Introduction to the Principle of High Frequency Switching Power Supply
The main circuit
The whole process of AC grid input and DC output includes: 1. Input filter: its function is to filter the clutter existing in the grid, and at the same time prevent the clutter generated by the machine from feeding back to the public grid. 2. Rectification and filtering: the grid AC is directly rectified 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 high frequency. 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.
Control circuit
On the one hand, samples are taken from the output terminal, compared with the set standard, and then the inverter is controlled to change its frequency or pulse width to achieve output stability; on the other hand, according to the information provided by the test circuit, it is identified by the protection circuit The control circuit carries out various protection measures on the whole machine.
detection circuit
In addition to providing various parameters in the protection circuit in operation, it also provides various display instrument information.
Auxiliary power
Provides power for different requirements of all single circuits. The principle of switch control and 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 E is supplied to the load RL through the switch K and the filter circuit. During the entire switch-on period, the power E Provide energy to the load; when the switch K is turned off, the input power supply E interrupts the energy supply. It can be seen that the energy provided by the input power supply to the load is intermittent. In order to provide continuous energy to the load, 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. Release to the load when disconnected. In the figure, the circuit composed of inductor L, capacitor C2 and diode 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 switch on time TON and off sum of 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).
