Mains voltage stabilizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Mains voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The voltage of the household electrical network often differs from the standard one (220 V + 10%). Voltage losses or surges can reach significant values and cause malfunctions in household electrical appliances. Modern television and radio equipment is equipped with switching power supplies, which ensure its normal operation at a mains voltage of 160 to 230 V, but devices from previous years require a more stable mains voltage.

Mains voltage stabilizer

Particularly affected by unstable voltage are household appliances equipped with electric motors: refrigerators, washing machines, vacuum cleaners, power tools, etc.

Increased mains voltage leads to intense heating of the motor windings and wear of the collector, insulation breakdown is possible. At low voltage, electric motors do not start or turn on jerkily, which leads to premature wear of ballasts. When illuminating the premises, incandescent lamps burn dimly, and it is necessary to increase their power, which further reduces the mains voltage.

The way out of the created situation is quite simple - to install a booster transformer, the voltage of the secondary winding of which is added to the mains and brings it closer to the standard voltage. Such a device does not have a negative effect on the power grid.

The presence of a universal device for maintaining the mains voltage allows you to protect electrical appliances from both high and low voltage.

Voltage stabilization can be achieved using electromechanical stabilizers, in which the electric drive, depending on the input voltage, changes the position of the sliding contact on the toroidal autotransformer. The disadvantages of this solution are: burning of the winding due to loss of contact with the roller, a large mass of the stabilizer, since the full load power is transmitted through the autotransformer, high price.

In the proposed device, a small power transformer is used to increase the voltage, its power is not more than 10% of the load power.

To stabilize the voltage, it is enough to install a key regulator (field-effect transistor of sufficient power) in the primary circuit of the transformer.

The parameters of the stabilizer are mainly determined by the applied transformer. Power transformers can be used in the device. TS180 ... TS320 from old TVs. Transformers of the TN-59 or CCI type with a permissible secondary winding current of 6 ... 8 A with a total voltage of 24 ... 36 V have proven themselves well.

The stabilizer circuit is shown in Fig. 1. The device contains:

voltage stabilization unit - transformer T1, powerful diode bridge VD1 and key transistor VT1;
error voltage selection node - diode bridge VD2 and optocoupler VU1 with RC circuits for setting the mode:
input anti-interference filter - capacitor C1;
circuit breaker-SA1.

Mains voltage stabilizer

Mains voltage is supplied to the terminal. XT3 load through the secondary winding of the booster transformer T1 and directly to the XT4 terminal. The primary winding of the transformer is powered from the network through the diode bridge VD1, the mode of operation of which depends on the state of the key transistor VT1. If it is open, the voltage at the KhTZ, XT4 terminals is maximum. Resistor R1 and capacitor C3 facilitate transients when switching bridge diodes VD1 and transistor VT1.

The absence of voltage on the primary winding of the transformer T1 or a malfunction in the circuit will lead to the absence of voltage boost, otherwise the load will work as before. A small voltage drop (several volts) due to the passage of load current through the secondary winding of a disconnected transformer will not significantly affect the operation of the connected electrical equipment.

The error voltage is removed from half of the secondary winding of the transformer, rectified by the diode bridge VD2 and through resistors R3, R4 is fed to the LED of the optocoupler VU1.

Capacitor C2 reduces the sharp dips in the output voltage.

With an increase in the mains voltage, the optocoupler LED current increases, a phototransistor opens, which shunts the bias voltage at the gate of the key transistor VT6 through the R8-R1 installation circuits. The transistor turns off and the load voltage drops. At the initial moment, the transistor VT1 is open with a voltage from the drain supplied to the gate through the resistor R5.

Capacitor C3, when turned on and charged from the diode bridge VD1, has a low resistance, which increases after a few milliseconds, so it is advisable to turn on the load with a standard switch after starting the stabilizer.

The HL1 LED indicates the presence of a secondary voltage when the transistor VT1 is open, the Zener diode VD3 protects the gate of the field-effect transistor from exceeding the bias voltage above the permissible value.

The device is assembled on a printed circuit board, the drawing of which is shown in Fig.2.

Mains voltage stabilizer

The transistor is mounted on a radiator measuring 50x50x10 mm. Parallel connection of two identical transistors is allowed. The board and the transformer are installed in a suitable case, the dimensions of which depend on the dimensions of the transformer T1, the device operation indicator HL1 and the SA1 mains switch with fuses FU1, FU2 are located on the top and side of the case. When using a metal case, a mains plug with a grounding contact is required, the ground wire is connected to the transformer case. The power wires indicated in the diagram (Fig. 1) with thick lines are made with a stranded wire with a cross section of at least 4 mm2, the rest - 0,5 mm2.

The stabilizer uses fixed resistors of the MLT or C29 type, tuning resistors - SP or SPO. To replace the transistor VT1 (operating voltage - at least 400 V, current - more than 3 A), you can use the data in the table.

series transformers. TS for use in the device need to be improved. To do this, they will have to be disassembled. First, the tie rod is removed. The connection of the primary two windings should be preserved by redrawing the conclusions. The disassembled halves of the U-cores must not be interchanged, this will cause the transformer to hum after reassembly. Since the ends of the cores are tinted during factory assembly and are poorly separated during disassembly, you can lightly tap the end of one of the halves with a hammer. Old paint from the joints is scraped off with a knife. The secondary windings are removed. In the filament winding (6,3 V), the number of turns is preliminarily recalculated and, based on these data, new windings are wound with a PEL wire of 1,78 ...

The transformer is assembled in the reverse order (the primary winding leads must be on the same side, as before). Frames with windings are installed on U-shaped cores, the ends of the halves of the cores are "stained over" with any thickened paint (except for nitro paint). After half an hour, the upper halves are inserted into the frames, the tie rods are installed and tightened. After complete assembly, the primary winding is connected to the mains (in compliance with safety regulations), the voltage of the secondary windings is measured with an AC voltmeter (should be within 12 ... 18 V each). The total voltage of two series-connected secondary windings is 24 ... 36 V. When the assembled transformer is buzzing, it is recommended to tap it with a wooden hammer handle to "settle" the mount and iron in place.

When using transformers of the TN or CCI type, no alteration is required, their secondary windings are connected in series.

To obtain an increased secondary voltage compared to the mains, terminal 1 of the primary winding T1 is connected in series with the extreme terminal 7 of the secondary winding. The voltage between terminal 6 T1 and the free end 9 of the secondary winding must be higher than the mains voltage by the amount of the total voltage of the secondary windings.

Adjusting the circuit consists in setting the limits for stabilizing the output voltage.

After switching on (preferably with an active load, for example, with a table lamp), resistor R8 with a minimum resistance of R3 sets the output voltage to 225 V. By connecting a more powerful load (1 ... 1,5 kW), the output voltage is adjusted by resistor R3 (about 215 V ). After 5 ... 10 minutes of operation, the device and the load are disconnected from the network, and the thermal conditions of all radio components are checked. If the key transistor overheats, you need to increase its radiator.

Due to the spread of the parameters of a powerful field-effect transistor, its initial bias can be corrected by selecting the resistance R5. With the upper position of the R8 slider, the drain current of the transistor should be about 1,2 A.

In the author's version, a computer fan and an ammeter with a limit of 10 A are additionally installed, although these "excesses" turned out to be unclaimed.

Author: V.Konovalov

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