Main circuit of high frequency switching power supply circuit
Main circuit of high frequency switching power supply circuit
The whole process of input and output from AC power grid includes:
1. Input filter: Its function is to filter the clutter existing in the power grid, and at the same time, it also prevents the clutter generated by this machine from being fed back to the public power grid.
2. Rectification and filtering: the AC power supply of the power grid is directly rectified into a smoother DC power supply for the next level of conversion.
3. Inverter: Convert the 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 and weight to output power.
4. Output rectification and filtering: provide stable and reliable DC power supply according to the load needs.
Circuit modulation of high frequency switching power supply
1. pulseWidthModulation (abbreviated as pWM) has a constant switching period, and the duty cycle is changed by changing the pulse width.
Second, pulseFrequencyModulation (pFM) has a constant on-pulse width, and the duty cycle is changed by changing the switching frequency.
Third, mixed modulation
The mode that the on pulse width and the switching frequency are not fixed and can be changed with each other is a mixture of the above two modes.
Principle of switching control voltage stabilization
The switch K is repeatedly turned on and off at a certain time interval. When the switch K is turned on, the input power supply E is provided to the load RL through the switch K and the filter circuit, and the power supply E provides energy to the load during the whole switch-on period. When the switch K is turned off, the input power supply E interrupts the supply of energy. It can be seen that the input power supply to the load is intermittent. In order to make the load get 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 off, the energy stored in inductor L is released to the load through diode D, so that the load can get 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 formula.
EAB=TON/T*E
Where TON is the time when the switch is turned on each time, and T is the duty cycle of the switch (that is, the sum of the on-time TON and the off-time TOFF).
From the formula, it can be seen that the average voltage between AB changes with the change of the ratio of switch on time and duty cycle. Therefore, the output voltage V0 can be kept constant by automatically adjusting the ratio of TON to T with the change of load and input power supply voltage. Changing the ratio of ON time TON and duty cycle, that is, changing the duty cycle of pulse, is called "TimeRatioControl" (abbreviated as TRC).
