# HOW is Frequency Altered in a Circuit?

Discussion in 'General Electronics Chat' started by quicksilver, Jul 2, 2008.

1. ### quicksilver Thread Starter Member

Mar 6, 2008
19
0
Mains frequency comes from the wall at 60Hz, we design a power supply and the energy is routed directly to a transformer in our example.....Is that 12Vac power supply frequency (at that point) still 60Hz? What acts upon a given frequency to alter it within a simple power supply design?

Are voltage altering transformers EVEN CAPABLE of altering frequency? A TRANSFORMER IN A MICROWAVE OVEN JACKS UP THE VOLTAGE BUT THE SAME FREQUENCY EXISTS. Yet superficially (it seems) that there are situations where other designs of transformers alter the frequency....I don't know if this is a short sighted observation.

Thank you for taking the time with this issue. I searched and found only definitions and conditions of frequency; not altering conditional situations.

2. ### silvrstring Active Member

Mar 27, 2008
159
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quicksilver,

A simple power supply can step the voltage up or down--whichever you design it for. The AC induced will still have the same frequency before the rectifier bridge. After the full wave rectifier bridge, the frequency will be doubled because what were the negative halves of the wave will now also be positive. The period is halved and the frequency is doubled. Is this what you mean?

3. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Transformers only change voltage. If you are thinking of SMPS, they first rectify the mains into DC and use a device like a power FET to drive a small transformer at a high frequency.

For circuits that do alter frequencies, look up "oscillator" as a subject.

4. ### quicksilver Thread Starter Member

Mar 6, 2008
19
0
You've BOTH been very helpful. I actually thought that the rectifier might alter the frequency but was unsure. My confusion began when studying the concepts involved in a Tesla Coil and the alteration of AC frequency therein.

There are many sources of free useful parts but to accomplish certain things the theories & study sources often don't take a concrete example and state "a full bridge rectifier will double the input frequency" (that's very simplistic, but you get the idea).
So I am correct in understanding that transformer dynamics cannot alter a given input frequency yet in the use of a rectifier I have a simple tool that does a complex job. Now I am beginning to understand why certain circuits ARE designed the way they are.

And oscillators......wow! Voltage-controlled crystal oscillators are fascinating in that they can allow for the development of radio jamming devices as well as electronic music. As I understand it Tesla Coils accomplish this phenomenon without the need for a VCO.

The whole subject began for me by looking at the way microwave oven capacitors are designed for 60Hz and was a free source of a potentially powerful and expensive cap-bank - but limited by their frequency. I wanted to learn more about how to alter frequency to put all the free parts available to the hobbyist to use. The MWO transformer yields a powerful (& free) way of getting a high voltage source. Albeit potentially lethal, if understood, could give the hobbyist several directions to go.

Boosting the frequency and altering the current allows a darn good HV source for a lot of experiments. Learning how to alter current alone provided hours of some interesting material. Frequency opens a whole new world! I would look at circuit designs and wonder why they need DC. principally because I didn't understand what the passive parts DO (in totality)....I can read theory, but having someone simply explain "this part does this" shows me "why" a circuit is built the way it is.....I love this stuff because it CAN be made understandable if the right examples are given.

Good stuff. Thanks!