On Mon, 14 Apr 2003 13:29:47 -0400, you wrote:

>> I am using ST 7812 regulator the problem I face is the voltage out I
>> get normally is constant 11.9 or 12.03 V.  Some of the parts after
>> use for fews day or 1 month, the voltage out drop to 8.9 V and it is
>> unstable waving between 8.9 to 11.9 V. What is the reason of this and
>> how to avoid this ?
>>
>> James
>
>
>James, just to awake a possible problem;
>
>In 2001 we bought hundreds of 7805 produced by TI in Mexico, all of =
them,
>without exception presented several different voltages, from 4.01 to =
5.12V,
>not a single one did show a voltage between 4.95 and 5.05V, not one.
>
>Unfortunately we only found it out, after 5 months of purchase, so the
>supplier "could do nothing" about it.
>
>By other technical point of view, I can suggest you to check the current
>and temperature over such 7812.
>What is the Voltage at its input? what is the load to it?
>
>Are you using any electrolytic capacitor at the 7812's output? if yes,
>remove it, keep only a small 100nF to filter high freq noises.  Any
>electrolytic capacitor should be used at the input of the 78XX family, =
not
>output.  The reason is that it can cause regulation delays and problems =
and
>the 78XX "can" do some messy regulation.  By the same reason, the 100nF
>capacitor is REQUIRED to avoid high freq to mess with the regulation.

Actually, I've had 7805's go unstable with any LESS than about 10uf on =
the output...!
=20

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