[SOLVED] capacitive power supply - microcontroller

[bmandl]

Hello guys,
I built this power supply for my microcontroller project (simple diode thermometer for my laminator project). But when I connect my mcu circuit to this power supply, it keep getting reset. If I use my lab power supply with 5V, it runs smootly. What could be the problem? I already tryed bigger filter capacitor (first 470uF, then 2200uF and now 3300uF) and result is the same.

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Let me answer myself. 100nF decoupling capacitor did the trick

 

[Disha Karnataki]

Let me answer myself. 100nF decoupling capacitor did the trick

you mean when you replaced 1000uf capacitor with 100nf cap you got proper results??

 

[bmandl]

No, I just added 100nF capacitor between +5V and GND. I had none before.

 

[Disha Karnataki]

hmm..... you are using decoupling cap inorder to reduce the ripples i.e get a smooth dc supply(regulated) But even the zener diode is doing that job by keeping the voltage at a preffered level then too you faced problems!?

 

[bmandl]

I am not using decoupling capacitor for filtering. I just added decoupling capacitor between +5V and GND on mcu board to solve problems with disturbances, which caused microcontroller to reset. Filter capacitor is on power supply pcb and is 470uF, as in beginning. Why you don't want to understand? Do I have to draw it?

 

[Disha Karnataki]

lol..I will just decode the circuit : In your circuit you have used a 470uf as a filter capacitor to bypass ac component ok.. But, the voltage across this capacitor is not exactly 5v so you put a zener diode across it inorder to exactly regulate it to 5v.
PROPERTIES OF ZENER DIODE:
if you look in the datasheets of the zener diodes working at the voltage levels which you are using them at, The zener diodes are put in their noisy mode due to which they start injecting noise in your circuit and you have to place a decoupling capacitor.
Otherwise if you donot want to worry about these stuffs then just place a 7805 voltage regulator instead of zener diode and a decoupling capacitor you will get a clean dc supply. GOT IT?

 

[bmandl]

Ok Clear as a water

 

[godfreyl]

....you have to place a decoupling capacitor.
GOT IT?

Yeah, yeah, we got it - no need to shout.
Actually, that's pretty much what the OP said in post 1. What's your point? Or are you just letting us know you finally figured out what's going on?

 

[Disha Karnataki]

I have already told you my point. Again what you want me to tell??

 

[Disha Karnataki]

by the way you just read last two sentences that is that you have to place a decoupling capacitor i gave him an alternative to it that is he can do so by using ic 7805

 

[godfreyl]

Yes, a 7805 would probably be better than a Zener, but it would also need a decoupling capacitor at the output.