I want to add a charger circuit to my build. Unfortunately this circuit does not have a reverse polarity protection.
Obviously I can not use a diode since it will not allow charging.
Do you have an idea how to protect the circuit?
https://www.fasttech.com/products/5054400
i think it might have some built in reverse protection, the blocking diode action is done by the FETs, which must be active to operate. It is using a 4056 Li charger chip plus a DW01 single cell protection chip and the third chip is likely a dual FET but i can’t read the part number. It’s dirt cheap, for that price it’s worth buying a few and just test one in reverse to see how it does. It protects for both charging and discharge, and it has a 3A current limit when driving a load, so that might affect your build?
But on page 12 it shows how to add a P-FET (with body diode) in a Drain and Source swapped configuration to provide reverse polarity protection.
4056 datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/405642f.pdf
Here’s another 4056 chip datasheet, which one is being used—probably not the Analog Devices? But still could use the same swap-ended P-Fet trick to add reverse protection.
http://www.tp4056.com/d/tp4056.pdf
DW01 datasheet and sketch:
http://www.tp4056.com/d/dw01a-fs.pdf
And the 3rd chip dual FET may be an 8205A.
“how to add a P-FET (with body diode) in a Drain and Source swapped configuration to provide reverse polarity protection.”
Some ideas below:
Depending on what IC is using, it may have reverse battery protection built in. I know a project utilizing the LTC4053 does. Still I wanted to know if the battery was inserted backwards which is why I have R11, R12 & D5 giving me a low or high signal back to the microcontroller
+1 hiuintahs, excellent FET diagram and interesting schematic.
replae tp4056 with tp4056x
tp4056x
YuvalS,
On that schematic where I showed, R11, R12, & D5, they don’t do anything for reverse polarity protection on the LTC4053 as the LTC4053 has internal protection, but what those components do is prevent –4.00 volts (or whatever the battery voltage is when backwards), from taking out the input to a micrcontroller since a negative voltage that high would be detrimental to the microcontroller……….but is not a problem for the LTC4053. So those are irrelevant to what you are trying to do.
For input power reverse voltage protection use the diagram with the p-channel FET (2nd one down). This is a very common technique. Probably used in a lots of flashlights. I don’t think this is relevant to you because you are trying to protect the output of the charging device from a backwards battery. It’s a different scenario when you have power sources on both sides of the FET………you have to think it through.
I was trying to come up with a way of using just one FET for the ouput and I just couldn’t come up with a fail safe operation. What you have to look at is what happens when just the battery is in place and no charging power yet, or the battery is in backwards and not charging power yet, or you do have charging power and then the battery is put in backwards. You have to go through these scenarios in your head with an understanding of how p-channel and n-channel FETs turn on.
For me what I have done is put two back to back p-channel FETs such as shown in the 4th diagram. Nothing happens (no current flows in either direction) until the Gates are pulled to ground. It doesn’t matter what polarity the battery being charge is at, no current flow and nothing gets burned up. But what you need is a notification means that the battery is in backwards or some type of interlock preventing the gates from going low until the backwards battery is corrected. That just means a little more cicuitry.
I’d have to really think about this for awhile to come up with just a simple passive way of protecting the output with just one FET. What you could do is get yourself a couple of FETs and just prototype them in a couple of different configurations to see what is happening. Just remember that a P-channel FET is turned on when the Gate voltage is lower than the Source. And an N-channel FET is turned on when the gate is higher voltage than the Source. Knowing that you can play around with configurations.
Also keep in mind that current typically goes from Drain to Source on an N-channel FET and from Source to Drain on a P-channel FET. And this is usually dictated because of the orientation of the internal body diode. But keep in mind that current can flow in either direction D to S or S to D as long as the Gate is held at a lower voltage than the Source pin on a P-channel FET. In the case of blocking current in both directions, the FETs have to be positioned such that the body diodes won’t conduct. And thus one of the FETs current flows D to S and the other S to D.
Thanks for the detailed explanation
First off all do not buy crap. Get TP4057 or better this one
low voltage protection? drivers have low voltage protection
Not all drivers.
¯\/¯ So get proper one or use protected battery or with separate battery protection board
Apparently the revers polarity is an issue for the protection features and not for the charging board