555 dc to ac inverter

[stop4stuff]

found a circuit for an inverter today, 5 - 15 v DC input, 120 - 240 (50 - 60 hz) AC output, uses the 555 timer.

http://www.uoguelph.ca/~antoon/circ/555dcac.html

Part of Tony van Roon's site;

http://www.uoguelph.ca/~antoon/

not sure if it's a pure sine inverter tho

paul

[drdongle]

Square wave out put, though the inductor will probably round off the edges a bit, out put will be limited unless you realy beef up the tranistors.

[stop4stuff]

Could this circuit be made to work as a pure sine inverter if the transistors were fed a pure sine feed?

If yes, could a very small alternator be used? The alternator could be driven by a motor or if the unit required a cooling fan, the alternator could run from the same motor as the fan... could the same alternator be monitored and the motor speed adjusted accordingly to ensure the correct frequency?

'As is' would this circuit be any good for running 240v CFL's?

cheers,

paul

[drdongle]

Yes it could do sine wave, and yes it could CCFL's just use a 240 to 12 transformer rather than a 120 to 12 transformer. I cant imagine why would want to make it so overly complicated just us a 741 op amp as an oscillator and drive it with that.

[johnlm]

Just a note here.  The Transistor drivers here are a push-pull emitter follower configuration so the voltage level coming out of them going to the transformer will be slightly less (0.6V less) than the voltage being fed into the base(s) of the transistors.  So if you fed the output stage with a small alternator (or sine wave oscillator) the output of the generator / oscillator would have to be around 12 to 13V (rms)to match the 12 V input of a transformer.  Which brings up the question of how well this ckt works as the 12 V rating on a transformer is in rms (34V peak to peak) and the voltage being fed out of the 555 timer in this ckt is whatever the VCC input voltage is being fed to the 555, which if one goes by the schematic is 15V DC which gets turned into a 0 to 15V peak square wave so is less than 1/2 the peak to peak voltage needed to get 120 V RMS on the output of the transformer.  Make sense?

John

[johnlm]

I suspect one would need to really use a 120 to 6.3V transformer running backward to feed it with the 12V peak from the 555 to get 120 RMS.  The text on the circuit is somewhat vague on this just says "using a transformer with the appropriate turns ratio"

john

[drdongle]

The RMS voltage is more like 20.5 volts 12 X 1.707

[johnlm]

Dr D,

Not sure where you came up with 1.707

To convert rms to peak multiply by 1.414

To convert peak to rms multiply by 0.707

To convert rms to peak to peak multiply by 2.828

To convert peak to peak to rms multiply by 0.3535

To convert rms to avg multiply by 0.9

To convert avg to rms multiply by 1.11

Right out of any book.

12v rms = 33.936 v peak to peak

John