Something about USB AC adapter

September 14,2021

When you are wearing blank polyester socks and driving a car equipped with a VW oxygen sensor to travel, don't forget to bring a 45L mountaineering backpack, an ottoman, a delonghi ec702 portafilter and a bbq digital thermometer. These will make you easier. Of course, if you bring a laptop, a USB AC adapter is also necessary.


What is a USB AC adapter?



custom usb AC adapter



AC adapter is the abbreviation of alternating current, also known as AC/DC adapter or AC/DC converter. It is a type of external power supply, usually enclosed in a case similar to an AC plug. Adapters for battery-powered equipment can be described as chargers or rechargers (see also battery chargers). USB AC adapters are used for electrical equipment that requires power source but does not contain internal components that obtain the required voltage and power from the main power source. The internal circuitry of an external power supply is very similar to the design that used for the built-in or internal power supply.


The external power supply can be used for devices without other power sources or for battery-powered devices. When plugged into a power source, in addition to powering the device, it can sometimes charge the battery.


The use of an external power supply can make the equipment powered by the mains or battery portable without adding a large number of internal power components, and there is no need to produce equipment that only uses the specified power supply;


Material of USB AC adapter


The power adapter shell is generally made of plastic materials, of course, some industrial power supplies use metal shells. Commonly used power adapter shell materials mainly include ABS material, ABS+PC material, and PC material. Let's introduce the differences of these materials one by one.




Pure PC material has ultra-high strength and elastic coefficient, and it can be used in a wide temperature range. (The general material of ABS can only be used at -25℃ to 60℃ ). In addition, PC material has high transparency and free dyeability, so the power adapter is very good in various colors. Moreover, this material is also fatigue-resistant, weather-resistant, odorless and harmless to the human body, which is in line with hygiene and safety.




ABS material characteristics, first of all, low strength, not temperature resistant, under normal circumstances, the maximum use temperature can not exceed 60 degrees Celsius, this is a lot worse than PC materials, ABS is generally used in household appliances.




Taking the characteristics of the above two, it has excellent molding processing performance, good fluidity and high strength. ABS/PC material is easy to process, and has good processing dimensional stability and surface gloss, is easy to paint and color. It can also be used for secondary processing properties such as spraying metal, electroplating, welding and bonding. Because of the characteristics of ABS combined with the characteristics of its three components, it has excellent comprehensive performance and becomes one of the preferred plastics for electrical components, home appliances, computers and instruments.


Nowadays, pure PC and PC/ABS has become the main material of power adapter shell. Although the cost will be much higher than before, but in terms of environmental protection and safety, ABS is less and less suitable for the current market demand!


Common problems and solutions


Line failure


Circuit failure, including the power cord is damaged and not energized, the contact port is oxidized and the contact is poor. Focus on checking whether the input line and output line are energized.


If the line is faulty, it can be solved by replacing the power cord.


The output voltage is too low


The following are the main causes of low output voltage:



  • Switching power supply load short-circuit failure (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 the load is too heavy; or it is still abnormal, it means the switching power supply circuit is faulty.


  • The failure of the filter capacitor or rectifier diode at the output voltage end can be judged by the replacement method.


  • The performance of the switching tube is degraded, causing the switching tube to fail to conduct normally, which increases the internal resistance of the power supply and reduces the load capacity.


  • Poor switching transformer not only causes the output voltage to drop, but also causes insufficient excitation of the switching tube and damages the switching tube.


  • The 300V filter capacitor is poor, resulting in poor load carrying capacity of the power supply, and the output voltage will drop as soon as the load is connected.


The output voltage is too high


Excessive output voltage generally comes from voltage stabilization sampling and voltage stabilization control circuits. In the closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any one of the components will cause the output voltage to rise.


The fuse is normal and there is 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 starting voltage of the starting pin of the power control chip. If there is no starting voltage or the starting voltage is too low, check whether the external components of the starting pin and the starting resistor are leaking.


If the power control chip is normal, the fault can be quickly found through the above monitoring. If there is a starting voltage, measure whether there are high and low level jumps at the output terminal of the control chip at the moment of power-on. 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. Control by replacement Chips, check the peripheral components, and check them one by one; if they are changing, most of them are bad or damaged switch tubes.


Fuse burned out or blown up


You should mainly check the rectifier bridge, each diode, switch tube and the large filter capacitor on 300 volts and other parts. If there is a problem on anti-interference circuit, it may cause the fuse to burn or turn black. It is especially worth noting that the fuse is burnt due to the breakdown of the switch tube, which usually burns the power control chip and the current detection resistor. The thermistor is also easy to burn out along with the fuse.