radiated emissions inside power supply effecting microcontroller?

[SArepairman]

Can I put a MCU on the same board as a switchmode power supply? It is galvanically/optically isolated on its own ground plane. The MCU is 3 inches away from any mains connections, which is switching 5A@110V@10KHz. The gap between the two ground planes is ~0.3 inches.

Should I put the option for a shield can around the mains SMPSU? There is no analog stuff that is exposed to anything, just a MCU/RS232 interface.

Could a shield like this possibly be effective?

*star washer under screw

[Rerouter]

there should only be 2 cases where a micro can be upset inside a noisy enviroment, the first is noise coupling through long or high impedance traces, the second is its supply rails / reset line, follow good decoupling practices on the supply rails, and add a pull up or pull down resistance on every pin that is not being driven hard, to ensure that both noise cant cause a glitch and secondly positive or negative going spikes have somewhere to go if coupled that strongly,

[SArepairman]

If there is a long trace between two devices (such as a RS232 chip) should I distribute the pull down resistor between the two chips b/c of the trace inductance (5 inches )?

Would the shield that I described get rid of a need for the extra pulldown?

[T3sl4co1l]

I don't see how there'll be enough noise to cause problems at pretty much any distance... it's just logic...

Tim

[T3sl4co1l]

If there is a long trace between two devices (such as a RS232 chip) should I distribute the pull down resistor between the two chips b/c of the trace inductance (5 inches )?

Would the shield that I described get rid of a need for the extra pulldown?

Pulldowns have very little effect on signal quality.  You need resistors on the order of Z_0 to do that.  Typical trace impedances are around 100 ohms.

Tim

[poorchava]

10kHz seems way low for a mains psu. It's gonna emit audible noise. Why don't you move the frequency to somewhere around 30kHz?

[SArepairman]

10kHz seems way low for a mains psu. It's gonna emit audible noise. Why don't you move the frequency to somewhere around 30kHz?

as the pic programs it I can put a time delay on it, so it fools the customer into thinking that it is quiet and then wham bam 5KHz switching

i wonder if its possible to play music with a switcher, or even speech...