Main circuit of high-frequency switching power supply circuit
Main circuit of high-frequency switching power supply circuit
The entire process of input and output from the AC power grid, including:
1. Input filter: Its function is to filter out the clutter present in the power grid, while also hindering the feedback of the clutter generated by the machine to the public power grid.
2. Rectification and filtering: Directly rectifying the AC power supply of the power grid into smoother DC power for the next level of transformation.
3. Inversion: Transforming rectified DC power into high-frequency AC power, which is the core part of a high-frequency switching power supply. The higher the frequency, the smaller the ratio of volume, weight to output power.
4. Output rectification and filtering: Provide stable and reliable DC power supply according to load requirements.
High frequency switching power supply circuit modulation
1, Pulse Width Modulation (pWM) is a method of changing the duty cycle by keeping the switching period constant.
2, Pulse Frequency Modulation (pFM) is a method of changing the duty cycle by keeping the conduction pulse width constant and changing the operating frequency of the switch.
3, Mixed modulation
The conduction pulse width and switching frequency are not fixed and can be changed from each other, which is a combination of the above two methods.
Principle of switch controlled voltage stabilization
Switch K repeatedly turns on and off at certain time intervals. When switch K is turned on, input power E is supplied to the load RL through switch K and filtering circuit. Throughout the entire switch on period, power E provides energy to the load; When switch K is turned off, the input power supply E interrupts the supply of energy. It can be seen that the input power supply provides energy to the load intermittently. To enable the load to receive continuous energy supply, the circuit composed of switches C2 and D has this function. Inductance L is used to store energy. When the switch is disconnected, the energy stored in inductance L is released to the load through diode D, allowing the load to obtain continuous and stable energy. Because diode D causes the load current to be continuous, it is called a freewheeling diode. The average voltage EAB between AB can be represented by the following equation
EAB=TON/T * E
In the formula, TON represents the time each time the switch is turned on, and T represents the working cycle of the switch on/off (i.e. the sum of the switch on time TON and off time TOFF).
As can be seen from the formula, changing the ratio of switch on time and working cycle also changes the average voltage between AB. Therefore, automatically adjusting the ratio of TON and T with changes in load and input power voltage can maintain the output voltage V0 unchanged. Changing the on time TON and the duty cycle ratio, also known as changing the pulse duty cycle, is a method called Time Ratio Control (TRC).
