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Brian
Guest
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 Posted:
Wed Feb 16, 2005 4:49 pm Post subject:
Re: 5V regulator for batteries cheap efficient? |
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"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cut2f2$6nk$2@blue.rahul.net...
| Quote: | In article <n4-dnSxDCb3rW4zfRVn-qA@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[.. +/- 9V batteries ..]
Then I would lose the regulator and run straight from the batteries.
At low currents, straight off the battery makes sense. At higher current,
a switcher would greatly increase the battery life.
In a battery circuit ground usually is false, no?
Yes effectively
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kensmith@rahul.net forging knowledge
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I assume yoy mean boosting the voltage.
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Ken Smith
Guest
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| Posted:
Thu Feb 17, 2005 3:01 pm Post subject:
Re: 5V regulator for batteries cheap efficient? |
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In article <TZydnZyl5qab6InfRVn-pg@centurytel.net>,
Brian <brian@w3gate.com> wrote:
| Quote: |
"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cuvlvb$i5n$1@blue.rahul.net...
In article <8JmdnaefCoMeu47fRVn-sw@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[.. +/- 9V batteries ..]
At low currents, straight off the battery makes sense. At higher
current,
a switcher would greatly increase the battery life.
[...]
Would the added efficiency come from the devices drawing less current at 5V
than they do at 9V?
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No, is because:
P= I * V
P9 = 0.1A * 9V = 0.9W
P5 = 0.1A * 5V = 0.5W
0.5/0.9 = 0.5555
So if the switcher is more than 56% efficient, the switcher starts saving
you power. If the switcher is 90% the product should run 62% longer with
the switcher.
--
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kensmith@rahul.net forging knowledge |
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Brian
Guest
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| Posted:
Thu Feb 17, 2005 4:42 pm Post subject:
Re: 5V regulator for batteries cheap efficient? |
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"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cuvlvb$i5n$1@blue.rahul.net...
| Quote: | In article <8JmdnaefCoMeu47fRVn-sw@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[.. +/- 9V batteries ..]
Then I would lose the regulator and run straight from the batteries.
At low currents, straight off the battery makes sense. At higher
current,
a switcher would greatly increase the battery life.
[...]
I assume yoy mean boosting the voltage.
No, with a 9V battery making 5V with a bucker will extend the battery life
quite a bit when the current requirments are enough that the overhead to
run the chip is not important in the total system power.
Unfortunately, there are no large P-MODFETs that can be certain to be
biased to a low on resistance by 5V. Parts like Supertex's TP0604 would
be a good choice for the pass element of a bucker at modest currents.
You can also "abuse" a booster swither chip to make a minus side bucker.
Since the OP is making +/-5V from a pair of 9V batteries, you could do
this twice and wire the resulting 5V circuits in series. The 9V batteries
would not have any common connection.
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Would the added efficiency come from the devices drawing less current at 5V
than they do at 9V?
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