sinking and sourcing current

[Wong]

Hi,
If I use a GPIO pin on a IC to drive LED, which configuration is the
best ?
1.) LED's negative pin to GPIO, positive pin to other power source.
or
2.) LED's negative pin to Ground, and positive pin to GPIO. Of
course both with current limiting resistor.

Is this related to the current sinking and sourcing ?
Thanks in advance.

 

[Bernhard Roessmann]

Wong wrote:

Hi,
If I use a GPIO pin on a IC to drive LED, which configuration is the
best ?
1.) LED's negative pin to GPIO, positive pin to other power source.
or
2.) LED's negative pin to Ground, and positive pin to GPIO. Of
course both with current limiting resistor.

In most cases, 1) ist better, because many IO-Pins can sink more current
than source, but newer Microcontrollers/Processors often have equal
sink/source capabilites.
Consult your data sheet, section "DC characteristics".

Is this related to the current sinking and sourcing ?

Yes, 1) GPIO sinks current, 2) sources current.

LG,

--
Bernhard Roessmann
Don't Fear The Penguins!

 

[Bernhard Roessmann]

Wong wrote:

Additionally, don't forget: If you use the "sink design", your software
has to invert the outputs (because of writing "1" means H voltage level
and led OFF, "0" means low voltage level and therefore led ON").


Regards,

--
Bernhard Roessmann
Don't Fear The Penguins!

 

[Spehro Pefhany]

On 25 May 2004 05:46:33 -0700, the renowned tatto0_2000@yahoo.com
(Wong) wrote:

Hi,
If I use a GPIO pin on a IC to drive LED, which configuration is the
best ?
1.) LED's negative pin to GPIO, positive pin to other power source.
or
2.) LED's negative pin to Ground, and positive pin to GPIO. Of
course both with current limiting resistor.

Sinking is better (the first one).

Is this related to the current sinking and sourcing ?
Thanks in advance.

Look at the voltage drop curves for why it is better. The maximum
current rating may well be the same in either direction, however the
sinking (n-channel) transistor will typically have less voltage drop
at the same current.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com