External Power supply for 15 TLC5940 for LEDs

Forum 2005-2010 (read only) Hardware Interfacing
1

Thanks to Acleone, I connected 10 TLC5940 chips in control .

But then, next problem came up. LEDs on from 6th chip onward are dimmed and even blinking while LEDs on 1~5th chips are just constantly bright. It seems like 5 * TLC5940s are enough to dissipate all the power from arduino.

So, If I want to use more than 200 leds controlled by 15 TLC5940s, I definitely need to use external power supply, dont I? If so, how can I do it?

Somebody please tell me what I should do. .. Thanks in advance!

2

If you have an external power source plugged into the Arduino, you might be overloading the voltage regulator by drawing too much current through the +5V line. If you have 5*16 LEDs, this is 1.6A! of current. You could try powering all the LEDs from the external power supply directly: hook the positive legs of the LEDs to the "VIN" pin on the Arduino.

3

Remember to keep the grounds common between your external power supply and the arduino.

4

Thanks a lot Acleone and Grumpy Mike!!

I'll try it tonight! Wish me luck!

5

i have an external power supply for the TLC5940 (3V @ 1 amp) and a common ground between the chip and arduino.

It should work for u too

6

Further questions!

  1. There are two power required for TLC5940 - one is directly into the chip (Vcc), another is VLed to LEDs. I understand that all GND should be shared but how about + when I use two sources of power?

(a). Vcc-5v on Arduino | VLed-5v from Vin (or EXT power)
(b). Vcc & VLed both - Vin

Which one is correct? Do they make any difference?

  1. If I connect an external power to Arduino, its voltage should be 7~12 (arduino's recommendation) so the Vin is same as the external power which is too much for VLed. I might need to down the voltage with a resistor or regulator or something that I don't know how. Anybody can give me a hint?
7

you should power the chip from arduino (either 3.3v or 5v depending on your resistor for IREF).

what i meant to say in my post is that i have an external power supply for the LED's (not the TLC5940).... and a common ground between all three (the ground of the power supply is connected to ground on arduino and the TLC5940).

8

aha... thanks nimo! NOw it's very clear!

9

Note that if you are using 3V3 to power the TLC5940 you should not connect the anodes of the LED to +5V directly as this would take the inputs to the chip outside it's rails. There is a TI application note that shows the LEDs going through a FET with the gate set to Vcc in order to protect it.

If you are using 5V then everything is as stated above.