Charge battery from speaker audio

[Smollett]

Hi,
I want to put LEDs inside a speaker box and I'm looking to charge a battery to power them off the high power audio inside. I only want to use a tiny amount of the power so I don't change the audio.
Any suggestions for a circuit that would allow me to charge a battery from a variable voltage, variable frequency source?

Thanks in advance!
Toby

 

[Gryd3]

Hi,
I want to put LEDs inside a speaker box and I'm looking to charge a battery to power them off the high power audio inside. I only want to use a tiny amount of the power so I don't change the audio.
Any suggestions for a circuit that would allow me to charge a battery from a variable voltage, variable frequency source?

Thanks in advance!
Toby

If we approach this from a frequency/voltage side of things...
You will need some way to rectify and regulate the output to be able to use it for LEDs or batteries.
Use a bridge rectifier to begin with, and a capacitor behind it to help smooth out the ripple.
The problems you will have though, is that the circuit will simply draw what it needs with no regard for the audio signal, this will change the audio.
You could potentially use a low-pass filter so it only effects the low-end, but you will still run into issues with current draw with your device.
Is it absolutely required to have this powered passively by the audio signal?

 

[Colin Mitchell]

You just need one diode and a resistor.

 

[Gryd3]

You just need one diode and a resistor.

That would deform one side of the waveform, and not the other.
A value of resistor too low will cause distortion and value too high will not allow sufficient current through to top up a battery

 

[Audioguru]

Do you want the LEDs to light from the battery when the music is not charging the battery or do you want the LEDs to flicker to the music or both?

For the LEDs to only flicker to the music then you do not need a battery and charger.

White, blue or bright green LEDs need at least 3.5V plus another 3V for a fullwave rectifier and current-limiting circuit. For the average voltage to be 6.5VDC then the peak audio RMS voltage must be about 20.5V. Then the power to an 8 ohm speaker must be 52W which is loud. If you turn down the volume then the LEDs will barely light or will not light.