### Key Takeaways

●     Learn about linear power supplies.

●     Gain a greater understanding of the advantages and disadvantages of linear power supplies.

A DC power supply is also a linear power supply.

We define “linear” as extending or arranging along a straight line, or nearly straight line. We also define it as the stage-to-stage progression in a single series. However, linearity is also a mathematical relationship which we represent graphically as a straight line.

Furthermore, we closely relate this property to proportionality. You can observe examples of this type of relationship within the area of physics. One such example is the linear relationship between current and voltage in a power supply or an electrical conductor.

The Linear Power Supply

The linear power supply is in use in various applications. Its widespread use is a direct correlation to the overall advantageous performance it affords. It comes as no surprise that in the field of electronics, most designers and engineers prefer to utilize components with a track record of success and longevity. This also describes the linear power supply since it is an established and trusted technology.

Although the linear power supply is generally not as efficient as a switch-mode power supply (SMPS), they do afford better performance. If you scrutinize the electronics landscape, you will see the widespread use of linear power supplies in applications that require strict noise mitigation.

One such area where we see linear power supplies is in the field of audio and video, which includes amplifiers. Since the linear power supply does not produce the noise and switching spikes of an SMPS, it makes it ideal for these types of sensitive applications.

The linear power supply affords numerous advantages, including an overall relatively lower cost and simpler design. However, like nearly all things in existence, with advantages come disadvantages. In the case of the linear power supply, these disadvantages consist of lower efficiency and excessive heat, which equates to loss.

Linear power supplies are reliable, simplistic, produce minimal noise, and are cost-effective to manufacture. Linear power supplies are also called linear regulators (LRs). The need for fewer components to build a linear power supply lends itself to more straightforward designs and lower manufacturing costs. This also means that designers and engineers tend to prefer them for the same reasons.

Keeping in line with the rules of mechanics and electronics, a device (linear power supply) that utilizes fewer components will, by nature, develop fewer issues. This increased reliability is another benefit to using the linear power supply.

A linear power supply is ideal for low-power applications which makes it equally unsuitable for high-power applications. In summary, the disadvantages of linear power supplies are higher heat loss, a larger size, and being less efficient in comparison to the SMPS.

The primary issue attributed to the linear power supply’s inadequacy in high-power applications is its size and weight. This stems from its requirement for large transformers and other sizable components in its construction. Aside from size disadvantages are the issues of high heat loss that present during the regulation of high-power loads. Due to its design, high output currents pass through the power transistor and the thermal stress requires heat sinks to dissipate this energy.

Lastly, the issue with efficiency is one of the significant problems of a linear power supply when assessing a design. The lower efficiency means that there is a substantial difference between the input and output voltage, which is a crucial factor in the consideration of utilizing linear power supplies in your design. There are other factors to consider, like load voltage and dropout voltage, when assessing a linear power supply for your design. Typically, when evaluating power supplies for a particular application, one must consider all factors, not just cost, efficiency, and size.

## Linear Power Supply vs. SMPS

An SMPS differs from a linear power supply in how it converts the primary AC voltage into the output DC voltage. The SMPS utilizes a power transistor to produce a high-frequency voltage that passes through a small transformer, and then filters it to remove the AC noise. However, a linear power supply delivers DC by distributing the principal AC voltage through a transformer before filtering it to remove the AC noise.

SMPS incorporate higher efficiency, reduced weight, smaller size, increased durability, and they allow a more extensive input voltage range. However, the linear power supply is typically more cost-effective, less capable, larger in size, weighs more, and less efficient.

In terms of percentages, a linear power supply operates, typically, at about 60% efficiency, whereas an SMPS operates around 80% efficiency or higher.

The linear power supply possesses a longer historical track record versus the SMPS. However, the Linear power supply is not without its flaws. Overall, the application requirements will generally dictate which power supply best fits your individual needs.

Once you select the type of power supply that is best suited to your specific circuit design, you can simulate all aspects of circuit behavior with the front-end design features from Cadence and the powerful PSpice Simulator. Once you’ve designed your circuits, you can use the PSpice modeling application and simulator tools to examine efficiency and other parameters of your linear power supply or SMPS.