How the power adapter works?

First briefly introduce the application scope of the power adapter

Power adapter, whose English name is Power adapter, is a Power Supply conversion device for small portable electronic equipment and electronic appliances. It is generally composed of a casing, a power transformer and a rectifier circuit. According to the connection method, it can be divided into wall type and desktop type. It is widely used in telephones, game consoles, language repeaters, Walkmans, notebook computers, cellular phones and other equipment.

dell adapter

According to the connection method:

It can be divided into desktop type and wall type;

According to the type of output current:

It can be divided into AC output type and DC output type.

Widely used in notebook computers, mobile phones, household IT equipment and others.

How the power adapter works:

In reality, most of the power adapters we come into contact with are switching power supplies. Switching Power Supply refers to a power supply that controls the time ratio of switching on and off to maintain a stable output voltage through modern electronic technology. The switching power supply of a power adapter is generally composed of a pulse width modulation (PWM) control IC and a MOSFET. Benefits: The conversion efficiency is high, the volume is small, and it can work in a wide voltage range. Disadvantages: It is more difficult to repair when a fault occurs, and it has a large interference to the power circuit.

Power Troubleshooting:

1. Power line failure
Line faults, including damage to the power cord, no power supply, poor contact port oxidation, etc. Focus on checking whether the input line and output line are powered on.
If the line is faulty, it can be solved by replacing the power cord.

2. The fuse is normal, no output voltage

The fuse is normal and no output voltage indicates that the switching power supply is not working or has entered a protection state. The first step is to check the value of the start-up voltage of the start-up pin of the power control chip. If there is no start-up voltage or the start-up voltage is too low, check whether the external components of the start-up pin and the start-up resistor are leaking.

If the power control chip is normal, the fault can be quickly found through the above monitoring. If there is a start-up voltage, measure whether there is a jump between high and low levels at the output end of the control chip at the moment of booting. If there is no jump, it means that the control chip is damaged, the peripheral oscillation circuit components are damaged or the protection circuit is faulty. Chip, check peripheral components, check one by one; if it is jumping, in most cases, the switch tube is bad or damaged.

3. The fuse is burned out or blown up
Mainly check the rectifier bridge, diodes, switch tubes and large filter capacitors on 300 volts. It may cause the fuse to burn and become black, or it may be caused by a problem with the anti-jamming circuit. It is especially worth noting that the fuse is burned due to the breakdown of the switch tube, which usually burns out the power control chip and the current detection resistor. The thermistor is also easy to burn out along with the fuse. [1]

4. The output voltage is too low

The following are the main reasons for low output voltage:

A. Switching power supply load short-circuit fault (especially DC/DC converter short circuit or poor performance, etc.), at this time, first disconnect all loads of the switching power supply circuit, and check whether the switching power supply circuit is faulty or the load circuit is faulty. If the load circuit is disconnected and the voltage output is normal, it means that the load is too heavy; or if it is still abnormal, the switching power supply circuit is faulty.
B. The failure of the filter capacitor or rectifier diode at the output voltage end can be judged by the replacement method.
C. The performance of the switch tube is degraded, which causes the switch tube to fail to conduct normally, which increases the internal resistance of the power supply and reduces the load capacity.
D. The poor switching transformer will not only cause the output voltage to drop, but also cause insufficient excitation of the switch tube to damage the switch tube
E. The 300V filter capacitor is bad, resulting in poor load capacity of the power supply, and the output voltage will drop as soon as the load is connected.

5. The output voltage is too high

The high output voltage generally comes from the voltage-stabilizing sampling and voltage-stabilizing control circuits. In the closed control loop formed by the DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any problems in any of these parts will cause the output voltage to rise.

Best regard.

Mandy Huang