Common Base output characteristic

Hello people!

I am reading some transistor theory, and curently i am reading about the common base connection. I have seen that we need to calculate some metrics to get the Ic (which equals -approx- to Ie) and Vcb values of the polarization, so that we can draw the load line on the Ic -> Vbc characteristic. This characteristic is something like this:

http://ecelab.com/vcb-ic-curves.htm

Funny thing is that, no matter how many transistor datasheets i have open (and i have open A LOT), i could not find not a single one datasheets which has this characteristic. I mean, i have seen the output characteristic for Common Emitter connection, but there is nothing for the Common Base....

What is wrong here?????? Where can i find these characteristics for a transistor?

Nothing wrong. It's just that, since the common base connection is seldom used in electronics, the characteristic curves for such a configuration are not typically shown in a data sheet. But they can be derived, to a good approximation, from the common-emitter curves that are shown.

hi,
The common Base configuration has the lowest impedance of the basic configs of a transistor, in the order of 50R.
Its got the highest output impedance ~1megR.
Current gain less than 1, same voltage gain as a common Emitter, no phase inversion of the signal .

crutschow said:

Nothing wrong. It's just that, since the common base connection is seldom used in electronics, the characteristic curves for such a configuration are not typically shown in a data sheet. But they can be derived, to a good approximation, from the common-emitter curves that are shown.

Click to expand...

thank you all for your reply.

Carl, can you explain me how can i change the CE curves to gain the CB curves? I understand that Ic axis will remain as is, and the Ie characteristics are almost parallel to Vcb. But how does Vcb changes on the shaft?

Thanks

hi,
Look here for the Common Base curves.
http://ecelab.com/vcb-ic-curves.htm

ericgibbs said:

hi,
Look here for the Common Base curves.
http://ecelab.com/vcb-ic-curves.htm

Click to expand...

meliomelenios said:

thank you all for your reply.

Carl, can you explain me how can i change the CE curves to gain the CB curves? I understand that Ic axis will remain as is, and the Ie characteristics are almost parallel to Vcb. But how does Vcb changes on the shaft?

Thanks

Click to expand...

. .

Why are you using common base?
I use common base in fast video amplifiers to remove Miller capacitance feedback.
In RF amplifiers where the part is run very fast.
A couple times in off line switching power supplies (10000Vce), I will not do that again.
You will see data sheets mention common base only on fast and fast high voltage transistors. RF & Video output transistors.

ronsimpson said:

Why are you using common base?
I use common base in fast video amplifiers to remove Miller capacitance feedback.
In RF amplifiers where the part is run very fast.
A couple times in off line switching power supplies (10000Vce), I will not do that again.
You will see data sheets mention common base only on fast and fast high voltage transistors. RF & Video output transistors.

Click to expand...

Can you please provide me some links for datasheet from transistor with such a characteristic (Ic-Vcb). I don't use CB connection, i am only doing a research.

(Ic-Vcb) is almost the same as (Ic-Vce).
Vcb + Vbe = Vce
Vbe is about 0.7 volts.
The Vcb can go slightly negative. Collector below Base, when the transistor is turn on hard.
If you really need Vcb then do some math with the data you have.

ronsimpson said:

(Ic-Vcb) is almost the same as (Ic-Vce).
Vcb + Vbe = Vce
Vbe is about 0.7 volts.
The Vcb can go slightly negative. Collector below Base, when the transistor is turn on hard.
If you really need Vcb then do some math with the data you have.

Click to expand...

Thank you ronsimpson a lot! You saved me another day of searching!