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Old 22nd Nov 2018, 10:19 am   #12
Al (astral highway)
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Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
Default Re: Quick query: IC with 2 ENA pins and at least 2 input / outputs

Hi Hugo,

Sorry it if wasn’t clear but absolutely not intending to use the little 7400 as a gate driver. I’m dropping the gate drivers in the circuit shown and instead using beefier devices, TC4451 and TC4452. These can source 23A pulses to quickly charge a large gate capacitance - 20 or 30nF - typical of the larger IGBT half-bridge bricks (Qg=Ig x t).

Some people parallel the driver chips shown but this isn’t very satisfactory at all, and one of a parallel pIr can easily end up doing more work or see more noise. They ‘only’ source around 6-9A each, ideal for directly driving largish MOSFETs but a bit under-powered for physically larger devices with 2-3 times more gate capacitance.

So the additional circuitry I’m describing isn’t to provide a substitute for a gate driver, it’s to provide a signal stage with a virtual enable pin to these two burly gate drivers. A gate driver -driver! The TC4451 and TC4452 don’t have an enable pin.

I have already built the gate driver power supply capable of providing big gulps of power to the IGBT drivers, , designed and built the huge gate drive transformer, and am now working on the logic circuit . Outsmarting the missing ENA pin is mandatory!

Thank you for you alternative solution with the hex Schmitt trigger inverting buffer; I like this chip a lot. I’ll look again at the input waveforms that a TC4451/2 can cope with.

Cheers
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Al

Last edited by Al (astral highway); 22nd Nov 2018 at 10:35 am.
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