How to Reduce Current in a Circuit

Other Hardware General Electronics
1

Very basic I know, but trying to learn. I understand that resistors allow you to drop the voltage in a circuit to whatever you need via a voltage divider or whathaveyou.

What if you have the correct voltage, but too much current?

Context: I have an LED Tower light rated for 12 & 2W, which means I should be supplying 166mA (I think) but the only closest DC PSU I can find is 12V 500mA and I know too much current is not good for LEDs. What's the solution here?

How would I go about using resistors to make the current safe for the LEDs but not drop the voltage?

2

If voltage is 12VDC and you want to dissipate 2W you need 166mA of current flowing.

You now must know the voltage drop of your LED(s).

Let us say the Vf of your LED is 3V.

This leaves 12-3=9V across a limiting resistance.

9V/.1667A = R = 54Ω

9V*.1667 = Rwatts = 1.5Watts choose 3Watts.

A 12V 500mA supply will do just fine with a 3 watt 54 ohm resistor.

3

How would I find the voltage drop if this is what I have?

4

2W/12V=166.7mA, therefore you need a 12V @ 166.7mA power supply ‘at least’.

A 12V 500mA power supply can be used as the light will only take the current it needs.

In fact you could use a 12V @ 50,000A power supply too, just don’t accidentally short the supply :wink:

5

So I really don't need the resistor at all then? The LEDs will only take the current they need?

6

You’ll find the resistors are already inside the stack light, so, no, you don’t a resistor in such devices, just apply the correct voltage and the device manages the current.

7

AlexComputerWiz:
So I really don't need the resistor at all then? The LEDs will only take the current they need?

For those lights that’s correct.

8

The LEDs will only take the current they need?

No, in general LEDs require a current limiting device. For low power LEDs ( 20- 50mA ) a simple resistor will do. When you get into high power LEDs you need a constant current drive. That is a circuit that constantly monitors the current and tweaks the voltage it outputs up and down to maintain that current.

However, that product you linked to, is a product that is designed to run from 12V so some form of current limiting must already be included. The actual details of what wires do what are somewhat missing on that page, which indicates that the people selling them have no idea about what they are selling, but I guess that one wire is +12V and the other four wires need to be grounded to activate one of the three lights or the buzzer.

Note that this was a classic X-Y Problem where you should have asked what you wanted to know, not your take on the solution.

9

AlexComputerWiz:
Context: I have an LED Tower light rated for 12 & 2W, which means I should be supplying 166mA (I think) but the only closest DC PSU I can find is 12V 500mA and I know too much current is not good for LEDs. What's the solution here?

Complete non-issue. The LED tower requires 12V, give it 12V and it will work so long as the supply can provide at least 0.17A.

If the supply can supply 0.5A it doesn't mean it will unless asked for it. The load determines the current drawn from a voltage supply.