Troubleshooting SpeedVal Kit Half Bridge Motherboard

SNaidoo

Good Day,

I am using the Wolfspeed Speedval Kit Half Bridge Motherboard with the Buck/Boost Filter Board. When I previously used the motherboard it worked fine but for our application, we desoldered the film capacitors and re-soldered 2 of them and the board is not working as before. The main issue I think is that when I apply the 12V, ~15 V shows up on the output. When I try to run the boost converter, I get an overcurrent error so I think that for some reason both FETs are being driven at the same time but I could be wrong. Could I get some help troubleshooting?

Thanks,

Surendra Naidoo

Forum_Moderator

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AAnders

Hello,

Can you provide a few additional details.

1. When you say you apply 12V and 15V shows up on the output, are you referring to the 12V control power? Is 15V showing up on the HV bus?
2. Can you check the gate signals to make sure that the MOSFETs are not both gated on?
3. Remove the power daughter card and verify the MOSFETs are not shorted by checking the body diode with a multimeter. Meaning a diode drop is measured from source to drain of each MOSFET, not a short.
4. Monitor the current on the DC power supply when you apply bus voltage. It should draw <10mA until you turn on the converter.

With this information, we can continue to debug the issue.

Thanks,

Adam

SNaidoo

Good Day,

1) Yes, 12V control power from the DC power supply, I am reading 14.19V on the HV bus (and 7.1 V at the midpoint)

2) On both MOSFETs the Gate-Source voltage is -3.3 V.

3)The MOSFETs are not shorted, I am reading about 1.10 V drop across the body diode of both MOSFETs

4) The current on the DC power supply reads 0.36A with no bus voltage applied and before I turn on the converter.

Regards,

Surendra Naidoo

AAnders

Hi Surendra,

Which gate driver board are you using? Some of the cards have a DESAT detection circuit, which has a pull-up to the +15V gate bias rail that is then connected to the drain of the MOSFET through a blocking diode. I believe the DC bus charging may be due to this circuit providing a trickle charge to the DC bus when the control power is on and no load is connected to the bus. You can check this by unplugging the gate driver card and verify that the DC bus remains at 0V. This behavior would not indicate a problem, it is an expected result from the way the DESAT circuit is designed.

Circling back to the main issue, can you provide more details about the overcurrent error. Where is this error being triggered (DESAT fault, SpeedVal GUI, power supply, load)? Is it occurring immediately when the converter is turned on, or at a specific power level? Can you share a scope image of the lower Vds, lower Vgs, the IDS of the lower device measured in the current shunt, and the boost inductor current? This will help to pinpoint the issue.

Thanks,

Adam

SNaidoo

Good Day,

I am using the CGD1700HB2M_UNA gate driver board. When I remove the gate driver board the bus voltage remains at 0V so it's good to know that that behaviour is expected. I was getting the overcurrent error on the SpeedVal GUI immediately as I turn the converter on even with no input voltage but I noticed I was getting that fault when I selected "Unspecified" for the gate driver and when I select the correct driver I do not get that fault.

Unfortunately, I currently do not have the available lab equipment anymore to run the tests with a load and input voltage but I will try to once I get the equipment.

Regards,

Surendra Naidoo

SNaidoo

Good Day,

I was able to get the board working. Thank you for your support!

Regards,

Surendra Naidoo

TBhatia

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.