Fun with LEDs, unexpected discoveries

 In an earlier blog post, I talked about the knee region. This is the area of an LED's voltage-current curve, where the current begins to increase sharply. For most 3v LEDs, the knee region is a fairly small voltage range. Controlling the knee region requires a very careful adjustment of voltage.  There is a way to expand the knee region: connect multiple LEDs in series !  All the LEDs voltage aspects are cumulative, when connected in series. So the overall vFwd increases by the number in series, but so does the voltage range of the knee region. The basic assumption here is that all the LEDs you are connecting in series have the same data sheet part description, and also they were binned together voltage wise. A single LED might have a knee region that is only 0.1v-0.2v wide. By placing five in series, the voltage rage of the knee region now becomes a range of 0.5v-1.0v wide. An additional advantage of five (or six) in series, is that you can power it with a 15-20 volt su...

 Not every LED selling source can supply high quality datasheets. When the prices are too good to ignore, it's time to do your own characterization. What is needed ... • a voltage source - My voltage supply is a Ryobi 18v battery, with an adapter found on eBay for powering Hot Wheels go karts. The adapter has both an on/off switch and an inline fuse. The default fuse is 30A, but I've changed mine to 3A. • a mini board that holds a regulator - These are little PCBs that will hold one adjustable regulator (AMS1117-ADJ or LM317LZ, your choice, they both have a 1.25v Vadj terminal. You will be using this device as a two-terminal constant current regulator circuit. This means that There is a Vin, a Vadj, and a Vout. You have to supply a resistor to program what current value the regulator is targeting. The regulator will then home in on the desired current, while dropping any excess voltage required to do this. • a mini board with positions for 8 SMD resistors - I'm partial to ...

  In the beginning , sometime in 2019, I wanted to do some indoor hydroponics. One thing begat the next thing, and I began to learn things. The first attempt was to order some Samsung COBs that were designed/engineered for growing. At the time, I did not have a way to cool them properly or to supply the high current required, so they have sat unused. But an examination of them prompted me to look around at what LED devices were available, in what quantities and at what prices. If I wanted to roll my own, I did not have any intention of tossing lots of money at the problem, I just wanted to find a better way to make it happen. The 2835 white LEDs One day, while scrolling thru eBay, I came upon a seller who had some reels of 2835 1 watt LED chips (Cree J Series JK2835 18v). After reviewing the datasheet, I ordered a reel. Meanwhile I was looking for a power source. At a local thrift store, I found an HP printer wall-wart that supplied 15.5v and 30v. It was purchased because of the 3...

 This is a Voltage/Current curve of a typical light emitting diode. The exact values of each spot on the curve are less important, but the curve and what happens in each segment, is more important. Segment A - Voltage is increasing, but has not yet reached the point where the diode junction is emitting enough light to be visible. If you have a datasheet for the device, this will probably be the first 75%-80% of the rated forward voltage (Vfwd). Segment B - As the forward voltage enters the knee part of the curve, light may be perceived. Depending on the exact voltage and/or the current, the light may be faint. Once you have entered the curve area, forward current will begin to change as the voltage increases. Depending on the exact device ratings, the device may begin to dissipate some heat. Heat will be low to negligible, increasing as you approach the device rated forward current. Light should be obvious, and increasing as you move deeper into the knee area. Segment C - The light...

 Hello and Welcome ! This is a blog to share discoveries about LED devices and their associated LED circuits. Around 2019-2020 I began exploring LEDs and how they might be used in hydroponics, and the indoor growing of food items. One thing caused me to investigate another, and my explorations branched off into unexpected directions. Down the rabbit hole we went 🐇 Thanks for stopping by 😀