Well
What are Vcc and Vbb?What is the difference between them?

 

Both are symbols for supply voltage.

Vcc is from Bipolar days and refers to the Collector.
Vdd is more modern, refers to the Drain on FET devices.

This representation has changed many times over the years as electronics technology has evolved. I remember when it was always referred to as B+.

0x34

 

Suggestion, do not try and memorize and/or make sense out of popular supply designators. They are just DC voltages from a low impedance source. People can (and do) call them whatever they like. If one is going to give labels it makes more sense to label them like +5V or -15VD etc..

At least you can get some information about the actual value of the supply.
It is of little importance making labels that describe where on a transistor they were connected in the old days..

 

However, these designations are pretty much industry-standard and do usually make sense.

The first letter indicates the parameter (v = voltage, i = current, r = resistance, etc.) Lower-case letters mean an ac value, upper case letters a dc value.

The subscripts indicate specific transistor elements ("b" is base, "c" is collector and "e" is emitter) and work this way:

If a twin letter subscript (e.g., cc, bb, ee), it indicate a power supply source. Vcc is the collector supply; Vbb is the base supply; Vee is the emitter supply. You usually only see Vcc as Vbb is usually derived from Vcc via voltage divider bias and Vee from a ground connection, although plenty of circuits do use a negative Vee supply.

A single-letter subscript indicates a voltage measurement with respect to (WRT) ground. So, Vc is the voltage on the collector wrt ground; Vb is the base voltage wrt ground.

A double letter subscript such as Vce indicates a voltage that is measured between transistor elements. Vce is the voltage between the collector and base; Vbe is the voltage between base and emitter.

FETs work the same way with "d", "g" and "s" as the subscripts.

Dean

__________________
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

-How can that be?V for Voltage-OK; c for Collector-OK; but e for base?I think it would be e for Emitter from what u wrote earlier.


Anyway,
Thanx

 

I would guess that was a typo, but apart from that I think Dean has given a very comprehensive and informed reply to your question.

 

I agree it is industry standard and that is unfortunate. The problem is the IC guys still use it and while technically correct(IC's having trsnsistor circuits), it is totally out of context for the part usually.

And to further complicate matters VCC, VEE etc... are usually on the other side of resistors and so really should be treated like any other supply. Very rarely does Vc = Vcc. And of course, imagine a multi-trans schematic with both NPN & PNP.. now using double sub labels makes even less sense.

But I am in total agreement with Vb, Ve, Vc and Vg, Vs, Vd for FETS and of course Vgs, Vds etc... all make sense and work out nicely. I only take issue with the double subscript labels.. and come on! it doesnt really bother me that bad! :-)

I guess I feel that these labels made alot of sense when _single_ discrete transistor amplifier design was rampant but they should have faded in proper proportion with the popularity(necessity) of trans. amp design.

 

ok the first person to respond to your question made a typo when he changed your Vbb to Vdd. Vbb, Vcc, and Vee have to do with your biasing of a bjt in a circuit. If not biased properly then the bjt will not allow current to flow through it causing the circuit to fail. NPN bjt is ground or low, or even negative sometimes, supplies to the Emitter, A larger or more positive supply to the Base, and an even larger supply to the collector. PNP BJT is largest supply to emitter, medium supply to base, and smallest supply to collector.

 

Simply Vcc means Collector to ground Biasing Voltage in a transistor.While Vbb means Base to Ground Voltage.

alwaysVcc>Vbb

 

Quote:
Vce is the voltage between the collector and base

Yes, it was a typo. Thank you for the kind words, John.

Dean

__________________
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.