7812 and 7805 for powering a stamp and 2 IC''s
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Posts: 46,084
I gave up on 7805's and use the regulator that is on the Stamp's board of
education. I am at work and dont have the number, and have my board of
education packed away anyhow at home. Maybe somebody else can give you the
regulator number. I also got a 2nd regulator from the MFG website. They have
free samples. The BOE regulator has much less current drop then a 7805 and
is much more efficient.
Sorry I cant be more help at this time.
-kerry
At 06:37 PM 9/27/2001 -0000, you wrote:
>The data sheet that I have for a 78MxxC/LM340 lists the Vo at 4.8 to
>5.2 at 5mA < Io < 1A.
>
> I can forward the data-sheet if you would like (or go to the
>National Semiconductor site and down load it.)
>
>Phil
>
>--- In basicstamps@y..., Kevin Olalde <kolalde@h...> wrote:
>> Can the 7812 be skipped? I'm not saying that's what the original
>problem is,
>> just wondering why the whole curcuit can't just be run from the same
>7805 (or is
>> there a specific need for 12V)?
>>
>> Kevin
>>
>> "James R. Parish" 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@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/
>
>
>
Sincerely
Kerry
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1132
education. I am at work and dont have the number, and have my board of
education packed away anyhow at home. Maybe somebody else can give you the
regulator number. I also got a 2nd regulator from the MFG website. They have
free samples. The BOE regulator has much less current drop then a 7805 and
is much more efficient.
Sorry I cant be more help at this time.
-kerry
At 06:37 PM 9/27/2001 -0000, you wrote:
>The data sheet that I have for a 78MxxC/LM340 lists the Vo at 4.8 to
>5.2 at 5mA < Io < 1A.
>
> I can forward the data-sheet if you would like (or go to the
>National Semiconductor site and down load it.)
>
>Phil
>
>--- In basicstamps@y..., Kevin Olalde <kolalde@h...> wrote:
>> Can the 7812 be skipped? I'm not saying that's what the original
>problem is,
>> just wondering why the whole curcuit can't just be run from the same
>7805 (or is
>> there a specific need for 12V)?
>>
>> Kevin
>>
>> "James R. Parish" 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@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/
>
>
>
Sincerely
Kerry
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1132