AC/DC Switching Power Supply Working Principle
AC/DC switching power supply supplier, also called external power supply, AC/DC power adapter supplier of power adapter, (switching power supply switching power supply supplier), is a small portable electronic equipment and electronic Power supply voltage conversion equipment for electrical appliances, which can convert 100-240V AC voltage into DC mode for normal operation of electrical equipment.
AC/DC switching power supply circuit composition
The main circuit of the AC/DC power adapter is composed of an input electromagnetic interference filter (EMI), a rectifier filter circuit, a power conversion circuit, a pWM controller circuit, and an output rectifier filter circuit. Auxiliary circuits include input over-under voltage protection circuit, output over-under voltage protection circuit, output over-current protection circuit, output short-circuit protection circuit, etc.
AC input rectifier filter circuit principle
Lightning protection circuit: When there is a lightning strike and high voltage is introduced into the power supply through the power grid, the circuit composed of MOV1, MOV2, MOV3: F1, F2, F3, and FDG1 provides protection. When the voltage applied to both ends of the varistor exceeds its working voltage, its resistance decreases, causing high-voltage energy to be consumed on the varistor. If the current is too large, F1, F2, and F3 will burn out the protection circuit.
Input filter circuit: The double π filter network composed of C1, L1, C2, and C3 mainly suppresses the electromagnetic noise and clutter signals of the input power supply to prevent interference with the power supply. It also prevents high-frequency clutter generated by the power supply itself from affecting the power supply. Grid interference. When the power is turned on, C5 needs to be charged. Due to the large instantaneous current, adding RT1 (thermistor) can effectively prevent surge current. Since all instantaneous energy is consumed on the RT1 resistor, the resistance of RT1 decreases after the temperature rises after a certain period of time (RT1 is a negative temperature coefficient component). At this time, it consumes very little energy and the subsequent circuit can work normally.
Rectifier and filter circuit: After the AC voltage is rectified by BRG1, it is filtered by C5 to obtain a relatively pure DC voltage. If the capacity of C5 becomes smaller, the output AC ripple will increase.
DC input filter circuit principle
1. Input filter circuit: The double π filter network composed of C1, L1, and C2 mainly suppresses the electromagnetic noise and clutter signals of the input power supply to prevent interference with the power supply. It also prevents high-frequency clutter generated by the power supply itself from affecting the power supply. Grid interference. C3 and C4 are safety capacitors, and L2 and L3 are differential mode inductors.
2.R1, R2, R3, Z1, C6, Q1, Z2, R4, R5, Q2, RT1 and C7 form an anti-surge circuit. At the moment of starting up, Q2 is not conducting due to the presence of C6, and the current forms a loop through RT1. Q2 turns on when the voltage on C6 charges to the regulated value of Z1. If C8 leaks or the downstream circuit is short-circuited, the voltage drop generated by the current on RT1 increases at the moment of starting up. Q1 turns on and Q2 does not conduct without gate voltage. RT1 will burn out in a short time. Protect the downstream circuit.
