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Isolation or Non-isolation: How to Choose the Right Power Supply?

An important point to consider when choosing a power module is whether to use an isolated or non-isolated power solution. Before proceeding with the discussion, let us first understand the concept of isolated power supply and the main characteristics of isolated and non-isolated power.


What is the isolated power supply? 

The isolated power supply is defined conceptually as the conversion of the voltage through a transformer to realize the isolation between input and output.


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Then, what are the isolation features? For example, safety isolation, common-mode noise isolation, ground loop elimination, or for occasions with floating ground requirements, are its key features.

 

In addition to isolation, voltage conversion is also one of the important characteristics of power supply, including AC to DC, DC to AC, conversion between high and low voltage, and so on. What is more, with some peripheral devices, it can also stabilize the voltage, so as to protect and filter noise.

What are the advantages and disadvantages of isolation and non-isolation?

 

What are the advantages and disadvantages of isolation and non-isolation? Combining commonly used isolated and non-isolated power supply, we know some of their advantages and disadvantages intuitively, which are almost opposite.

 

In order to use isolated or non-isolated power supplies, you need to understand what the actual project’s power requirements are. But before that, you can understand the main difference between isolated and non-isolated power supply:

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Common application scenarios of isolated and non-isolated power supply

We know that isolated and non-isolated power supply have their own advantages through the above understanding. For some commonly used application scenarios, we can make the following preliminary judgments.


 Non-isolated solution is preferred when choosing the IC or part of the circuit power supply in the circuit board from the perspective of cost performance and volume. For example, for high-current applications such as FPGA, DSP, ASIC, and other high-speed chips, the K12T series has an efficiency of up to 96% and an output current of up to 16A. It is difficult to achieve such excellent parameters if the non-isolated solution is unselected.


For occasions where safety is required, such as where the human body is in direct contact, an isolated power supply must be used to ensure personal safety, and a high-isolation withstand voltage power supply is even required in the medical industry. Such as G_S-1WR2 series’ isolation voltage is up to 4200VAC/6000VDC, which meets the requirement of 1xMOPP/2xMOOP, 5mm of transformer clearance & creepage distance, 5.5mm of PCB clearance & creepage distance.


Generally speaking, safety is the primary consideration for mains power supply products, so usually for AC-DC, products that meet safety certification are required. For example, the LDE/LHE series of MORNSUN, etc., meet the requirements of reinforced insulation and comply with UL/CE certification. However, not all AC-DC power supply connected to the mains need to be isolated. For example, in the Internet of Things industry, where the volume requirements are high, and people are not in direct contact, a non-isolated AC-DC power supply is selected. Such as the LSxx-K3BxxSS series, feature wide input voltage range, small size, and low power consumption.


For the power supply of long-distance industrial communication, in order to effectively reduce the influence of the ground potential difference and wire coupling interference, an isolated power supply is generally used to power each communication node separately. Such as applications of isolation 485 and isolation CAN.


So, in addition to isolation and non-isolation features, how do we choose a relatively suitable power supply?


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Most engineers still focus on meeting the input and output voltage and power load requirements when selecting power supplies, which is only the most fundamental requirement. With the continuous development of the industry, the needs of customers vary accordingly. Some only require the function realization and low price; some require to meet the high reliability and low fault tolerance rate, which is caused by the different directions in selection. In general, the selection mainly focuses on conventional parameters, important parameters, and some hidden parameters that are not usually noticed. Of course, reliability is the most concerned parameter at this stage.

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