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LM7805 unstable

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bogdant:
For Vin=35V then Vout of Lm7805 is 9.5V! The Cin =0.1uF and Cout=0.1uF. This is a surprize for me, I would expect to work, even is on maxim specified voltage. Even more, for Vin>20V the stability of LM7805 dependes on load.
Can you find this in datasheet ?  What would be a solution in my case for Vin=35V?

ebastler:
35V is specified as the "absolute maximum rating", i.e. the LM7805 will not be damaged if you apply this voltage. But if you look at the "electrical characteristics" table, you will find that the output regulation propoerties are only specified for up to 25V input voltage.

For such a large step down in voltage, I would prefer a buck converter which does not convert the excess power into heat. Off the cuff, I don't know one with 35V input voltage range, but I trust you can get them. Google for "step-down converter" or "buck converter". You can get the bare ICs, and also little piggyback modules which come complete with the required passive components. The latter are cheap on ebay, Aliexpress etc., and are convenient for a one-off or a small number of units.

Nerull:
Just below "Absolute Maximum Ratings", it the TI datasheet states:


--- Quote ---Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied.

--- End quote ---

The 7805 is designed to survive 35V, not operate at 35V.

Just below that are the "Recommended Operating Conditions", where Vin max is 25V.

https://www.sparkfun.com/datasheets/Components/LM7805.pdf

bogdant:
thank you

wraper:
In addition to already said, isn't it some counterfeit junk from ebay?

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