1. AC power input is rectified and filtered to DC;
2. Operate the switch by high frequency PWM (Pulse Width Modulation) or Pulse Frequency Modulation (PFM) and add this DC to the primary of the switching transformer;
3. The secondary frequency of the switching transformer generates a high frequency voltage, which is supplied to the load through rectification and filtering.
4. The output part is fed back to the control circuit through the positive circuit to manipulate the duty ratio of PWM and achieve the purpose of stable output.
When the AC power supply is input, it is usually filtered through inductive and capacitive filters to remove the interference to the grid and the power supply to the grid. Under the same power, the higher the switching frequency, the smaller the size of the switching transformer, but the higher the requirements for the switching tube; The secondary of the switching transformer may have multiple windings or windings with multiple taps to obtain the desired output; In general, some protection circuits should be added, such as no-load, short circuit and other protection functions, otherwise the switching power supply may be burned.
Reasons why switching power supply secondary does not need bridge rectifier
Reasons for switching power supply secondary not to use bridge rectifier Switching power supply secondary does not use bridge rectifier because of its own characteristics. There are about two types of switching power supply, one is forward, the other is flyback. The primary function of the secondary diode is to rectify the cutoff wave to remove the reverse peak voltage. Both of these are waveforms that do not require an input voltage because the switching power supply has a PWM chip.
The composition of switching power supply control chip
Switching power supply control chip is a kind of chip in switching power supply. Before switching power supplies, they were linear power supplies. Switching power supply is a kind of high efficiency and energy saving power supply, and it is also the mainstream of switching power supply.
Switching power supply 300V filter capacitors are measured using a multimeter DC file. AC file does not have 300V measurement value, we usually measure the AC current, 220V is actually the effective value of AC, after conversion and filtering can obtain the DC voltage is about 311V, but if the load can not maintain the maximum value, it should be directly measured DC filter electrolytic capacitor.