Hey everyone,
I am a newbie to electronics and I have seen a lot of schematics where people use 555 timer to drive bunch of leds. Why use 555 when the leds can be driven without it. Thanks in advance.

J

 

You use the 555 if you want to flash or time them. If they are to be on steady, then all you need is a DC supply and a resistor.

 

You use the 555 if you want to flash or time them. If they are to be on steady, then all you need is a DC supply and a resistor.

Thank you MikeML for you quick reply.

 

you can dim them using a 555 timer using Pwm.

 

I've even seen the 555 used not to flash the LEDs or control brightness, but as a simple on/off switch in a night light.

It used the comparator section to read a light sensor and only turn the LED on in a dark room.

The 555 is quite a useful device with an incredible potential for many many uses.

 

you can dim them using a 555 timer using Pwm.

Dodgydave,
Thanks for the reply. I guess what I was asking is that a variable resistor can dim the leds too so why go with a 555? You still need to use a variable resistor to dim even though you'd be using 555, right? Is using 555 for PWM more effecient?

 

I've even seen the 555 used not to flash the LEDs or control brightness, but as a simple on/off switch in a night light.

It used the comparator section to read a light sensor and only turn the LED on in a dark room.

The 555 is quite a useful device with an incredible potential for many many uses.

Hi ErnieM,
Thanks for you reply as well. I am sorry if I sound like I am against using 555. I really am not. I am just trying to understand its implementation when it comes to simple circuits.

Thanks

 

yes, pwm is more efficient and creates less heat.

 

It is a matter of efficiencies. A 555 can do it with much greater efficiency than a resistor, less waste heat among other things.

LEDs, 555s, Flashers, and Light Chasers

 

It is a matter of efficiencies. A 555 can do it with much greater efficiency than a resistor, less waste heat among other things.

LEDs, 555s, Flashers, and Light Chasers

Super. I appreciate your help! And thank you for the article. I just joined the site yesterday and I did a search on 555 and thats the first article I ended up reading. Thank again!

 

yes, pwm is more efficient and creates less heat.

Thanks Ernie.

 

Using PWM to dim a 20mA LED is stupid, however...

 

Using PWM to dim a 20mA LED is stupid, however...

That would depend on the application, would it not?

I once used PWM via a micro controller to control the brightness of a single LED. We sold them for about $30 a piece to someone who used them as cockpit lighting as incandescent replacements.

The trick was getting the brightness of a LED to mimic that of an incandescent over a 10 to 28V range. The other trick was getting the whole thing to fit into a metal barrel about the size of the eraser holder on a #2 pencil.

 

That would depend on the application, would it not?

I once used PWM via a micro controller to control the brightness of a single LED. We sold them for about $30 a piece to someone who used them as cockpit lighting as incandescent replacements.

The trick was getting the brightness of a LED to mimic that of an incandescent over a 10 to 28V range. The other trick was getting the whole thing to fit into a metal barrel about the size of the eraser holder on a #2 pencil.

I have several LEDs run off the dimmer bus in my Cessna. I was able to get the LEDs to match the incandescent dimming curve using a couple of diodes, a transistor and some resistors...

 

anyone else here think that the 555 rivals the invention of sliced bread?

such a versatile ic

 

yes, pwm is more efficient and creates less heat.

Only if you use an inductor in series to average the current.
If you still use a resistor in series with the LED to limit the current then there will be little change in the efficiency for a given average LED current and supply voltage.

 

This is what's going on inside a 555
aa-555-01.gif

 

This is what's going on inside a 555
aa-555-01.gif

This is great man. Thanks.