| 摘要 |
PROBLEM TO BE SOLVED: To attain a simple and inexpensive protective circuit device, which stops switching operation at overcurrent or overvoltage time by providing a voltage monitor circuit which supplies an operation stopping command signal for a control circuit, when the DC voltage of a rectifying and smoothing circuit connected to a primary winding for control power supply exceeds its reference value. SOLUTION: If overcurrent or overvoltage occurs at one of the output sides of three channels, large input current flows into the primary winding 11 of a transformer, and the DC output voltage of rectifying and smoothing circuits D2, C2 is increased at a primary winding 15 for control power supply. If it exceeds its reference value, a Zener diode 73 of a voltage monitor circuit 7 is turned on, so that a transistor 74 is turned on, and an operation stopping command signal is supplied to the on/off control terminal of a control circuit 3. Switching operation by the control circuit 3 is stopped, so that power supply to a load is stopped.
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