Abstract: A supply voltage for signal processing circuits of a television signal processing system is developed in the secondary circuit of a transformer. AC power is coupled to the primary of the transformer through a circuit breaker whose operation is controlled in response to the supply voltage. The circuit breaker includes a normally nonconductive (i.e., high impedance) path which is rendered conductive (i.e., low impedance) with the development of the appropriate supply voltage and rendered nonconductive when the supply voltage falls below a predetermined threshold. A normally conductive (i.e., low impedance) path is coupled across the normally nonconductive path and is rendered nonconductive (i.e., high impedance) as current flows through it. The circuit breaker is particularly useful when the transformer is of the ferroresonant type, since the primary current of a ferroresonant transformer remains substantially constant with changes in the secondary current even under fault conditions.