Help me in connecting 30 LEDs in Parallel with microcontroller 89v51

hi friends ! i need to connect 30 LEDs in parallel to microcontroller 89v51 as a single pin output.. i tried a lot but i couldn't.. please help me with some ideas..
Madhu..

How much current would be required to light the 30 LEDs in parallel?

How much current can the single output pin supply?

You will need a buffer/driver type of circuit, to supply that much current; probably a single-transistor circuit (basically a small amplifier), or some paralleled digital inverter/drivers outputs, or maybe a comparator (or several, depending on their current-sink rating). There are lots of ways to do it, once you realize that the single output pin cannot supply that much current. Just use it to trigger something that can provide that much current.

Use some transistor like 2N3904 NPN or something like that and switch it ON/OFF by connecting it, via series resistor, to your uController's output pin. Hang as many LEDs as you want on the collector side of NPN. Now,They will get their required currents from the source instead, because uController will not be able to provide a sufficiently large current all by itself on a single pin.

tgootee said:

How much current would be required to light the 30 LEDs in parallel?

How much current can the single output pin supply?

You will need a buffer/driver type of circuit, to supply that much current; probably a single-transistor circuit (basically a small amplifier), or some paralleled digital inverter/drivers outputs, or maybe a comparator (or several, depending on their current-sink rating). There are lots of ways to do it, once you realize that the single output pin cannot supply that much current. Just use it to trigger something that can provide that much current.

Click to expand...

i have a 5v 2A dc supply, can i trigger it with output high from controller ? if so what transistor (& range) and resistance i need to use ?

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styx1.618 said:

Use some transistor like 2N3904 NPN or something like that and switch it ON/OFF by connecting it, via series resistor, to your uController's output pin. Hang as many LEDs as you want on the collector side of NPN. Now,They will get their required currents from the source instead, because uController will not be able to provide a sufficiently large current all by itself on a single pin.

Click to expand...

i have a 5v 2A dc supply, can i trigger it with output high from controller ? if so what transistor (& range) and resistance i need to use ?

Use a 2N3904 NPN transistor. Connect a resistor of about 1k resistor value to the base. It will work great. And don't forget to series connect some resistance to each LED you connect. For your 5V supply use a 10k resistor.

How bright do you want the LEDs?

Have you selected the LEDs?

What is the Vd [voltage drop] of the LEDs?

Some key points.

you can NOT connect LEDs in parallel - unless they are perfectly matched, one will hog the current and burn out, then the next one will do the same, and so on. You NEED to put a resistor in series with EACH LED. IF the voltage present is 3V5 [as an example] and the Vd of the LEDS is 2V and you want 10mA then the resistor value is (3.5 - 2) / 0.01 ; use a 330 or 390 ohm resistor.

You need a transistor or such as a driver BUT if it is connected in CC then the voltage for the LEDs will be LOGICAL HIGH voltage minus 0V7 volts. Which could be too low. The 0V7 is the voltage drop of the transistor.

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styx1.618 said:

Use some transistor like 2N3904 NPN

Click to expand...

The 2N3904 is limited to 200mA which would mean a max current of 6.7mA per LED.

Yup, kam1787 is absolutely right. 2N3904 transistor has a rated current of about 200mA and an LED draw almost 20mA current (most of them especially Red and Green ones). So you will not be able to connect more than 10 anyway. So i would suggest you to use a 2N2222 general purpose transistor as it is rated for 1.0Amps collector current.

2N2222 is 1A or 800 mA?

you can also use n-chanal mosfet for driving more current

It's 1.0 Amp. Here's a datasheet from one of the many manufacturers out there:

https://www.fairchildsemi.com/ds/PN/PN2222A.pdf