In the Fig exist a voltage converter circuit from 12VDC in 220VAC, with output power roughly 50W. The circuit is constituted by the oscillator, round the IC1, one divader IC2, one unstable multivibrator IC3, which give in the output symmetrical square signal of frequency 50HZ, follow a buffer stage with Fet Q1-2, the drive stage Q3-4 and the power stage Q4-5, the power transistors Q5-6, should they are placed in heatsink.
The diodes Zener D2-3, protect the power transistors from voltage peaks, that are produced by the transformer T1. Transformer T1 are a simple power transformer, with intermediate reception, which is connected in the contacts of CO1. For the use that him we want, the T1, is placed in reverse, with secondary convolution it is used as primary, with the intermediate reception she is connected in the positive point of battery 12V and the two other contacts are connected in the emitters of Q5-6, that are connected in the potential of ground alternately, depending on the rythm that determine outputs 10 and the 11 from IC3.. With this way while in being primary flow AC current, in secondary is created 220V AC square voltage. The use of crystalic oscillator ensures very good reference frequency 50HZ, and use a simple crystal (CR1). For bigger precision, parallel with the C1, exist a variable capacitor Cx, that ensure the regulation of frequency, so that we take in point P1, frequency 204.8 KHZ. Its obvious that the output voltage in void of load is bigger than the voltage with load. Also the output voltage depend from the output voltage of battery. Thus for battery voltage 14V, the output voltage is increased at 10%, compared to the battery voltage 12V. If the converter work in load power 40 until 60W, then it can be used transformer 2X9V.
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