Boost voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The voltage of the household electrical network (especially in rural areas) is often low, never reaching the nominal 220 V. In such a situation, the refrigerator does not start well, the lighting is dim, and the water in the electric kettle does not boil for a long time. The power of an old voltage regulator designed to power a TV is usually insufficient for all other household appliances, and the mains voltage often drops below the allowable voltage for such a stabilizer.

There is a simple way to increase the voltage in the network, using a transformer with a power much less than the load power. The primary winding of the transformer is connected directly to the network, and the load is connected in series with the secondary (step-down) winding of the transformer. With appropriate phasing, the voltage at the load will be equal to the sum of the network and taken from the transformer.

The circuit of the mains voltage stabilizer operating according to this principle is shown in fig. 1. When the field-effect transistor VT2 included in the diagonal of the diode bridge VD2 is closed, the winding I (primary) of the transformer T1 is disconnected from the network. The voltage at the load is almost equal to the mains voltage, minus a small voltage drop on the winding II (secondary) of the transformer T1. If the field-effect transistor is opened, the power supply circuit of the primary winding of the transformer will be closed, and the sum of the voltage of its secondary winding and the mains will be applied to the load.

Rice. 1 Voltage regulator circuit

The voltage at the load, reduced by the transformer T2 and rectified by the diode bridge VD1, is fed to the base of the transistor VT1. The engine of the tuning resistor R1 must be set to a position in which the transistor VT1 is open, and VT2 is closed if the voltage at the load is greater than the rated voltage (220 V). At a voltage less than the nominal transistor VT1 will be closed, and VT2 - open. The negative I feedback organized in this way maintains the voltage on the load approximately equal to the nominal

The voltage rectified by the VD1 bridge is also used to power the collector circuit of the transistor VT1 (through the integral stabilizer DA1). The C5R6 circuit suppresses unwanted drain-source voltage surges of the transistor VT2. Capacitor C1 reduces interference that enters the network during the operation of the stabilizer. Resistors R3 and R5 are selected to achieve the best and most stable voltage stabilization. Switch SA1 turns on and off the stabilizer along with the load. By closing the SA2 switch, the automation is turned off, which maintains the voltage at the load unchanged. In this case, it becomes the maximum possible at a given voltage in the network.

Most parts of the stabilizer are mounted on a printed circuit board, shown in fig. 2. The rest connect with it at points A-D.

When choosing a replacement for the KTs405A (VD2) diode bridge, it should be borne in mind that it must be designed for a voltage of at least 600 V and a current equal to the maximum load current divided by the transformation ratio of the transformer T1. The requirements for the VD1 bridge are more modest: voltage and current - at least 50 V and 50 mA, respectively

Rice. 2 Mounting the printed circuit board

The KT972A transistor can be replaced with KT815B, and the IRF840 with IRF740. The field-effect transistor is equipped with a 50x40 mm heat sink.

The "booster" transformer T1 is made of the ST-320 transformer, which was used in the power supplies BP-1 of the ULPCT-59 TVs. The transformer is disassembled, and the secondary windings are carefully wound, leaving the primary ones intact. New secondary windings (the same on both coils) are wound with enameled copper wire (PEL or PEV) in accordance with the data given in the table. The more the voltage drops in the network, the more turns will be required and the lower the permissible load power.

After rewinding and assembling the transformer, the terminals 2 and 2' of the halves of the primary winding, located on different rods of the magnetic conductor, are connected by a jumper. The halves of the secondary winding must be connected in series so that their total voltage is maximum (if connected incorrectly, it will be close to zero). According to the maximum total voltage of the secondary winding and the network, it is necessary to determine which of the remaining free terminals of this winding should be connected to terminal 1 of the primary, and which to the load.

Transformer T2 - any network with a voltage on the secondary winding close to that indicated in the diagram with a current consumed from this winding of 5O ... 1OmA.

Table 1

By connecting the assembled stabilizer to the network, set the voltage at the load to 1 V with a trimming resistor R220. It should be borne in mind that the described device does not eliminate fluctuations in the mains voltage if it exceeds 220 V or falls below the minimum adopted in the calculation of the transformer.

A stabilizer installed in a damp room must be placed in a grounded metal case.

Note. In some operating modes of the stabilizer, the power dissipated by the VT2 transistor turns out to be very significant. It is she, and not the power of the transformer, that can limit the permissible load power. Therefore, you should take care of good heat dissipation from this transistor.

Author: V. Konovalov, Irkutsk; Publication: radioradar.net

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