The discussed concept was designed and presented in a few of my previously published posts: 300 watt sine wave inverter circuit, and 556 inverter circuit however since the waveform were not confirmed by me the relevant circuits weren’t completely foolproof.
Now it’s been tested, and waveform verified by Mr. Robin Peter, the procedure revealed one hidden flaw in the design which has been hopefully sorted out here. Let’s go through the following email conversation between me and Mr. Robin Peter.
I built the simpler modified sine wave alternative version IC555’s,with no
transistor. I changed some of the values of the resistors and caps
and did not use[D1 2v7,BC557,R3 470ohm]
waveform. IC1 produces the 200hz 90% duty cycle pulses(1 image), which
clock IC2 (2-images) and therefore IC3(2 images, min duty cycle & max
Your modified sine wave circuit diagram looks correct but the waveform isn’t, I think we’ll need to
use a separate oscillator stage for clocking the 4017 with frequency fixed at 200Hz,
and increase the frequency of the topmost 555 IC to many kHz,
then check the waveform.
That’s great, exactly what i was expecting, so it means a
separate astable for the middle IC 555 must be employed for the intended
results….by the way did you vary the RMS preset and check the
waveforms, please do update by doing so.
So now it looks much better and you can go ahead with the inverter design by connecting the mosfets.
Thanks very much
More Updates from Mr. Robin
apply to pin 5,and how would you synchronise it so that when pin 2 or 7
go + the peak is in the middle
to ground.And the triangular wave looked like this(attatched).Not too
The following images show the various waveform images taken from across the output mains winding of the transformer. Courtesy – Robin Peter
No PWM, no Load
No PWM, with load
With PWM, without load
With PWM, with load
The above image magnified
The above waveform images looked somewhat distorted and not quite like sinewaves.
Adding a 0.45uF/400V capacitor across the output drastically improved the results, as can be witnessed from the following images.
Without load, with PWM ON, capacitor 0.45uF/400v added
With PWM, with load, this looks very much like an authentic sinewaveform.
All the above verification and testing were conducted by Mr. Robin Peters.
More Reports from Mr. Robin
that if I increase the batt voltage to 24v the sinewave did not
distort when I increased the duty/cycle.( ok,I’ve regained my
noticed a few things that were taking place,as I increased the D/C the
trafo makes a noisy humming sound(as if a relay is vibrating back and
forth very quickly),The IRFZ44N’s get hot very quickly even with no load
system.The humming noise is not so bad and the Z44n’s don’t get so
hot.[of course no sinewave}
they are toriodal} out of a switch-mode power supply.The result was no
improvement in the output wave(no change),The trafo output voltage also dropped.
Adding an automatic load correction feature to the above modified sine wave inverter circuit idea:
The above shown simple ad-on circuit can be used for enabling automatic voltage correction of the inverter output.
The fed voltage across the bridge is rectified and applied to the base of the NPN transistor.
The preset is adjusted such that at no load the output voltage gets settled at the specified normal level.
To be more precise, initially the above preset should be kept at the ground level so that the transistor says switched OFF.
Next, the 10k RMS preset at pin#5 of the PWM 555 IC should be adjusted to generate around 300V at the transformer output.
Finally, the load correction 220K preset should be realigned to bring down the voltage to may be around 230V mark.
Done! Hopefully the above adjustments would be enough for setting up the circuit for the intended automatic load corrections.
The final design might look like this:
The following filter circuit can be employed at the output of the above inveter for controlling Harmonics and for enhancing a cleaner sinewave output
The above design was studied and further improved by Mr Theofanakis, who is also an avid reader of this blog.