Fixed voltage regulator for simple circuit

I want to use TPS799 for an LED driver circuit. Here is the datasheet: http://www.ti.com/lit/ds/sbvs056k/sbvs056k.pdf

I am assuming that input will be 5V through power jack on the board, and I will be driving an LED , after regulating the voltage to 3 V.

By what I understand, I don't need a capacitor at either, EN or NR terminals.

I am I understanding its usage correctly? And I am not sure how to have the output to 3 V. I am very new to idea of using a regulator so any help is appreciated.

• What LED or LED driver are you using? How much current do you need? Sep 25, 2015 at 17:25
• You should not apply a voltage to a LED, the current a LED will consume will very all over the place and be very unpredictable. That's why we drive LEDs with a current. In practice a simple series resistor from a slightly higher voltage (your 5 V is ideal) does the job ! Sep 25, 2015 at 17:28
• It's not clear to me if you are using TPS799 to provide power to an LED driver, or if want to use TPS799 as an LED driver. Sep 25, 2015 at 17:32
• If you want low noise output use a cap at NR (page 1 stuff). EN is an enable input and normally they don't need a cap. Sep 25, 2015 at 18:02
• I HAVE to use the specified regulator, according to requirement. Else, ideally, I would stick to a simple setup of LED and a resistor. Sep 25, 2015 at 18:23

Are you just driving an LED? If so you don't need a regulator. Also you shouldn't be driving an LED with a constant voltage, you need to drive it with a reasonably well defined current. You can do that with just a resistor.

simulate this circuit – Schematic created using CircuitLab

EDIT:

If the input voltage only changes over a moderate range (2:1) then you don't need a regulator. Just choose an appropriate resistor value to give the LED current you need.

If for example if you have a 5V supply and you want 20mA through the LED which has a 3V drop (common for a white LED). Then the resistor you will need is:

R = (Vinput - Vled) * 1000/LED_Current.

For the example values this gives (5 - 3) * 1000/20 = 100 Ohm.

The LED voltage will vary with the color. A Green LED is probably about 2.1V and a Red LED about 1.7V, Infra red ~1.2V.

If the input voltage varies the current will as well but you probably won't even be able to see a 30% change in brightness. This would occur if the voltage changes between 4.4V and 5.6V.

• m.imgur.com/miGfLNP is the specified circuit Sep 25, 2015 at 18:30
• Op's comments point out that they are required to use the regulator. Sep 25, 2015 at 20:09

Assuming you are using a TPS79930DDCT which is a fixed-voltage regulator that outputs 3.0V nominal, you should refer to the recommended circuit in the datasheet:

The only required component is the 2.2uF ceramic capacitor on the output. You can leave the NR terminal open. The EN input should be tied to the input if you want it to be on continuously.

If you are powering something else from the regulator besides the LED (such as an active circuit - a microcontroller or whatever)- then the input capacitor would be a good idea.

Since you are outputting 3.0V, the circuit is unsuitable for many LEDs of shorter wavelength than yellow, but presumably you've covered that off already.