[SOLVED] Is 20v power supply enough to drive 1470 LEDs with 470 ohms resistor each?

[marieclein_08]

Hi guys,

I'm confused about how much volts my project needs to light 1470 LED with 470 ohms resistor each. I am using 7447 and 74192 to drive LED and 7410 NAND gate for switch debounce. If I used 20 volts as power supply, will it not be a problem with the ICs? I'm afraid it will make the ICs busted.

Thanks for your help.

marie 8-O

 

[jayanth.devarayanadurga]

If LEDs in parallel then You will supply V a little more than the LED voltage it is enough. If LEDs are in series then current will be less. If in parallel 15 to 20 mA current is needed for each parallel branch of LED. It is the current that makes difference and not voltage.

 

[betwixt]

...and don't forget TTL devices run on a 5V supply! If you apply 20V to them they will certainly die.

Brian.

 

[marieclein_08]

OMG!

How much volts do i need for 1470 LEDs?

 

[jayanth.devarayanadurga]

Post your circuit for finding exact current driven by LEDs and circuit.

 

[dr pepper]

Use a mosfet to switch the low side to your leds, then your led supply can be whatever voltage you like.
Maybe strings of x many leds in series paralleled up to make the qty required.
To answer your question as above any voltage above vf of one led (assuming they are all the same colour) is enough.

 

[betwixt]

marieclein_08, I think where you are misunderstanding is that LEDs are current driven, not voltage. However, the ICs do need a constant 5V supply to operate them

To make the LED light up, you have to pass current through it. Up to it's design limit, the more current passing through it, the brighter it lights up. Of course, to make it pass current you have to apply a voltage across it but it only has to be a little more than the LED needs and that is probably only a 2 - 3 volts. An LED is a constant voltage device, if you try to 'force feed' it you will destroy it and that's the reason the series resistor is used, it limits the current so the LED can decide what voltage it wants across it's wires.

So what you need is a regulated 5V, which you can derive from 20V if you like, and an interface circuit to convert the output of the ICs to a voltage suitable for driving the LED/resistor combination. It should be very simple, if you post a schematic, or at least a sketch of how you want to wire it up, we can advise on the best interface circuit to use.

Brian.