High Frequency Switching Power Circuit Modulation
High frequency switching power supply circuit main circuit
The whole 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 at the same time prevent the clutter generated by the machine from feeding back to the public power grid.
2. Rectification and filtering: directly rectify the AC power of the grid into a smoother DC for the next stage of transformation.
3. Inversion: Convert the rectified direct current into high-frequency alternating current, which is the core part of the high-frequency switching power supply. The higher the frequency, the smaller the ratio of volume, weight and output power.
4. Output rectification and filtering: According to load requirements, provide stable and reliable DC power supply.
High Frequency Switching Power Circuit Modulation
1. Pulse Width Modulation (pulseWidthModulation, abbreviated as pWM) The switching cycle is constant, and the duty cycle is changed by changing the pulse width.
Second, pulse frequency modulation (pulseFrequencyModulation, abbreviated as pFM) conduction pulse width is constant, by changing the switching frequency to change the duty cycle.
3. Mixed modulation
Both the conduction pulse width and the switching frequency are not fixed, and both can be changed. It is a mixture of the above two methods.
Principle of switch control voltage regulation
The switch K is repeatedly turned on and off at a certain time interval. When the switch K is turned on, the input power E is supplied to the load RL through the switch K and the filter circuit. During the entire switch-on period, the power supply E provides energy to the load; When the switch K is turned off, the input power E interrupts the supply of energy. It can be seen that the energy provided by the input power supply to the load is intermittent. In order to provide the load with continuous energy, the circuit composed of switches C2 and D has this function. The inductance L is used to store energy. When the switch is turned off, the energy stored in the inductance L is released to the load through the diode D, so that the load can obtain 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 duty cycle of the switch on and off (that is, the sum of the switch on time TON and the off time TOFF).
It can be seen from the formula that the average value of the voltage between A and B will also change by changing the ratio of the on-time of the switch to the duty cycle. Therefore, automatically adjusting the ratio of TON and T with the change of the load and the input power supply voltage can make the output voltage V0 stay the same. Changing the on-time TON and the ratio of the duty cycle means changing the duty cycle of the pulse. This method is called "Time Ratio Control" (TimeRatioControl, abbreviated as TRC).
