What is an AC DC adapter ?

January 22, 2024

What is an AC DC adapter ?

What is an AC DC adapter ?

AC/DC power adapter, also called external power supply (switching power supply), is a power supply voltage conversion device for small portable electronic equipment and electronic appliances. It can convert 100-240V AC voltage into a DC mode for normal operation of electrical equipment.

How to distinguish AC/DC adapters

From the appearance, it can be divided into: wall-mounted type, desktop type, integrated type, and assembled type.

divided into: Japanese (JP), American (US), British (UK), European (EU), Australian (AU), Korean (KR),China(CN) national standards, etc.

working purpose, it can be divided into: power supply and charging.

The certification mode can be divided into: PSE, UL, cUL, CE, BS, GS, SAA, C-TICK, KC, EK, CCC, BIS,NOM.

AC/DC adapter operating voltage

AC input voltage: 100-240V 50-60Hz

DC input voltage: 3-58V 0.3-20A

Conventional power: within 300W

AC/DC power adapter certification reference standard

UL/cUL62368,UL1012,UL1310,,UL61347, cUL/CSA C22.2;PSE/J60950,J55022,J3000,JD50195547,JD50113618 CE/EN55032,EN61000; FCC part 15,

CB/IEC60950, EN60065 ,EN61558 CCC/GB4943,GB9254,GB17625;

C-tick/N17653, SAA/Q061232;

Energy ErP V ,MEPS,Narcan,CEC; EK KC/K60950,K00022,K00024; RoHS:EN2002/95-EC TUV,GS/EN60950,EN60335,EN61558,EN62233,EN61347,EN61547,

EN55032 ,S150203696,S150205925,S150086826

AC/DC adapter service objects

Roomba automatic robot sweeper, electric vehicle, battery (lead-acid battery, polymer lithium battery, lithium iron phosphate battery, nickel metal hydride battery, nickel cadmium battery), electric toys, humidifier, air purifier, motor massage beauty equipment, security Monitoring systems, precision testing and measuring instruments, electronic information product peripherals, printing imaging equipment, home audio amplifiers, LED indoor lighting, digital communication appliances, LCD, LED liquid crystal displays, LED outdoor lamps, etc.

How AC/DC adapter works

AC/DC adapter 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, the energy consumed by it is very small, 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.

AC/DC power adapter power conversion circuit

Working principle of MOS tube: The most widely used insulated gate field effect tube at present is MOSFET (MOS tube), which uses the electroacoustic effect on the semiconductor surface to work. Also called surface field effect device. Because its gate is in a non-conductive state, the input resistance can be greatly increased, up to 105 ohms. The MOS tube uses the gate-source voltage to change the amount of charge induced on the semiconductor surface, thereby controlling the drain current. .

Working principle: R4, C3, R5, R6, C4, D1, D2 form a buffer and are connected in parallel with the switch MOS tube, so that the voltage stress of the switch tube is reduced, EMI is reduced, and secondary breakdown does not occur. When the switch Q1 is turned off, the primary coil of the transformer is prone to generate peak voltages and peak currents. The combination of these components can absorb the peak voltages and currents well. The current peak signal measured from R3 participates in the duty cycle control of the current working cycle and is therefore the current limit of the current working cycle. When the voltage on R5 reaches 1V, UC3842 stops working and switch Q1 is turned off immediately.

The junction capacitances CGS and CGD in R1 and Q1 together form an RC network. The charging and discharging of the capacitor directly affects the switching speed of the switching tube. If R1 is too small, it will easily cause oscillation and electromagnetic interference will be great; if R1 is too large, it will reduce the switching speed of the switch tube. Z1 usually limits the GS voltage of the MOS tube below 18V, thereby protecting the MOS tube.

The gate controlled voltage of Q1 is a saw-shaped wave. When the duty cycle is larger, the conduction time of Q1 is longer, and the energy stored in the transformer is more; when Q1 is turned off, the transformer passes through D1, D2, R5 , R4, and C3 release energy, and at the same time achieve the purpose of magnetic field reset, preparing the transformer for the next storage and transmission of energy. The IC constantly adjusts the duty cycle of the ⑥ pin saw-shaped wave according to the output voltage and current, thereby stabilizing the output current and voltage of the entire machine.

C4 and R6 are spike voltage absorption circuits.

Push-pull power conversion circuit

1.Q1 and Q2 will be turned on in turn. 2. Power conversion circuit with drive transformer: T2 is the drive transformer, T1 is the switching transformer, and TR1 is the current loop.

Output rectifier filter circuit

1. Forward rectifier circuit

2. Flyback rectifier circuit

3. Synchronous rectification circuit

Power factor correction circuit (PFC)

The input voltage passes through the EMI filter composed of L1, L2, L3, etc., and the BRG1 rectifies one path and sends it to the PFC inductor. The other path is divided by R1 and R2 and sent to the PFC controller as a sample of the input voltage to adjust the duty of the control signal. Ratio, that is, changing the on and off times of Q1 to stabilize the PFC output voltage. L4 is the PFC inductor, which stores energy when Q1 is on and releases energy when Q1 is off. D1 is the startup diode. D2 is the PFC rectifier diode, C6 and C7 filter. One channel of the PFC voltage is sent to the downstream circuit, and the other channel is divided by R3 and R4 and then sent to the PFC controller as a sample of the PFC output voltage to adjust the duty cycle of the control signal and stabilize the PFC output voltage.

1. Passive PFC

2. Active PFC


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