LED flashlight from ... a calculator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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LED flashlight from ... a calculator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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The use of an old calculator, or rather its details, in particular a pulse transformer, made it possible to create an economical LED flashlight. Super-bright LED flashlights are rapidly gaining popularity. In the described designs, including in the Radio magazine, descriptions of flashlights are given, mainly on specialized microcircuits that are scarce for many radio amateurs, and winding pulse transformers requires a certain skill.

When developing the flashlight, the following tasks were set: maximum simplicity, minimum scarce parts, efficiency and the ability to work from a single 1,5 Volt battery. Attention was drawn to the power supply of the B3-30 calculator (now you can always find them). The fact is that the switching power supply uses a transformer only 5 mm thick, which has two windings. The converter was based on the B3-30 calculator circuit, excluding a 7,5 Volt stabilizer from it. The result is a very simple circuit using the details of the calculator in Fig. 1.

LED flashlight from ... a calculator. LED flashlight
Fig. 1

The test used the cheapest AA battery costing only 3 rubles. The initial voltage under load was 1,28 V. At the output of the converter, the voltage measured on a super-bright LED was 2,83 V. The brand of the LED is unknown, the diameter is 10 mm. The total current consumption is 14 mA. The brightness of the glow is comparable to a lantern made according to the description in the Radio magazine 2004-9-54. The total operating time of the flashlight was 20 hours of continuous operation. When the voltage on the battery drops below 1 V, the brightness drops noticeably. The voltage converter is made according to the scheme of a single-cycle generator with inductive feedback on a transistor VT1 and a transformer T1. The impulse voltage from the windings 1-2 (according to the B3-30 calculator circuit diagram) is rectified by the VD1 diode and fed to the super-bright HL1 LED. Capacitor C3 filter. The design is based on a Chinese-made flashlight designed to install two AA batteries. The transducer is mounted on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick fig. 2 sizes replacing one battery and inserted into the flashlight instead of it. A contact made of double-sided foil fiberglass with a diameter of 15 mm is soldered to the end of the board marked with a "+" sign, both sides of the foil are connected by a jumper and soldered.

LED flashlight from ... a calculator. Lantern printed circuit board
Fig. 2

Board drawing in .lay format (16Kb)

After installing all the parts on the board, the "+" end contact and the T1 transformer are filled with hot glue to increase strength. A lantern layout option is shown in fig. 3 and in a particular case depends on the type of lamp used. In my case, no modification of the lamp was required, the reflector has a contact ring, to which the negative output of the printed circuit board is soldered, and the board itself is attached to the reflector with hot glue. The printed circuit board assembly with the reflector is inserted instead of one battery and is clamped with a cover.

Rice. 3 (click to enlarge)

The voltage converter uses small parts. Resistors of the MLT-0,125 type, capacitors C1 and C3 are imported, up to 5 mm high. Diode VD1 type 1N5817 with a Schottky barrier, in its absence, you can use any rectifier diode suitable for the parameters, preferably germanium due to the lower voltage drop across it. A properly assembled converter does not need to be adjusted if the transformer windings are not reversed, otherwise swap them. In the absence of the above transformer, you can make it yourself. Winding is carried out on a ferrite ring of size K10 * 6 * 3 with a magnetic permeability of 1000-2000. Both windings are wound with PEV2 wire with a diameter of 0,31 to 0,44 mm. The primary winding has 6 turns, the secondary 10 turns. After installing such a transformer on the board and checking its performance, it should be fixed on it with hot glue. Flashlight tests with an AA battery are presented in Table 1.

The operation of the lantern during the year showed good results.

Table 1

Time, h	V batteries, V	V conversion, V
0	1,28	2,83
2	1,22	2,83
4	1,21	2,83
6	1,20	2,83
8	1,18	2,83
10	1,18	2.83
12	1,16	2.82
14	1,12	2.81
16	1,11	2.81
18	1,11	2.81
20	1,10	2.80

Author: I.V. Ankudinov, aiv55 [dog] mail.ru; Publication: cxem.net

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