CNC high-precision constant current source circuit - Power Circuit - Circuit Diagram

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Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

As shown on the left, the circuit consists of constant current source, signal synthesis, coarse adjustment, fine adjustment, and CPU control. In the constant current source circuit, we can see that in the case where the beta values ​​of the two transistors are sufficiently large, the current flowing through the reference resistor (2 Ω) is substantially the same as the current flowing through the load, that is, IL=VO3/RL. . And to generate 1mA of current in the load, VO3 will output 2mV. The signal synthesis part is an adder whose output expression is V03=-(V02+V01). Both the coarse and fine adjustments are implemented with an 8-bit D/A converter. The CPU can transmit the 20 state values ​​from 0 to 19 to the coarse adjustment part. By adjusting the potentiometer to set the appropriate amplification factor, the value of the D/A converter can be increased or decreased by one bit, and the output of the VU3 can be increased or decreased by 500 mV. Increase or decrease the current of 250mA in the load to achieve coarse current adjustment. The fine adjustment part can receive the 251 state values ​​from 0 to 250 sent by the CPU. After adjusting the amplification factor, the value of the D/A converter is increased or decreased by 1 bit, and the value of V03 is increased or decreased by 2 mV. The current is increased or decreased by 1 mA. The flow chart of the whole work process is shown on the right.

High precision is achieved through the combination of low resolution D/A converters. In theory, by combining in this way, a 16-bit resolution function can be achieved. For this circuit, the current resolution can be increased to 0.1 mA.

In this system, the current is generated by the voltage V03 on the reference resistor. Because V03 is very stable, the resulting current is also very stable, the ripple coefficient is very small, and the fluctuation of the beta value of the triode and the fluctuation of the +50V supply voltage The effect of the current is also very small. The whole system has stable performance, high precision and low cost.

It can be seen that in the case of high precision requirements and low conversion speed requirements, we can realize the functions of high-resolution devices through the combination of low-resolution devices, and the cost of the system is greatly reduced.