Configurable negative high voltage divider

Discussion in 'The Projects Forum' started by garyk, Dec 25, 2015.

  1. garyk

    Thread Starter New Member

    Dec 25, 2015
    Happy holidays,
    I am trying to design a UV light measurement circuit using a PMT (photon multiplier tube). These PMTs require a very high negative bias voltage (I'm using -500V) and include a number of dynodes that are used to convert received photons into a large, proportional number of electrons, via multiplication.

    The dynodes are all connected via a multi-stage resistor divider (picture ten 330K resistors in series, from -500V to ground). To configure the circuit gain, I would like to enable and disable the divider elements applied to some of the dynodes.

    I'm looking for a circuit that lets me remotely enable and disable the resistors feeding each dynode. The circuit needs to handle at least -500V (assume 10 dynodes in my PMT), and have a mechanism to switch between either of two resistor values.

    I'm perplexed. Any suggestions for paths to pursue?
  2. bertus


    Apr 5, 2008
  3. garyk

    Thread Starter New Member

    Dec 25, 2015
    Thanks, Bertus. I have reviewed all of the Hamamatsu app notes and reference material. Unfortunately, the only mechanisms they suggest for PMT gain adjustment are bias voltage change, a potentiometer between dynodes, and manually changing out dynode resistor divider components.
    I'm looking for a way to REMOTELY configure the number of dynodes that are enabled (e.g. perhaps GPIO control of some FETs or BJTs ???). I've checked with Hamamatsu already, and they don't have any suggestions for how to do this.
  4. crutschow


    Mar 14, 2008
    You could use high voltage relays to configure the dynode resistor values.