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Best Protection for noise and switching for Relay

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baby_1

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here is my circuit that i use

2_1327341237.jpg


i switch on and off a relay (24v) with bdx53 transistor.but i have a problem that is when relay swtich on for 1second my digital circuit reset!!! why it occurs? its related to noise of relay?how can protect it?
 

The noise from the relay will occur when you release it. There shouldn't be any noise 1 second after you've energized it. Your problem is probably somewhere else.
 

If you run the high-power lines close to your digital circuitry, interference can and does happen as you observed.
I noticed you do not show in your schematic any DC blocking capacitor at +Vcc (the top point). You can also use a small ~ 1 nF capacitor from base to ground, to reduce "sharp" transistor action.
If the interference still persists, I would advise to replace the transistor (or insert before it) an optocoupler (optoisolator), so the DC power circuit switched by the relay is completely insulated from your digital circuits. Maybe you should separate the power supplies, too.
 
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    baby_1

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Check ground or supply noise of you digital circuit to see if you have noise which resets it. Since the driver circuit is a bus buffer (not a register) maybe the program resets the the control signal driving the relay.
Normal relay driving from a microcontroller looks like decribed here: **broken link removed**

Enjoy your design work!
 

Thanks dear
the circuit that i attached use multiple supply(220AC Relay-Contact,24V DC for switching relay and 5volt dc to bias digital circuit)

when i switch it with relay or without it is works fine but when i attached ac power supply it occurs.my relay it out of my board and the ac supply is for from the board (it controls a 3Phase ac motor)

i use 74hc244 to isolated my digital part form relay(if somethings happen it burns and don't harm another section .exactly it doesn't good as optocopler for complete isolation)

how can reduce this noise? and what exacply happen?
 

Maybe the high inrush current when switching the motor on is causing your control logic power supply to get a spike which resets it. Maybe you can reduce the inrush current by switching only at the zero crossing of the 220V AC wave. Other option of inrush current reduction you find here as a thread.

Enjoy you design work!
 

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