All ABOUT SWITCHED MODE POWER SUPPLY (SMPS)

What does SMPS mean?

Switched Mode Power Supply is a converter. Switching devices at higher frequencies and storage components like capacitors or inductors are used to convert the power. It is used as an AC to DC converter and for power efficiency instead of a Linear Power Supply (LPS).

The Linear Power Supply (LPS) is a regulated power supply that losses a lot of power in the form of heat through a series resistor to control the output voltage, resulting in minimal ripple and noise. A linear power supply has a worse energy efficiency (40 - 50%) since it needs larger semiconductor devices to manage the output voltage and produces more heat. So, to reduce the heat and improve efficiency ‘Hewlett Packard’ used an SMPS in its first pocket calculator. 

An SMPS converts the voltage and current characteristics as it distributes power to DC loads like personal computers from a DC or AC source (often mains power; see AC adapter). In contrast to a linear power supply, a switching-mode supply's pass transistor alternates between full-on and full-off states with low dissipation and spends comparatively less time in transitions with high dissipation, minimizing wasted energy. In an ideal switched-mode power supply, there is no power loss. The ratio of on-to-off time can be changed to control voltage (also known as duty cycles). A linear power supply, in contrast, controls the output voltage by continuously releasing power from the pass transistor. A key benefit is the greater electrical efficiency of the switched-mode power supply.

Comparison between LPS and SMPS

Switched Mode Power Supplies are complex. The key benefit of this increased complexity is stabilised designs made possible by switched mode operation, which may provide more power for a given size, price, and weight of power unit. The AC is rectified and smoothed by a reservoir capacitor when the input is the AC mains (line) supply before being processed by what is essentially a DC-to-DC converter to generate a regulated DC output at the desired level. Therefore, an SMPS can be used in many different battery-powered systems to convert DC to DC, either step up or step down, or AC to DC, such as in a desktop computer power supply.

Blog diagram and working of SMPS

AC Input: Without utilising a transformer, the rectifier and filter circuit combination receive the 50 Hz AC input supply signal directly. That AC input sends to the rectifier bridge. 

Switch: In this portion, a fast-switching device, such as a MOSFET or Power transistor, is used. It switches ON and OFF in response to fluctuations, and its output is connected to the primary of the transformer located in this section.

Output Stage: To obtain the necessary DC voltage, the output signal from the switching portion is once more rectified and filtered. The control circuit receives this regulated output voltage. 

Control circuit: The signal is picked up by the output sensor, which connects it to the control system. Any rapid spikes shouldn't harm the circuitry because the signal is segregated from the other section. The signal and a reference voltage are both sent as one input to the error amplifier, a comparator that compares the incoming signal with the necessary signal level. 

Classification of SMPS

SMPS is classified into two types:

1. Non-isolated Topology 2. Isolated topology

1. Non-isolated Topology

The Buck converter Circuit has a transistor with a flywheel circuit (Dl, L1 and C1). The inductor L1 is used to conduct current through the load while the transistor is turned on. Any inductor's activity opposes variations in current flow and serves as an energy reserve. In this instance, the inductor stores energy taken from the increasing output; this energy is later released back into the circuit as a back e.m.f. as the current from the switching transistor is quickly switched off, preventing the switching transistor output from increasing immediately to its peak value.

It is a DC-to-DC power converter that steps up the voltage from its input (supply) to its output while stepping down current (load). This type of switched-mode power supply (SMPS) has at least two semiconductors (a diode and a transistor) and at least one energy storage component, such as a capacitor, inductor, or both. To reduce voltage ripple, filters built of capacitors are typically attached to such a converter's input (load-side filter) and output (occasionally in conjunction with inductors) (supply-side filter). Since boost converters are extremely nonlinear systems, a range of linear and nonlinear control approaches have been investigated to achieve good voltage regulation with significant load changes.

Perhaps the most popular isolated topology is the flyback. Typically, it is used in low-cost, low-power applications. In addition to the transformer, the flyback topology only needs one active switch and no additional output inductor. As a result, the topology is simple to utilise and inexpensive. Due to the single-ended architecture and the large input and output ripple currents, additional capacitors are needed at both the input and the output.

A full bridge converter is one of the often-employed types that provides isolation in addition to stepping up or down the input voltage. Other capabilities might include switching the polarity and delivering numerous output voltages at once.

Advantages of SMPS:

• The effectiveness is between 85 and 95 per cent.
• Less power is wasted, and less heat is produced.
• Reduced harmonic feedback
• Compactable size and portable.
• Low Manufacturing cost
• having a capability of providing required voltage

Disadvantages of SMPS:

• Switching at high frequencies causes the noise to exist.
• The circuit is complicated to analyse.
• electromagnetic interference is produced.