reverse polarity protection and charging circuit

Other Hardware General Electronics
1

hey

so i'm working on a battery power project witch mens i need reverse polarity protection on my inputs i found that p-channel ore a n - channel mosfet properly is the bedst way to go as there is no voltage drop...

but i'm having truble choosing the bedst circuit / designing the specifiks off this here is my stats

it's gonna run a 18650 li-ion 4.2 to 2.8 volt battery
max current draw peaks around 200 ma
most off the time current draw is gonna be less then 1ma ( deepsleep mode off an esp8266)

i made this circuit to see the effekt off a p-channel mosfet but i'm unable to simulate the advance diffrences on the mosfet
falstad.com

any one that can sugest a good p mosfet for this job ?

also any one aware off a circuit with allow the option to charge and have reverse voltage protection ?

2

Before we get into any discussion about your issue could you please tell us what your electronics experience is ? (how did you learn electronics and how long have you been doing electronics)

This information is necessary to compose replies that can be understood by the OP. It is pointless to post replies siting datasheet specs if the OP doesn't have a clue how to read a datasheet. If we know this in advance we can word the replies to suit the poster. This is a standard policy on the forum.

Post a schematic of the proposed circuit.

Standard reverse polarity protection is simply a diode in series with the input with the cathode connected to the load. A diode from Vcc to GND with the cathode connected to Vcc is also common.

I don't think your P-channel circuit is relevant to your post.

3

i have no real experience only on circuit bulding and in the use off mosfets ... :frowning:

i don't wan't to use a diode becouse off the efficiency sinse it's a battery powered project and learning perpeses

check the cercuit on the falstad link

4

Let me spell it out for you. If you ASK for reverse polarity protection, you are in effect asking for a diode. The circuit you linked has nothing to do with what you are asking for.
Eigher use a diode or you use KEYED battery connectors that PREVENT reverse polarity.
Those are your options.

5

http://provideyourown.com/2012/reverse-polarity-protection-circuits/

so whats bescribe in above article under p-channel FET is all wrong?

6

No. That will work. However I would advise testing it with a reversed LIPO battery to see if it works.
(apply -5V to input)
( using a 470 ohm resistor "dummy" load)
You need a small P-channel mosfet rated for 500 mA.

Look for LP0701N3-G

7

i will test every thing before i connect to my microcontroler :stuck_out_tongue:

as for the dioed is there any speficik karakteristisk it need's ? ore will a basic 1N5400 work fine?

8

Any 1A or better rectfier diode will work, including the 1N5400.

9

thanks for alle the replays :stuck_out_tongue:

so i been looking for a place to bay the "LP0701N3-G" but i'm having truble finding at a price where shipping is not like duble item cost :frowning:

any othere sugestions ?

10

Do a search on a local vendor website for 500 mA P-channel mosfet

11

so i found this FQP47P06

http://pdf1.alldatasheet.com/datasheet-pdf/view/52386/FAIRCHILD/FQP47P06.html

shut work right?

12

simondid:
shut work right?

Not likely.
Unless your battery is something like 8volt.
You need to find a P-channel fet with a max gate threshold voltage less than half your lowest battery voltage.
Good luck with that.
Leo..

13

so thats like 1.4 v right where as the one i link has a minimum off threshold 2v ?

won't this just mean that it will shut off the battery if it's go below 3v?

i watch this video witch How to protect circuits from reversed voltage polarity! - YouTube is it wrong ? and way are you saying it's half?

14

This can be good for you.

Ciao, Ale.

15

seems to fit what i need :stuck_out_tongue: but agien sourcing seems to be a problem also is there a thruhole version off this?

16

Thru hole version of a P-channel MOSFET?
Here's a big listing of what's available. Lot of duplication due to lot-sizes to buy and delivery packaging methods (tube, reel, loose, etc)
http://www.digikey.com/product-search/en/discrete-semiconductor-products/transistors-fets-mosfets-single/1376381?k=p-channel+mosfet&k=&pkeyword=p-channel+mosfet&pv69=80&FV=fff40015%2Cfff8007d&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

17

is there a thruhole version off this?

No. If there was it would be on the same datasheet.

18

No TH version, but you can use this as adapter. Both are sourced by Farnell, and problably others.

Ciao, Ale.

19

simondid:
so thats like 1.4 v right where as the one i link has a minimum off threshold 2v ?

I said maximum, not minimum.
These low Vgth fets are almost impossible to get in through hole.
Leo..