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2N3906 reverse collector-emitter

J

Jean T.

Jan 1, 1970
0
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

Thanks!
John
 
L

legg

Jan 1, 1970
0
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

If you'd tried it, you would have found out pretty quick.

EB junctions typically zeners below 7V.

RL
 
J

Jim Thompson

Jan 1, 1970
0
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

Thanks!
John

What do you mean by "reverse" voltage? Opposite of normal operation?
If so, as soon as you pass thru zero **collector-base** it will start
to forward conduct just like a diode. Depending on what's happening
at the base in your circuit you can get inverse PNP action.

...Jim Thompson
 
W

Winfield Hill

Jan 1, 1970
0
legg wrote...
If you'd tried it, you would have found out pretty quick.

EB junctions typically zeners below 7V.

Many PNP transistors have higher reverse-base-emitter breakdown
voltages than NPN types, some much higher. The datasheets spec
5V, but restricting the reverse voltage to 6V to avoid breakdown
is probably a sufficient rule of thumb.

Jean, one penalty for causing reverse base breakdown current in
a transistor is a severe loss of beta, the forward current gain.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
J

Jean T.

Jan 1, 1970
0
legg said:
If you'd tried it, you would have found out pretty quick.

EB junctions typically zeners below 7V.

RL

I tried. The transistor is still alive but... let me be more precise in my
request:

Does this condition destroy it slowly or it can withstand this indefinitely?
 
T

Tam/WB2TT

Jan 1, 1970
0
Jean T. said:
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

Thanks!
John
Jean,
I once measured the BE breakdown voltage for a number of Si switching
transistors. Most were around 10 -11V. Don't recall that any were as high as
18. This was at room temperature only.

Tam
 
K

Kevin Aylward

Jan 1, 1970
0
Jim said:
What do you mean by "reverse" voltage? Opposite of normal operation?
If so, as soon as you pass thru zero **collector-base** it will start
to forward conduct just like a diode. Depending on what's happening
at the base in your circuit you can get inverse PNP action.

You might want to limit the impedance on the base (to avoid the diode
clamp to OV), so that Vce can go negative without clamping. For example,
in driving a push-pull centre taped transformer. You might want one side
to spike up to 2*Vcc + Vclamp, whence the other side will want to go
to -Vclamp, i.e. a reverse voltage. This is to allow for an extra
voltage to reset the core duing dead time to eliminate flux imbalance.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
J

Jim Thompson

Jan 1, 1970
0
I tried. The transistor is still alive but... let me be more precise in my
request:

Does this condition destroy it slowly or it can withstand this indefinitely?

Jean T.,

You need to be more precise in your problem description. You are
saying "emitter-collector", but the responders are saying
"emitter-base".

Perhaps you could post a schematic, so we can see what your
application is?

Even if you non-destructively break down the emitter-base, you will
suffer gradual beta degradation.

...Jim Thompson
 
F

Fred Bloggs

Jan 1, 1970
0
Jean said:
I need to know how much *reverse* voltage a 2N3906 can withstand
accross emitter-collector as well as base-collector. Datasheets only
specify emitter-base which is 6V.

Is 18V too much?

Thanks! John
If this reverse voltage results from switching action in your circuit
then you should consider something like a diode in the collector circuit
to stand it off.
 
L

legg

Jan 1, 1970
0
Jean, one penalty for causing reverse base breakdown current in
a transistor is a severe loss of beta, the forward current gain.

Inverted gain isn't so hot to begin with.


RL
 
P

Paul Burridge

Jan 1, 1970
0
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

Nope. I just simulated it. It will handle at least 6Gv.
 
P

Paul Burridge

Jan 1, 1970
0
Does this condition destroy it slowly or it can withstand this indefinitely?

They can be destoyed over time by this; it's not just a case of a
one-off "phut-bang"
 
J

Jean T.

Jan 1, 1970
0
Jim Thompson said:
Jean T.,

You need to be more precise in your problem description. You are
saying "emitter-collector", but the responders are saying
"emitter-base".

Perhaps you could post a schematic, so we can see what your
application is?

Even if you non-destructively break down the emitter-base, you will
suffer gradual beta degradation.

----------------------------------------
Hi Jim,

I meant collector-emitter.

Normal operating condition:
- I have a 18V supply
- emitter at +18V
- base pulled-down to 0V (ground) through a 10K resitor
- I added a diode between base and emitter, anode to the base
- then the collector "outputs" +18V (less 100mV may be) to some load

Now if we reverse the 18V supply:
- the diode protects the base-emitter
- I end up with a full reverse 18V accross collector-emitter (there is a
minimal load at collector)
 
T

Tim Wescott

Jan 1, 1970
0
Jean said:
----------------------------------------
Hi Jim,

I meant collector-emitter.

Normal operating condition:
- I have a 18V supply
- emitter at +18V
- base pulled-down to 0V (ground) through a 10K resitor
- I added a diode between base and emitter, anode to the base
- then the collector "outputs" +18V (less 100mV may be) to some load

Now if we reverse the 18V supply:
- the diode protects the base-emitter
- I end up with a full reverse 18V accross collector-emitter (there is a
minimal load at collector)

Then:

- collector-base junction forward-biases regardless of diode
- base - emitter junction sees nearly 18V for just a little while
- you let the smoke out.

If you really want to protect the transistor you should add a diode
between the emitter and +18V. You'll see a drop in forward operation
but you won't see smoke.

If the reverse supply situation is a fault and not normal operating
procedure then you can put a fuse followed by a high-current diode --
putting things in backwards will blow the fuse, but it won't destroy you
transistor.
 
J

Jean T.

Jan 1, 1970
0
Tim Wescott said:
Then:

- collector-base junction forward-biases regardless of diode
- base - emitter junction sees nearly 18V for just a little while
- you let the smoke out.

If you really want to protect the transistor you should add a diode
between the emitter and +18V. You'll see a drop in forward operation
but you won't see smoke.

If the reverse supply situation is a fault and not normal operating
procedure then you can put a fuse followed by a high-current diode --
putting things in backwards will blow the fuse, but it won't destroy you
transistor.

Reading all the replies, seems I have to put some kind of protection.

I was kind of hoping the transistor would have "behaved" like a 100mV drop
diode in foward operation and blocked in reverse.
But the high-current diode/fuse is a better idea.
 
P

petrus bitbyter

Jan 1, 1970
0
Jean T. said:
I need to know how much *reverse* voltage a 2N3906 can withstand accross
emitter-collector as well as base-collector. Datasheets only specify
emitter-base which is 6V.

Is 18V too much?

Thanks!
John

John,

When you reverse the emitter-collector voltage, the base-collector junction
will conduct. The only reverse left is the emitter-base voltage. The rest of
the circuit may make things more complicated but not better. Once I
encountered a problem like this, I solved it by placing a diode in series
with the emitter.

petrus bitbyter
 
R

Robert Baer

Jan 1, 1970
0
Winfield said:
legg wrote...

Many PNP transistors have higher reverse-base-emitter breakdown
voltages than NPN types, some much higher. The datasheets spec
5V, but restricting the reverse voltage to 6V to avoid breakdown
is probably a sufficient rule of thumb.

Jean, one penalty for causing reverse base breakdown current in
a transistor is a severe loss of beta, the forward current gain.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

However, the effect is very much like radiation: total current / dose
rate.
And damage from both can be annealed out in an oven.
Unfortunately, it has been over 30 years, so i have forgotten the
temperature and time.
 
R

Robert Baer

Jan 1, 1970
0
legg said:
Inverted gain isn't so hot to begin with.

RL

If you want transistors withgood beta in forward and reverse
configurations, see theZetek line.
 
R

Robert Baer

Jan 1, 1970
0
Jean T. said:
I tried. The transistor is still alive but... let me be more precise in my
request:

Does this condition destroy it slowly or it can withstand this indefinitely?

See my previous comment related to dose rate.
 
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