| 摘要 |
PROBLEM TO BE SOLVED: To prevent the fluctuation of the on-period of a main switch and to obtain the low-noise, highly-efficient circuit at a low cost by providing the on-period control means of the main switch, which turns on the main switch after the elapse of a specified period by the voltage generated in the control winding of a transformer. SOLUTION: A control winding 18b of a transformer 18 performs the retrieval of a current. The current is taken out from a capacitor 14 through a resistor 16 and a low-current diode 15 from an on-period control means C of a main switch. The capacitor 14 is reversely charged. When the reverse charging voltage of the capacitor 14 becomes the forward voltage of a diode 13, the diode 13 conducts, and a current path is switched. Thus, the charge-starting voltage of the capacitor 14 after the switching is fixed, and the on-period of the transistor 4 becomes constant. Therefore, the on-duty is not fluctuated by the voltage fluctuation and the ripple component of the DC power supply, and the low-noise, highly-efficient device can be realized at the low cost. |
