CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@Pranjali Desai • 02 Jul, 2009
hi....
when we say that a transistor is in active or in saturated mode;
what is the practical (physical) meaning behind ?
@ashutoshglamour • 02 Jul, 2009 transistor is in active mode that means it is used as amplifier.
when it is in saturation mode it is used as switch.😁
@Harshad Italiya • 02 Jul, 2009 If your Emitter-Base Junction is Forward Bias and Collector-Base junction is Reverse Bias Then your Transistor works in Active State.

While your Emitter-Base Junction is Forward Bias and Collector-Base Junction is also in Forward Bias Then your Transistor works in Saturation Mode.

While your Emitter-Base Junction is Reverse Bias and Collector-Base Junction is also in Reverse Bias Then your Transistor works in Cut-off Mode.

Internal Working:
in Active State it works as a Amplifier. (as said by Ashutosh)

While in Saturation State: Here both EB and CB junctions are in forward bias so there is a large value of current available and you can use transistor as a CLOSE switch.

and in Cutoff state:both EB and CB junctions are in Reverse bias so there is no flow of current through transistor and in this case you can use transistor as a OPEN switch.

PS: Apply simple PN junction rule at the both junction you will get the answer why there is Large current and why there is no current flow in saturation and Cutoff State.

Here is the Characteristics of transistor : https://i39.tinypic.com/302a0r8.jpg
@mithunganesh • 06 Jul, 2009 Sine wave formula

Sine wave formula is
128+128sin(degrees)
is also correct friend,,
@skipper • 06 Jul, 2009 A transistor is a bimodular device; the charge 'flowing" across the junction is set by the width of a diffusion layer. The reverse (or forward) bias effectively pinches the flow off (or lets it through).

In that sense a FET or a bipolar junction device is a kind of valve; setting the valve is like governing an engine, which is why amps have feedback to do this and keep the circuit out of saturated mode.
@Pranjali Desai • 14 Jul, 2009 thak you all!!and specially godfather.
@Harshad Italiya • 14 Jul, 2009
Pranjali Desai
thak you all!!and specially godfather.
Welcome PD!
@Munguti • 30 Jul, 2009 The important thing is to know were the Q point lies in the load line, we have the cut-off, active and saturated point all corresponding to the off, amplifier mode and on mode of a transistor respectively.
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