7805 voltage output = 5.8 volts?
I have a 7805 voltage regulator in a circuit that's producing 5.8 volts
(instead of 5.0v) - does this means it's failing? Should I replace it?
(instead of 5.0v) - does this means it's failing? Should I replace it?
Comments
powered electronics is at all voltage sensitive, I would replace it.
Bob
>
Original Message
> From: mark allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=xSNJEtde-yanVxea5UjobvX8Wp0Obyd26c69rMU90y1ZkVj-9qe_WlJm156y6t6ReIqMmyeGyT5LNA]mallen@c...[/url
> Sent: Thursday, September 19, 2002 7:09 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] 7805 voltage output = 5.8 volts?
>
>
> I have a 7805 voltage regulator in a circuit that's producing 5.8 volts
> (instead of 5.0v) - does this means it's failing? Should I replace it?
>
>
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>
Allan
bob-2000 wrote:
>
> I'd define it as failed since the voltage is about 16% too high. If the
> powered electronics is at all voltage sensitive, I would replace it.
>
> Bob
>
> >
Original Message
> > From: mark allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=oE3C8l8G37yzELcAjvKIuiTuGaJK9lPvbHRzxyrFVkFxKCAX0QZm--3BQZfc3GF0OceOzHqecd5FdIZb]mallen@c...[/url
> > Sent: Thursday, September 19, 2002 7:09 PM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] 7805 voltage output = 5.8 volts?
> >
> >
> > I have a 7805 voltage regulator in a circuit that's producing 5.8 volts
> > (instead of 5.0v) - does this means it's failing? Should I replace it?
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
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they won't regulate. Most of the Stamp-related stuff uses low drop-out
regulators that will work with a lower input voltage.
If you don't have the caps on the input and output, its quite possible the
thing is going out of regulation because of noise.
Original Message
> I'd define it as failed since the voltage is about 16% too high. If the
> powered electronics is at all voltage sensitive, I would replace it.
> > I have a 7805 voltage regulator in a circuit that's producing 5.8 volts
> > (instead of 5.0v) - does this means it's failing? Should I replace it?
> thing is going out of regulation because of noise.
Correct me if I'm wrong (after all, that's how I'm going to learn), isn't
the cap before the regulator needed only if the wires between the
battery and the regulator are long or if perhaps if there's another
drain on the battery that may drop the input voltage to the 7805?
I use the LM2940T-5. It's a low drop out regulator that requires
only 5.25 volts to produce 5.0 volts.
Paul
don't take up much space.
Original Message
> > If you don't have the caps on the input and output, its quite possible
the
> > thing is going out of regulation because of noise.
>
> Correct me if I'm wrong (after all, that's how I'm going to learn), isn't
> the cap before the regulator needed only if the wires between the
> battery and the regulator are long or if perhaps if there's another
> drain on the battery that may drop the input voltage to the 7805?
>
> I use the LM2940T-5. It's a low drop out regulator that requires
> only 5.25 volts to produce 5.0 volts.
input voltage to the output voltage you will see a strange voltage at
the input (which you think is the output).
Worth checking.
Al Williams
AWC
* Floating point math for the Stamp, PIC, SX, or any microcontroller
http://www.al-williams.com/awce/pak1.htm
>
Original Message
> From: verhap@o... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=RpFLl3Mhytp_BAh1p-lClxUeJyE3sNIeds4gQ8Yo3KBWY1nAEyesj-wwh3LTUhK0Ejpb1WkUJrfMIXw18aQdNO_yuQ]verhap@o...[/url
> Sent: Friday, September 20, 2002 9:17 AM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] 7805 voltage output = 5.8 volts?
>
>
> > If you don't have the caps on the input and output, its
> quite possible
> > the thing is going out of regulation because of noise.
>
> Correct me if I'm wrong (after all, that's how I'm going to
> learn), isn't
> the cap before the regulator needed only if the wires between the
> battery and the regulator are long or if perhaps if there's another
> drain on the battery that may drop the input voltage to the 7805?
>
> I use the LM2940T-5. It's a low drop out regulator that requires
> only 5.25 volts to produce 5.0 volts.
>
> Paul
>
> To UNSUBSCRIBE, just send mail to:
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> http://docs.yahoo.com/info/terms/
>
>
on a regulator question, but did not get a response. Maybe this time
I will!
I originally wrote...
I was wondering if I could get some insight as to the design and
configuration of the voltage regulator design on the BOEBoard and the
Stamp II OEM. They both use the LM2940 5 Volt Regulator.
Question 1: I assume the OEM uses it to regulate the voltage going
to the rest of the circuits on the OEM. Why does the BOEBoard have
one when the Stamp has one? It seems as though the BOEboard produces
a clean regulated 5 volts for the Stamp (which has the capability to
produce it's own clean regulated 5 volts). Is this redundant or am I
missing something?
Question 2: Why does the OEM only use a 10uF filter capacitor on the
Vout side of the LM2940 when the BOEBoard uses a 47uF on the Vin side
and a 1uF on the Vout side. Do I need one capacitor or two? What
should the values be? I am very confused on this, especially when I
read the spec sheet which states that... "The minimum output
capacitance required to maintain stability is 22 µF (this value may
be increased without limit). Larger values of output capacitance will
give improved transient response." It seems that both the BOEBoard
and the OEM are both using smaller values than called for.
The reason for my questions is that I am building a small robot
(powered by a Stamp II, of course) that will use the Devantech SRF04
Sonar Ranger. It seems as though the Devantech should be powered by
its own battery since it draws the maximum amps that the Stamp can
safely supply. I want to build my own regulated voltage supply for
the Devantech (using a LM2940) and am not quite sure what value
capacitors I should be using for filters. I also don't know if I
need a filter capacitor on the Vin side.
I have come to have great respect for all Parallax products and I am
sure that there is a good, simple reason for the design decisions
made (after all, the BOEBoard and OEM are used by thousands without
any problem!). I would just like to learn more about it so I can
make the right choice for my robot.
Thanks so much,
Steve
regulator can't handle.
You can run the Stamp from a regulated 5-volt supply *or* use a higher input
voltage and use the regulator on the Stamp. You either use the Vdd pin or
the Vin pin. If you supply power to Vin on the Stamp, you can borrow 5 volts
off the Vin pin within the limits of the regulator.
Are you sure the regulator on the OEM Stamp and the BoE are the exact same?
There are often variations in parts between manufacturers. In my experience,
if you are not sure what to do, go with what the manufaturer's data sheet
says.
Original Message
I was wondering if I could get some insight as to the design and
configuration of the voltage regulator design on the BOEBoard and the
Stamp II OEM. They both use the LM2940 5 Volt Regulator.
Question 1: I assume the OEM uses it to regulate the voltage going
to the rest of the circuits on the OEM. Why does the BOEBoard have
one when the Stamp has one? It seems as though the BOEboard produces
a clean regulated 5 volts for the Stamp (which has the capability to
produce it's own clean regulated 5 volts). Is this redundant or am I
missing something?
Question 2: Why does the OEM only use a 10uF filter capacitor on the
Vout side of the LM2940 when the BOEBoard uses a 47uF on the Vin side
and a 1uF on the Vout side. Do I need one capacitor or two? What
should the values be? I am very confused on this, especially when I
read the spec sheet which states that... "The minimum output
capacitance required to maintain stability is 22 µF (this value may
be increased without limit). Larger values of output capacitance will
give improved transient response." It seems that both the BOEBoard
and the OEM are both using smaller values than called for.
The reason for my questions is that I am building a small robot
(powered by a Stamp II, of course) that will use the Devantech SRF04
Sonar Ranger. It seems as though the Devantech should be powered by
its own battery since it draws the maximum amps that the Stamp can
safely supply. I want to build my own regulated voltage supply for
the Devantech (using a LM2940) and am not quite sure what value
capacitors I should be using for filters. I also don't know if I
need a filter capacitor on the Vin side.
>(instead of 5.0v) - does this means it's failing? Should I replace it?
Another possibility I haven't seen mentioned is a "sneak" source of
higher voltage connected to the output of the regulator. For
example, it might be an RS232 input of +10 volts connected to a
regular stamp input pin, finding its way through Stamp protection
diodes back to the +5 volt power supply. Most voltage regulators
like the 7805 are able to source current, but not sink current. So
that "sneak" power source effectively overrides the regulator. It
is always something to be aware of when circuits are connected
external signals >5 volts.
-- Tracy
regulator circuit using the LM2940. This powers the stamp and the devantech
srf04.
I tied a 10 mfd cap across the leads of the lm2940. I know the specs say to
do this and that, and the other, but I did not fiddle around. Maybe I should
have, but it seems to work fine as is.
I always put a .1 mfd cap across the power supply pins of the Stamp and any
IC chips I have on boards. This is supposed to filter out high frequency
voltage spikes. I don't know if it does or not, but most manuals say to do this.
You also can place any high MFD cap across the power supply to your stamp or
the devantech to act as a voltage filter and a capacitor/battery. To supply
temporary power for heavy voltage draws that motors may cause.
It does seem like redundant power supply regulators onboard the stamp and
onboard the robot doesn't it. I guess because the stamp is made as a stand
alone unit, it has the built in regulator.
You may have to use the 2nd section of code for the Devantech that Acroname
supplys. I could never get the 1st section of code to work with my stamp II.
Use the RCTIME code that acroname supplied as a revision.
www.acroname.com
-kerry
At 03:31 PM 9/20/02 -0000, you wrote:
>Glad that someone is asking about this... I had written to this group
>on a regulator question, but did not get a response. Maybe this time
>I will!
>
>I originally wrote...
>
>I was wondering if I could get some insight as to the design and
>configuration of the voltage regulator design on the BOEBoard and the
>Stamp II OEM. They both use the LM2940 5 Volt Regulator.
>
>Question 1: I assume the OEM uses it to regulate the voltage going
>to the rest of the circuits on the OEM. Why does the BOEBoard have
>one when the Stamp has one? It seems as though the BOEboard produces
>a clean regulated 5 volts for the Stamp (which has the capability to
>produce it's own clean regulated 5 volts). Is this redundant or am I
>missing something?
>
>Question 2: Why does the OEM only use a 10uF filter capacitor on the
>Vout side of the LM2940 when the BOEBoard uses a 47uF on the Vin side
>and a 1uF on the Vout side. Do I need one capacitor or two? What
>should the values be? I am very confused on this, especially when I
>read the spec sheet which states that... "The minimum output
>capacitance required to maintain stability is 22 µF (this value may
>be increased without limit). Larger values of output capacitance will
>give improved transient response." It seems that both the BOEBoard
>and the OEM are both using smaller values than called for.
>
>The reason for my questions is that I am building a small robot
>(powered by a Stamp II, of course) that will use the Devantech SRF04
>Sonar Ranger. It seems as though the Devantech should be powered by
>its own battery since it draws the maximum amps that the Stamp can
>safely supply. I want to build my own regulated voltage supply for
>the Devantech (using a LM2940) and am not quite sure what value
>capacitors I should be using for filters. I also don't know if I
>need a filter capacitor on the Vin side.
>
>I have come to have great respect for all Parallax products and I am
>sure that there is a good, simple reason for the design decisions
>made (after all, the BOEBoard and OEM are used by thousands without
>any problem!). I would just like to learn more about it so I can
>make the right choice for my robot.
>
>Thanks so much,
>
>Steve
>
>
>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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>
>
>
Very respectfully, your obedient servant.
Kerry
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1575
>>(instead of 5.0v) - does this means it's failing? Should I replace it?
>
>Another possibility I haven't seen mentioned is a "sneak" source of
>higher voltage connected to the output of the regulator. For
>example, it might be an RS232 input of +10 volts connected to a
>regular stamp input pin, finding its way through Stamp protection
>diodes back to the +5 volt power supply. Most voltage regulators
>like the 7805 are able to source current, but not sink current. So
>that "sneak" power source effectively overrides the regulator. It
>is always something to be aware of when circuits are connected
>external signals >5 volts.
>
> -- Tracy
I should add that this kind of "sneak" power would be a consideration
only in low power circuits. For example, especially when the Stamp
a'SLEEP, or when it is operating at minimum power. When the power
demand increases, the main regulator takes over again it is able to
source the required current.
Also I should clarify that the p16 RS232 serial port on the Stamp
does not have this problem. It is only the p0--p15 (when connected
via a resistor to a voltage>5 volts). There are also cases where
there is a sneak path through a pull-up resistor or something like a
relay driver to a higher voltage.
>Question 1: I assume the OEM uses it to regulate the voltage going
>to the rest of the circuits on the OEM. Why does the BOEBoard have
>one when the Stamp has one? It seems as though the BOEboard produces
>a clean regulated 5 volts for the Stamp (which has the capability to
>produce it's own clean regulated 5 volts). Is this redundant or am I
>missing something?
The original BS2 uses the LM2936 micropower regulator, which is only
able to supply 50 milliamps. That is enough to supply the Stamp
itself (8 milliamps when operating), but not enough for many LEDs etc
etc that you might want to connect to the pins or directly to the +5
power. Thus, the external regulator capable of supplying 1 amp.
The BS2sx, BS2e, and BS2p use the LT1121, which is capable of 150ma,
but that is still not enough for power hungry projects.
-- Tracy
when you refer to "mfd", is this the same as "uF"?
Also, just to make sure I understand, when you say that you put a .1
mfd cap across the power supply pins of the Stamp and any IC chip, do
you mean that the wire from the Stamp I/O pin should have a
cap "spiced" into it so that it looks like this:
I/O Pin
IC Chip
|
|
---
___ <---.1 cap here
|
|
ground
Thanks,
Steve
--- In basicstamps@y..., Kerry Barlow <admin@m...> wrote:
> Steve: I have a robot running a stampII and a devantech. I built an
external
> regulator circuit using the LM2940. This powers the stamp and the
devantech
> srf04.
> I tied a 10 mfd cap across the leads of the lm2940. I know the
specs say to
> do this and that, and the other, but I did not fiddle around. Maybe
I should
> have, but it seems to work fine as is.
> I always put a .1 mfd cap across the power supply pins of the Stamp
and any
> IC chips I have on boards. This is supposed to filter out high
frequency
> voltage spikes. I don't know if it does or not, but most manuals
say to do this.
> You also can place any high MFD cap across the power supply to your
stamp or
> the devantech to act as a voltage filter and a capacitor/battery.
To supply
> temporary power for heavy voltage draws that motors may cause.
> It does seem like redundant power supply regulators onboard the
stamp and
> onboard the robot doesn't it. I guess because the stamp is made as
a stand
> alone unit, it has the built in regulator.
> You may have to use the 2nd section of code for the Devantech that
Acroname
> supplys. I could never get the 1st section of code to work with my
stamp II.
> Use the RCTIME code that acroname supplied as a revision.
> www.acroname.com
> -kerry
>
>
>
>
> At 03:31 PM 9/20/02 -0000, you wrote:
> >Glad that someone is asking about this... I had written to this
group
> >on a regulator question, but did not get a response. Maybe this
time
> >I will!
> >
> >I originally wrote...
> >
> >I was wondering if I could get some insight as to the design and
> >configuration of the voltage regulator design on the BOEBoard and
the
> >Stamp II OEM. They both use the LM2940 5 Volt Regulator.
> >
> >Question 1: I assume the OEM uses it to regulate the voltage
going
> >to the rest of the circuits on the OEM. Why does the BOEBoard
have
> >one when the Stamp has one? It seems as though the BOEboard
produces
> >a clean regulated 5 volts for the Stamp (which has the capability
to
> >produce it's own clean regulated 5 volts). Is this redundant or
am I
> >missing something?
> >
> >Question 2: Why does the OEM only use a 10uF filter capacitor on
the
> >Vout side of the LM2940 when the BOEBoard uses a 47uF on the Vin
side
> >and a 1uF on the Vout side. Do I need one capacitor or two? What
> >should the values be? I am very confused on this, especially when
I
> >read the spec sheet which states that... "The minimum output
> >capacitance required to maintain stability is 22 µF (this value
may
> >be increased without limit). Larger values of output capacitance
will
> >give improved transient response." It seems that both the
BOEBoard
> >and the OEM are both using smaller values than called for.
> >
> >The reason for my questions is that I am building a small robot
> >(powered by a Stamp II, of course) that will use the Devantech
SRF04
> >Sonar Ranger. It seems as though the Devantech should be powered
by
> >its own battery since it draws the maximum amps that the Stamp can
> >safely supply. I want to build my own regulated voltage supply
for
> >the Devantech (using a LM2940) and am not quite sure what value
> >capacitors I should be using for filters. I also don't know if I
> >need a filter capacitor on the Vin side.
> >
> >I have come to have great respect for all Parallax products and I
am
> >sure that there is a good, simple reason for the design decisions
> >made (after all, the BOEBoard and OEM are used by thousands
without
> >any problem!). I would just like to learn more about it so I can
> >make the right choice for my robot.
> >
> >Thanks so much,
> >
> >Steve
> >
> >
> >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/
> >
> >
> >
>
> Very respectfully, your obedient servant.
> Kerry
> Admin@M...
> WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
> Kerry Barlow
> p.o. box 21
> kirkwood ny
> 13795
> 607-775-1575
typically be a small cap near pin 1 of each chip. This capacitor is
connected between the power pin of the chip and ground. Its purpose is to
reduce noise on the power bus. This does not replace any filtering on the
power supply circuit itself.
mFd = uF = microfarads = 1 x10-6 or 0.000001 Farads
pFd = pF = picofarads = 1 x 10-12 or 0.000000000001 Farads
And a relatively new term, nanofarad is in between these two:
nFd = nF = nanofarad = 1 x 10-9 or 0.000000001 farads
For some reason the capacitance scale on newer digital voltmeters reads in
nF.
Original Message
Kerry - Thanks so much for the insights! A real newbie question, but
when you refer to "mfd", is this the same as "uF"?
Also, just to make sure I understand, when you say that you put a .1
mfd cap across the power supply pins of the Stamp and any IC chip, do
you mean that the wire from the Stamp I/O pin should have a
cap "spiced" into it so that it looks like this:
I/O Pin
IC Chip
|
|
---
___ <---.1 cap here
|
|
ground
>
> nFd = nF = nanofarad = 1 x 10-9 or 0.000000001 farads
>
> For some reason the capacitance scale on newer digital voltmeters reads in
> nF.
It seems to me that nanofarads are a European unit. However, we
in the US should have using them all along.
Paul
I think that it may be the same mentality that caused the industry to use
"micro-microfarads" for sooooooo many years instead of picofarads. The
scientists that I have worked with for the past 30 years have always
referred to 1X10-9 as nano, wether it be farads, volts, or amperes.
Mike
At 02:48 PM 9/20/2002 -0700, you wrote:
>It seems to me that nanofarads are a European unit. However, we
>in the US should have using them all along.
_________________________________
Mike Walsh
walsh@i...
[noparse][[/noparse]Non-text portions of this message have been removed]
for about 10 years. I get back and meters and components are in
nanofarads -- whoa!
I learned the metric system in the 7th grade (1975) because the US was going
to adopt it any time -- I'm still waiting.
Original Message
> > And a relatively new term, nanofarad is in between these two:
> >
> > nFd = nF = nanofarad = 1 x 10-9 or 0.000000001 farads
> >
> > For some reason the capacitance scale on newer digital voltmeters reads
in
> > nF.
>
> It seems to me that nanofarads are a European unit. However, we
> in the US should have using them all along.
a long time, but the electronic manufacturers were apparently slow to adopt
it in reference to capacitor value.
Original Message
> I think that it may be the same mentality that caused the industry to use
> "micro-microfarads" for sooooooo many years instead of picofarads. The
> scientists that I have worked with for the past 30 years have always
> referred to 1X10-9 as nano, wether it be farads, volts, or amperes.
> >It seems to me that nanofarads are a European unit. However, we
> >in the US should have using them all along.
>
> _________________________________
> Mike Walsh
> walsh@i...
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> 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 you can just replace the LT1121 regulator with a MIC5201
from Micrel. It has a guaranteed 200 mA output. So if you need more
power it is an option.
The MIC5201 is available in several fixed voltages and
accuracy configurations. It features the same pinout as the
LT1121 with better performance.
Of course you are going to need a decent soldering iron and lay off
the caffine for a while before you attempt this. For me this is a 2
minute task with my Metcal iron but with a clunky Rat Shack iron your
results will be less than spetacular.
I use this Micrel part instead if the Linear Tech part on my homebrew
stamp boards. I have many uses for basic stamps around the lab where
I work, at home, and my dad's farm that I layed out a single layer
board and plop on a BS2p40 interperter, resonator, eeprom, and
regulator for about $30. I etch my own boards using the Dynart
designs paper and an iron to transfer the mask. I use a right angle
header for my pins. The Econostamp, as I call it, is the same length
but 3 times the width as a Parallax 2p40. I can sacrafice space for
cost on my projects. Reliability has been excellent.
Jason
--- In basicstamps@y..., Rodent <daweasel@s...> wrote:
> The nano has existed with the scientific community and the metric
system for
> a long time, but the electronic manufacturers were apparently slow
to adopt
> it in reference to capacitor value.
>
>
Original Message
>
> > I think that it may be the same mentality that caused the
industry to use
> > "micro-microfarads" for sooooooo many years instead of
picofarads. The
> > scientists that I have worked with for the past 30 years have
always
> > referred to 1X10-9 as nano, wether it be farads, volts, or
amperes.
>
> > >It seems to me that nanofarads are a European unit. However, we
> > >in the US should have using them all along.
> >
> > _________________________________
> > Mike Walsh
> > walsh@i...
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terminals correct, then check your ground pin. If it is a poor connection it
will cause the output to increase.
Alan Bradford
Plasma Technologies
>(instead of 5.0v) - does this means it's failing? Should I replace it?
>
Is that open circuit voltage, or is that under a load?