480VAC buck design using the LNK305GN-TL
Posted by: rctrue
on
I'm using a LNK305GN-TL in a 240VAC to 5.8V buck design. I would like to operate up to 480VAC with this architecture but the peak voltage would exceed the rating of the internal mosfet. I see that you have a fly-back reference design that is good to 580VAC using an external Mosfet. Is there a way to use an external mosfet on the buck architecture to extend the operating voltage?
Comments
We do not currently have a circuit to extend the volage range of device in buck application
rctrue -
Besides exceeding the breakdown voltage on the MOSFET, one of the problems that you'll run into with designing a 480 VAC (680Vpk) to 5.8Vdc buck is that the effective duty cycle to accomplish this will become incredibly small.
Running some very quick calculations, I would expect duty cycle for this kind of application to be in the territory of 1% or less. Given the switching frequency for LNK305, this %DC will start getting you pretty close to the MOSFET minimum on-time which will cause a whole bunch of problems besides the issue with the MOSFET breakdown voltage.
Besides safety isolation (which you may or may not need), using a flyback topology would help get your required duty cycle back into a manageable territory. If you really do intend to operate at 480 Vac line voltages, these designs would make a good starting point: DI-124 and DER-58 .
-The Traveler