Hi

I am after getting some LEDs to light in a 5v circuit. There are different attributes e.g forward voltage and forward current.

My LEDs I already have don't light up in 5v circuit seemingly.

What should I be buying for My circuit

Thanks

 

Hello,

What are the specifications of your leds?
What is the forward voltage at what current?

Bertus

 

Did you have a resistor in series with the LEDs?

 

The LEDs have no spec or should I say I don't know the spec.

I need new ones so I can at least know what I have bought.

The ones I have actually just light up at 5v

What do I look to buy for 5v circuit

Forward voltage 2v?

 

The simplest solution is to buy LEDs in the colour of your choice that are described as 5v LEDs, otherwise you need to add a resistor in series. If you do neither any standard led will blow nearly instantly.

 

So forward voltage is the attribute?

 

Is there a way to work out what my existing LEDs forward voltage is

 

Is there a way to work out what my existing LEDs forward voltage is

It will be different based on the manufacturer but you can take a rough guess by using the color.

http://www.oksolar.com/led/led_color_chart.htm

But the best thing to have is your datasheet.

For 5V your most LEDs should light. There are three issues that could cause the LED not to light.

1. The LED is connected in reverse.

2. You have exceeded the max current of the LED and it is now fried.

3. The LEDs were bad out of the box (unlikely).

While forward voltage is important to get the LED to light. Probably the most important rating is the max current of the LED. The purpose of the series resistor is to reduce the amount of current flowing through the LED. More advanced techniques would use a buck current regulator to maintain current more efficiently.

 

Is there a way to work out what my existing LEDs forward voltage is

The best way I've found, is to gradually/slowly....turn up your bench power supply.
Never fails.

 

Put a 220 ohm resistor in series with the LED, connect that pair to the 5 volts, and measure the voltage across the LED. You will probably only have about 10 milliamps flowing, but it will get you a voltage number to calculate the real size of resistor it needs.