Two of a kind?
Some radio amateurs, especially those who are new to the hobby, may not even know there are two main types of power supplies. They could be forgiven for that. When you need a power supply, you just jump online, pick out that one suits your needs and budget, and click. No one really thinks about what goes on in the guts of a power supply. Juice is juice, right? Well, sort of. There are huge differences between linear and switching power supplies even if the final product is the same. linear vs. switching power supply
Old School. linear vs. switching power supply
Linear power supplies are one of the grand elders of ham radio. They’ve been around as long as radio itself. The principle of operation is fairly simple. Household AC voltage is fed to a transformer and dropped down to 12-15 volts. The low voltage AC goes through a rectifier which changes it to DC. That raw DC still has some residual AC in it, so it must be cleaned up. To solve that issue, the power goes through a capacitor to filter out any leftover AC “ripple”. After that, it’s ready for your radio.
In the early days of radio, rectifiers were a series of vacuum tubes that themselves gulped a lot of power. Later models had solid state diodes, which were much smaller and more efficient. Today, diodes are still used but manufacturers use components with several diodes mounted into one integrated rectifier package (these devices are sometimes referred to as “bridges”). The diagram below shows the basic parts of a linear power supply. Some better quality linear power supplies have additional regulation & control circuitry, as well as chokes for filtering. You’ll also see linear power supplies with variable outputs, multiple outputs, built-in meters, and other handy add ons. Regardless of the “bells and whistles,” all linear power supplies perform the same basic function.
Used linear power supplies are very easy to find because they’ve been around so long. New models are still available but they will typically cost more than equivalent switching power supplies, and they’re also large and heavy. A linear power supply may be a good choice if you have a fixed station where space/weight is not a big concern or you want to reduce RF interference. linear vs. switching power supply
A new breed. linear vs. switching power supply
Switching power supplies are a relative newcomer to ham radio. In a switching power supply, AC input is immediately converted to DC, but it is not stepped down to a lower voltage right away. The high voltage DC is fed into a switching transistor. The switch pulses or “switches” the DC on and off at a very high frequency, effectively making it AC again. While the AC in your house is 60 Hz, the switch cycles much faster, usually between 30kHz and 150 kHz. After that, it’s basically a traditional linear power supply: The high frequency AC goes through a transformer to become low voltage AC, then it’s rectified, filtered, and sent to your radio.
The obvious question is, why bother to go through the AC-DC conversion process twice? There’s a one-word answer: Physics. High frequency voltage coming out of the switch requires a much smaller transformer. This is why switching power supplies are less expensive, more efficient, smaller, and lighter than their elders. And like old school linear power supplies, they can also include extra features. On the down side, switching power supplies have the potential to generate RF interference, especially on the HF bands. Switchers may be a good pick if you are on a budget or have space/weight limitations.
So which one should you have? linear vs switching
Most hams today use switching power supplies and are very satisfied, but don’t let popularity alone decide for you. Many old timers swear by tried-and-true linear power supplies, and the belief is not without merit. After all, linear power supplies have been around this long for a reason. I personally use a switching power supply. I’ve used linear versions in the past and they were fine too. For my situation, it’s a moot point anyway because my entire radio station is powered directly from storage batteries charged by solar panels. I rarely pull power from the grid through a power supply to run my gear.
The concerns about RF interference from switching power supplies is probably more hype than reality. Unless you’re using a junky low-end unit or have incorrect grounding, it’s not likely to be a problem.
Linear power supply.
- Time-tested design and principle of operation.
- Very clean output-no RF noise.
- Widely available on the used market.
- Generally better build quality…decades-old units are still in service going strong.
- Large & heavy compared to switching equivalents.
- More expensive.
- Less efficient.
Switching power supply.
- Small & light weight compared to linear equivalents.
- Most popular type used today.
- More efficient.
- Do your research! There is a lot of cheap junk on the market.
- Potential for RF interference.
What we learned today.
There is no clear winner in the linear vs switching power supply debate. Like everything, what’s “best” will vary with each individual. Chances are good that you’ll be happy no matter what you ultimately get. Understanding the difference between the two and their respective principles of operation gives you the information you’ll need to make a decision as well as expand your skills as a radio amateur.