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KUOWENYUNG
Level 3
Level 3
25 replies posted 100 sign-ins 50 sign-ins

Dear IFXer,

We use the IMW120R140M1H to design for LLC converter and seems the Vgs has oscillating duration opposite MOSFET Vgs turn to off.

Could you help us to provide the optimization suggestion for Vgs oscillating? sorry about we can not up load schematic on web because project confidential.

CH1 Hide side Vgs;  CH2 Low side Vgs; CH4 Vo

Vin:760V

Vo:48V/18A

Io:18A

VGS turn off level:0.6V , RG_on=5.79 , RG_off=39

 

KUOWENYUNG_0-1675928663079.png

 

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1 Solution
4 Replies
Jingwei
Moderator
Moderator
Moderator
250 sign-ins 10 likes given 100 solutions authored

Dear user,

The gate oscillation in LLC converters is a common problem that can occur when the gate drive circuit is not designed properly. The following steps can help optimize the design to minimize the oscillation:

  1. Selection of gate driver: A gate driver with a fast switching speed, low propagation delay, and high drive current is required for efficient gate drive of the main switch in LLC converters.

  2. Selection of gate resistor: you can try many types of combination of Rgon and Rgoff.

  3. Selection of snubber circuit: The snubber circuit is used to suppress the ringing of the main switch. A snubber circuit consisting of a capacitor and a resistor can be used to damp the ringing effectively. The value of the snubber components should be chosen carefully to ensure the stability of the converter.

  4. Proper gate drive layout: The layout of the gate drive circuit is important for reducing the susceptibility to noise and reducing the ringing. The layout should be designed to minimize the parasitic inductance and capacitance of the gate drive circuit.

  5. Proper PCB layout: The printed circuit board (PCB) layout is important for reducing the electromagnetic interference (EMI) and reducing the ringing. The power ground and signal ground should be separated and the critical components should be placed close to the main switch to reduce the trace length.

Thanks and BR,

Steven

Thank you Steven.

I'm afraid that I may have not fully understood your explanation, may I know the gate oscillation happen in LLC converter whether as following figure? 

SO, the root cause was that TO247-3 package have no kelvin source to suppression common source inductance and poor Cgd/Cgs ratio, so need use that Rg_on&Rg_off and separate power loop and signal loop, right?

KUOWENYUNG_0-1676250019547.png

 

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Jingwei
Moderator
Moderator
Moderator
250 sign-ins 10 likes given 100 solutions authored

Hi, 

Your idea is right. But this is only one action. A robust galvanic isolation gate driver to isolate gate signal and power loop signal.  You could do more to improve your gate signal.  Such as snubber circuit to absorb the oscillation energy. Minimize the inductance of source side and signal loop.

There are several loops which can cause gate ringing. I will find out a article and give you later.

Thanks and BR,

Steven

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