Readout Electronics: High Voltage -1.25kV PMT Bias Supply

This is part of my readout electronics system.

This is an adjustable high voltage power supply I built for biasing the dynodes of photomultiplier tubes (PMTs). It uses a Hamamatsu C4900 high voltage DC-DC converter.

Control can either be local (potentiometer on the front panel) or remote (external 5V DAC). The orange LED on the front panel indicates that remote control is active. Whether the unit is in local or remote control is controlled from a microcontroller on an external board. This is done by the white relay at the top which switches the reference voltage between the potentiometer and an input on the backplane connector.

The unit furthermore has a relay that disconnects the C4900 module from it’s supply. This is used by an external safety lockout board to disable high voltage if i.e. a PMT tube is exposed to room light in order to avoid burnouts.

The voltmeter on the front panel requires a potential free power supply which according to the manual ought to be a 9V battery. I decided to use a small isolated 12V DC-DC module followed by a 78L09 to accomplish the potential free supply, such that I don’t have to use a battery for something as stupid as the voltmeter.

This is definitely not one of my cleanest builds, but it works.

Amplifier PCB Amplifier Front Panel