| 摘要 |
PROBLEM TO BE SOLVED: To provide an intermittently operating switching power circuit which prevents excessive output power from being generated on a secondary side, even if a circuit element breaks down, only by adding a simple protective circuit to a former circuit configuration. SOLUTION: An output power monitor circuit (2c, 53, 70) for monitoring the output power of a rectifying smoothing circuit (4, 13), and a protective circuit (51), which outputs a suspension control signal to the control terminal (3a) of an intermittent oscillating element (3), when the monitor circuit (2c, 53, 70) detects that the output power exceeds a reference power, are provided, and the protective circuit (51) is connected to the control terminal (3a) in parallel to a photocoupler light-receiving element (39). As a result of doing it this way, the suspension control signal is outputted from the protective circuit (51), and oscillation operation of the oscillating element (3) is stopped, even if a circuit element fails, and malfunctioning occurs and the suspension control signal is not outputted to the control terminal (3a) from the photocoupler (39).
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