# TLC5940 + 5v relay?

Is it possible to close a 5v relay using one of the pwm channels in the TLC5940?

I tried once again to wire it up.

The relays im using has a coil power of 0.36W. 0.36w/5v = 0.072a So im assuming the coil need around 80ma to engange. Using the formula provided by the tlc project on google code http://tlc5940arduino.googlecode.com/svn/wiki/images/breadboard-arduino-tlc5940.png im pretty sure it should be something like: 39.06v/0.08a = 488ohm

Using 440ohm limiting resistor the relay still won't close and the tlc gets really really warm. Any suggestions? Is this even really possible?

Im making a project that has a tlc and a CD4071 shift register wired up. so theres not many pins left for the 6 relays that i need to power. if i could run it with another tlc module it would save alot of wireing for me. Frankly im not even sure how i should multiplex relays properly

-Thomas

[quote author=Thomas Hodnemyr link=topic=88940.msg667275#msg667275 date=1327551607] ...The relays im using has a coil power of 0.36W. 0.36w/5v = 0.072a... So im assuming the coil need around 80ma to engange. Using the formula provided by the tlc project on google code http://tlc5940arduino.googlecode.com/svn/wiki/images/breadboard-arduino-tlc5940.png im pretty sure it should be something like: 39.06v/0.08a = 488ohm

Using 440ohm limiting resistor the relay still won't close and the tlc gets really really warm. [/quote]

What is this 39,06V? In your project?

Cheers, Kari

What is this 39,06V? In your project?

Absolutly no clue... its used in the example to calculate the resistor needed to limit all the channels, but i don't know where that number came from.

Using 440ohm limiting resistor the relay still won't close

I assume you have this resistor in the current set pin of the chip and not in series with the relay. Also you are setting the "brightness" of that channel to full.

The relays im using has a coil power of 0.36W.

OK

0.36w/5v = 0.072a

Only if it is a 5V relay. You can get 12V or indeed any other voltage of relay that takes 0.36W. They will not work on 5V.

I assume you have this resistor in the current set pin of the chip and not in series with the relay. Also you are setting the "brightness" of that channel to full.

Correct the ressistor i connected to the IREF pin in the TLC5940

Only if it is a 5V relay. You can get 12V or indeed any other voltage of relay that takes 0.36W. They will not work on 5V.

It is a 5v relay, i have tested it at 5v and it does indeed close The relay is a: HUIKE KH3FF-DC5V-SHG

Then assuming it is wired up right I wonder if the power spec is a bit out. Have you tried to measure the current it takes with a meter?

Hello,

just to explain the39,06 number:

To set the correct current for the relais, you can choose the correct Iref at the TLC’s pin 20. The Voltage at this pin is fixed at 1,24V . The current for the current sink will be amplified by31,5 compared to the current which goes through R Ref-> 31,5 *1,24V is 39,06.
You can findthis on page14 in the TI’s TLC datasheet.
Just to give you a clue…

Regards

Got it! Thanks!

Cheers, Kari