Electronics > Beginners
When are SMPS not used these days?
David Hess:
--- Quote from: ejeffrey on June 25, 2019, 06:10:31 pm ---
--- Quote from: Doctorandus_P on June 25, 2019, 04:48:56 pm ---After that the traces on the CRT were all wobbly because of the stray magnetic field of those transformers. Even though the transformers were in a separately shielded compartment ( More than 1mm thick aluminum between the transformers and the CRT's).
--- End quote ---
Of course. Aluminum hardly shields low frequency magnetic fields at all. You would need a few cm thick plate to do much of anything. Or: a thin layer of steel or mu-metal or both.
--- End quote ---
My Tektronix 7603 has the fan modification which was *not* used in the other 76xx oscilloscopes. The fan has a standard shaded pole motor but Tektronix bolted a heavy folded piece of steel around the stator to shield the CRT from leaking flux.
digsys:
I've designed many linear, fanless powers supplies for mining and intrinsic locations, where they are almost exclusively used.
Also, we still get a lot of orders from critical hospital locations. They are mandated not just for noise, but also are less likely to HV spark, especially in a fault condition.
Haven't seen any talk of S/Mode being approved in these areas to date. Also, still get orders from other "high risk" places.
T3sl4co1l:
I did a multichannel SMPS some time ago, under 1mV noise over an unusually wide bandwidth. Straightforward design: tight layout, extra filtering on the input and outputs, and a little faffing with snubbers. (The customer is in this thread, actually; I'd better not talk about it in too much depth. ;D ) I don't think it can be much better without actually shielding the circuit board.
Tim
exe:
--- Quote from: T3sl4co1l on June 26, 2019, 03:49:33 am ---Straightforward design: tight layout, extra filtering on the input and outputs, and a little faffing with snubbers.
--- End quote ---
How many layers did your board have? Did you use post-regulators? 1mv of noise was p-p or rms value? :)
T3sl4co1l:
Multilayer (>=4). No postreg. Peak voltage, at 100kHz RBW (measured with spectrum analyzer).
Tim
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