| 摘要 |
PURPOSE:To suppress fluctuation of the collector-emitter voltage of a transistor by providing means for comparing the collector-emitter voltage with a reference voltage to produce a switching signal and varying the resistance of an emitter driving current detecting resistor according to thus produced switching signal. CONSTITUTION:When a motor enters into steady state rotation, the temperature rises and the load decreases and thereby the collector-emitter voltage of an NPN transistor increases. Consequently, a control section 1 detects a switching control signal G0 and an N-channel MOS transistor 31 is turned OFF by a switching signal G1 whereby the emitter voltage VE is increased and the collector-emitter voltage of NPN transistors 21, 22, 23 decreases thus preventing heating thereof. When a heavy load is applied on the motor due to fluctuation of power supply voltage, the collector-emitter voltage of the NPN transistor decreases. Consequently, the N-channel MOS transistor 31 is turned ON by the switching control signal Go and the collector-emitter voltage is increased thus preventing saturation. |
