Cout of super carrier board voltage regulator
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Posts: 46,084
I was comparing the data sheet of the LM2940-5.0, which I downloaded
from National Semiconductor, and the schematic for the super carrier
board. While reading through the data sheet I discovered that it was
very strongly recommended that the output capacitor, Cout, be NO less
then 22uF. The super carrier board schematic shows the value of Cout
to be only 1.0uF as do the markings on the capacitor itself. I am
curious to know, has anyone had, or heard of, problems from this?
from National Semiconductor, and the schematic for the super carrier
board. While reading through the data sheet I discovered that it was
very strongly recommended that the output capacitor, Cout, be NO less
then 22uF. The super carrier board schematic shows the value of Cout
to be only 1.0uF as do the markings on the capacitor itself. I am
curious to know, has anyone had, or heard of, problems from this?
Comments
ie - if the electronics you are driving is greater than 10cm away from the
regulator, use a cap that is 22u or higher.
> From: "nofinger22 <nofinger22@y...>" <nofinger22@y...>
> Reply-To: basicstamps@yahoogroups.com
> Date: Thu, 13 Feb 2003 02:28:19 -0000
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Cout of super carrier board voltage regulator
>
> I was comparing the data sheet of the LM2940-5.0, which I downloaded
> from National Semiconductor, and the schematic for the super carrier
> board. While reading through the data sheet I discovered that it was
> very strongly recommended that the output capacitor, Cout, be NO less
> then 22uF. The super carrier board schematic shows the value of Cout
> to be only 1.0uF as do the markings on the capacitor itself. I am
> curious to know, has anyone had, or heard of, problems from this?
>
>
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filtering needed. If the circuit draws a constant amount of current or the
current demands change slowly, a smaller cap would be fine. However, if you
have motors or relays running off the regulator, it may shut down or go out
of regulation if alot of current is suddenly needed. More filtering is not
going to hurt you.
My large robot has run fine with a Cout of 22 uF for a long time. I added a
small relay with an 80 mA coil to switch an external device and when the
relay coil is fired the voltage drops and my Stamp resets. I added a 220 uF
cap in parallel with the 22 uF and the problem went away.
Original Message
> I was comparing the data sheet of the LM2940-5.0, which I downloaded
> from National Semiconductor, and the schematic for the super carrier
> board. While reading through the data sheet I discovered that it was
> very strongly recommended that the output capacitor, Cout, be NO less
> then 22uF. The super carrier board schematic shows the value of Cout
> to be only 1.0uF as do the markings on the capacitor itself. I am
> curious to know, has anyone had, or heard of, problems from this?
>I was comparing the data sheet of the LM2940-5.0, which I downloaded
>from National Semiconductor, and the schematic for the super carrier
>board. While reading through the data sheet I discovered that it was
>very strongly recommended that the output capacitor, Cout, be NO less
>then 22uF. The super carrier board schematic shows the value of Cout
>to be only 1.0uF as do the markings on the capacitor itself. I am
>curious to know, has anyone had, or heard of, problems from this?
This is a problem. The 2940 is part of a family of low drop-out regulators
that REQUIRES large output capacitors to keep the regulator stable. You
may not notice a problem with very small output currents, but you will
certainly have problems if the current starts to approach the rated
capacity of the regulator.
Good catch on your part! Parallax - are you listening?
dwayne
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
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