White LED Supply Driver II

  
The article describes a simple and very cheap to drive white, blue or UV LEDs, used for example in small lamps and testers. The cost of components shall not exceed CZK 10. Converters for white LED has been on the pages of journals described quite enough. When I recently needed a similar drive, I wanted to use the drive transistors . This drive was not the desired range of supply voltages (2 normal cells) very convenient. A solution would be to use a specialized integrated circuit, the drive should not be the cheapest. So I tried some of us published the involvement of simple inverters plus a few others. With no I was not too pleased.
White LED Supply Driver II - schematic

Some drives have performance more suitable for demonstration purposes only, while others have very little effect. Several authors have vowed to stabilize or reduce the output current. While such a converter from a really nezv?toval voltage LED current, the "stabilization" was due to saturation of the collector current of the transistor or the supersaturation reactor. For more voltage converters, the efficiency rapidly dwindled. So I suggested a simple involvement in two variants, which in Figure 1 The main connection I replaced one resistor and capacitor component values ??optimized. The drive does not stabilize the current, but with two rechargeable batteries power NiCd or NiMH does not matter because the voltage discharge for most of the time do not change. The drive comes in two variants - with and without the rectifier. When experimenting with the traditional components of the more attractive option rectifier. The drive was more effective. The final implementation of the SMD, however, showed relatively large negative resistance of a small Schottky diode (BAS85), while the efficiency of converters with a rectifier was larger, probably due to less parasitic capacities. Efficiency drive can be larger in both cases about 10% using improved coil winding with less resistance. The tests used a cheap miniature axial choke ¬ęPharmaceuticals (in GM for 3 Electronic CZK). LED current can be adjusted by changing resistor R1 (more...



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