how can I make a circuit for more than 70 leds (20mA/2.5V) with 555 timer

[Merdan]

how can I make a circuit for more than 70 leds (20mA
/2.5V) with 555 timerI want them all to run at the same time.

 

[emc2]

It depends on how many you want running at one time?

 

[Handel]

I have the same question. I need to drive apprx. 90 LEDs to strobe at variable cycles of ~ 4 ms to 50 ms, say. (2 potentiometers, .047 uF capacitor, ground capacitor, 555 timer, LEDs @ 96, 13.8v input with current of 35 amps to supply the LEDs).

Each of my LEDs draws 350mA. Supplied by a 13.8v power supply, if I put them all in several series of 6, the voltage drop (2.3 fV each LED) across each LED will not require a resistor for the series.

Is it possible to have the positive input line run through all the LEDs before going through the timer somehow?

My circuit is going to draw 35 amps, more or less.

Do I need to find a different way to create a strobe effect?

I don't understand how current affects a 555 timer in a circuit where other components can suck up that current.

Thanks for any advice, and I apologize for being a dunce on this one.

Handel

 

[Merdan]

how can I make a circuit for more than 70 leds (20mA
/2.5V) with 555 timerI want them all to run at the same time.

 

[emc2]

This circuit requires 9v with 600mA to run. If you wanted to connect this to a 555 timer you can, but you would need to add a few components like sinking the output with a transistor to pass enough current to the led array.

Hope that helps.

 

[Merdan]

I have made one and I think it will work; also I put the picture of circuit.

I would like you to look and write your opinion about, if it needs some components please put them on the same picture( with spesifications, exact names) and send it back. Thanks for your previous circuit!

 

[emc2]

Because the 555 can only output around 200mA you need to use a buffer transistor.

Check out this page, it pretty much explains it:
http://www.555-timer-circuits.com/increasing-output-current.html

 

[Merdan]

emc2, thanks for all; but my questions haven't end. How can I calculate the output currency up 2 my circuit? (each led is 20mA and 3.4V )

 

[Merdan]

I have calculate it as follows: 20 mA*24=576 mA

 

[Admin]

Merdan,

I have calculate it as follows: 20 mA*24=576 mA

That would be if you want to run them at max capacity and it would burn out the LEDs pretty quickly.
Look at the attached circuit. It requires 9v with 300mA.

Regards,
Phil

 

[Merdan]

for 12V input and leds(3.00V; 20 mA) what will change in the circuit??? Could you post a new picture again???(3 leds in a series)

 

[Admin]

You don't need to change anything. The circuit I posted will work with 12v as well.

 

[Merdan]

but with 12V input, voltage per a led in a single serie will be: [12-(68*0.02)]/3=3.54V and it is too much for a led (my leds work with 3.00V /20 mA). will the circuit be ok if I use 130 Ohm /0.125W instead of 68 Ohm????
I don't know how much BC337 will increase output currency but I have TIP31(it is for 1A) CAN I use it instead of BC337???

 

[Merdan]

but with 12V input, voltage per a led in a single serie will be: [12-(68*0.02)]/3=3.54V and it is too much for a led (my leds work with 3.00V /20 mA). will the circuit be ok if I use 130 Ohm /0.125W instead of 68 Ohm????
I don't know how much BC337 will increase output currency but I have TIP31(it is for 1A) CAN I use it instead of BC337???