Proction circuit for the output of a protection recharger

Hi all,


The title is wrong ! I am sorry!

That should be "Protection circuit for the output of a battery recharger".

Any way, I am implementing a way to protect my recharger output against reverse battery polarity connection.

I am using a P-MOSFET (low Rds during ON state) and a TIP31C (or any other NPN) as its driver, the way that is shown above.

**broken link removed**


What do you think about it ?

Is there any common way to do the protection I am looking for?

During simulations (using Multisim) it seems to work fine.

Is there any other suggestion?

Thank you

A common way would be just a single rectifier diode.

What turns on the TIP31C? It seems that it is off if the battery polarity is correct, meaning that the P-Fet is off too. Something is wrong. Maybe if you reverse the emitter and collector of the TIP31?

MikeMl said:

What turns on the TIP31C? It seems that it is off if the battery polarity is correct, meaning that the P-Fet is off too. Something is wrong. Maybe if you reverse the emitter and collector of the TIP31?

Click to expand...

The TIP31 is turned on by a correct connection of the battery (+Vbat at the R4 and -Vbat at the TIP emitter).

Nigel Goodwin said:

A common way would be just a single rectifier diode.

Click to expand...

That could be the simplest way for me, but the battery recharger uses the voltage level from the battery to control the current to supply. (It's a tree state recharger for 12V baterries), so the drop at the diode is not wellcome.

rprodrigues said:

The TIP31 is turned on by a correct connection of the battery (+Vbat at the R4 and -Vbat at the TIP emitter).

Click to expand...

I dont see it. For that to happen, as I said above, the emitter and collector would have to be reversed... You are saying the right words, but your diagram has the transistor backwards...

rprodrigues said:

... so the drop at the diode is not wellcome.

Click to expand...

So just set the trip points for the controller higher by Vf of the diode. Use a Schottky.

MikeMl said:

So just set the trip points for the controller higher by Vf of the diode. Use a Schottky.

Click to expand...

MikeMl,

You are right!!!!
It was inverted in the schematics, but I fixed it now.
Thank you for your informations!