Switched-Mode Power Supply and Its Classification

Switched-Mode Power Supply (SMPS) is a device which uses a switching regulator for controlling and stabilizing the output voltage by switching the load current on and off. It offers efficient power conversion and reduces overall power losses. It’s basically a device in which energy conversion and regulation is done by using capacitors, the mix of inductors, and other electronic units that are continuously switching "on" and "off" at high frequency.

Classifications of The Switched Mode Power Supply(SMPS)

According to the type of input/output voltages:

• AC to DC
• AC to AC
• DC to AC
• DC to DC

On the basis of working:

• DC to DC Converter
• Forward Converter
• Flyback Converter
• Self-Oscillating Flyback Converter

DC-DC converter

The power received from AC is rectified and filtered as a high voltage DC converter. Then it’s switched at high speed and fed to the primary side of a step-down transformer. The step-down transformer is smaller in size thereby relieves the problem of size and weight. The filtered and rectified output on the secondary side of the transformer is sent to filters, rectifiers, and regulators. Apart of this is sent back to the switch for controlling the output voltage.

Forward converter

It is a type of SMPS which transfers energy from primary to the secondary part of the transformer while the switching element is "on," -opposite of a flyback converter. The output voltage is determined by input voltage which depends upon the transformer’s turn ratio and duty cycle. During the "OFF" period of a transistor, the diode carries the current, and thus energy flows to the load during both the periods. It is also known as a DC-DC buck converter.

Flyback converter

This type of converter is derived from buck-boost topology where the inductor split to form a transformer. This is done to multiply voltage ratios with the additional advantage of isolation. Here, the inductor's magnetic field stores the energy during the "ON" period of the switch. This provides a voltage ratio from input to output and the advantage of galvanic isolation. And then energy is then passed into the output voltage circuit while the switch is in the open state. This converter can be used in both AC-DC and DC-DC conversion with the galvanic isolation between the input and output sides.

Self-Oscillating Flyback Converter

In this is a type of SMPS where flyback converter doesnot require a separate oscillator, but the switching of the primary current is achieved by built-in self-oscillatory action. During the conduction time of switching transistor, the current through the transformer starts primarily by ramping up linearly with the slope equal to Vin/LP. The voltage induced in the feedback winding and secondary winding makes the fast recovery rectifier reverse biased and hold the conducting transistor "ON." When the primary current reaches the peak value IP, the core begins to saturate, and the current starts rising very sharply. This sharp rise can’t be supported by a fixed base drive provided by the feedback winding as a result; thus, switching begins to come out of saturation.

Linda Hudson is a IETP professional with more than 5 years of experience and fond of reading new topics and upcoming technologies on internet.