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Collector current begins to rise after the delay time, td.

The saturating charge, Qs storage time constant of the transistor.

To calculate the extra charge (saturating charge), determine the emitter current.

This results in charges being stored in the base region.

Normally apply more base current than needed to saturate the transistor.

This capacitance must charge up to the base-emitter forward bias voltage, causing a delay time before any collector current flows.

since A is usually negative (phase inversion), the Miller capacitance can be much greater than the capacitance Ccb.

Miller Capacitance, CMiller = Ccb(1 – A).

Large-Signal Model of a BJT KCL > IE = IC + IB βF = hFE = IC/IB IC = βFIB + ICEO IE = IB(1 + βF) + ICEO IE = IB(1 + βF) IE = IC(1 + 1/βF) IE = IC(βF + 1)/βF

Looks like a pn junction volt-ampere characteristic.

As VCE increases, more VBE required to turn the BE on so that IB>0.

Bipolar Junction Transistors (BJT) NPN PNPīJT Cross-Sections Emitter Collector NPN PNPĬommon-Emitter NPN Transistor Reverse bias the CBJ Forward bias the BEJ