Can a square wave generated using an astable NE555 be used as input of a transformer instead of AC? Say, I generate a square wave of 60Hz using NE555 and a 24V at 6A supply and feed it into a transformer with 50:1 turns ratio, will I get 0.48V at 300A out?
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1\$\begingroup\$ I think that is how most chopper circuits in switch mode power supplies work. A transformer just needs changing current to prevent saturation and to cause induction, a square wave should fit the bill. \$\endgroup\$– Jarrod ChristmanOct 6, 2014 at 2:31
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4 Answers
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You'll need to couple the square wave with a capacitor to the transformer because standing DC voltages will just cause heat but there is no problem feeding a transformer with a square wave in principle.
In practice, if you fed a 60Hz "power" square wave to a transformer, the higher order harmonics in the square wave would mean that a regular AC power transformer wouldn't be as efficient as being fed with a sine wave.
A 24V 6 A supply is capable of providing a power of 144 watts and your output requirement is also 144 watts so you need to be aware that you might only get 90% efficiency and expecting 144 watts from the transformer output is a little naive.
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1\$\begingroup\$ But wouldn't adding a capacitor make the square wave back to normal DC voltage? \$\endgroup\$– AvZOct 6, 2014 at 9:19
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1\$\begingroup\$ The capacitor couples the square wave to the transformer i.e. it is in series - it removes the dc content of the square wave - it isn't connected to ground. \$\endgroup\$– Andy akaOct 6, 2014 at 9:30
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1\$\begingroup\$ @AvZ it needs to be a value of several microfarads I think because you don't want to square wave to droop or become differentiated under load. Do you use a simulator (LTSpice is pretty much everyone's free-favourite) \$\endgroup\$– Andy akaOct 6, 2014 at 15:04
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\$\begingroup\$ @AvZ are we done here now or do you still have questions on this subject? \$\endgroup\$– Andy akaOct 31, 2021 at 20:07
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For every action there is a reaction, and think how a transformer can buzz with AC. Now make it a square wave and you could hammer it around a bit, even more so than with sinusoidal AC. So, it depends on your frequency a bit, too, I'd say, for you to set up a noticeable or worse mechanical standing wave in your transformer itself. However, depending on the size and robust quality of the transformer it should be OK to do at your power level, at least. On the other hand, will you get square wave out? I think it won't be "as square" as the input. The windings (and their proximity to the plates, if any), also create a changing inductive environment, so it may goof with the shape of electrical wave(s) a bit. And the fact that the transformer will have those mechanical waves (manifested as vibration or sound), assumedly worsening at certain frequencies, leads me to believe that it will not pass all frequencies at the same efficiency, thereby further distorting the "squareness" of the wave. That may be saying the same thing twice in two different ways, but maybe at least for more than one reason. It may be, though, that the two are just manifestations of the same condition. Not sure at the moment. Either way, not going to be a perfect representation of the input. Also, I wonder if you are going to get EMF (or reverse EMF) effects at the points of voltage reversal, which may grossly distort the output.
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\$\begingroup\$ First upvote since 2014! And you just had 1 reputation score until now. \$\endgroup\$ Mar 14, 2019 at 5:10
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This is exactly what happens in the ignition system of older cards with points. The make-and-break of the points provided a 12 V square wave to the ignition coil (a transformer)!, which then output several thousand volts. A similar method was also used in "the olden days" to produce high voltage AC from a battery, such as in spark-gap radio transmitters.
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I don't see why it would harm anything other than your efficiency, and the fact that it may saturate if the core isn't rated for the frequency and pulse width you provide until it is tuned to function.. All car audio amplifiers pretty much use pulse width modulated power supplies and they could use tiny to massive transformers in the audio section. It's the circuitry you use along with it that will aid it's output.. smoothing capacitors generally change the square wave to a sinewave under load so I think youll be just fine, however, ensure you will not be blocking lower frequencies with the cap as the cap in series is a crossover. Measure your impedance of the circuit to . Try adding a capacitor to your load and fire up a 100ohm resistor with a capacitor of say 47uF to your fgen with a square wave of the same frequency you are thinking of using, then scope it's output to see what happens.. I think you'll be pleasantly surprised. Square wave inverters have been known to work much better than the choppy, spiky and really crappy modified sinewave inverters.. In fact, I've bought several of those clunkers come to find out that the oscillator circuit could easily be swapped with a true sinewave oscillator board in some of the most standard brands out there. If you look in the circuit for the inverter, you'll see a pcb that normally plugs in vertically and they are pretty standard in China and on Ebay. 99% of the inverter and amplifier manufacturers produce these units for all of the manufacturers worldwide, so, they make it easy upon them selves so swaps can be made in the time of demand. If you are trying to invert dc to ac using this method, it's simple to change, and buy if you pull the oscillator out of the device before ordering!
