Hi,
I wanted to share my experience of Chinese TL431 super capacitor balance and protection board design and it's flaws. There are many of them available from various sellers.
This is photo of the board:
![](https://www.eevblog.com/forum/projects/chinese-tl431-super-capacitor-balancer/?action=dlattach;attach=661260;image)
The designer wanted probably do something like this:
![](https://www.eevblog.com/forum/projects/chinese-tl431-super-capacitor-balancer/?action=dlattach;attach=661308;image)
And circuit would work so, that it limits the capacitor voltage to 2.65 as seen in this plot:
![](https://www.eevblog.com/forum/projects/chinese-tl431-super-capacitor-balancer/?action=dlattach;attach=661272;image)
However the board had some design flaws and it actually was more like following circuit:
![](https://www.eevblog.com/forum/projects/chinese-tl431-super-capacitor-balancer/?action=dlattach;attach=661293;image)
Which was drawing current as soon as voltage was above 0.7V.
![](https://www.eevblog.com/forum/projects/chinese-tl431-super-capacitor-balancer/?action=dlattach;attach=661284;image)
So, there was two problems. TL431 was connected incorrectly, the layout would work with TL432, since it has ref and cathode swapped. And another problem was that SOT23 with marking Y2 was actually 12V zener(I verified this by desoldering it and measuring the breakdown voltage) and not SS8550, which would work and has also Y2 marking...
Cheers,
Wictor