"Switch control voltage regulation principle
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 entire 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 provides energy to the load intermittently. In order to enable the load to obtain continuous energy supply, the switching regulated power supply must have a set of energy storage devices. When the switch is turned on, a part of the energy is stored. When disconnected, release to load.
The circuit composed of inductor L, capacitor C2 and diode D has this function. The inductor L is used to store energy. When the switch is turned off, the energy stored in the inductor 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 as:
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 (ie, 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 AB also changes by changing the ratio of the switch on time and the duty cycle. Therefore, with the change of the load and the input power supply voltage, the ratio of TON and T can be adjusted automatically to make the output voltage V0 stay the same. Changing the on-time TON and the duty cycle ratio is to change the duty cycle of the pulse. This method is called ""time ratio control"" (Time Ratio Control, abbreviated as TRC).
According to the TRC control principle, there are three ways:
1. Pulse Width Modulation (Pulse Width Modulation, abbreviated as PWM)
The switching period is constant, and the duty cycle is changed by changing the pulse width.
2. Pulse Frequency Modulation (Pulse Frequency Modulation, abbreviated as PFM)
The turn-on pulse width is constant, and the duty cycle is changed by changing the switching frequency.
3. Mixed modulation
The on-pulse width and the switching frequency are not fixed, and can change each other. It is a mixture of the above two methods."
