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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Power supply of LEDs from 1,5 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / LEDs Super-bright LEDs have recently come into fashion more and more, either in a toy, or in a night light, or in a flashlight, etc. But this is not what prompted me to create a module. Somehow it was necessary to power the microcontroller from 1,5 volts - I had to make a blocking generator on the board similar to that used in the module. Then I regretted that there were no microcircuits of the type, I applied 1,5 amperes at the output of 5 volts or something. Then the idea was born to create a universal module for such purposes, which could be soldered into a board or mounted in a flashlight or toy. The scheme is traditional, there are a lot of such schemes in the internet. What's the point then? Chip in size and versatility. The size of the module is 10x7x5 millimeters, in shape and size it resembles the KT815 transistor. It can be installed in the device, and when the device is not needed, it can be unsoldered and saved for another occasion. Details and design. The module uses a 2SC1740S switch transistor, with low saturation voltage, high switching speed and small size. But any other will work. SMD did not try, but in the SOT-89 package they should fit. A little about the ferrite ring, size 3x1,5x1,5 mm. Somehow I needed to put a ferrite bead on a powerful field worker to remove incomprehensible bursts.
I searched the whole house and when I finally found a bag of beads, I found that it did not fit on the conclusion. That's when I got these ferrite rings from some black, compound-filled block labeled FB2022 or LPT100-05, which was in the old 10 megabit coax network card. These parts were in all network cards, and there were 5 rings. It's not very easy to get, but you can. There is also a large black block filled with compound (converter 5 -> 9 volts, there are also rings there, but larger. A little about winding, you need to wind it with a double wire, I took 40-50 centimeters of wire 0.1 folded in half (do not cut it). The place of the inflection turned out to be hard and without a shuttle wound 20-25 turns, as before. After winding, cut the place of the inflection, solder one output with the output of the beginning of the winding, this wire will go to +1.5. The resistor and capacitor in the module are SMD. Located on the side of the foil. The transistor is inserted into the drilled holes 0.8mm, the ring is glued to the board. After manufacturing, you can fill it with varnish. Instead of R1, you can solder a 1.5-2 KΩ SMD trimmer, then you can adjust the brightness of the LED and the current consumption. In my version, the module consumed a current of about 30-35 mA, the current through the LED was 15 mA at a voltage of 2.8-2.9 volts on the LED (to measure, you need to connect the LED through a diode and put a 1 uF capacitor in parallel). At the moment, 5 modules have been produced. Of these, 2 nightlights were made - in a cylindrical jar of vitamins, a 373 battery with soldered wires and a piece of foam rubber (so as not to hang out), in the lid a miniature switch and a blue matte LED. Very convenient. I also made 2 key fobs with a watch battery (I don’t remember the brand, it’s about a centimeter in diameter), I had to give it back a day after production, my friends begged for beer. The key chains were made from a felt-tip pen and had a diameter of about a centimeter and a length of three centimeters, at the end there was a button, a 5mm LED. I'm thinking of making some flickers, but haven't decided what shape it will be yet. In all these devices, you can put two batteries of 1,5 volts and no modules are needed, BUT! There will be two batteries, and when the voltage drops to 1,25 volts per battery, the LED will turn off. And with the module it will work from one battery until it sits down to 0,7-0,8 volts. According to exactly the same scheme, a converter for a night lamp was made from 2-5 LEDs, but two matte blue and green LEDs turned out to be optimal for a night lamp.
The circuit is identical to the module circuit, except for a more powerful transistor and transformer. The transformer is wound on a 7x4x2 ring with a wire folded three times. The ends of the three wires are stripped to a length of 1-1,5 cm, soldered together and their end is rounded with a file or sandpaper (so that it does not cling when winding). It is wound without a shuttle, using the place of soldering as a needle. After winding, the soldering point is bitten off and one of the wires is connected to the end of the winding - this will be +. The second end of this wire is to the base of the transistor, the other two wires of the beginning are to the collector. Those. the primary winding is wound with a double wire. The switch is applied to three positions, the central one is "Off". In one position, the battery minus is connected through a 3-20 ohm resistor - this is for a fresh battery, otherwise the brightness will be excessive. The switch is switched to the second position when the battery is dead, when the brightness is insufficient. !!! If you look closely at the circuit, it turns out that in the "Off" position, the LEDs are constantly connected to the battery through the transformer winding! This is not a mistake, the current consumption of an LED connected to a 1.5 volt battery ranges from 1 to 5 μA, depending on the power of the LED. A current of 1 uA will not discharge the battery. The current consumption is 30-50 mA, with 373 batteries this is enough for 400-500 hours according to the calculation, I really think much more. A bedroom of 5x4 meters illuminates decently, and most importantly, when going to the kitchen to sip beer from the refrigerator, you can take a night light with you so as not to step on the tail of a German shepherd sleeping in the hallway. Illumination is sufficient at a current of 10-15 mA, i.e. You can also use the module. Advice. The current consumption must be controlled by the tester, and selected by the resistor R1 *. Sometimes, with a certain resistance of this resistor, the current consumption increases greatly without increasing the brightness of the LEDs, you need to choose a compromise option - the brightness is sufficient and the current is small. You can replace transistors with KT315, KT503, KT605, etc., but a key transistor with low saturation Uke is preferable.
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