Converter 12/220 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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The problem of powering consumers designed to operate from a 220 V power supply in a car has been raised more than once on the pages of radio magazines.
Here is a brief description of one such device that produces an unstable 220 V AC voltage when powered by a 12 V DC source (car battery).
The maximum load power is 30 W, with such a load the output voltage drops to 200 V, at idle - 240 V. One of the advantages of this converter is that it produces an alternating voltage with a frequency of 50 Hz, which can be very important for many consumers.
The converter can be successfully used to power an electric razor, LDS, low-power boiler, and soldering iron.
The schematic diagram is shown in the figure. The integrated timer D1 has a pulse generator, the frequency of which can be set using trimming resistor R1 (before turning it on for the first time, you need to make sure that it is in the middle position).
(click to enlarge)
Pulses from output D1 pass to D-trigger D2.1, which creates antiphase pulses at its opposite outputs with a frequency two times lower than the input frequency (arriving at pin 3 of D2.1).
Inputs R and S are not used, so pins 4 and 6 are connected to a common minus.
The second trigger of the D2 chip (D2.2) contains a quasi-touch switch that switches the circuit to an energy-saving mode when the output voltage is not needed. Control of two buttons S1 and S2, as well as capacitor C3, which pre-sets the circuit to the off state. Buttons S1 and S2 without fixation. To turn it on, you need to press S2. In this case, a logical unit appears at output D2.2, which opens elements D3.1 and D3.3, and through them the pulses pass to inverters - buffers on D3.2 and D3.4 and then to transistors VT1 and VT2. MJ3001 transistors are Darlington transistors, that is, each of them contains not one, but two transistors connected in a composite circuit. The transmission coefficient of such a transistor is many times higher, and the input resistance is lower. This allows the basic circuits of these transistors to be quite adequately coordinated with the outputs of logic inverters. CMOS.
The collector circuits of the transistors include two halves of the low-voltage winding of the transformer T1.
Another positive point is that a ready-made toroidal power transformer with a power of 40 W is used, with a secondary winding of 18 V with a tap from the middle, which is turned on in reverse (as a step-up). In principle, here you can use any power transformer with similar parameters, but, for example, the more common one, with an W-shaped core.
It is also possible to use a miniature military transformer at 400 Hz, but it will be necessary to correspondingly increase the frequency of the generator on D1, and the output voltage will now be at a frequency of 400 Hz, which may cause difficulties with powering some consumers designed to operate at 50 Hz. However, if we are talking about a boiler and a soldering iron, there will be no problems.
To turn it off, you need to press S1, and the output D2.2 will be logical zero. Elements D3.1 and D3.3 will be blocked and the outputs D3.2 and D3.4 will have logical zeros. Both transistors will be closed and the current through the low voltage winding of the transformer will be zero.
The HL1 LED serves as an indicator of the presence of supply voltage. The output voltage indicator is the “neon” H1.
This is a “neon” from an old device that was powered from the mains, I don’t know its brand, it’s clear it’s just 220 V. R6 is a 250 V varistor, it serves to protect against high-voltage surges, if such arise.
Rectangular pulses arrive at the bases of the transistors; they are, of course, smoothed out by the inductance of the transformer windings, but the shape of the output voltage is still far from sinusoidal. Therefore, it is not advisable to use the device to power devices that are critical to the form of the AC supply voltage. It is also necessary to take into account the instability of the output voltage, which is highly dependent on the load.
The adjustment consists only of setting the frequency of the output voltage (50 Hz) by adjusting R1 (at pin 3 of D2 the frequency will be 100 Hz). The transistors must be placed on radiators.
Author: Yunusov A.L.
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