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Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Sulaiman wrote ...
The nett result is, core size is INVERSELY proportional to frequency so a very large core is required at low frequencies.
Just in case you missed this, I'll emphasize that it is a VERY important fact to consider. Even for SSTC frequencys I found that a lot of the cores I tried simply did not have enough crosssection to work without saturating, and I had to use way more turns that people usually suggest here. What is the size of your cores?
Registered Member #120
Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83
Oh this is for a flyback h-bridge.
I never knew that the size of the core had a impact on the windings. I never really took this in to concideration. The outer hole is 2.5cm, the inner hole is 1.5cm and the width is 1cm. I have pspice, but I don't understand how to use it yet. I need to read some documentation, however, homework is first still my priority :() Too bad i'm not take any electrical classes this semester.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
OK, so the core is 0.5cm wide by 1cm thick, cross-sectional area = 50 mm2 For most ferrites you can use 0.2T peak an the 5-40 kHz region so the peak magnetic flux is 0.2T x 50mm2 = 10 x 10-6 Wb (10 uV.s)
At 5 kHz and 50% duty the ON time is 100 us For 10 V gate drive that's 10V x 100 us = 1 mV.s
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Technically I think 50 turns should be ok. (In the steady state the flux will swing from -10 to +10 uv.s per each half cycle, not 0 to 10)
I notice Tom said that he already tried a toroid with 100 turns and it didn't work, though. I'm going to guess this is because he just wound two separate windings instead of using the multifilar technique with its much lower leakage inductance. (good luck making a 100 turn 5-filar winding!)
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
5Khz is pretty low frequency for flyback driving!
You'l be in toruble fitting 100 turns on a small core using thick enough wire, and mantaining low enough leakage inductance and resistance!
For 50kHz, steve ward used 10 turns and I frequently use this as experimentally-confirmed orientation point
40kHz would probably requirefew more turns on core of same size, but on very small core (5mm^2) you will have trouble fitting everything.
For 5kHz and around, I would use a high-perm iron powder toroid (I guess that from ATX supplies could serve) and hope it would work for up to some 10kHz. It would allow you to use much more fair number of turns. (I need someone to veryfy this as I didn't try it^^)
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GDT's for low frequencies
