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Author Topic: Voltage step up alternatives  (Read 1262 times)
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Sweden
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Hi!

I need to build a boost converter (step up to 30-40V 100mA 20mA to drive a IV-18 VFD) and have found three alternatives.

Alt 1.  555 IC, Inductor, Diode and capacitor (http://www.benjscott.com/2009/07/555-boost-converter/)
I tried alt 1 this week and it worked fine. By modify the frequency on the 555 I could change step up voltage easy.
First try I got 120V from 5V smiley

Alt2. MC34063
Bought 10 pieces of MC34063 from ebay. Never used them but should be able to work as a step up converter to 40V.

Alt3. Voltage tripler circuit (http://www.electronics-tutorials.ws/blog/voltage-multiplier-circuit.html)
If I could find a 12v AC/AC adapter, I could triple the voltage to 36V DC.


What is the pros/cons with the three alternatives?

/Olof
« Last Edit: October 27, 2012, 10:43:54 am by olof_n » Logged

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1: cheap and stable;
2: cheap. but not as efficient;
3: not workable for your purpose.

You can also configure your arduino into a boost controller.
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Sweden
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Thanks for the quick reply!
That is good because alt 1 was very easy to build.

/Olof
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I'm not familiar with the current requirements of the VFD, but the 555 solution is only ideal if the load never varies.  The MC34063 is a regulator and will provide a stable output as load as the load is within its specs.
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You can also configure your arduino into a boost controller.
By simulating a 555 (oscillator with variable frequency) ?
If there's more about it, can you please tell a bit more?
Controller means regulating, right? Is the Arduino ADC fast enough to work in a closed loop in that area?
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Quote
but the 555 solution is only ideal if the load never varies.

Depends on how you have implemented it. For example, applying the feedback to Pin 5 will help hold the voltage steady under varying load.
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I tried the 555-based step up circuit last night, just to see how I got on with it using the parts I had on-hand... it worked surprisingly well! For the 555 stage I used:  

R1 & R2 = 100ohms
C = 0.22uF

And for everything else:
Diode = UF4007
MOSFET = 2SK2718 (pulled from an old dot matrix printer)
L = 470uH

Setting my bench supply to 7.2V I was getting well over 700V on the output with a current draw of around 100mA, and it charged a small bank of photoflash caps very quickly smiley-grin Think I might build a permanent version, it's got to be useful for something!
« Last Edit: October 28, 2012, 10:09:56 am by BulletMagnet83 » Logged

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Some people will use the 555-based boost converter for tube amplifiers so yes, it can work.

However, 7.2v -> 700v means 10% duty cycle and that may be pushing closer to the chip's limit - I think they are like 5% to 95%. Check your datasheet to be sure.
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South England
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I just checked on a 555 calculator, and according to that it's 66.6% duty cycle and 21.8KHz. Oh well, it was fun to play with anyway... with a few tweaks I might be able to make something useful out of it. I quite fancy playing with an IV-18 (or similar) myself, they're cool looking tubes!
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700V smiley - maybe you could build a fly killer racket.



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