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Recent developments in airborne radars call for low-noise power supplies at voltages very much greater than the maximum voltage ratings of available transistors. This paper discusses problems in the design of precision high-voltage regulators which can tolerate severe overloads and also meet the stringent requirements of, for example, an f.m. reflex klystron operating over the temperature range Â¿55Â°C to +65Â°C. Three basic circuits are described and their inherent power and voltage limitations are discussed. It is shown that high-voltage regulators operating in either the series or shunt mode provide a satisfactory solution, particularly where only a single output is required. However, the most economical approach for the particular case of a reflex-klystron supply is a low-voltage series regulator followed by a square-wave-oscillator type of d.c./d.c. convertor, since the convertor may have a multiplicity of output windings which can, for example, feed the resonator, reflector and filament of the klystron, respectively. The convertor type of design uses a high-current 20-volt regulated supply to control the amplitude of a square-wave oscillator operating at 8.5 kc/s. The output is 500 volts at 90 mA, the conversion efficiency from 20 volts is 80%, and the d.c. stability at the 500-volt level is better than Â±0.75 volt from Â¿55 to +65Â°C. The noise, including ripple, is less than 2 mV (r.m.s.). The addition of a negative-feedback loop between the output of the supply and the low-voltage series regulator improves the d.c. stability and reduces the output impedance.