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.

According to safety standard, the leakage current in EN60950-1 Class I cannot exceed 3.5mA; in EN60601-1 cannot exceed 0.3mA. Others criteria like safe distance and numbers of fuse are also different. Please consult the diagram below:

  The AC power line shall be turned off, and live wire connections shall not be exercised. Turn on AC power after all connections have been properly made to avoid the electrical hazard.

 It is recommended to install the power supply horizontally per datasheet. If there are space limitations and power supply cannot be installed horizontally, please de-rate the power supply output as necessary and keep the ventilation holes unobstructed to ensure proper ventilation affecting power supply lifetime.

 Pay attention to the maximum length of mounting screws as specified in the datasheet. If the length exceeds the specifications, the screw may come in contact with internal components and cause electrical failures or even endangerment. Please refer to the installation manual for the appropriate torque settings and wire gauge.

 When the system is Class I installation, connect the power supply frame ground (FG) with the system frame ground (FG). For more details on installation precautions, please visit Selection Guide-Installation Manual and download the corresponding installation manuals per product types.

As specified in the MEAN WELL datasheets, power supplies typically have 3 different types of cooling methods: free air convection, built-in fan cooling, and external fan cooling. The installation of the external fan needs to be considered in the end system. If there is no external fans added, output power needs to be de-rated according to the datasheets.

MEAN WELL power supplies comply to EMC requirements by themselves, but since power supplies are components, the EMC performance of the end system my not be compliant and needs to be evaluated as a whole. When there are EMC related issues, you may try the suggestions below:
1 Add EMI filter to the power supply input
2 Add grounding choke
3 Add EMI cores to the AC or DC cables

Medical products have very stringent requirements for leakage currents, and MEAN WELL medical power supplies are designed to meet the safety requirement levels. However, the system level leakage current will increase when there are multiple power supplies in the system, thus when the end system needs to utilize multiple output voltages or power supplies, it is highly recommended to use medical grade modular power supplies, such as the NMP series, in order to ensure the leakage current requirements are met.

Power supplies are not medical equipment nor applied parts, and the power supplies shall not come in direct contact with the patients. Most medical equipment has medical grade power supplies, but only the parts of the equipment that comes into contact with the patients are classified as applied parts.

Applied parts for medical systems can be classified into Type B, BF, or CF:
 

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.

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.

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.

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.

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.

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)

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.

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 whereby 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 is 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.

The decision on whether to use Class I or Class II power supplies is typically dictated by the end system. If the end system is Class I type, please select Class I power supply, and if the end system is Class II type, please select Class II power supply to avoid performance issues with EMI, hi-pot, etc.

If the system is in the early development stage, it is suggested to switch to a power supply with -V and AC FG isolated or directly use a Class II power supply. If the system is already in late design stages and the power supply can no longer be changed, then the grounding test must be conducted to ensure the proper connection to ground and note that the wire gauge needs to be thick enough (16AWG recommended). In addition, the system’s enclosure should have a grounding screw with a grounding cable, and the purpose shall be explained in the function manual.

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

 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.

Suggest customer add a ferrite core near the power supply side of the output cord, which can help suppress interferences. If the power supply is an adaptor, it is most effective to clamp the core within 25mm of the strain relief (SR).

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.

a. MOOP: provide adequate protection to the operator
b. MOPP: provide adequate protection to the patient
c. MOP: only one protection
The end system needs to utilize power supplies with the appropriate ratings to ensure safety for the patients or operators.

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.

When current drawn exceeds the rated output current of the power supply, the protection circuit will be triggered to protect the power supply against overload/overcurrent. 
Protections of overload/overcurrent can be divided into several forms:

(1)FOLDBACK CURRENT LIMITING
Output current decreases about 20% of rated current, shown as curve (a) in the figure below. 

(2)CONSTANT CURRENT LIMITING
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. 

(3)OVER POWER LIMITING
Output power remains constant. As output load increases, the output voltage decreases in proportion, shown as curve (c) in the figure below.  

(4)HICCUP CURRENT LIMITING
Output 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 the output load reaches the protection range. 
NOTE: Protection mode of some of the products combines with different types of forms mentioned, such as constant current limiting + shut down.

Recover method:
(1)Auto Recovery: PSU recovers automatically after fault condition is removed.
(2)Re-power on: PSU restarts by manual AC re-power on after fault 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.