J. David Irwin

Transistors in Switching Circuits

The.transistor.characteristic.equations.presented.in.Chapter.4.constitute.the.transistors’.“large-signal. modeling,”. which. includes. all. modes. of. operation. and. a. current–voltage. relationship. for. any. input.. These.equations.must.be.used.when.operating.the.transistor.as.a.switch.[3]..When.the.transistor.is.operating.as.an.amplifier,.only.small.input.signals.are.used,.which.are.amplified.to.large.output.signals..In. this.case,.simpler.linear.models.can.be.used.for.the.transistor. When.a.transistor.operates.as.a.switch,.the.input.changes.from.a.high.voltage.to.a.low.voltage.and. back,.which.causes.the.output.to.move.from.a.low.voltage.to.a.high.voltage.and.back..When.the.output. moves.between.a.high.and.low.voltage,.the.transistor.changes.regions.of.operation,.from.saturation.to. linear,.or.active.to.saturation,.depending.on.whether.it.is.a.FET.or.BJT.[3]..Therefore,.to.model.the.device. in.this.operation,.or.design.a.device.for.this.operation,.the.large-signal.characteristic.equations.must.be. considered.