another gate driver

Sep 09, 2017 2 Replies
J

PV gate drivers are nice, but they are slow turning on when supplying a lot of gate charge. The ADI parts, with internal power isolators, are expensive and insane power hogs.



So maybe we could separate the power transfer from the gate drive functions:



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Another possibility would be to use the single PV driver, but blast the LED side with extra current at the turn-on edge.



Or just stick with my flyback gate driver.



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Or maybe use a standard DC/DC converter as an isolated gate driver, if we could find a cheap one that was fast enough on/off and didn't waste a lot of power.



John Larkin Highland Technology, Inc lunatic fringe electronics
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L

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fig. 11

how fast? some of these

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claim a typical startup of a few 100 us into 10uF

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J

The PV optocouplers use the same trick (Q1) to fast discharge the gate capacitance. But the PVs have low output current, so can't turn on a fet very fast of it has a lot of gate charge. Some fat fets need 100 nC.

Something like that would work. A cheap converter probably won't have much output capacitance, so turn-off time might not be bad. We'd like well under 1 ms on/off times. We could load the output with a resistor or a depletion fet. I think we have some of these bricks around; I'll play with one.

My home-made flyback thing above isn't bad, about 75 cents for parts. The little potted dc/dc converters run around $2.50 each. This sort of thing:

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The 2KV isolation spec is nice.

John Larkin Highland Technology, Inc lunatic fringe electronics
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