Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Reverse Polarity Protection - Bridge Rectifier

Status
Not open for further replies.

mkay9

New Member
Hi Guys

I need to Polarity Protect a 24v Dc to 12v Dc converter, the unit is rated to 3Amps. Having read the various different threads on this topic i was looking to go with a bridge rectifier to switch the polarity automatically. Any ideas on a suitable model Schottky Barrier Rectifier that will be suitable for this use.

Also would it be wise to install a fuse in this circuit to protect from overload as the supply is upward of 3Amps? Would
the fuse need to be fitted after the bridge rectifier on the posotive side or can it be positioned before it with the unknown polarity?

Any help and ideas would be much appreciated..
 

MikeMl

Well-Known Member
Most Helpful Member
I have worked on avionics and ham gear which typically has a series fast-blow fuse, and a shunt normally reversed-biased Silicon diode. That way, there is only a tiny forward drop across the fuse. The diode conducts only if the input polarity is reversed, and the fuse vaporizes...

Putting one or two diodes in the forward path would create an unacceptable voltage drop on most of the gear I am familiar with...
 
Last edited:

RODALCO

Well-Known Member
You can also fit a double pole double throw relay in line which you can wire up so that the polarity is always correct.

Haven't got the schema but have seen it in operation on a 12V accu fed PA amplifier.

No voltage drop in the latter.
 

Roff

Well-Known Member
A bridge rectifier sounds like it should work for you, assuming the converter can tolerate the voltage drop of the bridge. I'm wondering why you want to use Schottky?
 

mkay9

New Member
A bridge rectifier sounds like it should work for you, assuming the converter can tolerate the voltage drop of the bridge. I'm wondering why you want to use Schottky?

I was thinking the schotty would be the least loss in voltage having read other threads..
 

Roff

Well-Known Member
I was thinking the schotty would be the least loss in voltage having read other threads..
What sort of circuit is your converter? Is it a linear regulator, or a switcher? Most converters with 12V output can tolerate 22V input as well as 24V.
 

mkay9

New Member
What sort of circuit is your converter? Is it a linear regulator, or a switcher? Most converters with 12V output can tolerate 22V input as well as 24V.

Not sure what type it is but i have tested it on a controllable DC source and it worked fine down to 22v..
 

Roff

Well-Known Member
I don't know where you are, but a bridge like this should work. You might find something cheaper or more suitable. A Schottky bridge might save a little power if your converter is switch mode.
 

mkay9

New Member
Ok thanks for that.

What do you think about the use of an in-line fuse. Would this be better situated before the rectifier or positioned on the posotive output after it?
 

Roff

Well-Known Member
Ok thanks for that.

What do you think about the use of an in-line fuse. Would this be better situated before the rectifier or positioned on the posotive output after it?
I would put it in front of the bridge, which will also protect the bridge in case of a short on its output.
 

Hero999

Banned
The problem with a fuse is it needs to be replace, if you use a polyswitch it doesn't.

A single Schottky diode could be used if you don't like the idea if shunt protection.

The problem with using a bridge is that there's two diode drops.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top