Photomultipliers (PMT), avalanche photodiodes (APD), ultrasonic transducers, capacitance microphones, radiation detectors and similar devices require high voltage, low current bias. Additionally, the high voltage must be pristinely free of noise; well under a millivolt is a common requirement with a few hundred microvolts sometimes necessary. Circuits featuring outputs from 200V to 1000V with output noise below 100µV measured in a 100MHz bandwidth are detailed in this video. Special techniques enable this performance, most notably power stages optimized to minimize high frequency harmonic content. An additional aid to achieving low noise is that load currents rarely exceed 5mA. This freedom permits output filtering methods that are usually impractical. A lab-based circuit noise measurement demonstration concludes the presentation.
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