SMPS filtering?

[jmariano]

Dear All,

I'm sorry if this question was already answered. English is not my native language and I'm not even sure what are the exact words to use for this subject, so I don't know how to look this for in the forum.

I plan to use a smps to supply +12v and +24v to my circuit. It is basically a digital circuit with an arduino turning on and off a bunch of LED strips, DC motors and solenoid valves. The LED's are PWM with 2 A consumption (2 strips, 1 AMP each) and the valve's inrush current can go up to 1A each (according to specs). DC motor uses 150mA. The arduino is getting +5V from a DC-DC converter attached to +24V followed by a 7805.

I'm in the process of designing the PCB board to accommodate all this and my question is: should I just attach the +24 and +12 to the board and use these rails as they arrive to the PCB from the smps enclosure or should I filter (?) them? I see many examples of the power supply rails being filtered (? - I'm not sure if this is what is going on) by 2 capacitors near the PCB PS input, typically 50u//0.1u, but I'm not sure if smps like that. I also see a LC filter at the input, but this I guess is to filter high frequency noise, which is not an issue in my application.

Regards
jmariano

 

[BradtheRad]

One guide is that a device which is affected by supply voltage changes (or droops) should be given its own stable supply.

Conversely loads which change suddenly (have the effect of creating voltage droops elsewhere) should be on their own supply.

Led's don't light at all unless applied voltage is above a certain threshold. PWM across a smoothing capacitor filter needs experimenting (if needed at all) so it allows even brief pulses to rise above the threshold voltage.

 

[KlausST]

Hi,

whats your concern:
* noise generated by the SMPS --> then look up the SMPS datasheet on noise specification about magnitude and frequency range.
* noise generated by your PCB --> then you need to investigate the niise sources, frequencies (including overtones)

***
In either case: It´s generally a good idea to install capacitors on your PCB. Maybe some bulk capacitors and in parallel some fast ceramics capacitors.

Klaus

 

[jmariano]

Hello,

Thanks for your reply.
I will take Klaus advice and install capacitors close tothe PS input at the boad.
Regards
jmariano