| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that, when a slope correction signal is added to an overcurrent detection signal, the value of the amplitude of the slope correction signal is changed according to an input voltage Vi so that the value of the output current for starting an overcurrent limit depends upon an input voltage Vi in a switching power supply circuit which has functions of detecting the current flowing to a switching element 3 at each on period Ton of a switching pulse signal Vout and performing the overcurrent protection. SOLUTION: The switching power supply circuit forms the slope correction signal obtained by superposing a ramp waveform becoming large in time proportion to the on period Ton of the switching pulse signal Vout on a rectangular wave synchronized with the switching pulse signal Vout outputted from a PWM control IC 9 so that, when the input voltage Vi becomes high, the amplitude of the rectangular wave component becomes large and the ramp waveform component becomes small. Thus, a predetermined slope correction signal can be added to the overcurrent detection signal without depending upon the input voltage Vi. COPYRIGHT: (C)2005,JPO&NCIPI
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