Why You Should Use Configurable Power Supplies
Edis Osmanbasic posted on March 27, 2020 |
A look at the MEAN WELL NMP and UMP-400 series of configurable power supplies.
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Power supplies are a crucial part of any electrical system, and it’s important to choose the right power supply for your needs. In this article, we’ll examine the benefits of configurable power supplies such as the MEAN WELL NMP and UMP-400 Series.

The MEAN WELL NMP power supplies. (Image courtesy of MEAN WELL.)
The MEAN WELL NMP power supplies. (Image courtesy of MEAN WELL.)

Configurable Power Supplies

Standard power supplies with a fixed output are low cost and widely available, but they’re not always the best solution. These power supplies compel designers to adapt their system to pre-determined power specifications.

Configurable power supplies, which offer programmable outputs, can be far more effective. Configurable power supplies consist of a front end power supply along with modules that provide DC-DC regulation. The front end is connected to the modules by either quick connect or plug-and-play style. The power modules can be used to create simple and compact distributed power supply systems.

Figure 1. A traditional configuration with multiple AC-DC power supplies (left) versus a distributed system with configurable power supplies (right).
Figure 1. A traditional configuration with multiple AC-DC power supplies (left) versus a distributed system with configurable power supplies (right).

Flexibility is the main benefit of configurable power supplies, which makes them attractive for various applications. The configurable power supplies we’ll discuss in this article are the MEAN WELL NMP1K2 and NMP650.

“We provide different flavors of output modules that are compatible with the front end supplier, so the users can just mix and match what they need in terms of output-voltage, output-power levels, etc.,” said Kai Li, Project manager at MEAN WELL. “Sophisticated machinery requires multiple output voltage levels. A 3D printer, for example, would need 24V to drive the motor, 12V to drive the display panels and 3.3V to control some wireless features. With a configurable power supply, I just need a single unit to support all of those different voltages.”

MEAN WELL NMP Power Supplies

The MEAN WELL NMP series of 1U low profile configurable power supplies includes the NMP-650 (650W) and NMP1K2 (1,200W), and four adjustable output modules that cover the full range from 3V to 55V. The NMP series also offers intelligent control functions.

“It enables intelligent controls from its various control signals. We can remotely turn the unit on and off, and we can do that with a global control signal to the front end, or we can do it locally at each of the output modules,” Li explained.

Besides the flexibility and control features, there are many additional advantages of configurable power supplies, as exemplified by the MEAN WELL NMP Series.

Low Leakage Current

The current that flows through the protective ground conductor to the ground is known as the leakage current. If the grounding connection is damaged, the current could flow to ground through any conductive part—including a human body.

Leakage current can be AC or DC. Power supplies primarily see AC leakage caused by a parallel combination of capacitance, as well as DC resistance between a voltage source and the grounded conductive parts. Power supply manufacturers must limit this current value so that it is safe for anyone who touches the power supply case.

For standard power supplies, leakage current is usually loosely controlled, which causes difficulties in meeting the requirements for specific appliances. Configurable power supplies can offer a lower leakage current. They are designed and certified as a whole unit considering all leakage current performance. Ultimately, the total leakage current of configurable power supplies is lower than the combined leakage currents from multiple power supplies in a traditional approach.

The MEAN WELL NMP supplies have a very low leakage current:

  • Earth leakage current <400uA/264VAC
  • Touch current <100uA/264VAC

EMC Performance

Electromagnetic compatibility (EMC) refers to a device's ability to maintain performance in spite of electromagnetic interference (EMI) from nearby devices, while also not generating EMI itself. Depending on their design characteristics, power supplies can generate EMI that impacts nearby devices.

Using several standard power supplies increases the electromagnetic interference in an electrical system. However, using a single configurable power supply reduces this effect and saves design engineers from EMI debugging, the most time-consuming part of designing electromechanical products. Configurable power supplies can limit the need for additional filters and design corrections.

High Power Density

Many applications require high power in a limited space, so power supply manufacturers work to reduce the size of supplies while maintaining the same output power. A good measure of this relationship is power density, or power per unit volume. High power density means more power in less space.

To achieve a high power density for power supplies, efficient cooling is a must. This is how the NMP power supplies attain an efficiency of up to 91 percent. The NMP-650 (650W output power) has one built-in cooling fan and the NMP-1K2 (1,200W) has two, as Li explained.

“When we were designing the [NMP], we had to very carefully consider the aerodynamics, the air flow of the fans and how the airflow interacts with the components,” he said. “So it's overall a combined design experience from MEAN WELL's over 35 years of designing switching power supplies.”

Functions of Configurable Power Supplies

The MEAN WELL NMP series includes additional functions to improve the flexibility of the supplies. An active power factor correction (PFC) function improves conversion efficiency and protects the device. Active current sharing and parallel control capabilities allow users to increase the total output current by connecting up to four (NMP650) or six (NMP1K2) modules of the same output voltage rating (meaning the difference in voltage should be less than 0.2V).

Higher output voltages can be achieved by connecting output modules in series (where the total output current should not exceed the current rating of the lowest rated module connected in series).

Figure 2. Parallel connection of six NMS240 modules. (Image courtesy of MEAN WELL.)
Figure 2. Parallel connection of six NMS240 modules. (Image courtesy of MEAN WELL.)

The output voltage of the modules can be adjusted via the step voltage regulator (SVR), which is trimmed by turning the VR60 potentiometer near the output terminals. Turning the VR60 clockwise increases the voltage, and turning it counter-clockwise reduces the voltage. The output voltage is programmable in the range of  3 – 6V (NMS-240-05), 6 – 15V (NMS-240-05), 15 – 30V (NMS-240-24), and 30 – 55V (NMS-240-48). Additionally, the voltage and current can be trimmed to 40 – 100 percent of the rated values by applying external DC voltages (see graph below).

 Figure 3. Output current can be adjusted by applying an external DC voltage. (Image courtesy of MEAN WELL.)
Figure 3. Output current can be adjusted by applying an external DC voltage. (Image courtesy of MEAN WELL.)

“We only have four different modules, with the nominal voltages of 5V, 12V,  24V and 48V,” Li explained. “Each module has a very wide adjustment range. Some of our competitors make over one hundred different modules. Our users do not have to go through many pages of spec sheets just to find the right module.”

The NMP series has a built-in remote sense output module that can compensate for voltage drops up to 0.5V. The voltage sense wires should be twisted or shielded to prevent external noise interference. The DC OK signal output monitors the status of the power supply. When the output module is operating properly, the DC-OK signal is HIGH (4.5~5.5V) and the LED indicator is lit.

Configurable power supplies should also offer built-in protections. The NMP output modules have current protections that activate when the output is short-circuited or the output current exceeds 115% ± 10% of the rated output current. The output will automatically recover when the faulty condition is removed. Each output module also has built-in over-voltage protection. Once the protection is triggered, the units shut off for 10 seconds before re-cycling AC power to power on the unit. There is also a built-in fan-lock protection circuit. The output of all modules shuts off when the DC fan stops operating (in case of fan-lock, loose connectors or broken wires). It is necessary to turn off the AC power and remove the conditions causing the fan-lock.

Additionally, the NMP series includes over-temperature protection with a built-in thermal detection circuit. If the internal temperature exceeds a pre-set value, the system will send a HIGH signal. If the internal temperature continues to increase and exceeds the “safe limit” value, the output shuts down automatically. When the internal temperature is within a normal value, this signal is LOW.

Power Supply Safety

Safety is a critical factor when it comes to power supplies, and the NMP series complies with regulations including the medical 2x MOPP and ITE standards.

Means Of Patient Protection (MOPP) is a safety standard establishing basic safety requirements for medical electrical equipment. These regulations mainly stipulate the isolation level of the power supplies. Electrical safety for medical devices is administrated by IEC/EN 60601-1, with detailed measures to guard against electric shock.

There are two MOP protections: MOOP and MOPP. MOOP stands for Means Of Operator Protection, and it is meant for devices that will not come into contact with the patient. MOOP typically has a lower level of isolation and leakage requirements, mainly dictating the isolation level of the units of the power supplies.

In the case of medical applications where patients could come into contact with the device, at least one means of patient protection (MOPP) is required. This includes numerous medical applications such as ultrasound scanners, MRI machines, defibrillators and dialysis machines.

The highest level of protection specified in the standard requires at least 2x MOPPs. The 2x MOPP classification requires an isolation voltage of 4,000 VAC, creepage/clearance of 8mm/5mm and double insulation. This regulation makes the power supplies suitable to be used in BF (body floating) applications where the device will be used for conducting the body of the patient. There are also other requirements for leakage current, EMI, EMC emission and immunity, isolation level, etc.

“Another key feature [of NMP] is that both medical and the ITE [Information Technology Equipment] safety standards are approved,” Li said. “So customers can use this for industrial applications, such as 3D printers, and also for medical machines like imaging or surgical machines.”

According to MEAN WELL, due to its stringent safety standards, the NMP series is applicable in a wide range of applications such as medical equipment; diagnostic or biological facilities; MRI, CT and PET scanners; test and measurement systems; telecommunication equipment; factory automation and laser equipment.

The Fanless MEAN WELL UMP-400

MEAN WELL provides another configurable power supply, the UMP-400 series, that can operate as an independent 400W (24V or 48V) single output power supply. The UMP-400’s main feature is that it is a completely configurable fanless power supply. Due to its special design, no forced airflow is required to cool the unit. As such, it is a noiseless device and a very popular solution for noise-sensitive environments such as hospitals or shopping centers.

 Figure 4. A MEAN WELL UMP-400 power supply. (Image courtesy of MEAN WELL.)
Figure 4. A MEAN WELL UMP-400 power supply. (Image courtesy of MEAN WELL.)

The UMP-400 can be configured into a multi-channel modular power supply by incorporating the NID series non-isolated DC-DC converters. The NID output modules have output power up to 100W adjustable for common voltages of 5V, 12V, 15V and 24V. Like the NMP series, the UMP-400 is certified to ITE 62368-1 safety standards and designed to meet 2x MOPP safety standards.

Forced-air cooling can be inconvenient for some applications, so eliminating the fan from a power supply can improve its reliability, reduce system design cost, and eliminate acoustic noise. A fanless power supply such as the MEAN WELL UMP-400 avoids issues with fan failures and reduces maintenance costs. MEAN WELL recommends the UMP-400 for applications including diagnostic or biological facilities, test or measurement systems, telecommunication equipment, industrial automation machinery, industrial control systems and mechanical and electrical equipment.

To learn more about the benefits of configurable power supplies, visit onlinecomponents.com for more information on the MEAN WELL NMP-1K2, NMP-650, and UMP-400.

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