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Old 25th December 2006, 08:20 PM   #1
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Default what use for a boost converter ?

I built a boost converter yesterday without knowing it @ first, now the question is, what can one of these be used for ?

Heres a schem and some pics of the thing.

Click the image to open in full size.
http://img207.imageshack.us/img207/1...ture009uj7.jpg

Heres a video of it doing 12-24 (guessed) volt out to a little motor.
http://www.youtube.com/watch?v=Ub6SzmrP0Ak

Input is 12v from a battery pack, and a estimate that it doubles the voltage. The inductor is from a energysaver lamp ballast so i dunno inductance.
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Old 25th December 2006, 08:35 PM   #2
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Congratulations
You just build a 12 to 24 V DC to DC converter

Great for driving 24VDC equipment fron your ordinary car battery
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Old 25th December 2006, 08:40 PM   #3
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The weird thing is i built it without myself knowing it, dident know what the heck it was until i checked that smps site.

Does that mean i suck on electronics ? Any easy way to find out the inductance of the coil ?


What factors determines the output voltage, caps max volt<age, switching fet, diode ?
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Old 25th December 2006, 08:50 PM   #4
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Why do you think you suck at electronics ???
I consider my self very experienced, but I don't no a s*** about smps designs, so I would feel like you if I had build it

You ask what determines the output Voltage....
I may not be the right to reply, but I guess that the 555 toggling frequency and the cap sets the max load you can connect
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Old 25th December 2006, 09:50 PM   #5
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Maybe Eva knows the answer, Tho my switching fet only takes 100V so maybe i shouldent attemt to get the voltage up much more as i dunno what it is unloaded.

I have seen a boost converter doing 100v from a 8.5V source, it wasent too different from mine except diff 555 topology.
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Old 26th December 2006, 12:02 AM   #6
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Tekko,

You can find thousands of good references to boost converters on the Web. IC and magnetic vendor information is especially helpful. See for example; www.linear.com.

The circuit you have shown is indeed a boost converter, but it has no voltage regulation, because it is open loop.

A simple way to understand boost converters is to think of energy balance. Assuming discontinuous operation, the inductor energy is
1/2 L I^2. This energy goes into the load and the output cap. The cap will charge up until this is satisfied. This could lead to excessive cap voltage without the necessary feedback.

Rick
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Old 26th December 2006, 08:46 AM   #7
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In your case output voltage depends on frequency, higher freq., higher output voltage.But if there is current demand, voltage will fall down, as you would have current limiting. I think...
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Old 26th December 2006, 10:20 AM   #8
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I had closed loop earlier but i removed that as i was so high in voltage that it threatened to blow up the 555.
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Old 26th December 2006, 12:27 PM   #9
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Now i have done some measurements and calculations and found out that total effecienty is around 90-95%, not bad for something tossed together over an mxas eve.

Unloaded output voltage is 65 volts, when loaded with 400mA voltage is around 20-22V, at input this corresponds to 6.4 volts on the battery back that reads 11.95V unloaded, and 1.5-1.8 Amps. So output 8 watts and input 8.25 watts, the measurements and math says 96% eff, not bad!!
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Old 26th December 2006, 12:59 PM   #10
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haha thats really good. probably it could be better if you had higher input voltage, something like 12v.
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