Overall circuit design of solar wireless charging

　　The principle of solar power generation is mainly that solar panels receive sunlight, and a photoelectric effect occurs on the substrate of the solar panels, thereby converting light energy into electrical energy; the electrical energy is then stored in batteries.

　　The solar wireless charging circuit can be designed as shown in Figure 4. In Figure 4, we use a transistor emitter-coupled multivibrator and an analog Darlington tube to form a wireless charging circuit. The emitter-coupled multivibrator is composed of two low-power triodes. According to the component data in Figure 4, the oscillation frequency is about 350kHz. Among the components, only the last-stage triode VT4 has a larger power dissipation, and the others are relatively simple and easy to obtain components.

　　The 12V power supply is provided by the solar charging circuit. The power signal is converted into a high-frequency signal through the emitter-coupled multivibrator circuit and then amplified by the analog Darlington tube amplifier circuit after passing through the coupling circuit composed of C3 and R7. L1 and L2 are the primary and secondary coupling coils respectively. The amplified signal is wirelessly transmitted to the secondary receiving circuit through the coupling of L1 and L2. The high-frequency AC signal is rectified and filtered to become DC power to charge the 3.7V lithium battery.