Purpose of serpentine routing on battery balance circuit PCB

Question

I need a battery balance circuit, that I will either buy or design. I have seen serpentine routing between the load resistor and switching component in these photos (from china). In addition, it is not on the gate pin.

Could you please give some information about that?

I checked this question:Purpose of "wave shaped" PCB traces

I don't think I need "delay" and "Equalisation of length of pairs of traces". What could be the purpose of this routing?

Thanks a lot.

Why did you expect it on gate? And what is on the other side of the board. — , Dec 06 '17 at 06:14
@GregoryKornblum It is just estimation. I don't know what is on the other side of the board. What do you thinking about this serpentine routing? — Ugur Baki, Dec 06 '17 at 06:55
@GregoryKornblum Thanks for your reply but I think it is for high speed circuits, isn't it? — Ugur Baki, Dec 06 '17 at 07:30
Could be, but didn't you say it's switching power something? For high speed you expect smaller termination resistors and other components on the right. Although indeed they may or may not be trandidtors. — , Dec 06 '17 at 07:45
I'd guess it's intended to be resistive. Whether it's trimming the '430' resistors up to some other value ??? or a cheap non-replaceable fuse ??? or there's a buried connection we can't see and it a potential divider with the '430' ???, who knows? <-- Finger trouble, this should not have been an answer, but a comment. — Neil_UK, Dec 06 '17 at 11:03
A fuse in case the giant 43 Ohm resistor fails short? I admit that it is the most likely of several unlikely explanations. — user57037, Dec 06 '17 at 21:47
Since it's a balancer, it bleeds excess power as heat. My assumption is using the longer traces as heatsinks. — Bryan Boettcher, Dec 19 '17 at 16:18

score 4 · Answer 1 · answered Dec 22 '17 at 16:48

4

It is thermal decoupling of the relatively small transistor from the power resistor. Such that they can be physically close without risking the power resistor heating up the transistor and causing it's characteristics to change.

Guessing this is a MOSFET (the top mark A2xxx is too vague to be sure) The source-drain resistance increases with temperature, leading to a rise in power dissipation and hence thermal runnaway.

Preventing the initial external heating would help prevent the possibility.

answered Dec 22 '17 at 16:48

Jay M

3,753
15
30

I wonder how much the "meander" helps, considering that the source trace is thicker, straight and passes right by the power resistor.. – Wesley Lee Dec 22 '17 at 16:56
I could not think of a better reason (other than mechanical decoupling which would not make sense given other things on the board). As I don't know the parameters or the circuit design there is no way for me to model it. I think this one would be down to the experience of the original engineer. My guess is they got it wrong first time and then added the meander to fix the issue. – Jay M Dec 22 '17 at 17:16
2

Btw the fuse idea is daft. The sot23 is good for at least 100mA, whereas that size of copper could probably handle 30-40A for a short while or 5A+ indefinately. Much longer than the sot23 would last. – Jay M Dec 22 '17 at 17:33
Yeah, I'm not saying I disagree with you, just that it looks like a poor implementation of the idea. – Wesley Lee Dec 23 '17 at 02:03

Purpose of serpentine routing on battery balance circuit PCB

1 Answers1