DC to AC

[Annakin4]

How can you create AC from DC? Are you able to use MOSFETs and caps in an H-bridge configuration? And if you do all of this, how'd you control it?

[AG6QR]

An oscillator is a device for creating AC from DC.  They come in many configurations, frequencies, power levels, output waveforms, etc.  There are many strategies for controlling them. 

Special types of oscillators include an "inverter", designed to produce something usable as a substitute for mains power, usually from a DC input as might be found from a car's electrical system.  Another special oscillator is a "function generator", designed for wide range control of frequency and amplitude, usually with some control of waveform, and maybe with some ability to modulate the output with another signal.

There are many chapters of textbooks written about oscillators.  Do you have more specific applications in mind?

[Annakin4]

Im trying to create a small inverter that can make a small AC voltage to play with filters, I have some transformers but I would like to control the proporties of said waveform. I was thinking a H-bridge would work, but could you explain how an ocilliator would create an AC voltage from DC? And why wouldnt an H-bridge work?

[Grapsus]

What kind of filters do you want to study ? Using a switching bridge will probably not give you a pure sine AC, it will be more like a distorted square wave.

[Annakin4]

High pass and low pass filters, trying ways to go from AC to DC, messing with capacitors and resistors. It would create a square wave, but if you had a micro-controller, could you have a large cap and a digital pot to turn the square wave into a proper sine-wave?

[AG6QR]

Im trying to create a small inverter that can make a small AC voltage to play with filters, I have some transformers but I would like to control the proporties of said waveform. I was thinking a H-bridge would work, but could you explain how an ocilliator would create an AC voltage from DC? And why wouldnt an H-bridge work?

It sounds like you're describing an application for a function generator.  It's an already-built box that allows you to create waveforms of varying properties, making it easy to control the amplitude and frequency, as well as the shape.

The classic way to study filter design is to use a function generator to create an input signal, put a filter of some sort in the middle, perhaps put a load on the output, and use a two-channel oscilloscope to look at the input and output waveforms of the filter.  More channels of a scope might be useful to look at intermediate points in the filter.

An H bridge is a circuit that allows you to switch the polarity between a power source and load.  It might be used as a piece of an inverter, or perhaps even part of a function generator, but you need something to drive it.  It needs control signals to drive the switches on the legs of the H, plus you need some sort of input power supply, perhaps with a controlled waveform.  If the input power is a steady DC, the H bridge can only generate squarish waves of alternating polarity DC, and it can only do that if you've got some kind of oscillator driving the switches of the H bridge.  Many times, a microcontroller of some sort is used, and the oscillator that ends up driving everything is the clock signal for the microcontroller.

I don't know what your budget is, nor do I know how much you want to learn about generating AC waveforms versus learning about filter design.  If you want to concentrate on filter design and can afford a function generator, I'd recommend getting one.  There are a number of choices, from basic kits built around a AD9833 DDS chip, through full-featured arbitrary waveform generators.  If you're willing to be limited to audio frequencies, a PC or smartphone can be used as a reasonable function generator, within limits, and it may be free.  Look for "function generator software" on your favorite search engine, and you'll find lots of examples.

If you want to learn how to generate AC signals instead of acquiring a black box that will do it for you, that's a good thing to pursue, as well, but it's a different goal.  Some terms to search for: "BJT Astable Multivibrator", "555 timer", and "Wien Bridge".  Lots more types of oscillator circuits are described here: http://en.wikipedia.org/wiki/Electronic_oscillator#Circuits .

[Simon]

You need a cheap signal generator and possibly an amplifier if you need any power but after 20 KHz that could ecome more difficult and expensive. You need to be clearer on what your doing.

[Ian.M]

PC running a waveform generator with soundcard output => line level audio isolating transformer => cheap small audio amplifier appropriate to the power level you want => 47R shunt across the amp output and 10R series to the load.

The amp needs to have one grounded output terminal, so not a bridge configuration.  The 10R resistor need to be rated for 80% of the amp's max continuous output power into 8R and the 47R resistor rated for 20%.   The resistors provide damping and some isolation so that difficult loads don't blow the amp.