Diode Selection Case for Chargers

Project Analysis ：

①   As shown in the figure. 1-1 In the red area, at the entrance. 220V The AC input is rectified by a half-wave rectifier at one end, while the other end is connected in series with a resistor and then filtered by a capacitor. This… 10 The resistor in the circuit serves as a protective device: if a subsequent fault causes an overcurrent, this resistor will blow, thereby preventing more serious damage.

②   Figure 1-1 In the yellow area, The one on the right 4007、4700pF Capacitor, 82 kΩ A resistor forms a high-voltage absorption circuit; when the switching transistor… 13003 During turn-off, it absorbs the induced voltage across the coil, thereby preventing high voltage from being applied to the switching transistor. 13003 This can lead to breakdown.

③   Figure 1-1 Medium green area, 13003 It is used as a switching transistor to control the on-off state between the primary winding and the power supply. When the primary winding is repeatedly switched on and off, a varying magnetic field is established in the switching transformer, inducing a voltage in the secondary winding. The left end of… 510 kΩ For the startup resistor, it supplies the base current required to turn on the switching transistor. 13003 The one below 10Ω The resistor serves as a current-sensing resistor; after the current passes through it, it is converted into a voltage. ( Its value is 10*I) , this voltage passes through the diode 4148 Afterwards, add it to the transistor. C945 On the base of.

      When the sampled voltage exceeds approximately 1.4 V—corresponding to a switch‑transistor current greater than 0.14 A—the C945 transistor turns on, pulling down the base voltage of the 13003 switch transistor and thereby reducing its collector current. This limits the switching current, preventing excessive current that could cause damage or burnout. The winding at the lower left of the transformer ( Sampling winding ) The induced voltage is rectified by a rectifier diode. 4148 Rectification, 22uF After capacitor filtering, a sampled voltage is generated. The sampled voltage then passes through… 6.2V After the Zener diode, apply it to the switching transistor. 13003 to the base, thereby achieving a regulated output.

Diode Recommended Selection Option 1:

Transistor Recommended Selection Option 2:

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