Introduction

　　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. Normally， switching regulator configurations cannot achieve this performance level without employing special techniques. One aid to achieving low noise is that load currents rarely exceed 5mA. This freedom permits output filtering methods that are usually impractical.

　　This publication describes a variety of circuits featuring outputs from 200V to 1000V with output noise below 100μV measured in a 100MHz bandwidth. Special techniques enable this performance， most notably power stages optimized to minimize high frequency harmonic content. Although sophisticated， all examples presented utilize standard， commercially available magnetics—no custom components are required. This provision is intended to assist the user in quickly arriving at a produceable design. Circuits and their descriptions are presented beginning with the next ink.

　　Resonant Royer Based Converters The resonant Royer topology is well suited to low noise operation due to its sinosoidal power delivery1. Additionally， the resonant Royer is particularly attractive becausetransformers originally intended for LCD display backlight service are readily available. These transformers are multiply sourced， well proven and competitively priced. Figure 1’s resonant Royer topology achieves 100μVP-P noise at 250V output by minimizing high frequency harmonic in the power drive stage. The self oscillating resonant Royer circuitry is composed of Q2， Q3， C1， T1 and L1. Current flow through L1 causes the T1， Q2， Q3， C1 circuitry to oscillate in resonant fashion， supplying sinewave drive to T1’s primary with resultant sine-like high voltage appearing across the secondary.

　　圖1.目前美聯儲羅耶諧振變換器產生高壓輸出。A1偏見Q1電流下沉，強制執行輸出電壓穩定反饋回路。A1的0.001μF–1kΩ網絡相位超前輸出濾波器，優化暫態響應。d5-d6，低漏夾，保護A1