the simplest way of creating ac from dc

[mielke]

I'm am trying to understand electronics by playing around with them, and I want to know the very simplest way of creating any periodically time varying current (AC)from a DC power source. I don't care about the shape or amplitude of the AC currnet as long as it has a periodic frequency...

Ive seen lots of diagrams in google searches about the above but i want to have an even more basic understanding of electronics than what I've found. They had a bunch of other stuff in the circuits to produce a certain voltage but for my knowledge level that distracts me from how an electronic device can convert a direct current to an alternating...So i am basically looking for a circuit design that has a battery and a couple wires and if you only add some simple electronic device (transistor, capacitor, etc...) than you can measure an alternating current.

thanks i hope that made sense...

 

[xnuke]

Inverters convert DC to AC. Learn about H-bridges used in inverters - the basic concept of H-bridges are about as simple as it gets. They have a DC supply and four transistor switches with associated control signals.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Noway2]

As you said, AC is a time varying waveform, whereas the DC is constant. When many think of AC, especially in regards to the AC power that is delivered at the common outlet, they think of it in terms of having positive and negative portions. It is important to realize that these portions are only positive and negative relative to another, completely arbitrary, reference point and are not inherently special. Creating the AC from DC generally requires switching. The simplest form would be to simply switch the output on and off. A simple circuit would be a common emitter transistor with a pull up to +V on the collector. When the transistor is on, the output (collector) would be (near) ground and when the transistor is off, the output (collector) would be +5V. You could use any number of means to cause the transistor to periodically turn on and off (for examples, look at harmonic oscillators). The end result would be an AC waveform of square shape and V volts. The same thing can be done with a relay, and just turn the relay on and off.

As I said, creating the AC waveform requires switching, at least in any sense that I can think of. I know you said a simple circuit, but I still sense that you are wondering about how does one create useable (sinusoidal) AC power from DC. This gets into a lot more complexity in implementation, but the underlying principles are the same, in that a DC source is applied to the load in an on-off fashion. In most applications, the DC is switched on and off at a rapid frequency (several kHz) and the duty cycle (time on - off) is varied, or rather modulated at the desired AC output frequency (much like AM Radio, but in this case at 50 or 60 Hz). The resulting waveform is then usually passed through a transformer to provide isolation which lets you pick a new zero/ground reference (typically the center of the transformer). So for example, if you had big batteries in series and the switching process gave you 0 and 200Vdc and you passed this through a 1:1 transformer, relative to the center of the transformer coil, you would have 0 and 200V which would be -100 and +100 with respect to the center of the transformers output coil. (In reality this is a bit of an over simplification as the transformer has a frequency dependent response and probably won't pass a square wave which consists of a lot of higher frequency elements - see Fourier Series).

 

[mikekilroy]

look up 555 ic. couple resistors, a cap, and periodic output.

 

[DRWeig]

You could make a simple L-C oscillator... Not a steady-state or long-lasting AC output, but a good one.

It's a good teaching tool for inductance and capacitance, especially if you have access to an oscilloscope or graphing multimeter.

Example:

http://www.electronics-tutorials.ws/oscillator/oscillators.html

Read more about L-C and resonance here:

http://en.wikipedia.org/wiki/LC_circuit

Best to you,

Goober Dave

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[IRstuff]

Since you don't care about shape, then simply switching between two voltages will result in a periodic voltage change. You can do this with a 555 and a relay.

TTFN
faq731-376

 

[RyreInc]

You can't get much simpler than a relaxation oscillator, which requires only a resistor, capacitor, and neon lamp.

 

[berkshire]

http://talkingelectronics.com/FreeProjects/5-Projects/Page16.html

B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[waross]

Use a DC motor to drive an alternator at varying speeds.


Bill
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