High-stability and high-precision current source circuit

[0013] The output terminal of the D/A converter is connected to AGND in series with resistors R1 and R2. When the output voltage Uin of the D/A converter, a voltage U1+=Uin*(R2/(R1+R2)) will be generated at the connection point between R1 and R2.

[0014] The negative terminal of the first operational amplifier OP1 is connected to the connection point of the resistors R1 and R2. The positive terminal of the first operational amplifier OP1 is divided into two paths, one is connected to AGND through a resistor R3, and the other is connected to the drain of the first field effect transistor V1 to form a positive feedback connection to generate a voltage U1-. The output terminal of the first operational amplifier OP1 is connected to the gate of the first field effect transistor V1. The negative feedback circuit formed by OP1 and V1 makes U1+=U1-, and then I2=U1-/R3=U1+/R3. Because the first operational amplifier OP1 is a positive feedback connection, the setup time of U1- is shortened by 50%; the leakage current of the first FET V1 is very small, which improves the accuracy of I2 by more than 5%.

[0015] The negative terminal of the second operational amplifier OP2 is divided into two paths, one is connected to one end of the resistor R5, and the other is connected to the source of the second field effect transistor V2 to form a negative feedback connection and generate a voltage U2-. The positive terminal of the second operational amplifier OP2 is divided into two paths, one is connected to one end of the resistor R4, and the other is connected to the source of the first field effect transistor V1, and generates a voltage U2+. The output terminal of the second operational amplifier OP2 is connected to the gate of the second field effect transistor V2. The negative feedback circuit formed by OP2 and V2 makes U2+=U2-. It can be seen that the partial pressures on R4 and R5 are equal, so the ratio of the current through R4 and R5 is the inverse ratio of the resistance values ​​of R4 and R5, that is, I0: I1=R4:R5. Since I1 and I2 are on the same loop, I1=I2.

[0016] The other ends of R4 and R5 are directly connected. The +15V power supply is connected to the connection point of R4 and R5 through the diode V3. The voltage drop (0.7V) of the diode V3 makes the voltage of the positive and negative terminals of the second operational amplifier OP2 do not exceed 14.3V when the circuit outputs a small current, which can avoid the nonlinear region (above 14.5V) and always work stably in the linear region.

[0017] The drain of the second FET V2 is connected to the external output interface. The leakage current of the second FET V2 is also very small, so Iout=I0=(R4/R5)*I2=(R4/R5)*(U1+/R3)

[0018] That is, Iout=Uin*(R4/R5)R2/R3(R1+R2)=Uin*(R2R4/(R1+R2)R3R5)

[0019] Choose LF147J for the first and second operational amplifiers; choose VPO300 for the first and second FETs; choose 1N5806 for the diodes; use 15KΩ, 5KΩ, 500Ω, 1KΩ and the resistance values ​​of the resistors R1, R2, R3, R4, and R5 respectively 5Ω is 0.1% accuracy of B range.

[0020] Substituting each parameter into the formula: Iout=100Uin; the unit is mA.

[0021] When the D/A converter outputs a voltage of 0V, the output current is 0mA.

[0022] When the D/A converter outputs a voltage of 10V, the output current is 1000mA.

[0023] It can be seen that the output current range is 0-1A, and the application range of the circuit is very wide.

[0024] The invention is applied to the brake control system. The circuit is designed according to the circuit principle proposed in the invention, which effectively improves the current output accuracy and speeds up the response time, and at the same time increases the stability of the circuit in the output low current domain, and improves The pressure servo valve controls the efficiency.