Re: Batteryless mod.

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Author: Kaz Kylheku
To: ada-mp1
Subject: Re: Batteryless mod.
On 27.09.2013 00:45, Kaz Kylheku wrote:

An alternative approach may be to switch to rechargable button cells rather than going batteryless.

The key part is to modify the circuit so that when the given device like your ADA MP-1 is powered up, it trickle charges the battery. 

(Of course, this only makes sense, though, if the shelf life of the rechargeable cell beats that of the non-rechargable coin battery. 

If we refer to the MP-1 schematic, we see that the SRAM is powered by two power sources, and two diodes are used to isolate them, in a textbook manner.

Suppose D42 is bypassed by a resistor (of sufficiently high value to limit current). Then when D43 is forward-biased (we have main power), current can trickle into the battery. D42 drops the voltage somewhat, and that may just be enough. If a lower charging voltage is required, then the bypass resistor can have one more diode in series with it.

Original circuit:

Proposed mod: