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Gate Driver ICs Forum Discussions

User20969
Level 1
Level 1
Hello, dear collegues! I'm currently designing H-bridge converter for DC-motor drive.

I decided to use bootstrap driver for driving converter MOSFETs. IRF8721PBF were choosen as switches, IR2184 was chosen as a gate driver.
To quickly test their performance I soldered bread board with Half-bridge converter. You can see the circuitry on the figure. There is also decoupling capacitors on inputs of L7815 and IR2184, and on Vcc pin of IR2184
4875.attach
The problem is the gate voltage drop on upper switch during switching on or it better to say oscilation on upper switch gate.
The oscillograms was pictured and you can see voltages on load, on upper and lower gates, and on Vboot and Vcc pins of IR2184.
4879.attach 4878.attach 4877.attach
I have tried different valiues of Cboot from 6.8nF to 1uF but there is no significant difference between results.

It would be great to get any suggestions concerning the problem.

Thanks
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1 Solution
Srivatsa
Moderator
Moderator 5 sign-ins 50 replies posted 25 solutions authored
Moderator
You try with a bulk capacitor of around 10 uF at the Vcc pin. This should make sure the 1A current limit of LM7815 is not tripped when the driver is switching the MOSFETs.

Make sure the 10 uF capacitor is placed closed to the driver IC.

View solution in original post

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2 Replies
Srivatsa
Moderator
Moderator 5 sign-ins 50 replies posted 25 solutions authored
Moderator
You try with a bulk capacitor of around 10 uF at the Vcc pin. This should make sure the 1A current limit of LM7815 is not tripped when the driver is switching the MOSFETs.

Make sure the 10 uF capacitor is placed closed to the driver IC.
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User17346
Level 2
10 replies posted 5 replies posted 5 questions asked
Level 2
Hi,

Your gate capacitance of that FET is 1040pF and your reverse transfer capacitance is 114pF, with a gate threshold of ~1.8V.

Therefore, with fast switching speeds, at VBus voltages above ~18V, you are likely to get parasitic turn on (You are using 24V). See:
https://www.infineon.com/dgdl/Parasitic_Turn-on_of_Power_MOSFET.pdf?fileId=db3a30431ed1d7b2011eee756...
Choose a better FET, that one is ancient, from 2007. There are much better FETs now from Infineon (and others) that are completely immune to this parasitic turn-on.

This explains the rapid on-off funniness I think...

The slower ringing is on the 24Vbus, not related to your gate driver. You probably don't have a sufficient supply, or need larger capacitance to cover it.
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