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    Ar/Kr Ion Laser Power Supplies

    Sub-Table of Contents

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    Introduction, Related Information, Acknowledgement, Safety

    Basic Ar/Kr Ion Laser Power Supply Considerations

    Small air-cooled Ar/Kr ion tubes require an operating voltage of around 100 to 110 VDC at 3 to 10 AMPs and a starting voltage of about 8 to 10 KV (but almost no current). While these basic requirements are in some ways similar to those of a HeNe tube, the shear value of the current - measured in AMPs - means that providing a power supply that doesn't self destruct, destroy the laser tube, or fry you in the process, is much more of a non-trivial task:

    Note: Most parameters here are given for argon ion tubes since these are most common. However, while physically interchangeable krypton and mixed gas ion tubes are very similar electrically, they will have slightly lower starting and operating voltages. This isn't a problem for starting, but the difference in operating voltage can be significant enough to cause some power supply compatibility problems such as excessive power dissipation in the regulator circuits. This should be kept in mind if substituting tube types. See the section: Comparison of Argon and Krypton Ion Tube Characteristics for a specific example.

    Note that what we are talking about are Ar/Kr ion tubes putting out up to a few hundred mW of beam power. These are not small by HeNe laser standards. The lowest power models are still about 12 inches (30 cm) long with a diameter (including all the cooling fins and other attached structure) of about 4 inches (10 cm).

    Large frame Ar/Kr ion tubes can be over a meter in length and nearly everything about them is, well, much larger. :-) There are even 8 FOOT (2.5 m) long monster medical lasers that output 35 W or more and require over 600 V at 35 A to power the tube. Figure on a direct feed from a local electric utility substation for this kind of power! Ion lasers like these may also have axial permanent or electro-magnets surrounding the tube to concentrate the discharge and other 'stuff' that we will kind of ignore. ;-) They also require several gallons per minute from a tap or chilled water source to prevent a melt-down.

    For these reasons, while the offer of a cheap or free large frame ion laser may sound tempting, consider the power and cooling requirements before dragging it home. It will likely end up as a coffee table support or high-tech sculpture if you don't have industrial strength three-phase power at your disposal! Cooling water may also be a problem. Nonetheless, most of the basic information on small air-cooled ion lasers DOES apply to their bigger brothers as well if the numbers are adjusted appropriately. And, the power supplies are quite similar. In fact, the same power supply can often be used for a wide variety of ion lasers by selecting the AC input and changing some jumpers.

    Throughout this chapter, references will be made to several commercial Ar/Kr ion lasers systems. Two of the most common are:

    Complete schematics of the power supplies and typical laser heads for these units are provided in the chapter: Complete Ar/Kr Ion Laser Power Supply Schematics.

    Web Site with Related Information

    Evergreen Laser Corporation has a Web site which includes a significant amount of information on ion laser tube and power supply adjustment, alignment, failure modes, troubleshooting, and repair.

    Unfortunately, most of this did not work with Netscape V3.04. Perhaps, it will work with your browser and/or the problems have since been corrected.


    Thanks to Steve Roberts (email: osteven@akrobiz.com) for his extensive contributions of ion laser documentation and email discussions which were invaluable in the preparation of this chapter. This in addition to those sections specifically attributed to Steve!

    SAFETY When Dealing with Ar/Kr Ion Laser Power Supplies

    Whether you have constructed your own power supply, are testing an old one, or just checking out a newly acquired Ar/Kr ion tube, SAFETY must come first:

    See the section: Laser Safety with respect to the optical hazards associated with these higher power lasers. While generally not in the metal cutting class, careless use of Ar/Kr ion lasers can certainly result in instant and permanent damage to vision. There are all going to be at least Class IIIb and some are CLASS IV.

    However, when compared even to large HeNe lasers, there are many additional very real dangers associated with Ar/Kr ion laser power supplies:

    Read, understand, AND FOLLOW, the guidelines provided in the document: Safety Guidelines for High Voltage and/or Line Powered Equipment.

    In addition:

  • Back to Ar/Kr Ion Laser Power Supplies Sub-Table of Contents.

    Types, Alternatives to HomeBuilt System

    Not Quite as Many Choices

    While there may be some variations on the type of operating and starting voltage supplies, there are far fewer options for ion lasers compared to HeNe lasers. Partly this is because there are far fewer variations in Ar/Kr ion tube characteristics and partly because the magnitude of the discharge current eliminates certain approaches from practical consideration.

    Some basics:

    So You Still Want to Build an Ar/Kr Ion Laser Power Supply?

    With the need to provide all this high power and dangerous circuitry to power even a 'small' air-cooled ion tube, it should be clear that if you can beg, borrow, buy, or otherwise liberate a commercial Ar/Kr ion laser power supply for your needs, by all means do so! Even if the unit is in absolutely total disrepair (including being run over by a fork-lift, dropped from a 10 story building, or having suffered a China-Syndrome style melt-down), it will likely be far easier to revive and restore something that once worked than to create your own. Any required modifications will almost certainly be far easier than starting from scratch. This isn't like a little HeNe job as any faults can be spectacular and depressing.

    If you really have no choice, or just like a challenge, by far the most straightforward approach is to use a line connected rectifier/filter with a linear regulator. While not quite as efficient as a switchmode or inverter type, the hassles are fewer and parts are more readily available. For initial testing, a low value high wattage ballast resistor can substitute for the regulator. Just don't be tempted to leave it this way permanently. And, in any case, don't neglect the essential current monitor!

    Note that if all you want to do is test a newly acquired Ar/Kr ion tube, there may be a considerably simpler alternative to a continuous high current power supply. See the section: Pulsed Operation of an Ar/Kr Ion Tube.

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    Organization of Linear, Switchmode, Inverter Types

    Typical Organization of Ar/Kr Power Supply with Series Regulator

    A bridge rectifier and filter network (C-R-C or C-L-C typical) provides about 150 VDC directly from the 110 VAC line input.

    The igniter (starter) circuit may operate off of this DC+ supply or an additional low current 'boost' source to use a higher voltage (which reduces the turns-ratio of its high current pulse transformer - a hard to wind (or high cost) part.

    The current regulator uses bipolar or MOSFET transistors in a linear or switchmode (buck converter) configuration. Feedback based on current, light (beam) sensing, or an external modulation signal, is used to maintain the proper discharge current through the tube. For initial testing, this can be done manually using a high power adjustable ballast resistor and possibly a a large Variac on the AC line input to the power supply.

                  +----------+ DC+                     +-----------------+
         H o------|          |-------------------------| Igniter Circuit |-----+
                  |   Main   |                         +-----------------+     |
           AC     |  Bridge  |                                                 |
          Line    |   and    |     +------------+    Light Feedback (option)   |
                  |  Filter  | DC- | Linear or  |<-------------------------+   |
         N o------|          |-----| Switchmode |       F1 +-----------+   |   |
                  +----------+     | Regulator  |   +------|-+         | )-+   |
                      |   |        +------------+   |      |  )      |-|-------+
                      |   +------+        |         | +----|-+         | Tube+
                      |           )   +---|---------+ | F2 +-----------+
                      |  Filament )||(    |           |    Ar/Kr ion tube
                      |   Supply  )|| +---+ Tube-     | 
                      |           )||(                | 
                      |           )   +---------------+
    This type of supply with a linear regulator would be the easiest to construct. While efficiency is lower (abysmal instead of just terrible - probably about 40% more heat generated than for a well designed switcher), the difficulties of implementing a robust and fool-proof Pulse Width Modulator (PWM) controller are eliminated. Just provide a large enough heat sink and jet turbine driven cooling fans!

    Since everything except possibly some logic or low level analog circuits are 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 adherence to ALL safety precautions, implementation of ALL safety, electrical, and thermal interlocks and protective devices. In many cases, even that control circuitry is line-connected as this simplifies the implementation since no isolated interfaces are required.

    Typical Organization of Inverter Type Ar/Kr Power Supply

    A bridge rectifier or voltage doubler and filter network (C-R-C or C-L-C typical) provides about 150 VDC or 300 VDC respectively from the 110 VAC line. This is used by the DC to DC inverter to produce the required 100 to 110 VDC to the Ar/Kr ion tube.

    The igniter (starter) circuit may operate off of this DC+ supply, a separate winding on the inverter transformer, or an additional low current 'boost' source to use a higher voltage (which reduces the turns-ratio of its high current pulse transformer - a hard to wind (or high cost) part.

    Feedback based on current, light sensing, or an external modulation signal, throttles the DC to DC inverter by Pulse Width Modulation (PWM) - controlling the duty cycle of the drive to its chopper transistor(s) in a manner similar to that for controlling a series pass switchmode regulator. However, there are added design considerations in dealing with the characteristics of the high frequency ferrite inverter transformer.

                  +----------+ DC+ +------------+      +-----------------+
         H o------|          |-----|  DC to DC  |------| Igniter Circuit |-----+
                  |   Main   |     |  Inverter  |      +-----------------+     |
           AC     |  Bridge  |     | --+    +-- |                              |
          Line    |   and    |     |    )||(    |    Light Feedback (option)   |
                  |  Filter  | DC- |    )||(    |<-------------------------+   |
         N o------|          |-----| --+    +-- |       F1 +-----------+   |   |
                  +----------+     +------------+   +------|-+         | )-+   |
                      |   |               |         |      |  )      |-|-------+
                      |   +------+        |         | +----|-+         | Tube+
                      |           )   +---|---------+ | F2 +-----------+
                      |  Filament )||(    |           |    Ar/Kr ion tube
                      |   Supply  )|| +---+ Tube-     | 
                      |           )||(                | 
                      |           )   +---------------+
    While still very dangerous to troubleshoot, at least the main tube circuits are isolated from the AC line by the inverter transformer. Aside from the slightly reduced risk of frying yourself, I would probably not recommend the inverter approach unless you already have its foundation such as the HV power module from a solid state microwave oven! For more information, see the chapter: Ar/Kr Ion Laser Power Supply Design.

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    Making Measurements, Testing, Repair

    Measurements of Current and Voltage in Ar/Kr Ion Laser Power Supplies

    Monitoring of discharge current is essential to maintain the health of your Ar/Kr ion tube (and power supply). Various voltage measurements may be needed as well. However, because of the high currents involved AND the non-isolated nature of the power supply, this isn't as trivial as connecting your Radio Shack DMM into the circuit:

    Initial Power Supply Testing

    Ideally, one would possess 5 or 6 functioning eyeballs to keep tabs on all aspects of a new Ar/Kr ion tube and power supply combination as it is being tested for the first time.

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

    Where there is no robust current regulator, for initial testing it is wise to start at 7 or 8 Ohms and work down, even with the pi section CLC or CRC filter as these discharges do possess a negative runaway characteristic despite what the literature says. For some reason it always seems to need a 2 to 4 ohm offset above the calculated value or it will run away.

    They also need a minimum current of about 3.5 amps to sustain the discharge with a new tube and about 4.35 A as the tube grows older, this was just measured in my shop with a new tube versus a tube with 2000 hours on it. The new one (an Omnichrome 532 with a buck converter) dropped out on line voltage dips when it came from the factory set for a 3.25 A lower limit. This was on 118.2 V AC.

    Therefore when firing up a 'heater' (space heater ballast) based supply, you often have to lower the resistance a little at a time to find the minimum stable current point. It is better to start a high resistance and work down. Of course, you will have a permanent current monitor in the system!

    Also see the sections: Measurements of Current and Voltage in Ar/Kr Ion Laser Power Supplies and Testing with a Dummy Load.

    Testing with a Dummy Load

    It should be possible to use a Variac and dummy load to determine basic functionality of these power supplies. However, there is no easy way to simulate the Ar/Kr tube I/V characteristics. The best that can reasonably be done is to use a HUGE power resistor. A 1,200 W space heater element can be used for the load since this will draw about 10 A at 100 V. A space heater with more than one wattage setting (not only a thermostat!) can be used to test at multiple simulated tube currents (but DON'T switch while powered!). For example, assuming a nominal tube voltage drop of 100 V, use 600 W for 5 A, 900 W for 7 A, 1,200 W for 10 A, 1,500 W for 12 A.

    It will be necessary to power the logic and control circuits separately for this test so that their supply voltage is constant.

    Provide wired-in monitoring of BOTH load (tube) current AND regulator voltage drop. (See the section: Measurements of Current and Voltage in Ar/Kr Ion Laser Power Supplies.)

    Select the load rating, with the Variac at 0, power on the main supply. Bring up the voltage slowly.

    CAUTION: Do not apply power suddenly - without a Variac - as the momentary voltage drop across the regulator will be the full DC+ value which may blow the transistor(s). The voltage will also be excessive if you try to run at a lower current than for what you based the load resistor for similar reasons.

    Ar/Kr Ion Laser Power Supply Repair

    Since these are high power devices, it isn't too surprising that failures are common either due to problems in the power supply or the laser head. While various protection devices are generally present, we all know that the most expensive parts often blow to protect the fuses! Such 'events' can be quite spectacular resulting in smoke, flames, aroma of burnt stuff, and parts which launch portions of themselves over considerable distances. With these line-connected circuits, a shorted bridge rectifier can turn the analog control board to molten slag!

    Needless to say, when designing such a power supply and selecting components, err on the side of being conservative. Select parts to run at much less than their rated voltage, current, or power (maximum stress of 1/2 the part's rating isn't too bad a rule-of-thumb). This is especially important for devices that fail in a sudden catastrophic manner like power semiconductors!

    Where any type of failure occurs, don't just replace the obviously blown parts. Check everything in the vicinity as well. Replace anything that is questionable even if not an outright failure. Make sure all your (or someone else's) connections are secure using lock washers for screws and bolts, a proper tool for crimps, and an adequate iron or gun for soldered connections. When powering up after such an 'event' proceed as you would for a brand-new or newly constructed power supply.

    There are also some comments on the repair of specific power supply models in the chapter: Complete Ar/Kr Ion Laser Power Supply Schematics.

    For much more information on the servicing of these types of devices, see the following (as appropriate for your power supply):

    Troubleshooting Check List

    The following is summarized from the Omnichrome 150R power supply manual and slightly modified to be more general:

    Before beginning a lengthy troubleshooting session, check the following:

    1. Is there AC power to the laser system?

    2. Is there power at the laser head (LED on)?

    3. Is there anything blocking cooling air flow to the power supply or laser head (which would activate the thermal protection devices)?

    4. Is the beam block closed or something else blocking the laser beam?

    5. Did you wait long enough from initial turn-on (typically 2-3 minutes for filament preheat and tube start)?

    6. Are all the interlocks closed?
    Two types of problems are common:

    Troubleshooting Where There is No Beam at All

    1. Check to make sure that power is on and interlocks are closed. Go through the normal startup sequence - give it enough time!

    2. Where power and interlocks check out, see if the discharge is present - the tube has started. This can be done by checking the current monitor or test points, or by placing a white card in at the output coupler or mirror of the Ar/Kr tube. Even if there is no laser beam, there should be a diffuse purple glow from the discharge itself.

      WARNING: Do not put your eyeball (or any other part of you!) near the tube. Aside from the high voltage, there is considerable UV which isn't any good for organic matter either!

    3. If there is a discharge and it is at a sufficient current for laser action to take place, either the mirror alignment is off or the optical surfaces are dirty, damaged, or contaminated (external mirror lasers only).

      If under light control, the current will likely be pegged at the maximum (e.g., 10 A) attempting to get a proper power beam.

      Check the mirror alignment and/or clean and/or realign the resonator as appropriate. See the sections: Checking and Correcting Mirror Alignment of Internal Mirror Laser Tubes or Argon/Krypton Ion Laser Cleaning and Alignment Techniques (external mirror tubes) depending on the type of laser tube in your system.

    4. If plasma is flashing off and on (at about a 1 second or so rate), line voltage (or your Variac) may be too low or there may be a problem with the regulator or its control circuitry.

    5. If there is no discharge, this can be due to a bad main supply, regulator, starter, or any of the supply voltages used to run these.

      • Check for main DC+ at the output of the line rectifier/filter network.
      • Check for the (boost) supply to the igniter and its oscillator.
      • Check voltages to the logic and analog circuitry.
      • Check the tube filament voltage.

      WARNING: Some or all of these power supplies are line connected - take extreme care with measurements! See the section: SAFETY when Dealing with Ar/Kr Ion Laser Power Supplies.

    6. If all voltages are present and there are no signs of arcing, listen for the 'tick-tick-tick' of the igniter. If this is present, the igniter is probably working.

      If there is no evidence of the tick-tick-tick sound, check the (boost) supply supply directly at the igniter circuit. It is also possible to test the output of the igniter by disconnecting it from the tube (with power off and everything discharged!) and checking that it will arc 1/3" to 1/2" to a suitable ground point.

    7. If the igniter is working, put a piece of white paper in front of the laser output port. If there are momentary flashes of diffuse purple or laser light but the discharge does not remain on, turn the light control to its maximum setting. If the discharge still does not stay on (or there were no flashes of light), the Ar/Kr ion tube may be faulty or the regulator is cutting out.

      Where the power supply and igniter check out, the tube pressure may be too high (from non-use) or the tube may be misbehaving just because it felt like it - but this may be reversible. It may be possible to the tube to start using an Oudin coil and then run it for several hours to drive down the pressure. See the section: Hard-to-Start Ar/Kr Ion Tubes - Outgassing and Keeping Your Laser Healthy.

    Troubleshooting Where There is No or Low Output

    Check the mirror alignment and/or clean and/or realign the resonator as appropriate. See the sections: Checking and Correcting Mirror Alignment of Internal Mirror Laser Tubes or Argon/Krypton Ion Laser Cleaning and Alignment Techniques (external mirror tubes) depending on the type of laser tube in your system.

    Troubleshooting Linear Pass-Banks

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

    I cannot stress enough the need to have a curve tracer around, even a home-built one, for checking pass-bank transistors in-circuit. However, the following procedure using only a multimeter will also work for identifying bad transistors in the Lexel-88 (or most any other) pass-bank in-circuit (where all the collectors are tied together) is:


    2. Set your multimeter on low ohms and measure from each emitter lead to the collector.

    3. Establish an average from unit to unit, as he emitter resistors isolate you from the others and the bad transistor will usually be a short or sometimes an open. You'll see something like 23-23-44-23-24-23.2-12-23-23.3. The 12 and 44 Ohms are the bad ones provided all the transistors are the same type in the pass-bank.

    4. Replacement transistors should be of the same type and matched for Hfe if possible. Otherwise, depending on the design of the driver circuits, the collector currents could end up being seriously unequal despite any emitter current balancing resistors. This may result in significantly unequal stress (current and thus power dissipation) leading to spectacular failures!

    5. After installation, check for proper current balancing under load.
    That's also why the Lexel has the 'stress' meter on the pass-bank. If the meter won't get out of the 10 to 30 Volt range, there is a shorted pass-bank transistor. The correct 'green' range is 10 to 70 volts. For a combination of a power supply configuration and Ar/Kr ion tube that should work, selecting the proper tap on the line input buck/boost transformer will aid in getting the transistors operating in the right range and is the first thing to check when firing up the laser.

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    Pulsed Ion Tube Test Circuits

    Pulsed Operation of an Ar/Kr Ion Tube

    For determining if a new or used ion tube is good, there may be no need to run it on a full blown power supply. That way, you can hold off committing the time, money, and other resources to obtain or build one until you know that you have a working tube. (Once you read the chapter: Ar/Kr Ion Laser Power Supply Design you will know why this is worth considering - these are not like little HeNe types!) A simple pulsed circuit created using the tube as the active device in a relaxation oscillator will suffice. This has a number of other attractive benefits as well: However, there are several caveats: WARNING: Despite the low pulse rate and short pulse duration, the optical output from the laser running on these circuits could be enough to result in eye damage. For example, a 60X at startup may produce almost a half watt of peak laser output power for a brief period as the igniter and multiplier caps discharge into the tube - which is a similar situation to what is presented here (especially when you decide to increase the value of the storage capacitors to boost output!) - and it is banging away at the tube repeatedly! Take care and NEVER look down the tube bore while the circuit is active - even if it appears to be dead as a brick!

    Having gotten that out of the way, here are two circuits that should be adequate for a typical small air-cooled Ar/Kr ion tube.

    Ar/Kr Ion Tube Pulse Test Circuit 1

    This circuit forms a relaxation oscillator using the tube as the discharge device.
                  +-------------+ +     R1                       R2
        Vin+ o----|             |------/\/\-----+-----+---------/\/\-------+
                  | HV DC Power |      400K     |     |         140        |
                  |   Supply    |      10W      |     |         10W        |Tube+
                  | 2 KV, 10 mA | -             |     |                  .-|-.
        Vin- o----|             |---+           |     /                  | | |
                  +-------------+   |       C1 _|_    \ R3               |   |
                                    |    .25uF ---    / 10M              |   | LT1
                                    |   2,500V  |     \                  |   |
                                    |           |     |                  |   |
                                    |           |     |                  ||Z.|
                                    |           |     |   o - Test + o   '+-+'
                                    |           |     |   |    Rs    |  F1| |F2
                        NC o-+ T2   +-----------+-----+---+---/\/\---+    | |
                              )||  _|_                         1     |    | |
               AC o----------+ ||   -                                |    | |
                              )||                                    |    | |
                       Variac )<--------------+ T1                   |    | |
                       0-140V )||              )|| +-----------------|----+ |
                           1A )||     Filament )||(           Tube-  |      |
                              )||  Transformer )|| +-----------------+      |
                          +--+        3VCT,15A )||(                         |
                          |                    )|| +------------------------+
               AC o-------+-------------------+
    This will form a relaxation oscillator using the tube with current limiting to about 10 A. Adjust the pulse rate by either varying the input voltage or changing R1 (with power off!).

    Running this at a few pulses per second for a reasonable length of time (i.e., not for days on end) should result in no significant damage to the tube or shorten its life by any detectable amount. You shouldn't need to run it this way for very long in any case - just don't think that this setup can be used in place of a REAL power supply!

    As long as the peak current exceeds the tube's lasing threshold, there should be visible flashes of laser light from its OC (output coupler) end if it is working and aligned correctly.

    WARNING: This circuit is still dangerous - just less so than a full blown ion laser power supply. The anode of the tube (including the mirror mount at that end!) will have a voltage of up to 1.5 KV with respect to ground (for this example). While the amount of energy stored in C1 is fairly small - less than .5 J (W-s), it can still be lethal under the wrong conditions. The HV power supply itself can deliver up to 5 mA through R1. Either of these are at least enough to evoke a reflex response which may ruin your whole day even they do not kill you. Take care.

    Note: I show the entire setup earth grounded including the tube cooling fins and support structure. This makes it safe to touch everything BUT the tube anode (and of course, the HV power supply). Floating the entire affair is also possible but most of the same problems exist since portions of the tube will still be at the negative potential of the power supply and, if you use the scope monitor points across Rs, will be grounded through the scope (unless you isolate that as well - which is not recommended).

    Ar/Kr Ion Tube Pulse Test Circuit 2

    The following circuit is a somewhat more powerful alternative and there are absolutely no safety claims for it! With the relatively large energy storage capacitors for C3 and C4, it must be treated with great respect.

    It may also be possible to use this approach for starting small to medium size tubes since it provides a 'boost' voltage like that used by the igniter of the ALC-60X/Omni-532, SG-IT1, and SG-IL1. See the section: Pulsed Operation of an Ar/Kr Ion Tube.

    What this design provides is two power supplies driven from a single 650 VRMS center-tapped transformer (T3). Many other approaches for the power sources are possible. See the chapter: HeNe Laser Power Supplies for ideas.

                                 R4    D3                 
                            |   10K   1KV    |    |                |
                            |   10W      C3 _|_   / R5             |
                            |          75uF ---   \ 220K           |
                            |          350V  |    /         +-------------+
                            |                |    |         |  Constant   |
                            |                +----+         |  Current    |
                            |                |    |         |  Regulator  |
                            |            C4 _|_   /         | (Optional)  |
                            |          75uF ---   \ R6      +-------------+
                            |          350V  |    / 220K           |
                            |                |    |          D5    |
                            |                +----+      +---|<|---+
                            |               _|_          |   3KV
                            |                -           |  2.5A 
                            |                            |
               T3     R1    |   C1       D1              |        R2
               ||(    2M    | .01uF  |   3KV   |    |             5       |
               ||(          |  3KV   |         |    |            10W      |Tube+
       AC o--+ ||( 325V     |        |         |    |                   .-|-.
              )||(          |        |     C2 _|_   /                   |   |
              )||(          |        |  .01uF ---   \ R3                |   |
              )|| +---------+        |    3KV  |    / 20M               |   | LT1
              )||(                   |         |    \                   |   |
              )||(                   |   D2    |    |                   |   |
       AC o--+ ||( 325V              +---|<|---+    |                   ||Z.|
               ||(                       3KV   |    |    o - Test + o   '+-+'
               ||(                             |    |    |    Rs    |  F1| |F2
                  +----------------------------+----+----+---/\/\---+    | |
             650VCT                                           1     |    | |
              50mA             NC o-+ T2                            |    | |
                                     )||                            |    | |
                      AC o----------+ ||                            |    | |
                                     )||                            |    | |
                              Variac )<---------------+ T1          |    | |
                              0-140V )||               )|| +--------|----+ |
                                  1A )||      Filament )||(  Tube-  |      |
                                     )||   Transformer )|| +--------+      |
                                 +--+         3VCT,15A )||(                |
                                 |                     )|| +---------------+
                      AC o-------+--------------------+
    Setup and operation is similar to that described in the section: Ar/Kr Ion Tube Pulse Test Circuit 1. Adjust T2 to obtain the proper filament voltage for your tube and modify the value of R1 to vary the pulse rate.

    The remaining details are left as an exercise for the student! A switchmode buck converter will be needed for the optional regulator unless you have a bank of really high power transistors gathering dust in your junk box. :-) The problem with using a linear regulator is the peak power dissipation and keeping inside the SOA (Safe Operating Region) for the transistor(s). A common BUT12A would handle the current and voltage individually for this example but not the peak 4,000 WATTs - 400 V AND 10 A at the same time!

    WARNING: Take care as C3 and C4 can pack quite a wallop - especially once you increase their size - as I know you will. ;-) And, both supplies can deliver dangerous levels of current continuously even without the capacitors!

    An alternative which may work for some small tubes like the Cyonics (those which will start without help from a boost source) is to use a line powered (non-isolated or 1:1 isolation transformer) supply for the pulse current source followed by an (optional) linear or switchmode regulator.

    Without the regulator, it would look like the following:

                           R1                 D1       R2
             +2 KVDC o----/\/\-----------+----|>|-----/\/\---+--------+
                          100K           |    3KV     100    |        |Tube+
                                     C1 _|_+  1A      10W    |      .-|-.
                                    1uF ---                  |      | | |
                                    3KV  | -                 |      |   |
                           R3            |    D2       R4    |      |   |
            +150 VDC o----/\/\-----+-----|----|>|-----/\/\---+      |   | LT1
                        100,25W    |     |    3KV      4            |   |
                               C2 _|_ +  |    6A      10W           |   |
                            500uF ---    |                          |   |
                             200V  |     |                          ||Z.|
                                   |  -  |                          '+-+'
              DC RET o-------------+-----+----------------------+  F1| |F2
                                                                |    | |
                           NC o-+ T2                            |    | |
                                 )||                            |    | |
                  AC o----------+ ||                            |    | |
                                 )||                            |    | |
                          Variac )<---------------+ T1          |    | |
                          0-140V )||               )|| +--------|----+ |
                              1A )||      Filament )||(  Tube-  |      |
                                 )||   Transformer )|| +--------+      |
                             +--+         3VCT,15A )||(                |
                             |                     )|| +---------------+
                  AC o-------+--------------------+
    Details of this, too, are left as a exercise for the student!

    Ar/Kr Ion Tube Pulse Test Circuit 3

    Finally, here is another pulse circuit with an organization very similar to that of many HeNe power supplies (see the chapter: Complete HeNe Laser Power Supply Schematics).

    A 600 VCT power transformer (T2) charges the energy storage capacitor (C1) to approximately 425 VDC and also drives the parasitic voltage multiplier to generate an additional starting voltage of up to more than 2,500 VDC. When the Ar/Kr ion tube starts, C1 discharges through D9 with a current limited to about 10 A by R3. The uF value of C1 may be changed to provide the desired discharge energy. Adjust the values of R2 and/or C3 to assure that C1 charges in a shorter time than it takes for the HV to build up to the point at which the tube starts.

    My first version of this circuit was built as an all-on to a 30 year old home-brew tube-type bench power supply (remember the 5U4GB rectifier tube?). I never thought I would ever find a use for that again but it did have all the connections required to attach the output and voltage multiplier conveniently located on front panel binding posts!

                  C2              C3              C4
           |          D3   |  D4      D5   |  D6      D7   |  D8
        R3 /       +--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+--|>|--+
        1M \       |      C5       |      C6       |      C7       |   R4
           /       +------||-------+------||-------+------||-----+-+--/\/\--+
           |  D1   |      R1                      D9        R5   |    100K  |
     T2 +--+--|>|--+-+---/\/\-------+----+--------|>|------/\/\--|----------+
     ||(             |    1K        |    |        3KV       30   |          |
     ||(             |   10W   C1 +_|_   / R2    2.5A      10W  _|_ C3      |Tube+
     ||( 300V        |       10uF  ---   \ 470K                 --- .01uF .-|-.
     ||(             |       450V - |    / 1W    o - Test + o    |  5KV   | | |
     ||(             |              |    |       |    Rs    |    |        |   |
     || +------------|--------------+----+-------+---/\/\---+----+        |   |
     ||(             |                                1          |        |   | LT1
     ||(             |         T2: 600VCT, 50mA                  |        |   |
     ||( 300V        |         D1-D8: 1N4007                     |        |   |
     ||(             |         C2-C7: .01uF, 1.2KV               |        ||Z.|
     ||(      D2     |                                           |        '+-+'
        +-----|>|----+              AC o--------+ T1             |       F1| |F2
                                                 )|| +-----------|---------+ |
     (Ac input and                      Filament )||(  Tube-     |           |
      T2 primary                          Supply )|| +-----------+           |
      not shown)                                 )||(                        |
                                                 )|| +-----------------------+
                                    AC o--------+
    Like the other pulse supplies, this can also be used as a starter for some small ion tubes. All that is needed is a high voltage high current blocking diode between the ion tube anode and the DC+ output of a the normal ion laser power supply.

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