as the picture shows. After the AC power is rectified, power is directly supplied to the switch. After the circuit starts to oscillate, the lamp is turned on. At this time, the filament end (point A in the circuit) has a high-frequency AC voltage. This voltage is rectified by D6 and charges C1. When the AC voltage instantaneous value drops to about 130V. C1 discharges to the load via D5. Because the impedance of point A in the circuit is relatively high, the voltage charged on C1 is not high, and the actual measurement is only about 130V. Therefore, a capacitor with a withstand voltage of 250V is selected. SHENZHEN CHONDEKUAI TECHNOLOGY CO.LTD , https://www.szsiheyi.com
This circuit skillfully uses the high-frequency oscillation energy in the electronic ballast to control the charging process of the capacitor. Although the energy of the latter stage circuit is fed back to the front of the circuit, most of the AC power for one cycle is directly powered by 220V. The filter capacitor is only at the voltage. Only discharge the load when it is low. Moreover, due to the isolation effect of D5, the rectifying circuit cannot directly charge Cl, and no peak current will be formed by charging the capacitor, thereby increasing the power factor. The power factor of this circuit can be increased to 0.95, and the total current harmonic distortion THD is reduced to about 20%.
The main advantages of the above two circuits are the improvement of the power factor and the reduction of the THD. The power factor of an ordinary single capacitor filter circuit is about 0.6, and the THD is about 120%. I measured the two circuits. The power factor is 0.92~0.95. The rectification and filtering part of the circuit in Fig. 1 is simulated with Multisim software. The power factor can reach 0.942.
Although these two kinds of circuits can greatly improve the power factor, due to the large voltage pulsation, the peak ratio of the lamp current is too high, which will accelerate the damage of the filament and affect the lamp life. Especially when the lamp is used for a period of time, the ability of the filament to emit electrons becomes more pronounced. 