Two smartphone charging circuit diagrams

The first circuit principle: After the AC220V voltage is rectified by D3 half-wave and filtered by C1, a voltage of about +300V is obtained. One channel is added to the c-pole of the switching tube Q2 through the primary winding L1 of the switching transformer T, and the other channel is added to the b-pole of Q2 through the starting resistor R3. , Q2 enters the micro-conduction state, an upper positive and lower negative induced electromotive force is generated in L1, and an upper negative and lower positive induced electromotive force is generated in L2. The induced electromotive force in L2 is positively fed back to the b pole of Q2 through R8 and C2, and Q2 quickly enters a saturated state. During the saturation period of Q2, since the current in L1 increases approximately linearly, a stable induced electromotive force is generated in L2. This electromotive force charges C2 through the be junction of R8, R6, and Q2. As C2 charges, the voltage of the b electrode of Q2 gradually decreases. When it drops to a certain value, Q2 exits the saturated state, and the current flowing through L1 decreases, and L1 , the polarity of the induced electromotive force in L2 is reversed. Under the positive feedback of R8 and C2, Q2 quickly retreats from the saturated state to the cut-off state. At this time, the +300V voltage reversely charges C2 through R3, R8, L2, and R16, and the potential at the right end of C2 gradually rises. When it rises to a certain value, Q2 is turned on again under the action of R3, and the above process is repeated, and so on. , forming a self-excited oscillation.

During the period when Q2 is on, the polarity of the induced electromotive force in L3 is up and negative, and D7 is cut off; during the period when Q2 is off, the polarity of the induced electromotive force in L3 is up and down, and D7 is on and supplies power to the outside. 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 increase, and the voltage obtained by D1 rectification and C4 filtering will increase. Since both ends of VD1 always maintain a stable voltage value of 5.6V, the Q1 b-pole voltage increases, and the Q1 conduction process deepens, that is, the shunting effect on the Q2 b-pole current is enhanced, Q2 cuts off early, and the output voltage drops. If the output voltage drops, The voltage stabilization 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 on R6 increases, Q1 is turned on, and Q2 is turned off to prevent Q2 from being damaged by overcurrent.

The second circuit principle: 220V AC input, one end passes through a 4007 half-wave rectifier, the other end passes through a 10 ohm resistor, and is filtered by a 10uF capacitor. This 10 ohm resistor is used for protection. If a fault occurs later and causes overcurrent, then this resistor will be burned to avoid causing a larger fault. The 4007, 4700pF capacitor, and 82KΩ resistor on the right form a high-voltage absorption circuit. When the switch tube 13003 is turned off, it is responsible for absorbing the induced voltage on the coil, thereby preventing high voltage from being added to the switch tube 13003 and causing breakdown. 13003 is a switching tube (the complete name should be MJE13003), which is used to control the on and off between the primary winding and the power supply. When the primary winding is continuously switched on and off, a changing magnetic field will be formed in the switching transformer, thereby generating an induced voltage in the secondary winding.

Since the same terminal of the winding is not marked in the figure, it cannot be seen whether it is a forward or flyback type. However, from the structure of this circuit, it can be inferred that this power supply should be a flyback type. The 510KΩ at the left end is the starting resistor, which provides the base current for starting the switch tube. The 10Ω resistor below 13003 is a current sampling resistor. The current is sampled and turned into a voltage (its value is 10*I). This voltage is added to the base of transistor C945 after passing through diode 4148. When the sampling voltage is approximately greater than 1.4V, that is, when the switch tube current is greater than 0.14A, transistor C945 is turned on, thereby pulling down the base voltage of switch tube 13003, thereby reducing the collector current, thus limiting the switch current and preventing The current is too large and burns out (in fact, this is a constant current structure, which limits the maximum current of the switch tube to about 140mA).

The induced voltage of the winding (sampling winding) on ​​the lower left side of the transformer is rectified by the rectifier diode 4148 and filtered by the 22uF capacitor to form the sampling voltage. For the convenience of analysis, we take the emitter end of the triode C945 as ground. Then the sampling voltage is negative (about -4V), and the higher the output voltage, the more negative the sampling voltage is. After the sampling voltage passes through the 6.2V Zener diode, it is added to the base of the switch tube 13003. As mentioned earlier, when the output voltage is higher, the sampling voltage becomes more negative. When the negative reaches a certain level, the 6.2V Zener diode is broken down, thereby pulling the base potential of switch 13003 low, which will cause the switch tube to Disconnecting or delaying the conduction of the switch controls the input of energy into the transformer, which also controls the increase in the output voltage and realizes the function of voltage-stabilizing output. The 1KΩ resistor and the 2700pF capacitor in series below are the positive feedback branches. The induced voltage is taken out from the sampling winding and added to the base of the switching tube to maintain oscillation.