Linear voltage stabilizers with high efficiency. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The main disadvantage of linear stabilizers of medium and high power is their low efficiency. Moreover, the lower the output voltage of the power source, the lower its efficiency becomes. This is due to the fact that in the stabilization mode, the power transistor of the power source is usually connected in series with the load, and for the normal operation of such a stabilizer, a collector-emitter voltage (Uke) of at least 3,5 V must operate on the regulating transistor. At currents of more than 1 A, this gives significant power losses due to the release of thermal energy dissipated by the bulk transistor.

Which leads to the need to increase the area of ​​the heat sink or use a fan for forced cooling. Integrated linear voltage regulators based on chips from the 142EN(5.14) series, which are widely used due to their low cost, have the same drawback.

Recently, imported microcircuits from the "LOW DROP'' (SD, DV, LT1083/1084/1085) series have appeared on sale. These microcircuits can operate at a reduced voltage between input and output (up to 1 ... 1,3 V) and provide a stabilized voltage at the output in the range of 1,25 ... 30 V at a load current of 7,5 / 5 / 3 A, respectively.

The closest domestic analogue of the KR142EN22 type in terms of parameters has a maximum stabilization current of 5 A.

At the maximum output current, the stabilization mode is guaranteed by the manufacturer at an input-output voltage of at least 1,5 V. The microcircuits also have built-in protection against exceeding the current in the load of an acceptable value and thermal protection against overheating of the case. These stabilizers provide output voltage instability of 0,05% / V, output voltage instability when the output current changes from 10 mA to a maximum value of no worse than 0,1% V.

A typical circuit for switching on such voltage stabilizers is shown in fig. 4.1.

Rice. 4.1. Scheme of inclusion of stabilizers from the series "LOW DROP"

Capacitors C2 ... C4 should be located close to the microcircuit and it is better if they are tantalum. The capacitance of the capacitor C1 is selected from the condition of 2000 microfarads per 1 A of current.

Microcircuits are produced in three types of package design, shown in fig. 4.2. The hull type is specified by the last letters in the designation.

Rice. 4.2 View of the housing and the location of the terminals of the stabilizers

It is economically feasible to use such voltage stabilizers at a load current of more than 1 A, as well as in case of a lack of space in the structure.

On discrete elements, you can also make an economical power supply. Shown in fig. 4.3, the circuit is designed for an output voltage of 5 V and a load current of up to 1 A. It ensures normal operation with a minimum voltage on the power transistor (0,7 ... 1,3 V). This is achieved by using a transistor (VT2) with a low voltage Uke in the open state as a power regulator, which makes it possible to ensure the operation of the stabilizer circuit at lower input-output voltages.

Rice. 4.3. Scheme of a voltage regulator operating at a reduced input-output voltage (click to enlarge)

The circuit has protection (trigger type) in case of exceeding the current in the load of an acceptable value, as well as exceeding the voltage at the input of the stabilizer of 10,8 V.

The protection unit is made on a transistor VT1 and a thyristor VS1. When the thyristor is triggered, it turns off the power to the DA1 chip (pin 7 is shorted to a common wire). In this case, the transistor VT3, and hence VT2 will close and the output will be zero voltage. It is possible to return the circuit to its original state after eliminating the cause that caused the overload, only by turning off and on the power supply again.

Capacitor C3 is usually not required - its task is to facilitate starting the circuit at the moment of switching on.

The topology of the printed circuit board for mounting elements is shown in fig. 4.4 (it contains one bulk jumper).

Rice. 4.4. Topology of printed circuit board for mounting elements

Transistor VT2 is mounted on a radiator.

The following parts were used in the manufacture: a tuned resistor R8 of the SPZ-19a type, the rest of the resistors are of any type; capacitors C1 - K50-29V for 16 V, C2 ... C5 - K10-17, C5 - K52-1 for 6,3 V.

The circuit can be supplemented with an LED indicator of protection operation (HL1). To do this, you will need to install additional elements: a VD3 diode and a resistor R10, as shown in Fig. 4.5.

Rice. 4.5. Connection of protection operation indicator

Author: Shelestov I.P.

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