Previously I wrote about How 12V to 220V AC TL494 Inverter Works whose circuit diagram is shown below. This circuit is a Push-Pull DC-to-AC Inverter (often used for 12V to 220V conversion) built with TL494 Pulse Width Modulation (PWM) controller. It uses a high-frequency switching topology to drive a center-tapped transformer. Talking about the TL494 push pull inverter configuration, it used C1 of 15nF and 2.2k POT connected to pin 5(CT) and pin 6(RT) to tune and set the frequency to match with the transformer optimal frequency. The output control pin 13 was connected to pin 14 which means that the pin 13 was set to 5V by the internal 5V reference by pin 14. This means that the TL494 was put in Push Pull mode. In push pull configuration the TL494 outputs E1(pin 9) and E2 (pin 10) will alternate their pulses to drive the two halves of the transformer. Similarly, the DTC pin 4 was tied to ground which means minimum dead time. v. It used BC327 driver stage cleans up these signals to ensure the MOSFETs switch on and off as fast as possible. The MOSFETs acted as high-speed switches, "chopping" the DC input into the transformer primary. The center tapped Transformer stepped up this low-voltage chopped DC into a high-voltage AC output.
This TL494 push pull inverter can be modified to build a pure sine wave inverter, but this involves lots of tedious work and replacement of the TL494 PWM controller with EGS002 (EG8010 + IR2110) module or similar dedicated sine wave generator IC. Also, it involves replacing the push pull circuit with full H-bridge, replacing the center tapped transformer and adding LC filter at the output. One might also try another method, which is to feed 50/60Hz sine wave into the TL494 error amplifier which is running at high frequency like 20kHz. But this is complex and rarely produces clean sine wave. So, in these cases it is better to replace the TL494 with an Arduino or STM32. These can generate SPWM signals using look-up tables as in Pure Sine Wave Inverter Design with Arduino & IR2110 Gate Driver.
So, the easier and better way is to modify the above TL494 push pull inverter into a modified sine wave (MSW) inverter. A modified sine wave is a great "middle ground." It will run motors, lights, and most power supplies much better than a square wave. However, on must be aware that some sensitive clocks or high-end audio equipment may still "hum" because of the harmonic content.
Also, we need to address the transformer issue. For modified sine wave inverter, we can either use Large Iron-Core or a Small Ferrite-Core transformer. In the above Push-Pull square wave TL494 inverter we have used a Small Ferrite-Core transformer. Choosing between a Large Iron-Core transformer and a Small Ferrite-Core transformer depends entirely on the goal: do you want a "simple" heavy-duty build, or a "complex" high-efficiency modern build? Since the current design already uses Small Ferrite-Core transformer I will stick to the same.
I will continue writing about this in my next note. You can read about it in Push Pull TL494 Inverter to Modified Sine Wave Inverter - How to modify? blog post.
