| 摘要 |
PROBLEM TO BE SOLVED: To downsize a unit itself and reduce its cost by switching an operation mode to a standby mode, without the use of a detecting resistor or the like resulting in power loss. SOLUTION: This unit includes a main rectifying and smoothing circuit 40 and a sub rectifying and smoothing circuit 50 which rectify and smooth output, respectively, obtained by a secondary winding 22 of a converter transformer 20, in which switching output from a switching element 30 of switching a DC input is supplied to a primary winding 21, main rectifying and smoothing output supplied to a load from the main rectifying and smoothing circuit 40 is detected by an error detecting circuit 60 driven by the sub rectifying and smoothing output from the sub-rectifying and smoothing circuit 50 to control the switching operation of the switching element 30 by a PWM control circuit 80, so that the main rectifying and smoothing output may be under a predetermined condition. The voltages of the main and sub-rectifying and smoothing outputs are compared with each other, and the operating condition of the PWM control circuit 80 is switched to the standby mode, when the voltage of the sub rectifying and smoothing output drops below that of the main rectifying and smoothing output by a prescribed value or more.
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