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    Complete Ar/Kr Ion Laser Power Supply Schematics

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    Introduction and Summary of Schematics

    Introduction Ar/Kr Ion Laser Schematics

    This chapter provides detailed schematics of a variety of power supplies suitable for use with the 'small' air-cooled Ar/Kr ion tubes available to the hobbyist on the surplus market. Included are examples of commercial designs as well as simplified versions (those with names starting with "Sam's") that may be constructed from readily available parts. These will be satisfactory for typical experimental and light show applications. There is even a stripped down unit which can be 'thrown together' relatively quickly and inexpensively and is useful for basic testing of Ar/Kr ion laser tubes (and can be enhanced for general use at a later time).

    There are now four fairly complete designs:

    Note: The "Sam's" designs are currently under development so there are no real guarantees of anything! However, they should give you the general idea :-).

    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.

    See: Photos of Various Laser Systems, Power Supplies, and Components for multiple detailed views of several argon/krypton ion lasers.



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    Omnichrome 150R Power Supply and 532 Laser Head (Omni-150R/532)

    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!

    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.

    Photos of Various Laser Systems, Power Supplies, and Components 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.

    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 diagrams are available in both PDF and GIF format. There are three (3) 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.

    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.

    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)).

    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.

    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.

    However some of the wires require special attention:

    The head cable should be limited to a maximum length of around 9 feet.

    Omni Power Supply Failures

    (From: Steve Roberts (osteven@akrobiz.com)).

    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.



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    Lexel-88 Power Supply and Laser Head (Lexel-88)

    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.

    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 Laser Power Supply (SG-IL1) for the exciting details.

    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 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.

    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! :-)

    The diagrams are available in both PDF and GIF format. There are three (3) 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.

    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.

    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.

    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.

  • Rectifier/filter - This is a high current bridge with an L-C filter.

    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!

    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.

    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:

    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.

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    Sam's Super Simple(tm) Ar/Kr Ion Laser Test Power Supply (SG-IT1)

    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!

    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.

    That's all there is to it! The complex :-) block diagram is shown below:
                                   +--+
                +----------+ DC+   |  | Rb          +-----------------+
       H o------|          |-------+-/\/\-----------| Igniter Circuit |-----+
                |   Main   |        7 1,500 W       +-----------------+     |
       AC Line  |  Bridge  |        +-----+                                 |
       (Variac) |   and    |      +-|0-10A|-+ M1                            |
                |  Filter  | DC-  | +-----+ |                               |
       N o------|          |------+--/\/\---+           +-----------+       |
                +----------+     Rs .1 50 W |    +------|-+         |       |
                     |  |                   |    |      |  )      |-|-------+
                     |  +------+ T1         |    |  +---|-+         | Tube+
                     |          )   +------------+  |   +-----------+
                     | Filament )||(        |       |   Ar/Kr ion tube
                     |  Supply  )|| +-------+ Tube- |
                     |          )||(                |
                     |          )   +---------------+
                     +---------+
    
    
    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.)

    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.

    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?).

    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.

                   PH-H To Filament Transformer
                             o                        D1-D4: 20A, 400V, (bridge)
                     Preheat |               R5       
                     S2      | D5 1N4007   330 5W     R1: .1, 25W
                   +---o/ o--+----|>|-------/\/\---+  R2: 1, 200W (see text)
                   |                               |  R3, R4: 5K, 5W (bleeder)
                   |     OP-H To PS Fan/Igniter    |
                   |         o                     |  C1, C2: 3,000uF, 200V
           Main    | Operate |                     |
           S1      | S3      |    D1          R1   |           R2
       H o---o/ o--+---o/ o--+-+--|>|-----+--/\/\--+-+-----+--/\/\--+-----+--o DC+
               |              ~|  D2      |+         |     |        |     |
               |               +--|<|--+  |        +_|_    /      +_|_    /
               | SW-N             D3   |  |      C1 --- R3 \    C2 --- R4 \
               |   o           +--|>|--|--+        - |     /      - |     /
               |   |          ~|  D4   |-            |     |        |     |
       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 Igniter

    This is basically similar to the igniter from the Omnichrome 150R power supply and 532 laser head except that a neon lamp is used instead of a unijunction transistor for the relaxation oscillator.
                       - C3 +         - C4 +
      OP-H o-------------||----+--------||---------+           D6-D9: 1N4007
                         D6    |   D7        D8    |   D9      C3-C6: 10uF, 400V
                     +---|>|---+---|>|---+---|>|---+---|>|---+
                R6   |      - C5 +       |      - C6 +       |
      SW-N o---/\/\--+---+----||----+----+---+----||----+----+---+---o Boost
                         |    R7    |        |    R8    |        |    (>400 V)
                         +---/\/\---+        +---/\/\---+        |
                              1M                  1M             |
            +---------------------------+------------------------+
            |                           |
            /                           /            Igniter pulse transformer
         R9 \                       R10 \                Stepup ratio 20:1
       100K /                      100K /                       T1  o
            \                           \                          +-----+--o HV+
            |                           |  600 V               |:|(      |
            +---------------------------|-------------+        |:|(      |
            |                           | C8  1uF     |        |:|( 40T _|_ C9
        R11 /                    SCR1   +---||----+----------+ |:|( #14 --- 500pF
         8M \            DL1   2N6508 __|__       |   |    2T )|:|(      |  15KV
            /            NE2H    600V _\_/_       /   |   #14 )|:|(      |
            |            +--+     25A / |     R14 \   |   +--+     +-----+
            +--------+---|oo|----+---'  |      .1 /   |   | o            |
            |        |   +--+    |      |         \   |   |              |
            /        |           /      |         |   +---|--------------+
        R12 \    C7 _|_      R13 \      |   D10 __|__     |              |
         3M /  .1uF ---      180 /      | MR826 _\_/_     |         D11 _|_
            \  200V  |           \      |         |       |    1N1190AR /_\
            |        |           |      |         |       |    600V,40A  |
            +--------+-----------+------+---------+-------+--------------+
                                                           R15 .1 25W    |
                                                  DC+ o---+---/\/\---+---+
                                                          |          |
                                                          o + Test - o
                                                             .1 V/A
    
    
    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.

    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.

    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 should be fine on a Variac.

    SG-IT1 Current Meter

    This is implemented with a 0-10 mA 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
          Tube- o======+===============/\/\==================+======o DC-
                       |                                     |
                       |    +--+                 M1          |
                       | R1 |  v      R2   + +---------+ -   |
                       +----+-/\/\---/\/\----| 0-10 mA |-----+
                    Calibrate  10     91     +---------+
                                           10 A Full Scale
    
    
    Wires from M1 and R1 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.



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    Sam's Linear Ar/Kr Laser Power Supply (SG-IL1)

    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 :-).

    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!

    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.

    Components are number independently for the for each module or board as follows:

    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.



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    Ben's Linear Ar/Kr 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. I should have complete schematics of this *built and tested* unit in the near future. No excuses now :-).

    (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:

        +----------------------------------------------------------------------+
        |     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 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:

    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.

    Now I wonder how I can get rid of that damn annoying 12 second delay on the start board of the NEC3030 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 :).



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    Description of Other Ar/Kr Ion Laser Systems

    Lexel-95 PSU

    (From: Steve Roberts (osteven@akrobiz.com)).

    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!

    Spectra Physics 265 Exciter with a 165-3 Argon Head

    (From: Steve Roberts (osteven@akrobiz.com)).

    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.

    The 'Gold Box' 60X PSU

    (Portions from: Steve Roberts (osteven@akrobiz.com)).

    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!

    High Performance PSU for High-End Ion Laser

    (From Steve Roberts (osteven@akrobiz.com).

    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.



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