Know more about the design of the MORNSUN AC/DC Power Supply LOF550 Series


AC/DC as a primary power supply for the user's entire system is the cornerstone to ensure the stable and efficient operation of the system. With the continuous development and innovation in the power electronics industry, switching power supply technology is developing in the direction of standardization, miniaturization, high efficiency, energy-saving, environmental protection, etc.

There is a wide range of power supply products available in the market, but the capabilities of design, manufacturing, and service of the manufacturers are different. The wide variety of products makes it difficult for engineers to select the right product.

For any power supply manufacturer, it is not easy to achieve any subjects of the optimal size, high reliability, good EMC performance, and high suitability in an AC/DC power supply, not to say all of them in one module.

Mornsun 120-550W high power density AC/DC power supply LOF series is the product that features compact size, high reliability, and good EMC performance. This article takes the LOF550 series as an example to let you know more about the design essentials of the LOF series power supply.

1. Innovative Process Design For Continuous Improvement

Optimized design to create ultra-high power density products

The efficiency of the LOF550 series is as high as 94% and its power density is up to 23W/Inch3, meeting the application of the 1U standard system. The LOF550 series fits the trends of miniaturization and portability of power products.

① It is designed with an active PFC circuit and the power factor is up to 0.99. It uses the SiC diode instead of the traditional quick recovery diode to reduce the peak current superimposed on MOS caused by diode reverse recovery, improve EMC performance, reduce the MOSFET switching loss and improve efficiency. (Figure 1, 2)

MORNSUN PFC MOSFET Current Waveform.jpg

② The main power conversion part adopts a soft switch design, and the primary side MOSFET realizes zero voltage conduction to reduce the switching loss. (Figure 3, 4)  

MORNSUN a soft switch design & zero voltage conduction.jpg

③ The output adopts a synchronous rectifier design 

MOSFET rectifier is used to replace the diode rectifier, and the lower Rdson (milliohm level) of MOSFET is utilized to greatly reduce the conduction loss and improve the efficiency.

④ Planar transformer design

Low-voltage high-current transformers designed by common winding methods in the market often cannot avoid flying wire, which not only makes operation difficult but also increases the product size and affects the overall appearance of the product. (Figure 5)

MORNSUN adopts a synchronous rectifier design.jpg

LOF550 series adopts planar transformer design, with its input adopting winding design, output adopting copper or flat wire design, and fan power supply adopting PCB winding. The whole transformer realizes no flying wire design, which greatly reduces its size, casts off the transformer skeleton, simplifies assembly, and makes a beautiful appearance. (Figure 6)

MORNSUN design of planer transformer without flying wire.jpg

2. Safe,  Reliable And Protection-upgraded

Complete protection functions without external additions.

①The product comes with OCP / OVP / SCP and other output protection functions.

②The dual OTP function design of the primary and secondary sides can realize reliable protection under various abnormal conditions. (Figure 7, Figure 8)

MORNSUN OTP test of the primary side.jpg

③ Low ripple and noise. The output of ripple and noise of the whole series is within 200mV. (Figure 9) 

MORNSUN measurement drawing.jpg

④Its output capacitor part adopts 105℃, long life, low ESR electrolytic capacitors.

⑤Special welding process designed. Compared with the traditional wave soldering process, it can greatly reduce the proportion of poor welding and repair welding after the device passes the furnace and improve its reliability.

⑥The product comes with the PG communication function:

   a. When the AC is powered on, after the power output, the PG signal delays starting and informs the customer that the system power output is OK.

   b. When the AC is powered down and abnormal output protection, the PG signal will be turned off in advance and inform the system power output is a failure.  

3. Compatible Design and Wide Application Range

Compatible with a variety of system installation modes

At present, most of the open-frame products on the market are designed without bases, which will make them not fully compatible with the customer system and cannot be installed directly when they encounter systems without convex plates or support columns.


The LOF550 series is designed with the customer's system application scenario in mind, with the addition of an insulating sheet and metal base on the bottom.

The four screw holes in the metal base are shared by the power supply board and the customer system, and the customer system screws can go 3mm deep inside the base plate for fixing, which is perfectly compatible with systems without convex plates or support columns. (Figure 10)

Outer design of MORNSUN LOF550 series.jpg

Applicable for the Class I and class II types of equipment

The power supply can be divided into class I and class II types of equipment according to the grounded or ungrounded shells, and the input terminals also correspond to 3pin and 2pin respectively, which have limitations in use. If the 3pin terminal is used, class II equipment cannot be directly compatible with a 2pin terminal.

LOF550 series products are relatively flexible in design. While adopting a 2 pin terminal, a grounding tab is reserved for users (Figure 11). The open-frame products are applicable to class I equipment, and the products with derived cases can be applied to both class I and class II equipment.

Extend the packages of the outer shell

The application scenario of a pure open-frame power supply is relatively simple. In order to expand the product application scenario, the LOF550 series adopts a 5' × 3' standard size, with different types of outer shell designs. (Figure 12, Figure 13)

MORNSUN LOF550 Series' derivative in enclosed shell/bulit-in fans.jpg

Wide input voltage range

The universal AC mains supply range is 90-264VAC. Due to the unstable power supply in some areas, the grid voltage often fluctuates beyond 264VAC, and if the power supply design is not reliable enough, such as withstand voltage of a large electrolytic capacitor is too low, the power supply will be easily damaged.


In the same case, the higher the withstand voltage of the high-voltage electrolytic capacitor, the larger the size. For high power density products, in order to save space, it is often compromised to use high-voltage electrolytic capacitors with relatively low withstand voltage, which greatly reduces the adaptability of power supply products to grid voltage fluctuations. The LOF550 series features both high power density and high voltage input resistance. It adopts 450V high voltage electrolytic capacitor, which is safe and reliable, ensures that it's not be damaged in case of 305VAC input. (Figure 14)

MORNSUN 450V high-voltage electrolytic capacitor.jpg

Separate 5Vsb auxiliary backup power supply and PS_on control function to expand the application range

For high-power-density products, the main control IC scheme with a high-voltage startup is often used at present. When AC is powered on, the product will have output without other control switches. It is not compatible with systems with auxiliary power standby requirements.


In order to improve customer experience and the product versatility, the LOF550 product adds a separate 5Vsb auxiliary backup power supply and PS_on control function on the basis of the above common design schemes:

   a. AC power on, PS_on signal defaults to a high level and can be output normally.

   b. When the PS_on signal is connected to the low level, the main output is turned off and only 5Vsb auxiliary power supply has output.

4. Comprehensive Certifications And Applicable To A Variety Of Applications

In addition to meeting IEC/EN61000, IEC/UL/EN62368, and GB4943, the LOF550 series is also compatible with the following standards:

Meet EN60601 medical industry certification standard

① The leakage current is as low as 0.1 mA, which is suitable for class BF applications of medical equipment.

②Isolation withstands voltage and safety distance meet medical standards.

MORNSUN High-Quality Medical Device Power Supply: a Brief Analysis of Design.jpg

MORNSUN Meet EN60601 medical industry certification standard.jpg

Outstanding EMC design

Medical power supply requirements of ultra-low leakage current, high safety distance and ability of high-voltage withstand and miniaturization, high power density design are mutual constraints. Most products on the market compromise on EMI to meet only the CLASS A standard, which greatly increases the risk of interference from power supply products to other functional circuit modules inside the medical device.

The conducted emission and radiated emission of the LOF550 series meet class B:

   ① The input EMI filter module, the PFC module, and the main power module are respectively arranged in a centralized manner and effectively isolated by a radiator (grounding), which minimizes EMI interference, reduces some EMC components, and optimizes space. At 550W full power output, only a level 1 Y capacitor is applicable at the front end of the input rectifier bridge. (Figure 15)

MORNSUN Outstanding EMC design.jpg

   ② The input terminal is designed with a flat line common mode inductor, fully automatic winding and without overlapping, with a small capacitance between turns, and has a good impedance balance. EMI performance is much better than traditional magnetic ring common mode inductor and provides a small size and beautiful appearance. (Figure 16)

LOF550-20B12 Conducted emission Curve in 115V(Grounded test).jpgLOF550-20B12 Conducted emission Curve in 230V(Grounded test).jpg

LOF550-20B12 Conducted emission Curve (Grounded test)

LOF550-20B12 Conducted emission Curve in 115V(Grounded test).jpg

LOF550-20B12 Radiated emission Curve in 230V(Grounded test).jpg

LOF550-20B12 Radiated emission Curve (Grounded test)

Meets IEC 60335 certification test standard for household appliances

The LOF550 series meets the requirements that the primary and secondary sides are designed with double Y in series.

5. Summary

Mornsun HIGH power density power supply LOF series always take safety and reliability as the design premise, on this premise, we have fully considered different application scenarios and common problems in different applications of different clients, taken the lead in breaking the original thinking mode, adopted innovative circuit design, combined with the cutting-edge technology and structure design, concentrated solved a large number of problems and pain points in the use. It has the advantages of powerful function, strong compatibility, and nice appearance, fully showing mornsun's accumulated advantages in the power supply industry. On this basis, we will also devote more R&D efforts to breakthroughs in power supply technology to provide suitable power solutions to customers.

Please refer to the technical manual for specific product parameters:

Series Power(W) Vin(VAC) Vin(VDC) Vout(VDC) Iout Efficiency(%) Isolation Footprint & 3D Markings Datasheet Sample Buy
LOF550-20B12 499.2 90-264 127-370 12 41.6A 91 4000VAC
LOF550-20B12-C 499.2 90-264 127-370 12 41.6A 91 4000VAC
LOF550-20B12-CF 499.2 90-264 127-370 12 41.6A 94 4000VAC
LOF550-20B15 499.5 90-264 127-370 15 33.3A 92 4000VAC
LOF550-20B15-C 499.5 90-264 127-370 15 33.3A 92 4000VAC
LOF550-20B15-CF 499.5 90-264 127-370 15 33.3A 94 4000VAC
LOF550-20B18 500.4 90-264 127-370 18 27.8A 92.5 4000VAC
LOF550-20B18-C 500.4 90-264 127-370 18 27.8A 92.5 4000VAC
LOF550-20B18-CF 500.4 90-264 127-370 18 27.8A 92.5 4000VAC
LOF550-20B19 499.7 90-264 127-370 19 26.3A 92.5 4000VAC
LOF550-20B19-C 499.7 90-264 127-370 19 26.3A 92.5 4000VAC
LOF550-20B19-CF 499.7 90-264 127-370 19 26.3A 92.5 4000VAC
LOF550-20B24 549.6 90-264 127-370 24 22.9A 93 4000VAC
LOF550-20B24-C 549.6 90-264 127-370 24 22.9A 93 4000VAC
LOF550-20B24-CF 549.6 90-264 127-370 24 22.9A 94 4000VAC
LOF550-20B27 550.8 90-264 127-370 27 20.4A 93.5 4000VAC
LOF550-20B27-C 550.8 90-264 127-370 27 20.4A 93.5 4000VAC
LOF550-20B27-CF 550.8 90-264 127-370 27 20.4A 94 4000VAC
LOF550-20B36 550.8 90-264 127-370 36 15.3A 94 4000VAC
LOF550-20B36-C 550.8 90-264 127-370 36 15.3A 94 4000VAC
LOF550-20B36-CF 550.8 90-264 127-370 36 15.3A 94 4000VAC
LOF550-20B48 550 90-264 127-370 48 11.46A 94 4000VAC
LOF550-20B48-C 550 90-264 127-370 48 11.46A 94 4000VAC
LOF550-20B48-CF 550 90-264 127-370 48 11.46A 94 4000VAC
LOF550-20B54 550.8 90-264 127-370 54 10.2A 94 4000VAC
LOF550-20B54-C 550.8 90-264 127-370 54 10.2A 94 4000VAC
LOF550-20B54-CF 550.8 90-264 127-370 54 10.2A 94 4000VAC

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