Efficient 555 (CMOS 7555) circuit design - help needed

Thread Starter


Joined Sep 25, 2012
I am hoping somebody will be able to offer me some help with a 555 circuit design. I previously worked with the 555 during college, but it was the mass produced variant with a standard data sheet.

The project that I am working on at the moment requires 2 LED panels (3v @ 20ma each) to be driven from a single CR123 lithium battery, with the ability to dim the brightness.

The reason I was considering a 7555 is:

1. It can provide a dimming via PWM with the inclusion of a potentiometer/variable resistor
2. It could pulse a full output with a duty cycle that would increase battery life

This is operating on the threshold of most 555 chips, except those mentioned in this thread: http://forum.allaboutcircuits.com/threads/555-3v-led-flasher-circuit-help.47486/

I did not want to hijack the thread, but it is similar to my requirement.

These are the LED backlights I am hoping to run (x2) from the CR123: https://www.coolcomponents.co.uk/white-led-backlight-module-large-45mm-x-86mm.html

Any help appreciated...

(If there is an existing module - like those used in torches as drivers - then links would be welcome)


Joined Sep 17, 2013
If the LEDs have a Vf of 3V then a 3V supply leaves no headroom, so the LEDs won't be able to run at their max when the battery voltage sags.
What colour LEDs?
Do the panels incorporate current-limiting resistors?
Do both panels need to be dimmed simultaneously by the same amount?

Thread Starter


Joined Sep 25, 2012
I am trying to make myself a cheap version of an existing product.

It is a C2R tacpad, using a single CR123 to power a large EL panel. With dimming!

This circuit must be bespoke and a custom job - I cannot find anything online that suggests such a panel (photos show it is in fact two thinner tapes placed in parallel along the long edge) could be powered by a CR123, let alone dipped.

So, I turned to the LED backlight modules as the circuits is simpler, and the batteries will last longer :)

Any thoughts on how they accomplished this? And my intention to develop an LED version for the reasons stated...


http://soldiersystems.net/tag/c2r/ (a top article, and a video half way down)