As illustrated on the left, the circuit design comprises a constant current source, signal synthesis, coarse adjustment, fine adjustment, and CPU control. Within the constant current source circuit, it is evident that when the beta values of the two transistors are sufficiently large, the current passing through the reference resistor (2Ω) is nearly identical to the current flowing through the load, i.e., IL = VO3/RL. To generate a current of 1mA in the load, VO3 will output 2mV. The signal synthesis section acts as an adder, with its output expressed as V03 = -(V02 + V01). Both coarse and fine adjustments are executed using an 8-bit D/A converter. The CPU can send 20 state values ranging from 0 to 19 to the coarse adjustment module. By tuning the potentiometer to set the appropriate amplification factor, the value of the D/A converter can be incremented or decremented by one bit, resulting in a change of 500mV in the output of VU3. This leads to a coarse current adjustment of ±250mA in the load. The fine adjustment module can receive 251 state values from 0 to 250 transmitted by the CPU. After adjusting the amplification factor, the value of the D/A converter is incremented or decremented by 1 bit, causing the output of V03 to increase or decrease by 2mV, thereby achieving a fine current adjustment of ±1mA. The flowchart of the entire operational process is depicted on the right. High precision is attained through the integration of low-resolution D/A converters. In theory, by combining them in this manner, a 16-bit resolution function can be achieved. For this circuit, the current resolution can be enhanced to 0.1mA. In this system, the current is generated by the voltage V03 across the reference resistor. Since V03 is extremely stable, the resulting current is also highly stable, with a minimal ripple coefficient. Variations in the beta value of the transistor and fluctuations in the +50V supply voltage have negligible effects on the current. The entire system exhibits stable performance, high precision, and low cost. It is evident that under conditions requiring high precision but not high conversion speed, we can achieve the functionality of high-resolution devices by combining low-resolution devices, significantly reducing the cost of the system.
In conclusion, this innovative approach not only reduces costs but also ensures reliability and accuracy in critical applications. The modular design allows for easy adjustments and maintenance, making it an ideal solution for industries demanding both precision and affordability. The future of such systems lies in their ability to adapt to evolving technological needs while maintaining simplicity and efficiency.
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