Offline Switchers Come in Tiny Packages

When engineers consider offline switchers for systems ranging from telecom and datacom equipment to PCs and industrial supplies, they mainly think of bulky AC/DC front-end solutions in a variety of forms such as bricks, modules, and open-frame. However, there are many applications where offline switchers powered by AC mains are needed in small packages or must occupy a small space on the motherboard. Some examples: USB adapters to power media players, e-readers, and GPS devices; and low-cost, offline LED drivers in lighting applications with high power factor to meet international requirements for total harmonic distortion (THD), EMC, and safety. Offline switchers are also used as standby power supplies in PCs and laptops, as well as in compact chargers for smartphones and other mobile devices. The point is that there are many applications where offline AC/DC switchers are needed in small form-factors.

This article will explore solutions from CUI Inc., Phihong USA, RECOM Power, and XP Power. Besides shedding some light on the properties of compact offline switchers, it will also identify key features and benefits of specific products available to engineers.

Compact external switchers

CUI, Inc., for instance, has readied an ultra-compact 5 W wall-plug adapter with integrated USB connector (Figure 1), the EPSA050100U-I38-EJ. With a footprint of just 1.61 x 1.18 in. (41 x 30 mm), the adapter is among the industry’s smallest AC/DC power supply to integrate USB connection, making it suitable for small mobile devices. In addition, it offers level V energy-efficiency compliance for green design requirements with a no-load power draw of less than 0.1 W. Rated for an output of 5 V_DC at 1 A, the high-density EPSA050100U-I38-EJ operates at AC input voltages ranging from 90 to 264 V_AC. Safety marks include UL/cUL, PSE, and LPS (limited power source). What is more, the external adapter also meets EN55022 Class B limits for conducted and radiated EMI and provides protection for overvoltage, overcurrent, and short-circuit conditions.


Figure 1: CUI’s ultra-compact 5 W wall-plug adapter comes with an integrated USB connector.

Another supplier competing in this arena is Phihong USA. Like CUI, Phihong has also launched a low-power adapter with USB connector. The 2.75 W rated PSM03A is available in 5, 7.5, 9, 10, and 12 V_DC outputs and features a constant current/constant voltage (CC/CV) function, making it suitable for battery charging in applications such as medical testing equipment, personal electronics, cameras, and cordless tools. This fixed-wall plug adapter is compact, low-profile, and fully protected against overvoltage, overcurrent, and short-circuiting. According to Phihong, this Class B EMI wall plug is also compliant with UL safety regulations, featuring a no-load power draw of less than 0.15 W to meet the requirements for a level V efficiency rating.

For LED lighting applications including decorative lights, RECOM Power has released a line of compact AC/DC modules for driving multiple LEDs (Figure 2). While its 3 W RACD03 can drive up to three 1 W LEDs with 350 mA constant current, or one 3 W LED with 700 mA, the slightly larger version RACD06 can drive up to six 1 W LEDs, or two 3 W LEDs. Both modules can handle wide universal AC input and deliver CC/CV output for driving LEDs. The power supplies are designed to meet EMC, harmonics, and safety standards.


Figure 2: RECOM’s compact AC/DC modules, RACD03 and RACD06, can handle universal AC input and deliver constant current to drive multiple, high-power LEDs for lighting applications.

Internal AC/DC converters

For applications where on-board AC/DC power conversion is required and real estate is at a premium, CUI has introduced the ultra-compact PBK series in SIP packages (Figure 3). Operating at universal AC input voltages between 85-264 V_AC with single output voltages of 3.3, 5, 9, 12, 15, and 24 V_DC, the PBK series meets internationally-recognized UL 60950-1/EN 60950-1 standards and complies with EN55022 Class B limits for conducted and radiated EMC using only a few external components. Furthermore, for high-voltage DC/DC applications like solar converters, the modules can also handle a high DC input range spanning 100 to 400 V.


Figure 3: CUI’s miniature AC/DC power supplies in SIP packages maximize board-space utilization.

Other features include 3,000 V_AC input-to-output isolation, overcurrent, and continuous short- circuit protection, and a wide temperature operating range of -40° to +85°C for 1 W (PBK-1) and 3 W (PBK-3) units and -25° to +85°C for 5 W (PBK-5) models. The PBK series is aimed at applications such as automation systems, industrial controls, and telecom equipment.

For primary or auxiliary power conversion in space-constrained ITE, consumer electronics, and industrial control, CUI has announced encapsulated AC/DC power modules measuring an ultra-compact 1.32 x 0.87 x 0.70 inches (33.7 x 22.2 x 18 mm). With industry-leading no-load power consumption of 100 mW, the 1 W VSK-S1 series and 2 W VSK-S2 series modules handle a wider input range of 85 to 305 V_AC to address the needs of lighting and smart building systems that operate from 277 V_AC input. Offering up to 78 percent efficiency with an operating temperature range of -25° to 70°C, the 1 and 2 W families deliver output voltages of 3.3, 5, 9, 12, 15, and 24 V_DC with very-low ripple and noise. Aside from protection against overvoltage, short-circuit, and over-temperature, they deliver 3,000 V_AC isolation between input and output, and carry CE and UL/cUL 60950-1 safety certifications, as well as compliance with the EN55022 Class B EMI standard.

In addition, the manufacturer has also crafted low-power encapsulated AC/DC modules for medical applications, such as home healthcare and dental equipment. Configured as 5 W and 10 W solutions, the VSKM modules come with pins for PCB mounting. While the footprint for the 5 W unit VSKM-S5 measures 2.0 x 1.0 in. (50.8 x 25.4 mm), the 10 W model VSKM-S10 occupies an area of 2.10 x 1.12 in. (53.34 x 28.45 mm). These modules also carry UL/cUL 60601-1 safety certifications, EN55011 class B EMI compliance, and a nominal leakage current of 100 µA at 230 V_AC input. Furthermore, the VSKM series offers universal input (85 to 264 V_AC) and is available in output voltages of 3.3, 5, 9, 12, 15, and 24 V_DC. The modules are also protected against overcurrent and short-circuit, and feature a primary to secondary isolation voltage of 4,000 V_AC.

Encapsulated board-mount power supplies in small form-factors are also available from XP Power (Figure 4). The maker claims to offer the world's smallest 5 W single-output AC/DC switcher series designated ECE05 and measuring just 1.0 x 1.0 x 0.6 in. (25.4 x 25.4 x 15.24 mm). Complementing the ECE05 series, the ECE10 series provides 10 W output from an equally-compact encapsulated package measuring only 1.5 x 1.0 x 0.6 inches (38.1 x 25.4 x 15.24 mm). The models in both series cover nominal output voltages from 3.3 to 48 V_DC, all from a wide universal input of 85 to 264 V_AC with Class II construction, meaning no earth or ground connection is required. All models meet the internationally-recognized no-load power consumption limit of less than 0.3 W and average efficiency limits ensuring end-products can comply with global energy-efficiency standards. Both series modules are convection cooled and operate without the need for additional heatsinking or forced airflow. The operating temperature range is -25° to +70°C with no derating until +50°C.


Figure 4: XP Power’s 5 and 10 W AC/DC power supplies are housed in ultra-compact encapsulated packages to deliver single-output DC from 3.3 to 48 V over a wide universal AC input.

In addition, the units meet international IT safety standards EN60950-1, UL609501-1, and CSA22.2 No. 234, as well as comply with EN55022 level B limits for conducted and radiated EMC without the need for any additional filtering components.

RECOM Power is a good source for compact, low-power AC/DC switchers generating clean and reliable DC voltage to power board components with full protection and safety from the AC lines. Recently, the supplier added a new 2 W unit to its RAC family with a wider input voltage range of 90 to 305 V_AC and input-to-output isolation of 3,000 V_AC. Designed to deliver single DC output voltage of 3.3, 5, 12, or 24 V, the RAC02-SC/277 can be used without derating up to +75°C (Figure 5). Protected against short-circuit and overvoltage, the unit complies with the EN55022, class B standard, including the safety standard EN/UL60950-1. With a standby consumption of only 35 mW, RAC02-SC/277 is being aimed at energy-saving sleep-mode and standby applications in home automation, telecom, consumer appliances, industrial controls, and measurement equipment.


Figure 5: RECOM’s 2 W AC/DC switcher RAC02-SC/277 can be used without derating up to +75°C.

In summary, low-power AC/DC switchers come in a variety of compact packages to address both the external and internal needs of a myriad of applications ranging from wall-plug adapters, standby supplies in PCs and laptops, to LED drivers in lighting. For more information on the products discussed in this article, use the links provided to access product pages on the DigiKey website.