Valley fill circuit with protection function

Abstract

The invention provides a valley fill circuit with the protection function. A charging diode D3 of an existing valley fill circuit is connected with a third capacitor C3 in parallel, so that the withstand voltage of the third capacitor C3 is a half of the maximum peak of input pulsating direct currents, and high frequency ripple currents of a later-stage switching power source 300 can be fully and effectively absorbed. The front and the back of a rectifier bridge 101 are provided with a multi-stage double-direction filter circuit composed of a voltage dependent resistor RV1, a voltage dependent resistor RV2, a thermistor NTC and a safety capacitor C and a protection circuit composed of an inductor L respectively. The valley fill circuit has the advantages that the power factor is large, the value of the C3 does not influence the power factor, the circuit topology structure is simple, the absorbing effect on surge voltage is good, the cost is low and the size is small. When the later stage is the switching power source, the difference module conducted interference degree accords with the grade of CLASSB in GB9254.

Description

technical field [0001] The invention relates to the field of rectification and filtering, in particular to a valley-filling circuit with a protection function in a switching power supply. Background technique [0002] Industrial and civil use need to change the AC voltage of various power grids into DC. With the further requirements of the national standard on the power factor of electrical appliances, there are power factor requirements for switching power supplies with power consumption above 75W, that is, the operating current of the circuit is required The waveform is basically the same as the voltage waveform. At present, energy-saving lamps above 5W have proposed power factor requirements. [0003] Note: The 75W data comes from the Chinese national standard GB17625.1-1998, named "Limits of Harmonic Current from Low-Voltage Electrical and Electronic Equipment (Input Current ≤ 16A per Phase of Equipment)". [0004] At present, there is a power factor correction circuit...

AI Technical Summary

Problems solved by technology

[0017]2. Poor protection performance

[0028]The shortcoming of the parallel capacitor CL is that the working voltage of the capacitor CL is high; the capacity of the capacitor CL is large, and due to the filtering function, Figure 4 shows the power factor (PF) drop of the traditional valley filling circuit 200 ; The capacity of the capacitor CL is small, and the high-frequency ripple current absorption generated by the flyback circuit 300 of the rear stage is not obvious, which causes the conversion efficiency (η) of the flyback switching power supply circuit to decline, and the external differential mode conduction interference is very large ; Since the capacitor CL needs to absorb high-frequency ripple, if a high-voltage ceramic capacitor is used, because of the piezoelectric effect of the high-voltage ceramic capacitor, the higher the operating voltage, the smaller the capacity, and a capacitor with a large capacity is required, which is expensive and bulky. If a high-voltage capacitor similar to CBB (polypropylene capacitor) is used, the cost is high and the volume is larger

[0031] (1) Capacitor CL has a high working voltage and needs to absorb high-frequency ripple current, resulting in large size and high cost; the large value of capacitor CL results in a valley-filling circuit The power factor decreases; the capacity value is small, the absorption of high-frequency ripple current is not obvious, and it is difficult to compromise

[0032](2) The absorption effect on surge voltage is poor, and it is easy to be damaged during use;

[0033](3) A more complex additional circuit needs to be designed in front of the rectifier bridge, so that the differential mode conduction interference can meet the CLASS B level in GB9254, and the cost is high and the volume is large

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