Results 1 to 8 of 8

Thread: Can someone please look over my schematic?

  1. #1
    Join Date
    Nov 2007
    Location
    Cairns, Australia
    Posts
    1,896

    Default Can someone please look over my schematic?

    OK well, I have parts coming in to build a driver for my argon laser tube.

    Once I save enough to buy the 2 500VA transformers, it's go time!

    Just to make sure I don't blow myself or anything else up, could someone please make sure I haven't done anything blatantly wrong here? The tube calls for 70-100VDC @ 9.1A.



    Also, the filament, on the laser itself is says 3.3VDC @ 13A. If I make sure I get exactly 3.3V out of the filament transformer, should I be OK? I've heard that getting the filament too hot or too cool will ruin the laser. Also, it says DC, though I've read everywhere that most tubes require AC for the filament?

    Do you guys use bleeder resistors on your filter caps?


    Cheers,
    Dan
    Last edited by Things; 06-20-2010 at 05:36.

  2. #2
    Join Date
    Aug 2009
    Location
    Bristol, England
    Posts
    333

    Default

    Filament winding should be centre tapped with the cathode current injected into the centre tap (at least for most ion lasers).

    Yes bleed resistors are normally used, that cap can hold a dangerous charge for a long time without them.

    Is D1 the correct way around?

    On startup, the 10uF cap on the control pin of the 317 will be fully discharged, causing the regulator to initially try to limit the current to IIRC about 1.4A or so, but what limits the regulator voltage drop?

    You will have about 160V or so at the top of the ripple across the main smoothing cap, it the tube is only dropping 70V then you are dropping 90V across the passbank (~800W), and about 40V across the regulator IC, I cannot be bothered to look it up but does the 317 actually survive 40 odd volts?

    You will want a delay between the filament power up and ignition to allow the cathode to heat.

    HTH.

    Regards, Dan.

  3. #3
    Join Date
    Nov 2007
    Location
    Cairns, Australia
    Posts
    1,896

    Default

    Filament winding, I intend to wind that myself so can add a centre tap.

    I think bleed resistors are calculated by t = 5rc (t = time, r = resistance, c = capacitance)

    That schematic is revised from a schematic I found on the FAQ, I think thats how the diode was, however I need to find the original and check.

    I am aware the passbank is going to be dissipating a lot of heat, and have planned a nice tunnel heatsink for that reason.

    On the diagram, you can see that it's a LM317HV, the HV version can handle up to 60V I believe.

    Didn't even consider the delay, although the tube has an onboard igniter. Maybe it has a timer built in?



    Cheers,
    Dan

  4. #4
    Join Date
    Jan 2006
    Location
    Switzerland
    Posts
    129

    Default

    Hi Dan,

    I included in the package various high power resistors so you don't need to buy any (I believe).

    As for the filament transformer, take the considerable voltage drop at like 25A along the wires to the laser into account. Ideally you use a rheostat on the primary side to tune the voltage to that you get your 3.3V _at the tube terminals_. Or you need to provide a few taps at the transformer for adjusting the voltage. Better on the primary as on the secondary; some transformers have several taps at the primary such as to accommodate 210..240VAC, that would help. The transformer can be made very simple, take almost any older 100W transformer where there is some space for windings left and add a few turns of heavy wire, I don't remember exactly but I think it was like 5 turns or so. A toroid transformer will to as well, perhaps even better.

    -W

  5. #5
    Join Date
    Nov 2007
    Location
    Cairns, Australia
    Posts
    1,896

    Default

    I am planning on using 2 500VA toroidal transformers, so I may be able to get away with adding a few more turns for the filament on 1, and then another few turns on the other for fans, light etc.

    As for the resistors, thank you very much

    Will save me a fair bit of money buying them.

  6. #6
    Join Date
    May 2008
    Location
    nerdtown, USA
    Posts
    1,165

    Default

    Have you considered using power IGBTs for the passbank? They tend to be more stable and since hybrid cars are built around them they're pretty cheap in high powers these days.

  7. #7
    Join Date
    Nov 2007
    Location
    Cairns, Australia
    Posts
    1,896

    Default

    I found a broken switchmode PSU I might be able to use

    Although, I have all the parts for the linear regulator if I can't get the switchmode one working.

    Thanks

  8. #8
    Join Date
    Sep 2006
    Location
    Netherlands
    Posts
    1,403

    Default

    Take a look at this schematic too.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •