JPS6454912A - Power amplifier - Google Patents

Abstract

PURPOSE:To prevent chattering of a FET and to keep a junction temperature of the FET to a permitted range by providing a means detecting the temperature of a case, a means comparing the case temperature with a reference temperature and a pulse generating means. CONSTITUTION:When the junction temperature of a FET 24, that is, the case temperature rises, and the resistance of a thermister 35 is decreased and the inverting input voltage of a comparator 33 is less than a noninverting input voltage, the output of the comparator 33 goes to 'H'. Simultaneously, a pulse generating means outputs an 'H' pulse with a prescribed pulse width. Thus, transistors(TRs) 30, 31 are respectively turned off, a drain bias power supply 32 is shut off and the FET 24 is turned off for a prescribed time only. When the case temperature is lower than the reference temperature after a prescribed time elapses, the output of a pulse generating means 28 goes to 'L', the TRs 30, 31 are turned on respectively, the drain bias voltage 32 is given and the FET 24 is conductive.