# DC to AC converter

Discussion in 'General Electronics Discussion' started by popgalop, Aug 27, 2012.

1. ### popgalop

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Aug 27, 2012
How would I make a basic circuit that would convert 9 volts dc to over 100 volts ac what parts would I need

2. ### CocaCola

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Apr 7, 2012
What do you plan to do with the output?

You can go from very simple pulsing the 9V into a 1:11-ish transformer that will get you about 100V out pulsed DC that will work for many AC applications, to using a center tap transformer and switching the 9V polarity from side to side to get about 100V AC out, or go all the way to a full blown advanced design like those found in commercial power inverters...

3. ### BobK

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Jan 5, 2010
The main question is how much current are we talking about.

Bob

4. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011

What frequency AC? What waveform? What current?

The simplest thing would be just to tell us all about what you want to do. We can then make useful suggestions rather than stabbing in the dark which wastes everyone's time.

5. ### richie

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Sep 4, 2012
I'm also interested in an answer to this, i'd like to convert 9 volts dc to over 100 volts ac, somewhere in the range around 100MHz-1GHz (any point in here is good) if possible.
sine wave is good, (and later a modulated sine wave in the khz range)
low current is fine

6. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
richie, generating 100VAC at a frequency of 100~1000 MHz requires a huge amount of power to overcome the stray capacitance. Even just one picofarad of stray capacitance has a reactance of 160 ohms at 1 GHz so you will waste 625 watts of power for every picofarad of stray capacitance at 100V RMS! In other words, it's not really practical. What do you want to do with this voltage?

7. ### richie

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Sep 4, 2012
thanks krisbluenz, appreciate the response!
assuming that i need to get it working, and i can work on the lower end, say ~50-70 peak to peak (or even slightly less, maybe 30-40 at a push), and I could go down to ~100MHz?
the total power can be ~<1 W

Last edited: Sep 5, 2012
8. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
Do you have a specific piezoelectric crystal in mind? Can you link to a data sheet?

Piezoelectric transducers have significant capacitance. Calculate the amount of energy required to make 50Vp-p at 100 MHz appear across even just 1nF of capacitance:
V=50/2/sqrt(2) = 17.7V.
Xc = 1/(2 pi f C) = 1/(2 pi 1e8 1e-9) = 1/(0.2 pi) = 1.6 ohms
P=V^2/R = 17.7^2 / 1.6 = 200W.

What kind of "waves" are you talking about? If you're talking about physical motion, the only things that have low enough mass for you to move them any significant distance at 100 MHz will be electrons, I think!

9. ### richie

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Sep 4, 2012
Yeah, i'm using lithium niobate, used for generating surface acoustic waves.
i have that side of things all sorted. it's just the power source side that i want to make portable and battery operated, and i know that ~1W at 100MHz is heaps for my purposes

Last edited: Sep 5, 2012
10. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
OK, I'm way out of my depth talking about lithium niobate.

Are you serious about making things physically vibrate at 100 MHz?

I think if you only want 1W dissipation, you'll have to reduce the voltage a lot. Do you have a figure for the capacitance between the electrodes? I assume you will be attaching electrodes to a piece of this stuff?

You should be able to calculate the voltage you'll need using the formulas in my previous post. Once you know the capacitance, you can calculate the reactance at your desired frequency, and from that, and the power dissipation you want, you can calculate the voltage you will need.

I would imagine a radio transmitter might be a good place to start. It's not too hard to generate 1W at 100 MHz at a relatively low voltage. Do a google search.

11. ### richie

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Sep 4, 2012
Heh yeah. With LN it's not so hard to wake waves which, while small, have huge huge accelerations (millions of g's) for use with fluids etc..

i've had a look at the transmittors, the ones i've found are all quite large and probably overkill. i was hoping more to build a small simple circuit to put a battery in, and generate the waves. basically just something to take the DC -> AC, and amplify a little.

12. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
Describing what you want using simple terms doesn't magically make it simpler to make! When you're dealing with high frequencies and significant power, simple electronic design principles don't apply, and special techniques are needed to make something that will actually work.

I'm not sure what size you're hoping for, but I think a radio transmitter rated for the amount of power you need is probably your best starting point, at least, for finding something that will work for your application. This project is way outside my experience, so that's all I can say.