[Heath] Off Topic Switching Power Supply

[ChrisIwata at aol.com]

A switching PS converts the AC to high voltage DC, then uses a square wave  
oscillator to feed a step-down transformer. The output is rectified back to 
DC.  The oscillator typically runs at 100Khz or so creating lots of RF  
noise. Running at high frequency allows for a much smaller transformer,  uses 
less metal, is lighter. The filter capacitors at the DC output can be  
smaller as well. Using square waves make the PS more efficient,  converts more of 
the energy to power instead of heat. The on-off cycle of the  square wave is 
adjusted to regulate the output voltage. For a more technical  explanation, 
there's always Google.
 
Unless you are well-versed in electronics, forget about attempting to  tame 
the noise.  Buy a switcher that as part of its description says little  or 
no RF noise is generated. Astron makes a bunch. 
 
BTW, the Apple II computer from bygone days was the forerunner of PCs and  
other gadgets using switchers. Kudos to Steve Jobs, the guy was eccentric 
but  brilliant. 
 
Chris, KL7DM
 
 
 
In a message dated 11/2/2015 5:47:56 P.M. Pacific Standard Time,  
kd6edv at gmail.com writes:

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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