[SOLVED] Full-Bridge CLLC, high-side Mosfet Vgs self-turn-on

[kinghero89]

I am working on full-bridge CLLC, and the waveform I got is quite weird.
Is there anyone who has such kind of experience?

 

[Easy peasy]

Of course your resonant caps get hot they have a lot of current and a lot of AC voltage, what is the DF for your cap ? what is the peak DC & AC voltage rating at the frequency you are using ?

Watts ( heat ) in the res cap = Vac x Iac x DF, so for 100Vac and 5A ac and DF = 1% the heat will be 5W

quite a lot for a cap that is not designed for an heavy duty AC application at higher frequencies ....

So - look at the data sheet and do the calcs ....

 

[kinghero89]

After modifying the PCB according to your suggestion, the waveform got a lot better. This is the waveform when the circuit works at 2kW. Thank you for your valuable information.

--- Updated Aug 14, 2023 ---

Of course your resonant caps get hot they have a lot of current and a lot of AC voltage, what is the DF for your cap ? what is the peak DC & AC voltage rating at the frequency you are using ?

Watts ( heat ) in the res cap = Vac x Iac x DF, so for 100Vac and 5A ac and DF = 1% the heat will be 5W

quite a lot for a cap that is not designed for an heavy duty AC application at higher frequencies ....

So - look at the data sheet and do the calcs ....

Thanks for your information but my cap wasn't hot. The resonant inductor in series with the transformer is hot.

 

[Easy peasy]

Oh - OK - the resonant inductor - yes these require expert design due to skin effect, proximity effect and core losses at higher frequencies and of course losses if you run the peak B too high

glad to see you are making some progress . . . . !

--- Updated Aug 15, 2023 ---

. . . what were the key changes you implemented ?

 

[Easy peasy]

Is chanel 2 inverted ?

also you seem to be running a lot of magnetising current - looking at the purple waveform

 

[kinghero89]

Is chanel 2 inverted ?

also you seem to be running a lot of magnetising current - looking at the purple waveform

Yes, the peak of magnetizing current is about 13.4A. Do you think it contributes to resonate components heating?

 

[Easy peasy]

Yup it certainly does, you could easily halve it

 

[Easy peasy]

It would be nice if you could re-pay the group and list all of the exact changes you made that allowed your converter to run correctly - it would allow others to learn also - which is how the group continues . . .

 

[kinghero89]

Hi guys, I am doing the bidirectional power switch. I am wondering if could I use the same gate driver and the same gate resistor for both N-channel Mosfet as in the picture below, or do I need to separate them?

 

[Easy peasy]

Only one device is ever turning on in the forward direction - so - that should tell you the answer

( hint the other device has it's diode fwd biased )

 

[kinghero89]

Hi guys, is there any way to turn on/off a GPIO signal at the dead-time period of PWM? I used the ePWM event trigger of TI DSP 28335, but it seems it doesn't work well.

 

[Easy peasy]

you should start a new thread in the relevant section

 

[kinghero89]

Cảm ơn mọi người đã hỗ trợ, tôi bố trí lại PCB và sử dụng gói Mosfet 4 chân và nhận được kết quả tốt hơn.

Thanks everyone for the support, I rearranged the PCB and used a 4-pin Mosfet package and got better results.