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Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
Is it feasible to get 450v from a 12vdc source from a 555 driven boost converter? This would require something like a 97.33% duty cycle, however, I can't find the max duty cycle rating for the mc1455 I'm trying to use. The data sheet says nothing about it, though I've seen mentions of other 555 timers having ~95% max duty cycle on the old boards.
If a single 555 isn't possible, I could just use two seperate boost converters, right? One to go from 12 to 75v, then 75v to 450v? (Only 84% duty cycle for both)
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
I've gotten up to about 200V with a simple boost converter like that, but that was under no load. With such a low duty cycle you cannot really pump out much energy, so it would be good to know your application. This is what my implementation on a piece of cardboard looked like:
If you actually want to draw some current from the converter, I think using a transformer would be much better.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Although the ON:OFF ratio seems to be 450:12 = 37.5:1 you actually NEED a longer OFF time due to the rise-time of the output you can use UP TO 37.5:1 anything lower will still work, just not at maximum power throughput for components used, this is not a problem. You could use ANY ON:OFF ratio less than 37.5:1......e.g. 10:1.
The only real problems I see are; 1) between 12V and 450V the off time NEEDS to be less you may draw excessive current during this phase. 2) you need some way of controling the 555 to stop the output voltage exceeding 450V.
Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
Sulaiman wrote ...
Although the ON:OFF ratio seems to be 450:12 = 37.5:1 you actually NEED a longer OFF time due to the rise-time of the output you can use UP TO 37.5:1 anything lower will still work, just not at maximum power throughput for components used, this is not a problem. You could use ANY ON:OFF ratio less than 37.5:1......e.g. 10:1.
The only real problems I see are; 1) between 12V and 450V the off time NEEDS to be less you may draw excessive current during this phase. 2) you need some way of controling the 555 to stop the output voltage exceeding 450V.
Second, I failed to mention, but I'm going to be using this to charge a bank of capacitors, possibly up to 4700uf, for a coil-gun, so high current output isn't necessary. Mainly my question was: Can a typical 555 have a duty cycle of 97.33%? And if not, if 555 timers have a maximum duty cycle, could two be linked together?
Registered Member #215
Joined: Sun Feb 19 2006, 09:14PM
Location:
Posts: 30
I was messing around with my boost converter today; it runs off 36v @ 3 amp from a cheapo wall adapter I found at Princess Auto (surplus store). I tested it, and output is charging 330 @ 600 uF in under 4 sec ( I almost crapped myself when I saw! ) I'm soldering together a perminant version tonight. Switching device is N-channel IGBT, 600v @ 24 amp. Datasheet here:
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
aahz; the equation you are using is for an idealised CONTINUOUS MODE boost convertor; which is the most efficient type, however.... DISCONTINUOUS MODE doesn't need such conditions and if you used say 50% duty you would have much less problems charging up the capacitor(s)
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
aahz wrote ...
Is it feasible to get 450v from a 12vdc source from a 555 driven boost converter?
No. Typical boost converters are almost always low voltage devices and i wouldn't recommend using the topology for something greater than 100V.
One reason is isolation, another is efficiency, and there are others. I would never make a 450V step-up converter without providing some sort of isolation. There is no isolation in a standard boost converter. Efficiency would be extremely poor as well.
Why the boost converter? There are many other topologies out there which will do a much greater job attempting a 12V to 450VDC boost converter. Try for a transformer based topology.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I have built an IGBT based boost converter (Tl494 controller) for charging photoflash capacitors and this works very good. The duty cicly isn't at max because it would overheat in the low-voltage phase (because of too high dutycycle->saturation).
I got powers up to 20W from a 12V source for a small 4x10 board.
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
EastVoltResearch wrote ...
aahz wrote ...
Is it feasible to get 450v from a 12vdc source from a 555 driven boost converter?
No. Typical boost converters are almost always low voltage devices and i wouldn't recommend using the topology for something greater than 100V.
Boost converters have been popular for charging coilgun caps for some time on this forum. I think it was William who kicked off the craze with his very effective charger. It was fast.
Isolation and efficiency aren't crucial in that particular app. Isolation? Heck, chargers inside disposable cameras aren't exactly isolated either. Efficiency? When your coilgun is 10% efficient, you feel good.
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555 boost converter: 450v from 12v?
