Hi! This is my first post here and sorry if not is the correct topic..

I'm designing a circuit to control a DC motor using DRV8837 H-Bridge driver. This circuit also have a LED lamp with 3x 3528 SMD LED connected in parallel.

The problem here is that if i meassure between +9V pad and -VCC_LEDS terminal i get 9v but mosfet's gate is not receiving any voltage from SW1 or SW2. How it's possible that mosfet are flowing current between source and drain without apply any voltage to the gate?

Hope that you can help me.

Thanks in advance!

 

Don't understand your problem.
Please state clearly what all the DRV8837 input and output voltages are.

 

cross-posted over here https://www.eevblog.com/forum/beginners/ao3400-mosfet-problem/

 

The MOSFET gate is connected to input pins on the H-bridge driver? How is that supposed to work?

 

Your SW1 and SW2 nodes need pull-down resistors. Without them, any gate voltage which they supply directly will stay high and the associated FETs will stay on.

 

Thanks by your answers. The problem was a faulty mosfet. I bought it from aliexpress and all of them are faulty...

 

Your SW1 and SW2 nodes need pull-down resistors. Without them, any gate voltage which they supply directly will stay high and the associated FETs will stay on.

In the schematic, there is nothing driving those pins.

 

The problem was a faulty mosfet. I bought it from aliexpress and all of them are faulty...

I have this thread in the Marketplace forum for reporting bad experiences with AliExpress, and other sources.

I include information about the Seller, product, and dispute resolution.

That being said, I have not had problems with faulty MOSFETs from AliExpress. Improper handling certainly, but they were power devices and passed 100% testing for leakage current, threshold voltage, and basic functionality. The lots of AO3400/1 I bought from several different sellers were okay.

 

In the schematic, there is nothing driving those pins.

A modified schematic is shown way down in the post #3 link. Pity the TS didn't think to post it here.