Protective circuit for output transformer-less circuit

摘要

A protective circuit for a class B OTL circuit such as a vertical deflection circuit and a sound output circuit of a television set. The protective circuit comprises a first voltage comparator circuit having one input terminal applied with a detection signal in the form of an average voltage of an output signal of the OTL circuit and the other input terminal applied with a first reference voltage, and a second voltage comparator circuit having one input terminal applied with the detection signal and the other input terminal applied with a second reference voltage which is different from the first reference voltage. Either one of the voltage comparator circuits is operated when the output terminal of the OTL circuit is short-circuited to either the power supply voltage line or earth. A control circuit is operated by an output of the voltage comparator circuit to cut off output transistors of the OTL circuit so that the output transistors can be protected from being damaged by large currents due to the short-circuiting.