A Precision Adjustable Constant Current Source Can Be Used On Inductive Loads

This paper describes a design of a precision adjustable constant current source based on a low load coefficient resistance which can be used on an inductive load.The article first analyzes the basic principles of the constant current source and the serial feedback constant current circuit, then discussed the main factors affecting the stability of the constant current source and the error distribution principle. The article introduces the basic framework of the precision adjustable constant current source which includes the serial feedback constant current circuit, low load factor distributed sampling resistor, voltage reference module, the smallest single-chip system, the main power supply module, the regulator feedback compensation circuit, protection and compensation circuit and power management circuit and current test circuit.Several work was finished in this paper. Firstly, I made a precision voltage reference module which can export any voltage between 0-10 V. The relative standard deviation of the output voltage within a short time is 2.34 × 10-07. Its voltage stability(time shift) is 3.4 × 10-08 V / h. Using it as the voltage reference of the constant current source make it possible to realized the 0-1A adjustable feature. Secondly, I’ve made an 1?distributed low load factor sampling resistor and tested it. The load factor is 3.46 × 10-07? / W, the temperature coefficient is 0.34 ppm / ℃and the Long-term stability is ± 0.48 ppm / 3000 h. Thirdly, I’ve designed a inductive load compensation circuit and adjusted the circuit structure and the control algorithm, so the constant current source can be used on inductive loads. Fourth, I’ve designed a method to control the main power, so the constant current source can guarantee the same accuracy when the output current is between 0-1A and the load power is under 300 W. Fifth, I’ve designed a regulator feedback circuit for the voltage between the regulator to solve the problem of drift due to the power heating of the load. The MCU controls the main power by the voltage drop between the regulator. Sixth, I’ve designed the overvoltage protection and automatic charging circuit which improves the safety and reliability of the constant current source.The final test shows that the relative standard deviation of the constant current source is 2.97 × 10-7 during normal operation, the current stability(time shift) of-3.6 × 10-7 / 30 min, differential nonlinearity is 0.59 LSB, maximum load power is capacity 300 W and the output impedance is 120M?.