SWITCHING POWER SUPPLY
Switching Power supplies are one of the best examples of high efficiency power sources in this age of energy conservation. Known also as "Switchers" and "Switch Mode" supplies, these feature a wide range of outputs from voltages lower than a volt to many thousands of volts. Switching power supplies come as "Enclosed" or "Open Frame" also known as "Board Supplies" that require both mounting standoffs and connectors
"Enclosed" supplies are generally mounted in a aluminum case with a cover and terminal strips for connections. Multiple outputs are easily derived and fit in a compact case. This type of supply rectifies & filters the incoming AC Mains then switches the resultant High DC Voltage at a high "on/off", variable frequency to reduce the size & weight of internal components such as transformers & capacitors. This in turn lowers heat, weight, size & cost. Generally these supplies are regulated, meaning that the output voltage remains close to it's rating; usually within 1% and better over the load range. Should the output become shorted or overloaded, Switching Power Supplies generally enter a "Chirp" mode where they will continue to "test" the load and thus recover upon removal of problem. Switching Power Supplies make possible our high tech devices such as Cell phones, laptops, notebooks and even the Mars Rovers (etc.). All computers feature switching supplies to keep them small while providing hundreds, even thousands of watts of power. Switching have brought us Compact Fluorescent Lamps (CFL) to replace the incandescent bulb and the latest innovation in lighting, Light Emitting Diodes (LEDs). As small a unit that easily plugs into a wall outlet, to units that drive locomotives, switching supplies are the choice for many applications.
LINEAR POWER SUPPLY
Linear Power Supplies are the choice where robustness, low noise, and a less complicated power supply is needed. No need for high frequency/EMI filtering, or noise reduction. Linear Power Supplies are chassis mounted with solder terminals. Generally limited to three or four outputs, they use the tried and true method of using a transformer operating at the incoming AC line frequency followed by rectification and filtering to provide a lower DC voltage in a step-down supply or a higher voltage in a step-up unit. Some units stop there and are then listed as "Unregulated" and will provide an approximate output dependant on the load; like a linear power supply listed as "12VDC at 1Amp." That Power Supply might have an output of 17.5V with no load, 11.9-12.2V at full load (1A) and still provide 10VDC at a 1.5A load. With the addition of Pass Transistors, control circuits, etc, the supply becomes a "Regulated" power supply. This means the output voltage(s) remain within a few millivolts of output setting over the full range of no load to rated load. Different control circuits can provide power supplies that "fold back" when overloaded, meaning that both voltage & current become limited. Another mode is "Constant Current" where the output voltage decreases while still providing a current at the rated output. Many Lab/Adjustable Bench Supplies use this last mode. Many audiopiles and labs favor this use where their low radiated noise, low ripple, hardiness is needed.