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

Full range MOS power ICs

Probing current and voltage pins with a head diameter of 5.0mm. Supports pin 420*4450 for overcurrent and voltage detection.

Industrial router crystal, size 3.2*2.5mm, model 3225, frequency 26M (26.000MHz), capacitance 12PF, temperature stability 10PPM, 20PPM, 30PPM.

As depicted on the left, the circuit comprises a constant current source, signal synthesis, coarse adjustment, fine adjustment, and CPU control. In the constant current source circuit, when the beta values of the two transistors are sufficiently large, the current flowing through the reference resistor (2 Ω) is almost identical to the current flowing through the load, i.e., IL = VO3 / RL. To generate 1mA of current in the load, VO3 will output 2mV. The signal synthesis section is an adder, with its output expressed as V03 = -(V02 + V01). Both coarse and fine adjustments are implemented using an 8-bit D/A converter. The CPU can send 20 state values ranging 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, thereby increasing or decreasing the output of VU3 by 500mV. This results in a coarse current adjustment of ±250mA in the load. The fine adjustment part can receive 251 state values ranging 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, which increases or decreases the value of V03 by 2mV, thus adjusting the current by ±1mA. The flowchart of the entire workflow is shown on the right. High precision is achieved through the combination of low-resolution D/A converters. In theory, by combining them in this way, a 16-bit resolution function can be achieved. For this circuit, the current resolution can be increased to 0.1mA. In this system, the current is generated based on the voltage V03 across the reference resistor. Since V03 is extremely stable, the resulting current is also very stable, with a very small ripple coefficient. The fluctuations in the beta value of the transistor and the +50V supply voltage have minimal impact on the current. The entire system exhibits stable performance, high precision, and low cost. It can be observed that under conditions requiring high precision but not high conversion speed, we can mimic the functionality of high-resolution devices using combinations of low-resolution devices, significantly reducing the cost of the system.