AC/DC switching switching supplier power supply power supply supplier also called external power supply, AC/DC power adapter power adapter supplier, (switching power supply switching power supply supplier switching power supply), is a small portable electronic equipment and electronic appliances power supply voltage conversion equipment, it can be 100-240V AC voltage into electrical equipment It can convert 100-240V AC voltage to DC mode for normal operation of electrical equipment.
The main circuit of AC/DC power adapter is composed of input EMI filter (EMI), rectifier filter circuit, power conversion circuit, pWM controller circuit, and output rectifier filter circuit. Auxiliary circuits are input over-undervoltage protection circuit, output over-undervoltage protection circuit, output overcurrent protection circuit, output short circuit protection circuit.
Lightning protection circuit: When there is a lightning strike, generating high voltage through the power grid into the power supply, by MOV1, MOV2, MOV3: F1, F2, F3, FDG1 circuit for protection. When the voltage added to both ends of the varistor exceeds its operating voltage, its resistance decreases, so that high-voltage energy consumption in the varistor, if the current is too large, F1, F2, F3 will burn to protect the back stage circuit.
Input filter circuit: C1, L1, C2, C3 composed of double π-type filter network is mainly for the input power supply electromagnetic noise and clutter signal suppression, to prevent interference with the power supply, but also to prevent the power supply itself from generating high-frequency clutter on the power grid interference. When the power supply is turned on instantly, to charge C5, due to the instantaneous current is large, add RT1 (thermistor) can effectively prevent the surge current. Because the instantaneous energy is consumed in the RT1 resistance, after a certain period of time after the temperature rises RT1 resistance decreases (RT1 is a negative temperature coefficient components), then it consumes very little energy, after the circuit can work normally.
Rectifier filter circuit: AC voltage rectified by BRG1, filtered by C5 to get a more pure DC voltage. If the capacity of C5 becomes small, the output AC ripple will increase.
1. Input filter circuit: C1, L1, C2 composed of double π-type filter network is mainly for the input power supply electromagnetic noise and clutter signal suppression, to prevent the power supply interference, but also to prevent the power supply itself from generating high-frequency clutter on the grid interference. C3, C4 for the safety capacitors, L2, L3 for the differential mode inductance.
2. R1, R2, R3, Z1, C6, Q1, Z2, R4, R5, Q2, RT1, C7 form an anti-surge circuit. At the instant of starting, Q2 does not conduct due to the presence of C6, and the current constitutes a circuit through RT1. Q2 conducts when the voltage on C6 is charged to the regulated value of Z1. If C8 leakage or short circuit phenomenon in the back stage circuit, the current in the instant of starting RT1 voltage drop increases, Q1 conductive so that Q2 does not gate voltage does not conduct, RT1 will burn in a very short period of time to protect the back stage circuit.
