Quick check: isolation driver ok for N-channel high side MOSFET?

[User_name_]

L.S.,

Just a quick verification for a software guy who tries to build a 1 kV H-bridge: if I want to switch a **broken link removed** at the high side of my H-bridge, would it suffice to use an isolated gate driver, like the Silicon Labs SI8238AD-C-IS? This would cause the gate-source voltage become independent of my circuit ground, thus easily adjustable by PWM, correct?

Thanks in advance!

 

[FvM]

Yes, but you need to provide a floating DC supply with 1 kV isolation or use a bootstrap supply circuit, with respective limitations for the duty cycle and restrictions in start-up behaviour.

 

[User_name_]

Hmm, I was of the understanding that this driver would be able to provide the floating and isolation by itself. The data sheet states "The operation of an Si823x channel is analogous to that of an optocoupler and gate driver"; doesn't this mean that the driver channel automagically floats or did I miss something elementary?

 

[FvM]

Refer to the datasheet, a high-side power supply is necessary. The example circuit uses bootstrap technique.

 

[User_name_]

Thanks! Would I be able to put an optocoupler in between the driver voltage supply and the driver to create a floating supply, thereby avoiding the need for a bootstrap circuit?

 

[FvM]

An opto coupler doesn't help. Problem is the power supply, not the siggnal isolation which is well performed by the SiLabs driver.

 

[User_name_]

Forgive me my small understanding of the matter, but wouldn't a high current optocoupler not be able to create a floating power circuit?

 

[FvM]

but wouldn't a high current optocoupler not be able to create a floating power circuit?

Available photovoltaic optocouplers have up to several 100 µW output power, for gate drivers, you'll want at least 10 or 100 mW. So that doesn't look like a reasonable option.

Truely floating gate drivers with integrated power supply are using transformers for isolation. A few gate drivers with on-chip integrated transformers exist, e.g. from Analog Devices. But probably not in the isolation and gate voltage range required by SiC MOSFET.

 

[erikl]

Truely floating gate drivers with integrated power supply are using transformers for isolation. A few gate drivers with on-chip integrated transformers exist, e.g. from Analog Devices. But probably not in the isolation and gate voltage range required by SiC MOSFET.

Infineon also provides such .