Low voltage alkaline battery powered mobile phone emergency charger

With the current development trend of multi-functional mobile phones, the power consumption of mobile phones has gradually increased, which has increased the requirements for batteries. However, on the other hand, batteries have become smaller and smaller as the size of mobile phones has gradually shrunk. Power supply technology has not improved accordingly, which has brought about the problem of reduced standby time and caused a lot of trouble for people who often go out to use mobile phones. In order to solve this problem, many people adopt a dual-battery and dual-charging configuration when purchasing mobile phones to solve the problem of high power consumption. Not only does this increase the cost of purchasing a mobile phone, but it is not as convenient to use as expected. Either you forget to bring a second battery or forget to charge the second battery, which affects the performance of your mobile phone due to insufficient battery power when you go out. Normal use. In order to solve this problem, this article introduces a mobile phone emergency charger, which uses two AA alkaline batteries or rechargeable batteries. After being boosted by the circuit, the mobile phone is charged by direct charging, which does not affect the normal use of the mobile phone during charging. Since all common components are used in the circuit, it is not only low in cost but also simple to manufacture.

Circuit working principle:

The circuit of the emergency charger is as shown in the figure. It is a single-tube DC conversion circuit in the form of a single-ended flyback converter circuit. The so-called single-ended in the circuit means that the magnetic core of the high-frequency converter only works on one side of the hysteresis loop. The so-called flyback means that when the switch tube VT1 is turned on, the induced voltage of the primary coil Np of the high-frequency transformer T1 is 1 positive and 2 negative, and the rectifier diode VD3 is in a cut-off state, storing energy in the primary coil. When the switch VT1 is turned off, the energy stored in the primary coil of the transformer T1 is rectified by VD3 and filtered by the capacitor C4 and then output to the load.

Transistor VT1 is a switching power supply tube, which forms a self-excited oscillation circuit with T1, R1, R2, C2, etc. After adding the input power, the current flows to the base of VT1 through R1, causing VT1 to conduct, and R1 is called the starting resistor. Once VT1 is turned on, the input voltage is added to the primary coil Np of the transformer, and its collector current Ic increases linearly in Np. The feedback coil Nb generates an induced voltage of 3 positive and 4 negative, so that VT1 obtains a positive base and a negative emitter. Feedback voltage, this voltage injects base current into VT1 through C2 and R2, further increasing the collector current of VT1. Positive feedback generates an avalanche process, causing VT1 to saturate and conduct. During the saturated conduction period of VT1, the primary coil Np of T1 stores magnetic energy.

At the same time, the induced voltage charges C2. As the charging voltage of C2 increases, the base potential of VT1 gradually becomes lower. When the base current change of VT1 cannot satisfy its continued saturation, VT1 exits the saturation zone and enters the amplification zone. After VT1 enters the amplified state, its collector current decreases, and an induced voltage of 3 negative and 4 positive is generated in the feedback coil Nb, which reduces the base current of VT1, and its collector current decreases accordingly, and the positive feedback again occurs an avalanche process. VT1 cuts off quickly. After VT1 is cut off, the energy stored in transformer T1 is provided to the load. The 1 negative and 2 positive reverse voltage generated by primary coil Np is rectified and filtered by diode VD3, and a DC voltage of 5.8V is obtained at C4. Charge your phone through its dedicated charging plug.

When VT1 is cut off, the DC power supply input voltage and the 3 negative and 4 positive voltages induced by Nb reversely charge C2 through R1 and R2, gradually increasing the base potential of VT1, causing it to re-conduct, flip again and reach the saturation state. The circuit Just keep oscillating repeatedly.

VD1, VD2, C3, etc. form a voltage stabilizing circuit. During the cut-off period of VT1, the 3 negative and 4 positive voltages induced by Nb charge to C3 through VD2. When the voltage on C3 (upper negative and lower positive) is greater than 6.2V. The zener diode VD1 begins to conduct and acts as a shunt, reducing the base current of VT1, thereby controlling the collector current Ic of VT1 to stabilize the output voltage.

It should be noted that because the input DC voltage is low and isolation is not required, and the input DC voltage is relatively close to the output DC voltage, the high-frequency transformer does not have a secondary coil, and the energy of the load circuit is obtained directly from the primary coil. This has two advantages: first, it improves the conversion efficiency of the circuit; second, VD3, C4, R4, etc. also form a surge voltage absorption circuit to absorb the reverse high voltage generated at the moment when VT1 is cut off.

Component selection, installation and debugging:

VT1 requires Icm>1A, hEF is 50~100, and 2SC2500, 2SD965, etc. can be used. VD1 is a voltage-stabilizing diode tube with a voltage stabilization value of 6.2V. The parameters of other components are shown in the figure.

The high-frequency transformer T1 must be homemade, using an E16 ferrite core, and Np and Nb are wound with 16 turns of Φ0.44 enameled wire. When winding, pay attention to the starting ends of each coil so as not to cause the circuit to vibrate. During assembly, a layer of plastic film with a thickness of approximately 0.05mm is placed between the two magnetic cores to serve as the core air gap.

Emergency charger : In order to solve the problem of temporary insufficient power of mobile phones, MP3, MP4 and other digital products, the emergency charger uses lithium batteries, solar panels or ordinary AA dry batteries by hand as a power storage unit, and after appropriate voltage conversion, the emergency charger can You can power or charge mobile digital electronic products anytime, anywhere. It brings a lot of convenience to our lives!