Proction circuit for the output of a protection recharger

[rprodrigues]

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

 

[Nigel Goodwin]

A common way would be just a single rectifier diode.

 

[MikeMl]

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?

 

[rprodrigues]

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?

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

 

[rprodrigues]

A common way would be just a single rectifier diode.

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.

 

[MikeMl]

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

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...

 

[MikeMl]

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

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

 

[rprodrigues]

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

MikeMl,

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