Electronic automatic button for power screwdriver on the LM393 chip

An electronic automatic button for a screwdriver, which increases the speed when the rotor of the engine is loaded. In the normal state, without a load, the engine speed is minimal and the current consumption is small. But as soon as the rotor is loaded, the engine receives full power, and the greater the load on the rotor, the greater the incoming power. The button is made on a dual comparator LM393. On the left side of the microcircuit, a sawtooth pulse generator is assembled, on the right side, a comparator or PWM is assembled, it is not exactly known here, a rectangular signal from which is sent to the gate of the field-effect transistor. How does the microcircuit know that it is necessary to change the signal on the gate of the transistor when the rotor is loaded? This is possible with a

feedback chain from the engine, made on the resistor R9 and the diode. Depending on the load, there will be a voltage drop on the engine, through the chain

this signal goes to the microcircuit. The setup comes down to selecting the resistor

R9