High-frequency switching power supply circuit composition and voltage regulation principle

The high-frequency switching power supply consists of the following parts:

1. Main circuit

The whole process from AC grid input to DC output includes:

1. Input filter: Its function is to filter out the noise in the power grid, and also to prevent the noise generated by the machine from being fed back to the public power grid.

2. Rectification and filtering: directly rectify the AC power of the grid into smoother DC power for the next level of conversion.

3. Inversion: Converting rectified DC into high-frequency AC, which is the core part of high-frequency switching power supply. The higher the frequency, the smaller the ratio of volume, weight and output power.

4. Output rectification and filtering: Provide stable and reliable DC power supply according to load requirements.

2. Control circuit

On the one hand, samples are taken from the output end, compared with the set standard, and then the inverter is controlled to change its frequency or pulse width to achieve output stability. On the other hand, based on the information provided by the test circuit and identified by the protection circuit, the control circuit is provided to take various protection measures for the entire machine.

3. Detection Circuit

In addition to providing various parameters of the protection circuit in operation, it also provides various display instrument data.

4. Auxiliary power supply

Provide power supply for different requirements of all single circuits.

Section 2 Switch Control Voltage Regulator Principle

The switch K is repeatedly turned on and off at certain time intervals. When the switch K is turned on, the input power E is provided to the load RL through the switch K and the filter circuit. During the entire period when the switch is on, the power E provides energy to the load; when the switch K is turned off, the input power E interrupts the supply of energy. It can be seen that the input power supply provides energy to the load intermittently. In order for the load to be continuously supplied with energy, the switching power supply must have a set of energy storage devices to store part of the energy when the switch is turned on, and release it to the load when the switch is turned off. In the figure, the circuit composed of inductor L, capacitor C2 and diode D has this function. The inductor L is used to store energy. When the switch is turned off, the energy stored in the inductor L is released to the load through the diode D, so that the load obtains continuous and stable energy. Because the diode D makes the load current continuous, it is called a freewheeling diode. The average voltage EAB between AB can be expressed by the following formula

EAB=TON/T*E

Where TON is the time the switch is turned on each time, and T is the on-off duty cycle of the switch (i.e. the sum of the switch on time TON and the switch off time TOFF).

It can be seen from the formula that by changing the ratio of the switch on time and the duty cycle, the average voltage between AB will also change. Therefore, by automatically adjusting the ratio of TON and T as the load and input power voltage change, the output voltage V0 can be kept unchanged. Changing the ratio of the on time TON and the duty cycle is also changing the duty cycle of the pulse. This method is called "Time Ratio Control" (abbreviated as TRC).

According to the TRC control principle, there are three ways:

1. Pulse Width Modulation (PWM) The switching period is constant and the duty cycle is changed by changing the pulse width.

2. Pulse Frequency Modulation (PFM) keeps the on-pulse width constant and changes the duty cycle by changing the switching operating frequency.

3. Hybrid Modulation

The conduction pulse width and the switching operating frequency are not fixed, and both can be changed. It is a mixture of the above two methods.