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LM7805 unstable
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JackJones:
Some of the 78xx datasheet do mention a minimum load current. For example here: https://www.st.com/resource/en/datasheet/l78.pdf


--- Quote ---Note: Minimum load current for regulation is 5 mA.
--- End quote ---

Other datasheets don't, I guess that depends on the manufacturer. Better always to double check the datasheet from a particular manufacturer.

Edit: Actually, I checked a bunch of other 7805 datasheets. While they don't explicitly mention minimum of 5mA, they all seem to use that 5mA as minimum in their electrical characteristics. So maybe it is a requirement for all of them.  :-//

Here's a couple datasheets to check:

http://ee-classes.usc.edu/ee459/library/datasheets/LM7805.pdf
https://www.sparkfun.com/datasheets/Components/LM7805.pdf
https://static1.squarespace.com/static/5416a926e4b09de8832655bc/t/54427078e4b03de3b67b89af/1413640312811/lm7805.pdf

They all have that output voltage parameter test conditions as "Io = 5 mA to 1 A"

And you're absolutely correct about those fake LM2596s. I recently bought some of them from several different sellers, all of them fake. Most of them didn't work in the inverting configuration at all, and even those that did had only ~50kHz switching frequency. I wouldn't bother with ebay/ali for those, LCSC seems to have the for dirt cheap and the western sellers for next to dirt cheap.
wraper:

--- Quote from: JackJones on February 18, 2019, 10:05:51 am ---Some of the 78xx datasheet do mention a minimum load current. For example here: https://www.st.com/resource/en/datasheet/l78.pdf


--- Quote ---Note: Minimum load current for regulation is 5 mA.
--- End quote ---

Other datasheets don't, I guess that depends on the manufacturer. Better always to double check the datasheet from a particular manufacturer.

Edit: Actually, I checked a bunch of other 7805 datasheets. While they don't explicitly mention minimum of 5mA, they all seem to use that 5mA as minimum in their electrical characteristics. So maybe it is a requirement for all of them.  :-//

--- End quote ---
Some might say minimum load but any of them will work without a load just fine. It's only that some spec might not be met. Unless op says where he bought it, I expect it to be counterfeit.
CJay:

--- Quote from: wraper on February 18, 2019, 11:10:19 am ---
--- Quote from: JackJones on February 18, 2019, 10:05:51 am ---Some of the 78xx datasheet do mention a minimum load current. For example here: https://www.st.com/resource/en/datasheet/l78.pdf


--- Quote ---Note: Minimum load current for regulation is 5 mA.
--- End quote ---

Other datasheets don't, I guess that depends on the manufacturer. Better always to double check the datasheet from a particular manufacturer.

Edit: Actually, I checked a bunch of other 7805 datasheets. While they don't explicitly mention minimum of 5mA, they all seem to use that 5mA as minimum in their electrical characteristics. So maybe it is a requirement for all of them.  :-//

--- End quote ---
Some might say minimum load but any of them will work without a load just fine. It's only that some spec might not be met. Unless op says where he bought it, I expect it to be counterfeit.

--- End quote ---

I've always found them to be on the mark for rated voltage output too when unloaded but...

Must, must must check capacitor requirements for regulators, there's a batch I have which give really odd output voltages if you don't have a suitable capacitor on the output, add the capacitor and it behaves perfectly.

I found out the hard way and now the box has a large handwritten comment with capacitor specs.
ebastler:

--- Quote from: wraper on February 18, 2019, 09:39:31 am ---Based on fake LM2596 which does not even operate at the same frequency as original.

--- End quote ---

Hmm... How do you know that? Can't recognize anything obvious that seems suspicious  (beyond the low price, of course) in the Amazon description?
bogdant:

--- Quote from: StillTrying on February 18, 2019, 09:21:14 am ---You don't mention any mA load on the output, most regulators need at least some small load to stop the output rising.

--- End quote ---
if you add a load 500 the voltage drops from Vout= 9V-> 5V, but does not regulate.
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