7812 and 7805 for powering a stamp and 2 IC ''s
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Posts: 46,084
Put one on the input(s) to ground and the output(s) to ground.
Original Message
From: timevex@o... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=i0-A8rm5X1sQ0Et9xcGh-v8KMUZeW6CTHWIFiXDK1LjpaQguPk6vHNwwi4Kzh5u1VlUwJ8mqwtLG_rheBpo]timevex@o...[/url
Sent: Thursday, September 27, 2001 2:09 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: 7812 and 7805 for powering a stamp and 2
IC's
James,
For the 100uf cap, do you mean put it on the input to output
or connect one on the input to ground and anouther on the output to
ground.
thanks
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:
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Original Message
From: timevex@o... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=i0-A8rm5X1sQ0Et9xcGh-v8KMUZeW6CTHWIFiXDK1LjpaQguPk6vHNwwi4Kzh5u1VlUwJ8mqwtLG_rheBpo]timevex@o...[/url
Sent: Thursday, September 27, 2001 2:09 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: 7812 and 7805 for powering a stamp and 2
IC's
James,
For the 100uf cap, do you mean put it on the input to output
or connect one on the input to ground and anouther on the output to
ground.
thanks
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/
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/