# BJT biasing

Discussion in 'Homework Help' started by raks_universe, Aug 30, 2009.

1. ### raks_universe Thread Starter Active Member

Mar 15, 2009
67
0
In biasing(fixed bias,voltage divider bias,collector to base bias),why the resistors are connected in such a manner .........

Please give the REASON for each and every resistor to be connected in their place of their respective biasing circuits.

2. ### Wendy Moderator

Mar 24, 2008
21,500
2,961
How about you GIVE us schematics, and then we can help. There are way too many schemes out there to answer such an open ended question without a lot of WORK on our part.

This sure looks like a homework assignment.

It all starts with the basic β or hfe equation, Ic = β Ib . All answers usually derive from this basic premise.

3. ### ELECTRONERD AAC Fanatic!

May 26, 2009
1,146
16
If we were to do that, you'd be sitting there for a year or two. Transistors aren't quite as easily understood as you may think. In fact, I will probably never know everything about transistors.

Last edited: Sep 2, 2009
4. ### hobbyist AAC Fanatic!

Aug 10, 2008
885
87
The collector resistor is used to set the colector voltage at a specific value so as to first have a proper impedance ratio between the collector resistor and the load impedance, so as to develope a signal voltage at the collector to be transfered to the load.

The emitter resistor is used to give negative feedback so as to keep the transistor temperature stable, and also used in conjunction with the collector resistor to establish the gain of the amplifier making it more INdependant of device parameters.

The base resistors used as voltage divider is used to establish the proper input impedance ratio between the source impedance and the parrallel effect of the two base resitors as well as establishing the proper voltage ratio between the source voltage input to the base voltage bias. Also to make the base voltage more INdependant of base current loading effect due to device parameters.

All in all the bias resistors are used to set the transistor into its linear region of operation for amplification and establish impedance and voltage values, with respect to the circuitry feeding into it as well as circuitry it is feeding to. (input and output impedances and voltages)

This is just for amplifing stages linear amplification common emitter amp.

There are other uses and classes of operation where the bias resistors are used in other ways, there are many uses for biasing a transistyor stage depending on the aplication needed.

Last edited: Sep 2, 2009