Power supply, 1-29 volts 2 amps. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply, 1-29 volts 2 amps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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In many modern stabilizers, to improve their performance, operational amplifiers are used, which have a large gain and stable characteristics. However, a relatively simple modification of a traditional transistor stabilizer can significantly improve its technical characteristics and avoid some of the difficulties that arise when designing stabilizers using an op-amp (especially in devices with wide output voltage regulation). The high stabilization coefficient of the described power supply (Fig. 3.4) is due to the use of an amplifier with a dynamic load.

The exemplary voltage source is assembled on a field-effect transistor, which makes it possible to reduce the output impedance of the stabilizer and obtain deep regulation of the output voltage.

(click to enlarge)

Main technical characteristics:

Voltage at the input of the stabilizer - 30 V;
Output voltage regulation limits - 1...29 V;
Maximum load current, 2 A;
Voltage stabilization factor - 60 dB;
Output impedance 5...10 mOhm.

The voltage regulator consists of two serially controlled dynamic load amplifiers. The first one is assembled on transistors V13, V12, where V13 is connected according to a common gate circuit, and V12 - with a common collector: the second one is on transistors V14, V15 (V14 - with a common emitter, and V15 - with a common collector). The feedback signal from the engine of the resistor R9, applied to the source of the transistor V3, is amplified without phase inversion and fed to the base of the transistor V14. Transistor V13 operates in a mode close to the current cutoff. The voltage between the source and the gate is exemplary in the stabilizer.

The circuit R2, R3, V11 serves only for temperature compensation of the change in the drain current of the transistor V13 (without it, with the gate of this transistor closed to a common wire, the output voltage of the stabilizer changes by 3 ... 5% in the temperature range of 20 ... 50 ° C). From the collector of transistor V14, the inverted and amplified signal is transmitted to the base of a powerful regulating transistor V15. The control element is powered by a parametric stabilizer on a zener diode V10 and a transistor V9. To obtain a higher voltage utilization factor of the main rectifier V1 ... V4, the stabilizer on the transistor V9 is powered by a voltage multiplier on diodes V5 ... V8 and capacitors C1, C2. The multiplier is connected to the secondary winding of the transformer T1.

Lamp H1 serves to limit the collector current through transistors V9, V14 and the base current of transistor VI5 in the event of a short circuit in the load circuit, as well as to indicate overload. At the moment of overload, due to an increase in the base current of transistor VI5, the voltage at the input of the parametric stabilizer decreases to a level of 30 V, where this voltage almost completely drops on the lamp H1 minus the voltage drop across transistors V9, V14 and the emitter junction of transistor V15. The current in this circuit does not exceed 120...130 mA, which is less than the maximum allowable for its elements.

The stabilizer uses a wire-wound variable resistor with a permissible dissipation power of 3 W (PPB-3, PPZ-40). Transistor V13 must be selected with a low value of the initial drain current, only then the lower limit of the output voltage of the stabilizer will be close to 1 V. The drain current of this transistor at a voltage between the drain and source of 10 V and a gate closed to the source should be within 0,5 ...0,7 mA. When mounting the stabilizer between the diode V11 and the transistor V13, it is necessary to ensure good thermal contact, for which it is enough to glue their cases. Transistor V15 is desirable to choose with a large static current transfer coefficient of the base.

In addition to those indicated in the diagram, you can use silicon transistors of the KT203, KT208, KT209, KT501, KT502, KT3107 (V12), KT814, KT816 (V14) series, transistors KT815, KT817 with any letter index, KT807B (V9), KT803A, KT808A, KT819 with any letter index (VI5).

The stabilizer can also use MP40A germanium transistors, as well as any of the MP20, MP21, MP25, MP26 (V12), GT402, GT403, P213 ... P215 (V14) series. Instead of KS527A, zener diodes D813, D814D (two in series), D810, D814V (three in series) can be used. It is desirable to install transistors V9 and V14 on small radiators (with a usable area of 20 ... 30 cm2). Transistor VI5 requires a heatsink.

In order to facilitate the thermal regime of this transistor, a step change in the voltage at the input of the stabilizer is provided by the toggle switch S1, designed for a current of 2 A. In position 1, 15 V is supplied to the input of the stabilizer, and in position 2 - 30 V. When the toggle switch is in position 2 and the load resistance close to the minimum, the stabilized voltage should not be set below 15 V.

The network transformer is wound on the magnetic circuit of the transformer TS-60. The primary winding is left unchanged, the secondary is rewound; it contains 200 turns (100 turns for each coil) of PEV-2-1,16 wire.

The high-frequency generation that sometimes occurs in the stabilizer can be suppressed either by increasing the value of the capacitor C6, or by including a resistor with a resistance of 15 ... 5 Ohms with a power of 10 W in the base circuit of the transistor V1. To ensure stable operation of the stabilizer, its installation must be carried out with conductors of minimum length, having a large cross section of the conductive core.

Author: Semyan A.P.

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