By Dr. Leon Ku/Research and Development Dept. 

Normally, SPS with fan built-in has a certain weakness such as unavoidable noise, vibration, additional power consumption, unexpected mechanical failure, short term reliability, dust debris, etc. On the contract, fanless SPS are smaller, more reliable and more flexible with lower noise. For the understanding of thermal characteristics of fanless SPS and SPS with fan built-in, different thermal dissipation methods of SPS will be introduced below.
 

SPS efficiency and power loss

Efficiency is the percentage ratio of total output power to input power. This is normally specified at full load under nominal input voltage. It is impossible to attain 100 % efficiency due to energy dissipated in the form of heat in passive and active components, such as switching devices, junction-based devices, capacitors, inductors, and so on. However, it is still possible to achieve above 95% efficiency by suitable electrical design, thermal design and component chosen. Electric characteristic and dissipation could be affected due to low energy efficiency, and excessive power lose can even decrease the life time of power supply, as well as deviation of electric characteristic performance.
 

SPS power levels and thermal dissipation methods

Based on different application, thermal dissipation methods can be different. Generally, natural convection, forced convection, and water cooling are common thermal dissipation methods and possess different thermal dissipation capabilities. Please refer to the following description of comparison based on different thermal dissipation methods.

(1) Comparison of heat transfer coefficient between  different  thermal dissipation methods

Heat dissipation method	Heat transfer coefficient (W/m2K)
Natural convection	3-12
Forced air convection	10-100
Water cooling	3000-7000

 
(2) Comparison of heat dissipation capability between different thermal dissipation methods

 
From the table and graph above mentioned, it is obvious that water cooling possesses higher thermal dissipation capabilities, but a higher cost on system mechanism design is expected. Comparison between three different thermal dissipation methods of SPS includes advantage, disadvantages, and applications as shown in the table below.
  
 

	Advantages	Disadvantages	Applications
Natural convection (Passive)	? Widely available. ? Low Cost. ? No extra power consumption. ? No acoustic noise and vibrations, silent operation. ? Minimal maintenance. ? Simple construction, easy installation.	? Low heat dissipation capability. ? Large heat dissipation area requirement. ? Strongly orientation dependence. ? Hard to control the efficiency of heat dissipation under different environmental conditions. ? Convection surfaces must be free from debris and corrosion.	? Low power density applications. ? No noise, vibration requirements, such as low power medical equipment, indoor lighting, home electronics, security, precision instruments, etc.
Forced air convection (Active)	? Lower thermal resistance for the same volume compared to passive thermal dissipation methods. ? Greater thermal dissipation capability compared with passive thermal dissipation methods. ? Customized cooling performance.	? Short term reliability. ? Costly. ? Require regularly maintenance and replacements. ? Foreign object debris such as dust ? Acoustic noise and vibrations. ? Require an additional energy source for operation.	? Medium to high power density applications. ? Systems with existing air flow. ? Normally used in Industrial equipment, information and communications, outdoor lighting, etc.
Water Cooling (Active)	? Much greater heat dissipation capability. ? High thermal dissipation efficiency. ? No noise and vibration, quiet operation. ? Effective cooling with high ambient temperatures. ? Increase of SPS lifetime. ?Very wide operating temperature range.	? Complexity. ? Costly. ? Susceptibility to leaks. ? Require an additional external liquid chiller.	? High to ultra power density applications. ? Low profile applications. ? Require constant heat cycling equipment. ? Harsh Environments. ? Mostly used in the high power industrial equipment such as industrial laser, charging station, etc.

 
The brief introduction of MEAN WELL high power fanless SPS products

 The features of UHP/PHP series SPS are shown below include smaller dimension (size reduction about 50%), high operating efficiency, wider temperature operating range, covering wide safety approvals and high value (performance/price) for all kinds of applications. The UHP/PHP series are the best choices for integrated into your end system.
 

1. Compact design to provide the solution for modern miniaturized equipment.
2. Fanless design is suitable for equipment used in a silent environment and increased reliability in the system as an extra benefit.
3. High efficiency and low power consumption to allow better energy saving on the final system
4. -30 ~ +70 ℃ wide operating temperature suitable for various environments or installations.
5. Certified by UL/TUV62368-1, IEC/EN60950-1 regulations.
6. Meet IEC/EN60335-1, EN61558 OVC III regulations.
7. Operational altitude up to 5000m.

 
UHP/PHP series SPS have fanless and half encapsulated design, can provide the best solution for precision instruments, charging stations, distribution board/cabinet, robot applications for industrial4.0 and ITE equipment.
The brief comparison show in the table below gives the quick reference of UHP/PHP series SPS  to identify the major difference:
 

	UHP-500	UHP-750	UHP-1000	UHP-1500	UHP-2500	PHP-3500
Cooling method	Passive cooling	Passive cooling	Passive cooling	Passive cooling	Passive cooling	Water cooling
Input voltage	90~264Vac	90~264Vac	90~264Vac	90~264Vac	90~264Vac	90~264Vac
Output voltage	4.2/ 5/ 12/ 15/ 24/ 36/ 48V	12/ 24/ 36/ 48V	24/ 48V	24/ 48V	24/ 48V	24/ 48V
Efficiency	95%	95%	96%	96%	96%	96%
Communication interface	─	─	─	CANBus PMBus	CANBus PMBus	CANBus PMBus
Dimension (L x W x H mm)	232*81*31	237*100*41	240*115*41	290*140*41	310*140*60	380*140*60