Light powered LED Project

Discussion in 'The Projects Forum' started by njs707, Jun 9, 2014.

  1. njs707

    Thread Starter New Member

    Feb 26, 2014

    Please see attached.
    I’m looking to use a photo-voltaic cell and 2 inductors to use light to wirelessly power an LED. I don’t want to use any other power source (battery, mains, etc.). The schematic shows a DC source (photo-voltaic cell) in parallel with a capacitor and an inductor. The second inductor would ideally be an inch or so away from the first, connected to a bridge rectifier, which provides DC current to an LED. Again, the important thing is to be wireless (2 inductors) and to be only powered by light. So, if I were to walk in a room and flip on a switch, the LED would come on. If I flip off the switch the LED turns off. The only confusion I have is on the photo-voltaic side. I’m not sure how to use the photo-voltaic cell to create a constant AC signal for the inductor. Help please.
  2. timwhite


    Apr 10, 2014
    The output of a photo-voltaic cell is a DC voltage, you will need to look into using a small inverter to switch to AC. You'll most likely want to use something along the lines of the second image here.


    Edit: You could also use an LC circuit as a resonant inverter.
    Last edited: Jun 9, 2014
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    You will need a very large PV cell to generate enough power from room light to operate an LED, especially if you want to do it inefficiently via two coils an inch apart :(.
  4. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    Your project idea as stated will be very difficult to achieve, and the schematic shown simply will not work. You are correct in that an oscillator of some kind will be needed to drive the source inductor or zero steady-state energy will be transferred to the load inductor (after the turn-on transient). Darn that Michael Faraday...

    Two things:

    1. Two inductors an inch apart form an air-core transformer, something very very inefficient at transferring energy. Current products for non-contact battery charging (a variation of what you are trying to do) rely on air gaps from 0.010" to 0.250". One inch would be much less efficient than that. (Not automatically 16 times less, since these systems use shaped fields).

    2. As noted above, the photocell array would have to be huge to make enough light to be useful in a room, and huger to overcome the transformer limitations.

    And - what is the light source for the photo cells?

  5. DickCappels


    Aug 21, 2008
    You didn't say how bright you need the LED to be, so we can't say for sure that it can't be done!

    A decent (whatever that is) white LED with a clear lens can be seen to be glowing at tiny power levels -I dare say only a very few milliwatts.

    Take your solar battery (You will need more than the 0.6 volts produced by a single cell unless you use germanium transistors) and use it to power an oscillator like the circuit timwhite posted, but add a 100 uf (for example) capacitor across the solar battery, then start experimenting with your inductors.

    A couple of comments on the circuit you posed (thank you for the schematic -it really makes clear what you are trying to do):

    You might find the bridge rectifier looses about half your power (1.3 volts total drop unless Schottky). Consider using two LEDs in parallel, one conducting in each direction.

    The resistor might not be needed since you are trying for 1" between the coils.

    You might find that tuning the "receiving" coil with a capacitor to resonate at the "transmitting" coil's frequency will improve power transfer.

    This project will take a lot of experimenting, but that's a great way to improve your understanding of what you are trying to do!
    Last edited: Jun 10, 2014