Power supply with light voltage indication. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply with light voltage indication. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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When checking the performance of parts or electronic devices, smoothly varying voltage power supplies are needed. For this, a power supply unit with a light voltage indication is offered, which will satisfy all lovers with the following features: ease of manufacture, small size, affordable radio components, accurate setting of the desired voltage, lack of a voltmeter at low financial costs.

Device. The power supply circuit with light voltage indication is shown in Fig. 1.

(click to enlarge)

A low alternating voltage of 20-25 V from the power transformer T1 is supplied to the bridge rectifier VD1-VD4 and smoothed by the capacitor C1. The presence of a rectified DC voltage is signaled by one or more LEDs HL1-HL7, depending on the output voltage. Capacitor C2 stabilizes the operation of the power supply at high frequencies, and C3 is an additional output decoupling. The final voltage stabilization and its adjustment are carried out by the DA1 stabilizer [1]. Transistors VT1VT7 are connected to the output of the power supply according to the scheme with a common emitter.

Between the plus of the power source and the bases of the transistors, resistors R1-R7 and zener diodes VD5-VD11 are connected, which introduce the corresponding transistors into the robot, depending on the magnitude of the output voltage. The load of transistors VT1-VT7 are LEDs HL1HL7, which are connected between the collectors of transistors and the positive on the capacitor C1 through load resistors R8-R14 and signal the output voltage.

Resistor R16 is set to the leftmost position, which corresponds to a minimum voltage of 1,5 V. When it is smoothly rotated clockwise until the output voltage of 3 V is reached, the zener diode VD5 opens, the transistor VT1 turns on and the HL1 LED lights up, signaling the presence of a given voltage. By further rotation of the potentiometer R16, we achieve a voltage of 4,5 V, the VD6 zener diode fires, the VT2 transistor opens, the HL2, HL3 LEDs light up, etc. up to HL7. In the extreme right position of the potentiometer, all LEDs work at a maximum source voltage of 25 V [2].

Installation. The case for the power supply is a plastic cylindrical box with a diameter of 120 mm and a height of 56 mm, consisting of two identical parts. In its lower part, a transformer T1, a diode bridge VD1-VD4, capacitors C1-C3, a resistor R15 and a voltage regulator DA1 are mounted. All other parts are mounted in the upper part of the power supply housing. The resistor R16 is placed as close as possible to the center, and the LEDs HL1-HL7 are placed around a circle with a radius of 3 cm in the sector of the extreme positions of the resistor R16 (minimum and maximum voltages).

Near the LEDs, inscriptions of the corresponding voltages are applied after complete installation and testing of the power supply (Fig. 2) according to the readings of a parallel-connected voltmeter.

Power supply with light voltage indication

The number of LEDs (transistors, zener diodes, resistors) can be increased or decreased depending on the purpose and purpose of the power supply. In this case, the base current of the transistor must be within the limits of the minimum and maximum stabilization currents of the zener diode at the minimum and maximum voltages.

In the side part of the case, a connector of any type is installed for connecting DC consumers. All parts are mounted on two getinax plates.

This power supply is designed for a load current of 0,3 A. If necessary, increase the current to 1,5 A, replace the rectifier diodes with more powerful ones, install DA1 on the radiator and increase the power of the transformer T1 to 20 W [3].

Details. Linear potentiometer, type SP: R16 = 6,7 kOhm; capacitors: C1 \u1000d 3 microfarads, C47 \u50d 2 microfarads (electrolytic, 0,1 V), C50 \u1d 4 microfarads (paper or polystyrene, 226 V); rectifier: diodes VD405-VD5 type D133 or diode bridge KTS6I; zener diodes: VD147 type KS7A, VD814 type KS808A, VD8 type D814A or D809, VD9 type D814B or D810, VD10 type D814V or D811, VD11 type D814G or D813, VD1 type D142D or D12; voltage stabilizer: DA1 type KR7EN315A; transistors VT1-VT7 type KT307; LEDs: HL1-HL4.709.111 type AL0,25 in different colors; transformer T1 type Ua620; carbon or film resistors 2 W: R680=3 Ohm, R4=5 Ohm, R1=R6=R1,3=7 kOhm, R1,5=8 kOhm, R14=2,4 kOhm, R15...R330=XNUMX, XNUMX kOhm, RXNUMX=XNUMX Ohm.

References:

Tooley M. Handbook on digital electronics. -M.: Energoatomizdat, 1990. -S.118-122.
Tereshchuk R. Handbook of a radio amateur. -K.: Nauk. dumka, 1982. -p.170.
Bosenko V. Improved simple power supply // Radioamator-Electrician. -2000. -#9. -C.4.

Author: V.M. Bosenko

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