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electrical noise from DC motor

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Saboy

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basically, the system is shown below:
PIC-->TD340(Mosfet driver)-->Full brigde mosfet-->DC motor (12V, MAX current=12A).


Everything seems ok. But I saw some electrical noise in the power input of PIC (5V), sometimes, the peak of the noise will reach 1V. When the motor change the direction, the peak of the noise will reach 4V. The peak of the noise synchronize the rise of PWM.

Can you give me some suggestions to get rid of this kind of noise?
 

You should regulate well the PIC power lines. Use 7805. Connect 100nF bypass capacitor near the PIC power pins. Additonally separate the control and power stage grounds (and positive supply). Use wide conductor for GND. I hope these will help...
 

Bypassing only with capacitors may not be efficient enough.
Try to use inductors (or DC chokes) of, say, 100µH - 1mH between +5V and +V of the PIC and then de-coupling caps..
You ca do the same on the unregulated side of the 5V voltage regulator..
Regards,
IanP
 

It won't do any good how well you regulate the 5V for the PIC if your grounds keep being tied together, the noise will come to your PIC by the shared ground.

I recommend you decouple the grounds, using optocouplers, this way you will aisolate the motor ground from the control (PIC) ground, avoiding the noise to get to the PIC, the catch is, you need separate power suplies to do this, cause if you are using the same power supply is the same as nothing, noise will come through the power supply.

Needless to say, use capacitors (0.1uF) at the digital inputs and use the capacitors for your crystal input aswell.

Hope this helps.
 

Thank you for your suggestions.

Actually, I did these before I posted my question:
pic_power.gif

1. Used ferrit between the power supply and 7805.
2. A capacitors is placed close PIC16F.
3. Separat the digital ground and anolog ground(MOSFET motor driver) and connect them together in one point.

Since I use the battery for power supply, seems it is not easy to install two batteries.
 

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