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Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
I have built both of these flyback drivers, but which one is best and whats the difference between the two? How can i get better power output and not destroy the 555 timer. (i already have a ZVS flyback driver). Why does audio modulating draw so much current ?
Also which one is better to audio modulate? if these are no good could you post some good audio modulation circuits. Thanks :)
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
No one seems to design these very well. Build the first one but put a snubber or quasi-resonant circuit on the primary side of the flyback. If you don't do this, you will waste lots of energy causing the FET to avalanche every cycle. If you do insist on building this with no snubber, use a high voltage FET (like 1200v) so that the output voltage is not clamped by the FET avalanching.
The 555 drivers are somewhat bad anyway because there is no way to adjust duty cycle and frequency independently. I would recommend a TL494 or other PWM based driver over this one.
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
cjk2 wrote ...
No one seems to design these very well. Build the first one but put a snubber or quasi-resonant circuit on the primary side of the flyback. If you don't do this, you will waste lots of energy causing the FET to avalanche every cycle. If you do insist on building this with no snubber, use a high voltage FET (like 1200v) so that the output voltage is not clamped by the FET avalanching.
The 555 drivers are somewhat bad anyway because there is no way to adjust duty cycle and frequency independently. I would recommend a TL494 or other PWM based driver over this one.
Do you have a simple circuit of the tl494. When i ordered some i accidently ordered them in surface mount but that shouldn't change the specs right where would i find a quasi resonator circuit ?
For quasi resonant drive you should choose a cap to stick across the FET that will resonant with the inductance of the flyback at maybe 20 khz or so. Use a resonant frequency calculator if you know the inductance of the flyback. Then use a scope to watch the D-S voltage of the FET and twiddle the frequency of the 494 until you see a critically dampened waveform.
If this is too hard, I suggest buying a 1200v FET with the lowest Rds(on) you can afford.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
cjk2 wrote ...
No one seems to design these very well. Build the first one but put a snubber or quasi-resonant circuit on the primary side of the flyback. If you don't do this, you will waste lots of energy causing the FET to avalanche every cycle. If you do insist on building this with no snubber, use a high voltage FET (like 1200v) so that the output voltage is not clamped by the FET avalanching.
The 555 drivers are somewhat bad anyway because there is no way to adjust duty cycle and frequency independently. I would recommend a TL494 or other PWM based driver over this one.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
yeah, i think the commercial plasma globes use a 4069 as these can be used in linear mode to make a tesla coil-like resonant setup. IIRC this is so that when someone touches the globe the power goes up so it doesen't waste energy running it at 100% all the time. -A
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
i made the top circuit and when i connect an 18v 2.5 amp bat. the irfp250 gets supper hot what do i do to prevent this or is there something i can add to make it more efficient.
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
"i made the top circuit and when i connect an 18v 2.5 amp bat. the irfp250 gets supper hot what do i do to prevent this or is there something i can add to make it more efficient."
Like I said, you need a proper high voltage FET to build a proper flyback driver. The fet is hot because it is analanching every cycle. Use a 1200v part and build a snubber to limit the peak D-S voltage to 1200v. If you don't do this, then the FET will avalanche and hence will be very hot.
To summarize: Use a real PWM driver with a TL494. Use a 1200v FET. Try a snubber if the FET still gets too hot.
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Which one ?
