Welcome back to the second part of our TL494 Modified Sine Wave Inverter series. In our
We will use Proteus simulation to measure real-time voltages and analyze the signal waveforms at every stage—from the high-frequency transformer output to the final 220V Modified Sine Wave.
Step 1: Measuring Stage Voltages
To understand the power flow, we first place meters across the key stages of the inverter.
The High-Voltage DC Rail (Stage 1)
The first stage uses a high-frequency switching signal generated by the TL494 to drive a ferrite transformer.
Observation: The DC voltmeter confirms an output between 310V and 340V DC.
Function: This serves as the high-voltage reservoir that the second stage will "chop" into AC.
The Inverter Output (Stage 2)
Next, we place an AC voltmeter across our load (a 220V bulb).
Observation: The second stage successfully converts the high-voltage DC into a standard 220V AC (50/60Hz) signal.
The Magic of the DTC Pin (Dead Time Control)
A critical part of this design is Pin 4 (DTC) of the second TL494. We’ve added a DC voltmeter here to monitor the control voltage.
The Result: With the POT set to provide 0.75V to the DTC pin, the inverter creates a specific "dead zone" in the pulse.
Why it matters: This dead zone is exactly what transforms a harsh square wave into a Modified Sine Wave, making it safer for your household appliances.
Step 2: Oscilloscope Waveform Analysis
With the voltages verified (315V DC in, 220V AC out), we now switch to the oscilloscope to visualize the signals.
| Channel | Color | Signal Description |
| Channel A | Yellow | Transformer Output ($V_t$): A high-frequency square wave. |
| Channel B | Blue | DC Filter Output ($V_o$): A smooth, high-voltage DC line after the capacitor filter. |
| Channel C | Pink/Red | Inverter Output ($V_a$ + inverted $V_b$): The final Modified Sine Wave across the load. |
The Waveform Breakdown
The Yellow Waveform shows the raw energy being pumped by the first stage at high frequency.
The Blue Waveform demonstrates how our 1000µF capacitor smooths that switching noise into a flat DC rail.
The Pink Waveform is the star of the show. You can clearly see the "steps" created by the 0.75V DTC setting, confirming that our H-bridge (or Push-Pull) logic is correctly alternating the pulses to mimic a sine wave.
Video Demonstration
Conclusion
This measurement phase confirms that the TL494 is an incredibly versatile PWM controller for both high-frequency DC-DC conversion and low-frequency AC inversion. By simply adjusting the voltage on the DTC pin, we can precisely shape our output waveform to hit that 220V RMS target.
Don't miss the previous tutorials in this series to master the full design:
Thanks for reading! Stay tuned for the next update where we take this design to the physical PCB.
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