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60 hz square wave to sine wave circuit has issues...?
How would i create a 60 hz or 50 hz square wave to sine wave low pass filter?
I have a neat little square wave circuit i created using a 555 timer, yet, i wanted to create a sine wave. There was a 2700 uf capacitor and a 1 uh coil of wire at the end of one of the outputs, yet that did absoultely nothing to change the circuit into a sine wave, as the circuit says its supposed to be. http://www.scribd.com/doc/8539824/Small-%E2%80%A6 is the page i got the circuit from, and i used the power transistors 2n3055 and 2n3791. I'm getting a square wave, and not a sine wave. What am i doing wrong? And i also, used a handmade 1 uh coil of thin gauge magnet wire as the inductor. Any thing wrong with this circuit?
also then, what would i need to do to get a sine wave from this? and i tried hooking it up to a 60 hz laminated iron core transformer. It didn't really work. It still output a square wave i believe. Does it need to be a filament or whatever transformer for this to work? Or will any regular transformer fit the job correctly? ANNDDD, how exactly would i go about making a filter for this to work correctly? Thanks, and please help. xD
2 Answers
- Mr. Un-couthLv 71 decade agoFavorite Answer
A pure sine wave contains only one frequency. A perfect square wave contains a sine wave of a smaller and unique amplitude of every frequency in the spectrum. Neither of yours is going to be pure nor perfect. However to covert a perfect square wave to a pure sine wave you must filter out all the frequencies contained in the square wave except the one desired frequency. In doing so the peak amplitude of the remaining sine wave will be attenuated to somewhat less than the peak of the square wave.
In your circuit C4 in series with L1 and the primary windings of T1 form a series resonate circuit whose impedance is minimum at the desired frequency of 50 - 60 Hz. That means that maximum current will flow through the primary winding of T1 at a frequency of 50 to 60 cycles. All other frequencies will be blocked or greatly attenuated.
It was recommended that a filament transformer be connected in reverse and used because of it`s low price and availability I suppose. Other transformers may possibly be used. The problem you must remedy first is the one with the filter formed by C4, L1 and the primary winding of T1. They must have a capacitive value and a total inductive value such that when connected in series they resonate somewhere in the neighborhood of 50 to 60 Hz. When you have accomplished this and have a 50 - 60 Hz square wave input from the amplifier to C4 then you will have a 50-60Hz sine wave of sorts out of the secondary of T1 assuming the circuit is connected as shown in the diagram.
- billrussell42Lv 71 decade ago
The transformer should have a secondary voltage equal to the output voltage of the oscillator. If you have a 12 volt supply, and the output is a sine wave, the output is 12 volts p-p, which is 4.2 volts RMS. So if you have a transformer with a 4 volt secondary and a 120 volts primary, you will get 120 volts RMS out of it.
A square wave is a little different. A 12 volt P-P square wave has an RMS voltage of 6 volts, so you would need a 120 to 6 volt transformer.
As I said, filtering out the harmonics is difficult. You would be better off making a sine wave oscillator to start with.
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