Simple and fast charging power module circuit design

　　This design uses NEC upd78F0547 microcontroller as the main controller. The output current of the DC power supply is set through the keyboard, and the output voltage and current values ​​can be displayed on the LCD. The main circuit uses the operational amplifier LM324 and Darlington tube to form a regulation circuit. The circuit design is reasonable and the programming is correct. In addition to completing the requirements of the topic, the circuit is designed with a step setting function, which can set different constant current and voltage regulation values.

　　Constant current and constant voltage charging circuit: This part of the circuit is the core of the entire circuit, mainly composed of D/A conversion circuit, constant current and constant voltage adjustment circuit, and detection circuit.

　　The digital signal transmitted by the control circuit is converted into an analog signal as a reference voltage by the D/A conversion circuit IC205, and then sent to the positive input terminal of the voltage comparator IC201. The sampling voltage signal obtained from the output sampling resistor is sent to the negative input terminal of the voltage comparator IC201, and compared with the reference voltage. The comparison result is fed back to T202 from the output terminal of IC201 to control the conduction state of T202. A constant current source A is composed of D201, D202, R201, and T203, and the constant current value is I=2Ud-Ube/R201. The conduction state of T202 affects the absorption current of the constant current source A, thereby changing the driving current of the constant current source A to the base of the adjustment tube T201 and stabilizing the output value of the adjustment tube T201. In order to reduce the output ripple, the adjustment tube T201 uses a Darlington transistor. The base current of the adjustment tube T201 is provided by a constant current source, which further reduces the impact of power supply voltage fluctuations on the adjustment tube T201. The circuit adopts suspension drive.

　　Potentiometer W103 and single-chip microcomputer (with built-in A/D conversion) form a voltage detection circuit. W103 sends the sampling signal of the output voltage to the A/D circuit inside the single-chip microcomputer for conversion. The converted digital signal is processed by the single-chip microcomputer, and the measured value is displayed on the LCD display. Sampling resistor R202, IC202 and single-chip microcomputer (with built-in A/D conversion) form a current detection circuit. The sampling signal on the sampling resistor R202 is sent to IC202 for processing and to the A/D circuit inside the single-chip microcomputer for conversion. The converted digital signal is processed by the single-chip microcomputer, and the measured value is displayed on the LCD display.

　　Figure 2.1 Schematic diagram of constant current and constant voltage charging circuit

　　Figure 2.2 Schematic diagram of D/A conversion circuit

　　Control circuit: The control circuit is mainly composed of NEC upd78F0547 single-chip microcomputer and peripheral circuits, keyboard circuits, etc. The single-chip microcomputer receives the signal transmitted by the detection circuit, and displays the voltage and current values ​​on the LCD after A/D conversion. This circuit can set the output voltage and current values ​​of the power supply through buttons, and control the output voltage and current values ​​by controlling the set value of the D/A chip. And after comparing the actual output current (voltage) value with the set value, adjust the set value of the D/A chip to make the output of the power supply stable and reliable.

　　Figure 2.3 CPU circuit schematic

　　Figure 2.4 Keyboard circuit schematic

　　Display circuit: A 4-row 8-column Chinese character LCD screen is used to display the actual set current value, set voltage value, actual output current value, and actual output voltage value. The voltage resolution is 0.1V. The current resolution is 1mA. The LCD screen can display the set voltage and current values ​​during setting.

　　Figure 2.5 LCD display circuit schematic

　　Power supply circuit: It has 2 sets of DC outputs, one set is the main output DC18V, which is used as the energy input of the charging circuit; the other set outputs ±DC 12V and DC 5V, which provide working power for the control circuit, constant current (voltage) adjustment circuit, display circuit and other parts of this power supply.

　　Figure 2.6 Power supply circuit schematic

　　When the constant current is output, on the basis of 100mA (slow charge) and 200mA (fast charge) which can be set, the current value is increased from 100MA---200MA adjustable function, the step is 20 mA. A variety of constant voltage output states can be set, and the constant voltage output values ​​are: 10V, 9V, 12V. With the DC power supply as the core, the NEC upd78F0547 single-chip microcomputer is the main controller. The output current of the DC power supply is set through the keyboard, and the output voltage and current values ​​can be displayed on the LCD display. The digital signal is set by the single-chip program control, and the analog quantity is output through the D/A converter, and then isolated and amplified by the operational amplifier to control the base of the output power tube, and different currents (voltages) are output as the base voltage of the power tube changes. It can stably realize constant voltage or constant current charging state, and the current can be set to 100mA slow charge and 200mA fast charge when the constant current is output. The voltage (current) fluctuation and ripple voltage (current) are small, and it has overheat protection and automatic recovery functions.