If you have questions on MEAN WELL’s products, please read the FAQ first. If the listed answers still cannot solve your problems, please contract our local distributors , they should reply to you as soon as received your request.

As a dedicated manufacturer of standard power supplies, MEAN WELL provides a wide variety of  power supplies to meet different demands from the markets. However, selecting the right products relies heavily on the correct electrical characteristics and specification, we listed the frequently asked questions for your reference.

Functionality Aspect


Notes on choosing a switching power supply?


  1. To increase the reliability of the S.P.S., we suggest users choose a unit that has a rating of 30% more power than actual need. For example, if the system needs a 100W source, we suggest that users choose a S.P.S. with 130W of output power or more. By doing this, you can effectively boost the reliability of the S.P.S. in your system.
  2. We also need to consider about ambient temperature of the S.P.S. and whether there is additional device for dissipating the heat. If the S.P.S. is working in a high temperature environment, we need to make some derating to the output power. The derating curve of "ambient temperature" versus "output power" can be found on our spec sheets.
  3. Choosing functions based on your application:
    • Protection function: Over Voltage Protection (OVP), Over Temperature Protection (OVP), Over Load Protection (OLP), and etc.
    • Application function: Signaling Function (Power Good, Power Fail), Remote Control, Remote Sensing, and etc.
    • Special function: Power Factor Correction (PFC), Uninterruptible Power Supply (UPS) function.
  4. Make sure that the model qualifies for the safety standards and EMC regulations you need.


Can MEAN WELL's power supply be used in the range of 45Hz ~ 440Hz? If YES, what will happen?


MEAN WELL's power supply can be used within this frequency range. But if the frequency is too low, the efficiency will also be lower. For example, when a SP-200-24 is operated under 230VAC and rated load, if the frequency of AC input is 60 Hz, the efficiency is around 84%; however, if the frequency of AC input reduces to 50 Hz, the efficiency will be around 83.8%. If the frequency is too high, the power factor of the S.P.S. with PFC (power factor correction) function will reduce and this also will cause higher leakage current. For example, when a SP-200-24 is operated under 230VAC and rated load, if the frequency of AC input is 60 Hz, the power factor is 0.93 and the leakage current is around 0.7mA; however, if the frequency of AC input increase to 440 Hz, the power factor will decrease to 0.75 and the leakage current will rise to around 4.3mA.


When testing a dual output power supply, the +5V channel is correct, but the +12V channel is over the specification. What is going on?


There are some minimum-load requirements on MEAN WELL's multi-output power supplies, please refer to the specification first before connecting the load. When the load condition is 5V/4A, 12V/0A, the output voltage of the 12V channel will be around 12.8V that is over the ±6% of voltage deviation (12.72V) specified in the spec. sheet. If we add in the minimum load 0.2A to the 12V channel, the 12V channel will reduce to around 12.3V which is within the specification.


Why did the power supply shuts down during operation and after turning it off, I can restart the power supply again?


In general there are two circumstances that will cause the power supply to shut down. The first one is the activation of the over-load-protection (OLP). To deal with this situation, we suggest increasing the rating of the output power or modifying the OLP point. The second one is the activation of over-temperature protection (OTP) when the internal temperature reaches the pre-set value. All of these conditions will let the S.P.S. enter protection mode and shut down. After these conditions are removed, the S.P.S. will be back to normal.


Why the fan is not running after turning on certain models?


Some models control the fan based on internal temperature to extend its life time. For example, the Fan ON temperature for the LRS-350 series is ≧ 50℃ (RTH3). If the internal temperature does not reach the preset value, the fan will remain still until receiving the start up signal.


What is "Inrush Current"? What will we notice?


At input side, there will be (1/2 ~1 cycle, ex. 1/120 ~ 1/60 seconds for 60 Hz AC source) large pulse current (20~60A based on the design of S.P.S.) at the moment of power on and then back to normal rating. This "Inrush Current" will appear every time you turn on the power. Although it will not damage the power supply, we suggest not turning the power supply ON/OFF very quickly within a short time. Besides, if there are several power supplies turning on at the same time, the dispatching system of AC source may shut off and go into protection mode because of the huge inrush current. It is suggested that these power supplies start up one by one or use the remote control function of S.P.S. to turn them on/off.


What is PFC?


PFC stands for Power Factor Correction. The purpose of PFC is to improve the ratio of apparent power and real power. The power factor is only 0.4~0.6 in non-PFC models. In PFC models, the power factor can reach above 0.95. The calculation formulas are as below: Apparent Power=Input Voltage x Input Current (VA) Real Power= Input Voltage x Input Current x Power Factor (W) From the environment friendly point, the electric power plant needs to generate a power which is higher than apparent power in order to steadily provide electricity to the market. The real usage of electricity should be defined by real power. Assuming the power factor is 0.5, the power plant needs to produce more than 2VA to satisfy 1W real power. On the contrary, if the power factor is 0.95, the power plant only needs to generate more than 1.06VA to provide 1W real power need. It will be more effective.


What is the difference between -V and COM which are marked on the output side?


COM (COMMON) means common ground. Please see below: Single output: Positive pole (+V), Negative pole (-V) Multiple output (Common ground): Positive pole (+V1, +V2,.), Negative pole (COM)


In MEAN WELL's catalog, we see AC and DC at input, what is it all about?


Due to different circuit designs, MEAN WELL power supply's input consists of three types as below:
c.85~132VAC/176~264VAC by Switch; 250~370VDC

        • In a and b inputs models, power supply can work properly no matter under AC or DC input. Some models need correct connection of input poles, positive pole connects to AC/L; negative pole connects to AC/N. Others may require opposite connection, positive pole to AC/N; negative pole to AC/L. If customers make a wrong connection, the power supply will not be broken. You can just reverse the input poles and power supply will still work.
        • In c input models, please make sure that you switch the 115/230V input correctly. If the switch is on the 115V side and the real input is 230V, the power supply will be damaged.           


What is MTBF? Is it distinct from Life Cycle?


MTBF and Life Cycle are both indicators of reliability. MTBF can be calculated by two different methodologies, which are “part count” and “stress analysis”. The regulations, MIL-HDBK-217F Notice 2 and TELCORDIA SR/TR-332(Bellcore) are commonly used to calculate MTBF. MIL-HDBK-217F is a United States military standard, and TELCORDIA SR/TR-332(Bellcore) is a commercial regulation.MEAN WELL uses MIL-HDBK-217F(Stress Analysis) as the core of MTBF. The exact meaning of MTBF (Mean Time Between Failure) is, after continuously using the power supply for a certain amount of time, the average time that the probability of proper operation is down to 36.8%(e-1=0.368). Currently MEAN WELL is adopting MIL-HDBK-217F, forecasting the expected reliability through Stress Analysis (excluding fans); this MTBF means the probability the product can continue the normal work after working continuously up to the calculated MTBF time is 36.8% (e-1=0.368). If the power supply is continuously used at double the MTBF time, the probability of proper operation becomes 13.5%(e-2=0.135). Life Cycle is found by using the temperature rise of electrolytic capacitors to estimate the approximate life of the power supply. For example, SP-750-12 MTBF=769.3K hours; electrolytic capacitor C108 Life Cycle=202.2K hours (Ta=45℃)


What is the fan control mechanism for SPS with cooling fan?


Cooling fans have a relatively shorter lifetime (typical MTTF, Mean Time To Failure, of around 5000-10000 hours) as compared with other components of power supplies. As a result, changing operating method of cooling fans can extend the operation hours of the fans. The most common control methods are shown below:

  1. Temperature control: if the internal temperature of a power supply detected by a temperature sensor is over the set threshold, the fan will start working at full speed, whereas, if the internal temperature is less than the set threshold, the fan will stop working or at half speed. In addition, cooling fans in some power supplies are controlled by a linear control method whereby fan speed can be changed with different internal temperatures synchronously.
  2. Load control: if the loading of a power supply is over the set threshold, the fan will start working at fullspeed, whereas, if the loading is less than the set threshold, the fan will stop working or at half speed.


What is power good and power fail signals and how can use it?


Some power supplies provide a "Power Good" signal when they are turned on, and send out a " Power Fail" signal when they are turned off. This is usually used for monitoring and controlling purpose. Power Good: after the output of a power supply reaches 90% rated voltage, an TTL signal (about 5V) will be sent out within the next 10-500ms. Power Fail: before the output of a power supply is less than 90% rated voltage, the power-good signal will be turned off at least 1ms in advance.


What is minimum load requirement and how can I read it from the spec?


MW's multi- output power supplies, such as dual channels or more, will have minimum load requirements. It is highly suggested reading the spec before using them. For operating properly, each channel must deliver a minimum current or the output voltages will become unstable or be over the defined tolerance range. Minimum load requirement can be seen on spec's "CURRENT RANGE" as the following table shows: CH1 requires a minimum current consumption of 2A, CH2 requires 0.5A, CH3 requires 0.2A and CH4 requires 0.2A.


I have an TN-1500 inverter. Why the LED indication of AC IN is not lit after mains input has been applied?


According to the mains voltage of different countries, the output of TN-1500 inverter 110VAC version can be altered to 100/110/115/120VAC. In the same way, TN-1500 inverter 220VAC version can be changed to 200/220/230/240VAC as well. When the inverter is set in UPS mode and the mains voltage fluctuates over ?5% of the set AC output voltage, the inverter will shift its power source from the city power to battery to remain the accuracy of the AC output Voltage. Meanwhile, the AC IN indicator on the front panel of the inverter will be turned off.