Using gate drive power supply to provide power to Isolated Error Amplifier

Thread Starter

SiCEngineer

Joined May 22, 2019
320
Hi all,

I have got the following design to generate an isolated 12V power supply for my upper and lower gate drivers. There is one for the high side and one of the low side. See:
1605544114477.png

I now need to give an isolated 12V supply to an isolated error amplifier which I am using to feedforward the supply voltage to my DSP. It requieres a voltage supply between 5-20V. I was wondering, am I able to just supply the chip with one of these gate driver voltage supplies? If so, does it matter whether I use the upper or lower gate driver supply voltage?

My concern is that the isolated error amplifier would share the ground of the return path of the gate driver chips. I am not sure whether it is instead better practice to create another seperate isolated 12V supply which is used by all other components requiring isolation other than the gate drivers, since these will have high current, whereas the isolated analog components I want to use will only have low power disipation and therefore low current.
TIA!

I want to provide isolated power to: https://www.mouser.co.uk/datasheet/2/609/ADuM4190-1551405.pdf
 

crutschow

Joined Mar 14, 2008
27,928
No, that will not provide isolated power, since all the circuits you show need to share the same ground.
If you truly need ground isolation then that is typically done with a transformer.

Why not use the power that is supplying the DSP since that also needs an isolated supply?
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
No, that will not provide isolated power, since all the circuits you show need to share the same ground.
If you truly need ground isolation then that is typically done with a transformer.

Why not use the power that is supplying the DSP since that also needs an isolated supply?
In the gate driver circuit there are indeed transformers to isolate the gate drivers voltages, this is lablled T1. It just doesn't look clear in the image because the Altium schematic picture doesn't come up as the general transformer symbol.

I don'th think I could use my isolated DSP 5V because I plan to power the primary side (VDD1) of the isolation amplifier with that. Surely if I then use it also for the VDD2, I would be providing a path between VD1 and VDD2 which means the isolation is no longer valid?

I am looking at taking the 5V DSP output voltage, and using this: https://www.mouser.co.uk/datasheet/2/468/R0.5S_D-958215.pdf (5V to 5V version).

Since these are unregulated I may put a linear regulator on the end also to give a stable 5V. But I'm not sure how critical that will be since the input voltage range is quite wide.
 

crutschow

Joined Mar 14, 2008
27,928
I don'th think I could use my isolated DSP 5V because I plan to power the primary side (VDD1) of the isolation amplifier with that.
I don't understand.
If you do that, then there is no isolation between the input and output of the isolation amp if the output goes to the DSP (?}.
If you want isolation than the output and input power can have no common connection.
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
I don't understand.
If you do that, then there is no isolation between the input and output of the isolation amp if the output goes to the DSP (?}.
If you want isolation than the output and input power can have no common connection.
Understand your confusion. I am probably not getting myself across properly. I plan to use the 5V from the DSP, to supply the right hand side of the analog isolated amplifier (the low voltage side). I then plan on having an isolated DC/DC supply which also is supplied by this 5V from the DSP. So the 5V DSP voltage is used twice, once for the ADUM and once for the RECOM supply. The output of the RECOM supply will be 5V, but isolated to more than a kilovolt. The output of this is then fed into a linear regulator, providing a regulated 5V. This is then a regulated and isolated 5V that does not share a connection with the 5V non-isolated side due to the RECOM DC/DC supply. THIS 5V is then used on the left hand "hot" side of the analog isolator. Does that make sense?
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
Okay,that does.
So if the drivers have complete isolation with a transformer, then you should be able to use that to power the primary side of the isolation amplifier.
Okay, so there’s no need for the additional 5 Isolator? I have some other components which require a 5V supply, so I’m thinking it might Actually be a good idea to generate an isolated 5V supply separate to the 12V for those and the isolator rather than just supply from the 12V ISO. I would need to step it down from 12 to 5V as well anyway.
as a side note would it matter whether one chose to use the upper or lower gate drive supply voltage? I have a feeling it would be safest to use the lower one but I can’t really think of a reason why.
 
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