Hello,
I studied a BTEC course a couple of years ago and was taught how to determine (for a standard BJT in common emmitter config) the Hfe /Rin / Rout by using the output / input characteristic graphs for the Transistor model. This involved plotting load lines etc
for large signal analysis these relations are
Rin = deltaVBE/delta IB - this seems fine
Hfe = delta IC/ delta IB - where ''delta'' means ''change''
This last formula is now causing me problems at university. All the previous output graphs for transistors I have seen had a clear gradient in the active region (increasing left to right) so these ''deltas'' were easy. Now it seems the active region has a constant current (IC) for all base currents, with no gradient!
I am confused now
Is it the case that people like to pretend that the IC current is constant in the active region or is it the case that I may be looking at completely different output characteristics?
I do have issues with the active region - I fail do understand how increasing VCE has no effect on the current unless the effective resistance of the transistor increases in proportion to the applied voltage - I guess this would be another great question to ask -
If anyone could tell me how this IC is (apparently) constant in the active region in terms of transistor resistance it would be a massive help to me as I prefer to think of them as resistors which often works for me.
hope most of that was clear.
Thanks, G
I studied a BTEC course a couple of years ago and was taught how to determine (for a standard BJT in common emmitter config) the Hfe /Rin / Rout by using the output / input characteristic graphs for the Transistor model. This involved plotting load lines etc
for large signal analysis these relations are
Rin = deltaVBE/delta IB - this seems fine
Hfe = delta IC/ delta IB - where ''delta'' means ''change''
This last formula is now causing me problems at university. All the previous output graphs for transistors I have seen had a clear gradient in the active region (increasing left to right) so these ''deltas'' were easy. Now it seems the active region has a constant current (IC) for all base currents, with no gradient!
I am confused now
Is it the case that people like to pretend that the IC current is constant in the active region or is it the case that I may be looking at completely different output characteristics?
I do have issues with the active region - I fail do understand how increasing VCE has no effect on the current unless the effective resistance of the transistor increases in proportion to the applied voltage - I guess this would be another great question to ask -
If anyone could tell me how this IC is (apparently) constant in the active region in terms of transistor resistance it would be a massive help to me as I prefer to think of them as resistors which often works for me.
hope most of that was clear.
Thanks, G