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Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Well I've gone full circle with my driver designs, having built and tried a few complicated schemes including fixed and variable 'boot pulse', and other Kooky stuff. And funnily enough I have arrived at the definate conclusion that simple is best, and proven is better. So I have taken the best from various other peoples designs: -Steve Ward's elegently concise driver logic and OCD, and new GDT drive bridge (not shown on schematic,but on PCB). -The minibrute's sample/hold led bar graph driver.
I have come up with the attatched circuit which is even simpler, but achieves the same logic, now using only two chips in the entire drive logic block, one D flip-flop, and one S-trig Nand.
I concidered adding a pulldown option on the second FF data input for synchronised OCD shutdown, and even 'odd pulse drive' to drive every second pulse only when 'near' ocd, but realised I was getting carried away again .
I hope the way I have wired the led bar driver, it will run in bar mode, and switch to dot mode to indicate OCD (but I suspect a hold delay and pulldown transistor may be needed here) At first I was concerned about timing on the left hand D-FF with the clock and preset tied together, but I've built the logic block (using 74F series) and it works perfectly.
I have ordered some boards, and once I have built the final product and tested it in the real world I will post the expressPCB files for all. Anyway, here it is:
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Coming along.. Got the boards and have built one up. Turns out my suspicion about the timing on CLK /PRE of the 74x74 was right. It works perfectly with 74HC series, has some glitches with 74F series, and outright doesn't work with 74ALS series. So for now Im just using HC, but will probably add a 30ns delay line later (got a bag of em in the junk box).
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Sure did I had to make a few changes to the led bargraph/sample-hold, but all good now. I'm driving a fullbridge of toshiba MG200 bricks at 180Khz no problems. The logic block works great, the descreet GDT drive bridge (not shown on schematic above) is great (Cudos to Steve). I will update this thread with the final circuit I suppose:) , or I may put up a progect thread as I have been meaning to do for some time.
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Another (but simplified) DR/SSTC driver.
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