Floating ground

Thread Starter

Marie

Joined Nov 20, 2007
24
Hi,

I need to mount an inverter using MOSFET IRF740. I decided to use IR2111 as gate drive and 6N137 as optocoupler.

For the purpose of testing, i decided to use the circuit attached. The circuit works. My question is why must i connect the gate drive Comm to the ground of the power circuit; shouldn't these two grounds be different for the sake of isolation?

Thanks
 

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scubasteve_911

Joined Dec 27, 2007
1,202
What nanovate said

I just wanted to add one thing, you may want to play with your gate resistor. From experience, I found that they are typically a bit lower than 22 ohms. I have used typically under 10 Ohms with the best results.

Last year I had to design a boost converter from discrete components, so I had a lot of lab time playing with different values for the best results. Ended up with about 93% efficiency :D

Steve
 

Thread Starter

Marie

Joined Nov 20, 2007
24
Hi,

I took note of what you all said, but what happen if instead of using an optocoupler, i use an isolated dc supply for Vcc of gate drive. Will isolation still be provided if the gate drive and high side driver are on the same ground?

By the way, i'll try to use a resistor < 10ohms and see what happen. Thanks a lot.
 

Thread Starter

Marie

Joined Nov 20, 2007
24
You can get complete isolation using a pulse transformer (as shown in the first two links I provided).

In my experience going from 20R to 10R will not make a difference between working and not working. The 20R will simply slow down turn-on and may lead to more heating. John
Thanks for the links. In fact, i had already read them. The first link about gate driver mentions an isolated power supply. What i would like to know is if with an isolated supply + bootstrapping can i say that i'm providing isolation?

About pulse transformers, they are not available on the local market:(
 
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