Question about transistor breakdown voltage

It depends on the concept you're trying to understand. If you simply want to have an idea of the maximum voltage that can be applied between collector and emitter before breakdown, assuming that the polarity is in the usual direction, then it could be said that they are the same.

However, to be technically correct and also specify the polarity at the same time, they are not the same. For example:

The voltage applied to the collector of an NPN transistor is normally positive with respect to the emitter. Therefore, the collector-emitter voltage (whether breakdown or normal operating) would be given as X volts, whereas for a PNP transistor, it would be -X volts.

If you give X volts as the emitter-collector voltage, it would mean that the emitter is positive with respect to the collector. This is the reverse of the way an NPN transistor is normally operated. The breakdown voltage would also probably be different because the base-emitter junction and the base-collector junctions are made different in practice, although their basic principles are the same.

Let me add some clarification to my earlier statement.

The darlington transistor is an NPN device used as a low side switch. Emitter is tied to ground. I am interested in understanding what happens when the collector goes negative with respect to ground.

In this instance, wouldn't the emitter to base junction break down first (max rating of 10V)? Current would flow from the emitter, to the base, then from the base to collector (one diode drop). So, total breakdown voltage in the reverse direction (assuning the connection scheme listed above) would be approximately 10.7VDC?

Thank you

Gerb

Let me add some clarification to my earlier statement.

The darlington transistor is an NPN device used as a low side switch. Emitter is tied to ground. I am interested in understanding what happens when the collector goes negative with respect to ground.

In this instance, wouldn't the emitter to base junction break down first (max rating of 10V)? Current would flow from the emitter, to the base, then from the base to collector (one diode drop). So, total breakdown voltage in the reverse direction (assuning the connection scheme listed above) would be approximately 10.7VDC?

Yes, that's what would happen unless the base is prevented from being pulled below ground by some other circuitry. This can be qualitatively demonstrated with a single (non-darlington) transistor and an analog multimeter set at the high ohmmeter range. The 9V battery generally used to drive the high resistance range is higher than the e-b breakdown voltage (usually around

5V). In fact, I often use this to identify the leads of an unknown transistor. The collector-emitter path is essentially open in one direction, but conducts in the other direction, but at a lower level than a single p-n junction.

--
Version 4
SHEET 1 880 680
WIRE 32 32 -208 32
WIRE 224 32 112 32
WIRE 352 32 224 32
WIRE 224 144 224 32
WIRE 32 192 -64 192
WIRE 160 192 112 192
WIRE 352 240 352 32
WIRE -208 256 -208 32
WIRE -64 256 -64 192
WIRE 224 288 224 240
WIRE 288 288 224 288
WIRE -208 384 -208 336
WIRE -64 384 -64 336
WIRE -64 384 -208 384
WIRE 352 384 352 336
WIRE 352 384 -64 384
WIRE -208 432 -208 384
FLAG -208 432 0
SYMBOL npn 160 144 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL npn 288 240 R0
SYMATTR InstName Q2
SYMATTR Value 2N4401
SYMBOL res 128 176 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 3600
SYMBOL voltage -64 240 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -208 240 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(10 -10 0 1 0 1.1)
SYMBOL res 128 16 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 100
TEXT -184 416 Left 0 !.tran 1.1 uic


JF

** Look at the diagram of the darlington - see a diode drawn from collector to emitter?

All power darlingtons have them.

Means full conduction from 0.6 volts when subjected to reverse polarity.

...... Phil

what's connected to the base?

Bye. Jasen

--
Phil 1, everyone else 0.

JF

Where did you get the idea that the OP was referring to POWER darlingtons?

Besides, it's not true that all power darlingtons have antiparallel diodes. The General Electric D40K doesn't have one. And, as GE says in one of their manuals, "The modern monolithic Darlington may contain all or none of the auxiliary components shown in Figure 7.2 (referring to the antiparallel diode and built-in base-emitter resistors). It only takes one counterexample to falsify your assertion.

Apparently not.

--
OK. 

Phil 1000, you 1

JF

Given Phil's normal tendency to mercilessly rag on anyone who makes any assumption that he considers unwarranted, he must be held to his own high standard in that respect. Since the OP didn't use the word "power" in any of his posts, Phil gets 0, not 1000, a forfeit for bad behavior.

If anyone else had said what Phil did, he would probably say something like this:

CONSIDER THE CONTEXT, IDIOT!!!! THE OP WOULD HAVE SEEN THE DIODE IF IT WERE IN THE DIAGRAM, AND WOULDN'T BE ASKING THE QUESTION HE DID!!!!!

Only Phil made the assumption that the OP's darlington has a diode; everybody else assumed that it doesn't. Why do you suppose that is? Which is the more reasonable assumption?

Just because I only cited one power darlington without a diode doesn't mean that there aren't more.

But more to the point, it doesn't matter how many power darlingtons have diodes. If the OP's darlington isn't a power darlington, then it's irrelevant how many power darlingtons have diodes. You don't get points for conclusions based on an unwarranted assumption.

Furthermore, if we don't know for sure whether the OP's darlington has a diode or not, and have no good reason to assume that it does, treating the case where it doesn't is the useful thing to do.

"Dr. Posturing Pig "

** 100 volt, NPN low side switch ..... so has all the earmarks.

Plus see the " ? " at the end of the line ????

That means something.

** All the popular, readily available ones do.

** Really.

Why don't you go jump in front of an express train - f****it.

..... Phil

If there were a diode in the diagram he wouldn't have been asking the question.

Small signal darlingtons are very often used as low side switches to turn on LED's, energize small relays, and they are also often NPN. These things don't imply power.

It means he was asking a question. If a diode were visible in the diagram, he wouldn't need you to ask him if he could see it.

So that means he couldn't be asking about one of the less popular ones?

Really. And more besides.

After you.

100 volt, NPN low side switch. Those qualities are the exact "earmarks" of a BC372 small signal darlington for example, and don't imply "power". The diagram shows there is no diode. If the spec sheet he was looking at had a diagram with a diode, he would have seen it, and wouldn't have been asking the question he asked. That's the context you're ignoring, as you so often accuse others of doing.

I notice he hasn't responded to your question. The answer was so obvious it didn't merit a reply. If there had been a diode in a diagram, he wouldn't have been asking about reverse breakdown.

Vceo, Vceb or Vcev ?

Graham

And why would that happen ?

Never heard of inverse parallel diodes ?

Graham

A fairie.

--
Perhaps the OP will come forward with the device he was referring to and
end the squabbling?


JF