hello everyone
I am making a project that works with dc voltage that I don't know its polarity which if reversed will fry it
so I am searching for something that takes dc voltage and makes sure that its output polarity is correct

please be easy with me it is my first thread and I am just a beginner
Thank you

 

Look up "rectifier".

 

You need a bridge rectifier.

https://en.wikipedia.org/wiki/Diode_bridge

 

A diode or bridge rectifier will work if you can tolerate the voltage drop of of one or two diodes in series with the supply.

If you just need to protect against reverse polarity then you can use a MOSFET as discussed here, which will give a very small voltage drop in the normal direction with the selection of a MOSFET with sufficiently low ON resistance (which can go to the low milliohm region).

 

Thank you very much MRchips

You need a bridge rectifier.
https://en.wikipedia.org/wiki/Diode_bridge

and Wbahn

Look up "rectifier".

 

A diode or bridge rectifier will work if you can tolerate the voltage drop of of one or two diodes in series with the supply.

If you just need to protect against reverse polarity then you can use a MOSFET as discussed here, which will give a very small voltage drop in the normal direction with the selection of a MOSFET with sufficiently low ON resistance (which can go to the low milliohm region).

No, I need a something that will take a DC input with unknown polarity and output voltages with one polarity
not just protection against reverse polarity

and also thanks crutshow for the reply

 

A bridge rectifier will do what you need. The output voltage will be a bit lower than the input voltage by two diode drops, or about 1.4 VDC.

 

A bridge rectifier will do what you need. The output voltage will be a bit lower than the input voltage by two diode drops, or about 1.4 VDC.

Yes I can deal with that 1.4V drop
Thank you for mentioning that

 

A bridge rectifier will do what you need. The output voltage will be a bit lower than the input voltage by two diode drops, or about 1.4 VDC.

You can reduce that a bit (generally to less than a volt, depending upon the current) by using Schottky rectifiers.

 

hello everyone
I am making a project that works with dc voltage that I don't know its polarity which if reversed will fry it
so I am searching for something that takes dc voltage and makes sure that its output polarity is correct

please be easy with me it is my first thread and I am just a beginner
Thank you

Engish doesn't seem to be Morad's first language. I see the possibility of a different interpretation of the question. Does he actually have a project (or device) that requires DC and he doesn't know the correct polarity. (or it will fry)
Of course a bridge will ensure that random power sources can be made to present the same polarity at the device but Moran needs to confirm what he actually wants.
An examination of the circuitry in the project would probably help if the polarity of major electrolytics were looked at.
But I may be wrong..

 

Engish doesn't seem to be Morad's first language. I see the possibility of a different interpretation of the question. Does he actually have a project (or device) that requires DC and he doesn't know the correct polarity. (or it will fry)
Of course a bridge will ensure that random power sources can be made to present the same polarity at the device but Moran needs to confirm what he actually wants.
An examination of the circuitry in the project would probably help if the polarity of major electrolytics were looked at.
But I may be wrong..

I don't know the polarity of the DC input (Telephone line) so I was searching for a device that will correct the output polarity if it was reversed to make it match my projects polarity (Which I know)
And I have been advised to use a bridge rectifier for this task in the previous replies
So do you recommend anything else ?

Thanks for bearing with me

 

Ok..so if the source of DC is a telephone line, one thing you can rely on is that in a given country the polarity will not change. I believe that in the UK for instance the +ve is at or near ground potential and the "live" line is - 48v. Can you not just protect your device with a fuse and a reverse biased power diode, having determined what the telephone line is supposed to be ?.

 

I suppose you could use a Cen-Tech give-away voltmeter to measure the polarity.

http://www.ebay.com/itm/like/361578595082?lpid=82&chn=ps&ul_noapp=true