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).
The output of the transformer, a diode bridge fed on the feedback output voltage. Thus the output voltage stabilisator.
Input voltage 12 … 14V
output voltage 50 Hz 220 + /-2V
Max power 50W
Efficiency … 90%.