Design considerations of AC/DC power supplies for input power

Design considerations of AC/DC power supplies for input power

AC/DC power supplies are the most common and widely used power supplies. From small smartphone chargers to cabinet power supply systems for large data centers, most of them are AC to DC power supplies. Power supplies have a very important task, which is no matter what the quality of the AC power is like, they must sacrifice themselves as much as possible to convert the power and provide stable DC output for the back-end load (equipment) to use. Therefore, key considerations for designing a good power supply include the voltage range of the input power, permissible range of power waveforms, and even the anti-noise ability of the feedback to the power system, etc.

There are different specifications for AC Mains around the world. The country with the lowest single-phase voltage is Japan (100Vac) and the countries with the highest voltage are most countries in Africa (240Vac). A good power supply will be designed so that it can be used for all AC main ranges, which is known in the market as “Full Range Voltage” design, with the input voltage range labeled as 90Vac~264Vac. This range was considered using ±10% of the rated voltage, which is -10% of 100Vac countries and +10% of 264Vac countries. The input voltage range must be labeled on the rating label as a safety requirement. Readers who are interested can go take a look at your own power supplies. However, another important consideration is the cost. If the product itself does not have mobility features and will only be used in a fixed location, there’s no need to consider the full range voltage when designing it. This way the cost of the power supply will also be lower.

Different pieces of electrical equipment have different requirements for input power quality. Small chargers, for example, have lower input and output power, and have very little effect on the feedback of the power system. Also, the designs and functions of their power control IC are relatively sophisticated, so generally speaking they can usually operate normally with a nominal AC main input voltage. The only thing to beware of is abnormal surges or lightning, which may cause damages to these small chargers.


On the other hand, stereo equipment requires purer input power. Therefore, there are relatively more things to consider when designing power supplies for stereo equipment, especially for the processing of electromagnetic interference (EMI) and radio frequency interference (RFI). High-end stereo equipment usually has circuit designs with AC voltage and frequency stabilizers added to their preamp system. The purpose of these designs is to allow the audio output of the amplifier to have the best performance under pure sinusoidal input.

For undeveloped countries with unstable power, they usually face problems such as instant power surges, voltage sags, voltage spikes or frequency drift, etc., that cause damage to electrical equipment all the time. The design of a good power supply will have a better tolerance to these power problems, and will have a certain level of allowed range when the problems described above are met. But when the power supply does not have a high tolerance level for these power problems, in order to protect electrical equipment from damage, consumers will usually buy uninterruptable power systems (UPS) as the relay protection equipment between the AC mains and electrical equipment, especially for computer and server applications. These areas also have power losses quite frequently, so most people have power generators prepared for power supply. Therefore, whether it is the design of the power supply or selection of the UPS, they must all satisfy the requirements for power generator applications. The FSP Group is an expert in designing power supplies. We consider all application requirements when designing our products to provide stable quality standards in order to meet market expectations.

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