COSEL Power Supplies Meet Performance, Safety Requirements

COSEL has released a series of wide-range, low-profile AC-DC power supplies designed for medical applications. The WMA series comprises two families: the WMA-F series (three models), which support a universal, single-phase input of 85 to 264 VAC, and the WMA-H series (two models), offering two selectable input ranges across the nominal 85 to 264 VAC input span. The two product families support regulated DC output power levels up to 100 W and 350 W, respectively. 

 

WMA series medical power supplies. Image used courtesy of COSEL

 

The WMA power supplies comply with international safety standards and offer robust 2MOPP protection from input to output and 1MOPP-rated safety from input to frame ground. The supplies also feature a low height profile of 30 mm, less than the 1U (44.45 mm, 1.75 inches) standard adopted by the medical industry.  

In addition to medical applications, the WMA series is also well suited to industrial applications, such as semiconductor manufacturing equipment, demanding high isolation and supply performance.  

 

Regulated DC Output Power

Each model in the WMA series features a well-regulated DC output of 12, 24, and 48 VDC and is rated to deliver output power levels ranging from 35 W to 350 W. The WMA350H (350 W) features an additional 36 VDC output, while the WMA35F adds a 5 VDC option. All models incorporate a potentiometer that allows for trimming of the output voltage.

The supplies’ power conversion efficiency ranges between roughly 80% and 90%, depending on the AC input and DC output voltage levels. Higher input line voltages and lower output voltages yield better efficiency.

The supplies are designed to operate with convection cooling, except for the higher-power WMA350, which incorporates a fan to assist with heat removal. 

 

AC Input Level and Efficiency

The AC input level for a power supply will impact its operating efficiency. Efficiency at the low end of the AC input range (low-line) can be significantly less than at the higher end of the range (high-line). 

 

Efficiency vs. load and AC input voltage for a typical supply. Image used courtesy of XP Power

The higher-power WMA150H and WMA350H variants offer more narrow, selectable input ranges within their larger universal input range. This helps mitigate efficiency losses from high-line to low-line operations and can be achieved through adjustments to the operating characteristics of the supply or internal transformer taps.

 

Power Factor Correction Requirements

According to COSEL, the WMA-F models do not incorporate active PFC (power factor correction) into their design. Even so, the supplies comply with the IEC 61000-3-2 (Class A) standards for limits on input harmonics generated on the mains from a switching supply’s input rectification stage.

For the higher-power WMA-H models, COSEL suggests that an external PFC circuit may be needed to help meet power quality compliance standards. 

In addition to reducing input harmonics, PFC circuits also help ensure a more efficient power transfer between the mains grid and loads.

  

Patient Protection Standards

Electrical equipment safety can be defined from the perspective of either the equipment or the equipment operators. Protection from high voltage is designed into a system using insulation, clearance, creepage distances, and other techniques.

With medical devices, MOPP refers to Means of Patient Protection and defines the level of protection provided to a patient from potential electric shock. 

 

WMA series patient protection levels. Image used courtesy of COSEL

 

For the WMA series, 1MOPP protection between the AC mains input and chassis ground indicates a rated isolation of 1500 VAC with basic insulation and 4.0 mm of creepage distance. 2MOPP protection between the mains input and DC output means 3000 VAC of isolation with reinforced insulation and  8.0 mm of creepage.