Electronics > Beginners
HEF4013 flip flop question
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Chris Wilson:
Thanks again Tim!

I have wound the primary as you suggested, but I see very little change, I am sorry to say. I have added a SN74AHCT125N buffer as a level converter between the si5351a and the HEF4013, but before I did this, and after I am seeing something I do not understand, maybe you can explain? I have an adjustable 5V regulator off the main 12V supply for the HEF4013. next to it on my little board, and by chance, I found that as I lower the voltage to the HEF4013 the drain waveforms clean up, and just before the 4013 shuts down they are relatively good. I'll attach scope shots. I have also found increasing the cap values for C3 and C4 on the amp make the drain wavefoms a lot less spiky, but I am using much greater values, I stopped at 6nF ones. The schematic shows 1500pF. I have the driver board grounded right by the driver IC ground points to as near the FET source pins as the layout will allow. Before I go further (and to be honest, I am getting a headache from the damned thing... ;)) But for now I would like to know why reducing the voltage to the 4013 improves things!  I also see the gate waveforms go negative when the FET's have power to them, without voltage applied they are perfectly square. You can see this effect in the screenshots.
T3sl4co1l:
Seems to be something about changing the timing between Q and /Q.

If you have a 5V supply, why not use a 74HCT74 in the first place?  What's the point of using a CD4000 anything at all?

Tim
Chris Wilson:
I am hoping some will arrive tomorrow, the postman is terrified of dogs so he left a note saying he could hear barking and had made a hasty retreat today :) I'll have to tell him the one he had reason to fear has died and and he can now rest easy :) I just used what I had initially, point taken! Thanks Tim. I'll persevere.
Chris Wilson:
Thanks to the patient help here I am now getting pretty good traces and the amp is working well. For completeness:

Used a CD74HCT74 flip flop, used a pair of TC4420 Mosfet driver IC's, made everything on the output side of the driver IC's as wide and short as possible, used fast Schottky diodes instead of 1N4146's. I found occasionally applying voltage to the FET's with no drive applied at all saw a pair conducting. Adding a pair of 15k pull down resistors on the input pins of the FET drivers sorted that. Also added 4.7k pull down resistors on each gate pin. Things were a lot better, but whether this is good or bad practice i don't know, but I experimented with the 1500pF glass mica csnubber caps and ended up with high voltage poly caps of 6.6nF as the snubber caps into the 10 Ohm film resistors adding these made a remarkable difference. using Tim's transformer winding advice was less successful, I used Litz wire and basically it didn't (got MAD hot and terrible drain waveforms0, this may well be some error on my part. Whatever, I am now seeing  the waveforms below at 52V on the FET's, and it has run cool for 12 hours and got my pal into the USA a few times from here in the UK on 475 kHz.

Many many thanks!
T3sl4co1l:
Nice!  Cheers,

Tim
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