9

Semiconductor circuits

This chapter describes some of the ways in which transistors and diodes are used.

A MOSFET switch

The action of a MOSFET when used as a switch can be demonstrated by a simple circuit. The circuit is supplied from a 6 V battery and a variable voltage is obtained from a variable resistor VR1, acting as a potential divider. The potential at the wiper of VR1 is fed to the gate of an n-channel MOSFET, Q1. In this way we can set the gate-source p.d., VGS, to any value between 0 V and 6 V. We want to know what effect this has on the drain current, ID.

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The source of the transistor is connected to the 0 V line. The drain is connected ...

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