Stabilized 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 device is designed to power equipment designed for alternating voltage 220 V with a frequency of 50 Hz from the vehicle's on-board network or from a 12 V battery.

Main technical parameters of the converter

(click to enlarge)

The voltage converter, the circuit of which is shown in fig. 1, contains a master oscillator on a DA1 chip, its power supply stabilizer (DA2), bit field-effect transistors VT1-VT4, powerful transistors VT5 and VT6, switching current in the primary winding of transformer T1, current protection unit on relay K1, output voltage stabilization unit on chip DA3.

The generator generates rectangular pulses with a frequency of about 50 Hz with protective pauses, excluding the simultaneous opening of the switching transistors VT5 and VT6. When a low level appears at the output of Q1 (or Q2), transistors VT1 and VT3 (or VT2 and VT4) open, causing a rapid discharge of gate capacitances, and hence forced closing of transistors VT5 and VT6. The converter itself is assembled according to a push-pull scheme and has no special features. Let us consider in more detail the operation of the output voltage stabilization unit.

If the voltage at the output of the converter for any reason exceeds the set value, the voltage across the resistor R12 exceeds 2,5 V, the current through the stabilizer DA3 will increase sharply. This, in turn, will cause the photodiode of the optocoupler U1 to light up and a high level signal will appear at the FV input (pin 2) of the DA1 chip.

Its outputs Q1 and Q2 will switch to a low level, transistors VT5 and VT6 will quickly close and the current in the half-windings I.1 and I.2 will stop, causing a decrease in the output voltage. If the output alternating voltage decreases for any reason, the illumination of the photodiode of the optocoupler stops, the DA1 chip switches to an active state with the appearance of antiphase pulses at its outputs. The device also has a current protection unit assembled on the K1 relay. If the current flowing through the relay winding exceeds the set value, the contacts of the reed switch K1.1 will close. A high level will appear at the FC input (pin 1) of the DA1 microcircuit, and the outputs of the microcircuit will switch to a low level state, causing fast closing of transistors VT5 and VT6 and a sharp decrease in current consumption. After that, despite the fact that the contacts of the reed switch K1.1 will be open, the DA1 chip will remain in the blocked state (low level at the outputs).

To start the converter, a voltage drop is required at the input IN (pin 3) DA1, which is achieved either by a short-term power outage or a short-circuit of the capacitor C1. To do this, you can install a button without fixing, the contacts of which are connected in parallel with the capacitor C1 (Fig. 1 is not shown in the diagram).

Since the output voltage is a meander, a capacitor C8 is installed to smooth it and approach the sinusoidal form. LED HL1 serves as an indicator of the presence of the output voltage of the converter.

The T1 transformer is made on the basis of the industrial TS-180 from the power supply of a lamp TV. All its secondary windings are removed, and the mains voltage of 220 V is left. It serves as the output winding of the converter. Half-windings I.1 and I.2 are wound with wire PEV-2 1,8. They contain 35 turns. The beginning of one winding is connected to the end of the other and the midpoint of the primary winding is obtained. The relay of the current protection unit is homemade. The relay winding contains 1-2 turns (selected based on the required protection trip current) of an insulated wire rated for a current of 20 ... 30 A. The wire is wound on the body of the KEM2 reed switch or any other with closing contacts.

The details of the device, except for the transformer T1, the diode bridge VD4 and the capacitor C8, are located on a single-sided printed circuit board made of foil fiberglass with a thickness of 1,5 ... 2 mm, the drawing of which is shown in fig. 2. Transistors VT5, VT6 are soldered to the board and screwed through mica gaskets to a metal plate measuring 40x30 mm, which serves as a heat sink. The screws securing the transistors are insulated from the plate with fluoroplastic tubes and fiberglass washers. The terminals of the windings I are soldered to the contact petals screwed to the flanges of the transistors.

The cross section of the current-carrying tracks, through which a large current flows, is increased by soldering additional conductors and solder rollers on them. By selecting the resistor R3, the required frequency of the output voltage of the converter is set, and by selecting the resistor R12, the amplitude of the output voltage is equal to 215 ... 220 V, with a minimum supply voltage (10 V).

Author: M. Ozolin, p. Krasny Yar, Tomsk region; Publication: cxem.net

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