# Selection of power supply (linear power supply vs SMPS)

We know that, depending on the specification of our system, we design our power supply, which may be either a linear power supply or an SMPS.

If there are no constraints of size or efficiency for an application, how do we decide the trade off between the SMPS and the linear power supply? How do we decide or calculate that for a particular application an SMPS or a linear power supply would be better? How do we decide or calculate the losses in both the system, for a particular application, i.e., if the core losses would be more in a Linear Power Supply, or the switching losses and the core loss of an SMPS would be more.

How do we decide between the two, which one to use and where.

The SMPS being an isolated topology in the above question.

If you have no technical requirement that allows you to choose between two design options, then you will want to choose the option with the lowest cost.

Choosing between a linear and a switching power supply, the linear option will typically be the lower cost one. But if the power dissipation gets too great, the heat sink required for the linear supply could conceivably increase the cost enough to make the switching option preferable.

How do we decide or calculate, that for a particular application, SMPS or a Linear Power Supply would be better.

You'd have to consider the requirements of your application first, in order to determine what "better" means for a particular design. It might mean lowest cost. It might mean most efficient. It might mean lowest voltage ripple. It might mean smallest board area or least weight. Most likely it will be a balance between several parameters.

In some applications we might even choose to use both: A SMPS pre-regulator to achieve reasonable efficiency with a linear regulator to reach the final output voltage with low ripple.

How do we decide or calculate the losses in both the system, for a particular application, ...

You'd have to design two candidate supplies, and then analyze the efficiency of each one.

i.e., if the core losses would be more in a Linear Power Supply, or the switching losses and the core loss of an SMPS would be more.

Unless the output voltage is very close to the output voltage (say $$\V_{out}>0.9 V_{in}\$$) you will almost certainly be able to design a more efficient switching supply.

• I need the power supply for an embedded application and to run a small high torque dc motor.
– APM
Feb 1, 2019 at 5:57
• @ANIRUDDH, that's certainly interesting, but it isn't part of the question that was asked. Feb 1, 2019 at 5:58
• how to calculate the losses in the linear power supply and an smps
– APM
Feb 1, 2019 at 7:27
• @APM, losses in a linear supply are $(V_{in}-V_{out})I_{out}+V_{in}I_q$. Losses in an SMPS are much much more complicated and generally need to be worked out from simulation rather than a simple formula. With good design, and depending on requirements, losses in an SMPS can be between 5% and 15% of input power (i.e. efficiency can be 85 to 95%). Feb 1, 2019 at 16:02