[Heath] Off Topic Switching Power Supply

[JF]

On 11/1/2015 10:11 PM, Ron 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?

Ron,
Briefly, a regular linear power supply uses a transformer to step the 
AC line voltage up or down to near the required level, plus 
rectifiers and choke/capacitor filter circuits. They are heavier and 
often costlier than switching supplies, which use a lightweight 
transistor or IC oscillator in place of a transformer to directly 
change the AC or DC line voltage to a pulsating DC. The problem for 
hams is that the switching process generates RF hash, so if you are 
going to use a switching supply you have to get or build one that has 
good RF suppression. If you are connecting to a solar charger you 
will have to investigate that separately for possible RF noise.

Laptop power supplies are usually made as cheaply as possible, and, 
as that kind of computer is not susceptible to low levels of RF 
noise, they don't incorporate much (if anything) in the way of RF 
suppression. They will radiate RF hash directly from the chassis and 
from both the power input and output lines, so, if you are looking 
for a short easy fix for that kind of switching supply, there isn't 
one - it would require essentially a rebuild, with a shielded 
enclosure and extensive RF bypassing to ground. You may get some 
emails suggesting the installation of ferrite beads and clamp-on line 
RF chokes, but, although that will help a little, they will not be 
sufficient to quiet switching noise below the level a sensitive 
receiver needs. You likely would be better off by just building or 
buying a larger linear supply, or a fully RF-suppressed switching 
supply designed for ham radio.

For some some reading about linear and switching, Google for "linear 
vs switching power supply ham radio" and "how to build a switch mode 
power supply". Some results:

SWITCHING VS. NON SWITCHING POWER SUPPLY
http://www.eham.net/ehamforum/smf/index.php?topic=43091.0
http://www.eham.net/articles/12916
http://www.eham.net/articles/17225

SWITCHED-MODE POWER SUPPLY
https://en.wikipedia.org/wiki/Switched-mode_power_supply
    Also scroll down to
"Comparison of a linear power supply and a switched-mode power supply"
    and   "Radio frequency interference"

REDUCING SWITCHING SUPPLY RACKET (RF INTERFERENCE)
http://ka7oei.blogspot.com/2012/12/reducing-switching-supply-racket-rf.html
   and
http://ka7oei.blogspot.com/2014/08/completely-containing-switching-power.html
   and
http://ka7oei.blogspot.com/2013/09/quieting-high-current-switching-power.html

ANATOMY OF SWITCHING POWER SUPPLIES
http://www.hardwaresecrets.com/anatomy-of-switching-power-supplies/

LINEAR VERSUS SWITCH-MODE POWER SUPPLIES
https://www.valuetronics.com/Manuals/Lambda_%20linear_versus_switching.pdf

AC/DC POWER SUPPLIES
http://www.futureelectronics.com/en/power-supplies/ac-dc-power-supplies.aspx

BUILD A 40 AMP SWITCHING SUPPLY
http://electronics-diy.com/electronic_schematic.php?id=900


73
John   KE5ZB