SWITCHING POWER SUPPLY DEVICE WITH WIDE RANGE OF OUTPUT VOLTAGE AND SIMPLIFIED OUTPUT OF TRANSFORMER

摘要

PURPOSE: A switching power supply device is provided to widen the range of output voltage by controlling output values in accordance with the signal input from an external source, and simplify the output of a transformer. CONSTITUTION: A switching power supply device comprises an input rectifying unit(10), a pulse width modulation unit(20), a switching unit(30), a transformer unit(40), a control power unit(50), a control unit(60), a first feedback unit(70), second feedback units(80,81), and an output rectifying unit(90). The input rectifying unit rectifies an input voltage by a bridge rectifying diode(BD) and condensers(C1 to C6). The pulse width modulation unit adjusts control values by adjusting a duty ratio representing the ratio of time of a high signal with respect to one cycle of a pulse signal. The switching unit switches on/off a power in accordance with the control values of the pulse width modulation unit. The transformer unit induces output voltages proportional to a winding ratio to a secondary side in accordance with the on/off operation of the switching unit. The control power unit controls the voltages induced to the secondary side of the transformer unit. The control unit operates by the voltage supplied from the control power unit. The control unit includes a receiving portion for receiving a signal input from an external source, and transmits an output signal in accordance with the signal input from the external source. The first feedback unit receives the output signal from the control unit if the output signal is a low signal, and rectifies the received signal. The second feedback unit receives the output signal from the control unit if the output signal is a high signal, and rectifies the received signal. The output rectifying unit outputs the voltage rectified by the first or second feedback unit.