Two general-purpose mobile phone charger circuits - Power Circuits - Circuit Diagram

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Photocoupler

First mobile phone charger circuit

Figure 1 shows a Nokia mobile phone universal charger real circuit. AC220V voltage is D3 half-wave rectified, C1 filtered to obtain about +300V voltage, one way through the switching transformer T primary winding L1 is added to the switch tube Q2 c pole, the other through the starting resistor R3 is added to Q2 b pole, Q2 enters micro-conduction In the state, an induced electromotive force that is up and down is generated in L1, and an induced electromotive force that is positive and negative is generated in L2. The induced electromotive force in L2 is positively fed back to the Q2 b pole via R8 and C2, and Q2 quickly enters a saturated state. During Q2 saturation, a stable induced electromotive force is generated in L2 due to the approximately linear increase in current in L1. This electromotive force charges C2 through the be junction of R8, R6, and Q2. As C2 is charged, the Q2 b pole voltage gradually decreases. When falling to a certain value, Q2 exits the saturation state, and the current flowing through L1 decreases, L1 In L2, the induced electromotive force polarity is reversed. Under the positive feedback of R8 and C2, Q2 quickly retreats from the saturated state to the off state. At this time, the +300V voltage is reversely charged to C2 via R3, R8, L2, and R16, and the potential at the right end of C2 gradually rises. When it rises to a certain value, under the action of R3, Q2 is turned on again, repeating the above process, so that it is repeated. , forming a self-oscillation.

During the on-time of Q2, the induced electromotive force polarity in L3 is up-down and down-positive, and D7 is off; during the Q2-off period, the induced electromotive force in L3 is positively positive and negative, and D7 is turned on and externally supplied. In Figure 1, components such as VD1 and Q1 form a regulated voltage. If the output voltage is too high, the induced voltage of the L2 winding will also rise, and the voltage obtained by D1 rectification and C4 filtering will increase. Since the voltage regulation value of 5.6V is always maintained at both ends of VD1, the voltage of Q1 b is increased, and the Q1 conduction process is deepened, that is, the shunting effect of Q2 b pole current is enhanced, Q2 is cut off early, and the output voltage is decreased if the output voltage is lowered. Its voltage regulation control process is opposite to the above. In addition, R6, R4, and Q1 form an overcurrent protection circuit. If the current flowing through Q2 is too large, the voltage drop across R6 increases, Q1 turns on, and Q2 turns off to prevent Q2 overcurrent damage.