High side floating supply

Hi Guys,

Im looking at using the part below in a full bridge configuration, my issues is that the design I am looking it will see various extremes of duty cycles so the typical bootstrap diode/cap supply will not work for my situation, any ideas on what other robust ways of doing this are?

You mean your fet on times are sometimes very long or short?
Anyway, a good way is just to do a little flyback type high side isolated supply and reference it to the bridge node…in a full bridge do one for each side of the bridge.
Don’t put a y cap between pri and sec as it will just conduct huge pulse currents.
Put a third winding on the flyback and regulate that, so as to regulate the high side winding. Then you can couple your fet drive signal up with a digital isolator, or if you want the last word in transient immunity (100v/ns), then use the 1EDI20 by infineon.com

Don’t try and do two outputs from the one flyback because you will end up with the high dv/dt nodes being routed all over the place on the pcb, put the mini flyback next to the bridge node concerned.

Thanks, I was thinking that was possibly the way forward, I didn't really want to go down the charge pump route neither

Then you can couple your fet drive signal up with a digital isolator, or if you want the last word in transient immunity (100v/ns), then use the 1EDI20 by infineon.com

Click to expand...

Why would you chose to couple it up with a digital isolator?

purely because it will transfer the signal, then you could use a gate driver in the high side supply, to receive the digi isolator signal, or use a digital isolator/gate drive IC combined. As long as transient immunity is ok youd be fine with digi isolator

It may be cheaper or more convenient to use those small 1 watt isolated power modules, available with a wide range of input and output voltages.



https://www.ebay.com/sch/i.html?_od...power.TRS0&_nkw=1watt+isolated+power&_sacat=0

MCA12D15S Datasheet
https://www.farnell.com/datasheets/1520590.pdf

...yes that looks a good one, because it has max 60pF of capacitance between pri and sec which is good considering this use of this power module. some other ones have about 2nF between pri and sec