Low profile LED Circut Design

Thread Starter

tc61

Joined Feb 11, 2009
9
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.
 

Bernard

Joined Aug 7, 2008
5,227
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??
 

Thread Starter

tc61

Joined Feb 11, 2009
9
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
 

Bernard

Joined Aug 7, 2008
5,227
' 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.
 

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