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Topic: Voltage step up alternatives (Read 2076 times) previous topic - next topic

olof_n

Oct 27, 2012, 04:49 pm Last Edit: Oct 27, 2012, 05:43 pm by olof_n Reason: 1
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 :)

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

dhenry

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.

olof_n

Thanks for the quick reply!
That is good because alt 1 was very easy to build.

/Olof

James C4S

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.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

michael_x


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?

dhenry

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.

BulletMagnet83

#6
Oct 28, 2012, 12:36 pm Last Edit: Oct 28, 2012, 04:09 pm by BulletMagnet83 Reason: 1
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 :D Think I might build a permanent version, it's got to be useful for something!

dhenry

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.

BulletMagnet83

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!

olof_n

700V :) - maybe you could build a fly killer racket.




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