Overview of Cooling Methods for AC-DC and DC-DC Power Supplies

All electronics generate heat and therefore are not 100% efficient. Each unit must have a way to dissipate excess heat in order to prevent damage and maximize reliability. This is done via thermal management, also simply referred to as cooling. 

There are several ways to minimize losses in power supplied through use of various cooling methods. Efficiency and reliability are partly the result of a power supply unit's designed cooling method.

Heat Sink

Technically, heat sinks exist in two primary forms -- those with fins and those without. However, engineering jargon generally refers to "heat sinks" as being those with fins and "cold plates" as being those without. 

A heat sink with fins allows for a quick dissipation of heat due to increased surface contact with air and is frequently coupled with forced air cooling for maximum dissipation. Design considerations regarding space constraints usually limit this option to medium-large applications.

Cold Plate

In many cases, cold plate is an effective thermal management solution where simplicity and space constraints are concern. However, the application's overall design must also account for a way to allow the heat to escape from the cold plate (natural air flow, thermal compound, and/or forced air may be used.)

Liquid

Liquid cooling refers to a special cold plate with an embedded tube running a closed loop of cool liquid. This can be water, but in our applications it is usually 50% water/50% glycol mix.

With liquid cooling, the base plate is kept at a very steady temperature so thermal transfer is most efficient. It's a great solution for tight spaces where heat sinks and fans are not options. Liquid cooling is commonly used in aircraft, for instance, because of size and weight limitations.

Thermal Compound

Thermal compound is not a stand-alone cooling method, but greatly aids in the transfer of heat from a heat sink or cold plate. Thermal compound, also called thermal paste or thermal grease, is a thermally conductive material that allows even adhesion between the unit and heat sink or cold plate component. 

Natural Air Flow

Technically called convection cooling, natural air flow transfers heat away from a power device simply by surrounding the unit with cooler air. If the unit is enclosed, air vents may need to be included in the design to assist in circulation.

Natural air flow is often the least expensive thermal management option and certainly produces the best mean-time-between-failures (MTBF) rating due to the lack of additional mechanical components to create air movement. However, power supplies which rely on natural air flow for cooling are severely limited in their safe temperature operating range. 

For heavy-duty applications such as aircraft, industrial robotics, shipboard, and other high energy devices, natural air flow is not an option to cool the associated power supplies.

Forced Air

In this technique, one or more fans are built into the unit itself or specified elsewhere in the supported application's design as a requirement to cool the power supply and thus achieve maximum rated output.

One consideration when using forced air cooling is that fans also add to the inefficiency of a unit while simultaneously providing thermal management.

As a side note, fans may reduce the amount of internal dust build-up, contributing to the overall effectiveness and longevity of a power supply