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Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Hi all,
I need to wind a transformer that will be driven with a ZVS driver but its been a while since I have done this sort of thing, so I have naturally forgotten much about winding custom transformers.
I need about 1kV out and will be putting 48v in with the basic 10 turn center tapped primary coil.
How many secondary turns would I need to wind to get close to the 1kV target?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
assuming 48 Vdc, the theoretical primary voltage will be 48 x pi = 150 Vpk with a 10 turn primary that's 15 Vpk per turn so for 1000 Vpk you need 1000/15 = 66.66 turns secondary, or for 1 kVrms use 94.27 turns.
since it is unlikely that you will achieve the theoretical performance you will need more turns than the above ... 70 turns for 1 kVpk?
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Thanks Sulaiman!
I was having a complete mental block before but that explains it perfectly.
Edit: I have one more question, on Uzzors website he has a page about transformer building and mentions about number of turns, but he doesn't show how he made that calculation.
"I used 500 secondary turns in my transformer and 14 primary turns. Driven from my half-bridge this should give 5kV out".
Does anyone know how he calculated this? I can't seem to apply Sulaimans answer to Uzzors calculations.
He is using the rectified mains of 340vdc and halfbridge btw.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
from the page pointed to : "An important note: I used 500 secondary turns in my transformer and 14 primary turns. Driven from my half-bridge this should give 5kV out, but it gave 10kV"
Uzzors2k design used the self-resonance of the secondary inductance with self-and external capacitance to achieve a higher output than the pri:sec turns ratio would suggest.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The peak output from a HV trasformer driven by a square wave is always higher than the turns ratio, because the leakage inductance "rings" with the secondary coil's capacitance. It is the same mechanism which causes unwanted ringing on gates of your FETs/IGBTs driven from a GDT, only the damping factor of the HV transformer is much lower.
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Homewound transformer turns ratio
