Increasing brightness of LED using timer

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
I am using a 5vdc ww to supply power to a LM317 circuit. In between the ww and the LM317 I have a resistor and led to indicate that power is coming from the ww. I would like to increase the apparent brightness of LED so it is more visible however I don't want it to be visible flashing. What is the simplest way to do this so that I can order appropriate parts from Digikey. I was thinking of a LM555 however I would definitely need assistance in a schematic. Any other suggestions? Please keep everything very simple as my skills are extremely limited.
 

spinnaker

Joined Oct 29, 2009
7,830
What is a ww?

You need a brighter LED. That is pretty much you options.

I don't see how a timer is going to solve your issue. Driving an LED with PWM will only decrease its brightness.

You could flash it to make it more noticeable but brightness will not increase.
 

crutschow

Joined Mar 14, 2008
34,201
How much current do you have going through the LED?
If it isn't above it's maximum value, you can reduce the value of the resistor to increase the LED current and its brightness.
 

dl324

Joined Mar 30, 2015
16,788
As previously mentioned, just decrease the value of the current limit resistor while keeping LED current below it's maximum.

What are you powering with the LM317? The dropout voltage is a couple volts...
 

KMoffett

Joined Dec 19, 2007
2,918
Also some LEDs are brighter than others with the same current. I have some old red LEDs that are barely visible at 10mA, while new ultra bright almost blind you at 10mA.

Ken
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
Also some LEDs are brighter than others with the same current. I have some old red LEDs that are barely visible at 10mA, while new ultra bright almost blind you at 10mA.

Ken
Can you give me more info on the ultrabright LED. If you can a particular item at digikey.

Jan
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
As previously mentioned, just decrease the value of the current limit resistor while keeping LED current below it's maximum.

What are you powering with the LM317? The dropout voltage is a couple volts...
Dennis:
I am running the LED at 21ma. Max is probably 25ma. The LM317 is set for 'outputting approximately 1.8vdc and is supplemental charging a battery in a solar post light.

Jan
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
I believe that by 'flashing' the LED I can increase the current as long as the average current is below the maximum allowed for the LED. If the Led is on only 50% of the time I believe I can double the current. that is why I want to install a timer.

Jan
 

dl324

Joined Mar 30, 2015
16,788
If the Led is on only 50% of the time I believe I can double the current.
Luminous efficiency does increase with current; to a point. You should consult the datasheet to see what the absolute max current is and under what conditions. 40 years ago, some LEDs would take a 1A pulse (under the right conditions); don't think there are many that will tolerate that these days.

The allowed duty cycle for high current operation is always significantly less than 50%.
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
Dennis:
Thanks for your answer. I am trying to upload a schematic with not much success. I will respond once I figured how to upload a scanned schematic.

Jan
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
Ken: Upload is working on another/different laptop.

Dennis: Found the attached schematic. I don't have any specs on LED. Any suggestions? Change the resistor to decrease ma to 100( instead of 200 as per schematic)?

Jan
 

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Bernard

Joined Aug 7, 2008
5,784
Use a higher wattage LED. Really bright, 2 W, surface mount, 2.8 V @ 700 mA, Phillips
LXH8-PW 30, warm white, 150 lumen, 120 deg. Really over kill, but somewhere in between
might work.
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
Thanks Bernard. Unfortunately I already placed my order with Digikey. When I said I didn't have specs on the LED I forgot to say that it is an older existing red LED I already have.

Jan
 
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