Closing and opening S1 for a moment to charge the capacitor, the transistor conducts the load. The transistor will drive for a time that depends on its value and on the 1 to 10M resistor in the gate. The worthless resistor is typically 10k ohms. The MOSFET must be specified according to the load current. This circuit is from Newton C. Braga's Mechatronics Sourcebook, published in the United States. The circuit can be used as a shield for microcontrollers.
