Interpreting Oscilloscope Trace of Power Supply
Archiver
Posts: 46,084
I have used Basic Stamp and other device on 2 or 3 breadboards. I've
used the simple L7805-based regulator circuit as provided by Peter
Anderson with his stuff. I also built a little power supply from a kit
(board, components, schematic supplied).
I just received the old oscilloscope I bought (Tektronix T922). First
thing was to look at the signals from the 2 power supplies, just to
see how they looked out of curiosity.
The one supply shows a simple spike of about +0.2V over the nominal
4.9V output. The spikes appear to occur at a frequency of 8000 per sec
(8khz).
The other supply shows a more complex wave, with the maximum up and
down values about 0.1V above 4.9V and 0.1V below 4.9V, with a
frequency of about 40khz.
I don't have any power problems with the BS2, but wonder if these
characteristics of the supply would worry any one? I just don't have
any experience to say that this is normal, ok, or in the words of
recently departed Marlon Brando, "the horror ... the horror".
BTW I took digital pic of these traces but have not had time to load
them onto my PC, but I can do so tonite.
Thanks.
Harry
used the simple L7805-based regulator circuit as provided by Peter
Anderson with his stuff. I also built a little power supply from a kit
(board, components, schematic supplied).
I just received the old oscilloscope I bought (Tektronix T922). First
thing was to look at the signals from the 2 power supplies, just to
see how they looked out of curiosity.
The one supply shows a simple spike of about +0.2V over the nominal
4.9V output. The spikes appear to occur at a frequency of 8000 per sec
(8khz).
The other supply shows a more complex wave, with the maximum up and
down values about 0.1V above 4.9V and 0.1V below 4.9V, with a
frequency of about 40khz.
I don't have any power problems with the BS2, but wonder if these
characteristics of the supply would worry any one? I just don't have
any experience to say that this is normal, ok, or in the words of
recently departed Marlon Brando, "the horror ... the horror".
BTW I took digital pic of these traces but have not had time to load
them onto my PC, but I can do so tonite.
Thanks.
Harry
Comments
small .1 disc capacitors that are to get rid of those
signals but if it is not bothering anything don't
sweat it by the way you will see alkinds of strange
signals when you start poking aroud with a scope
it's is a real head scratcher to figure out what they
are good luck
--- harrybstoner <tedstoner@1...> wrote:
> I have used Basic Stamp and other device on 2 or 3
> breadboards. I've
> used the simple L7805-based regulator circuit as
> provided by Peter
> Anderson with his stuff. I also built a little power
> supply from a kit
> (board, components, schematic supplied).
>
> I just received the old oscilloscope I bought
> (Tektronix T922). First
> thing was to look at the signals from the 2 power
> supplies, just to
> see how they looked out of curiosity.
>
> The one supply shows a simple spike of about +0.2V
> over the nominal
> 4.9V output. The spikes appear to occur at a
> frequency of 8000 per sec
> (8khz).
>
> The other supply shows a more complex wave, with the
> maximum up and
> down values about 0.1V above 4.9V and 0.1V below
> 4.9V, with a
> frequency of about 40khz.
>
> I don't have any power problems with the BS2, but
> wonder if these
> characteristics of the supply would worry any one? I
> just don't have
> any experience to say that this is normal, ok, or
> in the words of
> recently departed Marlon Brando, "the horror ... the
> horror".
>
> BTW I took digital pic of these traces but have not
> had time to load
> them onto my PC, but I can do so tonite.
>
> Thanks.
>
> Harry
>
>
>
> 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.
>
> Yahoo! Groups Links
>
>
> basicstamps-unsubscribe@yahoogroups.com
>
>
>
>
__________________________________
Do you Yahoo!?
New and Improved Yahoo! Mail - Send 10MB messages!
http://promotions.yahoo.com/new_mail
different noise than the night before. So I believe you with respect
to noise. Even waving the probe near fluorescent lights causes lots waves.
Also went through an isolation transformer to see what that would do.
Another thing was to unplug X10 modules in the house in case they were
eminating junk. Didn't notice any changes.
I put up the scope pix here if anyone cares:
http://1930s.com/bs2/OscTracesForPowerSupplies.html
Thanks.
Harry
--- In basicstamps@yahoogroups.com, kenneth magers
<kenneth_m_73149@y...> wrote:
> what you see is normal thats why you somtimes see
> small .1 disc capacitors that are to get rid of those
> signals but if it is not bothering anything don't
> sweat it by the way you will see alkinds of strange
> signals when you start poking aroud with a scope
> it's is a real head scratcher to figure out what they
> are good luck
> --- harrybstoner <tedstoner@1...> wrote:
> > I have used Basic Stamp and other device on 2 or 3
> > breadboards. I've
> > used the simple L7805-based regulator circuit as
> > provided by Peter
> > Anderson with his stuff. I also built a little power
> > supply from a kit
> > (board, components, schematic supplied).
> >
> > I just received the old oscilloscope I bought
> > (Tektronix T922). First
> > thing was to look at the signals from the 2 power
> > supplies, just to
> > see how they looked out of curiosity.
> >
> > The one supply shows a simple spike of about +0.2V
> > over the nominal
> > 4.9V output. The spikes appear to occur at a
> > frequency of 8000 per sec
> > (8khz).
> >
> > The other supply shows a more complex wave, with the
> > maximum up and
> > down values about 0.1V above 4.9V and 0.1V below
> > 4.9V, with a
> > frequency of about 40khz.
> >
> > I don't have any power problems with the BS2, but
> > wonder if these
> > characteristics of the supply would worry any one? I
> > just don't have
> > any experience to say that this is normal, ok, or
> > in the words of
> > recently departed Marlon Brando, "the horror ... the
> > horror".
> >
> > BTW I took digital pic of these traces but have not
> > had time to load
> > them onto my PC, but I can do so tonite.
> >
> > Thanks.
> >
> > Harry
> >
> >
> >
> > 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.
> >
> > Yahoo! Groups Links
> >
> >
> > basicstamps-unsubscribe@yahoogroups.com
> >
> >
> >
> >
>
>
>
>
> __________________________________
> Do you Yahoo!?
> New and Improved Yahoo! Mail - Send 10MB messages!
> http://promotions.yahoo.com/new_mail
However you might try a simple low-esr cap such as a .1uf mono,
that should eliminate most of what you are seeing.
KF4HAZ - Lonnie
From: "harrybstoner" <tedstoner@1
> Thanks a lot for your reply. I did more tracing last night and got
> different noise than the night before. So I believe you with respect
> to noise. Even waving the probe near fluorescent lights causes lots waves.
>
> Also went through an isolation transformer to see what that would do.
> Another thing was to unplug X10 modules in the house in case they were
> eminating junk. Didn't notice any changes.
>
> I put up the scope pix here if anyone cares:
>
> http://1930s.com/bs2/OscTracesForPowerSupplies.html
>
> Thanks.
>
> Harry
>
> --- In basicstamps@yahoogroups.com, kenneth magers
> <kenneth_m_73149@y...> wrote:
> > what you see is normal thats why you somtimes see
> > small .1 disc capacitors that are to get rid of those
> > signals but if it is not bothering anything don't
> > sweat it by the way you will see alkinds of strange
> > signals when you start poking aroud with a scope
> > it's is a real head scratcher to figure out what they
> > are good luck
> > --- harrybstoner <tedstoner@1...> wrote:
> > > I have used Basic Stamp and other device on 2 or 3
> > > breadboards. I've
> > > used the simple L7805-based regulator circuit as
> > > provided by Peter
> > > Anderson with his stuff. I also built a little power
> > > supply from a kit
> > > (board, components, schematic supplied).
> > >
> > > I just received the old oscilloscope I bought
> > > (Tektronix T922). First
> > > thing was to look at the signals from the 2 power
> > > supplies, just to
> > > see how they looked out of curiosity.
> > >
> > > The one supply shows a simple spike of about +0.2V
> > > over the nominal
> > > 4.9V output. The spikes appear to occur at a
> > > frequency of 8000 per sec
> > > (8khz).
> > >
> > > The other supply shows a more complex wave, with the
> > > maximum up and
> > > down values about 0.1V above 4.9V and 0.1V below
> > > 4.9V, with a
> > > frequency of about 40khz.
> > >
> > > I don't have any power problems with the BS2, but
> > > wonder if these
> > > characteristics of the supply would worry any one? I
> > > just don't have
> > > any experience to say that this is normal, ok, or
> > > in the words of
> > > recently departed Marlon Brando, "the horror ... the
> > > horror".
> > >
> > > BTW I took digital pic of these traces but have not
> > > had time to load
> > > them onto my PC, but I can do so tonite.
> > >
> > > Thanks.
> > >
> > > Harry
> I have used Basic Stamp and other device on 2 or 3
> breadboards. I've
> used the simple L7805-based regulator circuit as
> provided by Peter
> Anderson with his stuff. I also built a little power
> supply from a kit
> (board, components, schematic supplied).
> I just received the old oscilloscope I bought
> (Tektronix T922). First
> thing was to look at the signals from the 2 power
> supplies, just to
> see how they looked out of curiosity.
> The one supply shows a simple spike of about +0.2V
> over the nominal
> 4.9V output. The spikes appear to occur at a
> frequency of 8000 per sec
> (8khz).
>
> The other supply shows a more complex wave, with the
> maximum up and
> down values about 0.1V above 4.9V and 0.1V below
> 4.9V, with a
> frequency of about 40khz.
The 78 and 79 linear regulators have all kinds of tricks like this to play on you. In
most cases the ripple won't give a problem with digital and processor circuits but it's
very undesirable if you have any analogue stages.
Also, in some cases, they can go into serious self-oscillation.
In all of my designs I now fit capacitors of 1uF or 100nF from input to ground and from
output to ground *as close as possible to the pins*.
If you're using plug-in protoboard you might like to solder the capacitors directly to
the regulator pins - you can use radial package electrolytics or even surface mount
devices which fit quite neatly across the pins. I do this in RF products where any
stray RF can cause the regulators to do all kinds of unpleasant things.
supply from the wall. Is the noise still there? If you still have noise
with the power supply disconnected from the wall, it is getting into the
system from outside sources.
The high frequency of the noise makes me suspect switchers somewhere.
The input inpedance of an oscilloscope is high enough to pick up almost
anything, though connected to a circuit, the circuit impedance should be low
enough to keep noise pickup of stray stuff low.
Also, 7805s like a minimum load on them, say 20 mA. I use a led to indicate
that it is on, and as a minimum load. I also put caps on the input and
output (as required in the ap notes) to help the beast deal better with
transients.
Original Message
From: Falcon Wireless Tech Support - KF4HAZ
[noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=USFZiKkVCd3iS9xzB2w9-kRbxuSBpE3fdwmdfUHJ5Hv2IWV67iJskZ8Dbqz50ufzyv7a91tEJFeteSWTrp85EsTC5D_Y]techsupport@f...[/url
Sent: Tuesday, July 06, 2004 3:43 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Re: Interpreting Oscilloscope Trace of Power
Supply
I see nothing that should cause any problems.
However you might try a simple low-esr cap such as a .1uf mono, that should
eliminate most of what you are seeing.
KF4HAZ - Lonnie
From: "harrybstoner" <tedstoner@1
> Thanks a lot for your reply. I did more tracing last night and got
> different noise than the night before. So I believe you with respect
> to noise. Even waving the probe near fluorescent lights causes lots
> waves.
>
> Also went through an isolation transformer to see what that would do.
> Another thing was to unplug X10 modules in the house in case they were
> eminating junk. Didn't notice any changes.
>
> I put up the scope pix here if anyone cares:
>
> http://1930s.com/bs2/OscTracesForPowerSupplies.html
>
> Thanks.
>
> Harry
>
> --- In basicstamps@yahoogroups.com, kenneth magers
> <kenneth_m_73149@y...> wrote:
> > what you see is normal thats why you somtimes see
> > small .1 disc capacitors that are to get rid of those signals but if
> > it is not bothering anything don't sweat it by the way you will see
> > alkinds of strange signals when you start poking aroud with a scope
> > it's is a real head scratcher to figure out what they
> > are good luck
> > --- harrybstoner <tedstoner@1...> wrote:
> > > I have used Basic Stamp and other device on 2 or 3 breadboards.
> > > I've used the simple L7805-based regulator circuit as
> > > provided by Peter
> > > Anderson with his stuff. I also built a little power
> > > supply from a kit
> > > (board, components, schematic supplied).
> > >
> > > I just received the old oscilloscope I bought
> > > (Tektronix T922). First
> > > thing was to look at the signals from the 2 power supplies, just
> > > to see how they looked out of curiosity.
> > >
> > > The one supply shows a simple spike of about +0.2V
> > > over the nominal
> > > 4.9V output. The spikes appear to occur at a
> > > frequency of 8000 per sec
> > > (8khz).
> > >
> > > The other supply shows a more complex wave, with the maximum up
> > > and down values about 0.1V above 4.9V and 0.1V below
> > > 4.9V, with a
> > > frequency of about 40khz.
> > >
> > > I don't have any power problems with the BS2, but
> > > wonder if these
> > > characteristics of the supply would worry any one? I
> > > just don't have
> > > any experience to say that this is normal, ok, or
> > > in the words of
> > > recently departed Marlon Brando, "the horror ... the horror".
> > >
> > > BTW I took digital pic of these traces but have not
> > > had time to load
> > > them onto my PC, but I can do so tonite.
> > >
> > > Thanks.
> > >
> > > Harry
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.
Yahoo! Groups Links