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Square wave current output to sine wave

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reservoirdog

New Member
Hi guys, this is my first post. It is something I require for a practical reason.

I bought a UPS that I found out, quite unfortunately, outputs square wave current. This does not sit well with my adapters (WiFi, modem, etc.) and I have to routinely buy new ones.

So I was wondering if I could juryrig a converter that'll convert the square wave output to sine wave. That way I won't have to buy a new UPS.
 

Vizier87

Active Member
what are the output details? You can take a look at this:
**broken link removed**

the capacitance and inductance values determine the smoothing of the square wave output from the 555 timer, you can try that.
 

Hayato

Member
Of course a low pass / band pass filter would smooth the square wave.

BUT... How would you amplify the sine wave without major issues? Think about it, a 500VA UPS would need a amp. with, lets say, 400W RMS output.
 

Hayato

Member
A square wave requires only switching. A sine wave requires amplifiers operating in the linear region, it is harder to design and more expensive. A filter is low power. You have to filter a square wave to get a sine and then amplify it.
 

crutschow

Well-Known Member
Most Helpful Member
You could use an LC filter to filter the output, but the parts would be large. To resonate at 60Hz requires a 50µf non-polarized capacitor and a 140mH inductor, for example.
 
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Sceadwian

Banned
The inductor would just be bulky. The capacitor might be a problem as it'd have to be highly over engineered to sustain ripple current for any serious power.
 

crutschow

Well-Known Member
Most Helpful Member
The inductor would just be bulky. The capacitor might be a problem as it'd have to be highly over engineered to sustain ripple current for any serious power.
The capacitor should probably be an oil-filled film capacitor such as they use for AC induction motor run (not start) applications.
 

audioguru

Well-Known Member
Most Helpful Member
A sine-wave inverter uses a high frequency DC to DC high voltage output converter using a small ferrite high frequency transformer then uses Pulse-Width-Modulation to construct a 50Hz or 60Hz modulated sine-wave that has the high frequencies filltered out with a little ferrite LC filter.
It does not use a linear amplifier that wastes a lot of power getting very hot.

A square-wave inverter has half of its output power in its harmonics so if it is filtered somehow (a filter will waste a lot of power) then its output voltage will be 0.707 times too low without counting the loss from the filter.
 

mbarazeen

Member
when you pass it through a transformer of bit higher rating, you may probebly end up with some good out put, but there will be a big power waste in the transformer.
 
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