: Additional small ceramic capacitors should be placed in parallel with
C1 and C2 to bypass high frequency noise (not shown).
It can be made by modifying the high voltage transformer from a defunct
microwave oven (assuming it died for other reasons - which is very likely).
Remove the high voltage secondary winding (hack it off, whatever) to prevent
the possibility of an unfortunate accident. Then, determine the voltage of
the existing filament winding and adjust the number of turns to produce just
over 3 VRMS under load (use some of your left over space heater element wire
as a dummy load for this test if necessary). Finally, add a secure centertap
connection.
I am actually using a Stancor P6433 'Filament Transformer' - probably left
over from the vacuum tube days. It is rated at 5 VRMS CT at 15 A. While
these specifications are not ideal, it runs fine on a Variac.
CAUTION: SG-IL1 has not yet been built so treat it as a 'Works-in-Progress'.
In other words, I will not be responsible should the universe collapse into a
singularity upon powering up a system based directly on these diagrams!
Components are number independently for the for each module or board as
follows:
K2 also enables the power supply fan and the igniter circuitry. (The fan
in the laser head runs as long as CB1 is in the ON position.)
WARNING: This and ALL of the associated control circuitry is line-connected!
The boost supply powers both a relaxation oscillator consisting of a neon
bulb, DL1, R4, R5, and C5, and the igniter storage capacitor, C6. Pulses are
generated several times a second until the tube starts. The igniter
transformer, T1, is wound on a 2.5" x 3.0" ferrite core from an old flyback
(with the core gap spacers removed) and has a 2 turn primary and 40 turn
secondary using #14 wire. SCR1 discharges the igniter storage capacitor,
C6, into the primary of T1 resulting in an 8 to 10 KV starting pulse. The
snubber components (D2 and R7) and tuning capacitor (C7) assure maximum
output pulse amplitude with minimal undershoot (which could just as easily
shut off the tube as start it up!).
(From: Ben (warp9_4@hotmail.com or macgyver@sub.net.au)).
Well, at about 8 PM tonight I pressed the operate button on my BJ/SGIL1 for
the first time. After extensive testing before hand (dry runs with no tube
connected), setting up the control currents and trip outs, and heavily
modifying the digital control logic (completely different and simpler than the
design you have suggested), the tube sprang to life and the supply is coping
quite nicely.
I think I scared the absolute F*** out of my house-mate when he walked into
the room while I was doing a low level beam effect (the sheet of light effect)
with the power cranked most of the way up and no lights on. We fiddled with
the laser for about 4 hours flat out, making vertical scans - the beam moving
up and down rapidly and scanning from side to side slowly, and even conjured
up a small beam shutter to cut off the beam at certain intervals. All these
effects are generated by 4 pots and 5 switches. Obviously, one set for
horizontal, and one for vertical, and the 5th switch being the manual beam
shutter.
All I can say is most of SGIL1 works OK (maybe all of it does, but I couldn't
get the logic board working). My design uses a 555 (running at 2 Hz) clocking
2 CD4017 decade counters to generate the 1 and 2 HZ blink clocks and the 40
second preheat delay. The 8th output on the second one disables the 555.
Opening any interlock kills power to the drive relays as usual, but it also
resets the 4017's so that when prehest is pressed again (or all interlocks are
reset), the standby and operate controls won't function until the preheat
delay expires.
I have added a beep for every button-press and a new display. Instead of
having just a preheat led, a circle of leds (five 3 mm units) bisected by a
pair of vertically mounted 5mmx2mm rectangular leds provide a standby/operate
indicator. It lights up red with the rectangular leds red when preheating the
filament, and turns green when the filament is warm; and the rectangular leds
go out.
Case heat isn't a problem, the 240 VAC fan is rated at 150 CFM and cools the
pass-bank and the 200 W, 2 ohm resistor I just happened across at an
electronics junk yard. I expect this resistor to handle the heat OK as it is
mounted on a gigantic heatsink from a 2 KW inverter. I'd say it's about a 3.3
degree/Watt heatsink.
It's running as we speak at half power at home. I trust my house-mate to keep
an eye on it - burning in the tube as it hasn't been fired in about a year.
I asked him to run it till he goes to bed. He doesn't mind the space heater
effect. I just spent most of my money on a bloody laser, but it is a LOT of
fun :) :).
(Two months later)
Well, here we go - I have made a few modifications to the supply, and
drastically changed the front panel layout (thank god for 19" rack cases
with replaceable panels!
The preheat/blink timer now consists of a 556 timer and few other components.
This all fits onto a board the size of a large DPDT mains switching relay. I
actually used a cable tie base and cable tie to stick it to the side of the
control relay. All my control logic is now done by relays and switches. Less
chips in the thing means less things that can blow up :)).
Front panel layout:
I am dying to get a camera and takes some photos of this thing to show you the
real thing rather than ASCII renditions. I can easily access a scanner, but
may have to buy a disposable camera. Oh well :).
I also have some circuits on the way for light shows:
Now I wonder how I can get rid of that damn annoying 12 second delay on the
start board of the NEC-3030 head? I don't want to probe around it, specially
when its trying to start. Wouldn't mind a schematic for it :(.
BTW, you need to increase your bleeder resistor on the main supply caps to
about 9 or 10 K as the 5K, 7 W tends to get a little too hot. Either that or
up its wattage - I am using a pair of 4.7K 5 W resistors and they bleed off the
charge in about 60 seconds - takes about that long to get the 8 lid screws
out :).
(Quoted text from: Ben (warp9_4@hotmail.com or macgyver@sub.net.au)).
I am supposed to do a light show tomorrow night and I think my laser has
died. The heaters come on and glow brightly, and the system is getting
ignite pulses. There is a flash of plasma every second or so, 3 dim ones,
then a bright one, but the tube fails to start. What would cause this? I
have checked the regulator on a dummy load and that's working fine, as are the
caps and front-end bits and pieces. I need to have this thing back up and
running tomorrow! :(
I don't like the thought of brute starting it with a Oudin coil (and I don't
possess one anyway - about the only thing that I have that comes close is a
solid state Tesla coil, a design using a TV flyback.)"
It doesn't matter where I set the current control, it just flashes. It seems
as though the igniter is in good condition. Could it be a dead filter cap in
the supply? I don't really have a means of testing large value caps. What is
the usual cause of this problem? I have tried to let it run for 15 minutes
trying to start but no change. I am worried i might do damage to the head or
supply trying to start it."
You could try bypassing the regulator with a suitable power resistor to limit
current to 10 A at 100 V on the tube and see if it will run unregulated, thus
confirming a problem in the supply. but do this with caution!
And, if it was something to do with the power supply, then this needs to be
determined before you attach another tube.
Well, its been fun - I'm going to get another head, and a commercial
exciter from Mark - He's gonna give me the head and all I have to pay for is
the exciter - $500 - for an exciter and a 300 mW head - not bad eh? :)
I will keep in touch and let you know when it arrives. I am going to put my
test supply up for sale to partially fund the new laser, but I will keep my
SG-IL1 as a reminder - and as a spare supply should the commercial unit die
catastrophically.
Sad outcome in some respects, but it wasn't the fault of your circuits - There
will be a happy ending to this saga :).
Keep me posted of any updates you make to the laserfaq, as I enjoy reading
it immensely - I probably visit about 10 times a week if not more :)."
You are the first person I know of to do something serious from the ion laser
portion of the FAQ. It is always being updated so you will just have
check frequently. Unfortunately, I cannot document every small change or
addition though major events will show up on the Sam's
Laser FAQ Welcome Page.
I will definitely watch the old eyeballs - 300mw seems a zillion times
brighter than the 3030 (the 60X is so bright that I can't look at the output
on the wall!). It's doing this at only about 7 amps."
WARNING: Where the power supply is line-connected (without isolation), this
measurement would have to be done differentially across the sense resistor if
the scope or meter has its case tied to ground. See the section:
Measurements of Current and Voltage in Ar/Kr
Ion Laser Power Supplies
We may never know exactly what went wrong. From the section:
Problems with NEC Argon Ion Tubes, it is
apparent that these laser heads sometimes fail to start due to no external
cause - and can be resuscitated using an Oudin Coil.
It did start and run once for about 10 seconds using the Tesla coil before
winking out so it isn't a problem with the ignite board.
I have changed everything (Excluding the transformer) in SGIL1. Its definitely
the tube as as we have discovered before, it happily powers a 60X."
Two weeks later:
It was running beautifully. I even had the clamp meter across it and in full
view of the TV so I could keep an eye on it, doing 6 A. Then, without
warning, the cathode gave out with the filament opening up half way between
the second and third windings back from the OC.
It was both disappointing and sort of heartbreaking to see such a project die
spectacularly considering I pumped more than $2000 into it over 3 years and
with 4 power supply rebuilds. We tried, we failed, but I intend to get a
new tube and hook it to BJ/SGIL1. I will be taking photographs next week
and sending them to you along with hand drawn schematics. I would like to
ask a favor from you and steve, silly though it sounds, we have all been
involved in Kes' operation and construction, and in her repair and demise.
(no, i don't blame either of you, it was a high mileage tube), and that is
for both of you to sign a small square of paper (say 2" square) to be stuck
to its chassis as a reminder of the fun I had putting it all together the
4th time over.
I would like to stress to everyone out there that when building any large
project (it being a laser or anything else) involving large voltages or
currents, that things can and DO go wrong, sometimes for unknown reasons. It
hurts, especially when you spend a large (or a small amount) of money on a
project only to have it die on you. Well, my small world did collapse into a
singularity, but only for a moment. The chassis of the NEC3030 (Kes) will be
placed on display in my living room. The strange (to the uneducated eye)
looking piece of equipment is sure to attract attention from newcomers and
friends alike. I think I will go and play some depressing music now....."
This PSU is 3-phase with a buck/boost transformer and 26 (!!) 2N6259s. It is
rated at 45 A continous. Other then the cold plate being a little bigger
to hold the extra transistors, the case being a little larger to hold a
massive three phase buck/boost transformer, and 6 diodes in the rectifier
instead of 4, it's the same beast as the Lexel-88 PSU. And, no, the passbank
drivers were not beefed up to drive the extra 2n6259s!
We spent the day working on this model so here is some information:
The exciter (a.k.a., power supply; Spectra-Physics seems to call all their
units 'exciters') will provide up to 35 amps off of the 220 VAC, three phase
line. The input pi C-L-C filter network uses a .5 mH inductor (HUGE) with two
3,500 uF capacitors. Keep in mind that the filament transformer is also a
minor inductor and helps some as well. And, this is on a three phase system
where the raw ripple is much lower to begin with!
The linear regulator uses *55* pass-bank transistors (that's right folks, 55
transistors!) wired in series-parallel strings and they are common 23N3055s!!
The pass-bank is on the low or cathode end, as is the igniter transformer.
The 165-3 argon laser head uses a tube that is 24 inches long nominally
dropping 232 VDC at 30 amps. This voltage will be lower if the tube pressure
is low and higher if it is too high. At first, it was only 206 VDC at 30 A.
There is a little reservoir (inside the tube) with a solenoid activated valve
that we used to fill it back up to the desired range.
The tube has the usual 3 volt 25 to 30 A cathode.
The laser head includes an axial electromagnet. Its power supply used 2N3442s
for the regulator which needs to provide around 108 to 216 VDC (adjustable)
into the 49 ohm electromagnet coil.
This laser would do about 4 watts at 32 A if the tube was good but the
particular version tested had a line selector prism on it, so we could only
run one line at a time.
This is a more modern power supply designed for the ALC 60X ion laser head.
It uses 2 MOSFETs driven by a PWM switchmode controller chip for the course
loop to keep the voltage low on the fine loop. Then, there are two MJE2500
NPN transistors, a quad op-amp to control the linears, a in line shunt
resistor to sense current for the whole mess. This is quite simple, uses
modern chips, and easily built. And, best if all if you don't want to build
something from scratch, a bunch of them were dumped on the market last year
and should be available at a reasonable price. The only downside is that they
are limited to nine A maximum. At 10.2 A they start to melt down! Xerox
started the tubes at 4.5 A and end of lifetime was 8.2 - never cleaning the
optics or peaking them, they tuned these lasers to do 23 mW through their
life, exactly the opposite of tuning them for max power, xerox turned them
down for whatever reason.
When one of these fails, the most common 'fault' is that the high limit was
turned up too much. Gold boxes use a sloping ramp PWM system, if you turn up
the high limit, you have to readjust the rest of the ramp generator, else boom!
Gold boxes are a huge rats nest of unmarked white teflon wire in bundles, with
parts mounted seemingly at random through out the case, on multiple boards.
Attempting to trace out the circuit is very difficult. It took me two months
to do the first one! They have multiple nested loop control systems. So it's
a lose-lose situation. And, you have untrained users with no budget who think
they are gods gift to electronic systems!
As an example of a sophisticated PSU, I have schematics for one that will
source 7 to 35 A using just four 2N6259s! How do they get away with it?
An SCR bridge upstream of the linear pass-bank keeps the voltage across the
2N6259s at about 8 volts maximum. Of course it's a three-phase beastie and
they use 6 SCRs for fine control, but I'm working on adapting it to my Lexels.
After all, most of the circuits are the same. They use diodes in series with
each of the transistor bases so if you get a short the rest of the transistors
are still in loop and the driver transistors have a chance of surviving.
Since the ripple from rectifying the three-phase is 360 Hz instead of 120 Hz,
filtering components (Cs and L) don't need to be as massive as for single-phase
designs.
They have a way around the SCR shorts as well (which if not dealt with would
result in cascade failures of the pass-bank transistors and other components).
A massive clamp diode array and 4 fuses made of #28 AWG wire (it's right on
the schematic|), for emitter fuses: "For F1-F4, stretch #28 copper from P1
to...".
The only other mod to the pass-bank compared to what we are familiar with is
adding 470 Ohm pull-down resistors from the base to the top of the emitter
resistors since they have the diodes in series with the base drive, I guess
they needed something to make sure the transistors turn off.
This supply is really complex cause it was made for a $45,000 laser, but most
of it is very much similar to the lexel, except they check to see if the
ignite pulse triggers, measure the cathode current and voltage, the tube
current and voltage, the pass-bank current and voltage, and available line
volts, controls each polarity of each phase independently, has linear and BCD
control inputs changes some circuit values automatically if it's driving a
krypton tube and autoswitches from 220 to 440 VAC depending on the available
line voltage and tube pressure from a gauge tube. The schematics and service
manual fill a three ring binder and its got more circuit cards then the space
shuttle. The linear opto-isolater based control voltage inputs and outputs are
a marvel of design, using 2 opto-isolaters, one for the signal, one for the
correction, and a bunch of PFM/PWM links to isolate the high side from the low
side. However the basic control circuits are simple but it does have shaping
and filtering of the comparator functions for a proper lead/lag loop.
The SCR chopper seems to be a excellent candidate for home built PSUs, if the
filter inductor can be kludged with a common part everyone can get, I think 4
to 6 2N3055s would do quite nicely air cooled.
Commercial Ar/Kr Ion Laser Power Supplies
There are now virtually complete sets of drawings for two very popular
commercial power supplies (and associated laser heads):
These two approaches are representative of a large number of other commercial
ion laser power supply designs though obviously, details may vary quite a bit.
Portions of the SG-IL1 presented later in this chapter are based to varying
degrees on modifications to these commercial power supply designs.
Omnichrome 150R Power Supply and 532 Laser Head (Omni-150R/532)
Introduction to Omni-150R/532 Schematics
The Omnichrome 532 and American Laser Corporation 60X are functionally very
similar (possibly identical for some versions). With the ALC-60X/Omni-532
being the most common argon ion lasers available surplus to the hobbyist,
experimenter, or budding light show enthusiast, having a detailed schematic
is a definite plus (what an understatement, huh?!). These circuit diagrams
can also serve as the basis for a simple switchmode power supply design of
your own!
Omnichrome 150R/532 Schematics
The schematics have been redrawn from poor originals of the Omnichrome 150R
power supply and Omnichrome 532 laser head. The only things that are missing
are wiring for the interconnect and remote cables, and some of the panel
switches and indicators.
The .gifs are quite legible for on-line inspection. However, if you have
Adobe AcroRead or Acroexchange or the corresponding plugin for your browser,
the .pdf versions will permit more flexibility in viewing and should result in
nicer looking hard-copy when printed.
Omnichrome 150R Power Subsystem
The Omnichrome 150R - Power Subsystem consists of of the (110 V) AC line
front-end/rectifier/filter and switchmode (buck) regulator, current sense,
filament supply, and boost multiplier, and low voltage supply.
WARNING: For these line connected designs with a bridge rectifier, NO part of
the circuit can be tied to earth ground (as is possible with a HeNe supply)
for safety. Therefore, troubleshooting must be done with extreme care
especially if no isolation transformer is used. Connecting the ground lead of
a properly grounded scope to any part of the circuit will result in smoke or
worse!
Omnichrome 150R Control Subsystem
The Omnichrome 150R - Control Subsystem consists of of the Preheat Timer,
PWM Controller and MOSFET driver, primary (inner) loop, and secondary loops
for Standby, Current Feedback, and Light Feedback.
(From: Steve Roberts (osteven@akrobiz.com)).
Omnichrome 532 Laser Head
The Omnichrome 532 laser head includes the air-cooled argon laser tube and
its HUGE fan(s), igniter, light sense circuitry, and test jacks.
ALC-60X/Omni-532 Interconnect Wiring
ALC-60X/Omni-532 head cables are wired 1 to 1 pin for pin from the laser head
to the power supply, there is no magic interconnect diagram for them.
The head cable should be limited to a maximum length of around 9 feet.
Omni Power Supply Failures
(From: Steve Roberts (osteven@akrobiz.com)).
Lexel-88 Power Supply and Laser Head (Lexel-88)
Introduction to Lexel-88 Schematics
Argon, krypton, and mixed gas ion lasers manufactured by
Lexel Laser, Inc. are the second most
common type available to the serious laser enthusiast after the
ALC-60X/Omni-532. Therefore, schematics for at least one version of
a Lexel-88 power supply and laser head should come in handy.
General Description of Lexel-88
(From: Steve Roberts (osteven@akrobiz.com)).
The same supply runs off 110 and 220 single-phase or three-phase, depending on
what tube is hooked to it and how you configure the input stage. It's a brute
force linear with pass-bank, uses a simple op-amp as the controller, is not a
fancy switcher, and just about anyone could adopt it to their needs. Lexel
used it to run lasers from 75 mW to 5 watts with only slight changes such as
sticking a buck boost transformer on it or a three phase bridge.
Lexel-88 Schematics
The schematics have been redrawn from poor originals of various parts of
several different versions of the Lexel-88. Although the actual interconnect
wiring is not shown, the relevant signals are labeled with a connector pin
(J or P number) and/or with a signal name indicating origin or destination.
In any case, recreating suitable circuits should be a simple exercise for the
student now that you are familiar with ion laser power supply design! :-)
Lexel-88 Power Subsystem
The Lexel - Power Subsystem consists of of the single-phase (220 V) AC line
front-end and rectifier/filter, regulator pass-bank and its driver, current
sense resistors, filament supply, dual-range meter, and relay logic power
control circuitry.
Lexel-88 Control Subsystem
The Lexel 88 - Control Subsystem consists of of the Current Control and Light
Regulator PCBs including high (floating) and low side low voltage power
supplies and overcurrent trip circuit.
Light Regulator PCB:
Lexel-88 Laser Head
The Lexel-88 laser head includes the water-cooled Ar/Kr ion laser tube and
electromagnet, igniter, and light sense circuitry.
Home-Built Ar/Kr Ion Laser Power Supplies
These designs have been developed with the objective of being relatively easy
to construct using readily available parts. There are currently complete sets
of drawings for both a 'brute force' power supply just to test your tube (but
which really shouldn't be used as a permanent solution) and a high quality
linear power supply derived from the Lexel-88 implementation (but with various
enhancements). Compatible laser head designs are also included for each one.
Note: The "Sam's" designs are currently under development so there are no real
guarantees of anything though Ben has successfully built one!! However, they
should give you the general idea. :-)
Sam's Super Simple(tm) Ar/Kr Ion Laser Test Power Supply (SG-IT1)
Introduction to SG-IT1 Schematics
This is about as basic as it gets! Everything is done manually. No control
loops, no op-amps - nothing. Your eyeballs and brain provide the feedback by
watching the current meter like a hawk! Even the slight line dip from turning
on a lamp elsewhere in the house can affect tube current in a detectable way!
That's all there is to it! The complex :-) block diagram is shown below
(Variac for filament supply and LARGE Variac for main supply not shown):
M1 +-----+
+---+ +-|0-10A|-+
+--------+ DC+ Rb | | | +-----+ | +-----------------+
H o--------| |--------/\/\-+---+--/\/\---+--| Igniter Circuit |--+
| Main | 10 1,500W Rs .2 50W +-----------------+ |
AC Line | Bridge | |
(on Variac) | and | |
| Filter | DC- |
N o--------| |----------------+ F1 +-----------+ |
+--------+ | +------|-+ | |
| | | | F2 | ) |-|---------+
| +--------+ T1 | | +---|-+ | Tube+
| ) +-----------+ | +-----------+
| Filament )||( | | Ar/Kr ion tube
| Supply )|| +-----+ Tube- |
| (on Variac )||( |
| ) +--------------+
+-----------+
Since the power supply is only for initial testing (GOT THAT?!) it does not
have an active regulator. Tube current control is provided by a large Variac
and/or the heating element from a 1,500 W space heater as a high current high
power ballast resistor. If the heating element is removed, then adjustments
can be made by changing its resistance by moving a tap and the Variac isn't
essential. If the space heater is used intact (it just looks kind of funny!),
the Variac will be needed. (Even if the space heater has multiple switchable
heat settings, this doesn't provide fine enough control.)
SG-IT1 Schematics
The diagrams are available in both PDF and GIF format. There are four (4)
separate sheets:
The .gifs are quite legible for on-line inspection. However, if you have
Adobe AcroRead or Acroexchange or the corresponding plugin for your browser,
the .pdf versions will permit more flexibility in viewing and should result in
nicer looking hard-copy when printed.
The ASCII schematics in the descriptions below are basically the same as those
in SG-IT1-PWR and SG-IT1-HEAD but some components not essential for explaining
basic operation may have been left out to simplify the diagrams. And, there
might an enhancement or two. :-)
Since the intent of this design is to provide something for testing of ion tube
and laser heads, the partitioning of subsystems between the main power supply a
d laser head is only a suggestion. Your actual arrangement may be dictated by
the design of the actual equipment under test. For example, modifications may
be needed if the existing igniter in the laser head is not directly compatible
with the outputs of the SG-IT1 as drawn.
SG-IT1 AC Line Front-End
The design described below can serve as the front-end to a linear or switching
regulator, inverter, or to a brute force power supply using only an additional
ballast resistor (for testing only, right?).
PH-H (Filament Suppy)
o D1: 35A, 600V
Preheat | R5
S2 | D5 1N4007 330 5W R1: .1, 25W
SW-H o--+---o/ o--+----|>|-------/\/\---+ R2: 1, 200W (see text)
(Fans) | | R3, R4: 5K, 7W (bleeder)
| OP-H (Igniter) |
| o | C1, C2: 3,000uF, 200V
Main | Operate | |
S1 | S3 | D1 (Bridge) R1 | R2
H o---o/ o--+---o/ o--+-+--|>|-----+--/\/\--+-+-----+--/\/\--+-----+--o DC+
| ~| |+ | | | |
| +--|<|--+ | +_|_ / +_|_ /
| SW-N | | C1 --- R3 \ C2 --- R4 \
| o +--|>|--|--+ - | / - | /
| | ~| |- | | | |
N o---o/ o--+-----------+--|<|--+-------------+-----+--------+-----+--o DC-
Note: S1, S2, and S3 can be switches or relays. Logic controlled relays are
highly desirable to enforce the sequencing requirements on the Ar/Kr ion tube
power. For initial testing, manually operated switches may be used.
SG-IT1 Ballast Resistor
Current control for SG-IT1 is provided by means of a LARGE Variac on the main
power input and a high wattage ballast resistor in the return (DC-) from the
laser head. This location permits SG-IT1 to be easily upgraded a regulated
supply (e.g., SG-IL1) by replacing Rb with a regulator pass-bank or chopper.
The only regulation here is via manual adjustment of the value of Rb or the
Variac setting while watching the current meter. :-)
A convenient ballast resistor can be made from the element of a 1,500 W space
heater by providing multiple taps or a clip-on jumper so that lower values of
resistance can be easily selected. See the section:
Constructing Low Ohm High Power Resistors.
SG-IT1 Filament Supply
A low voltage high current step-down transformer is the easiest way of
providing the 2.5 to 3 at 15 to 25 A required by the Ar/Kr ion tube filament.
SG-IT1 Current Meter
This is implemented with a 10 mA FS panel meter and .1 ohm, 50 W shunt as
described in the section: Measurements of Current and Voltage in Ar/Kr Ion
Laser Power Supplies:
Rs .1 50 W
From Rb o======+===============/\/\===================+======o DC+
| |
| +--+ M1 |
| Rs1 | v R2s + +----------+ - |
+-----+-/\/\---/\/\----| 10 mA FS |----+
Calibrate 10 91 +----------+
Reads 0-10 A
Wires from M1 and Rs1 are soldered to the leads of Rs (instead of the other
way around). That way, it is less likely that a bad connection can result in
the shunt opening - which would fry the meter movement in a very very small
instant! The 10 mA meter I used (from a pile I had acquired long long ago)
has a measured resistance of 3.5 ohms. With the addition of R1, the 10 ohm
Calibrate pot (R2) provides fine adjustment of full scale sensitivity.
SG-IT1 Laser Head
The SG-IT1 Laser Head is a intended as a suggestion
and may differ from what you have if you are testing a commercial laser head.
It includes the air-cooled argon laser tube and its HUGE fan(s) and igniter.
This stripped down laser head has no light sense circuitry or interlocks.
SG-IT1 Igniter
This is similar to the igniter from the
Omnichrome 532 Laser Head except that a pushbutton
switch is used instead of a unijunction transistor to trigger the SCR. Like
that design, it is assumed that the boost supply is in the main power unit with
the actual igniter located close to the tube anode in the laser head. Of
course, if you are testing commercial laser head, it may already have an
igniter so some or all of this circuit may not be needed.
- C3 + - C4 +
SW-N o-------------||----+--------||---------+ D3-D6: 1N4007
D3 | D4 D5 | D6 C3-C6: 10uF, 400V
+---|>|---+---|>|---+---|>|---+---|>|---+
R6 | - C5 + | - C6 + |
OP-H o---/\/\--+---+----||----+----+---+----||----+----+---+---o Boost
| R7 | | R8 | | (>400 V)
+---/\/\---+ +---/\/\---+ |
1M 1M |
+--------------------------+---------------------------+
| |
/ / Igniter pulse transformer
R9 \ R10 \ Stepup ratio 20:1
100K / 100K / T4 o
\ \ +-----+--o HV+
| | ::( |
+--------------------------|---------------+ ::( |
| | C8 1uF 600V | ::( 40T _|_ C7
R11 / SCR1 +---||----+------------+ ::( #14 --- 500pF
8M \ 2N6508 __|__ | | 2T )::( | 15KV
/ S4 600V _\_/_ / | #14 )::( |
| _|_ 25A / | R14 \ | +--+ +-----+
+-------+---- ------+---' | .1 / | | o |
| | Start | | \ | | |
/ | / | | +---|-------------+
R12 \ C9 _|_ R13 \ | D7 __|__ | | |
100K / .1uF --- 180 / | MR826 _\_/_ _|_+ | D8 _|_
\ | \ | | --- | 1N1190AR /_\
| | | | | | | 600V,40A |
+-------+---------+-+------+-+-------+-----+---+-------------+
| | | C10 10uF
o C12 _|_+ C13 _|_ 600V
DC+ 10uF --- .1uF ---
450V | 500V | (Some Components Not Shown)
F1 o----------+----------+
The igniter pulse transformer is wound on a 2.5 to 3 inch diameter ferrite
core using #14 insulated wire for the primary and secondary. (The core from a
flyback transformer should also work - remove the gap spacers). Take care in
winding to distribute the turns uniformly approximately 3/4 of the way around
the toroid making sure that the end of the secondary is at least 1 inch from
the start and any possible conductor. Position the primary turns near the
starting end (bottom on the diagram) of the secondary. This will prevent
arcing and allow the use of wire with normal insulation rather than bulky high
voltage wire.
Sam's Linear Ar/Kr Ion Laser Power Supply (SG-IL1)
Introduction to SG-IL1 Schematics
The design presented here is reasonably simple but should safely and reliably
drive small air-cooled Ar/Kr tubes requiring up to 10 A at 100 V. I took
features from both the Omnichrome-150R and Lexel-88 power supplies and added
some bells and whistles of my own including a CMOS logic controller and
indicators on all interlocks. The result should be a system which can be
constructed with mostly common inexpensive parts but with more than enough
sophistication to put those older designs to shame. :-)
SG-IL1 Front Panel Layout
This is the anticipated control panel layout for SG-IL1.
+---------------------------------------------------------------------------+
| Power -------- Major Modes ---------- Current |
| O Idle Preheat Stndby Operate FAULT Interlocks V/I Level |
| ____ PSU Head Meter (O) |
| |_ _| O O O O O --+ _______ |
| ||''|| +- O Fans O | | Light |
| || || . +--+ +--+ +--+ +---+ | | \ _ | Level |
| |+--+| (|) |PH| |SB| |OP| |RST| +- O OT O |-------| (O) |
| |____| ' +--+ +--+ +--+ +---+ |_______| |
| Key | | | Panic Status <---> TPs |
| Main Lock +-- Mode Select -+ Off O Warm O Vo=) I o o o o |
| Power 1 2 3 4 |
| SG-IL1 Linear Argon/Krypton Ion Laser Power Supply |
+---------------------------------------------------------------------------+
Legend: O = Indicator (LED or neon), o = Test point, (O) = Control (pot).
SG-IL1 Schematics
The diagrams are available in both PDF and GIF format. There are four (4)
separate sheets:
The .gifs are quite legible for on-line inspection. However, if you have
Adobe AcroRead or Acroexchange or the corresponding plugin for your browser,
the .pdf versions will permit more flexibility in viewing and should result in
nicer looking hard-copy when printed.
The basic operation of the each of the major functional blocks are summarized
below. For a more detailed discussion of the operation of the individual
circuits, see the chapter: Ar/Kr Ion Laser Power Supplies.
SG-IL1 Power Unit
The SG-IL - Power Unit consists of of the (110 V)\
AC line front-end and
rectifier/filter, regulator regulator pass-bank and its driver, current sense
resistors, filament supply, dual-range meter, and low voltage power supplies.
WARNING: For these line connected designs with a bridge rectifier, NO part of
the circuit can be tied to earth ground (as is possible with a HeNe supply)
for safety. Therefore, troubleshooting must be done with extreme care
especially if no isolation transformer is used. Connecting the ground lead of
a properly grounded scope to any part of the circuit will result in smoke or
worse!
SG-IL1 Control and Interlocks
The SG-IL1 - Control and Interlocks subsystem consists of of the main control
amplifier, Standby reference and current level
network, light control amplifier, overcurrent trip, and interlock circuitry.
SG-IL1 Digital Board
Sequencing for this power supply is implemented with discrete CMOS/HCMOS logic
devices. Other common logic families (like LS TTL) could be used instead with
minimal redesign. Since speed is not an issue (for once!), the main design
issues for such a substitution would be logic level compatibility and drive.
SG-IL1 Laser Head
The SG-IL1 Laser Head includes the air-cooled argon
laser tube and its HUGE fan(s), igniter, light sense circuitry, and test jacks.
SG-IL1 Igniter
This is similar to the igniter from the Omnichrome 532
Laser Head except that a neon lamp is used instead of a unijunction
transistor to generate the repeating pulse trigger to the SCR. Like that
design, it is assumed that the boost supply is in the main power unit with the
actual igniter located close to the tube anode in the laser head.
Ben's Linear Ar/Kr Ion Laser Power Supply (BJ/SG-IL1)
Someone Actually Built This Thing!
This design is based on SG-IL1 but with modifications to the logic board.
It runs off of a 2:1 high current stepdown transformer on the 240 VAC line.
+----------------------------------------------------------------------+
| Circuit Idle Heating Tube Current |
| [o] o o _ _ _ |
| Breaker [[]] Preheat | | | || | |
| |_|.|_||_| |
| Main Power o Fault |
| On (O) |
| (o) Lock [[]] Fire Min Max |
| Off (|)Run Power Adjust |
| Argon Laser PSU MK IV |
+----------------------------------------------------------------------+
The rear panel consists of an 8 way DIN socket for the interlocks, a 30 A
Speakon socket for the head supplies (3 cores of 20 amp lighting cable) and an
IEC female chassis socket for the 240 VAC fan on the head. All 3 lengths of
wire were cable tied together about every 30 cm along the cable and wrapped in
black insulation tape (to make it kind of neat and tidy). I decided not to put
indicators on all the interlocks - if one goes out, use of ones grey matter
should work out where the problem lies. The meter is a Dick Smith LCD panel
meter. Looks kind of nifty with 2 decimal places for the tube current, and the
blue backlighting looks quite good too (blue leds behind it)
I should have those schematics within about a month and I will get them
scanned in for you. Unfortunately, we're just waiting on that camera.
Failure of the NEC-3030 Laser Head
Unfortunately, since the description above was provided, the NEC-3030 laser
head which the power supply was driving appears to have died and will not start
from either Ben's version of SG-IL1, his brute force 'heater' supply, or a
commercial ion laser exciter. While all indications are that this was a
natural death (it WAS a high mileage tube), some peculiar behavior of the
power supply cannot be ruled out as the cause. Therefore, anyone constructing
SGIL-1 or any other home-built power supply as well as using a commercial unit
in unknown condition should make double sure that its output current is
controllable, limited to a safe value for the laser head, and stable.
"****PANIC**** ****PANIC**** ****PANIC**** ****PANIC**** ****PANIC****
Was it working and quit or did it just not start? It still sounds like a power
supply problem - does the current control have any effect on the duration or
brightness of the pulse? Can you try it on your brute force supply? Do you
have a scope to look at waveforms (careful - non-isolated circuitry!)
"It was working 5 hours ago and went to start it up again about 2 hours ago
and it wouldn't go.
It could be a bad cap - or a lot of other things.
"It looks like I have done all this work only to have my laser die after less
than 5 hours of operation. The tube won't start even with my old test supply
(7 ohm resistor, 4700uf cap and transformer borrowed from BJ/SGIL-1 :(."
I hope these problems don't discourage you too much. I have had my share
of disasters (you can read about them in the FAQ though you have to hunt for
them - I don't make them *that* easy to find!). I rationalize them as learning
experiences though in this case we don't yet know if the cause, assuming the
tube really is dead, was within your/our control or was just due to old age.
"It looks like I can get my hands on a 20 mW Uniphase or Spectra-Physics head
for $250, and a matching supply for $750 - heads are definitely cheaper than
the supplies! This is from:
HB-Laserkomponenten in Germany."
Those prices still sound high.
"It's really weird though - the tube is capable of generating a plasma, but
can't sustain it. Everything about the tube is fine from my point of
view - the cathode lights up, there are igniter pulses."
Does it generate a beam for those instants when it flashes?
"Yes. And, we have just confirmed that the tube IS the problem. Mark (a
friend of mine who has access to all kinds of gadgets, has turned up with a
Spectra-Physics exciter and we coupled it to the head - same problem. Two
very sad looking faces here. I will admit that the tube was a high mileage
job, and could have gone any time. Pity - now i have a home-built supply and
no laser to use with it.
Well, I wish you the best of luck and watch those eyeballs - 300 mW is a LOT
of laser light. :-)
"Mark has brought round the 60X head and has been very brave and hooked it up
to the BJ/SGIL1. It works fine and we have been watching the current on a
clamp meter for the past hour, and it's been fine. Looks like I just had a
bad head (or a very elderly one in hours usage terms). Mind you, my head had
many, many hours use on an unregulated supply until I found out that it needed
regulation, and that's probably what killed it. Learning experience I think.
The only other test to perform to be doubly sure that it wasn't the power
supply at fault would be to get a scope (or true AC ammeter with a high enough
frequency response - say at least a KHz) and make sure there are no high
amplitude oscillations in the tube current at any setting due to inadequate
damping in the feedback loop. Since the panel meter only measures average
current, these might not show up in the reading if they are at more than a few
Hz or in flickering beam brightness if they are at more than 50 Hz or so.
However, the peaks could still be too high for the tube. If this is not
happening and the there are no intermittents resulting in excessive current
at random times, it must have been that the head just dies on its own.
"Well, I tried starting our little friend today but burnt out one of the
TIP32Cs in my Tesla coil after 2 minutes attempting to start it. Knew I
should have put them on a heatsink. I will have to get a replacement as all
others have now been pressed into service in the SGIL1 :).
"This morning at 2:33 am I was watching a Star Trek episode after previously
finally got my NEC3030 to run (now nicknamed Kes), she finally said goodbye
in spectacular fashion: Towards the end of the episode, the cathode opened up
letting off a large white flash of light and finally ending the saga.
Description of Other Ar/Kr Ion Laser Systems
Lexel-95 PSU
(From: Steve Roberts (osteven@akrobiz.com)).
Spectra-Physics 265 Exciter with a 165-3 Argon Head
(From: Steve Roberts (osteven@akrobiz.com)).
The 'Gold Box' 60X PSU
(Portions from: Steve Roberts (osteven@akrobiz.com)).
High Performance PSU for High-End Ion Laser
(From Steve Roberts (osteven@akrobiz.com).
