SWITCHING SYSTEM DC CONSTANT-VOLTAGE REGULATED POWER SUPPLY DEVICE

摘要

PURPOSE:To prevent the abnormal increase of an output voltage, by a method wherein an input voltage monitor circuit, detecting an input voltage information, is provided and the information of the circuit is employed as the decisive element of on-duty. CONSTITUTION:In a switching system DC constant-voltage regulated power supply device, the full-wave rectification of a commercial power source 1 is effected by a full-wave rectifier 2 while the commercial power source 1 is smoothed by a smoothing circuit 3 and is supplied to the primary coil of a transformer 4. A voltage, induced in the secondary side of the transformer 4 is outputted through a rectifier 5, a choke coil 6 and the like. The output voltage Vout is monitored by an output voltage monitoring circuit 8 and controls a main switching transistor 11 by PWM wave through an IC 9 for a switching regulator, a soft start circuit 10 and the like. In this case, an input monitor circuit 21 is provided and is constituted of first-third resistors, a transistor and the like. According to this constitution, the main switching transistor 11 is contrrolled so as to shorted the ON-time of the main switching transistor 11 when a smoothed input voltage is increased whereby the saturation of the transformer 4 may be prevented.