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

Industrial Router Crystal 3.2x2.5mm 3225 26M (26.000MHz) 12PF 10PPM 20PPM 30PPM

MOS Power IC Full Range

Photocoupler

First Mobile Phone Charger Circuit

Figure 1 illustrates a real circuit diagram for a Nokia mobile phone universal charger. The AC220V voltage is half-wave rectified by D3, and then filtered by C1 to produce a roughly +300V voltage. One part of this voltage passes through the primary winding L1 of the switching transformer T, applied to the collector of the switch transistor Q2. The other part goes through the starting resistor R3 to the base of Q2, causing Q2 to enter a slight conduction state. This generates an induced electromotive force in L1 that alternates between positive and negative directions, while simultaneously creating another induced electromotive force in L2, which is positive-negative. The induced electromotive force in L2 is positively fed back to the base of Q2 via R8 and C2, causing Q2 to rapidly enter a saturated state. While Q2 remains saturated, a stable induced electromotive force is produced in L2 due to the nearly linear increase in current in L1. This electromotive force charges C2 through the base-emitter junction of R8, R6, and Q2. As C2 charges, the voltage at the base of Q2 gradually decreases. When it drops to a certain level, Q2 exits its saturated state, and the current flowing through L1 decreases. Consequently, the induced electromotive force polarity in L2 reverses. Under the positive feedback of R8 and C2, Q2 quickly transitions from the saturated state to the off state. At this point, the +300V voltage is reverse-charged to C2 via R3, R8, L2, and R16, causing the potential at the right end of C2 to gradually rise. When it reaches a specific threshold, Q2 is turned on again under the influence of R3, restarting the aforementioned process and forming a self-oscillation.

During the on-time of Q2, the induced electromotive force polarity in L3 is positive-negative and negative-positive, and D7 is off. During the Q2-off period, the induced electromotive force in L3 becomes positive-positive and negative-negative, turning D7 on and supplying power externally. In Figure 1, components like VD1 and Q1 form a regulated voltage circuit. If the output voltage is too high, the induced voltage of the L2 winding will also rise, increasing the voltage after rectification by D1 and filtering by C4. Since the voltage regulation value of 5.6V is consistently maintained across VD1, the voltage at Q1's base increases, deepening the conduction of Q1, thereby enhancing the shunting effect on the base current of Q2, cutting off Q2 earlier, and lowering the output voltage. Conversely, when the output voltage decreases, the voltage regulation control process operates inversely. Additionally, R6, R4, and Q1 form an overcurrent protection circuit. If the current flowing through Q2 becomes too large, the voltage drop across R6 increases, causing Q1 to turn on and Q2 to turn off, preventing Q2 from experiencing overcurrent damage.