Table of Contents
Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) make for good switches. That is because all it takes is a voltage to determine whether they conduct fully or not.
- Low signal (typically 0 volts/ground) to the Gate, prevents Drain to Source conduction. This goes for any components that are in series with them as well. They are all off.
- In the diagram, a pull down (connected to 0V ground and Gate) resistor keeps the Gate low unless the switch is pressed. If left floating (no solid voltage applied to it), then the Gate will have an unpredictable voltage at any given time.
- High signal (often 5V) to the Gate, allows full Drain to Source conduction. any load in series with them will get the full supply voltage. They are on.
- In the diagram, a switch between the positive supply (+5V/Vcc/high) gives no voltage to the gate while it is open. When closed, it gives a high signal of a direct connection to +5V. That is enough to turn the transistor on fully. The switch does have to provide some current through the pull down resistor, but no current through the gate other than a brief, and small amount of capacitor like charge, plus a very small amount of leakage that will not be noticeable at all, in most circuits.
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