| 摘要 |
In a switching power unit for performing an overcurrent protecting operation by shortening a switching pulse, an oscillation frequency changing circuit drops an oscillation frequency of an oscillator when an overcurrent is detected by an overcurrent detection circuit, and an RS flip-flop circuit performs the overcurrent protecting operation. When an output voltage is dropped due to a short circuit etc., the oscillation frequency changing circuit further drops the oscillation frequency of the oscillator. In an arrangement in which a frequency under a normal loading condition is made higher by considering the response delay in the overcurrent protecting operation in this manner, an overcurrent detection output is given to the oscillation frequency dropping circuit via the RS flip-flop circuit, so that it is necessary to provide a time constant circuit which prevents hunting and it is possible to miniaturize chip size of an integrated circuit itself. As a result, in the switching power unit for performing the overcurrent protecting operation, it is possible to miniaturize externally provided parts by making a switching frequency higher and to miniaturize the integrated circuit itself.
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