Favorite reverse bias protection for battery circuits

I did a quick check and nobody mentioned the idea of a diode in series with a relay coil.

No food items. Keep canned goods in the cupboard and *remember* to take some on your way out the door :>

Of course, the whole purpose is *not* to need these things! Otherwise, one should *invest* properly in them! :-/

Kodak had a camera powered by a pair of AA NiMH cells glued into a plastic holder.

That's because a relay coil likely draws more power than the circuit you're trying to protect ;)

I like diode and polyswitch, or MOSFET circuit.

Grant.

Synchronous rectifier.

On a sunny day (Tue, 16 Mar 2010 17:13:43 -0700) it happened D Yuniskis wrote in :

I was joking! But on a more serious note: Most visually impaired have great sense in their fingers, they will have no problem feeling what side of an AA of AAA goes where.

I can do it too wit heyes closed :-)

rote:

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I tend to be designing things that are called "portable" and run from a car battery or the like. Right now I am doing the lowest powered product ever and that is 2.5W.

I have found that polyswitches can't be trusted if you have a significant battery to get hooked up backwards. They take too long to go open.

I have used the MOSFET trick

I used a diode to supply power to a little circuit that pumps the gate of the MOSFET up so that the battery voltage doesn't have to be enough to work the MOSFET.

"Grant" kirjoitti viestissä: snipped-for-privacy@4ax.com...

But you can solve that power problem with impulse relay. Connect coil thru diode so that it gets power when polarity is wrong and another flyback diode across coil to ensure it goes all way to another position. Then when polarity is wrong relay gets power and changes polarity.

Only problem is that you have to find someone how makes such relays...

schematic:

-ek

Bigger diode? Where I've seen them used was on 24V traction battery, lots heating power available.

Presently looking at

Thanks, Charlie

Yikes! $4.50 each at digikey! ouch...

Charlie

#3: If the input voltage terminals are shorted, this event is called "psst" in language of zurgs. For the same reason, you can't make an OR of two batteries on the load with a pair of FETs. The ESD while inserting the bateries will do "psst" to FETs also, unless you take precautions.

VLV

And over $2 in production qties, which is why I never used a solution like that and kept designing with discretes instead. LTC is a great company but the pricing on the more mundane parts such as this one is IMHO a wee bit out of touch.

It's a power NMOS plus a charge pump.

Gate drive requires no power in your application (slow).

Could you use discrete power MOS plus a 12V button cell? (Can't quote the part number, CR...., but there's one in my Q45 remote)

Jazzy would be push and release button, flyback inductor powers NMOS gate ;-) ...Jim Thompson

If source/body orientation is as shown, it can't handle reverse battery :-(

Ooops! Yes it will... Apply battery at terminal "D", load at terminal "VIN"... just as I showed in...

Message-ID:

Caution... who knows where "real" substrate is, so buy one and test :-) ...Jim Thompson

An additional Joerg-ian caution: Micrel's website has no E-mail contact info, you have to call... probably get someone who doesn't know s*it :-( ...Jim Thompson

This typically depends on the cause of the vision loss. E.g., those suffering from diabetic retinopathy will tend to have diminished sensitivity in extremities. (i.e., Braille is a non-starter)

WHAT is an MC1253? Maybe local protection? ...Jim Thompson