What are the choices of power adapter components

　　 Power adapters often appear in our lives as computer accessories. In fact, power adapters are also used in many places, but people don’t pay so much attention. So do you know what the options of power adapter components are? Let's follow the manufacturer to find out!

　　  AC input section

　　  The fuse selection is 250V3.15A; the type of negative temperature coefficient thermistor against surge current is 5D-13; the type of varistor is 14D471K.

　　Common mode power filter: Differential mode (X2) capacitors select 275V/0.47pF (CX1) and 275V0.luF (Cx2); common mode inductor model: WD03007; common mode (Y2) capacitors (CYA, CY2) select 400V/ 2.2nF.

　　   Rectifier and filter part

　　  1. Selection of rectifier bridge

　　  According to the relevant content in Section 5.2 of this book, it is known that the rectifier bridge requires at least 5A rated current and at least 600V rated voltage, and the 8A/600V GBU806 is actually selected.

　　  2. Filter capacitor

　　For a flyback power adapter powered by a 220V voltage level, the input rectifier filter capacitor actually needs to withstand a ripple current of about 0.8A. Due to the height limitation of the housing, a low-height electrolytic capacitor needs to be used. You can choose the 400V120μF low-height (400V120μF) produced in recent years. 25mm) electrolytic capacitor. The withstand voltage meets the requirements and can withstand 0.75A (general specification)-1.31A (high ripple current). This choice can basically meet the requirements.

　　  Main circuit part (excluding transformer design)

　　After the rectifier filter circuit is the main circuit of the flyback power adapter, the work that needs to be done mainly includes the determination of switching frequency, transformer design, selection of switch tube parameters and maximum duty cycle, selection of output rectifier and output filter capacitor.

　　In order to reduce costs, most of the switches choose a rated voltage of 600V. For a flyback power adapter with an output of 60W, the switch will withstand a peak current of about 2A. Considering that the on-resistance of 600V MOSFETs is relatively large, especially in the state of high junction temperature, it is necessary to There is a relatively large current margin, and the IRFBC40 (600V/6A/1.20) MOSFET is a better choice from the point of view of easy procurement.

　　The output rectifier needs to have a withstand voltage of not less than 90V. You can choose a Schottky diode with a 120V withstand voltage. If you want to reduce the cost, you can choose an ultra-fast reverse recovery diode. The withstand voltage can be 200V, so the voltage margin is relatively large. If you choose BYQ28X-200 (some brands can offer up to 0.45 yuan), this model has a withstand voltage of 200V and a rated RMS current of 14A. It can meet the design requirements.

　　  The output rectifier filter capacitor should choose 16V/1000F high-frequency low-resistance electrolytic capacitor to meet the requirements of 6A ripple current.

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