I have to run 3 5V relays and a micro controller from the 5V supply. Will = there be any noise related problems from relay switching if I run both the = relays and MCU from single 5V regulator? If yes, is there any solution to i= t without adding another 5V regulator. All the 3 relays have free wheeling = diode to counter back emf.
there be any noise related problems from relay switching if I run both the relays and MCU from single 5V regulator? If yes, is there any solution to it without adding another 5V regulator. All the 3 relays have free wheeling diode to counter back emf.
With reasonable filtering on the 5v rail, a few decent ceramic caps, there shouldn't be any problems. uPs aren't fussy about their power supplies. What drives the relay coils? What do the relays switch?
It's noise from the relay *contacts* that has a chance of crashing the uP, especially if it has an external memory bus. PCB layout matters, and a multilayer board with a solid ground plane is best.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
there be any noise related problems from relay switching if I run both the relays and MCU from single 5V regulator?
Noise that affects digital signals? Probably not if your relay current draw, bypassing, and layout are "reasonable".
Watch the current paths, including the return current path, particularly if you don't have power planes.
the 3 relays have free wheeling diode to counter back emf.
Improve the layout, decouple the relay drive with an R-C, maybe slow down the driver.
BTW, most problems that are encountered with noise and relays will not be as a result of the coil- that's very, very easy to deal with, but rather due to the variety of loads that might be connected to the contacts (surges, parasitic and not so parasitic inductance and so on) and the entertaining variety of ways the EM noise can couple back into the circuitry.
Will there be any noise related problems from relay switching if I run bot= h the relays and MCU from single 5V regulator? If yes, is there any solutio= n to it without adding another 5V regulator. All the 3 relays have free whe= eling diode to counter back emf.
er
Thanks. Relays switch the speakers between two audio amplifiers. One amplif= ier on the same board as relays and MCU and other is external. Amplifier is= powered by 12V and MCU and relays are powered by 12V-5V regulator.=20
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Will there be any noise related problems from relay switching if I run bot= h the relays and MCU from single 5V regulator?=20
or. All the 3 relays have free wheeling diode to counter back emf.
In my application, loads connected to the relay contacts shouldn't be a pro= blem. The load is from the audio amplifier and it goes to the outside of th= e board if the relay is closed. No ground connection as the amplifier outpu= t is bridged load with both lines differential.
What is the ideal RC value? 5V supply source and all the three relays toget= her draw max of 300ma. They each have 70 ohm coil.
If it's a concern, you could use a fat cap across the uc supply pins, isolated from the relay coil draw with a schottky diode, like this:
V+ -----+---------> to relay coils | [D1] | +---------> to uc + | + [cap] | Gnd ----+---------> to uc - and relays
Ed
Since you have 12 V available anyway, why not use 12 V relays anyway or put a 7 V zener in series between the +12 V supply and the top of the 5 V relay coils ?
l there be any noise related problems from relay switching if I run both th= e relays and MCU from single 5V regulator? If yes, is there any solution to= it without adding another 5V regulator. All the 3 relays have free wheelin= g diode to counter back emf.
Thanks all for the suggestions. I will go ahead and try it out with enough = bypassing.
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