All About Power Electronics - Types of PSU

A power supply unit (PSU) is a very critical part of  any electronic device or  circuit as it provides the power necessary for the device to operate. The primary aim of all power supplies is to take in an unregulated power from a source and convert it into a stable regulated power efficiently for the load. In power electronics, there are  basically two types of power supplies, namely:

• Linear power supply (LPS)

• Switch mode power supply (SMPS)

Every other kinds of power supplies  we see around us falls into either of these two categories. It must either be a LPS or a SMPS.

Linear power supply vs Switch mode power supply

So many factors determines how good a power supply is, including the efficiency, size, component count, and the maximum output power. A power supply circuit designer must consider all these factors while designing a power supply. Hence, the load is what really determines which power supply is best.

These two classes of power supply uses different methods of power conversion and regulation, which is peculiar in different kinds of loads. Let start from the LPS. 

From the term 'linear",

A linear power supply or LPS is a type of power supply that convert an unregulated AC voltage from the source into a regulated DC voltage to the load in a continuous manner. In this way, the excess  amount of electric power is dissipated in form of heat by a series pass component (Could be a resistor or a transistor) making the overall power conversion to occur continuously (or linearly). 

Below are both images of a typical linear power supply.

A linear power supply is a step down converter that can be used majorly to step down a high voltage AC into a constant low voltage DC or in some cases a high voltage DC can  also be stepped down into a low voltage DC. The high voltage AC is often gotten from the wall outlets from our homes and it operated at a low frequency(50-60 Hz). Since the excess power in a LPS is often regulated by dissipating it in form of heat, therefore it not always very efficient in high power applications as we will see later in this tutorial. There is a much more efficient type of PSU called a switch mode power supply.

 From the term "switch,

A switch mode power supply or simply SMPS is a type of power supply unit that regulate the output power from the source to the load efficiently  by switching the input power on and off via a high frequency switching semiconductor device(usually a transistor a mosfet). Making the overall power conversion to occur in pulses.

A SMPS can get it input source from either an AC or a DC voltage source and even though the output is always DC, an AC output can also be gotten from the output, making a SMPS very reliable. Since the method of conversion of power in an SMPS is not linear but switching, this highly increases the overall efficiency of a SMPS over a LPS as we will see why later in this tutorial.