Aux Power Supply Switching
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Posts: 46,084
hello,
I'd like to power my stamp with a 9volt battery going into a 7805 regulator, but
also have an auxiliary power input so I can bring power in from a 12v DC wall
wart or battery. Is there a way to hook up a transistor, or some sort of
super-fast switch, that would disconnect the 9v battery and switch to external
power when external power is supplied; without power interruption to the stamp?
I've been perplexed by this for a while. I found that Linear has a chip
(LTC4412) made to do this, but it is in an impossibly small sized surface mount
package so I can't use it.
Thanks,
Stewart
I'd like to power my stamp with a 9volt battery going into a 7805 regulator, but
also have an auxiliary power input so I can bring power in from a 12v DC wall
wart or battery. Is there a way to hook up a transistor, or some sort of
super-fast switch, that would disconnect the 9v battery and switch to external
power when external power is supplied; without power interruption to the stamp?
I've been perplexed by this for a while. I found that Linear has a chip
(LTC4412) made to do this, but it is in an impossibly small sized surface mount
package so I can't use it.
Thanks,
Stewart
Comments
If I understand you corectly, all you need to do is use a diode in series
with the battery, say a 1N4004. This will allow the battery to run when
required, and prevent the 12V supply from charging/exploding the battery.
Jonathan
www.madlabs.info
Original Message
From: "Stewart Mayer" <stamplist@k...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, November 26, 2003 1:56 PM
Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> hello,
>
> I'd like to power my stamp with a 9volt battery going into a 7805
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort of
> super-fast switch, that would disconnect the 9v battery and switch to
external
> power when external power is supplied; without power interruption to the
stamp?
>
> I've been perplexed by this for a while. I found that Linear has a chip
> (LTC4412) made to do this, but it is in an impossibly small sized surface
mount
> package so I can't use it.
>
> Thanks,
> Stewart
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort of
> super-fast switch, that would disconnect the 9v battery and switch to
external
> power when external power is supplied; without power interruption to the
stamp?
Lots of power jacks have provision to disconnect an internal power supply
when you insert the jack. There will be a few ms when you put the jack in,
when neither power supply is available, but if you put a capacitor across
the input power leads to the 7805, that will supply enough power to run
things for those few ms, as well as smoothing out any power noise from
inserting ther jack. It will also increase the drain on the battery a bit,
so it may not be a perfect solution. Depending on load, you probably don't
need much: a 12v 100 mf cap might be plenty. The only downside is that when
you remove all power, the circuit will stay live for some amount of time, as
the cap drains.
There are probably tricks you could do with diodes and resistors to make the
battery more slowly charge the cap, thus decreasing overall drain on the
battery. That's something to experiment with.
But Scott posted putting a '100mf cap' across a connection point....
I'm almost SURE what you mean....but want to clarify.
Do you mean 100uF (microFarad) or 100mF (milliFarad). I don't recall having
seen a 'milliFarad' cap, but would assume they are HUGE!!
sb
Original Message
From: Scott [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=M7FR_Bm4YRjxgh2LWQZDtSoA529Y_n0KJdtXZPgvsBdiaH_V-6EYv_mrTOIxSW27UES9pOOFDGLIzg]scott@m...[/url
Sent: November 27, 2003 7:42 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> I'd like to power my stamp with a 9volt battery going into a 7805
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v
> DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort
> of super-fast switch, that would disconnect the 9v battery and switch
> to
external
> power when external power is supplied; without power interruption to
> the
stamp?
Lots of power jacks have provision to disconnect an internal power supply
when you insert the jack. There will be a few ms when you put the jack in,
when neither power supply is available, but if you put a capacitor across
the input power leads to the 7805, that will supply enough power to run
things for those few ms, as well as smoothing out any power noise from
inserting ther jack. It will also increase the drain on the battery a bit,
so it may not be a perfect solution. Depending on load, you probably don't
need much: a 12v 100 mf cap might be plenty. The only downside is that when
you remove all power, the circuit will stay live for some amount of time, as
the cap drains.
There are probably tricks you could do with diodes and resistors to make the
battery more slowly charge the cap, thus decreasing overall drain on the
battery. That's something to experiment with.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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diameter and 1/4" high :-))))))))))).
They are used as a backup 'battery' in some electronic devices.
Regards,
Klaus
Oorspronkelijk bericht
Van: Brady,Steven [noparse]/noparse]PYR] [noparse][[/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=SXoFLkreCz415GjRldHZe6Q4NFG1kvli0dVAAlFHGsIigTYo7zLJj-FHnFkEvFTcthRz5TukdX768GTXa4E]steven.brady2@e...[/url
Verzonden: donderdag 27 november 2003 16:55
Aan: 'basicstamps@yahoogroups.com'
Onderwerp: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
Sorry to go a little OT here....
But Scott posted putting a '100mf cap' across a connection point....
I'm almost SURE what you mean....but want to clarify.
Do you mean 100uF (microFarad) or 100mF (milliFarad). I don't recall having
seen a 'milliFarad' cap, but would assume they are HUGE!!
sb
Original Message
From: Scott [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Od1QJeC3wntWtnTxf-WGV9X1Gja1nMRrt8hoIKzPQrR5N-p43_icBoB16iUgZRMIgCr7m_G1QTH5]scott@m...[/url
Sent: November 27, 2003 7:42 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> I'd like to power my stamp with a 9volt battery going into a 7805
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v
> DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort
> of super-fast switch, that would disconnect the 9v battery and switch
> to
external
> power when external power is supplied; without power interruption to
> the
stamp?
Lots of power jacks have provision to disconnect an internal power supply
when you insert the jack. There will be a few ms when you put the jack in,
when neither power supply is available, but if you put a capacitor across
the input power leads to the 7805, that will supply enough power to run
things for those few ms, as well as smoothing out any power noise from
inserting ther jack. It will also increase the drain on the battery a bit,
so it may not be a perfect solution. Depending on load, you probably don't
need much: a 12v 100 mf cap might be plenty. The only downside is that when
you remove all power, the circuit will stay live for some amount of time, as
the cap drains.
There are probably tricks you could do with diodes and resistors to make the
battery more slowly charge the cap, thus decreasing overall drain on the
battery. That's something to experiment with.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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for mF or do they actually mean 'milli'Farad?!
Original Message
From: K de Jong [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=_cq2eXP3STGMXo9mURHtLFl9cTFRQHUzPOrqGJp0dI1aXq-UNhBAMdJwymzXDkz5IJsVvPAb-YwnekK2VLD2]Klaus.Jong@n...[/url
Sent: November 27, 2003 12:46
To: basicstamps@yahoogroups.com
Subject: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
I'm the proud owner of a capacitor of 1 Farad at 5 V !!, it is only about 1"
diameter and 1/4" high :-))))))))))).
They are used as a backup 'battery' in some electronic devices.
Regards,
Klaus
Oorspronkelijk bericht
Van: Brady,Steven [noparse]/noparse]PYR] [noparse][[/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=fnLSlZM4GgcG4BgA1DLpG-RhSeU8YGpiTH3HuhqSzb3GL3aiE4-O6w1M2pPTBdnfayeL4cfLegR72Y5rYA]steven.brady2@e...[/url
Verzonden: donderdag 27 november 2003 16:55
Aan: 'basicstamps@yahoogroups.com'
Onderwerp: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
Sorry to go a little OT here....
But Scott posted putting a '100mf cap' across a connection point....
I'm almost SURE what you mean....but want to clarify.
Do you mean 100uF (microFarad) or 100mF (milliFarad). I don't recall having
seen a 'milliFarad' cap, but would assume they are HUGE!!
sb
Original Message
From: Scott [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=uXoeSycyPAJ1zl6NNukfWWboQSPgEjkzCWXd4NaGDLuaT8aaRkxREYvd5AdQ-WKe6pPKrsUDO9wh3Q]scott@m...[/url
Sent: November 27, 2003 7:42 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> I'd like to power my stamp with a 9volt battery going into a 7805
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v
> DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort
> of super-fast switch, that would disconnect the 9v battery and switch
> to
external
> power when external power is supplied; without power interruption to
> the
stamp?
Lots of power jacks have provision to disconnect an internal power supply
when you insert the jack. There will be a few ms when you put the jack in,
when neither power supply is available, but if you put a capacitor across
the input power leads to the 7805, that will supply enough power to run
things for those few ms, as well as smoothing out any power noise from
inserting ther jack. It will also increase the drain on the battery a bit,
so it may not be a perfect solution. Depending on load, you probably don't
need much: a 12v 100 mf cap might be plenty. The only downside is that when
you remove all power, the circuit will stay live for some amount of time, as
the cap drains.
There are probably tricks you could do with diodes and resistors to make the
battery more slowly charge the cap, thus decreasing overall drain on the
battery. That's something to experiment with.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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Body of the message will be ignored.
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there still be some current used from the 9volt battery, or will all the
current only come from the higher voltage source? Also, isn't there some
voltage loss across diodes?
The capacitor also sounds good, but i'm worried about the leakage eating
up battery power over time. Am I correct in assuming a larger capaciter
will leak more current?
I've been thinking of hooking up a transistor triggered by the 12v supply
to disconnect the 9v. I don't know if this would cause a voltage drop also.
Perhaps I should just experiment, hmmmm.
Thanks,
Stewart
>-- Original Message --
>To: <basicstamps@yahoogroups.com>
>From: "Jonathan Peakall" <jpeakall@p...>
>Date: Wed, 26 Nov 2003 18:50:44 -0800
>Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
>Reply-To: basicstamps@yahoogroups.com
>
>
>Stewart,
>
>If I understand you corectly, all you need to do is use a diode in series
>with the battery, say a 1N4004. This will allow the battery to run when
>required, and prevent the 12V supply from charging/exploding the battery.
>
>Jonathan
>
>www.madlabs.info
>
>
Original Message
>From: "Stewart Mayer" <stamplist@k...>
>To: <basicstamps@yahoogroups.com>
>Sent: Wednesday, November 26, 2003 1:56 PM
>Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
>
>
>> hello,
>>
>> I'd like to power my stamp with a 9volt battery going into a 7805
>regulator, but
>> also have an auxiliary power input so I can bring power in from a 12v
DC
>wall
>> wart or battery. Is there a way to hook up a transistor, or some sort
>of
>> super-fast switch, that would disconnect the 9v battery and switch to
>external
>> power when external power is supplied; without power interruption to
the
>stamp?
>>
>> I've been perplexed by this for a while. I found that Linear has a chip
>> (LTC4412) made to do this, but it is in an impossibly small sized surface
>mount
>> package so I can't use it.
>>
>> Thanks,
>> Stewart
>>
>>
>>
>>
>>
>> To UNSUBSCRIBE, just send mail to:
>> basicstamps-unsubscribe@yahoogroups.com
>> from the same email address that you subscribed. Text in the Subject
and
>Body of the message will be ignored.
>>
>>
>> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>>
>>
>>
>>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
>Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
reverse bias, so there will be many millions of ohms in series provided by
PN junction. In that case the current going to the battery will be almost
nothing (for all practical purposes, this will be zero draw, but there's
always SOME leakage - in this case the wrong direction, but certainly not
enough to charge the battery in any way). You'll probably want to add a
diode in series with the wall wart as well so the battery doesn't try to
power the wart if it's disconnected from the 120 VAC line, but still plugged
into the stamp.
As far as voltage drops across diodes go, for silicon PN junctions, it's
around 1/2 volt or so (typically 0.6 volts), and for germanium PN junctions
it's about 1/4 volt (typically 0.2 volts or so). Most diodes you'll use will
be silicon, so figure around 8.4 volts getting to the Stamp from the battery
supply, and 11.4 volts from the wall wart supply.
I think this is a very simple and elegant "backup" solution.
Mike Sokol
www.modernrecording.com
mikes@m...
" One should not increase, beyond what is necessary,
the number of entities required to explain anything"...
-William of Occam-
Original Message
From: <stamplist@k...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, November 28, 2003 1:36 PM
Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> That sounds good. If both supplies are hooked up at the same time, will
> there still be some current used from the 9volt battery, or will all the
> current only come from the higher voltage source? Also, isn't there some
> voltage loss across diodes?
>
> The capacitor also sounds good, but i'm worried about the leakage eating
> up battery power over time. Am I correct in assuming a larger capaciter
> will leak more current?
>
> I've been thinking of hooking up a transistor triggered by the 12v supply
> to disconnect the 9v. I don't know if this would cause a voltage drop
also.
> Perhaps I should just experiment, hmmmm.
>
> Thanks,
> Stewart
>
>
> >-- Original Message --
> >To: <basicstamps@yahoogroups.com>
> >From: "Jonathan Peakall" <jpeakall@p...>
> >Date: Wed, 26 Nov 2003 18:50:44 -0800
> >Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> >Reply-To: basicstamps@yahoogroups.com
> >
> >
> >Stewart,
> >
> >If I understand you corectly, all you need to do is use a diode in series
> >with the battery, say a 1N4004. This will allow the battery to run when
> >required, and prevent the 12V supply from charging/exploding the battery.
> >
> >Jonathan
> >
> >www.madlabs.info
> >
> >
Original Message
> >From: "Stewart Mayer" <stamplist@k...>
> >To: <basicstamps@yahoogroups.com>
> >Sent: Wednesday, November 26, 2003 1:56 PM
> >Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> >
> >
> >> hello,
> >>
> >> I'd like to power my stamp with a 9volt battery going into a 7805
> >regulator, but
> >> also have an auxiliary power input so I can bring power in from a 12v
> DC
> >wall
> >> wart or battery. Is there a way to hook up a transistor, or some sort
> >of
> >> super-fast switch, that would disconnect the 9v battery and switch to
> >external
> >> power when external power is supplied; without power interruption to
> the
> >stamp?
> >>
> >> I've been perplexed by this for a while. I found that Linear has a
chip
> >> (LTC4412) made to do this, but it is in an impossibly small sized
surface
> >mount
> >> package so I can't use it.
> >>
> >> Thanks,
> >> Stewart
> >>
> >>
> >>
> >>
> >>
> >> To UNSUBSCRIBE, just send mail to:
> >> basicstamps-unsubscribe@yahoogroups.com
> >> from the same email address that you subscribed. Text in the Subject
> and
> >Body of the message will be ignored.
> >>
> >>
> >> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >>
> >>
> >>
> >>
> >
> >
> >To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> >from the same email address that you subscribed. Text in the Subject and
> >Body of the message will be ignored.
> >
> >
> >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
> >
> >
> >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
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>
>
Thanks for the thorough answer, I'll definately go with the diodes, and
the input capacitor on the 7805 should be able to absorb any bumps when
switching inputs.
I hope everyone enjoys the holiday weekend!
Thanks,
Stewart
>-- Original Message --
>To: <basicstamps@yahoogroups.com>
>From: "Mike Sokol" <mike.sokol@m...>
>Date: Fri, 28 Nov 2003 14:02:07 -0500
>Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
>Reply-To: basicstamps@yahoogroups.com
>
>
>When the 12 volt power supply is on, the diode on the battery will be in
>reverse bias, so there will be many millions of ohms in series provided
by
>PN junction. In that case the current going to the battery will be almost
>nothing (for all practical purposes, this will be zero draw, but there's
>always SOME leakage - in this case the wrong direction, but certainly not
>enough to charge the battery in any way). You'll probably want to add a
>diode in series with the wall wart as well so the battery doesn't try to
>power the wart if it's disconnected from the 120 VAC line, but still plugged
>into the stamp.
>
>As far as voltage drops across diodes go, for silicon PN junctions, it's
>around 1/2 volt or so (typically 0.6 volts), and for germanium PN junctions
>it's about 1/4 volt (typically 0.2 volts or so). Most diodes you'll use
will
>be silicon, so figure around 8.4 volts getting to the Stamp from the battery
>supply, and 11.4 volts from the wall wart supply.
>
>I think this is a very simple and elegant "backup" solution.
>
>Mike Sokol
>www.modernrecording.com
>mikes@m...
>
Atomic clock reciver, because my power goes out all the time. The battery
that is in there is 6 months old, and is fine.
Jonathan
Original Message
From: <stamplist@k...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, November 28, 2003 10:36 AM
Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> That sounds good. If both supplies are hooked up at the same time, will
> there still be some current used from the 9volt battery, or will all the
> current only come from the higher voltage source? Also, isn't there some
> voltage loss across diodes?
>
> The capacitor also sounds good, but i'm worried about the leakage eating
> up battery power over time. Am I correct in assuming a larger capaciter
> will leak more current?
>
> I've been thinking of hooking up a transistor triggered by the 12v supply
> to disconnect the 9v. I don't know if this would cause a voltage drop
also.
> Perhaps I should just experiment, hmmmm.
>
> Thanks,
> Stewart
>
>
> >-- Original Message --
> >To: <basicstamps@yahoogroups.com>
> >From: "Jonathan Peakall" <jpeakall@p...>
> >Date: Wed, 26 Nov 2003 18:50:44 -0800
> >Subject: Re: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> >Reply-To: basicstamps@yahoogroups.com
> >
> >
> >Stewart,
> >
> >If I understand you corectly, all you need to do is use a diode in series
> >with the battery, say a 1N4004. This will allow the battery to run when
> >required, and prevent the 12V supply from charging/exploding the battery.
> >
> >Jonathan
> >
> >www.madlabs.info
> >
> >
Original Message
> >From: "Stewart Mayer" <stamplist@k...>
> >To: <basicstamps@yahoogroups.com>
> >Sent: Wednesday, November 26, 2003 1:56 PM
> >Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> >
> >
> >> hello,
> >>
> >> I'd like to power my stamp with a 9volt battery going into a 7805
> >regulator, but
> >> also have an auxiliary power input so I can bring power in from a 12v
> DC
> >wall
> >> wart or battery. Is there a way to hook up a transistor, or some sort
> >of
> >> super-fast switch, that would disconnect the 9v battery and switch to
> >external
> >> power when external power is supplied; without power interruption to
> the
> >stamp?
> >>
> >> I've been perplexed by this for a while. I found that Linear has a
chip
> >> (LTC4412) made to do this, but it is in an impossibly small sized
surface
> >mount
> >> package so I can't use it.
> >>
> >> Thanks,
> >> Stewart
> >>
> >>
> >>
> >>
> >>
> >> To UNSUBSCRIBE, just send mail to:
> >> basicstamps-unsubscribe@yahoogroups.com
> >> from the same email address that you subscribed. Text in the Subject
> and
> >Body of the message will be ignored.
> >>
> >>
> >> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >>
> >>
> >>
> >>
> >
> >
> >To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> >from the same email address that you subscribed. Text in the Subject and
> >Body of the message will be ignored.
> >
> >
> >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
> >
> >
> >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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Body of the message will be ignored.
>
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>
>
>
>
inrush current when charging by using a resistor in series with the power
supply when charging. High currents on charging can damage them internally!
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: Brady,Steven [noparse]/noparse]PYR] [noparse][[/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=4nMhGtNXSdo7hCHoADPWqYjU21QLh4fwSuDhSgNoG_HnDApEL-cAdUbIwqTXYYORQR32eZ_FCsF0ZP1TGhmhCvk]steven.brady2@e...[/url
Sent: Thursday, November 27, 2003 4:09 PM
To: 'basicstamps@yahoogroups.com'
Subject: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
Fantastic....but still. Are ppl using the first letter of the word micro
for mF or do they actually mean 'milli'Farad?!
Original Message
From: K de Jong [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=zxnpRxQWmm4mXufmir-G3MNzaVV-DF3bca7N3fM4u0stchHREG2eiNr9EspIJOxjWA6qm74oALqJUlg]Klaus.Jong@n...[/url
Sent: November 27, 2003 12:46
To: basicstamps@yahoogroups.com
Subject: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
I'm the proud owner of a capacitor of 1 Farad at 5 V !!, it is only about 1"
diameter and 1/4" high :-))))))))))).
They are used as a backup 'battery' in some electronic devices.
Regards,
Klaus
Oorspronkelijk bericht
Van: Brady,Steven [noparse]/noparse]PYR] [noparse][[/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=4nMhGtNXSdo7hCHoADPWqYjU21QLh4fwSuDhSgNoG_HnDApEL-cAdUbIwqTXYYORQR32eZ_FCsF0ZP1TGhmhCvk]steven.brady2@e...[/url
Verzonden: donderdag 27 november 2003 16:55
Aan: 'basicstamps@yahoogroups.com'
Onderwerp: RE: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
Sorry to go a little OT here....
But Scott posted putting a '100mf cap' across a connection point....
I'm almost SURE what you mean....but want to clarify.
Do you mean 100uF (microFarad) or 100mF (milliFarad). I don't recall having
seen a 'milliFarad' cap, but would assume they are HUGE!!
sb
Original Message
From: Scott [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=t8hSGUry6YFid7A1ilGBBZ5N9-99i6D3SIsF1G7jsuLe27R3Tro8-6im4r8lqTw66X2_uRIt2xD9]scott@m...[/url
Sent: November 27, 2003 7:42 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Aux Power Supply Switching
> I'd like to power my stamp with a 9volt battery going into a 7805
regulator, but
> also have an auxiliary power input so I can bring power in from a 12v
> DC
wall
> wart or battery. Is there a way to hook up a transistor, or some sort
> of super-fast switch, that would disconnect the 9v battery and switch
> to
external
> power when external power is supplied; without power interruption to
> the
stamp?
Lots of power jacks have provision to disconnect an internal power supply
when you insert the jack. There will be a few ms when you put the jack in,
when neither power supply is available, but if you put a capacitor across
the input power leads to the 7805, that will supply enough power to run
things for those few ms, as well as smoothing out any power noise from
inserting ther jack. It will also increase the drain on the battery a bit,
so it may not be a perfect solution. Depending on load, you probably don't
need much: a 12v 100 mf cap might be plenty. The only downside is that when
you remove all power, the circuit will stay live for some amount of time, as
the cap drains.
There are probably tricks you could do with diodes and resistors to make the
battery more slowly charge the cap, thus decreasing overall drain on the
battery. That's something to experiment with.
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