# Integrated LED + Resistor + Transistor

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?

• 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. – Asmyldof Oct 6 '14 at 0:03
• 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. – Passerby Oct 6 '14 at 0:18
• 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 – mFeinstein Oct 6 '14 at 4:00
• 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. – Passerby Oct 6 '14 at 6:04
• 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... – mFeinstein Oct 6 '14 at 22:02