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Mosfet driver giving strange respond

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FerdinS:
Hello everyone;

I am working on my project which is boost converter and currently and I have a question for all you smart and experienced electronic masters.
I am trying to drive my N mosfet with driver becasue IC pwm pin is obviously not capable to do so by itself.

So I am using:

* Mosfet : SQJ454EP-T1_GE3
* Driver : UCC27517AQDBVRQ1You can see my wireing also on the picture : 1 and also responses before and after resistor Res3.

So the question: What could couse that strange respond ? ... so driver is giving me pwm output but after that resistor that is working as current limiter pwm becomes really strange.
Thank you a lot for you answers.
Best regards,
Ferdin Shotani

jmelson:

--- Quote from: FerdinS on August 10, 2020, 05:24:11 pm ---
--- End quote ---
R42 is I000 Ohms.  FETs have huge input capacitance, your gate is not charging up enough to turn the FET on.
About 10 Ohms would be a normal value.

Jon

FerdinS:
So what would be best solution ? putting there smaller resistor ?

jmelson:

--- Quote from: FerdinS on August 10, 2020, 05:39:38 pm ---So what would be best solution ? putting there smaller resistor ?

--- End quote ---
Yes, try 10 Ohms.  But, you can look up the gate capacitance, and figure you want the transistor fully on in less that 1/10th of the PWM period, calculate how long it will take to charge up.  Note, the driver has some current capability, too.

Jon

BrianHG:
Check your datasheet on the GATE input capacitance of the 'SQJ454EP-T1_GE3'.
Then with a series of 1K from your 0-12v drive, calculate how fast the rise and fall time of the GATE on the mosfet will be.  This should answer if the 1K is a wise choice or not.  Note that some mosfets have GATE capacitances way above 5000pf.

Hint: There is a definite reason the GATE driver IC UCC27517 has a 4 AMP high and low drive.  Will using that series 1K end up using anything near that IC 4 amp drive capability?

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