Hi,
I am working on a project that runs off 5V dc... it will be destroyed if 12v dc is applied... what is the best way to achieve this? I read somewhere that adding a voltage regulator to the project could do the trick... but the problem is that they require at least 7v to give me 5vdc... I want to be able to plug in 5vdc, but not have the project be distroyed if someone accidently plugs in 12v...
Sounds like you need a crow-bar.
What you would like to happen if > 5V is applied? Using a sepic converter the circuit will work in any case, if like to stop it and have fault detection an LTC4365 and an external mosfet can do the job.
Ciao, Ale.
A zener diode in parallel with the load along with a with fuse will "crowbar" (short-out) when the zener voltage is exceeded, blowing the fuse. And, since a zener works like a regular diode in the forward direction, the circuit will also "crowbar" if the voltage is connected backwards.
ilguargua:
What you would like to happen if > 5V is applied? Using a sepic converter the circuit will work in any case, if like to stop it and have fault detection an LTC4365 and an external mosfet can do the job.Ciao, Ale.
I would be happy with either the project continuing to run (it is a touchscreen with an arduino due and an esp8266), or not running.... I just dont want to destroy the screen by accident since it costs $60 to replace...
DVDdoug:
A zener diode in parallel with the load along with a with fuse will "crowbar" (short-out) when the zener voltage is exceeded, blowing the fuse. And, since a zener works like a regular diode in the forward direction, the circuit will also "crowbar" if the voltage is connected backwards.
A zener will just fail. A crow-bar circuit is needed - typically a zener triggering an SCR - that will
definitely blow the fuse. Zeners dissipate lots of power when clamping, an SCR will crow-bar the
voltage down to 1V or so (thus not dissipating much power) and definitely force the fuse to blow
or the supply to cutout.
It says that the over current protection will trigger depending on the value of the r1 resistor? What should it be if i want to trigger it if it goes more than 5v?
Also, what should the fuse current be? I was thinking of pulling one of the fuses off an arduino mega as i have several of them lying around....
Also, is there a module that has all of this already in it? I'd sorta like to keep it as compact as possible and if i have to solder everything its going to be BIG....
You could try a low drop out regulator - eg the LP2950ACZ-5.0
less than 0.5v drop, take +30 input ( given dissipation constraints)
regards
Allan
Qdeathstar:
It says that the over current protection will trigger depending on the value of the r1 resistor? What should it be if i want to trigger it if it goes more than 5v?
Nope, that's a bad circuit, the crowbar voltage is complelely ill-defined.
Look at reply #6 here: https://forum.arduino.cc/index.php?topic=365247.0
Hmm...
I see
but there are no values on that.... also, if is search for an "scr" on mouser i'm not sure what i am looking for.... I googled it and know it is some sort of schottky diode..
http://www.mouser.com/Search/Refine.aspx?Keyword=scr
And, i saw on the last page the "TSM112" but it doenst look like it is in stock anymore...
What about a TVS diode? They are pretty good for crowbar-ing and blowing a fuse
I think/thought the are only good for signal.....I'm using about 1 amp peak /500ma continuous....
can someone show me a link to an scr?
An SCR is a "Silicon Controlled Rectifier".
If you use that as a search term, you'll have no trouble finding plenty of info.
Here's an article on them:- The Silicon-Controlled Rectifier (SCR)
If you got to the Digikey site and search "SCR" you'll find plenty, too.
Alternatively, a buck/boost DC-DC converter might be worth considering, (as ilgargua meant when he mentioned a "sepic converter").
You can input a wide range of voltages, above and below 5V, and still get 5V output. eBay sell them for a couple of dollars. Just search "buck boost module", then read the listing carefully to ensure it steps both up and down, because often the listing title says "Buck Boost" when they're only one or the other.
Here's an example:- Boost Buck DC adjustable step up down Converter XL6009 Module Voltage S
(I don't know how good that particular one is, it's purely an example, the first I found.)
clytle374:
What about a TVS diode? They are pretty good for crowbar-ing and blowing a fuse
Are you serious? The ratio between clamp voltage and working voltage can be nearly 2:1
and its not going to latch like an SCR.
Use a crowbar circuit, its the thing for the job.
Qdeathstar:
Hmm...I see
but there are no values on that.... also, if is search for an "scr" on mouser i'm not sure what i am looking for.... I googled it and know it is some sort of schottky diode..
The zener voltage depends on the voltage, the resistor depends on the current needed to trigger the
SCR, the SCR depends on the kind of current you'll have to handle if it activates.
Another word for SCR is thyristor. It is not any kind of diode, schottky or otherwise.
