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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I going for a pernament flyback driver setup, but I need some way of powering it off mains. Something like this But the only mains transformer I have is a 12volt one from a wall wart. I have plenty of SMPS parts, so I can reticfy mains, but making a usable voltage is a bit harder. Any suggestions? I thought of using a voltage divider, but the current would be very low and I would need heavy wattage resistors.
Am I missing something, or is there no easy way around a larger mains transformer?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
There are also solid state variac designs out there. Terry Fritz has one at i believe and i think Steve Connor has done some work as well, although i'm not too familiar with the specifics.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I've recently designed a mains running flyback driver around the International Rectifier IR2153 halfbridge driver. It works very well, producing just little heat. Please note that this circuit will not work well using fets with >3nf gate capacitance. Adjust P1 until you hit the resonance. Primary should have around 60-100 turns.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Transformers (linear) from old TVs give 80 volts on ne secondary and it is perfect for flyback driving, if TV is large enough you can get even more than 2 amps. Also lots of other low voltages for oscillator's and other needs.
If you find some C-core transformers you can remove the cores, unwind secondary and wind your own.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think the easiest/safest way is just to get a bigger mains transformer. I have seen people rewind the transformers from microwaves, but other appliances like hi-fis, TVs, those big old VCRs, and slide and movie projectors often have decent sized transformers too.
Iron bolts are no good- you need laminated iron or your power just gets wasted in heating the core.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
uzzors wrote ...
I like your circuit jmartis, think I'll use it instead.
I'm glad you like it, just be sure to make enough clearance between the pins of the IR2153, because it will have >300V across it... Also, don't use more than 14V for powering the IC or it will probably blow (use stabilised 12V). You must precisely adjust P1 to resonance (within about 5%), otherwise you won't get too high voltages. Also remember to not ground any part of the circuit. You can use any fets >400V >10A (eg. IRF740) with gate capacitance <3nf.
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Tapping power from mains
How can I avoid finding units with SMPSs though?