The MOS tube is a voltage control device, that is, it needs to use the voltage control G pin to realize the control of the tube current. How does the FET control the current in the circuit? here we come to find out.

The most common on the market is the Enhanced N-Communication MOS tube. You can use a voltage to control the voltage of G. The MOS tube's turn-on voltage is usually 2-4V, but to fully control, this value should rise to about 10V. Recommend a method for you.

Basic method: use a control voltage (comparator non-inverting input) and a reference voltage (comparator inverting input), and enter the voltage comparator at the same time (the comparator power is connected to positive 12V and ground, such as LM358 as a comparator), compare The output of the device is connected to the G pin after a pull-up resistor of 5.1K. If the control voltage is higher than the reference voltage, the control MOS transistor turns on the output current.

The reference voltage can come from the sampling resistor, that is, after the NMOS S pole is connected to a high-powered small resistor and then grounded. This resistor samples the current. When the current flows through the resistor, it forms a voltage, which is referenced after being amplified.

At the beginning, the current is very small, so the control voltage is much higher than the reference voltage. At this time, the G pin is basically added 12V, which can quickly turn the tube on. After a short time, when the current increases, it gradually reaches a certain level. When the value is high, the reference voltage rises rapidly. When it approaches and exceeds the control voltage, the comparator outputs a low level (close to 0V) to turn off the tube and reduce the current. After the current is reduced, the reference voltage goes down again, the tube turns on, and the current increases again. Then start again and again.

If you use the D/A output instead of the control voltage, you can get precise control of the MOS tube. We have previously achieved an output range of 10-2000mA, stepping 1mA, and an output current accuracy of plus or minus 1mA.