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Black Knight , 09-21-2024, 07:25 AM

I have designed a 2 layer gate driver board. It works with 12V supply. I have attached the schematic and PCB files.
If anyone could help me review the design and feedback would be very helpful.

I am testing it on a three phase three leg inverter of SiC Mosfets and trying to run a 5hp induction motor. The following are some of the issues that I am facing.
1. When board is supplied through a 12V/2.1A SMPS the motor does not run but when powered thorugh a DC regulated power supply set at around 12V the motor runs.
2. When motor is on no load it runs smoothly without any problems. On achieving full speed when the motor is loaded the DC power supply drops and sometimes the motor speed also drops drastically.
3. On higher frequencies above 50kHz the motor does not achieve full speed as well. There is a drop in the driver supply voltage and motor loses speed.
4. On resistive load at higher frequencies above 50kHz the outputs waveforms are distorted.
5. I chechked for shootthrough there is none. And there is sufficient dead times in the gate signals observed on the gate and source terminals of the mosfet.

Any more details needed I can share and would be happy if I can receive any assistance.

QDrives , 09-21-2024, 11:26 AM

We cannot review it as the schematic does not show any values of resistors, capacitors, etc.

Black Knight , 09-21-2024, 06:01 PM

I will fill in the values on the schematic and post it here

Black Knight , 09-22-2024, 05:08 AM

Black Knight , 09-22-2024, 05:09 AM

I have attached the schematic with values

Black Knight , 09-22-2024, 05:09 AM

Please review and help

QDrives , 09-22-2024, 12:36 PM

U2 and U3 are 12V input modules, not 24V. Same probably goes for U1.

Which capacitor is electrolytic and which is ceramic? Have different symbols for them.

When you talk about 50kHz, it is also important to know which SiC is on the output. How long is the connection between bridge driver and Fets?

Black Knight , 09-22-2024, 01:49 PM

No I am using 12V for everything like mentioned on schematic. I am not using 24V. Only the capacitors on power supply modules I am using electrolytic. Rest all on gate drivers are ceramic

Black Knight , 09-22-2024, 01:51 PM

nthl070n120m3s

Black Knight , 09-22-2024, 01:51 PM

Thats the sic device

Black Knight , 09-22-2024, 01:52 PM

Connection between bridge and fets is done from PCB to device mounted on a heatsink through wires.

Black Knight , 09-22-2024, 01:52 PM

Around 5 cm

Black Knight , 09-22-2024, 01:55 PM

Also what kind of snubbers should I be using?

QDrives , 09-22-2024, 03:36 PM

From -12V to +12V is 24V.
What do you have at the FETs?

Black Knight , 09-22-2024, 04:19 PM

No no that -12V means the 0 point. DC 0 point. It’s 12V only.

Black Knight , 09-22-2024, 04:20 PM

What do you mean by what do you have at FETs? I didnt get it

Black Knight , 09-22-2024, 04:22 PM

Also is it better to put the FETs on the PCb as well rather than outside of it?

QDrives , 09-23-2024, 12:28 AM

-12V means that, but if you mean Gnd, then name that net. Or make sure it is clear what the reference is of +12V.

And yes, it is better to have the fets close to the driver. I have not looked at the specs of the fets yet.

Black Knight , 09-23-2024, 12:46 AM

Okay will make sure to reference the nets properly.
And could you please have a look at the fets and suggest if there are any changes?
Could you suggest some values for snubbers I could use for the fets?

Black Knight , 09-23-2024, 01:05 AM

The kind of outputs I am seeing

Black Knight , 09-23-2024, 01:05 AM

QDrives , 09-23-2024, 01:32 AM

Output of what? The driver or half bridge?
What capacitance do you have at the fets, or are the fets kind of alone?

Black Knight , 09-23-2024, 01:43 AM

Output at the half bridge when 2 half bridges are connected in a 3 phase 3 leg configuration

Black Knight , 09-23-2024, 01:43 AM

Fets are alone in this without any snubber

Black Knight , 09-23-2024, 01:43 AM

Directly from driver to fet

QDrives , 09-23-2024, 01:53 AM

What is the current drawn? Are all still no-load?

Black Knight , 09-23-2024, 02:18 AM

The output waveforms I have shown above are for resistive load. Its very low voltage of 15V DC input to the three phase inverter. Current is around 50mA.

When I am running on motor I give full voltage of 560VDC. But the motor is not loaded.

The waveforms if you can see in the video are not continuous either.

Black Knight , 09-23-2024, 02:19 AM

Any suggestions what value of snubbers I need to use?

QDrives , 09-23-2024, 11:46 AM

I would say your biggest problem is the inductance of the traces between the driver and fets.
To start, you could increase the gate resistances - 10 ohm for off and 47 ohm for on.

Black Knight , 09-23-2024, 02:49 PM

Would it help if I extended the board and mounted the FETs on PCB itself?
And also please could you suggest what snubber would be suitable?

Black Knight , 09-23-2024, 02:49 PM

I will definitely change the gate resistors and see though

QDrives , 09-24-2024, 11:58 AM

First have the design right before doing snubbers. Yes they are needed, but values depend on the rest of the design.

Why are the fets not on the board?

Black Knight , 09-24-2024, 02:49 PM

We usually keep the FETs outside on heat sink to make our kits hence I did the same. Never kept the FETs or IGBTs on the same driver board before

QDrives , 09-24-2024, 03:12 PM

But I assume you were switching a lot slower then?
Faster switching requires more control.

Black Knight , 09-24-2024, 03:13 PM

Yes definitely the switching frequencies were much lesser.

Black Knight , 09-24-2024, 03:14 PM

By the way I changed the gate resistors and the driver works much better. Works on SMPS also. 5hp motor working well on low loads upto 500khz switching frequency

Black Knight , 09-24-2024, 03:14 PM

Tomorrow I am testing for full loading and will update you. It was a big help.

Black Knight , 09-24-2024, 03:15 PM

I am also extending the board to accommodate the FETs on it as well and try it out. 👍