Electronics > Beginners
LM7805 unstable
<< < (4/8) > >>
bogdant:

--- Quote from: alex-sh on February 18, 2019, 09:03:56 am ---Is your 7805 operating the same at, say, 24V? If yes, perhaps it is damaged?

--- End quote ---

If Vin <20V the LM7805 works Ok. I did try another sample, but it is the same. There are from ST.
ebastler:

--- Quote from: bogdant on February 18, 2019, 12:05:21 pm ---There are from ST.

--- End quote ---

But where did you buy them? Can you be sure they are genuine?
bd139:
None of the voltage regulators work properly above about 20V if you want 5V out. If you need to drop more, add a preregulator.

I found this out the hard way as well dropping 28V to 5V DC for logic in an RF PA driver. Currently waiting for a board spin. I only needed 50mA and didn't want RF noise so I went with a simple MOSFET/zener/resistor preregulator to drop it down to 18Vish. Because the current requirements are relatively low I don't need to heatsink either then as the load is spread evenly across both MOSFET and 7805.

Edit: also if you value the circuit it's driving, stick a 5W 5.6V zener across the regulator output. That will smoke the prereg / regulator not the load!
wraper:

--- Quote from: bogdant on February 18, 2019, 12:05:21 pm ---I did try another sample, but it is the same. There are from ST.

--- End quote ---
If it's from ebay/ali, 95+% of them are counterfeit. Post a picture.
bogdant:

--- Quote from: ebastler on February 18, 2019, 12:15:01 pm ---
--- Quote from: bogdant on February 18, 2019, 12:05:21 pm ---There are from ST.

--- End quote ---

But where did you buy them? Can you be sure they are genuine?

--- End quote ---

They are from tme.eu. I have no idee if there are contrafit.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod