Stringing HV Diode and HV PNP Transistor

Discussion in 'General Electronics Chat' started by 1o2o3o, May 28, 2008.

  1. 1o2o3o

    Thread Starter New Member

    May 28, 2008
    Hi everyone,

    I'm designing a circuit that need some comments, before I try to make it.

    I'm trying to block a pulsating High voltage DC 20kV top, with top frequency of 1 MHz.
    The ideas are:
    first, I don't have a single diode that capable of such high voltage:(. My idea is to series some diodes in series. Will it works? Someone told me to put paralel capacitor on each diode (enough bigger capacitance than the capacitance of the diode, but not to big that it would slow down the switching capability of the diode).
    Also, to put paralel resistor, in the order of Mega Ohm, to divide evenly the high voltage across the diode.

    Anyone have the detail circuit for this, anywhere? The things I couldn't figure out are the diode specification (the reverse recovery time, turn-on/off time etc., capacitance), the capacitor size and the resistor size.:confused:

    The other part is a protection circuit to limit circuit current to 1mA.
    My present design is to use High Voltage PNP transistor, with a current sensing resistor connected to emiter and base.

    Because there is no transistor capable to withstand 20kV, I'm going to series several HV transistor with its current sensing resistor, that all of them might withstand the voltage.

    Will this works? Is it necessary to put resistor or/and capacitor paralel to transistor's Emitter-colector pin (similar with HV diodes in series)?
    The working frequency would be the same as before, 1 MHz.
    What are the other transistor specs (besides VCEO) should I be looking for?
    Another thing crossing my mind is to use only one transistor and one current sensing resistor, and replace the other transistor with HV diodes of the same configuration of the first idea.:D Is this possible?

    Thank you for any comments and sugestions for my ideas.