Why my MCU get reset ?

[manish12]

When i trying to make on or off the high voltage line throu the relay of +12v
my Mcu get reset.
i try with other mcu but the result is same.
if i dont connect the high voltage devices such as motor , tube light , 3ph motor after relay + 3ph contactor than it works nice .
i am using ATMEL seri. MCU51 core archi.
thank you for your solution.

 

[eblc1388]

First make sure that you have a diode connected across the +12V relay/contactor coil. This would eliminate the switching transience produced by the relay coil.

If you have already done so, then the switching transiences of these high voltage load has found a way to affected your uC, either through the power supply or connection cables of your circuit board.

It is a very common but difficult problem to tackle as it is hardware related and requires good practices in designing circuit layout and bypassing power supply in order to minimise it. Sometimes it even requires shielding of the whole uC circuit in extreme situations.

Your first step is to try using battery supply for the uC to test if switching still causing reset when these high voltage load is switched. If it does not, then the transiences are mainly coming to your uC via the power supply and you'll need more filtering and bypassing.

If the uC is still resetting, then you should try shielding the whole uC circuit board inside a metal case and test again.

 

[tunedwolf]

If the power supply to the load is not de-coupled properly, it is possible that it is causing a brown out on the supply to the micro, or perhaps the load is putting down a transient that's pulling the gnd(Vss) below zero, most micros would become unstable with either condition.
As everyone has pointed out, fit protection diodes everywhere they are needed, ensure that the power supply you have can actually handle the load properly, make sure the load you are supplying has sufficient decoupling and feed your micro's Vdd with a small coil and a seperate decoupling capacitor.

 

[Papabravo]

Did you remember the flux capacitor?

 

[manish12]

Thank you to all,
But , my prob. is till there .
Yes , i dont know the FlUX capacitor.
It may possible that i know the concept, not know the name of that.
Any way i still not go for the metal case , next time i will go for the same.
I think it may be prob. of electro-magnetic feild EMF.

 

[philba]

doesn't the flux capacitor require around 1.2 jigawatts?

 

[Nigel Goodwin]

Well, as the poster hasn't entered his location in his profile, people can obviously only guess where he might be from (moderators that can check his IP though know it's Mumbai, India).

So yet another reason to enter your location in your profile, to stop people making 'jokes' that non-English/American's won't understand.

Assuming he didn't understand?, it's a reference to the film "Back To The Future", and 'flux capacitor' is an imaginary device involved in the time travelling car.