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Re: GDT --> Optron

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

>Why not using an optical coupler? Simple and
>reliable............... No headache with transformers..
>What do you think??????????

Some people do use optos. Terry Fritz designed a nice driver for his DRSSTC around the Toshiba TLP250. They are very popular in variable speed drives etc. where the gate drive waveform contains a low frequency component that a ferrite transformer can't handle.

But my own opinion is that for SSTC use, a transformer works better and is actually simpler to make, once you take into account the need for a floating DC supply and high current booster on the other side of the opto. (the TLP250 has the booster built in though.)

A ferrite transformer is also a lot cheaper than four fast optoisolators: you can buy a nice ferrite ring for about 2 dollars. Regular optoisolators like the 4N35 are far cheaper, but they are way too slow for SSTC work.

I'm currently w orking on IGBT brick drivers, and even for these I chose to use transformer isolation (along the lines of Steve Ward and Dan Strother's design) instead of optos. The page is somewhat out of date, I must get round to updating it.


Steve Conner