I need a LED driver circuit controlled by a PCI-DIO-96 board discrete output.

[Mark_Shelton]

I need to drive a typical 20 mA (1.6 V) LED using a discrete output from my PCI-DIO-96 board (NI 6507), actually 14 LEDs using 14 separate discrete outputs. The electrical information regarding the discrete output specifications of this board is not clear regarding max sink/source current and resulting voltage shift so I would rather use a discrete output to control an IC to power an LED instead of driving it directly from a discrete output. I would still use the +5 volt source from pin 49 of the PCI-DIO-96 as it is rated for 1A, plenty for all 14 LEDs. So what is the best (i.e., simplest) LED drive circuit? Thanks!

[dhuff]

try using a 7406 inverter. The 7406 is open collector, meaning it can handle high currents. Run the digital card output into the input of the inverter, then use the inverter gate output to drive the LED. The chips are cheap, and usually have 6 seperate gates on each chip. You can run the chip power from the DIO card connector 5V supply and ground.
You can run the LED 2 different ways,
1. Connect the LED anode (positive terminal) to 5v, and the cathode (negative lead) to the output of the gate. When the gate input goes high, the output goes low, trying to sink all current to ground. This will run the LEDs at the same state as the Digital card,(LED on when DIO card pin high)
2. Connect the LED Anode to the output of the inverter, and the cathode to ground
. This will give you an inverted signal from the input to drive the LED.

[RIO-Todd]

Hey Mark,

You could just use a basic emitter follower circuit to supply the current to the LEDs. The emitter follower uses a PNP transistor and you could input the digital TTL signal from the PCI-DIO-96 to the base of the PNP transistor to "turn-on" and "turn-off" the transistor. The link below has a circuit diagram. I hope this helps.

Emitter Follower
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npncc.html#c2

Regards,

Todd D.