Capacitor charge/discharge circuit for discharge lamp

Discussion in 'The Projects Forum' started by KenK, Apr 16, 2009.

  1. KenK

    Thread Starter New Member

    Mar 30, 2009
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    I'm somewhat stuck trying to build the electrical system for a discharge lamp, and could use some advice. It's an experimental sliding spark lamp for laboratory use. It's basically a pulsed discharge lamp, and I'd like to feed it with ~1kV pulses. Pulse width should be around 20 us long, and pulse frequency should be around 200 Hz.

    My initial idea is shown in the attached schematic. The Control signal is connected to a simple 555 timer circuit that produces the pulses as described above. The SCR is rated for 1600V and 105A continuous; the capacitor is rated for 2kV. The high voltage power supply can only output negative voltage (other terminal is connected to the chassis ground).

    The problem is, the discharge doesn't stop at the end of each pulse. I was hoping each pulse would terminate by itself as the capacitor is discharged, and the voltage dropped to a point where the lamp would no longer conduct. However it seems the power supply can maintain a high enough current and voltage so the lamp and SCR never shut down.

    If I connect another SCR in parallel with the lamp+SCR, and trigger it after each pulse, would that be a reliable way to shut off the SCR connected to the lamp? Or would it be better to have some sort of switch (solid-state relay?) between the capacitor and power supply and open this during discharge? Any other options? Or are more major changes called for?
     
    Last edited: Apr 16, 2009
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It would help if the powersupply was isolated from the capacitor before the discharge takes place.
    Perhaps a someting like an IGBT between powersupupply and capacitor to stop charging the capacitor.

    Greetings,
    Bertus
     
  3. KenK

    Thread Starter New Member

    Mar 30, 2009
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    0
    I'm sorry to have done a "ask and run" - I had to concentrate on another project and hadn't had time to come back to thinking about this issue.

    Thank you for the suggestion on using an IGBT for switching off the supply. However, is there a good way to do this with the NEGATIVE high voltage supply that I'm stuck with? Should I stick the IGBT between the capacitor and the negative supply, and use a pulse transformer to drive the gate?
     
  4. bertus

    Administrator

    Apr 5, 2008
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