A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a voltage-controlled switch. Apply a voltage to its gate pin and it turns on, allowing current to flow between its drain and source pins. Remove the gate voltage and it turns off.
MOSFETs can switch on and off very fast — nanoseconds — which makes them the standard component for generating the sharp-edged pulses that pulsed excitation requires.
In the experiments
A typical pulsed excitation setup in the Open Energy experiments looks like:
- A 555 timer or microcontroller generates a square wave at the desired frequency and duty cycle
- The square wave drives the gate of a MOSFET
- The MOSFET switches current through an inductor or resonant circuit
- On each "off" transition, the inductor produces a back-EMF spike
The MOSFET is the bridge between the control signal (the timing circuit) and the power circuit (the coil or cell being driven). Popular choices for the experiments include the IRF540N (for low-frequency, high-current work) and the IRF3205 (higher current capacity).