Switching Power Supplies

Switching power supplies are DC sources that use a switching element (normally a power transistor) to generate the desired voltage. Switching power supplies are also called switch-mode products or switching mode power supplies (SMPS). Switching power supplies incorporate electronic components that continuously switch ON and OFF at a very high frequency. This switching action connects and disconnects energy-storing devices (inductors or capacitors) to and from the input source voltage or the output load. SMPS design results in a smaller power supply since the size of the power transformers, inductors, and capacitors is inversely proportional to the switching frequency. Switch-mode operation also reduces the power consumption because when a switch is OFF, its current is almost zero. When a switch is ON, its voltage is very small. 

Switching power supplies may use buck, boost, or buck-boost conversion techniques. Buck or step-down converters are used to convert a higher DC input voltage to a lower DC output voltage of the same polarity. Using a transistor as a switch, buck converters alternately connect and disconnect the input voltage to an inductor. Boost or step-up switching power supplies are used to convert a lower DC input voltage to a higher DC output voltage of the same polarity. Buck-boost products can be used for either step-up or step-down conversions. They can also be used to reverse or invert voltage polarity. With buck-boost, the inverting regulator converts a DC input voltage to a DC output voltage that is opposite in polarity to the input. Buck-boost converters work by storing energy in an inductor during the ON phase and releasing it to the output during the OFF phase.

Switching power supplies differ in terms of mounting style and form factor. Board-mounted devices use either through-hole technology (THT) or surface mount technology (SMT). Switching power supplies with a printed circuit board (PCB) form factor are also available. Products with an open-frame design have exposed circuitry and components. Enclosed units protect these same circuits and components inside a case. Tool or chamber mounted switching power supplies can be mounted on a chassis or to a cabinet. Modular switching power supplies are designed to mount on desktops, racks, or walls. External linear power supplies, products that mount inside floor-standing cabinets, and units that mount on a standard DIN rail are commonly available. Rack-mounted switching power supplies may have rack mount size of 1U, 2U, 3U, 4U, or 5U. 

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Part Numbers for Switching Power Supplies