Hi side SMPS FET drive with isolated supply for FET drive IC

What's the highest switching frequency that the method of page 12, figure 4 (datasheet below) can be used for?

This is with reference to a full bridge LLC converter with vin = 400VDC. The actual signal to drive the fet drive ic is coupled up to the hi-side via a pulse transformer.


1EDI60N datasheet
https://www.infineon.com/dgdl/Infin...N.pdf?fileId=db3a3043427ac3e201428e5da08f372a

It listed on page 15. Max switching frequency is 4MHz

thanks, but that does not refer to the specific act of having a separate positive and negative hi side supply for the hi side fet. What is the maximum switching frequency viable for that method?

treez said:

thanks, but that
does not refer to the specific act of having a separate positive and negative hi side supply for the hi side fet. What is the maximum switching frequency viable for that method?

Click to expand...

Not quite understand the relation between positive and negative supply voltage for the FET Drive IC and the switching frequency of this driver ? Floating supply voltage for this driver is
DC voltage. Input signal is AC switching. Perhaps you need to post the circuit schematic.

..thanks, but I think you have understood correctly from what you say...I heard that there have been problems of using the method of supplying a high side gate drive supply to hi side fets...these problems relate to the fact that the rails of the high side supply are banging up and down from 400V to 0V at high frequency, and that this causes problems with interwinding capacitance in the switch mode transformer from which the high side supply rails come from. Thus, this method of using high side gate drive supply, is limited to say 200khz max?

Anyway, here s the schematic which shows the high side drive method, it is ok to post it because it is just a standard LLC stage.

treez said:

..thanks, but I think you have understood correctly from what you say...I heard that there have been problems of using the method of supplying a high side gate drive supply to hi side fets...these problems relate to the fact that the rails of the high side supply are banging up and down from 400V to 0V at high frequency, and that this causes problems with interwinding capacitance in the switch mode transformer from which the high side supply rails come from. Thus, this method of using high side gate drive supply, is limited to say 200khz max?

Anyway, here s the schematic which shows the high side drive method, it is ok to post it because it is just a standard LLC stage.

Click to expand...

Thanks for your explanation. I agree. Can we use transformer to drive the HS FET ?

you mean can we use a pulse transformer to drive a hi side fet?...yes you can, but as you know, the quality way to drive a hi side fet is to have a high side supply, and then couple the drive signal up as purely that..just a signal, the power drive being developed in the hi side fet driver ic that sits up in the hi side supply.

200KHz is too small a limit!
I am running a 300V full bridge neatly at 300KHZ.
Look at FAN7385 driver. It is a dual high side driver which supports up to 600V and propagation delay around 100ns.
Also look at IPD50R280CE power MOSFETs from Infineon. Cds is less that 50pF so there should be hardly any problem of current leakage into the transformer due to bouncing of rails.

Look at FAN7385 driver. It is a dual high side driver which supports up to 600V and propagation delay around 100ns.

Click to expand...

Thanks but no Thanks..
Yes.., though I urge you not to use bootstrap high side drivers in mains applications, as Dr Ray Ridley himself says they are not good, as you see on page 1 of the attached….

"High-side integrated drivers remove too much control from the designer, and do not provide the same level of protection, isolation, immunity from transients, or common-mode noiserejection as a well-designed and imple-mented gate drive transformer."

Use only Transformer drive for mains.
Also, the “open compute project” forbids the use of bootstrap high side fet drive.

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Also, the NCP5106 document (page 16) attached states another problem with bootstrap high side drive chips when used in mains applications......I think now you will throw them away for mains applications?