Linear vs Switching: Which Power Supply is Best?

24Aug17

For many decades there was only one choice. Power supplies had heavy iron transformers to convert house current (110/120 volts AC) to the lower voltage required by many solid-state devices. As the demand for more and more current increased so did the weight of the transformer and the complexity of the circuitry making the DC. These are referred to as linear power supplies.

Then a strange thing happened: The heavy transformer went away. Switching power supplies (also called switch-mode power supplies or SMPS) arrived and changed how DC was made. Without the heavy transformer (solid-state devices are used) power supplies could be made smaller and lighter while providing the same output current.

So… which method is best?

The answer to that question depends on your intended application. In applications where size and weight are major considerations the switching supply wins, hands down. Because large iron-core transformers are also expensive, switching supplies can be less expensive than linear supplies. Size weight and cost are three BIG advantages!

In applications requiring a low-noise highly regulated DC output, such as laboratory equipment, sensitive radio receivers, test equipment and bio-medical equipment, linear power supplies still have a slight edge. The requirement for completely noise free output overrides the advantages of the switching power supply in certain circumstances.

Noise?

Switching power supplies use high frequency switching transistors to make the output current. The generation of high-amplitude, high-frequency energy requires that a low-pass filter must block the high frequency noise at the output to avoid electromagnetic interference (EMI) and ripple voltage at the switching frequency and its harmonics. Very complex filtering developments have almost completely eliminated this problem. Very low cost SMPSs may couple electrical switching noise back onto the AC power line, causing interference with Audio/Video equipment and any other electronic equipment connected to the same AC phase. This is still a major problem in poorly designed, cheaply made SMPS units flooding into the US market from overseas.

What’s the bottom line?

Dollar for dollar switching power supplies usually provide more power for less cost. They are also smaller and lighter than standard iron-transformer linear power supplies. In applications where switching noise is not an issue, they are clear winners. Most switching power supplies sold for Amateur Radio use by reputable companies are noise free. Where size, weight and cost are secondary to high-quality low-noise DC output, linear supplies still have an edge.

Understand the requirements for your application and read the specifications for the available power supply types that meet your need. Then make your choice carefully, keeping your application solidly in mind.

Advertisements


No Responses Yet to “Linear vs Switching: Which Power Supply is Best?”

  1. Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: