front panel leds

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Hi im looking for some 5v leds for the front panel of my amp they will light up when a different input is selected they need to be small so i can drill small holes so they can be countersunk with flat tops. I've looked on the web but cant find them. what do you guys use? thanks
 

PRR

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LEDs don't really come "5V". A Naked LED needs 1.5V to 4V (depending on color), and typically needs 20mA for BRIGHT, though 2mA may be plenty for living room use. YOU compute a resistor to make that happen. (There are online calculators.)
 
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Have you a link to what you actually bought ?

To illustrate what happens, when you apply a rising voltage to an LED no current initially flows. When that voltage reaches a certain value (value depends on colour as PRR stated above) then the LED conducts and current flows. It lights. From that point on, any small increase in voltage causes a massive increase in current, massive to the point of destruction.

So we use a series resistor to swamp changes in supply voltage and to set an initial current suitable for our supply voltage and desired brightness.
 
Have you a link to what you actually bought ?

To illustrate what happens, when you apply a rising voltage to an LED no current initially flows. When that voltage reaches a certain value (value depends on colour as PRR stated above) then the LED conducts and current flows. It lights. From that point on, any small increase in voltage causes a massive increase in current, massive to the point of destruction.

So we use a series resistor to swamp changes in supply voltage and to set an initial current suitable for our supply voltage and desired brightness.

Hi these are what i ordered.
3mm 5mm Flat Top LED LEDs RED GREEN BLUE WHITE YELLOW Superbright NEW UK SELLER | eBay
 
In case you missed the LARGE RED LETTERS UNDERLINED WARNING repeated TWICE:

IMPORTANT: You should always use a current limiting resisitor when powering an LED, please see my other eBay listing for suitable resistors.

IMPORTANT: You should always use a current limiting resisitor when powering an LED, please see my other eBay listing for suitable resistors.
 
If you read the E-Bay advert, the seller has given you the data that you need.

All LEDs have a forward voltage Vf.

Let's say this is 1.3V as an example.

Most LEDs will operate quite happily at 5mA.

If you wish to use this LED at 5V you need to use the following formula.

R = (5v - Vf) / 5mA

R = 3.7 / 0.005

R = 740 Ohms

It is typical to use the closest value available which is 720 Ohms.

Power = I*I*R = 0.005 x 0.005 x 720 = 0.00175W

That is so small that any sized resistor will do the job as long as it is in the order of 720 Ohms.

If the LEDs are wired in parallel, each LED will require its own resistor.
 
In the real world the LEDs will actually work perfectly well with a current of anything between 5mA and their maximum rating (usually 20mA). 10mA is normally picked as a mid-point value.

The brightness of the LED is not normally controlled through the current. It usually has to be controlled through Duty Cycle - i.e. flashing it. 50% on 50% off equals half as bright.

Just to re-iterate, LEDs cannot be directly paralleled, each one needs it's own resistor.

The more usual solution is to connect the LEDs in series, but with a limiting factor of a 5V supply that gets awkward.

If you connect two LEDs in series, then the VF's can be added together in the following formula.

R = (5V-Vf1-Vf2) / 10mA

So using Vf at 1.3V as before

R = 2.4 / 10 mA = 240 Ohms.

Three LEDs in series

R = (5V-Vf1-Vf2-Vf3) / 10mA

R = 110 Ohms

Four LEDs in series would make Vf higher than the 5V supply and the LEDs might fail to illuminate.

You can of course mix the two solutions.
 

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LED resistor calculators

As people have already said, you need a resistor to current limit the LEDs so they don't die early.

There are bunch of on-line calculators where you enter the color and voltage to compute the resistor value (and wattage needed)-

Current limiting Resistor calculator for leds

LED Series Resistor Calculator | DigiKey Electronics

LED Resistor Calculator - Electrical Engineering & Electronics Tools

While the LEDs can take 20 mA, I dont think they are much dimmer at 10mA or even 5mA is ok most times.
 
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