Thank you very much Audioguru.

 

Hi people, i have a few questions which i know some of you may find annoyingly simple, but hey that's why i am seeking help on these forums.
I have got to a stage on my design where i have a PWM signal from discrete components. Where i am a bit lost is: i now want to drive a resistive load with a pure sine wave. My initial idea(which was not very successful) was to drive a complimentary pair of BJT's as a class B amplifier, then use an LC low pass filter. What i am getting out is just a negative square wave output. My questions are: Can you drive BJT's with a PWM signal? If so how do you connect them in a circuit? My sine wave reference signal is 50Hz, Triangular wave is 1.92KHz and PWM signal is 1.92KHz. Is this frequency enough? I need help on the amplifier circuit using BJT(they are available to me) and filter stage.Any ideas?

Thank you all.

 

You really need to post a schematic of the circuit you now have.
Otherwise, it will take a LOT of questions and answers before you get any kind of useful information.

 

Thanks SgtWookie,
Hereunder is my schematic. I also came across another circuirt on these forums which i am not sure if it can be used in the output stage of my circuit. I have also posted the circuit. Please help. I want to have the prototype up and running by the end of this week. Thanks.

 

I had forgotten to include my own output stage. Thanks once again.

 

Please save and post your schematic as a very clear PNG file instead of as a very fuzzy DOC file that cannot be seen clearly.

 

Sorry about that. I will try again.

 

Please don't post the same thread on more than one website.

PWM inverters do not use lousy slow old 741 and LM324 opamps.
They also do not use linear amplifiers (except to make the sine-wave oscillator).
They don't use a very low 2kHz frequency that makes a noise, they use 20kHz to 500kHz.

The output voltage of your circuits are very low. If you use a transformer to stepup the voltage then it might not work at a high frequency.
That is why pure sine-wave inverters that are sold have the PWM switching at 650V to make a 230VAC sine-wave. Then they use a small high frequency ferrite-core transformer in a power supply circuit to stepup the 12VDC to a high AC voltage that is rectified and filtered to make the 650VDC for the switching Mosfets.

 

I am trying to get as much help as i can. Also the output voltage and current i am looking for is only up to 50-60 v ac maximum and 2amps absolute maximum. Please what do you suggest so that i can finish this circuit? i really do appreciate you spending your time looking looking at my circuits.

 

An inverter provides 1000W to 3000W at the mains voltage and frequency.
What is your different little inverter for?

 

It is a challenge i have been set. I think it is precisely for that reason that it is difficult to achieve. I have redesigned the PWM output signal to 10khz with a voltage amplitude of 20v p-p. Can u please at least suggest a reasonable output stage i can use( amplifier,filter etc) to be able to drive a resistive load and get my sine wave output? i really need to finish this. Why were you saying this design is operating linearly?
Thanks.

 

The 43 years old 741 opamp is too slow to switch the output transistors quickly. So it is linear.
On the other website you showed an LM324 opamp that is even slower.

 

Thank you very much Audioguru.