Points on connecting wires used in power supplies?


To install a power supply into the system, you would need wires for the connection both to the loads and to the energy source. There are a couple of points that should be taken into consideration when choosing wires, one is current rating, it may cause high heat on the wires or burnt out in the worst case, if the rating is not enough. The other is voltage drop, there would be voltage reduction at load side as current moves through the wires owing to the internal resistance. If too much voltage drop in line, there could be no sufficient voltage to drive the loads. You can find the right wires for use by referring to the table below on the basis of your system design.


Why the input voltage marked on the spec. sheet is 88~264 VAC while the label on the power supply says that it is 100~240VAC?


During safety verification process, the agency will use a stricter standard ±10% (IEC 62368 uses +10%, -10% for the product with AC input rated) of the input voltage range labeled on the power supply to conduct the test. So, operating at the wider input voltage range as specified on the spec. sheet should be fine. The narrower range of input voltage labeled on the power supply is to fulfill the test standard of safety regulation and make sure that users insert input voltage correctly.


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.


What are the intelligent products of MEAN WELL?


MEAN WELL intelligent products are those equipped with communication interfaces, parameters and functionality can be adjusted or changed via the interfaces. Take the RPB-1600, the intelligent battery charger as an example, users can easily adjust charge curves to deal with various types of batteries owing to its PMBus communication protocol. Mean Well divides the intelligent products into four sections: PMBus, CAN bus, DALI, DALI-2 and KNX. Please read the following for more information.
>> PMBus

PMBus stands for Power Management Bus, which is an open standard power-management protocol, featuring flexibility and highly versatile standard. Those intelligent products with the protocol are able to do parameter settings, such as output voltage/current, status reports, etc. The models are as below:
>>CAN bus
The Controller Area Network bus is a serial communication bus designed for robust and flexible performance. Those intelligent products with the protocol are able to do parameter settings, such as output voltage/current, status reports, etc. The models are as below:
DALI stands for Digital Addressable Lighting Interface, a digital, internationally adopted language used to control lighting such as LED Drivers. Those products/drivers with the protocol are able to cooperate with DALI controller to form smart luminaires for interior use. The models are as below:
DALI-2 is an updated version of DALI. The main difference for DALI-2 is that specification of electrical tolerances is more precise and it added new commands, such as extended fade-time, making fades from 0.1 seconds up to 16 minutes. DALI-2 products/drivers not only can work with DALI-2 application controllers and input devices, but also can be installed into DALI system. The models are as below:
KNX is an open standard for commercial and domestic building automation. It controls all aspects of home and building control such as: lighting, heating, cooling and ventilation, blinds/ shutters. Those products/drivers with the protocol are able to cooperate with KNX controllers and switches to form small home network or being installed into smart commercial building. The models are as below:


What solution and products does MEAN WELL provide for building automation?


For Building automation, MEAN WELL utilizes KNX as the solution. Please refer to the KNX building automation website for detailed information and relevant applications.


Will MEAN WELL's products with CE marking meet the EMC requirements after assembling into my system?


We cannot guarantee 100% that the final system can still meet the EMC requirements. The location, wiring and grounding of the switching power supply in the system may influence its EMC characteristics. In different environment or applications, the same switching power supply may have different outcomes. Our test results are based on setup shown in the EMC report.


How to select adaptors with the correct AC plug for use in different countries?


An adaptor may need connection of a power cord to receive energy needed from the utility. You can refer to the specification of the adaptor for the connector (AC inlet) at the adaptor end of the power cord; Different countries/regions vary in type of AC socket and voltage, please look at the table below for the information of the AC plug 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.


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


There are some minimum-load requirements on MEAN WELL's multi-output power supplies. Please read the specification first before connecting to the load. In order to allow the power supply to work properly, a minimum load for each output is required, or else, the output voltage level will be unstable or outer tolerance range. Please refer to “Current range” in the specification as shown in the table below: Channel 1 requires a 2A minimum-load; channel 2 requires 0.5A; Channel 3 requires 0.1A ; Channel 4 does not need any minimum-load.


What is ENEC logo? What is the difference between ENEC logo and TUV logo in LED power application?


ENEC is the European safety standard mark.
The scheme is based on the European full certification scheme of ISO-type5, which was initially established in 1991. There are 24 member certification bodies including TUV, VDE, Demko, Nemko participating in the scheme. At the beginning, it was only applicable to all kinds of lamps and lanterns. With the efforts of European industrial and consumer organizations, the scope of application has covered lighting products and their accessories, switches, controllers, connectors, couplers, plugs, consumer electronic products, audio-visual equipment, information technology equipment, household appliances, safety isolation transformers, electrical appliances, filters and other products. ENEC is a more competitive enterprise High value reliable verification mark. The new generation LED power of MEAN WELL have apllied for the ENEC mark presently. The code of verification unit will be added after the ENEC mark. For example,ENEC05 represents the ENEC logo issued by DEKRA, and ENEC17 represents the ENEC logo issued by TUV RH. The common ENEC codes are as follows.

ID Country CB Acronym ID Country CB Acronym
02 Belgium SGS CEBEC 15 Denmark UL Int DEMKO
05 Netherlands DEKRA 16 Finland SGS FIMKO
12 United Kingdom BSI 17 Norway NEMKO
14 Sweden Intertek Semko 24 Germany TUV Rheinland
The difference between ENEC and TUV for LED power supply is that ENEC should also meet the requirements of performance EN 62384 in addition to the safety regulations EN 61347-1 and EN 61347-2-13. For example, LED power supply will require that it should be normally burned for 200 hours under TC environment to ensure the suitability of TC declaration.


A few things you should know before using the Remote Sensing function


First, use twisted wires, connect +S to the positive end of the output, then -S to the negative end of the output, as shown in the illustration. Also, keep the wires off the AC and output cables to prevent noise interference.
Add capacitors at output end where the Remote Sensing wires are connected to if dynamic load (frequency above 1K Hz) is used. The purpose is to reduce noise as Remote Sensing is a sensitive function. A suitable capacitor requires two factors:
a. Rated Ripple Current is 0.2 times greater than the output current
b. Rated Voltage is higher than the output voltage


What solution and products does MEAN WELL provide for wireless lighting control?


For wireless lighting control, MEAN WELL utilizes Bluetooth low energy Mesh. Currently, there are LCM-IOT and PWM-IOT series in the product line, which can be adopted in applications of constant current and constant voltage control. Please refer to the specifications for detailed information.


How many units can be controlled by CASAMBI app?


It is 125 nodes that can be controlled at a time by CASAMBI app.


What is class 2, class II and LPS? What is the difference between class I and class II?


Class I: Equipment where protection against electric shock is achieved by using basic insulation and also providing a means of connecting to the protective earth conductor in the building where by routing those conductive parts that are otherwise capable of assuming hazardous voltages to earth ground if the basic insulation fails. This means a class I SPS will provide a terminal/pin for earth ground connection.

Class II: Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation are provided, there being no reliance on either protective earth or installation conditions. This means a class II SPS does NOT have a terminal/pin for earth ground connection.

LPS: When an electronic circuit is powered by a limit power source (LPS), its output current and power are under the limitation shown in IEC 62368-1 Table Q1, and the risk of fire can be reduced significantly. So, the safety distances and flammability rating of components can be much lower. Therefore, the plastic enclosure of these power supplies could use HB flammability rating to reduce cost. This definition comes from ITE/AV product (IEC/EN/UL 62368-1).

Class 2: When an electronic circuit is powered by class 2, its output current and power are under the limitation shown in UL 1310 Table 30.1, and the risk of fire can be reduced significantly. So, the safety distances and flammability rating of components can be much lower. Therefore, the plastic enclosure of these power supplies could use HB flammability rating to reduce cost. This definition comes from UL class 2 power unit (UL 1310).



Is it possible to build your own charging curve on the smart chargers when the pre-defined charging curves do not satisfy battery charging requirements?(Video tutorial Inside)


Yes, charging curves of smart chargers including ENC series, RPB series and RCB series can be set and adjusted through SBP-001, the charging programmer.
SBP-001 utilizes the software with the connection between the charger and itself to allow users to programme charging curves.
Adjustable functions are:
Charging parameter adjustment: Values of constant current (CC), constant voltage (CV), float voltage (FV) and tapper current (TC) can be set and adjusted.
Battery temperature compensation: Various charging voltage compensation is provided for battery at different temperature conditions.
Timeout setting: Fully programmable timeout during stages enables to be set to shutdown the charger to prevent battery over-charge.
Please refer to the user’s manual as link below for detailed information:
Following video is an example of demonstrating the ENC-120.


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.


What is the control mechanism for cooling fans?


Cooling fans have a relatively shorter lifetime (typical MTTF, Mean Time To Failure, of around 5000-100000 hours) compared with other components of power supply. As a result, changing operating method of the fans can extend the operation hours. The most common control schemes are shown as below:

  1. Temperature control: if the internal temperature of a power supply, detected by a temperature sensor, is over the 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 run at half speed. In addition, cooling fans in some power supplies are controlled by a non-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 threshold, the fan will start working at full speed, whereas, if the loading is less than the set threshold, the fan will stop working or run at half speed.



Nowadays, customer implement magnetic component in their system to achieve fast installation and maintenance. The magnetic component should keep as far as possible from PSU to avoid interference in the control circuitry of PSU. If limitation of distance is unavoidable, install a well magnetic-conducted metal plate (ex: steel plate, copper plate) between PSU and magnetic component to minimize the interference.


What are the common safety standards in America and Europe If power supply is used in battery charger?


The common safety standards is UL 62368-1, UL 1012 and UL 1310. UL 1012 and UL 1310 belong to the local national standards of the United States and Canada and are not applicable to other countries. The European market is dominated by EN 61558-1 and EN 61558-2-16.


What solution and products does MEAN WELL provide for industrial automation?


For industrial automation, MEAN WELL suggests using PMBus and CAN bus for digital control and monitoring. Please refer to the tech note link below for introduction and difference between the buses.

Model / interface PMBus CAN bus
By request By request
As standard By request
 RCP-2000 As standard X


What is the difference between linear and logarithmic dimming curves in DALI?


The brightness increasing in a steady/linear rate isn't observed as a linear increase to the human eyes. It is light source whose dimming curve is in logarithmic mode shows a linear increase to the human eye. There are linear and logarithmic dimming curves selectable for users in DALI.


The status for WEEE and MEAN WELL's approach?


One of the most important changes to the new WEEE Directive 2012/19/EU was the changeover to open scope on 15 August 2018. 2018 therefore represents a turning point: since then, significantly more devices have been subject to compulsory registration than under the old Directive 2002/96/EC. For example, since 15 August 2018, the obligation has also applied to furniture and clothing or textiles with electrical functions. 

device categories (Recovery) (Reuse and Recycle)
  • Heat vectors
  • Devices that have an outer dimension of more than 50 cm (lare equipment)
85 % 80 %
  • Screens, Monitors and devices, that have a surface larger than 100 cm2
80 % 70 %
  • Devices that have an outer dimension of less than 50 cm (small equipment) Small devices for the information and telecommunication technology, where the outer dimensions are less than 50 cm.
75 % 55 %
  • Lamps
81 %
According to the WEEE regulations, in addition to providing 3R dismantling reports of products, each member country must also establish a complete recycling system for producers to register, and report the statistical results of the Executive Committee on time.
The above products generally refer to END system products. MEAN WELL will continue to provide the 3R dismantling report for the Adaptors and external Battery Chargers for the system vendor to perform the final recovery rate evaluation.


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 (20~100A 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.


How to choose a suitable power supply for a charging application?


MEAN WELL has launched ENC, HEP-600C, GC, PA, PB, RPB and RCB series for battery charge applications (30~360W). However, if these models still cannot fulfill customer’s requirements, there is an alternative for the purpose. Power supplies with constant current limiting as overload protection are suggested. Charge current varies in battery percentage (full or flat), there is high possibility to trigger overload protection when battery is low, those with overload protection as hiccup or shutdown will stop charging the battery in low battery condition. Yet, using a power supply as charging purpose is considered as over load usage, modification is required. Please contact MEAN WELL for the request.


What is PFC?


Power Factor Correction or PFC is to improve the ratio of apparent power to real power. The power factor is around 0.4~0.6 in non-PFC models. In models with PFC circuit, the power factor can reach above 0.95. The calculation formulas are as follows: Apparent Power=Input Voltage x Input Current (VA), Real Power= Input Voltage x Input Current x Power Factor (W).
From the point of view of environment friendly, the power plant needs to generate a power which is higher than apparent power in order to steadily provide electricity. The real usage of electricity is defined by real power. Assuming the power factor is 0.5, the power plant needs to produce more than 2WVA to satisfy 1W real power usage. 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, It will be more effective in energy saving with PFC function.
Active PFC topologies can be divided into single-stage active PFC and two-stage active PFC, the difference is show as in the table below.

PFC topology Advantage Disadvantage Limitation
 active PFC
 Low cost
 Simple schematic
 High efficiency in 
 watt application
 Huge Ripple
 complex feedback 
 1.Zero “hold up time”. The output is
    affected by the AC input directly.
 2.Huge ripple current results in lower LED life
    cycle.(drive the LED directly)
 3.Low dynamic responds, easily affected by
 Two-stage active
 High efficiency
 Higher PF
 Easy feedback control
 High adoptive against 
 load condition
 Higher cost
 Complex schematic
 Suitable for all kinds use



What is LVLE ? If the power supplies can meet LVLE, what is the benefit for the end product?


According from UL8750 definition below:
a. 0-30Vdc output voltage: Maximum 8 amps
b. 30-60Vdc output voltage: 150/V amps
If the power supplies can meet LVLE , the end product does not need the fire enclosure.


what are the applications for PSUs connected in series?


There are two different applications when PSU are connected in series. One is to generate plus minus voltage, another is to increase total output voltage. Connection methods are as follows:
(1) Connection for plus and minus voltage are shown as follow

(2) To increase the total output voltage (Output current remain the same). Diode connect in parallel at output
      side of the driver is necessary to prevent damage during start up. The voltage rating of diode shall greater
      than V1 + V2( shown as figure below), in addition, peak forward surge current rating shall greater than
      rated current.

* Because part of the signal ground is shorted with output ground, strongly suggest to use isolated signals to
   achieve control scheme, in order to prevent damage to the product.


What is the maximum communication distance for Mean Well products equipped with CAN bus communication interface?


MEAN WELL's CAN bus products meet ISO 11898 and the bus rate is 250kbps. Max. communication distance is at least 150m for the products.


What is main difference between DALI-1 and DALI2? Is there any precaution before use?


DALI-2 is an upgraded version of DALI-1. DALI-2 has been adjusted and optimized for the following contents.
1. More precise specification of electrical tolerances and restructuring of specification make DALI-2 less risk for
    malfunctions and increased data accuracy.
2. DALI-2 added 14 new commands/features and removed 1 command. The most important one is extended
    fade time, the range is from 0.1 second to 16 minutes.
3. DALI-2 optimizes its communication sequence between application controller, input device and control gear,
    allowing devices from different manufacturers to work together on the same DALI bus.
4. DALI-2 products must be fully certified by the DiiA Association before they are allowed to use the DALI-2
    DALI-1 and DALI-2 products can be used together. Compatibility issue is shown in the table below.

Configuration Description
DALI-2 application controller with
DALI-1 control gears
Compatible, but no DALI-2 new features in DALI-1 control gears
DALI-2 control gears installed into DALI-1 system DALI-2 control gears are compatible with the system


What is MOOP and MOPP?


a. MOOP: provide adequate protection to the operator
b. MOPP: provide adequate protection to the patient
c. MOP: only one protection
MW products declare 2xMOPP means that MW product can provide two adequate protections to the patient.
It minimum the risk and also suitable for the patient.


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)


What are the requirements of parallel connections? What are the differences between parallel and redundant.


When power supplies are connected in parallel, mostly, is intent to increase the output current. Due to the design of active current sharing, they are mostly without reverse current protection, therefore, they are not the best solution when talking about redundancy. For redundant purpose, please choose the PSU with redundant function or implement external redundant modules. Be sure that the difference in output voltage and wiring impedance, should be as small as possible.
1. Use PSP models as example, connect P(LP/CS) terminals together (Please refer to the parallel function of
    specification). Input and output should be connected in parallel before connecting to the AC source and
    loads. Shown as in picture below (some S.P.S. require a minimum load after paralleling).

2. Output voltage difference between S.P.S. units should be as small as possible, normally < 0.2V.
3. The power supplies should be paralleled with short and large diameter wiring together first, and then
    connected to the load.
4. After paralleling, the maximum usage of total power should be around 90% of the rated total power.
5. When power supplies are paralleled, if the load is lower than 10% of rated load of individual S.P.S. The LED
    indicator or signals (Power Good、Pok、Alarm Signal) may malfunction.
6. To ensure that the load current is effectively shared in parallel operation, in general, it is recommended not to
    use more than 4-6 power supplies at one time.
7. In some models, the +S, -S terminals should be used to reduce unstable pulsation of output voltage.


Why I can not turn on the power supply smoothly when the loads are motors, light bulbs or capacitive loads?


If you connect the S.P.S. to motors, light bulbs, or high capacitive loads, you will have a high output surge current when you turn on the S.P.S. and this high surge current will cause failure of start up. We suggest using S.P.S. with constant current limiting protection to deal with these loads.


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 the difference between EN 61558-1/EN 61558-2-16. EN 60335-1 and EN 62368-1?


No, they are different. SELV means the LED driver will use a safety isolating transformer with double or reinforced insulation and the output voltage shall not exceed 120Vdc.
This is good for the end product safety certified if the LED driver with SELV output.


What is the maximum communication cable length for DALI/KNX/CAN bus/PMBus?



Where can I have the communication protocol for the products I want?


For models equipped with PMBus, such as RCP-1600, you can refer to the communication interface chapter in the user’s manual. For those recognized as optional (non-standard), such as RCP-1600-48CAN, please apply for it through your local distributor.


What is Type HL?


The requirement of Type HL is from UL8750. It provide one option for evaluation of LED drivers that are intended for use in a Class I, Division 2 hazardous location luminaires.
It is simplify the procedure for the manufacture to apply the explosion-proof luminaires.


What is MTBF? Is it distinct from Life Cycle? What is DMTBF?


 MTBF (Mean Time Between Failure) 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 utilize MIL-HDBK-217F(Stress Analysis) as the core of MTBF. The exact meaning of MTBF 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 of 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 under maximum operating temperature to estimate the approximate life of the power supply. For example, RSP-750-12 MTBF=109.1K hours(25°C); electrolytic capacitor C110 Life Cycle=213K hours (Ta=50℃)
DMTBF(Demonstration Mean Time Between Failure) is a way of evaluate MTBF。Please refer to the following equation for MTBF calculation.


MTBF:Mean Time Between Failure

X2:Can be found in chi-square distribution

N:Number of sampling

AF:Acceleration factor, which can be derived from acceleration factor equation.


K(Boltzmann Constant)=(eV/k)

T1:Rated temperature of specification. Note: Kelvin will be the unit use for calculation

T2:The temperature that is used in the meaning of acceleration, and the chosen temperature could not result in physical change in materials. Note: Kelvin will be the unit use for  calculation.  


The output ground (GND) and frame ground (FG) is the same point in my system, can MEAN WELL's power supplies be used in such system?


Yes. Since our products are designed based on isolation concept, it will be no problem that the output ground (GND) and frame ground (FG) is the same point in your system. But, EMI may be affect by this connection.


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.


During the operation of your power supply, there is some leakage current on the case. Is this normal? Will this leakage current hurt human body?


Due to the requirement of EMI, capacitors are connected to FG(Case) for filtering, leading voltage encounter on the case. This effect is clearly state in IEC62384-1 regulation, such as equipment for IT application, <2mA is necessary, and it can be solved by proper grounding connection.


Why my DALI drivers cannot be addressed by a DALI master?


There are several reasons in the table:

Possible Cause Suggested Solution
There is no AC connected to the driver Try again after power on
DALI communication line is off Try again after connecting to the bus
Driver or controller is damaged Contact the maker for repair

If the problem still cannot be solved, please contact your local distributor or MEAN WELL for assistance.


If the concentration of Hexavalent chromium(Cr6+) exceed > 0.13ug/cm2(IEC-62327-7-1 2015), does it mean that it does not meets RoHs standard?


  1. according to IEC-62327-7-1 2015, if the test result of Hexavalent chromium (Cr6+) > 0.13ug/cm2, it only stands for the existing of Cr6+, but it doesn't mean it failed the RoHs requirement (<1000 ppm(mg/kg).
  2. By using ISO3613 is another easy way to evaluate the result. Multiply the thickness of coating and the density of coating (ug/cm2 -> ppm(mg/kg). Ex (Cr6+)2 ug/cm2, thickness of coating: 5um, density of coating :7.14 g • cm−3. The result is 2 ug/cm2 * 5um * 7.14 g • cm−3=71.4 ppm (mg/kg)
  3. If the result is still not clear, using regulation of 2011/65/EU、2015/863/EU for final evaluation.
Test item (Cr6+)
Test method IEC 62321-7-1:2015
Pre-process Boiling water extraction
unit ug/cm2
Judgement (1)Using n.d stand for < 0.10ug/cm2以n.d. Meaning no Cr6+ is measured.
(2)result from 0.10ug/cm2~0.13ug/cm2, Meaning the result of Cr6+ is unclear.
(3)if the result > 0.13ug/cm2, Meaning Cr6+ is presented.


There is communication problem in my PMBus/CAN bus devices, how can I solve it or improve it?


There are several reasons in the table.

Possible Cause Suggested Solution
Addressing error Try again after re-addressing
Data rate error Please set 100kHz for PMBus models and 250kbps for CAN bus models
The power is OFF Try again after power on
The communication line is off Try again after connecting to the bus
Noise interference Add isolation IC before you MCU or controller to reduce noise
If the problem still cannot be solved, please contact your local distributor or MEAN WELL for assistance.


For certain need, is it possible to reduce the noise of fan?


Noise is directly related to the fan which is build into the power supply. Lowering the airflow of the fan means reducing the heat dissipation ability. It will also influence the reliability of the products. Furthermore, minimum airflow of fans is defined by Safety Organization and a safety appendage will be needed if using a new fan. If fan noise is a critical concern, we suggest to select FANLESS products or contact MEAN WELL for other possibilities according to the conditions of use.


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.


What should be noticed when installing a power supply in vertical and horizontal directions?


Most small wattage and fanless power supplies are mainly installed in the horizontal position. If you have to install it vertically because of mechanical limitation, you should consider the output derating due to the heat concern. The temperature derating curve can be found on the spec sheet. Regarding the power supplies with built-in fan or the application has forced cooling system, vertical and horizontal installations have less difference. Ex. In SP-150 derating curve, the ambient temperature difference in application is 5 Celsius from vertical to horizontal. The output wattage in forced cooling can be 20% higher than air cooling convection.


What are the protection forms of overload/overcurrent?


When current drawn exceeds the rating of the PSU, the protection circuit will be triggered to protect the unit against overload/overcurrent. 
Protections of overload/overcurrent can be divided into several forms:
Output current decreases about 20% of rated current, shown as curve (a) in the figure below. 
Output current remains at a constant level and within the specified range while the output voltage drops to a lower level, shown as curve (b) in the figure below. 
Output power remains constant. As output load increases, output voltage decreases in proportion, shown as curve (c) in the figure below.  
Output voltage and current keep pulsing ON and OFF repeatedly when protection is activated. The unit automatically recovers when faulty condition is removed.
 Output voltage and current are cut off when output load reaches protection range. 
NOTE: Protection mode of some of the products combines with different types of the forms mentioned, such as constant current limiting + shut down.

Recover method:
(1)Auto Recovery: PSU recovers automatically after faulty condition is removed.
(2)Re-power on: PSU restarts by manual AC re-power on after faulty condition is removed.
Note:Please do not operate PSU in overcurrent or short-circuit condition for a long period of time to prevent a shorten lifespan or damaging the PSU.


What are the frequently asked questions for KNX products and where can I find them?



How to increase communication reliability for CAN bus?


As differential signaling, adding termination resistors at the both far end of the bus can minimize signal reflection and then increase communication reliability for the interface. A suitable resistor is 120 ohms +/- 10 ohms with mini power rated of 220mw.


What is Ripple & Noise? How to measure it?


It is the small unwanted residual periodic variation of the direct current (DC) output of a power supply which has been derived from an alternating current (AC) source. The wave form is shown as figure below.

There are two AC contents, also known as Ripple and Noise (R&N), on the DC output. The first one, coming from sine wave rectification, is at a low frequency which is 2 times of the input frequency; the second one is at high frequency which is from the switching frequency. For measuring high frequency noise, configurations of an oscilloscope with a bandwidth of 20MHz, a scope probe with shortest ground wire possible, and add 0.1uF and 47uF capacitors in parallel with test point for filtering out noise interference are requires to be made.


Can MEAN WELL charger use on Lithium battery or other type of battery?


All MEAN WELL chargers are preset for lead-acid batteries. For other products that can customize the charging curve (such as ENC / NPB series), customers can customize their charging curve depending on the charging and discharging characteristics of batteries. If you have other requirements, please contact MEAN WELL distributor.


What is Withstand Voltage?How to measure it?


Indicates Hi-Pot Test or Electric Strength Test. The input should be shorted together as well as the output before test. The test will proceed under particular loop, such as I/P-O/P, I/P-FG and O/P-FG with certain high voltage value for 1 minute. (The typical leakage current is 25mA when testing with AC)

  1.  Hi-Pot Test is a way to ensure if the isolation between primary to secondary is done properly, preventing damaging to S.P.S. when facing high voltage between input and output. The test voltage should be gradually increased from 0V to preset level and remains at preset level for 60 seconds with raise time greater than 1 second. In mass production, the test period could be reduced to 1 second. If the leakage current flowing through the isolation material increases rapidly when applying test voltage, it indicates ineffectiveness of isolation (dielectricbreakdown). Corona effect/discharge or transient electrical arc is not considered as failure.
  2. When AC test voltage is applied, Y capacitors are the main cause of leakage current. A 4.7nF capacitor can cause leakage current of 5mA. According to regulations of UL-554, the Y capacitors should be removed for Hi-Pot test, which is not practical for mass production. The only solution is to increase the leakage current setting, typically 25mA, of test instrument. Presently, the criteria of leakage current are not defined in safety regulations.
  3. According to regulations of IEC60950-1, DC test voltage can be substituted when there are bridging capacitors coupled between primary and econdary circuits, so as to solve the problem of leakage current.


Why cannot the current to be adjusted to zero when using CANBus?


The parameters of current adjustment when using CANBus are actually for current limitation adjustment. You can recognize this function as the PC function what MEAN WELL implements for other industrial PSU.


Does the power supply capable to operates at high altitude condition.


The limitation for MEAN WELL power to operate under high altitude are as follow:
1. Operating temperature should decrease every 3.5℃/1000m for fan-less power supplies.
2. Operating temperature should decrease every 5℃/1000m for power supplies with fan.
*Should there be any concern about safety insulation, please contact our sales representatives


Can I use BIC-2200 as an ordinary stand-alone inverter like NTS/NTU/TS/TN series?


No. The BIC-2200 is designed with grid-tie compatible, meaning that the BIC-2200 will enter anti-islanding protection and not generate any AC energy when disconnect the bidirectional power supply from the mains. Therefore, the BIC-2200 could not be used as an ordinary stand-alone inverter.


How does MEAN WELL define switching time of 1ms(BIC-2200)?


The switching time is the time period which current flow from one direction to another, under 5% of Vo variation. Please refer to the figures below for definition and actual waveform.

Test Result:

AC to DC Direction 1ms    888   us
DC to AC Direction 1ms    681   us


Why I cannot use battery mode and C/D control function in BIC-2200?


Battery mode and C/D control function only can be activated via CANBus communication interface. If you do need these functions, please contact our distributor and order BIC-2200CAN.


What is the definition of IP (Ingress Protection) ratings? And what is MeanWell’s IP68 definition.


MEAN WELL has incorporated dust proofing and water proofing into majority of its LED power supply design. Mainly based on the international standard IEC60529, detailed descriptions can be found in the following table:
(Note: PSUs with IP64 rating or above are suitable for indoor or outdoor applications in sheltered locations)

*IP64-IP66 level and IP67 with potentiometer products are suitable for damp indoor or sheltered outdoor environment. For actual installation limitations, please refer to the corresponding IP level tests.
*All products cannot be continuously submerged in water.
*The definition of IP68 by MEAN WELL: Immerse a unit under test in 1 meter below the surface of the water, tested with a dynamic condition where 12 hour AC on; 12 hour AC off.
Test duration: 1 month.


Why is that LED lamp designed with LED driver IC may sometimes cause power supply startup failure? (Output voltage gets clamped by LEDs and cannot rise to rated level)


Depending on circuit design, there could be different operational problems. See below:

  1. Boost mode driver IC:
    The startup voltage of such driver IC is significant lower than the total LED forward voltage. For this reason, the IC will start up at very low voltage level usually about 1/2 of the power supply’s rated voltage and to meet rated power requirement, the startup current will reach 2 times the power supply’s rated current. When the power supply is unable to provide this current, the LED CC driver will not activate.
  2. Buck mode driver IC:
    If the selected power supply voltage is significantly higher than the LED forward voltage. For example, power supply provides 48V and the LED lamp only needs 24V and the power ratings are equivalent. When power supply voltage reached the LED conduction voltage, the power supply will immediately go into constant current mode. At this moment, the required power to start up the LED + driver is larger than what the power supply can provide causing malfunction of the driver circuit and the power supply to be clamped at LED forward voltage. For boost mode design, we recommend raising the startup voltage of the driver IC to be as close to the power supply voltage as possible or incorporate soft start function (see fig. 3). Wait until the power supply voltage is established before starting the driver. When selecting power supply for buck mode, the output voltage of the power supply should be as close to the LED total voltage as possible with excess power available (LED power/0.85).

DIM PIN is the startup pin for most PWM based driver. It can also be designated as EN (Enable). DIM (or Enable) is at 0V the internal connection to SW pin will be open. When the DIM voltage reaches 1.5V (Typ), the IC will Turn ON. To set the Vstart for the DRIVER IC: Vstart = (VDIM/RB) x (RA+RB). The general rule is to set the Vstart at 5~10% higher than the total LED forward voltage.


How do you select suitable MW LED power supply?


  1. Select suitable wattage based on customers system requirements and application methods. Must also take excess power and driving method into consideration.
  • For selection key points when using MW power supply to “directly” drive LED lamp refer to LED configuration and installation notes.
  • For selection key points when using MW power supply in combination with LED driver IC to achieve high precision current control refer to LED configuration and installation notes.
  1. Based on LED power supplys operating environment select suitable IP level and mechanical type (metal enclosure, plastic enclosure, and open frame PCB) for that environment.
  2. Is PFC function required or not? Single stage PFC is only suitable for LED load. Dual stage PFC is suitable for general applications.
  3. If LED system is based on direct drive, units with adjustable voltage and current should be considered for flexibility in changing voltage/current levels. Dimming function may also come in handy when LED brightness control is preferred.
     * Comparison Chart
     * For those who chose to use single stage PFC products. Refer to What is the difference between single stage
       and two stage power supply.


What are the most common LED driving methods? What are its advantages and disadvantages?



For a particular LED lighting design, each LED strip consists of 12 LEDs connected in series (VF=3.5V), 4 strips in parallel, and each strip requires 0.7A of drive current. Based on the above conditions, how do you select a suitable power supply?


First of all, the LED power supply must be able to work in constant current mode. LED forward voltage of each strip = 3.5V X 12pcs = 42V LED lamp total current requirement = 0.7A X 4 strips in parallel = 2.8A LED power requirement = 42V X 2.8A = 117.6W LED power supply’s rated voltage/power should be greater than what is required but should be as close to the actual requirement as possible. Use 48V/150W as the basic criteria to pick LED power supply then make sure actual voltage/power usage meets constant current region and PF>0.9 specifications (117.6W/150W = 78.4% > 75%). CLG-150A-48V with output current set at 2.8A can be used in this design.
Note: Each LED production lot will fall within a VF rank (e.g.3.4~3.6V). This LED tolerance must be taken into consideration during design.


Same LED configuration as in question B1 with the exception of additional driver ICs. What is a suitable power supply unit to use?


First calculate for required voltage by combining total LED forward voltage and driver voltage drop of 2V. LED forward voltage of each strip = 3.5V x 12pcs = 42V Driver circuit required voltage = 42V + 2V = 44V LED total current requirement = 0.7A X 4 strips in parallel = 2.8A Driver circuit required wattage = 44V X 2.8A = 123.2W LED power supply's rated voltage/power should be greater than what is required but should be as close to the actual requirement as possible. Use 48V/150W as the basic criteria to pick LED power supply then make sure actual voltage/power usage meets constant current region and PF>0.9 specifications (123.2W /150W = 82.13% >75%) CLG-150A-48 with output voltage set at 44V can be used in this design


What to consider when selecting LED power supply?


  1. Lighting system designed to work in direct drive mode
    1. The combined LED forward voltage range (upper and lower) must fall within LED power supplys constant current voltage range. For example, the LED Vf spec is 3.4~3.6V, when 6 are connected in series the combined Vf will be 20.4~21.6V. In this case, a 24V unit must be selected with constant current region of 18~24V.Ø
    2. For models with active PFC and system PF requirement is >0.9, load usage must be higher than as specified in the PFC spec. Relationship between PF and output load can be found in figure 1. The typical requirement is 75% load or above. Double check the spec for the model you are using to confirm actual requirement.
    3. In areas with unstable AC voltage such as heavy industrial zone or generator supply utility, please select general usage LED series from table 1.
  2. Lighting system designed to work with driver IC
    1. The start up voltage of driver IC should be as close to the power supply rated voltage as possible.
    2. Driver IC needs stable voltage to function properly. So, it is highly recommended to use general usage series from table 1.
    3. For models with active PFC and system PF requirement is >0.9, load usage must be higher than as specified in the PFC spec. Relationship between PF and output load can be found in figure 1. The typical requirement is 75% load or above.
    4. Double check the spec for the model you are using to confirm actual requirement. When using driver IC, possible system EMI issue could arise. After completing lighting system design, EMI must be double checked.