| 摘要 |
PURPOSE: To provide a relatively simple structure of a switching mode power supply while keeping the limited property of the current supply to a lamp by adding a switching-signal generating function to a circuit means of detecting a current by an induction means. CONSTITUTION: When a switching means 1 is switched to a nonconducting state, a current whose value decreases flows in a choke coil 2 via a rectification means 4 which is in a diode configuration. At the same time, a current conducting path is formed via a capacitor 22, so that an oscillatory circuit having the choke coil 2 and the capacitor 22 is obtained. As soon as the current flowing in the chock coil 2 is again increased by the oscillation of the oscillatory circuit, a positive voltage is induced in an auxiliary winding 21. The voltage supplies a switching-on signal to the switching means 1 via a coupling capacitor 100 and a resistance 101. Thus, the auxiliary winding 21 forms a signal source for producing the switching-on signal. |
