load line of transistor

Outrageous

In order to draw the load line of transistor, we have to find out the saturation current (where the voltage is minimum or zero) and voltage of collector-base when collector current is zero.

In order to calculate maximum saturation current, we have to forward biased the base-emitter, and reverse biased the base -collector and then get the voltage of collector-emitter to be zero(V of collector minus voltage of emitter equals to zero), right??


Thank you

Outrageous

I think 'we have to forward biased the base-emitter, and reverse biased the base' instead of both forward because when we forward both we can't get a constant curve at saturation region, correct?

rbj

the base-emitter junction is always forward biased as long as the transistor is not in full "cut-off" (where the collector current is zero). so, from the POV of the load line, the base-emitter is forward biased, usually by about 0.6 volts.

Outrageous

what is POV?
The base-emitter is usually 0.7V.
How to draw a load line?

berkeman

POV = "point of view"

berkeman

Maybe this will help:

http://www.youtube.com/watch?v=KzfrxjCJ8Gg

.

Studiot

First of all there is not one load line for a transistor.

There are many and they depend upon the circuit configuration.

Having said that, for a resistive load the load line is a straight line so you only need to find two points and join them to be able to draw one.

To draw a load line for R ohms on the collector current (y axis) v collector voltage (x axis) curves:

1)Locate the point of the voltage axis corresponding to the supply voltage.

2)Locate the point on the current axis which the supply voltage would drive through R ohms.

3) Join these two points to form the load line for R ohms.

go well

Outrageous

Thank you, understand already.

rbj

okay. whatever. from long ago, when i was a graduate teaching assistant (and i was teaching a lab), it was most often 0.6v for silicon.

well, your transistor curve is that of a function [itex]I_c[/itex] as a function of [itex]V_{ce}[/itex] for various [itex]I_b[/itex]. so given an [itex]I_b[/itex], you still don't know what [itex]I_c[/itex] is without also knowing [itex]V_{ce}[/itex]. the load line is another equation that relates [itex]I_c[/itex] and [itex]V_{ce}[/itex]. and that equation comes from the rest of the circuit (assuming no [itex]R_e[/itex]:

[tex] V_{cc} = V_{ce} + I_c R_c [/tex]

or

[tex] I_c = \frac{1}{R_c} ( V_{cc} - V_{ce} ) [/tex]

plotting that equation on top of the transistor curves is your load line.

Outrageous

Understand.
when there is [itex]R_e[/itex] ,we can use the equation in this (transistor load line)
http://hyperphysics.phy-astr.gsu.edu.../loadline.html
But for this case , our Ic=Ib, correct?