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Forum Index : Electronics : Voltage doubler/ boost converter
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Gill Senior Member  Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day all, I am looking for a simple circuit that will provide 2 or more volts above battery voltage(11 to 15.5)@ 500ma. Application is for gate switching of N channel mosfets on the supply + as so much cheaper than P channel. Have found several possible circuits for 3,6,& 9volts but need modification to suit 12v battery supply, so maybe someone knows a suitable circuit?  was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| RossW Guru  Joined: 25/02/2006 Location: AustraliaPosts: 495 |
500mA ?? You shouldn't require much more than a mere sniff to drive fet gates :) Do yourself a favour and grab am IR2184 driver. It's a small (8-pin) and cheap ($2-3) beast that takes (in its simplest form) two inputs. The chip uses your PWM drive (high frequency) with an on-board bias generator to create the bias for high-side switching. It also includes a bunch of other circuitry that makes high-side and low-side drive simple and easy. If thats not to your taste, in the past I have used 3 LEDs in series in PV mode to create a nice, isolated bias. Each LED was in a small bit of heatshrink tube with another LED at the other end (6 in total). I used water-clear lens, orange LEDs because I had a few hundred. Drive the "drive" side in series at 10mA and was getting easily 4V out from the other side. Not terribly elegant, but simple, cheap, effective and very well isolated :) |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5031 |
Are you sure you need 500mA? If you can get away with less you could use those little step up inverters from old network cards. I used these to power a couple of LCD panel meters http://www.thebackshed.com/windmill/articles/PanelMeter.asp, they can source up to 200mA. This will give you a isolated 9 volts, that you could connect on top of your existing battery voltage to give 20+ volts. I like Ross's idea with the LED's, will have to remember that one. A LED will work like a tiny solar cell, so by facing 2 LED's at eachother, one lit, you create a isolated power supply. Not a lot of current, but it would work. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Chris Senior Member Joined: 12/09/2005 Location: AustraliaPosts: 146 |
Google, switch mode power supply, boost converter. They can be complicated to design one, but they are abosultely awesome once they work. Im building one at the moment, for one of those Oatley 200w motors that produce only about 3-6v, to bring it up to about 15v. You can get really nice efficiency too, about 80-95% efficient if you design it well. Ill post my design when its done, but it will be a while  |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Gee thanks for the quick response fellas, Ross, Downloaded data sheet on IR2184. Supplier awaiting delivery @ $6-9x wholesale. Will get one to play with. Never heard of the diode transformer method before, but had made opto coupler in similar manner many years ago. Must give that a test run too. Glenn, Knew I'd read about those network card thingies somewhere before, but was all very vague on the detail. Checked the junk box and low and behold I have one. Just need some Googleing. Chris, On a good day I'd love to play with boost converter but of late everything is turning to surely you know what I mean. So will pass on that one for now though have spent all last night looking into them so know that what you say is viable if not a bit expensive. Good luck with the project. Ok, thanks for all the help. That will get me started. Now back to the monster. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Just for a giggle.... I had 5 mins spare so threw one together for you.... just to prove it works :) (Each image should link to a larger version if you click on it) 
With the power on and the torch off (just a little single-LED toy torch, proves the concept)... 
And with the torch ON: 
Much more impressive in the dark: 
and 
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Wow! I am really impressed. I know a solar panel is a pn junction but never would have guessed there would be the surface area in 2 led or the light intensity from 1 led for that to have worked. Truly amazing. Thanks Ross. Like Glenn, I will keep that one stored in brain area called 'Handy Tricks' as I figure a few others will too. Noticed you used clear led's and not the tinted ones, and you say green? I know the different spectrum light emitted has different intensities, I wonder if thats why you chose green as it is also has a corresponding light receptiveness? I guess so. Thanks again. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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South Easter Newbie  Joined: 18/06/2007 Location: Posts: 36 |
Hey Gizmo, I checked out yr LCD panel page. and am sitting with an old network card in front of me (confounding the datasheet sites by looking for CFUS0509-C!). I am not sure I understand why you use a 7805 to get 5V, and then step that up to 9V? Would it work to just use a 7809 (or add a 4V zener to the 7805) and get the 9V directly? South Easter http://windpower.org.za |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5031 |
Hi South Easter. The power supply for the LCD meters needs to be isolated from the voltate they are measuring, by that I mean no electrical connection between their power supply input and measure input. I use the little 5->9 volt inverters to provide the isolation, easy to come by and usually free. Most of the inverts use the same pin connections, if it looks the same as the one on my web page then I would almost bet it will work the same. The 0509 in the model number is a give away, 5 to 9 volts inverter. Hope that helps Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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