# Lighting LEDs from high current source [duplicate]

I have an circuit with six high torque servos connected parallel to power brick that provides 5V @5Amps. Everything is running fine. But I wanted to add few LEDs to circuit but I dont know how do I do it ? Connecting LEDs parallel to other components will I think burst LEDs as current is too high from source. All servos needs to powered on all the times too. Current drawn by servos are very dynamic.

Any ideas?

Thanks

• Why would be current too high if in parallel? Add an appropriate limiting resistor, and it will be fine. Commented Apr 14, 2016 at 22:02
• Thanks, power brick is supplying 5 amps? will it affect LEDs ? Also what kind of current limiting resistor I can use? Commented Apr 14, 2016 at 22:05
• It's 5A max. As for a resistor, similar questions are asked here every day. Look around. Commented Apr 14, 2016 at 22:08
• @AmritSohal - the power brick will supply up to 5 amps, depending on what the load needs. Commented Apr 14, 2016 at 22:09
• so does it mean that I can add leds to circuit in parallel? Which means voltage across leds is 5V and current is one required by leds right> Commented Apr 14, 2016 at 22:13

simulate this circuit – Schematic created using CircuitLab

Figure 1. LED in parallel with motor controller.

I wanted to add few LEDs to circuit but I dont know how do I do it ?

You wire LED's across the 5 V supply with a current limiting resistor in each. Typical LEDs require 5 to 20 mA to give a bright indication. The resistor needs to be sized to limit the current to the chosen value.

Connecting LEDs parallel to other components will I think burst LEDs as current is too high from source.

Very dramatic prose but it shows a misunderstanding of voltage and current. The battery presents 5 V to whatever (reasonable load) you connect to it. The current drawn depends on the resistance of the load. The power supply can deliver up to 5 A but it doesn't force 5 A through whatever you connect it to. As an analogy, your house is connected to an electricity grid capable of supplying millions of amps but when you switch on your light the grid doesn't force it all through your lamp. The lamp just takes what it need.

All servos needs to powered on all the times too. Current drawn by servos are very dynamic.

All will be fine as long as you don't exceed 5 A total load.

Calculating resistor value

For standard LEDs you can figure on dropping about 2 V across the LED when passing 3 to 20 mA. (They're not linear and the actual voltage depends on the colour of the LED.) In your case that leaves 3 V to be dropped across the resistor. Let's make the maths easy by saying we want 10 mA through the resistor / LED. From Ohm's Law ($V = IR$) we can calculater $R = \frac {V}{I} = \frac {3}{0.01} = 300~\Omega$. Pick the nearest value that you've got (+/- 30%, say) and you should be fine.

For a more details see my answer to LED forward voltage - why does series resistor take excess voltage? (and thousands of other Q&A posts on this site).

• Thanks mate, this is a beautiful answer :D. Question : resistor is calculated using V = I R right? My V=5V, what would be value of I to calculate R ? This is where my main confusion is. Thanks Commented Apr 14, 2016 at 22:17
• See update, "calculating resistor value", and link. You can give both a vote. ;^) Commented Apr 14, 2016 at 22:37
• Mate, Thats exactly what I was looking for :D Thank you so much... you made everything clear :) Commented Apr 14, 2016 at 22:58