Battery circuit board shared the following design using NEC upd78F0547 microcontroller to set the DC power output current through the keyboard, and the LCD display voltage and current output value. The main circuit is composed of an operational amplifier LM324 and a Darlington transistor. The circuit design is reasonable and the programming is correct. In addition to the completion of the requirements of the subject, the circuit design step by step function, can set different constant current and voltage.
Constant current, constant voltage charging circuit: this part of the circuit is the core of the whole circuit, mainly by the D/A conversion circuit, constant current, constant voltage regulator circuit, detection circuit components.
The digital signal transmitted by the control circuit is converted into an analog signal by the D/A conversion circuit IC205 as a reference voltage, and then sent to the positive input end of the voltage comparator IC201. The sampling resistance signal is sent to the negative input end of the voltage comparator IC201, compared with the reference voltage, and the comparison result is fed back to the T202 by the output end of the IC201 to control the turn-on state of the T202. By D201, D202, R201, T203 composed of a constant current source A, constant current value I=2Ud-Ube/R201. The conduction state of T202 affects the absorption current of the constant current source A, so as to change the driving current of the constant current source A to adjust the T201 base of the tube, and stabilize the output value of T201. In order to reduce the output ripple, adjust the tube T201 using Darlington transistor. The T201 base current of the regulator is supplied by a constant current source, which further reduces the influence of the power supply voltage fluctuation on the T201. Suspension drive circuit.
Potentiometer W103 and microcontroller (including A/D conversion) composed of voltage detection circuit. W103 will output voltage sampling signal sent to the MCU A/D circuit for conversion, the conversion of the digital signal processing by the microcontroller, and display the measured value by the LCD monitor. Sampling resistor R202, IC202 and SCM (including A/D conversion) composed of current detection circuit. The sampling signal on the sampling resistance R202 is sent to the IC202, and the A/D circuit is sent to the MCU. The digital signal is processed by a single chip microcomputer, and the measured value is displayed by the LCD display.
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Fig. 2.1 schematic diagram of constant current and constant voltage charging circuit
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Figure 2.2 schematic diagram of the D/A conversion circuit
Control circuit: control circuit is mainly composed of NEC upd78F0547 MCU and peripheral circuit, keyboard circuit and so on. MCU receives the signal from the detection circuit, and the voltage and current are displayed on the LCD after A/D conversion. The circuit can control the output voltage value and current value of the D/A chip by setting the output voltage value and the current value of the power supply by the key. And according to the actual output current (voltage) value and set the value of the comparison, adjust the set value of the D/A chip, so that the power output is stable and reliable.
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Figure 2.3 schematic diagram of the CPU circuit
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Figure 2.4 keyboard circuit schematic
Display circuit: using 4 lines and 8 columns of LCD screen to display the actual set current value, set the voltage value, the actual output current value, the actual output voltage value. Voltage resolution 0.1V. Current resolution 1mA. The LCD screen can display the set voltage and current value when setting.
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Figure 2.5 schematic diagram of the LCD display circuit
The power supply circuit with 2 output DC output, a main output DC18V, as the charging circuit of energy input; the other group + DC 12V and DC 5V output to the control circuit, the power supply, Heng Liu (pressure) adjustment circuit, display circuit provides working power.
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Fig. 2.6 schematic of power circuit
Comment analysis:
Constant current output when the 100mA (slow charge) and 200mA (fast charge) can be set on the basis of the current value from the 100MA---200MA adjustable function, step up to 20 mA. Can set a variety of constant voltage output state, constant pressure output value: 10V, 9V, 12V. DC power supply as the core, NEC microcontroller upd78F0547 controller, through the keyboard to set the output current of DC power supply, and can be displayed by the LCD output voltage, current value. By single chip programmable digital signal through D/A converter output analog amplifier through isolating amplifier output power control of base, with the change of the base power tube voltage and the output current (voltage). Can stably realize constant voltage or constant current charging state, and set the current 100mA slow charge and fast charge 200mA at constant current when the output voltage (current) fluctuation and ripple voltage (current) is small, and with overheating protection and automatic recovery function.