Hi,
I’ve bought a ready kit from my local electronics shop.
(Yes, I still have one physical shop in my city.)
The kit is a MOSFET DC Motor speed driver.
Naturally, the kit never worked. After attaching a 12V power supply and a 12 volt motor nothing worked. Then I found out:
D3 was blown
ZD1 was blown
the mCU was blown
Then I reversed engineer the PCB and I am pretty sure the schematics is as follows (see attachments).
Questions:
1. Should there be a current limiting resistor in series with D3 and ZD1. The kit claims up to 90V in. That would always blow the zener, wouldn’t it? Is this a design mistake? I triple checked my reverse engineering process. Also the only resistor on the PCB is the 10 ohm in series with ZD2. There are no other resistors on the PCB.
2. D1A is reverse polarity protection. But why they attached D1B to ground? What is D1B doing? It seems like a waste.
3. What is the ZD2 doing? Is it over-voltage protection for the input of the mCU?
Thank you in advance for any hints.
P.S.
Info about the mCU can be found here:
https://www.eevblog.com/forum/beginners/identify-chip-mosfet-low-side-driver/