| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a power supply circuit that can rapidly discharge electric charges accumulated in a smoothing capacitor provided in the power supply circuit when an AC voltage being supplied to the power supply circuit from outside is cut off. Ž<P>SOLUTION: The power supply circuit 10 is equipped with a voltage detection circuit 13 and a discharge circuit 14. The voltage detection circuit 13 comprises a first voltage-dividing circuit 15 including a Zener diode ZD1 and resistive elements R1 and R2 which are connected in series; a second voltage-dividing circuit 16 including resistive elements R3 to R5 which are connected in series; and a transistor Q1. The transistor Q1 is put in the on-state when a potential difference between a voltage-dividing node N1 of the first voltage-dividing circuit 14 and a voltage-dividing node N2 of the second voltage-dividing circuit 16 exceeds a threshold voltage. When the transistor Q1 is put in the on-stage, a transistor Q2 provided in the discharge circuit 14 is in conduction to rapidly discharge the electric charges accumulated in a capacitor 12. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
|
