How to choose a switching power supply that does not fail [I will explain in an easy-to-understand manner]

For those who want to choose a switching power supply but do not know which one to choose

The designer said, “I want to use a long-life power supply for the device under design.”
The person in charge of materials said, “I want to reduce costs, but I don’t know which power supply to choose.” “I want to know an alternative model of power supply that will be scrapped.”
Are dealer salespeople thinking, “I want to compare specifications and prices with competing models.” “I want to know more about switching power supplies.”

I will answer these questions.

I’m comparing the power supplies of various manufacturers, but the specifications are different for each company, and is this the right way to see the load factor and life of the power supply? If you are uneasy, please see the article.

How to choose a switching power supply that will not fail

The following three are important.

Let me explain.

Confirmation of basic specifications

This basic specification is the most important.

The basic specifications of the power supply are “input voltage”, “number of outputs”, “output voltage”, and “output current”. Once these four specifications are decided, the power supply model can be selected.

Please refer to “Basic specifications important when choosing a switching power supply” for the basic specifications of the power supply.

Once the basic specifications are decided, the power supply of each manufacturer is searched, that is, the search is performed, but if you search using the specification search function of this site “dengen-navi”, you only have to search once, so it is the easiest. After all, we have a database of 35,000 power supply models from major domestic power supply manufacturers.

For how to use it, see “Search Guide for Switching Power Supply [Explanation of how to use and tips for searching in an easy-to-understand manner]“.

Confirmation of narrowing specifications

You can search without checking the refined search, but please check the specifications and standards that you can never remove.

By checking the narrowing items, you can sort out whether the specifications / standards are really necessary.
There are 56 specific items to narrow down by mechanism, function, standard, fan, manufacturer, and production status.

Important items to check

The search result table you searched for has the most important items. However, it is OK if you keep only the main points in the following three items.

Before that, I will explain each item. If you know it, please skip it.

The load factor indicates the percentage of load that can be taken when the ambient temperature is 50 ° C. There is a big difference between a power supply that can use 100% and a power supply that can only use 60% even with the same capacity. “0%” means that it cannot be used at an ambient temperature of 50 ° C.

The life of the electric capacitor is the expected life (year) of the electrolytic capacitor when the ambient temperature is 40 ° C and the load factor is 80%. This is the life under general environmental conditions. Select a power supply that is at least longer than the life of the equipment or equipment to be installed. The description “electric capacitor-less” means that the electrolytic capacitor of the life component is not used.

The lowest price shows the cheapest price on the net and the mail order company that sells the power supply. However, since it is the price for one unit, please use it as a reference price only. If the quantity is large, it will be much cheaper than this price. The reason why the lowest price is not stated is that the online sales company does not sell the model, or even if it sells, there is no price display.

In addition, this site has a convenient sorting function for comparison. You can sort in a complex manner using sort order 1 and sort order 2.

First, check “Load factor” in sort order 1. It is arranged in descending order of load factor, that is, in descending order of usable capacity, so how much is acceptable. In the case of a 100W power supply, 100% load factor can be used as 100W, and 80% load factor cannot be used as 80W.

Check “Electric computer life” for sort order 2. If the life of the device or equipment is 5 years, a longer life value of the electric controller is required. However, the life of the electric controller here is the number of years in 24h365 days.

Next, check “Lowest price” in sort order 1 and “Electrical controller life” or “Load factor” in sort order 2, and select a power supply that is cheaper and has a device life or longer or a load factor of 80% or higher.
If you do it several times, you can see that the low price does not mean that the life of the electric controller is short.

You should also choose a noise filter as a set with a switching power supply.

Next, I will explain the basics of noise.

What is noise?

Our lives are surrounded by electronic devices. These devices and devices always generate electrical noise. I think I’ve experienced noise and image distortion on the radio and TV. That’s fine, but it’s a big deal if the factory’s industrial equipment malfunctions, medical equipment (such as a pacemaker) stops, or the station radio is noisy.

Noise is divided into “conduction noise” and “radiation noise” according to its transmission path.

Conduction noise is noise transmitted from patterns on cables and printed circuit boards. Radiated noise is noise transmitted from the air.

It can be said that devices that operate on AC power are connected by a common power line called AC. Noise generated by other devices may be transmitted to the AC line and cause malfunctions, and conversely, noise generated by your own device may cause other devices to malfunction.
The AC input section is also a noise inlet and outlet, so attach a noise filter there.

What is Conducted Emission?

Since the switching power supply is a semiconductor that switches (turns on and off) at high speed to step down the voltage, high-frequency noise is generated.

The noise that the high-frequency noise travels through the input wire and returns to the input line is called “noise terminal voltage”.
There are regulations on noise terminal voltage in each country. The contents are almost the same.

The noise filter is placed in front of the switching power supply and is used to attenuate the noise transmitted through the cable. In other words, the main purpose is to prevent the noise generated from the switching power supply from being returned to the AC line.

The radiation noise emitted from the switching power supply cannot be attenuated by the noise filter.
The noise is regulated in each country as “Radiated Emission“.

How to choose a noise filter

Noise filters have fewer electrical specifications than switching power supplies and can be easily selected.

Once the following basic specifications are determined, you can select a noise filter.

That is all for the contents. Thank you for reading.