Circuit diagram of solar mobile phone charger design

Mobile phone crystal 3.2*2.5mm 3225 26M (26.000MHZ) 7.5PF 10PPM 20PPM 30PPM

Single chip microcomputer STM32L151CCU6

Photocoupler

Summary:

Solar energy is an attractive source of energy for portable devices. It has been used extensively for applications such as calculators and space shuttles for some time. Recently, solar energy is being considered for a wider range of consumer electronics applications, including mobile phone chargers. The power provided by solar panels is highly dependent on the work environment. This includes factors such as optical density, time and location. Therefore, batteries are commonly used as energy storage units. When there is more energy from the solar panel, the battery can be charged; when the solar panel provides insufficient power, the battery can supply power to the system.

At present, there are many solar panels on the market, which can be divided according to the materials used in solar panels:
1 silicon solar cell;
2 a solar cell using a mineral compound such as a gallium arsenide III-V compound, a cadmium sulfide, a copper indium selenium or the like as a material;
3 large energy battery prepared by functional polymer material (organic semiconductor);
4 nanocrystalline solar cells, etc. We are using silicon solar cells.

2 charger hardware design

The charger is shown in Figure 1. It mainly includes power conversion circuit, sampling circuit, processor, pulse width modulation controller and battery pack, etc., forming a closed loop system.

Among them, the single chip is the control part of the circuit, and the PWM circuit is the core part of the whole circuit. The following is a brief description of the working principle of the system.

2.1 processor

The processor uses the 51 series single-chip microcomputer 89C51. There are two timers inside the microcontroller, two external interrupts and one serial port interrupt, three eight-way I/O ports, and a 12MHz crystal oscillator. The task of the single-chip microcomputer is to collect the output voltage and current of the solar panel and the state of charge of the battery in real time through the sampling circuit, and determine how to find the maximum output power of the panel and determine the charging state of the rechargeable battery.

2.2 Sampling part

If the current is to be detected in the system, the current signal must be converted to a voltage signal before the A/D conversion can be achieved. A common conversion method is to add a precision resistor to the circuit, thereby converting the current signal into a voltage signal. The advantage of this method is that the measurement is simple and convenient, but when the current is very small, the measurement accuracy is affected, so it is difficult to select a suitable resistance value. Secondly, the obtained current detection signal can only enter the circuit after being amplified. The comparator increases the complexity of the circuit design debug. Therefore, the current and voltage conversion chip MAX472 can be used, which overcomes the shortcomings of the conventional measurement current method, such as small measurement range and large measurement error, can improve measurement accuracy, and can be accurately controlled by a single chip microcomputer.

Voltage and current sampling using the serial analog-to-digital converter TLC0834, 8-bit resolution is easy to interface with the microprocessor or independently use full scale operation or 4 or 8 input channel strobe with address logic multiplexer with 5V reference 5V power supply, input range 0-5V.

2.3 PWM control circuit

The controller uses pulse width modulation (PWM) to control the magnitude of the supply current.

The PWM generator is realized by the PWM wave outputted by the single-chip microcomputer through the control circuit, and the main controller communicates with the interrupt mode to control the increase or decrease of the pulse width. The PWM signal drives the MOSFET on the main loop through opto-isolation.
The switch tube, diode, and LC circuit form a switching regulator power supply. The switching power supply controlled by PWM can reduce power consumption and facilitate digital control, but the busbar ripple coefficient is relatively large. The PWM control circuit is shown in Figure 2.

For details, please download the instructions for use.