Know All About Switch Mode Power Supply

Power supply circuit plays an essential role in every electrical and electronic circuit to provide the electrical power to the owl circuit or loads like machines, computers, etc. These different loads require different forms of power at various ranges and characteristics. So, the power is converted into the desired form by using different power converters. Basically, different loads work with various types of power supplies like SMPS (switch mode power supply), AC power supply, AC to DC power supply, programmable power supply, high voltage power supply & uninteruptable power supply.

What is SMPS (Switch-Mode Power Supply)?

SMPS is defined as, when the power supply is included with the switching regulator from converting electrical power from one form to another form with necessary characteristics is called switch mode power supply. This power supply is used to attain regulated DC o/p voltage from the DC i/p voltage or unregulated AC.

SMPS is a complicated circuit like other power supplies, it supplies from a source to the loads. MPS is crucial for different electrical and electronic appliances which consumes power and also for designing electronic projects.

Topologies of SMPS

Topologies of SMPS are categorized into different types such as AC-DC converter, DC-DC converter, Forward Converter and Flyback converter.

Working principle of Switch Mode Power Supply

The working of a switch mode power supply topologies is discussed below.

DC-DC Converter SMPS Working

In this power source, a high voltage DC power is directly acquired from a DC power source. Then, this high voltage DC power is switched usually in the range of 15KHz-5KHz. And, then it is fed to a step down transformer unit of 50Hz. The o/p of this transformer is fed to the rectifier, them this rectified o/p power is used as a source for loads, and the oscillator ON time is controlled and a closed loop regulator is formed.

The switching-power supply o/p is regulated by using Pulse Width Modulation shown in the above circuit, the switch is driven by the PWM oscillator, then indirectly the step down transformer is controlled when the power fed to the transformer. Therefore, the o/p is controlled by the pulse width modulation, as this o/p voltage and PWM signal are inversely proportional to each other. If the duty cycle is 50%, then the max power is transferred through the transformer, and if the duty cycle drops, then the power in the transformer also drops by decreasing the power dissipation.

AC -DC Converter SMPS Working

This type of SMPS has an AC i/p and it is converted into DC by using rectifier & filter. This unregulated DC voltage is fed to the power factor correction circuits as it is affected. This is because around the voltage peaks, the rectifier draws short current pulses having significantly high-frequency energy that affects the power factor to reduce.

It is almost related to the above discussed converter, but in the place of DC power supply, here we have used AC i/p. So, the mixture of the rectifier &filter, this block diagram is used for converting the AC to DC and the switching operation is done by using a power MOSFET amplifier. The MOSFET transistor consumes low on-resistance & can resist high currents. The frequency of the switching is selected such that it must be kept low to normal human beings (above 20KHz) and action of switching is controlled by a feedback using the PWM oscillator.

Again, this AC voltage is fed to the o/p of the transformer shown in the above figure to step up or step down the levels of voltage. Then, the this transformer’s o/p is rectified & smoothed by using the o/p filter and a rectifier. The o/p voltage is controlled by a feedback circuit by likening it with the reference voltage.

Fly-back Converter SMPS Working

The SMPS circuit which has very low o/p power (less than 100W) is called as fly-back converter SMPS. This type of SMPS is very low and simple circuit compared with other SMPS circuits. This type of SMPS is used for low power applications.

The unregulated i/p voltage with a constant magnitude is changed into a preferred o/p voltage by switching fast using a MOSFET; the frequency of switching is around 100 kHz. The voltage isolation can be attained by using a transformer. The operation of the switch can be controlled by using a PWM while executing a practical fly-back converter.

Fly-back transformer shows dissimilar characteristics compared to normal transformer.Fly-back transformer includes two windings which acts as a magnetic coupled inductor. The o/p of this transformer is delivered through a capacitor and diode for filtering as well as rectification. As shown in the above figure, the o/p of the SMPS can be taken as voltage across the filter capacitor.

Forward Converter type SMPS Working

This type of SMPS is almost same to the fly back converter type SMPS. But, in this type of SMPS a control is connected at the o/p of the secondary winding of the transformer to control the switch. As compared to the fly back converter, the filtering and rectification circuit is complicated.

This is also called as a DC-DC buck converter, along with a transformer which is used for scaling and isolation. In addition to the “D1” diode & “C” capacitor, an inductor L & a diode D are connected at the end of the o/p. If ‘S’ switch gets switched ON, then the i/p is given to the transformer’s primary winding. Therefore, a scaled voltage is produced at the transformer’s secondary winding.

Therefore, the D1 diode gets forward biased & scaled voltage is passed through the LPF proceeding the load. When the switch S is turned ON, then the currents through the winding reaches to zero, However the current through the inductive filter & load cannot be changed shortly, and a lane is offered to this current by the coasting diode D2. By using the filter inductor, the required voltage across the D2 diode & to keep the electromagnetic force necessary for maintaining the stability of the current at inductive filter. Even though the current is falling against the o/p voltage, almost the constant o/p voltage is sustained with the existence of the large capacitive filter. It is regularly used for various switching applications with a 100 W to 200 W power range.

This is all about switch mode power supply and its types which involves Buck converter, Buck-boost converter Self Oscillating fly-back converter, Boost converter, Cuk, Sepic, Boost-buck. But, a few types of SMPS’s are discussed in this article they are AC-DC converter, DC-DC converter, Forward and Fly-back converter. Furthermore, any information regarding the types of SMPS, fell free to give your feedback to give your suggestions, comments in the comment section below.