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Power Supply filtering for microcontrollers

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Hi,
Can someone reccomend a good filtering technique for the power supply of the MCU. I am using some ready made filters but when a inductive loads are switching there is no use if them, the micro is still very sensitive to the noise
 

can you till me more information about your supply type is it linear or SMPS?
 

Try to use inductors on both supply lines; something like 100µH to several mH, depending on the current drawn by your µC circuit.
Also, there should be at least two capacitors placed directly after these inductors: combination of 100µF+100nF should finsh off the job..
Regards,
IanP
 
You need to look at the whole design and use good techniques for pcb layout, power distribution and decoupling.

Consider the current paths from the power supply through the inductive load and back. It is sometimes better to use a star topology for the power connections so the current going to a load is not running through the tracks going to the microcontroller.

Look at what is creating the power supply disturbance and try to stop it at the source.
Perhaps you need a diode across the inductive load to dissipate the energy left in the inductance when it is turned off. Perhaps a snubber close to the load.

Describe your hardware in more detail if you want more help.
 

There are many different techniques to suppress noises in the circuit.
Most common is to place an inductor coil in series with your 5 or 3.3V supply.
Another is to solder block capacitors ( usually 100nF ) very close to the IC's supply pins. Another is about extra ground planes on your PCB.
Those techniques may all be used at the same time or separately, depending on the requirements.
Sometimes, however, the source of the noise is not the supply line. The noise travels over your I/O pins. In that case optical isolation is quite a good solution.
Sometimes the Reset capcitor value is a culprit. It may be too small or of a wrong type. Stick to the manual in such case.

Regards, yego
 

the inductive loads generate back emf , try grounding their solenoid (else other metallic parts)
and surely use 10 uF 35 V tantalum capacitors in the psu ...this should surely solve ur problem
 

My problem is not the noise from my PCB and the loads that i am switching.
The problem is the noise that travel from some other device trough the power line.
For example when my supply and the soldering iron are plugged in the same AC socket when i start to switch the iron ON and OFF the microcontroller starts to do strange things - reading a input which is pulled LOW as HIGH for example. I have a filter before my 220/9V transformer but it doesen't help. :(
 

Do you have suitable decoupling capacitors close to the microcontroller supply pins?

Soemthing is wrong if AC line glitches are making it past your voltage regulator. Do you have enough voltage headroom on the input to your regulator for it to keep working if the AC supply drops a bit? 7805 type regulator needs at least 8V DC on it's input all the time.

Have you considered the posiblity of direct induction from the transformer in your soldering iron to long wires in your prototype causing problems with high impenace inputs to your micro?
 

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