This paper presents a design scheme for DC electronic load based on STC12C5A60S. The DC electronic load is designed mainly for high-speed, low-power, super-anti-interference STC12C5A60S microcontroller. It includes a control circuit (MCU), a main circuit, a sampling circuit, a display circuit, etc., and can detect various parameters such as a current value and a voltage value of the circuit to be tested, and can be visually displayed on the liquid crystal. The system is operated by the self-locking switch control circuit, and the working state between the constant voltage, constant current and constant resistance circuits is switched by the manual adjustment switch, and the corresponding working state is indicated by the LED light. The system's voltage regulation range is 1V-30V, the steady current range is 100mA-3.5A, and the error 0-5% is within the scope of the problem. It meets the requirements of the problem and extends the range of constant voltage and constant current. Controlled by the single-chip microcomputer, the control of the constant voltage value or the constant current value within a certain range is achieved by pressing the button, the overload protection is set, and the overload is displayed by the lighting.
The scheme controls the working state of the circuit through two self-locking switches, and switches between constant voltage, cross current and constant resistance. The stc12c5a60s microcontroller controls the values ​​of constant voltage and constant current through the D/A chip. The stc12c5a60s is high speed and low. The new generation 8051 microcontroller with power consumption and super anti-interference, the instruction code is fully compatible with the traditional 8051, but the speed is 8-12 times faster, and the 8-channel high-speed 10-bit A/D conversion. The high-power NMOS transistor IRF540 is used, the on-resistance of the tube is sufficiently small, and the source-drain resistance is sufficiently strong. The software and hardware junction method facilitates the simple conversion between different modules, and completes the basic functions such as constant voltage and constant current, and completes additional functions such as constant resistance.
Constant voltage circuit
TEXT and GND are test points. The circuit as a whole is a negative feedback: when TEXT is higher than the set value, the op amp outputs a high voltage, Q1 conductance increases, the load impedance becomes smaller, and the internal resistance of the power supply is divided, TEXT decreases until V+=V-; When TEXT is lower than the set value, the op amp outputs a low voltage, Q1 to the flux decreases, the load and the internal resistance of the power supply become larger, and TEXT increases until V+=V-.
Constant current circuit diagram
TEXT and GND are test points, and V+=V- in OP07. When V+"V-, the op amp outputs a high voltage, Q1 conductance increases, the current increases, and V- rises to V+=V-. When V+ "V-, the op amp outputs a low voltage, Q1 to the flux decreases, the load and the internal resistance of the power supply become larger, and the current decreases until V+=V-. The steady current = V - divided by the resistance.
Constant resistance circuit diagram
When the sliding rheostat hits 50%, the resistor divider V+=1/2Vin=V-, current I=Vin/4, R=Vin/I=4 ohms, and the power supply voltage changes in proportion to the current. It can be realized by a single chip microcomputer, R=VText/I, which is realized by the constant current principle. (If you need to test for a long time, it is better to connect the large heat sink to the MOSS tube).
A design scheme of DC electronic load based on STC12C5A60S is proposed. The DC electronic load designed in this scheme mainly uses high-speed, low-power, super-anti-interference STC12C5A60S single-chip microcomputer as the control core, and the working state of the self-locking switch control circuit is switched between constant voltage, constant current and constant resistance by manual adjustment switch. The working state between the circuits. The system's voltage regulation range is 1V-30V, the steady current range is 100mA-3.5A, and the error is 0-5% within the scope of the problem. It can control the constant voltage value or constant current value within a certain range, and set the overload protection. The display shows overload by lighting, and the scheme has practical application value.
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