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Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
I'm drawing a board for Conner's PLL driver ( ) for my SSTC (just a regular one). I've stripped alot of it off, mainly the synchronizer (dont think I have any use for it because I'm not going to use an interruptor and I'm not running a touchy DRSSTC) and the deadtime generator. I wouldn't mind having the possibility of adding deadtime so I'd like to design it in the board but I'm running into size constraints etc (the driver board is going to a readymade base I made before). and I cant really fit another flip flop, a hex inverter (replacing IC7A, B, C) + NAND or two NAND chips. Or well actually I can probaply fit them but it would require a total rework of the board and I dont really want do that since its almost completed. I could do the logic part in SMD but my local electronics store doesnt have some of the chips needed as SMD and I wouldnt want to order anything.
On my circuit (I havent bothered to draw a schematic) I basically have only the IC6 and IC7, no other logic chips.
So my thought was, would it work if I'd put the deadtime gen (pot in series, cap in parallel, diode over the pot to allow the GD chip input discharge at normal speed) at the input of both of the GD chips (they have schmitt trigger inputs)? Would I be able to adjust the rise and fall -side deadtimes independently with a circuit like this? If this wont work I guess I will have to order the parts to get SMD logic chips.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The enable inputs of UCCs have a much longer propagation delay to the output than the regular inputs do. I started off trying to use the enable inputs for deadtime control, but couldn't get it to work for that reason.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Using a pulse-squisher / pulse-stretcher circuit probably isn't too bad a way to go...
I'd advise though, don't try to apply them to the UCC inputs; their Schmitt triggers aren't all that Schmitt. Use a 74HC14 chip, pulse-squish/stretch the input going into that, and feed the output into the UCCs.
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