Current sensing on negative 1.1kV DC rail

Question

I searching for a way to do high side current sensing on a -1100V DC rail.

My HV is generated from the hamamatsu C9619 High voltage power supply module and it powers the hamamatsu R647P Photomultiplier tube together with the E849-90 D-type socket assembly also from hamamatsu.

My current region is up to 500 μA.

Any ideas or suggestions would be extremely helpful.

Answer 1

If your need is only for occasional measurements, it would be easy enough to create a battery-powered wireless milliammeter. For example a shunt resistor, op amp and a microcontroller with some kind of wireless communication (eg. WiFi or Bluetooth).

Another approach would be to make a current sink circuit using a high voltage MOSFET that operates at the -1100V rail. The Hamamatsu C9619 is capable of 2mA current so you have a fair bit to play with. You would have to use (continuous) high voltage rated resistors for the power dropper (and, to be prudent, in series with the high-voltage N-channel transistor drain). A very low power op-amp and a very low Iq shunt regulator for the power would complete the circuit. Recieving it would be a transimpedance amplifier referenced to ground. Pick the series drain resistor to limit the current to a few mA.

For example:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

You could use a hall effect current sensor. 500uA isn't much, but you can use multiple passes through the loop to get a large enough reading.

Another option would be to use an isolated current shunt. You can either do this with a dedicated device, or simply use a microcontroller, and then pass the signal through an opto-coupler. You'll need an isolated power supply for the microcontroller; or you could just run it on a battery.

Answer 3

I have 3 solutions for you:

1 - Replace the power source with one that has both voltage and current meters.

2 - Buy a clamp-on DC uampmeter. Make sure you use it in "floating" mode.

3 - Design and build your own DC uampmeter.