# BJT Large Signal

Discussion in 'General Electronics Chat' started by Mazaag, Feb 5, 2008.

1. ### Mazaag Thread Starter Senior Member

Oct 23, 2004
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0
Hey guys

Is there a value for the large signal resistance from the Collector to the emitter of a BJT ? like i know for MOSFETs there is a large signal Rds, and a small signal ro , what about BJTs ? and how do you calculate this value

thanks

2. ### scubasteve_911 Senior Member

Dec 27, 2007
1,202
1
BJTs go by a Vce(sat) parameter, which is a very dynamic. It depends very much on current through the transistor and temperature.

Steve

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
BJTs dont have a fixed resistance like FETs , it depends upon your circuit.

You can find it if you devide Vce by Ic for a particular circuit

4. ### Audioguru New Member

Dec 20, 2007
9,411
896
The collector of a transistor is a very high impedance. The circuit's output impedance is just the collector resistor in parallel with the load resistance.

5. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Output resistance can be estimated at least for the small signal model by dividing the BJT's "Early voltage" by the collector current. Here is the wikipedia article describing this relationship.

hgmjr