Power Supply Expert

  • If you have questions on MEAN WELL’s products, please read the FAQ first. If the listed answers still cannot solve your problems, please contact 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

    Q1Notes on choosing a switching power supply?

    Ans

    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. 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.

    4. 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.

    5. Make sure that the model qualifies for the safety standards and EMC regulations you need.

    Q2Can MEAN WELL's power supply be used in the range of 45Hz ~ 440Hz? If YES, what will happen?

    Ans

    1. 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.

    Q3What is minimum load requirement and how can I read it from the spec?

    Ans

    1. 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.

    Q4Why did the power supply shuts down during operation and after turning it off, I can restart the power supply again?

    Ans

    1. 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.

    Q5What is the control mechanism for cooling fans?

    Ans

    1. 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:
    2. 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.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.
    3. 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.

    Q6What is "Inrush Current"? What will we notice?

    Ans

    1. 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.

    Q7What is PFC?

    Ans

    1. 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.

    Q8What is the difference between -V and COM which are marked on the output side?

    Ans

    1. Single output: Positive pole (+V), Negative pole (-V)Multiple output (Common ground): Positive pole (+V1, +V2,.), Negative pole (COM)

    Q9In MEAN WELL's catalog, we see AC and DC at input, what is it all about?

    Ans

    1. Due to different circuit designs, MEAN WELL power supply's input consists of three types as below:(VAC≒VDC)a.85~264VAC;120~370VDCb.176~264VAC;250~370VDCc.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.

    Q10What is MTBF? Is it distinct from Life Cycle? What is DMTBF?

    Ans

    1. 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℃)

    2. DMTBF(Demonstration Mean Time Between Failure) is a way of evaluate MTBF。Please refer to the following equation for MTBF calculation.

    3.            

    4. WhereMTBF:Mean Time Between FailureX2:Can be found in chi-square distributionN:Number of samplingAF:Acceleration factor, which can be derived from acceleration factor equation.Ae=0.6K(Boltzmann Constant)=(eV/k)T1:Rated temperature of specification. Note: Kelvin will be the unit use for calculationT2: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.

    Q11What is power good and power fail signals and how can use it?

    Ans

    1. 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.

    Q12I have an TN-1500 inverter. Why the LED indication of AC IN is not lit after mains input has been applied?

    Ans

    1. 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.

    Q13What are the protection forms of overload/overcurrent?

    Ans

    1. 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:(1)FOLDBACK CURRENT LIMITINGOutput current decreases about 20% of rated current, shown as curve (a) in the figure below. (2)CONSTANT CURRENT LIMITINGOutput 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. (3)OVER POWER LIMITINGOutput power remains constant. As output load increases, output voltage decreases in proportion, shown as curve (c) in the figure below. (4)HICCUP CURRENT LIMITINGOutput voltage and current keep pulsing ON and OFF repeatedly when protection is activated. The unit automatically recovers when faulty condition is removed.(5)SHUT OFF 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.


    2. 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.

    Q14What is Ripple & Noise? How to measure it?

    Ans

    1. 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.

    2. 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.


    Q15What is Withstand Voltage?How to measure it?

    Ans

    1. 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)


    2. 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.

    3. 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.

    4. 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.

    Q16What is the definition of IP (Ingress Protection) ratings? And what is MeanWell’s IP68 definition.

    Ans

    1. 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)


    2. *IP64-IP66 level products are suitable for damp indoor or sheltered outdoor environment. For actual installation limitations, please refer to ther 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.

    Q17How do you select suitable MW LED power supply?

    Ans

    1. Select suitable wattage based on customer’s 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 questions (A2) and (A3).

      • For selection key points when using MW power supply in combination with LED driver IC to achieve high precision current control refer to questions (A2) and (A3).

    2. Based on LED power supply’s operating environment select suitable IP level and mechanical type (metal enclosure, plastic enclosure, and open frame PCB) for that environment.

    3. Is PFC function required or not? Single stage PFC is only suitable for LED load. Dual stage PFC is suitable for general applications.

    4. 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 http://www.meanwell.com/product/images/led/LED_comparison_chart_en.pdf*For those who chose to use single stage PFC products. Refer to Question D1for more instructions.

    Q18What are the most common LED driving methods? What are its advantages and disadvantages?

    Ans


    Q19What to consider when selecting LED power supply?

    Ans

    1. Lighting system designed to work in direct drive mode

      • The combined LED forward voltage range (upper and lower) must fall within LED power supply’s 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

      • 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.

      • 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

      • The start up voltage of driver IC should be as close to the power supply rated voltage as possible.

      • Driver IC needs stable voltage to function properly. So, it is highly recommended to use general usage series from table 1.

      • 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. When using driver IC, possible system EMI issue could arise. After completing lighting system design, EMI must be double checked. For suggestion on system EMI problem solving, refer to question 11.



    Q20What are CV, CC, and CV+CC which are often mentioned in LED power supply specification?

    Ans


    Q21How to use ELN-30/60-XXD(P) Dimming function in applications?

    Ans

    1. As shown in fig 11&12, an external signal can be applied to “DIM+” and “DIM-.” The signal can be either DC voltage (D Type) or PWM (P Type). By changing the signal levels as shown below, the output current limit can be controlled by the user. Please note, the relationship between external signal and output current level is non-linear. It cannot be used for high precision dimming control.


    Q22Does MW LED power supply allow adjustment of output voltage and current levels?

    Ans

    1. LED power supply comparison table to see which MW LED power supply allows for V/I adjustments. A suitable unit can be picked based on the type of adjustment required. For the allowed adjustment range, please refer to the spec sheet. Tuning of the voltage and current levels can be done through the built-in VRs/potentiometers. PLN/ELN requires removal of the top cover in order to access the internal SVR1 and SVR2, see figure 9 for VR locations. For other series, the VRs can be accessed through IoADJ and VoADJ holes after rubber stopper removal. After adjustments have been made, please make sure rate power is not exceeded and the rubber stoppers are properly reassembled.


    Q23What does the IP level found on MW LED power supply mean (i.e. CLG-100 = IP67)?

    Ans

    1. MW LED power has dust/water proof design, primarily based on international standard IEC60529. Description of IP levels can be found in the table below:


    2. *IP64-IP66 level products are suitable for damp indoor or sheltered outdoor environment. For actual installation limitations, please refer to ther corresponding IP level tests.*All products cannot be continuously submerged in water.

    Q24To design a LED street lamp, what solution can MEAN WELL offer?

    Ans


    Q25What is the main difference between 1~10V dimming and 0~10V dimming regarding applications?

    Ans

    1. With 1~10V dimming, the lighting unit can be dimmed down to 10%; with 0~10V dimming, it can be dim down to 0%, or say, dim to “off”.

    Q26What is the current accuracy of LED SPS?

    Ans

    1. For LED SPS output current accuracy, please refer to product specification. For CC model, “CURRENT ACCURACY” is listed in SPECIFICATION section. For CC+CV model, please reference the OVER CURRENT range in PROTECTION of the SPECIFICATION section.

    Q27What is the difference between Single Stage and Two Stage Power Supply?

    Ans

    1. There are 2 types of Power Factor Correction circuits; one is Single Stage and the other is Two Stage. Single stage power supply combines functions of power factor correction and converter in one circuit but two stage use two separate circuits. Compared to Single Stage, Two Stage design is more complex and costly but the immunity performance of Two Stage PSU against AC mains is much better than that of Single Stage PSU; in addition, Two Stage manifests better ripple noises performance on output. Owing to that Single Stage is only suitable for fields with quality AC mains but Two Stage can be used in serious circumstance for LED drivers or as industrial switching power supplies.

    Q28How am I supposed to read the LED V-I dotted line & tolerance definition in the specification?

    Ans

    1. Mean Well’s LED product specification normally exhibits V-I characteristics. Per the characteristics, there are generally two types of drivers, “CC” type and “CC+CV” type. “CC” type of driver is suitable only for LED applications whereas “CC+CV” for either LED applications or general switching power supply applications. The section that is not suitable for LED applications are represented by dotted line, and based on the protection procedures it can be categorized into hiccup mode and constant current mode; in this section, the tolerance of current is not defined but only the characteristic of current is displayed. If customers attempt not to see a very high current under short circuit condition, those models with hiccup mode for this section can be selected; if there are applications with motors or capacitive load, those with constant current can be chosen.







  • MEAN WELL’s power supplies have been used in a wide variety of electronic equipments, including factory control, IT, communication, appliances, medical, lighting, billboards, security, vehicle, etc…. , which is capable of meeting your needs.

    Application Aspect

    Q1Points on connecting wires used in power supplies?

    Ans

    1. 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.


    Q2How to select adaptors with the correct AC plug for use in different countries?

    Ans

    1. 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.



    Q3 A few things you should know before using the Remote Sensing function

    Ans

    1. 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 currentb. Rated Voltage is higher than the output voltage


    Q4Is 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)

    Ans

    1. 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:http://www.meanwell.com.tw/webapp/product/search.aspx?prod=SBP-001&pdf=U0JQLUMucGRm&a=4Following video is an example of demonstrating the ENC-120.

    Q5What should we pay attention to if system implemented magnetic component?

    Ans

    1. 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.

    Q6How to choose a suitable power supply for a charging application?

    Ans

    1. 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.

    Q7what are the applications for PSUs connected in series?

    Ans

    1. there are two types of the applications, one is to create positive and negative voltages, one is to build higher output voltage. Connection methods are shown as below: (1) Positive and negative voltage


    2. (2) Increase the output voltage (current does not change). If there is no reverse blocking diode in the power supply, we should add an external blocking diode to prevent the damage of power supply while starting up. The voltage rating of the external diode should be greater than V1+V2. Transit current rating of diodes shall be greater than rate output current of S.P.S.


    Q8Requirements on parallel operation?

    Ans

    1. When power supplies are connected in parallel, it is able to increase the output current or use them as the redundant (back-up) function. Be sure that the difference inoutput voltage and wiring impedance should be small when operating in parallel.1. Connect P(LP/CS) terminals together such as the PSP models (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. 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.

    Q9Why I can not turn on the power supply smoothly when the loads are motors, light bulbs or capacitive loads?

    Ans

    1. 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.

    Q10The 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?

    Ans

    1. 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.

    Q11During the operation of your power supply, there is some leakage current on the case. Is this normal? Will this leakage current hurt human body?

    Ans

    1. Due to the requirement of EMI, there will be some Y capacitors between line and neutral to the FG (case) to improve EMC. These Y capacitors will cause some leakage current flow from line or neutral to the case (normally case will be connected to earth ground). For example, IEC-60950-1 requires that this current should be less than 3.5mA for IT equipment, so basically the leakage current you find on the case will not hurt human body. Proper connection to Earth ground will solve the leakage current problem.

    Q12For certain need, is it possible to reduce the noise of fan?

    Ans

    1. 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.

    Q13What should be noticed when installing a power supply in vertical and horizontal directions?

    Ans

    1. 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.


    Q14How to select a suitable proper circuit breaker or fuse for MEAN WELL SPS?

    Ans

    1. At input side, there will be a large transient inrush current during the power on of an SPS. The inrush current is usually of 20~100A based on the design of SPS, which will last for 1/2~1cycle of AC input (ex. 1/120~1/60 seconds for 60Hz AC source). Every breaker or fuse will actually have its own time-current (V-I) characteristic curve. Users can choose a breaker or fuse which has a rated current just over input current of SPS and check whether the V-I curve of the breaker or fuse can withstand the high inrush current from the SPS with a maximum duration of 1 cycle of AC input (e.g. 1/60 second).

    Q15Can MEAN WELL charger use on Lithium battery or other type of battery?

    Ans

    1. All MW chargers are designed for lead-acid batteries. Every Lithium battery or other type of battery will have its own charging/discharging characteristic. Modification will be required for MW's charger in order to match the profile of each battery or users' requirements. Please contact your local distributor if you would like to have a modification for your own battery.

    Q16For 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?

    Ans

    1. 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.
    2. 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.

    Q17Same LED configuration as in question B1 with the exception of additional driver ICs. What is a suitable power supply unit to use?

    Ans

    1. 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

    Q18Why 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)

    Ans

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

      • 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.

      • 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).


    2. 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.

    Q19Can LED power supplies be connected in parallel?

    Ans

    1. MW LED power supply does not have parallel “current sharing” function so it is not suitable for parallel connection. For high power requirement, please select higher wattage power supply or divide LED load into smaller subsections to be powered by individual power supplies. Example of such LED configuration can be found in figure 5. As shown in fig. 5, the connection between -V of the LPC-35 units should be severed and not connected in common. On the contrary, small wattage LED loads can be connected in parallel and be powered by a single high wattage power supply. But, the ability to divide current evenly must be taken into consideration.


    Q20What surge level can MW LED power supply withstand?

    Ans

    1. Among MW LED power supplies, CEN/ CLG and HBG, HLG, HLN, HLP, HVG, HSG have the highest surge capability. It can withstand heavy industry level of 4kV. If higher level is required, external ZNR (470V) or gas tube (500V) can be added as shown in figure 8. But, overall safety compliance must be taken into consideration. For application with numerous lamp sets, a SPD (Surge Protection Device) can be installed to meet surge regulation requirements.


    Q21Can MW recommend the dimmers compatible to the 3 in 1 dimming circuit?

    Ans

    1. 3 in 1 dimming is the most commonly applications used in LED dimming with the feature that it does not have to work with any specific dimmer. The only thing that has to be verified is that whether the dimmer (1~10V/10V PWM/resistance) is compatible with the definition advised in our specs.

    Q22Which model should we select when attempting to dim a LED strip?

    Ans

    1. Generally speaking, LED strips would be connected with resistors in series, so the LED must be driven in CV mode. We will suggest those models offering CV dimming to be adopted, such as PWM series.

    Q23How can we learn how many units of the model with 3 in 1 dimming can be controlled by one dimming device?

    Ans

    1. 3 in 1 dimming circuit would drain 0.1mA per model. Dividing the rated current of the dimmer by the 0.1mA, and we could know how many units can be controlled by one dimming device. For resistance dimming applications, resistance for 100% dimming output would be 100K ohm divided number of models.

    Q24Can we use LED CC model as a charger?

    Ans

    1. MW has several charger products, and we suggest choosing them first. Chargers would be more suitable since they are designed for charging applications. Safety & Approvals should be taken into account. If you really cannot find a proper model in our chargers series, our LED CC models can be used as charger. Please choose suitable products after confirming the current and voltage specification on the datasheet of the battery.

    Q25There are so many MW dimming products. How can I make a choice? What are the pros and cons?

    Ans

    1. First, you have to know your Led lamp specification in order to screen out a suitable Led driver range (Wattage, Voltage, Max Current CC or CV). From those ranges, further check a compatible dimming function. Hereunder is a table to show you the pros and cons of Dimming Function you can find in MW's catalogue.


    Q26Can I use MW LED drivers at full load continuously? Most of the AC/DC power supply are suggested to use at 70% load.

    Ans

    1. LED Drivers are recommended operate at full load as long as it observes the working temperature specified in the datasheet, which means Tc measurement results should be equal to or less than the stated Tc in the datasheet. 5 years warranty complies as long as drivers operate within working Temp and Tc. Limit as well.

    Q27Can I wire LDD or LDH in parallel or series?

    Ans

    1. LDD/LDH series comprises switching components; series or parallel connection will damage these switching components.

    Q28How long can I extend DC cable of the driver?

    Ans

    1. Owing to line (voltage)-drop, we suggest the extension made from AC cable. In case DC cable extension is necessary, please consider Line-Drop leading to insufficient Vf so that the LED model or lamp may fail to switch ON. Moreover, EMC performance and characteristic may also be affected by DC cable extension.

    Q29Why is that during LED power supply operation the LED sometimes varies in brightness or flickers?

    Ans

    1. MW developed many power supplies series specifically for LED application. Single stage PFC was used in such developments due to low cost. This topology has the following restrictions:

      • AC fluctuationThis topology does not use input bulk capacitor. For this reason, in areas with low AC quality, output voltage and current may become unstable causing variation in LED brightness. If the input AC voltage is stable then this problem will not occur.

      • Output rippleThis is also caused by lack of input bulk capacitor. As compared to power supplies using dual stage PFC, the ripple will be significantly larger (see Figure 4). There could be instances where the low end of the ripple may be too low for the driver IC to operate properly and the LEDs will start to flicker. To solve this type of problem, the output voltage can be adjusted higher so the low end is higher than the driver’s minimum working voltage. Or simply select a PSU with higher rated voltage.

      • Current harmouicsSingle stage PFC power supplies are optimize for constant current drive. Using these supplies as constant voltage sources (such as application including cascading a constant current driver IC), the harmonics might be worsen in this case. When operating in areas with unstable utility voltage or with driver IC, we highly recommend using general application types as found in table 1. Avoid using single stage PFC if possible, or contact MEANWELL.


    Q30I cannot do dimming with MW LED drivers?? Why?

    Ans

    1. First, please make sure your LED lamp or modules are Constant Current (CC) driven or Constant Voltage (CV) driven. If you are using CC-driven LED applications, please verify that MW LED driver’s rated current on datasheet can match your LED current requirement. If you are using CV LED applications, we offer PWM series for CV dimming applications.

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