DS1307 RTC and Supercap - charging
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Posts: 46,084
> You could use a supercap, but you would have to provide means to
> charge it up to no more than 3.3 volts. You can't use diodes alone
> to drop the voltage from 5 to 3, because at those low current
levels
> diodes do not have much voltage drop.
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
I was thinking of a voltage divider to get the voltage to the cap
whenever 5v is applied.
The diode would prevent discharging with power off.
But, it does go back to the DS1307 NOT having a rechage circuit like
Sid said, whereas the 1302 chip does.
But, half the fun of this stuff is figuring out how to do something
that is not already done and written up into app sheets.
Dave
> charge it up to no more than 3.3 volts. You can't use diodes alone
> to drop the voltage from 5 to 3, because at those low current
levels
> diodes do not have much voltage drop.
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
I was thinking of a voltage divider to get the voltage to the cap
whenever 5v is applied.
The diode would prevent discharging with power off.
But, it does go back to the DS1307 NOT having a rechage circuit like
Sid said, whereas the 1302 chip does.
But, half the fun of this stuff is figuring out how to do something
that is not already done and written up into app sheets.
Dave
Comments
We have charged supercaps before, and when charging from an intelligent
charging circuit, it is possible that the circuit will become offended and
stop working. Specifically, the supercap appears to be a short circuit for
quite a while, until it gets a belly full of electrons. For circuits that
are not expecting the length of time that this takes, or that are expecting
to see a normal capacitor, this can cause problems.
While it is possible that your circuit will not mind this sort of treatment,
it is worth a quick double check just to make sure<G>.
Original Message
From: Dave Mucha [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=PMRih3JB0ikUdj89rSjat6gJsGO-DSafGMZAkt1GoZe5szfMWQACPQe2QEvXygQDbFMjvWw8YVQ4zdLWMQ]davemucha@j...[/url
Sent: Thursday, March 18, 2004 9:45 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: DS1307 RTC and Supercap - charging
> You could use a supercap, but you would have to provide means to
> charge it up to no more than 3.3 volts. You can't use diodes alone
> to drop the voltage from 5 to 3, because at those low current
levels
> diodes do not have much voltage drop.
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
I was thinking of a voltage divider to get the voltage to the cap
whenever 5v is applied.
The diode would prevent discharging with power off.
But, it does go back to the DS1307 NOT having a rechage circuit like
Sid said, whereas the 1302 chip does.
But, half the fun of this stuff is figuring out how to do something
that is not already done and written up into app sheets.
Dave
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