Electronic latr

Half a century ago, a laboratory autotransformer was very common. Today, electronic LATR, the scheme of which should be every radio amateur, has many modifications. Older models had a current-collecting contact located on the secondary winding, which made it possible to smoothly change the output voltage, quickly change the voltage when connecting various laboratory instruments, changing the heating intensity of the soldering iron tip, adjust the electric lighting, change the motor speed, and more. Of particular importance is LATR as a voltage stabilization device, which is very important when setting up various devices.

Laboratory Autotransformer

Modern LATR is used in almost every home to stabilize the voltage.

Today, when electronic consumer goods filled the store shelves, it became a problem to acquire a reliable voltage regulator for a simple radio amateur. Of course, you can find an industrial design. But they are often too expensive and bulky, and for home conditions it is not always suitable. So many radio amateurs have to “reinvent the wheel”, creating an electronic LATR with their own hands.

Simple voltage regulating device

Scheme of a simple model LATR

Diagram of a simple LATR model.

One of the simplest models of LATR, the scheme of which is shown in Fig. 1, is also available for beginners. The voltage regulated by the device is from 0 to 220 volts. The power of this model is from 25 to 500 watts. It is possible to increase the regulator's power up to 1.5 kW; for this, the VD1 and VD2 thyristors should be installed on radiators.

These thyristors (VD1 and VD2) are connected in parallel with the load R1. They pass the current in opposite directions. When you turn on the device in the network, these thyristors are closed, and the capacitors C1 and C2 are charged by means of a resistor R5. The magnitude of the voltage received at the load, change the need for a variable resistor R5. Together with capacitors (C1 and C2), it creates a phase-shifting circuit.

Scheme of a more complex LATR

Fig. 2. Scheme LATR, giving a sinusoidal voltage without interference in the system.

A feature of this technical solution is the use of both half-cycles of alternating current, therefore for the load not half power is used, but full.

The disadvantage of this scheme (fee for simplicity) is that the form of the alternating voltage on the load is not strictly sinusoidal, due to the specifics of the thyristors. This may cause network interference. To eliminate the problem, in addition to the circuit, you can install filters in series with the load (chokes), for example, take them from a faulty TV.

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Voltage regulator circuit with transformer

The LATRA circuit, which does not interfere with the network and gives a sinusoidal voltage at the output, is shown in Fig.2. The regulating element in the device used is a bipolar transistor VT1 (its power is calculated from the demand of the load), functioning as a variable resistor, it is included in the circuit in series with the load.

This technical solution makes it possible to regulate the operating voltage with active as well as reactive loads.

The disadvantage of the proposed solution is the allocation of too much heat used by the regulating transistor (requires a powerful radiator for heat sink). For this device, the radiator area must be at least 250 cm².

The transformer T1 used in this model should have a power of 12-15 W and a secondary voltage of 6-10 V. The current is rectified by a diode bridge VD6. Further, for any half-cycle of alternating current, a rectified current for transistor VT1 flows through the diode bridge VD2-VD5. When using a device with a variable resistor R2, the base current of the transistor VT1 is adjusted. This changes the parameters of the load current. At the output of the device, the voltage value is monitored by a PV1 voltmeter (it should be designed for a voltage of 250-300 V). To increase the load power, it is necessary to replace the VD1 transistor and VD2-VD5 diodes with more powerful ones and, of course, increase the radiator area.

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