摘要 |
<p>PROBLEM TO BE SOLVED: To protect a switch element of a switching power supply device from an overcurrent even if an input voltage changes.SOLUTION: A duty detection circuit 41 detects the ratio of an on time of a switch element Q1 to the sum of the on time and an off time, and generates a duty detection voltage Vrc proportional to the detected ratio. An overcurrent detecting reference voltage generation circuit 42 generates an overcurrent detecting reference voltage V42 proportional to the duty detection voltage Vrc. A comparator 4 compares a switching current detection voltage Vd with the overcurrent detecting reference voltage V42, and if the switching current detection voltage Vd is higher than the overcurrent detecting reference voltage V42, generates a high level overcurrent detection signal S4. A control circuit 100 turns off the switch element Q1 in response to the high level overcurrent detection signal S4.</p> |