Component count wise, a voltage regulator and a current regulator take about the same number of components.
Controlling the (linear) current to an LED is an easy way to vary the brightness, but the useable range is limited. You can test this with a typical voltage & current regulated bench supply. Set the output voltage at say 3 to 4 volts with the current limit set at 1 to 2 mA. The long lead of the LED is positive. Then adjust the current up to the rating of the particular LED you're testing. 50 mA is fairly high, so 20 mA might be a safe max amount, but you will see a definite variation in light output. Typically, component, or panel type LEDs are monochrome. That is, they emit a very narrow frequency band of light. A lamp designed for home use must however, emit a much wider band such that it's illumination quality covers about the same range as an incandescent filament light bulb. The quality of this light as well as the central band of energy is defined as a temperature in degrees* Kelvin. A "warm" light will typically emit light in the 2500 to 2700 K range, where-as the higher temperatures around 6500K are much "bluer", or more like daylight. The actual light is emitted NOT by the LED itself, but a phosphor coating inside the LED which is excited by the LED's output. Dirt-cheap hand flashlights can approach a wider band of light by combining a yellow and a blue LED in the same package. I may be wrong, but I believe panel type "white light" LED's use a combination of color LED's much like a TV screen to generate the white light. One characteristic of an LED is that it shuts off instantly when the current through it is cut off. With a phosphor driven LED there will be a noticeable time lag as the light output fades out on power down. 73, Charlie k3ICH *A particularly fascinating scientific concept is that any substance, when heated to the same (incandescent) color will be the same temperature. It doesn't matter if it's charcoal, a wire filament, or a feather, if it glows the same color, they'll all be the same temperature. Degrees Kelvin is just a convenient way of defining that temperature, or color. The item will go from red through orange, to yellow as the temperature rises. This was the at one time, the lab standard for measuring high temperatures. A filament, placed in the path of a lens was heated via an external calibrated current source. When the visible wire seemed to disappear through the scope when it was the same color as the observed item, the temperature was read off the current dial. Obviously, this was limited to the temperature range where the filament glowed. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
