Hi All, Is it possible to run a buck-boost or flyback SMPS from a 0.2Vpp signal line? My signal has bandwith from 1-5K with low output impedance. I am looking to trickle charge a 3.3V battery. I would be happy if I could get a couple of mA at 3 to 5 volts.
I also am looking for this to be in a small package. The switcher would need to fit in a footprint of about 25 X 25 mm.
Am I dreaming or is this possible?
James
** So, you are asking for about 8 mW to be delivered from a 70 mV rms source - hmmmmmm.
Means the 70 mV signal source will have to supply over 100 mA, so must be
*well under* 1 ohm impedance.Sure you are not dreaming ?
If by some chance you are not, then an audio step up transformer followed by a bridge rectifier is the simplest way.
The ratio will need to be around 40:1, for charging to occur on signal peaks.
Lotsa luck.
....... Phil
As long as you can power the control circuitry from the battery, then it could be possible. I.e, you might not be able to "start up" from a dead battery without another external power source.
It *might* even be possible to startup directly from the 0.2V somehow, anyone? I seem to recall a thread about this here before.
-- John Devereux
Actually I missed that your 0.2V is an AC signal, so Phils transformer suggestion is more appropriate.
-- John Devereux
I am actually experimenting with something quite similar right now, only my input signal a little higher -- closer to a schottky diode drop, so I am using a ladder multiplier. (I have other problems to deal with, such as: my input voltage range is nominally 0.5 but can reach several volts, so I need protection/pre-regulation after the multiplier.)
I like the idea of using an audio transformer -- I had considered that before, and now I think I'll revisit that. Thanks, Phil.
Tom P.
Thanks for the comments, my output impedance is about an ohm and my signal source is good for 10ma. As you pointed out this will not get me to 2mA at 3V. I am looking at moving to a 1.8V micro. With the voltage reduction and a closer look at sleep modes for the micro I should be able to get my current consumption down to 300 - 500uA. Even with these changes I think I will still be a bit short of full power from the signal line. I think I will still pursue a signal line charging approach as it looks to me like I will be able to extend my battery life by a factor of 3-5X.
James
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