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Most designers when are controlling an LED have to make the same old circuit of Vcc -> Resistor -> LED -> Transistor (you need the transistor in case your MCU/MPU pins can't handle the LED current, and many MCU/MPU can't give you more than a few milliamps).

I wonder if there is a LED that comes ready to just be connected to Vcc and GND with a signal pin to turn it on or off, this might save some board space, but I never heard of them. Does anyone know if they exist and their name?

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    \$\begingroup\$ I only know of RGB/RGBW LEDs with built-in colour controllers. The main reason this is not so common as you might expect (or want) is that only very few uses of LEDs are exactly the same (very low current, very high brightness, somewhere between, 3V, 2.5V, 9V, 5V, 12V, etc). Not to mention the added complexity to what is now a very easy and cheap to make thing. \$\endgroup\$ – Asmyldof Oct 6 '14 at 0:03
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    \$\begingroup\$ The sheer number of variety in VCC, Vout, VLed, Vf, desired current/brightness, Iout, etc, make this impractical for mass production. You can find this in hobbyist circles often, or through the use of dedicated led drivers, but discrete individual transistor-led pairs, in single led instances? Not often. Look at the rpi led indicator boards, arduino led matrix boards, or smart rgb leds like the ws series for examples. \$\endgroup\$ – Passerby Oct 6 '14 at 0:18
  • \$\begingroup\$ It's just that almost every PCB has a green LED...some are just tied to Vcc to indicate power but many use the LED to flash to indicate some different states, specially USB stuff which has 5V rails...so I kinda see some market application in there \$\endgroup\$ – mFeinstein Oct 6 '14 at 4:00
  • \$\begingroup\$ Honestly, most mcu's can give the 5~20mA needed for a single or two indicator led, directly, with just a resistor though. And while USB power is 5v, usb signaling is at 3.3v, lowering the need for transistors as well for a single indicator led as well. \$\endgroup\$ – Passerby Oct 6 '14 at 6:04
  • \$\begingroup\$ I once used an AVR32 that couldn't drive a proper LED, and some low voltage MPUs I guess will also have a hard time. Also using the USB signals directly with the LED doesn't seems to be a good idea...this will show there is USB activity but this can cause so many signal integrity problems in high speeds, and it's not something the user can really interact with... \$\endgroup\$ – mFeinstein Oct 6 '14 at 22:02
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Short answer: No

Explanation: Essentially what @Passerby said. While it sounds like a nice idea in theory, the variability in supply voltage, control voltage, max brightness/current, etc. all mean that these devices would have to be made in relatively small volume.

Small volume -> high price, so that product line likely wouldn't survive very long since the supply of transistors, resistors, and LEDs are so high that the same ol' circuit can generally be made dirt cheap.

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  • \$\begingroup\$ I see your point, but as far as I imagine most of the leds will be running on a 3.3V or 5V supply and logic, isn't it? \$\endgroup\$ – mFeinstein Nov 6 '14 at 22:50
  • \$\begingroup\$ Yes I would think so. Perhaps you'd like to suggest this idea to a fab and see what their response is? :) I'd also add that even controlling for supply/logic voltages the variability in brightness and LED color would still be pretty large. So why don't the manufacturers just pick a standard LED color (such as green) and a standard brightness level and make a few of those? I'd still go with the answer of "it's just not profitable". \$\endgroup\$ – Michael Leonard Nov 7 '14 at 0:27
  • \$\begingroup\$ I see your point, but honestly, I have no idea, just assumptions on the LEDs manufacture process, and there are so many things that I don't know that could influence this kind of thing that I rather not to assume. I posted this in here on the hopes that someone from the industry will find it, and comment on it, I have no contacts with anyone that could actually make it happen, or answer me \$\endgroup\$ – mFeinstein Nov 8 '14 at 22:03

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