Introduction to the main circuit of high-frequency switching power supply circuit
The entire process from AC grid input to DC output, including:
1. Input filter: Its function is to filter out the clutter present in the power grid, while also hindering the feedback of local generated clutter to the public power grid.
2. Rectification and filtering: Directly rectify the AC power supply of the power grid into smoother DC power for the next stage of transformation.
3. Inverter: Convert rectified DC power into high-frequency AC power, which is the core part of high-frequency switching power supplies. 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.
Modulation of high-frequency switching power supply circuit
1, Pulse Width Modulation (PWM) has a constant switching period and changes the duty cycle by altering the pulse width.
2, Pulse Frequency Modulation (pFM) is a method of changing the duty cycle by varying the operating frequency of a switch with a constant pulse width.
3, Mixed modulation
The way in which the width of the conduction pulse and the operating frequency of the switch are not fixed and can both be changed is a mixture of the above two methods.
Principle of switch controlled voltage stabilization
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 filtering circuit. During the entire switching period, the power E provides energy to the load; When switch K is disconnected, input power source E interrupts the supply of energy. It can be seen that the input power supply provides energy to the load intermittently. In order to ensure that the load can 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 turned off, the energy stored in inductance L is released to the load through diode D, allowing the load to receive continuous and stable energy. Because diode D keeps the load current continuous, it is called a freewheeling diode. The average voltage EAB between AB can be expressed by the following equation
EAB=TON/T*E
In the formula, TON represents the time it takes for the switch to be turned on each time, and T represents the working cycle of the switch's on/off state (i.e. the sum of the switch's on time TON and off time TOFF).
As can be seen from the equation, changing the ratio of switch on-time to duty cycle also changes the average voltage between AB, therefore, automatically adjusting the ratio of TON and T with changes in load and input power supply voltage can maintain the output voltage V0 unchanged. Changing the on-time TON and duty cycle ratio, that is, changing the pulse duty cycle, is a method called "Time Ratio Control" (TRC).
