proper way to simulate floating ground in UCC21220AD_TRANS

Thread Starter

yef smith

Joined Aug 2, 2020
841
Hello, I want to simulate the effect of UCC21220AD_TRANS floating ground in LTSPICE
My gate drive needs to create floating voltage for irf7854pbf MOSFET.
However i know that in LTSPICE floating ground is not possible.
I have attached bellow all symbols and simulation file.
How should make a floating ground in LTSPICE?
Is it possible to create two different types of ground in LTSPICE?

Thanks.



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Irving

Joined Jan 30, 2016
4,077
@yef smith Hi Yef, Reposting the same question on many threads isn't going to get any better results and will result in the moderators locking your threads. These simulation models are intended for PSpice and though different implementations of Spice are mostly compatible, this is an example where they're not. The way the driver output is implemented in the simulation model requires VSS to be grounded in LTSpice, but apparently works OK in PSpice (I've not been able to test this).

There are two solutions to this (other than switching to PSpice). One is to use the modified 5304 driver I gave you in post #26 of your other thread, its good enough for your needs. The second is to ground VSS, but to return the -ve side of the floating supply to the MOSFET source as shown below. The disadvantage of this approach is that it drives VDD to Vsource + Vfloat (which is 56v in your current examples) and this exceeds the chips VDD rating. Whle the simulation appears to work OK this couldn't be wired like that in reality, VSS would need to be connected to the MOSFET source in the real world.

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Thread Starter

yef smith

Joined Aug 2, 2020
841
Hello , the real life is what is important.
This is how I intend to connect them to them, Is it ok or should i change someshown the schematics?
Thanks.
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