Favorite reverse bias protection for battery circuits

Yes, there are fet "tricks" that when reverse biased bias the fet to turn it off. It is essentially an "active diode".

I usually use #2 on this page a shorting shottky.

This

That renders the unit dead and a blind or almost blind person will have a hard time finding or buying the proper fuse and installing it.

Charlie: Solution #3 is the ticket (look on Hammy's link). But make sure that the FET is guaranteed to be fully turned on at the lowest allowed battery voltage, IOW the point where an UVLO comes on.

I believe that's why they invented LCD to save power. Not sure how well it can be read by visually impaired.

LCD controllers are usually less sensitive to supply voltage than LED drivers. LCD segments need almost zero currents.

Some variation on this...

Do you have enough voltage to turn on MOSFET's?

Probably could do it with bipolar's... I'll ponder :-) ...Jim Thompson

Which HV CMOS process did that get rolled onto, if I may ask?

California Micro Devices (do they still exist?) for a LiIon charge/discharge controller. ...Jim Thompson

Solve this problem *mechanically*. You need to prevent the batteries from being *installed* wrong, in the first place. E.g., any sort of circuit that protects (the rest of) the circuit from reversed battery won't do anything to tell the VI user *why* your device isn't working. Are the batteries

"Key" the battery holder so the user can feel the correct orientation for the batteries *and* so it prevents the cells from making electrical contact if not oriented properly.

Think of how the *user* is going to interact with your device. Close your eyes and "figure out" why it doesn't work :-/

Thats what they have seeing eye dogs for:-) Jokeing.

Of course your right for a blind person either #3 or a keyed battery connection. With a brail instruction manual

Swallowed by ON, just like AMI was :-(

Ok, I'll ask our new Labrador when she is back :-)

She went through the first three phases of guide dog training and then had to be discharged for a medical condition (soft trachea, happens a lot with guide dog Labs).

It's actually even better these days. A nearly blind relative has a Casio watch that talks.

Would be the best result, but these are standard AA cells, no way to key them without using expensive custom battery packs. Not the way to go for inexpensive...

Will be looking for a good PMOS FET that will still conduct with two low AA batteries, probably around 1.8VDC, if they make one! ;-)

Thanks All!

Charlie

Called a PNP :-)

What's the load current? ...Jim Thompson

I take it you aren't making a custom (molded) case? Why not purchase COTS battery holder that *is* "keyed"?

If you go that route, consider how your design can tell the user "yes, I am working" vs. absence of that indication so the user can deduce "something is wrong with the batteries or their installation" (or the device)

Are you a foster dad for pups? You must dread having to give them up?

I just took my Golden Retriever to the vet. He started to develop a sunken eye. The vet doesn't know the cause yet. I'm hoping its nothing to serious.

That's nothing look at Hawkins chair that dude is wired for sound and then some. :-)

No, we are puppy sitters. So we jump in when a family goes on vacation or visits a sick relative where they can't take the guide dog puppy. Even then it's tough when they have to go back to San Rafael, especially for my wife since she sees them every week during trainings. But when you see them paired up with a blind person you know it's all worth it.

We used to also sit the one that came home now. She instantly remembered our other dogs, where everything is in the house, etc.

Hopefully not. Our Rottweiler is now at an age where it's just a matter of time :-(

No idea what a Hawkins chair is.

He's talking Stephen Hawkins (sp?) the physicist with MS.

Well, my wife's computer talks to her, she has two watches that talk (one red, one blue) a talking calculator that includes a calendar and timer function, and another talking calculator that just does math...

Charlie

Mine just turned 9. My last one was 11 when he died.

He's that British theoretical physicist who came up with a theory for the origin of the universe among other things.

He has amyotrophic lateral sclerosis. So he uses a chair with all sorts of gadgets on it.