Abstract: There is disclosed a bias circuit for a photo-avalanche diode in equipment such as a laser receiver which circuit utilizes the breakdown characteristics of the actual detector diode itself to regulate the applied detector diode bias voltage. This is achieved by providing means to charge a capacitor up to the breakdown voltage in response to a first timing pulse, and second means to offset the capacitor voltage to a lower level by the fixed amount of a positive reference voltage, responsively to a second timing pulse which renders a transistor conductive.