Voltage regulators fail high

[Eeyore]

Hammy wrote:

On Thu, 12 Feb 2009 19:08:42 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

or not having the common pin connected.


http://webpages.charter.net/jamie_5"

Yep never thought of that.That would do it.

I've accidently left them into a dead short for a few minutes and they
survivied even the T0-92 L series.

Try a few hours.

IDIOT !

 

[Eeyore]

Jamie wrote:

Chris Jones wrote:

also the electromigration lifetime due to current density in the metal
tracks would be reduced at high temperature.
That is totally insane!

YOU are totally insane.

 

[Eeyore]

TonyMS wrote:

One other suggestion that occured to me last night was simply using a
high wattage resistor to drop the 12V down to say 7V so that a failure
can't lift so high

I regularly use that trick for different reasons, except it won't stop the
lift that much. Can save on the cost of a heatsink. A power resistor's MUCH
cheaper.

The dissipation goes down, so the regulator won't blow. That's why I do it.

Graham

ps. just because it's rated at 1A doesn't mean it can survive 1A output at
ANY input voltage without being heatsunk. TO-220 in fresh unobstructed room
temp airflow will only survive around 2W without a heatsink.

 

[Jamie]

Eeyore wrote:

Jamie wrote:


Chris Jones wrote:


also the electromigration lifetime due to current density in the metal
tracks would be reduced at high temperature.

That is totally insane!


YOU are totally insane.

Do I need to paste in the upper half of the reply so that I can make

you look like a total asshole? Well, I guess that might to difficult to
do, since you're already there.

It's well known that you like to cut up messages so that you can
re'engineer it's meaning for your own little pathetic regressive child
play. Guess you have nothing of value to offer so you resort to
fabrication.

In short, its obvious that you're an old dog, and you know what they
say about that!


http://webpages.charter.net/jamie_5"

 

[Hammy]

On Sun, 15 Feb 2009 18:55:18 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Hammy wrote:

On Thu, 12 Feb 2009 22:44:01 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:

First question. What temperature are you running them at ? Do you
understand thermal calculations ? What is the max die temp ? Usually it's
125C on 7805s.

I've abused the 7800 series of regulators. They have thermal
protection I know it works from experience.

Eeyore wrote

And I know from experience that if you abuse the thermal protection, they can
explode.

Well then who's the bigger idiot?

I always catch them before thay get that far.

DipShit

I explained in another post how it happens when I do it you illiterate
pommy piece of shit.

 

[Jasen Betts]

On 2009-02-12, TonyMS <news@montgomery-smith.org> wrote:

I've been using 5V regulators - L7805ACV and others. I've had some
failures, no doubt due to careless wiring on my breadboard.

one sure way to kill 'em is to feed the reverse polarity.

The problem is that, when they fail, they fail high. Ie, instead of
regulating my 12V supply down to 5V, they leave it at around 10V, and
damage other components on the board.

one way to get them to do that is to not connect the earth pin

First question, is this normal behaviour?

most (few) failed ones i've seen did not pass any current.

Second question, is there any
way I can protect my boards against such failure?

connect the 7805 to the supply and the breadboard to the 7805,

use a screw terminal strip or similar. connect the supply negative to
centre pin and the circuit negative to the tab that way if any
connection (external to the device) fails you'll just get no
power from the 7805.

many devices have a diode before the 7805 to protect them from
accidentally reversed supply.

best solution may be to get a regulated 5V supply.
or use 4 NIMH cells if you need battery power, 4 of them in series
produce close enough to 5V for most "5V" chips.

 

[Jasen Betts]

On 2009-02-13, Chris Jones <lugnut808@yahoo.com> wrote:

I've abused the 7800 series of regulators. They have thermal
protection I know it works from experience.

I have heard of people shorting the output to ground and using them as
thermostatically controlled heaters - they heat until the thermal
protection temperature and then stop heating above that temperature. I
think the reliability is probably not good when used like that, because the
manufacturer may have set the thermal cut-out at a temperature that will in
the long term damage the die, the die attach or the moulding compound, and
also the electromigration lifetime due to current density in the metal
tracks would be reduced at high temperature.

that's nuts

Still, if you need to perform that heating function without needing high
reliability, then I can't think of a cheaper way to do it. It would be
nice if someone would make a part that was designed and specified for that
application, so that it could be used with more confidence.

a polyswitch ?

 

[Chris Jones]

Jasen Betts wrote:

On 2009-02-13, Chris Jones <lugnut808@yahoo.com> wrote:

I've abused the 7800 series of regulators. They have thermal
protection I know it works from experience.

I have heard of people shorting the output to ground and using them as
thermostatically controlled heaters - they heat until the thermal
protection temperature and then stop heating above that temperature. I
think the reliability is probably not good when used like that, because
the manufacturer may have set the thermal cut-out at a temperature that
will in the long term damage the die, the die attach or the moulding
compound, and also the electromigration lifetime due to current density
in the metal tracks would be reduced at high temperature.

that's nuts

Still, if you need to perform that heating function without needing high
reliability, then I can't think of a cheaper way to do it. It would be
nice if someone would make a part that was designed and specified for
that application, so that it could be used with more confidence.

a polyswitch ?
I believe that the manufacturer recommends that those are not used

continuously in the "overload" state. Also they don't have a nice copper
tab to bolt to the thing you want to heat. Someone should make something
like the 7805 but specified for heating and with a more accurate
temperature control. Of course it would cost more than a few cents then
due to smaller sales volume and less price competition.

Chris