High frequency power supply circuit modulation
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 existing in the power grid, while also hindering the feedback of the generated clutter 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 the 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, and 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) has a constant switching cycle, which is achieved by changing the pulse width to change the duty cycle.
2、 Pulse Frequency Modulation (pFM) has a constant conduction pulse width and changes the duty cycle by changing the operating frequency of the switch.
3、 Hybrid 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 load RL through switch K and filtering circuit. During the entire switch on period, power E provides energy to load; When switch K is disconnected, input power 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. Inductor L is used to store energy. When the switch is disconnected, the energy stored in inductor L is released to the load through diode D, allowing the load to obtain continuous and stable energy. Since diode D keeps the load current continuous, it is called a continuous diode. The average voltage EAB between AB can be expressed as follows: 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).
From the equation, it can be seen that 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 duty cycle ratio, also known as changing the duty cycle of the pulse, is a method called "Time Ratio Control" (TRC).
