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How to create a DC power supply filter?
I am programming a microcontroller, and it worked fine. By this time, the microcontroller is powered by the USB port. After programming, i do some testing, i used LM7805 paired with wall wart as the controller's power supply. When using this power supply, the controller's behavior is a little bit unpredictable. Based on observations, the problem is the ripple in the DC supply.
I there a filter method or topology that i can use?
Note: simple capacitor filter won't work.
i have a frequency counter...
it reads 0 Hz at the USB
and reads 60 Hz at the LM7805 powered by a wall wart.
Comments
Best Answer 8 years ago
Show your circuit. The real arbiter would be to use an oscilloscope to see what's happening.
I suspect the input to the 7805 isn't smoother. Put a nice fat 100uF cap BEFORE the 7805, put a 100uf cap on your circuit, and parallel that with a 100nF ceramic.
Steve
Answer 8 years ago
i 'll try that, thank you.
just asking...
i terms of ripple rejection, which is better? LM7805 or PI Filter (LC)?
Answer 8 years ago
the other end of the circuit is connected to the MCU
6 years ago
indeed is the first thing a lot of peoples think is increasing the the 10uf , that will only increase the ripple, only a bit large and indeed bypass with a small cap will do the trick and a bit ripple can't do no harm , but use a low imp cap , so it rises fast
8 years ago
A 7805 will beat most PI filters ! And neither a 7805 nor pi filter can't beat 100% input ripple.....
Steve