A schematic diagram of a 12V / 220V converter is shown in Figure 1.The scheme consists of such key elements:
transformer
two MOSFETs
4047 series integrated circuit.
Part of the circuit with components T3 ... T6, U2C, U2D performs only the auxiliary. Unused U2C and U2D inputs must be shorted to ground or to an auxiliary power source. In the simplest version, you can abandon the U2A, U2B gateways and send signals from the U1 chip directly to the MOSFET T1 and T2 field effect transistors. The energy source is a 12 V battery with a capacity of several tens of ampere-hours. The transformer TR1 plays a key role. This is an ordinary toroidal network transformer with two secondary windings (220V / 2x9V). The transformer works with two MOS transistors T1 and T2, which are alternately turned on at a frequency of 50 Hz. To keep the frequency stable, we used the popular CMOS 4047 chip, which works as a generator. The generator frequency is 100 Hz, and the outputs (legs 10 and 11) have inverted signals with a frequency of 50 Hz. In practice, the frequency of the generator (100 Hz) is determined by the elements R1, PR1, C1, and you can set it carefully using PR1. At the output, that is, on the transformer winding, there is a rectangular waveform. When operating on battery power, due to various types of losses and undervoltage, use a mains transformer with a rated secondary voltage of 2 × 9V, not 2 × 12V. Also, transformers with a voltage of 2 × 8V ... 2 × 10V can be used in the circuit. The output voltage depends primarily on the battery voltage and the transformation ratio, but the load also has a certain effect.
Elements D1, PR2, T4, T3, D3 operate in the battery voltage control circuit. Since the current consumption of the battery will usually be high, the battery can drain quickly. In this circuit, a deep discharge of the battery will occur, signaling the buzzer Y1 and the voltage drop on the diode D3 below the level set with PR2. Excessive voltage reduction will clog the already open transistor T4 and open T3. This will turn on the diode D3 and, in addition, a low state on the 12th gate output of U2D will result in a high state on the output. This will start the generator with the U2C shutter, and the Y2 piezo emitter (buzzer) will give an intermittent audible warning. The siren threshold voltage can be set using PR2. A circuit with elements R14, D5 ... D8, T5, T6, D4 with sound and the diode D2 glows - informs about overload and excess of the output current. On the resistor R14, a voltage drop is proportional to the output current. The voltage on this resistor is rectified by the diode bridge D5 ... D8. The delay circuit R11, C3 prevents false alarms resulting from instantaneous current pulses. Only when the average current exceeds the set level, transistors T5, T6 will open, the signal diode D4 will light up and a buzzer will sound.
Installation and commissioning
The control-alarm circuit can be installed on the board shown in Figure 2.
In the presented scheme, large currents will flow in some circuits. It is enough to calculate that at 12 V a power of 100 W is obtained at a current exceeding 8 A. Such a high current value means that the key connections must be made of thicker conductors, at least with a cross section of 1 ... 1.5 mm 2 . In a schematic diagram, these parts are drawn with thicker lines.
Particular attention should be paid to the installation of power transistors. The conductors leading to them should be as short as possible, up to 10 cm. It is better, after assembling the printed circuit board, before connecting the power transistors and the transformer, it is worth checking whether the control system produces rectangular pulses with a frequency of 50 Hz and a 50% filling.
If you have nothing to measure the frequency, instead of PR1 R1, you can use one resistor (or two in series) with a value of 45.5 kOhm. In this case, the frequency will not deviate from the nominal value, in addition, a deviation of 5, 10 or even 20% does not play a significant role. In the model device, a transformer with a power of 100 W was used, and transistors T1, T2, even with an output load of 80 W, do not heat up much. You can use a transformer with a different power, less or more. Control field-effect transistors have an open resistance of only 0.03 ... 0.04 ohms and can work with currents of several tens of amperes. Thus, you can try the circuit with a much higher power transformer, even 300 watts at an output load of 250 watts, using a fuse B1 with the appropriate rating.
The inverter has not been tested with all possible load types. Due to the shape of the output signal, which looks like a square wave, some devices may not work properly or even get damaged.
Attention ! The circuit has a voltage that is not safe for life. Minors should only initiate and implement a scheme if they are supervised by qualified adults.
Details
