DIY electronic load

Responsible for generating the reference voltage, a controllable precision voltage regulator tl431 is used. Here, three pins are used directly and two pins are used to provide a 2.5v reference voltage; R20 and RP1 are responsible for dividing the 2.5v reference voltage into the non-inverting input terminal of the operational amplifier through R19; the op amp It is used as a single-limit comparator here; the inverting input terminal is connected to the current-sense resistor and mos, and the voltage drop on the current-sense resistor is used to convert the current into voltage to form a negative feedback; the output terminal is connected to mosG level through R2 to control the mos to open; simply The working principle is that the comparator controls the constant current by comparing the voltage of the non-inverting and inverting terminals. When the voltage of the inverting terminal is higher than the voltage of the non-inverting terminal, the comparator flips and outputs a low voltage. Mos conductivity decreases and the current decreases, resulting in a decrease in the voltage drop on the current sensing resistor. The voltage at the reverse terminal drops until the voltage at the inverting terminal is lower than the voltage at the non-inverting terminal. When the comparator flips and outputs a high voltage, the MOS conductivity increases and the current increases, resulting in a voltage drop across the sense resistor. The voltage at the reverse terminal rises and so on. To achieve constant current c2, a small capacitor with a value of about 104 is connected in parallel to the current sensing resistor to bypass the high-frequency component so that there is only a low-frequency DC component on the resistor to increase stability. In actual use, each tube is controlled by a separate op amp. Therefore, the flow equalization effect is very good and it will not burn the tube as easily as simply merging the tubes.