Lm2940 ?
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Upon testing my new batch of National Semiconductor LM2940s, I find that
the voltage I get from my meter does not match the voltage printed on the
regulator. Do I need to test voltage on these things with a load or do I
have mismarked regulators? I have + v coming from a wall wart to the left
pin, ground to center, and I measure 12.3V from the right pin. Sorry for the
off topic question.
Jeff
the voltage I get from my meter does not match the voltage printed on the
regulator. Do I need to test voltage on these things with a load or do I
have mismarked regulators? I have + v coming from a wall wart to the left
pin, ground to center, and I measure 12.3V from the right pin. Sorry for the
off topic question.
Jeff
Comments
the input of the regulator and a 10 mfd cap on the output of the regulator.
Original Message
> Upon testing my new batch of National Semiconductor LM2940s, I find that
> the voltage I get from my meter does not match the voltage printed on the
> regulator. Do I need to test voltage on these things with a load or do I
> have mismarked regulators? I have + v coming from a wall wart to the left
> pin, ground to center, and I measure 12.3V from the right pin. Sorry for
the
> off topic question.
In addition to using high value filter capacitors on the input and output of
the regulator, I also strongly suggest you use a high quality 0.01 mfd disc
cap tied to the output of the regulator and to ground. The closer you can
get to the regulator, the better.
Burt Schultz
>the voltage I get from my meter does not match the voltage printed on the
>regulator. Do I need to test voltage on these things with a load or do I
>have mismarked regulators? I have + v coming from a wall wart to the left
>pin, ground to center, and I measure 12.3V from the right pin. Sorry for the
>off topic question.
>
>Jeff
The capacitor on the output is required for stability. This PNP pass
regulator simply will not work without it. The data sheet says 22uF
minimum from the output to ground.
-- Tracy