High frequency switching power supply circuit main circuit
On the one hand, the high-frequency switching power supply circuit samples from the output end, compares it with the set standard, and then controls the inverter to change its frequency or pulse width to achieve output stability. On the other hand, based on the data provided by the test circuit, Protection circuit identification, providing control circuits to implement various protection measures for the entire machine.
High frequency switching power supply circuit main circuit
The entire process from AC grid input to DC output includes:
1. Input filter: Its function is to filter the clutter existing in the power grid, and also prevent the clutter generated by the machine from being fed back to the public power grid.
2. Rectification and filtering: directly rectify the grid AC power into smoother DC power for next-level transformation.
3. Inverter: Convert rectified DC power into high-frequency alternating current. This 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 needs.
High frequency switching power supply circuit modulation
1. Pulse Width Modulation (pulseWidthModulation, abbreviated as pWM) has a constant switching period and changes the duty cycle by changing the pulse width.
2. Pulse Frequency Modulation (abbreviated as pFM) has a constant conduction pulse width and changes the duty cycle by changing the switching operating frequency.
3. Mixing and modulation
Both the conduction pulse width and the switching operating frequency are not fixed and can be changed by each other. It is a mixture of the above two methods.
Switch control voltage stabilization principle
Switch K is repeatedly turned on and off at certain time intervals. When switch K is turned on, input power E is provided to load RL through switch K and the filter circuit. During the entire switch on period, power E provides energy to the load; When the switch K is turned off, the input power supply E interrupts the energy supply. It can be seen that the input power supply provides energy to the load intermittently. In order to provide continuous energy supply to the load, the circuit composed of switches C2 and 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 receives continuous and stable energy. Because the diode D makes the load current continuous, it is called freewheeling. diode. The average voltage EAB between AB can be expressed by the following formula
EAB=TON/T*E
In the formula, TON is the time when the switch is turned on each time, and T is the working cycle of the switch on and off (that is, the sum of the switch on time TON and the switch off time TOFF).
It can be seen from the formula that when the ratio of the switch on time and the working cycle is changed, the average value of the voltage between AB will also change. Therefore, automatically adjusting the ratio of TON and T as the load and input power supply voltage change can make the output voltage V0 stay the same. Changing the on-time TON and the duty cycle ratio means changing the duty cycle of the pulse. This method is called "Time Ratio Control" (TimeRatioControl, abbreviated as TRC).
