why there is a continuity between 3.3V rail and GND?

Thread Starter

BrokenPin

Joined Oct 1, 2023
11
Howdy,

I have the EVAL_4kVA_230VAC_5LINV 5-level active neutral-point-clamped flying capacitor (ANPC-FC) inverter evaluation board at my university. When I tried to use it I found out that there is a partial short (low impedance ) between the 3.3V rail and the ground in the control board like 20 Ohms.

I tried to remove the 12V to 3.3V buck converter IC but the same thing the problem persists ..i thought maybe one of the decoupling caps might be causing the problem but there are like 20 of them and that's going to take lots of time to check them all.. plus there are no hot spots on the board !! I am thinking maybe the MCU is dead or at least some power pins are damaged..

I believe the problem started when a colleague of mine reversed the 12V polarity ...
you can find a schematic of the control board on pages 22 and 23 of the app note.
Here is a picture of the board..
r.jpg
what could be causing this problem on the board? is it the MCU?

Thanks,
 

nsaspook

Joined Aug 27, 2009
13,291
Howdy,

I have the EVAL_4kVA_230VAC_5LINV 5-level active neutral-point-clamped flying capacitor (ANPC-FC) inverter evaluation board at my university. When I tried to use it I found out that there is a partial short (low impedance ) between the 3.3V rail and the ground in the control board like 20 Ohms.

I tried to remove the 12V to 3.3V buck converter IC but the same thing the problem persists ..i thought maybe one of the decoupling caps might be causing the problem but there are like 20 of them and that's going to take lots of time to check them all.. plus there are no hot spots on the board !! I am thinking maybe the MCU is dead or at least some power pins are damaged..

I believe the problem started when a colleague of mine reversed the 12V polarity ...
you can find a schematic of the control board on pages 22 and 23 of the app note.
Here is a picture of the board..
View attachment 311371
what could be causing this problem on the board? is it the MCU?

Thanks,
Check D49 zener for a short.
 

Thread Starter

BrokenPin

Joined Oct 1, 2023
11
Check D49 zener for a short.
D49 isn't in the control board but is part of the main board ..
the whole kit consists of one main board which contains all the power circuitry, 3 gate driver boards, and a control board...
I connected the control board to an external DC power supply to test it separately.. the buck converter works fine, it gives stable 3.3V and the control board draws about 150mA while nothing seems to get hot ..
but the continuity between 3.3V and ground is still there.
 
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