| 摘要 |
PURPOSE:To make an electric power supply device small-sized, by setting the output voltage to a point near the lower limit value of the voltage precision in the rated load state and detecting the no-load state to change the reference voltage of a voltage detecting circuit and setting the output voltage to a point approximating the upper limit value of the voltage precision. in the no-load state. CONSTITUTION:When a transistor TR is switched by a pulse width control circuit 2, a driving positive power supply which is rectified and smoothed is attained from the secondary side of an output transformer T1. This voltage is divided by resistances R2 and R3 and is connected to one input terminal of a differential amplifying circuit 3, and the difference between this divided voltage and a reference voltage E1 supplied to the other input terminal of the circuit 3 is sent to the pulse width control circuit 2. The output voltage is set to a point near the lower limit value of the voltage precision in the rated load state; and when the no-load state is detected, the reference voltage E1 is changed to set the output voltage to a point approximating the upper limit value of the voltage precision. |
