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

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.

Why does the mark of the products show 100VAC-240VAC while the datasheet shows 85VAC-264VAC?

This is mainly for safety certification purposes. When certification authority tests product performance, they will make the input voltage range on the mark fluctuate by +10% and -15%, so the common practice in the industry is to set the input voltage range of 100VAC-240VAC on the mark.

The AC/DC Converters produce instantaneous high current upon load access. Does this influence the module?

If the large instantaneous current of the AC/DC Converters upon load access does not exceed the over-current protection point of the module, it will not have any impact on the module. See the datasheet for the over-current protection point of the module. If the current exceeds the over-current protection point of the module, the module will trigger the protection and voltage dip occur, and then recover.

How to meet the requirement for ripple & noise when using low-power converters?

Low-power converters have a higher requirement for ripple & noise which need further filtering. 

There are the following measures: 

(1) add a capacitor at the output terminal (the function of the capacitor is to further lower ripple & noise with a relatively low frequency); 

2) add a PI filter at the output terminal by filtering methods of capacitor + DM inductor + capacitor  OR capacitor + CM inductor + capacitor (this method lowers ripple & noise at the same time. If the frequency of the noise is high, it is recommended to use the pattern of capacitor + CM inductor + capacitor);

 (3) customers can choose a power module whose output voltage is one grade higher and add an LDO to reduce ripple & noise (for instance, customers practically need a 3.3V output power module but there are demanding requirements for ripple & noise. Please recommend customer to choose a 5V output power module and add an LDO to lower it to 3.3V, and the LDO can lower ripple & noise).

What are the minimum starting current and input current of a module?

The starting current of a module is generally about 1.4-1.6 times that of the Iin (max). The increase of capacitive load of the output terminal will also increase the starting current value of the module. It is recommended to select the forestage power supply with higher power. For the minimum input current in the unloading condition, please check the ‘No-load current’ section in the datasheet of the corresponding module.

The module fails to start up when the capacitive load is relatively large. How to solve it?

In practical application, the capacitive load exceeds the maximum capacitive load of operating module. In addition, when the output capacitance is extremely large, large starting current is required at the moment of start-up, resulting in the failure of starting the module.

It is recommended to decrease the connected capacitance of the output terminal or add a buffer circuit at the output terminal to improve the capacity of the module to withstand capacitive load

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