On Dienstag, 15. Dezember 2020 19:22:14 CET paul swed wrote: > Hello to the group Nigel is correct the way the schematic is drawn the > Regulator will feed the battery and most likely cause it to burst. > It should be 1 diode in series with the regulator and 1 in series with the > battery so that the regulator can not charge the battery.
Yes, that's what I discussed with Nigel off-list. The two diodes in series create a voltage difference of 1.4V, so as long the battery voltage is above 1.9V, no current will flow through the diodes at all and the battery is safe. However, there is a greater-than-zero probability that a board will just be dropped into a drawer with the battery in place, fully draining it eventually. If it's then powered up again, chances are that a substantial current will flow into the battery and potentially cause a fire, explosion, etc. I've therefore updated the design and put a small Schottky diode in series with the battery. I selected a part with small leakage current ( 0.5µA typical). But of course a regular silicon diode like 1N4148WS will work as well, at the expense of wasting some of the energy of the coin cell. > Nice design you have created. Thanks - Hopefully it will also work :-) > Regards > Paul > WB8TSL > > On Tue, Dec 15, 2020 at 11:55 AM Nigel gm8pzr via time-nuts < > > [email protected]> wrote: > > Hi Mathias, > > I'm assuming you're using a coin cell for back up, so wondering if one of > > the diodes shouldn't be in series with the battery, with both cathodes to > > V_BCKP? > > Nigel GM8PZR > > > > > > I've updated the repository on github with the latest design files. The > > breakout board is now final as far as I'm concerned. > > > > I managed to implement all the requested features, this includes the > > backup > > battery and also the buffered PPS output with SMA footprint. > > > > Next step on my side will be to order a small batch of PCBs. There's not > > much > > on them and I guess I will end up with around 25? for 5 boards fully > > assembled, shipping not included. > > > > I eventually removed the I2C pull-ups again, thanks to Patrick Tudor for > > the > > hint. The footprints are still there, I only removed them from the BOM. > > > > Schematic and a screenshot of the top and bottom sides attached. > > > > BR, > > Matthias > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow > the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
