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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I'm using the boost converter for my cap bank. Haven't tried the real large cap bank yet, but i can charge smaller cap banks quickly. I can get up to 330 volts with 8 AA batteries, on a 400µf bank in fair time.
The boost converter can also be built tiny, even without SMT or self-etched PBCs....
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
No. Typical boost converters are almost always low voltage devices and i wouldn't recommend using the topology for something greater than 100V.
Well, many active PFC (fancier boost converters) exist that run far greater than 100V (my 850V active PFC for example, though i would not call it typical).
Im going to agree and say that a boost converter probably isnt the best way to go. Id look at a forward converter, at least then you have turns ratio working with you. Its basically like a boost converter with your inductor coupled to another higher inductance.
Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
I used the simple 555 boost converter to charge 450V lytics from 12VDC. I used a small 1.2Ah 12V SLA battery. It charged the caps to that voltage quite well actually. As Steve said it is not the most effiecient thing to deal with, and I had to eventually drop that charger from my coil pistol. I couldnt get it to stop casuing my logic circuits to go nuts while charging. I eventually went with a small ferrite ecore transformer with a SMT tl494 in pushpull mode. Give the 555 a try! William
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I'm going to try and clarify this a bit: Designs like WilliamN's, that are just a plain boost converter with a high voltage switch, do work fine. But a more efficient way is to use two windings on your inductor, so it also works as a step-up transformer. It's still a flyback converter, but the switch doesn't see the full output voltage any more. If you use a 1:10 step-up then it only sees 45v when your caps are at 450v. This allows you to use a 100v MOSFET instead of an IGBT and get less losses. You can also operate at a less extreme duty cycle- it will be closer to 50%.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Steve, I agree that ultimate efficiency will not be achieved with a 12V : 450V boost convertor, but the simplicity of not having to wind a low-leakage transformer and the fact that the load forms the snubber may be enough to outweigh the slight efficiency loss for hobby convertors. (Personally I'm inclined to efficiency, but sometimes simplicity wins)
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555 boost converter: 450v from 12v?
