Odd power issue

Archiver

Hi All,

I am trying to power a Stamp 2p24 with a DC to DC converter, a MAX1703. If I
try to apply the output (5.02VDC) directly to VDD it will not power the
Stamp, and the VDD pin on the Stamp reads 4.3VDC. If I conect it to VIN, it
works fine, and the VDD pin reads 4.9VDC. Any ideas what gives here?

Thanks,

Jonathan Peakall

www.madlabs.info

Archiver

I bet you have switching noise on your DC output. Look at it with a
scope with a pig tail gnd on the probe. A DMM will not see these
spikes so ytou must use a scope. You will see transient spikes and
possibility ripple at the switching frequency. When you feed your
output through a linear regulator it will filter these spikes out.
The watchdog on the stamp monitors power going to the stamp and if it
detects an under or over voltage condition it will hold the stamp in
reset.

If you want to use a boost convertor and you are a novice at
switching power electronics then I would recomend using National
Semiconductors Simple switchers. They have a program that you can
download for free that will do the design work for you.

Jason



--- In basicstamps@yahoogroups.com, "Jonathan Peakall"
<jpeakall@m...> wrote:
> Hi All,
>
> I am trying to power a Stamp 2p24 with a DC to DC converter, a
MAX1703. If I
> try to apply the output (5.02VDC) directly to VDD it will not power
the
> Stamp, and the VDD pin on the Stamp reads 4.3VDC. If I conect it to
VIN, it
> works fine, and the VDD pin reads 4.9VDC. Any ideas what gives here?
>
> Thanks,
>
> Jonathan Peakall
>
> www.madlabs.info

Archiver

Actually, you can (sort of) see spikes using a DMM. Set it to AC, not DC. My
DMM goes to 1 decimal place in AC mode and I can spot semi-small
oscillations with it. Helped me figure out an op-amp was oscillating and
after making changes, I could tell I stopped it (my steady ADC readings were
proof enough really, but its nice to see it on a meter too [noparse]:D[/noparse] )

Now I wouldn't recommend it as a permanent diagnostic tool of course.It
really only shows noise in the 60Hz range since thats what the AC meter is
designed to do. But its enough to know its there for now - until I can find
a power cord for this Telequipment D75 - assuming the dinosaur still works!

---

Original Message

---

From: jbirnsch [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=O6ETtZv87i0VEi1WGCuGvhXImpguOBLlR2ghYCIBtuIKi-Y9TV9P3dQBsOMynFjFV5gHrovqc38]jbirnsch@v...[/url
Sent: August 6, 2003 12:52 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Odd power issue


I bet you have switching noise on your DC output. Look at it with a
scope with a pig tail gnd on the probe. A DMM will not see these
spikes so ytou must use a scope.

Archiver

For these spikes you will need a scope. The switching frequency is
300 kHz for this boost convertor. My Fluke 87 has too slow of a
responce time to see these. Not even sure that a PC scope could
capture them.

Jason



--- In basicstamps@yahoogroups.com, PatM <pmeloy@s...> wrote:
> Actually, you can (sort of) see spikes using a DMM. Set it to AC,
not DC. My
> DMM goes to 1 decimal place in AC mode and I can spot semi-small
> oscillations with it. Helped me figure out an op-amp was
oscillating and
> after making changes, I could tell I stopped it (my steady ADC
readings were
> proof enough really, but its nice to see it on a meter too [noparse]:D[/noparse] )
>
> Now I wouldn't recommend it as a permanent diagnostic tool of
course.It
> really only shows noise in the 60Hz range since thats what the AC
meter is
> designed to do. But its enough to know its there for now - until I
can find
> a power cord for this Telequipment D75 - assuming the dinosaur
still works!
>
>
>

---

Original Message

---

> From: jbirnsch [noparse][[/noparse]mailto:jbirnsch@v...]
> Sent: August 6, 2003 12:52 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Odd power issue
>
>
> I bet you have switching noise on your DC output. Look at it with a
> scope with a pig tail gnd on the probe. A DMM will not see these
> spikes so ytou must use a scope.