Mobile phone emergency charger circuit diagram produced by LM3578

 　　The portable emergency charger for mobile phones can be used to charge mobile phones in an emergency when there is no mains power supply, ensuring that mobile phone information is continuous and unobstructed. The characteristic of this charger is that it uses an imported PWM switching power supply chip lM3578 for DC/DC boost. The input voltage can be as low as 2V and the output current can reach more than 200mA. It can work satisfactorily with 2 AA rechargeable batteries.

　　Working principle: mobile phone portable emergency charger circuit. As shown in the attached picture. The core device IC 1 used is a single-chip PWM switching controller, which contains four major functions: oscillator, reference voltage, error amplification and driving transistor. The external circuit connects capacitors C1 to C6, resistors R1 to R6, inductors L1 and L2, and power switch BG1 to form a DC/DC boost circuit. The IC1③ pin is connected to C2 to determine the oscillation frequency of about 50kHz. C3, R3 and C4 facilitate the switch operation in the connected state. The collector (⑥ pin) of the driver tube is connected to the output voltage through R6 and LED1. To increase the driving capability, L2 and C6 must be added to prevent the output and input from causing parasitic oscillation. The emitter (⑤ pin) is connected to the power switch BG1. A sampling resistor R5 is added and connected to the ⑦ pin of IC1 to control the maximum operating current. The working process of the circuit is as follows: the operating voltage Vi is turned on, the switch controller IC1 starts to work, and the output square wave signal is amplified by BG1 and flows through the energy storage inductor L1. When BG1 is turned on, L1 stores energy; when BG1 is turned off, L1 boosts the voltage through Diode D1 releases electrical energy, thus obtaining a boost voltage several times Vi on capacitor C5. One way of this voltage is sampled through resistors R1 and R2 and sent to the inverting terminal of the error amplifier, which is pin ①, to keep the output voltage stable; the other way is sent to the collector of the internal driver tube of IC1, which is pin ⑥, to increase the injection current of BG1, in which LED1 for charging instructions.

　　Component selection: IC 1 model is LM 3578, dual in-line, available on the market. BG1 model D882, TO-126 package, choose a tube with β greater than 100. Available in L1 market. If you make your own L1, take a φ12mm high-frequency magnetic ring and wind it with φ0.15 colored wire for about 60T. It can be measured by an inductor and is about 330μH. The other inductor L2 is a color-coded inductor, which is very cheap on the market. Except for C6, which is a magnetic chip capacitor, the rest of the capacitors are CBB type, and there are no special requirements for resistors. D1 is a boost diode, using Schottky diode, the model is lN5817-5822, its forward voltage drop VF=0.2V.

　　Usage: After assembly is completed, 2 AA rechargeable batteries can be connected, and the capacity is greater than 1600mAh to work normally. The output end can be equipped with a special power plug matching the mobile phone, which can be removed from the old charger. Connect directly to your phone . When charging, LED1 flashes to indicate charging.