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Old 04-15-2010, 04:43 PM
RSmith RSmith is offline
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Join Date: Apr 2010
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Default Signal Inverter

I need some assistance, please, anyone, I'm a novice so I hope I can communicate what I need sufficiently for you to understand. I'm interfacing an off the shelf board that puts out a PWM (Dalf board from Robot Power) signal that I'm attaching to a Powerex hybrid IGBT driver. The Dalf board's PWM signal is 5VDC CMOS and the input on the IGBT driver is TTL. The documentation from Powerex says the PWM signal has to be inverted before it goes to the driver because the IGBT module is active when the PWM signal the driver gets is "low". The Powerex documentation also suggests using a CD74HC04E CMOS hex inverter. The hex inverter comes in a 14 pin DIP package and on a breadboard mockup with an led it works as expected as long as the input signal never floats. I don't know what kind of liberties I can take in mixing TTL and CMOS. I have not wired up the Dalf board, hex inverter and IGBT driver yet, only the hex inverter on breadboard with an led and 5VDC power supply. I would like to get a single channel inverter so I don't have to be concerned with what to do with the unused inputs and outputs. I have contacted Digikey and Mouser both and they say all they have in a single channel inverter is in a smaller package, so small I can't easily handle it. I also ran across logic to logic optocoupler buffers and inverters in a package that can be handled and used on breadboard and also gives an additional degree of isolation. The optocouplers I've looked (Fairchild 740L6001) at come in TTL and Cmos outputs (there may be others) but only LSTTL input, here again I don't know what liberties I can take in mixing. I also don't really have a good grasp on what additional components I should be adding to this interface circuit in the way of pull up/down resistors and/or filter capacitors before and/or after the inverter be it the CD74HC04E, 740L6001 or something similar. Sorry for the long windiness. Thanks in advance, Rod S.
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