Diodes in parallel to increase maximum current ?

Hi..

Is it possible to place 4 diodes in parallel to increase the maximum
current ?

In this case it would be 4 times 1N5408 diodes.

 

Yes for making fireworks. They will pop one by one.

 

Thats what i feared..

Thanks for the very quick reply..

 

YES..... all you have to do is make sure they share the current or, if you
don't care if they dont, then don't. Life is cool that way. Diodes have a
negative temperature coeifficient thing so if you do some sums you might
work out how much resistance you need to add to your circuit to make them
agree with the answer without wandering about too much or some other stuff.

It's all rather complicated but if you sign up here,
http://www.ijsklontje.nl then you won't find out how.

DNA

 

Well, you could put them in parallel, but it wouldn't serve your purpose.
The reason is that each diode will likely have a different Vf. The diode
with the lowest Vf will conduct first, possibly not allowing the others to
turn on. The diode with the lowest Vf will hog current, possibly to the
point of destruction, probably shorting, thus creating havoc with whatever
lies downline. If it fails open, then the diode with the next lowest Vf
conducts and repeats the cycle. A losing situation either way.
Solution is to get the correct diode.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

If your laid back approach were any more laid back you would be
horizontal!

And how is looking at porn going to solve this problem?

 

Thank you for admitting that I have an immensly huge cock. Obviously I
haven't but I appreciate the compliment (From A Texan) anyway.

DNA

 

Chemists learn things without an incentive to find out more.

DNA

 

And, as any woman will tell you, that's why a small one is better "in
the long run", so to speak. ;-P

Cheers!
Rich
--
Elect Me President in 2008! I will:
A. Fire the IRS, and abolish the income tax
B. Legalize drugs
C. Stand down all military actions by the US that don't involve actual
military aggression against US territory
D. Declare World Peace I.

 

Only problem with huge cocks is the same problem with huge tits and
asses - when the body makes that much investment in genitalia, there
isn't enough tissue left over to make an effective brain. ;-P

Good Luck!
Rich
--
Elect Me President in 2008! I will:
A. Fire the IRS, and abolish the income tax
B. Legalize drugs
C. Stand down all military actions by the US that don't involve actual
military aggression against US territory
D. Declare World Peace I.

 

On Mon, 20 Feb 2006 23:38:38 GMT, in sci.electronics.design Rich Grise

see
http://www.theregister.co.uk/2006/01/26/bat_revelation/


martin

 

On Mon, 20 Feb 2006 23:38:38 GMT, Rich Grise

[snip]

[snip]

That's just a restatement of Thompson's (40+ year old) Theorem... "The
sum of mammary tissue plus brain tissue is a constant" ;-)

...Jim Thompson

 

hmm, not really, i assume your referring to things
like supply line mains etc.
if you get perfectly matched diodes you could do it
how ever, the chance of getting 4 diodes to match the
current curve is slim with in reason.

 

What shall we deduce, after all the time you've spent convincing us that you
have a really huge brain?

 

"hihihi"

** Yes - it will likely work out just fine.

The ***fuckwit doomsayers** here have simply never tried it.

** To get reasonable current sharing, the diodes should all be from the same
batch and mounted in thermal contact.

This means installing them snugly side by side, with short leads into large
heat-sinking pads on a PCB.

Or else - twisting the four leads together at each end.

Long as the diodes are similar and the temps the same, close sharing is
assured.

However, four 3 amp diodes will not give you a 12 amp average current
rectifier.

Derating will be needed - to maybe 7 or 8 amps.





......... Phil

 

If there is something else in each diode's circuit to ensure that they
share the current approximately equally, then it is sometimes possible.

You can use a resistor if the power loss isn't going to be a problem, or
you might be able to make use of some existing loss, such as the winding
resistance of a transformer.

If you were using a mains transformer with four identical parallel
secondary windings, keeping the windings separate with one diode on each
winding would probably work - but you would have to test it thoroughly
and de-rate the diodes sufficiently to allow for any imbalance.
Similarly, if you are using a choke-input smoothing arrangement, a
quadrifilar choke could be designed to do the job.

I have used something like this in reverse, to distribute output
transistor current in a large audio amplifier with a multi-primary
output transformer.


In all probability, none of these solutions will be possible for your
particular problem - so the answer will be "no".

 

"Adrian Tuddenham"

" In all probability, none of these solutions will be possible for your
particular problem - so the answer will be "no". "



** **** off - you bloody idiot.




.......... Phil

 

Well, Yes, No, and maybe.

You can't put them directly in parallel, as the one with the lowest
voltage drop will hog the current, causing it to heat up.
Unfortunately diodes have a several millivolt negative TC, so when it
warms up it will hog more current, leading to more heat, more
current,.... I think you see where this is going.

You can definitely get this to work IF you add enough series resistance
to EACH diode individually to compensate for the negative TC.

"Enough" resistance is beyond my ability to compute, but a wild guess
would be enough resistance to equal the diode voltage drop.

Now this isnt too bad if we're talking about a high voltage power
supply where another 0.7 volts won't matter. It is bad for a under 10
volt PS where anotehr 0.6 volts is a big deal.

 

---
"Likely" isn't the same as an unequivocal "yes", which is what I
think the OP was looking for.

In any case, you've given him bad advice.

Connecting diodes in parallel is, at best, very poor practice, and
what you should have advocated was that he simply buy diodes
specified to carry the current that he needs.