[SOLVED] Issue with Contactor Driver Circuit – MOSFET Burns at Higher Voltage

Recker039

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Hello everyone,
I have designed a contactor driver circuit that operates in two modes:
  1. It initially provides an inrush current (limited) to the contactor coil to engage it.
  2. Immediately after engagement, it supplies a constant holding current of approximately 50mA.
This topology worked well for 95A contactors. However, when I scaled up to high-power 265A contactors, I encountered issues.
  • For the 95A contactor, it engages with an initial current of 3.5A.
  • For the 265A contactor, it requires approximately 6.5A to engage.
Problem:
When operating at voltages between 110V and 180V, the MOSFET does not burn. However, above 180V, the MOSFET burns immediately when I switch on the circuit.
Some colleagues suggested:
  • Increasing the gate resistance
  • Adding an RCD snubber in parallel with the existing snubber
However, these modifications did not resolve the issue.
Components used:
  • MOSFET: STP30N65M5
  • IGBT (tested but same result): FGH60N60SMD
I would appreciate any insights on what might be causing this issue and possible solutions.
Thank you!

 

Solution
C
It sounds like the voltage across your shunt is going up and deleting from the VGS...so the FET is in linear region.

What is the required coil voltage and current of the contactor's control coil?......surely the contactor's control coil shouldnt be across the rectified mains?
Or is that a "low side buck converter" for driving the contactors coil?....beware your 250m inductor is saturating?
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Connect the clamp diode directly on the contactor terminals. If the MOSFET survives, the problem is related to the clamp diode wiring.
You should not have long wires between the clamp diode and the contactor.
What is the purpose of R13? If it is for speeding up the contactor release, maybe it is better to have it in series with the clamp diode only.
 

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R13 is coil resistor.
 

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You told you are using a PMW'ed output to tune the MOSFET current drain, but there is no Capacitor at the Gate; once Contactors have very high inductance, you are in shorts just creating a huge EMI generator, having the Contactor coil acting as antenna. Review the LP filter caracteristics of the gate RC to cut off the switching frequency.

​

 

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Yes, it is very poor to use the contactor coil as a Buck converter inductor. Can you lash up a little buck converter with properly selected inductor, and use that to power the contactor coil. Also, please send us your PCB layout files.
 

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There is a very important tradeoff when slowing down the Gate Tr and Tf to lower EMI.
And that is power dissipation in MOSFET when increasing its time spent in linear mode.

The combo of Ciss and miller presents a lot of Cat gate. See gate waveform below -

 
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100 ns Tr, Tf and 10 uS Tr, Tf, spectrums -





But looks like the impact is positive overall......
 
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danadakk said:
100 ns Tr, Tf and 10 uS Tr, Tf, spectrums -

View attachment 197707

View attachment 197708

But looks like the impact is positive overall......
Click to expand...
Thank you very much for taking the time to analyze the circuit!
Basically, as the time Tr and Tf increase, the transition loss of the circuit increases. This is obvious... Now, is your suggestion to use a more powerful driver to drive the gate? UCC 27524 can't drive that fast?
 

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The sim implies average power seems OK.

Real question is part outside SOA (I dont think so), or is there a L generated
HV rupturing gate oxide ? Which also would lead to question is fast diode
used for clamp OK ? Possibly due to wiring/layout, the reason we keep asking
for pictures of prototype. And have OP see if there is a short of gate to
either source or drain.

Regards, Dana.
--- Updated ---


Generally look for increased current for driver. But first task is try to get
an idea of what hosed the MOSFET, excess V or out of spec SOA condi-
tions. Seems like its tied to excess drain V which your original post
called out. Yet part used has a lot of margin it seems.

Note I caught an error I made, in your original post on the schematic is
SIPC69N60C2, and thats what I called out for excessive input C for the
driver you have. The other two mosfets are in the range of C for your
driver. Take a look at driver and mosfet datasheets.

Do you have screenshots for driver and mosfet V's when operating att he <= 180 V
drain conditions ?

Regards, Dana.
 
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Which version of UCC3813 are you using...50% max duty or 100% max duty?
UCC3813

In your post #20 you still do not show the full schem.
Please show what voltage is for Vcc of ucc3813?
Please show version of ucc3813
Please give datasheet for contactor.
Please give the input voltage....you say "155v 310V".....do you mean 155VAC, 50Hz, ? etc etc

Attached pse find LTspice of your circuit......pse get this working first, then go to your cct.

BTW you have a waste of time cct from FB to COMP....just ground FB and leave COMP floating.
LT1243 is pin4pin with UCC3813 but we need you to tell us which version of ucc3813.

There is IMVHO a rule of electronics, just like Ohms Law or Faradays Law.......the rule is "get it working on the LTspice simulator before building it on the bench"

Thanks for posting schem so far BTW, i am sure all at your company will realise that this is just a standard schem, and will not accuse you of giving away deep secrets!
 

Attachments

  • Buck contactor coil driver.png
    57.1 KB · Views: 21
  • Buck contactor coil driver.zip
    1.3 KB · Views: 19
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Might look into pulsed SOA vs average / DC SOA and the duration of the "peak" phase of your peak / hold vs the pulse width dependence of SOA in the charts, if any.
 

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Thanks yes....and i am wondering, is that actually the diode thats there....pse i hope OP will double check.
 

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danadakk said:
The diode -

View attachment 197727
Click to expand...
i am using
BYC10-600.

--- Updated ---

I am using the ucc2802, which has a maximum duty of 100%.
I sent scheme.
I am using 155V to 310V Fullbridge rectifier.
what is IMVHO?
--- Updated ---

Easy peasy said:
you have no heatsink on the mosfet - that is why it is burning up
Click to expand...
i have used...
 

Attachments

  • Schneider Electric_TeSys-F_LC1F265.pdf
    273.4 KB · Views: 21
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IMVHO = in my very humble opinion
Thanks for the contactor datasheet....will need to examine it to see if the coil can handle the current without saturating, and without loss of inductance. I suspect at 1A it has well under 250mH of inductance. As you describe, You have used this coil as the inductor in the buck converter which is switching at low freq, as in the sim above in post #32. UCC2802 is pin4pin with LT1243 so you may use that sim to check it what you have done.

Why not fill out the simulation with what you have set up, (or a close representation) and then post it back here....i think then we will soon fix.

I think those contactors are designed that the coil is to literally go across the mains or rectified mains. I suspect they are not designed for high frequency buck converter switching currents.
 
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