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transistor concept

Following are conceptual diagrams of electricity flowing through a junction field effect transistor (JFET). The JFET normally allows electricity to flow through. When pulsed, it closes the gap and impedes the flow.

Analog or Digital
In an analog application, the JFET serves as an amplifier. As a continuously variable voltage is applied to the gate, an analogous, but larger voltage, flows from source to drain.

In a digital application, the JFET becomes an on/off switch. When the gate is pulsed, the switch changes its state from on to off. See transistor, n-type silicon, Boolean logic and FET.

Current Flows
When there is no pulse on the gate terminal, the JFET allows current to flow from source to drain. This example, although illustrated at the electron level, is nevertheless very simplified.

As the Gate Is Pulsed
As electricity is applied to the gate, the depletion region grows, impeding the current flow.

No Current
When sufficient electricity is applied to the gate, the depletion region expands to completely close the gap between source and drain.

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