7805 works fine, LM2940CT5 not!

[Bruce]

Most +5V non LDO regulators require at least 7.5VDC minimum input to maintain a regulated +5V output.
I couldn't find a datasheet for the LM2940CT5, but, some LDO types require specific capacitor values on
the output or they will oscillate, and that causes major problems.

Edit: I found a data sheet on the LM2940, and it looks like you need at least 22uF on the output, and
drop-out will be around 0.5V, so you don't have much overhead.

[BobP]

Hi Daniel,

Just checked the datasheet
http://www.national.com/ds/LM/LM2940.pdf#page=13

and it clearly states that the mimimum capacitance on the 5volt side is 22uF (Pg13).

Let us know if this solves the problem?

Bob

Edit oops Bruce has just giving this info

[Luciano]

Hi,

Datasheet:
http://www.national.com/ds/LM/LM2940.pdf

* * *

Application Note 1148 Linear Regulators:
Theory of Operation and Compensation

See page 7, Output Capacitor Selection:
http://www.national.com/an/AN/AN-1148.pdf

* * *

Source of the above PDF links:
http://www.national.com/mpf/LM/LM2940C.html

Best regards,

Luciano