[Explanation] What is a switching power supply? You can easily understand the switching power supply!


Shape of switching power supply

 Switching power supplies are classified by shape. “Unit type”, “Board type”, “DIN rail type”, “Onboard”, “Power module”, “Multi slot”, etc. I will explain each of them.


Unit type


The unit type has a box type (unit type) with a chassis and a cover. You can also choose without a cover. The advantage of not having a cover is that it makes it easier to dissipate heat, extending the load factor (derating rate) and the life of the power supply. Under the same environmental conditions, the temperature of the electrolytic capacitor will drop by about 10 ° C, so the life will be doubled.

The standard way to place the power supply is vertically in the photo above. Other placements are possible, but the load capacity (wattage) can only be obtained by 60 to 70% of the standard placement. Since the power supply manufacturer designs the heat based on this standard placement at the time of design, it has the longest load capacity and the longest life.
Check the manufacturer’s specifications for the load factor (derating factor) depending on how the power supply is placed.



 There is only one way to put the power supply, which should never be done. It is a way to place the chassis on the top. If this is used, heat will be trapped inside the power supply and the temperature of the electrolytic capacitor, transformer, and IC will rise too much, causing a trouble. Even the manufacturer does not guarantee this placement.

In addition, the capacity of the unit type power supply is from 15W to 3,000W, and a fan is attached to 300W or more (although 300W or fanless is also available). It has a relatively long life because high-temperature parts such as FETs are brought into close contact with the chassis to dissipate heat. It has a lot of functions and options, and the price is higher than the board type power supply.

Unit-type power supplies are widely used in equipment and devices that require reliability, such as control panels, FA machine tools, semiconductor manufacturing equipment, medical equipment, and communication equipment. In addition, unit-type power supplies account for a large proportion of sales for power supply manufacturers, and the span of discontinued product is more than 20 years.


Board type


The board type is a low-cost power supply for users who do not need a chassis cover (optional chassis and cover can be selected). The best feature is its thinness (height), which is often used side by side with other control boards in the user’s device.

Also, since the board type power supply does not have a fan, heat is dissipated by the heat sink fins on the board, but there is a limit to the size of the heat sink fins, and if the power supply is used vertically, only 60 to 70% of the rated current can be output. The life of the board type power supply is inferior to that of the unit type, but in terms of price, it is 70 to 80% of the unit type power supply, so it is ideal for consumer products and equipment.


DIN rail type


The DIN rail type is a power supply for the control panel, and it can be attached to the DIN rail with one touch by the attachment on the back of the power supply. Since the power supply floats in the air, it is not possible to attach a heavy object, but the structure is such that the wind escapes upward from the air hole on the bottom of the power supply.

The input voltage is generally AC100 / 200V and 3-phase 200V. Depending on the manufacturer, it is also characterized by having three-phase 400V, and the capacity is up to 1500W. Recently, high-performance models with communication that support IoT have also been released, and it is possible to constantly monitor input voltage, output voltage / current value, protection function setting value, cumulative operating time, remaining power supply life time, power supply internal temperature, etc. ..

You can also attach DIN rail brackets to the unit type power supply. Many users use the unit power supply because there are many types of output voltage and the price is cheaper than the DIN rail dedicated power supply.



On-board is a type of power supply that is directly mounted on the board, such as a DC / DC converter. The type shown in the photo is used by passing the pin through the hole in the board and soldering it. It is called DIP (Double Inline Package) because the pins are lined up in two rows. A single row of pins is called a SIP (Single Inline Package).

On-board is a type of power supply that is directly mounted on the board, such as a DC / DC converter. The type shown in the photo is used by passing the pin through the hole in the board and soldering it. A pin lined up in two rows is called a DIP (Double Inline Package). A single row of pins is called a SIP (Single Inline Package).

The capacity is about 1.5W to 30W, and recently, a power supply with a wide input voltage is preferred because there are many battery inputs and the voltage fluctuates. It is also characterized by the fact that it does not have an electric capacitor life because it does not use an electrolytic capacitor, which is a life component.

Also, DC / DC converters can be divided into “insulated” and “non-insulated”. Insulation is highly safe because the primary side (input side) and secondary side (output side) are not directly connected electrically. Non-insulated is not insulated, but it is used in circuits where insulation is not required due to its small size and low price.



Power module

The power module is also soldered directly to the pins on the board. For heat dissipation, attach a heat dissipation fin to the aluminum base plate on the opposite side of the pin and blow the wind, or make it adhere to the metal part of the device body to dissipate heat.

The power module cannot be used alone and requires peripheral circuit design. A power module is, so to speak, a package of a part of a power supply circuit. Considering that users design power supplies with discrete parts, using power modules makes circuit design easier and saves design man-hours. It has a capacity of up to 700W and various options are available.


Multi Slot

Source: Cosel ACE Series

The multi-slot has 4 to 6 slots in the output part of the case, and it is used by inserting the output module of the desired voltage and current. It is an epoch-making product that allows the custom-made power supply to be used with the standard power supply, and does not require any development cost, standard acquisition cost, development period, etc. required for the custom-made power supply.

Various output voltages (single output, 2 outputs) are prepared for the modules to be inserted into the slots, and the modules can be connected in series or in parallel. It has acquired various safety standards, has abundant options, and has a capacity of 300w to 3KW. The model name is registered for each combination, and the manufacturer puts the module in and ships it in a completed state.