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Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
Is it possible to use a 1:2:2 GDT to drive a fullbridge of MOSFET's? I know the norm is a 5 filar 1:1, but would a tri filar 1:2:2 do the trick? Just use a single winding to drive both gates of each side of the bridge? Or is this asking for trouble?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
This is a question that cannot be answered simply. There are many parameters affecting the design and number of turns a GDT has. If your gate driver was configured in a +15/-15V push-pull array, then a 1:1:1 may be the optimum set-up. If you were driving with only +/-10V, then perhaps a 1:1.5:1.5 would work. You need to look at what your gate driver circuit is outputting and what the input requirements on the MOSFETs are. The ratio, as well as number of turns also depends on the core being used, the frequency you are driving at, and the devices you are driving (loads)
A single primary winding will work so long as you have enough drive in the gate drivers to run each side of the bridge. Look at all the parameters before making a decision. Do not go blindly into the night!
Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
No. All variables aside, driving a full bridge will require four secondaries. This is because each fet turns on out of phase with the one across from it. This means each top fet requires its own isolated gate drive and the two bottom fets can not share the same winding because they must be switched out of phase with each other. Just take a look at the schematic of a full bridge and think about your signal timing and current paths.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
(Justin/Aron?) has pointed out the first difficulty: connecting the source/gate of two FETs will quite effectively short out your power supply, short your output, or short your power input to output =)
One would wonder if you're asking this because you're down to 1xUCC and 2xFETs... but after recent conversations I know you've got four FETs... hows the UCC count? ^^
Recently (for bastard-gate-drive) I'm trying using individual push/pull output stages for each FET (so UCC37321/2 for *each* FET) to push higher frequencies.. If you've got UCCs coming out your arse and FETs coming out your ears, this is fun..
Try it and see - wind your five-filar (or three-filar, for halfbridge) GDT with a few extra turns. If the waveforms aren't nice, remove one or two or three primary turns... With FAT (monitor-cable-RF-suppression-ferrite) cores you can get away with fewer turns... you'll notice pretty quick if it's saturating though.. (assuming you've got a scope) ^^
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GDT
