Electronics > Beginners
Using schematic to calculate transformer windings.
Jwillis:
Did you wind the feedback the right direction?
gkmaia:
Sorry for my late reply. I got stuck with another issue on the vertical board. A shorted tantalum brought the -8 rail up and messed with all the other rails. Toke a while to find the bastard. Just pulled it off for a while.
Back to the feedback winding. I managed to get the secondary to oscillate please see the attache image.
The start of the windings are 3 and 4. Clockwise both ending at 6 & 5 respectively. It only oscillates in one direction which is the direction the schematics mention.
R457 is fusing. With one turn it gets hot and will fuse after a while. Two turns or more it fuses immediately. Weird… I would expect R458 or R459 to fuse as per what T3sl4co1l said. Should most of the current flow over R457 and not R459?
Also the sine of the feedback (probe #1) is not correct as well as frequency. It is at 200khz instead of 50khz.
All components before Q454 have been pulled out of the board and tested on a BK curve tracer. That block is fine.
Q458 has been taken to the curve tracer and is fine.
+8v, -8v & +120v rail are spot on. The +120 unregulated is a bit above at 140v but the DS796 neon is solid and not accusing an issue as before so it is within margin for the rail. I also believe when the HV transformer is operative the unregulated voltage may get down a bit.
So that is all I got so far… any tips?
T3sl4co1l:
Is the core gapped?
If you can, try to reduce the gap, this will reduce the frequency. Evidently 4x is needed, so 16x inductance, which will be ballpark 16x thinner gap.
The higher frequency causes R457 to absorb more power. The RC time constant is 3us, so a 5us period is in the damping range. The intended 20us is just outside. (It still seems suspiciously aggressive for an RC damper, though. Eh, it's what they intended I guess..)
Tim
gkmaia:
--- Quote from: T3sl4co1l on October 27, 2019, 03:44:34 pm ---Evidently 4x is needed, so 16x inductance, which will be ballpark 16x thinner gap.
--- End quote ---
Yes the core is gapped at 0.5mm. Core diameter is 12.5mm. See photos for more details. I am a bit afraid to modify the core as it was supposed to work with it originally. And if I modify it there is no way back.
If we park the frequency issue for a moment is there anything to look at to try to get a proper sine and increase the primary sine pkpk? Or that is dependable of the frequency?
T3sl4co1l:
Oh, using original core. Implies the turns (or wire dia. or spacing) is different. By a fair factor I suppose. Which, *shrug*, Idunno.
What was feedback turns at? Did you try more? How about more bias?
The RC can be decreased, probably keeping the R about the same but reducing C by the frequency ratio. So, around 1nF I guess, or a bit less.
Tim
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version