[Heath] Off Topic Switching Power Supply

[rgroh at swbell.net]

Woof.  You asked a big question there but it is interesting.  Let's see if I can condense the subject down a bit. Most types of power supplies use a transformer to step up or down the voltage and to provide isolation between the input source and the output load. 

A transformer needs an ac waveform to work (i.e. you need a varying magnetic field).  You can use the regular 60 Hz power which is convenient but, because the frequency is low, it takes a fair amount of iron to get the job done (i.e. weight and size) and because the frequency is low, you need a beefier filter (more inductance, more capacity) which means more size and weight. 

If you increase the frequency, pretty much everything gets smaller. Which is good.
So we can plug into the wall socket - easy to do, nice'ish sine wave (i.e. low distortion) but large components.
Or we can rectify our ac from the socket, make DC and then chop the dc at a high frequency and use much smaller transformers, filter caps, etc. This is our 'switcher power supply'.  And because we are 'chopping' the dc we can use solid state switches to do the chopping and we get great efficiency there. So weight, size, heat .... all go down.

OK, so what's the downside?  Well, when we chop the dc we generate lots and lots of crud - electrical noise both conducted and radiated. Plus complexity goes up.  Oh, dear.
So bottom line: regular conventional power supply - typically bigger, less efficient but much less noise.  Switcher power - smaller, more efficient but more noise to cope with.
Can the noise be coped with?  Absolutely but it is a tougher job by far. Remember you are dealing with both conducted noise and radiated noise - ranging in frequency from 10's of kHz on up to 10's of MHz.  

Long winded but I hope it helps.
Bob Groh, WA2CKY
  


     On Monday, November 2, 2015 7:47 PM, Ron <kd6edv at gmail.com> wrote:
   

 I built an 18vdc 1.5 amp power supply using a transformer, bridge rectifier and a 7818 regulator. Works fine, but I need to go to 3 amps. I have been trying laptop switching power supplies that put out 3 amps that produce noise on my hf rig. If I unplug the laptop power supply, the noise goes away. The power supply is used for charging batteries through a solar charger.

Questions: what is the difference between a regular power supply and a switching power supply? Can I filter out the noise on a switching power supply?

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