Hello, I am trying to work up a schematic for a project.

The project involves running 2 30ma LEDS off of line voltage. The LEDs will be powered off line voltage until power is lost, then I need to power the LEDs of a small coin cell battery for about 2 hours, until the cycle starts again. The added kick to the project is that the circuit must be no more than 4mm in height; I can remotely move the battery to another location that I have some space 20mmx20mmx40mm.

Question can someone help me design a circuit up to accomplish this in a timely manor. I would be willing to compensate you for your time. I am sure I need to supply more details and can do so if needed,

Thanks in advance.

 

I hope you are working on the problem. Be kinda awkward if nobody bites....

 

Why would it be awkward?

Just looking for some expertise.

 

We work cheap. If efficiency is not a concern, use 3 resistors , 2 to 5 1N4004 diodes, batterys, and LEDs, might throw in a fuse 1/4A. Rechargable batteries??

 

Lost thumbnail??

 

yes it would be a coin cell rechargable battery

when you say efficiency what do you mean? The life of the LED's or Battery?

thanks for your help

 

Put a capacitor in front of the bridge, it will limit current without dissipating wattage.

This will reduce actual power used on the AC line, and reduce heating dramatically.

Check the AAC book article on LEDs, about ¼ of the way down.

http://www.allaboutcircuits.com/vol_3/chpt_3/12.html

 

' efficiency " referred to power disipation. As Bill said adding a cap would improve efficiency; my problem was finding a cap[ or several in parallel] under 4 mm. To properly assign values need to know voltage drop across LEDs @ 30 mA. How about moving every thing except LEDs in to " other space"? Battery voltage needs to be greater than LED & one Si, or Ge diode. I am still using a LED night light that I designed 3 yrs. ago, one bright white LED , a cap in each AC leg & a small resistor[ 1k +-] to protect against hv trancients.