| 摘要 |
PURPOSE:To improve the overall efficiency of a constant current circuit, by using a compensating power supply circuit, a control circuit which compares the voltage drop of the secondary side with the reference voltage, a means which cuts off an auxiliary power supply circuit when the load current exceeds a prescribed level and a conduction time setting circuit of the primary side. CONSTITUTION:When a transistor TRQO is turned on, the induced voltage of the secondary side is prevented by a diode DO. Thus no current flows to a capacitor CO and a load RL, and the energy is stored to a transformer TO. However, the current flows to the RL from the CO when the TRQO is off. The DO conducts with the voltage of a secondary winding NT when the TRQO is off, and the energy of the winding NR is supplied to a capacitor C6 and RL. The ON/OFF of the TRQO is decided by a pulse secondary control circuit 4. The circuit 4 is driven with the voltage of a capacitor CX or the voltage of an auxiliary power supply circuit 3 when the TRQO is on. The circuit 4 decreases or increases the ON time of the TRQO when the value of a load current detector 6 is larger or smaller than the reference voltage E. As a result, the load current is set constant. |
