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Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
What kind of amperage can you draw from that laptop PSU? My guess is that your frequency is too low, and your duty cycle is too low. The more power you put through this thing, the faster, and more efficiently you can charge your caps. I'm really confused right now though, because I can push a 1440uF bank to 100V with a 300V 6A .5 ohm Rds on in something like 10 seconds. Your IGBT should be able to do that in a second or two, without even breakin a sweat, let alone needing to be sinked.
For the record, what frequency and duty cycle are you running at, and how big is your inductor. THe larger it is, the more energy you can store in it's magnetic field, and the fewer cycles you need to put the circuit through to charge the capacitor. The energy of an inductor can be found with the equation E=.5LI^2. For something as nice as your IGBT, you should probably be using an inductor with 150uH or more of inductance. Also, if you plan to be running separate PSUs for your driver and power circuit, your'e going to have to make sure there are no common connections between the two halves.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
It can supply 4.5S, but i measured it, and it was drawing less than .5 amps :D. Do you think it would be feasible to put full wave mains through the inductor? For the frequency, i tried a 10nf ceramic capacitor, but that works worse.
EDIT: It turns out i dont need to current limit it, circuit ressitance is enough. Now it goes to 100v in a couple seconds. Is your inductor audiable?
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
No, it isnt really. I mean, I can barely hear it, but no one else can. I think I keep my frequency around 28kHz, and if I had a better transistor, I would take it lower to get a higher inductor current, and more power. Using your IGBT, and running around 15A inductor current, you could probably get around 50W of power through this circuit. Uzzors has a spreadsheet on his site that would help you immensly. I assume you are using a 100-200uH inductor, so you should run somewhere between 3 and 7kHz. Bigger, you should use a lower frequency, and smaller you should use a higher one. Also, because you have a nice IGBT, keep the duty cycle nice and high, around 75 or 80% is probably good. Just remember, you will be drawing 15A using these frequencies, but I think that will help you get to the charge you are looking for. Also, make sure your IGBT is turning on completely. Perhaps use a gate drive chip or a class B amp if you aren't sure.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
I ordered some IGBT drivers, so i will try it. As for the inductor, it is just a radomly wound one with a ferrite core (torodial). Heres a pic of the IGBT on the heatsink with the inductor. You cant see the wounds, but its single layer with ~1mm in between each winding.
EDIT: So it turnsout thers some scraped enamel or something on the inductor, so i took it of the heatsink. using 200ohm resistors and a 4.7uf cap in the 555 circuit, it now goes up to almost 200 exactly in a few seconds. I tried the ceramic capacitor, but not enough to do anything.
EDIT 2: it now works with a 10nf capacitor, and i got a inductor from a computer PSU. It jumps to 150v in under a second, but the IGBT gets very hot very fast, is this normal?
relized i didnt post the part:
i have 5 right now, 1 fried (i think it was gate over current)
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