what is the power switch
Power switch is to use the circuit control switch tube for high-speed channel pass and cut-off. The direct current into a high frequency of alternating current to provide transformer transformer voltage, so as to produce the required one or more groups of voltage!
Power switch function
1. Ac power supply input is rectified and filtered into DC;
2, through the high frequency pwm(pulse width modulation) signal control switch tube, the DC will be added to the switching transformer primary;
3, the switching transformer secondary induction of high frequency voltage, through the rectifier filter to supply the load;
4, output part through a certain circuit feedback to the control circuit, control pwm duty ratio, in order to achieve the purpose of stable output.
Working principle of power switch
There is a door in the power switch, an open power supply through, a closed power supply will stop through, so what is the door, some switching power supply use silicon controlled, some using switching tube, these two components are similar in performance, are based on the base, (switching tube) control pole (silicon) plus pulse signal to complete the conduction and cut-off, pulse signal is half a week to, When the voltage on the control pole rises, the switching tube or silicon is switched on. The 300v voltage output after 220v rectification and filtering is switched on, transmitted to the secondary through the switching transformer, and then the voltage is increased or decreased through the transformer ratio for each circuit to work.
When the oscillation pulse is negative for half a week, the base of the power regulating tube or the control pole voltage of the thyristor is lower than the original setting voltage, the power regulating tube is cut off, the 300v power supply is turned off, and the switching transformer has no secondary voltage. At this time, the working voltage required by each circuit is maintained by the filter capacitor discharge after the secondary rectifier. Repeat the previous process until the next pulse's positive half cycle signal arrives.
This switching transformer is called high frequency transformer, because its operating frequency is higher than 50hz low frequency. Then how to get the pulse of pushing the switching tube or thyristor, which requires an oscillating circuit. As we know, the transistor has a characteristic, that is, the base voltage to the emitter is 0.65-0.7v, which is the amplification state, and above 0.7v is the saturation conduction state. 0.1V-0.3V works in the oscillation state. Then the working point is adjusted, it depends on the deep negative feedback to produce negative pressure, so that the oscillation tube vibration, the frequency of the oscillation tube is determined by the length of time of capacitor charge and discharge on the base, high oscillation frequency output pulse amplitude is large, and vice versa, which determines the size of the output voltage of the power supply adjustment tube.
Power switch control voltage control principle
Switch k is repeatedly switched on and off at certain time intervals. When switch k is switched on, input power e is supplied to load rl through switch k and filter circuit. During the whole switch on period, power e provides energy to load; When switch k is 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 enable the load to get continuous energy supply, switching voltage regulator power supply must have a set of energy storage device, when the switch is on, a part of the energy is stored, when the switch is off, release to the load.
A circuit consisting of inductor l, capacitor c2 and diode d has this function. The inductor l is used to store energy. When the switch is off, the energy stored in the inductor l is released to the load through diode d, so that the load gets continuous and stable energy. Because diode d makes the load current continuous, it is called continuous current diode. The average voltage eab between ab and AB can be expressed as follows: eab=ton/t*e, ton is the time each switch is on, t is the on-off working cycle of the switch (i.e. the sum of ton and toff). As can be seen from the formula, the average value of voltage between ab will also change if the ratio of switching on time and working cycle is changed. Therefore, the output voltage v0 can be maintained unchanged by automatically adjusting the ratio of ton and t with the change of load and input voltage. To change the on-time ton and the working cycle ratio is to change the duty ratio of the pulse, this method is called "time ratio control"
