
How it work :
The master oscillator, a voltage reference and comparator collected on DA2. External elements DD1 and DD2 repeated internal structure of the TL494, in the part that works is unstable at low frequencies (false positive D-flip-flop).
Further, using the low-pass filter suppresses the upper harmonics of the PWM. LPF consists of two parts. First-DA1.1, with a smooth lowpass characteristic curves. Second-DA1.2 notch filter with a frequency of 150 Hz suppression. The analysis shows that the PWM contains only odd harmonics of the first and, because such a filter is enough to form a “beautiful” sine (oscillogram 2). And, as the level of the first harmonic is almost linearly dependent on porosity, we obtain a well-managed with precision sine constant component equal to 2.5 V. Further, in addition we get the inverse sine (Pin 14 DA1.4).
Tags: 12/220VAC inverter, car power inverter, dc ac inverter, inverter, inverter 12v to 220v AC, inverter circuit, sine wave converter