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Power density is defined as the ratio of output power per volume. It's typically represented as Watts/cm3 or Watts/In3. Power densities have increased greatly since the 1960s. Their evolution is synonymous with the evolution of the power supply industry as a whole. To understand the evolution of power supply density it's important to understand the types of power supplies, their relative power densities and ability to meet the needs of today's applications.

The two basic types of supplies:

1. Linear regulated: These supplies employ a bulky transformer to increase or decrease voltage followed by a rectification  and regulator circuit.  They have little  or no RFI/EMI.

They can waste up to 50-60% of their power as heat. Consequently they require large heat sinks and/or fans to cool the supply.  This causes the linear supply to have a much  larger footprint for the same power.  They have the least power density.

2. Switching regulated: This type of supply switches on and off thousands of times a second, varying the duty cycle of the on/off time to control the output voltage. The increase in frequency means smaller transformers, capacitors and inductors.

Switch mode designs use their controlled duty cycle to  minimize  power losses  as heat.  Efficiencies can now reach 90-95%. Reduced size and greater efficiencies has led to the greatest power densities.

Linear supplies continue to thrive in applications that require a stable and noise free output, however switch  mode supplies are the clear winner for power  density.

Switching power supplies have been around, at least in principle since the 1930s, but it wasn't until the 1960s and 70s that they began to overtake less efficient  linear supplies. Around this time, several things happened. Semiconductor technologies were making great advances, especially in the world of switching transistors. Controller ICs were also being developed to simplify switch mode designs. Power supplies employed faster switching transistors for more efficient, smaller supplies resulting in greater power densities.

As early as the 1960s, there was a need for increased power densities. The aerospace industry used switch mode supplies in satellites and other applications where small size and increased efficiencies were essential. In the early to mid 70s, the computer industry became  the primary driver for increased  power densities to satisfy the burgeoning mini (later microcomputer) industry and it's ancillary markets.

By 1976, the 60Hz transformer and it's large weight and size were becoming  less commonplace as switch mode designs continued to emerge. Initially cost prohibitive, switching supplies prices were coming down as volumes increased, making them even more competitive with linear supplies.

In conjunction, another major development was also made possible at this time, the advent of DC-DC converters and the proliferation of embedded systems and power distribution. Switch mode  DC/DC supplies were  becoming available everywhere in the form of modular "bricks".

In the early days of modular designs, power densities were limited by available components and switching losses which reduced efficiency.  Resonant topologies needed to be introduced such as Zero Current Switching and Zero Voltage Switching(ZCS/ZVS) which greatly reduced switching losses and increased power densities. Later on synchronous rectification technology moved power density forward. Multi-layered boards, planar magnetics, surface mount technology, power mosfets   all contributed  to superb brick densities. Optimization continues to this day, as new integrated circuit technology and innovative designs are keeping up with the demand for greater power densities. It's a tough task as power densities have roughly doubled every ten years since the inception of switch mode technology.

PSUI has a partner that's up to the challenge. TRACO Power offers some of the highest power densities in the DC/DC market, including best in class TWR 9 and TWR 9WI Series of  9W in a SIP package.

To see some of the highest power density DC/DC converters in the industry, click on slides below.

To see the complete TRACO Power's product line, Click here.

By John Benatti