Basics of switching power supply [Beginner] Easy-to-understand explanation without circuit and theory

I want to know about switching power supplies
“I handle switching power supplies at work, but I don’t know what they really are.
I’m in trouble because I can’t ask people anymore.　Even if you do a Google search, you will get disgusted because difficult stories such as circuit diagrams and theory will come up.
But for the time being, I want to understand the basics of switching power supplies. ”

We will answer these concerns.

In fact, our lives are made up of switching power supplies.
Although you cannot see it directly, you can see vending machines, ticket vending machines and home doors at stations, LED signs in the city, hospital consultation reception machines and CT / MRI, supermarket showcases and self-checkouts, mobile phone base stations, and smartphone electronics. It is used in equipment that makes parts (semiconductor manufacturing equipment), control panels in power plants and factories, and robots in factories.

So, this time, I will explain the basics of switching power supplies (beginner’s edition) without using circuit methods or technical theories.

Switching power supply and dropper power supply

Why we need a power supply

When asked why “power” is needed, it is difficult to answer.

Why do we need electricity before that? explain.
That is because electricity is easy to move and use.

Oil is a resource, but it is hard to move it as it is, and it is even harder to use it.
That’s why thermal power plants are turning oil into electricity.
In other words, electricity is the energy that oil has transformed.

After that, the electricity produced at the power plant is transmitted to factories and households. The electricity produced at the power plant is sent to the transmission line at an ultra-high voltage of 300,000 to 500,000 V, and while dropping the voltage at several substations on the way, it is finally a pole transformer (transformer) on the electric pole. It is transformed to AC100V or 200V and sent to each home. AC is convenient for power transmission.

Why you need a power supply
This is because the electronic components mounted on electronic devices operate on DC (direct current), so it is necessary to convert from AC100V/200V to a low voltage of DC. The device for transforming is the “power supply”.

Dropper power supply and switching power supply developed by NASA

By the way, when the United States was competing with the Soviet Union for landing on the moon, going back in time ~
A small and lightweight power supply was needed because the dropper power supply was too big and heavy to put the power supply on Apollo. The dropper power supply (linear power supply) is a heavy and large power supply that converts to DC (direct current) with a transformer and a three-terminal regulator. The circuit is simple, but it is 5 to 10 times heavier and 10 times heavier than a switching power supply.

NASA has developed a power supply that converts output voltage by high-speed switching (ON / OFF) of semiconductors such as transistors. Roughly speaking with a miniature bulb, if you halve the ON time, the brightness of the miniature bulb will be halved, and if you halve the ON time, the brightness will be 1/4. The brightness (voltage) is adjusted by adjusting the ON time with a semiconductor.

The switching method has the disadvantages that the circuit is more complicated than the dropper method, the number of parts is large, the cost is high, and the noise is large. Noise is switching noise, which causes a decrease in the reliability of electronic components and equipment. The noise of the switching power supply is about 10 times that of the dropper power supply, so put a noise filter in front of the power supply to reduce the noise.

In particular, medical electronic devices and measuring instruments still use dropper-type power supplies in some areas, but due to the improved performance of noise filters, they are now used in combination with switching power supplies and noise filters. Most of the time.

Types of switching power supplies

There are various classifications of switching power supplies, but …

The following three categories are the main ones.

Constant voltage power supply and constant current power supply

Inputs are broadly divided into AC (alternating current) input and DC (direct current) input.

They are called AC / DC converter and DC / DC converter, respectively.

The AC input voltage is AC100V, AC200V, and factory three-phase 200V. Others include three-phase AC400V for high power such as large presses and crushers.

For reference, it is the input voltage in the world.

Classification by input voltage

Inputs are roughly divided into AC (alternating current) input and DC (direct current) input.

They are called AC / DC converter and DC / DC converter, respectively.

The AC input voltage is AC100V, AC200V, and factory three-phase 200V. Others include three-phase AC400V for high power such as large presses and crushers.

For reference, it is the input voltage in the world.

The DC input voltage is 3.3V, 5V, 12V, 15V, 24V, 48V.
In the case of battery input, the voltage fluctuates greatly, so it may not be possible to handle it within the conventional input voltage range, and recently wide input types such as 18 to 76V have been released.

Classification by shape

It can be divided into several types according to the shape of the switching power supply.

There are three main types.

The unit type is a box type with a chassis (L sheet metal) and a cover.

The board type is a board-only AC / DC converter. A chassis and cover can be attached as an option.

Onboard is a power supply that is soldered onto the board. Mainly DC / DC converters.