7812 and 7805 for powering a stamp and 2 IC''s
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Great thanks, I'll give that a try.
Tim
--- In basicstamps@y..., "James R. Parish" <wiz@a...> wrote:
> Put a 100uf 16v electrolytic on the input and output of the 7805.
Also put
> a .1uf on the output to ground. On the 7812 do the same thing but
use 35vdc
> caps. IF the 20VDC supply has good filter caps, say 10,000uf at
50VDC then
> skip the cap on the input of the 7812. In fact, you can use all
35VDC caps
> if you have them. That should fix your problem.
>
>
> James R. Parish
> J-Tech Internet Services Division
> J-Com Enterprises, Inc.
>
>
Original Message
> From: timevex@o... [noparse][[/noparse]mailto:timevex@o...]
> Sent: Thursday, September 27, 2001 1:27 PM
> To: basicstamps@y...
> Subject: [noparse][[/noparse]basicstamps] 7812 and 7805 for powering a stamp and
2 IC's
>
>
> Hi,
>
> I'm using a 7812 regulator to power a stamp from a 20v source. I'm
also
> using a 7805 to power to IC's from the 12V from the 7812.
> My problem is that my 5v from the 7805 keeps drifting low, it
starts at
> around 4.5 and will drift slowly down to 3.0v . I can't figure out
why this
> is happening, I've tried other 7805's and I get the same result.
The circuit
> works fine off my bench 5v supply. I'm thinking that this could be
happening
> because I'm not drawing enough current that it can't keep a stable
voltage
> with a real low power draw.
> The only thing the 7805 is powering is 2 IC's (7 seg driver, RS232
level
> converter) 2 digit 7 seg display and one bi-color LED. I'm guessing
my total
> current load is less than 100ma perhaps more like 50ma.
> Is their a minimum current load for the 7805 or 7812 regulators?
> Should I just hang a shunt resistor on the 5v to load it down?
> Thanks for you help
> Tim
>
>
>
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Tim
--- In basicstamps@y..., "James R. Parish" <wiz@a...> wrote:
> Put a 100uf 16v electrolytic on the input and output of the 7805.
Also put
> a .1uf on the output to ground. On the 7812 do the same thing but
use 35vdc
> caps. IF the 20VDC supply has good filter caps, say 10,000uf at
50VDC then
> skip the cap on the input of the 7812. In fact, you can use all
35VDC caps
> if you have them. That should fix your problem.
>
>
> James R. Parish
> J-Tech Internet Services Division
> J-Com Enterprises, Inc.
>
>
Original Message
> From: timevex@o... [noparse][[/noparse]mailto:timevex@o...]
> Sent: Thursday, September 27, 2001 1:27 PM
> To: basicstamps@y...
> Subject: [noparse][[/noparse]basicstamps] 7812 and 7805 for powering a stamp and
2 IC's
>
>
> Hi,
>
> I'm using a 7812 regulator to power a stamp from a 20v source. I'm
also
> using a 7805 to power to IC's from the 12V from the 7812.
> My problem is that my 5v from the 7805 keeps drifting low, it
starts at
> around 4.5 and will drift slowly down to 3.0v . I can't figure out
why this
> is happening, I've tried other 7805's and I get the same result.
The circuit
> works fine off my bench 5v supply. I'm thinking that this could be
happening
> because I'm not drawing enough current that it can't keep a stable
voltage
> with a real low power draw.
> The only thing the 7805 is powering is 2 IC's (7 seg driver, RS232
level
> converter) 2 digit 7 seg display and one bi-color LED. I'm guessing
my total
> current load is less than 100ma perhaps more like 50ma.
> Is their a minimum current load for the 7805 or 7812 regulators?
> Should I just hang a shunt resistor on the 5v to load it down?
> Thanks for you help
> Tim
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@y... 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/