PURPOSE: To protect the power output circuit certainly by detecting an excessive current flowing in the transistor which is biased is such a way that it flows a fixed current for the detection input in an usual operation of the power output circuit.
CONSTITUTION: The detecting circuit 2 consists of transistors Q3 and Q4 biased by the biasing circuit, which comprises the diodes D1 and D2, in such a way that the transistors flow a fixed current for the detection input in an uaual operation of the power output circuit 1, an input is made an abnormal detecting input when currents flowing in the transistors Q3 and Q4 exceed a fixed range. The driving transistor Q7 which is turned on or off by the abnormal detecting input controls the switchsing means 5 provided between the power output circuit 1 and the load PL. In this way, the protection can be certainly realized by means of the power output circuit 1, detecting circuit 2 and switching means 5.
YAMAMOTO MASAHIRO
WATANABE KAZUO
KOMINAMI YASUO
| JPS4894349A | 1973-12-05 |