| 摘要 |
PURPOSE:To reduce the power consumption and to improve the reliability of used parts by detecting an overcurrent flowed to a power FET of a switching power source by a voltage drop generated by the resistance of itself. CONSTITUTION:A switching power source switches a DC voltage 1 applied to the pirmary side of a transformer 2 by a field effect transistor (FET)3 to convert it to a pulse voltage, rectifies, and smoothes as a DC voltage. In this case, a capacitor 23 is charged through a resistor 20 by a voltage higher than the saturated voltage of the FET3 and a diode 21, and charge stored in the capacitor is discharged through the diode 21 to the FET3. The product of the resistors 20, 22 and the capacitor 23 is selected to a value lower than the switching frequency. Thus, the voltage of a terminal 24 varies by the saturated voltage of the FET3 when the voltage drop of the diode 21 is constant, and the overcurrent of the FET3 can be detected by this amplitude. |
