Over-voltage protection

[Demon]

A little something I thought up in case a user doesn't use the proper power source (like use the Lab-X1 12V wall-adapter instead of the 5V model supplied with the unit).

This serves as both a POWER light, and a MAGIC-SMOKE-INCOMING light.

IF Zener receives under 5.6V THEN
  PNP transistor turns ON green light
ELSE
  NPN transistor turns ON red light
END-IF

Does it make sense? Am I forgetting something?

I've never touched a Zener before, and rarely have used a Transistor. So this also serves as a training exercise for me.

Robert

[richard]

the red led will never fly with base of tr shorted to gnd

try


red should light at 5.5v

[Demon]

the red led will never fly with base of tr shorted to gnd

try
Attachment 9386

red should light at 5.5v

But why reduce Zener to 4.7V? Out of all the PICs I'm looking at, the one with the lowest max VDD was 6.0V; hence why I chose 5.6V Zener as "fuse".

Is this because of influence of 1K resistor below it?

And how did you arrive at 4.7V? Math? or a spec in some doc?

In this particular case, I was doing this for the 18F14K22 which has absolute max VDD rated at 6.0V.


EDIT: I ask how, because I will have the same over-voltage circuit at other voltage levels(for other purposes).


EDIT SOME MORE: These are the specs for the 1N5232BTR that I was planning on using.

[richard]

But why reduce Zener to 4.7V?

i saw

the 5V model supplied with the unit

and assumed an over 5v alarm was indicated

Out of all the PICs I'm looking at, the one with the lowest max VDD was 6.0V; hence why I chose 5.6V Zener as "fuse".

if you use a 5.6v zenner in my cct then the red alarm led will be lit at 6.5 v

if you want the zenner to be a crowbar and blow a fuse, there are better ways.

https://www.ebay.com.au/itm/203643422252

i use these things , 3-15 v in adj to 3.3 or 5v out or whatever @up to 5w , cheap with no problems

[Demon]

... if you want the zenner to be a crowbar and blow a fuse, there are better ways.

I'm seeing this design a lot.

https://theorycircuit.com/crowbar-ov...ection-module/

It pops that fuse and puts an end to the shenanigans until the user corrects the situation.



I'd like to stay away from 3rd-party components as much as possible, and come up with a design as simple as possible.

Robert

[Demon]

... if you want the zenner to be a crowbar and blow a fuse, there are better ways.

How about this modification to that link I posted above?

- Green LED remains ON while voltage remains under 5.6V.

- Red LED turns ON when voltage reaches 5.6V, and Green LED turns OFF.

- SCR shorts out Fuse and protects everything to the right of this circuit.



This way I get a light on the unit that gives an indication as to what went wrong.

I absolutely hate products that DIE, and you're left clueless what went wrong.

Robert


EDIT: I'm just not sure about the need for that 1N4007 for my application. It will cost me a voltage drop to add that in.

[richard]

- Green LED remains ON while voltage remains under 5.6V.

Green LED remains ON , it will not extinguish

- Red LED turns ON when voltage reaches 5.6V, and Green LED turns OFF.

Red LED turns ON when voltage reaches 5.6V + at least 0.6 v , so more like
when voltage exceeds 6.3v Red LED turns ON and Green LED remains on.

- SCR shorts out Fuse and protects everything to the right of this circuit.

in practice :- just after every semiconductor device is destroyed SCR shorts out Fuse

[Demon]

... if you want the zenner to be a crowbar and blow a fuse, there are better ways.

https://www.ebay.com.au/itm/203643422252

Ok, so I found Alice on ebay Canada. Turns out to be $1.79 each when I buy 10.
https://www.ebay.ca/itm/313748820419


I guess nothing stops me from adding a zener/crowbar/fuse setup in front to make me feel like I'm doing something.


I can even afford a one-way diode in case someone uses a wall-adapter with a negative center (I think all the ones I have are positive center).


I hope you get a freebie for making her a sale.

Robert

[Demon]

So I started looking closer at Alice, she's using a B6289C IC; I can't even find a datasheet for that.

But I did find a relatively similar circuit using a LM2596 for $.99:
https://www.ebay.ca/itm/333463165949


Is this as good as Alice?


I can even order a batch from Amazon and avoid import/duty fees, $2 each:
https://www.amazon.ca/Yizhet-Convert...dp/B0B5GQTS64/


Robert


EDIT: just the LM2596 costs over $4 here:

https://www.digikey.ca/en/products/d...TVADJG/2003293

[richard]

I absolutely hate products that DIE, and you're left clueless what went wrong.

me too, that's why i use modern switch mode power modules with wide input supply ranges and generally fail safe outputs

[amgen]

A simpler circuit as 'crowbar' type circuit. Use 2 or 3 -5.6 volt zener diodes, if/when it trips, probably will short/ruin one z-diode. Has your .6 amp fuse and you can add one or more 1n4004 type diodes in series to raise the trip-out voltage by about .6 volt for each diode. Also add a, maybe a
1 or 10 microfarad cap across z-d's to absorb any high surge if over 5v