“I started working at Texas Instruments (TI) in 2002; since then, the overall power electronics market has more than quadrupled, with a compound annual growth rate of about 8%. This huge growth has benefited from some amazing advances in the power supply field.
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Robert Taylor is an applications manager for Texas Instruments.
I started working at Texas Instruments (TI) in 2002; since then, the overall power electronics market has more than quadrupled, with a compound annual growth rate of about 8%. This huge growth has benefited from some amazing advances in the power supply field.
In this article, I will review topics that seemed almost impossible to achieve in 2002. For example, one of my first projects is a two-phase converter for low-voltage high-current processor applications: input voltage is 12 V, output is 1 V, current is 40 A, power levels are both 250 kHz, and output ripple Is 500 kHz. I remember that because the voltage was too low, it was impossible to test the power supply with a traditional Electronic load. In order to quickly complete some tests, I used a 1-meter copper strap to achieve the equivalent resistance of the loaded power supply. When I turned on the power, the copper ring was actually twisted due to the electric field.
The latest specification provided by our team for this type of power supply is: 1 V at 550 A! The design uses a 12-phase power supply, with advanced current sharing and transient response technology. We now have a complete set of test benches equipped with special test equipment. As consumer demand for the Internet and the cloud increases, application-specific processors are becoming more and more power hungry.
Another exciting technological advancement is the increase in the use of wide band gap devices, such as gallium nitride (GaN) and silicon carbide (SiC). GaN and SiC have been around for some time, but in 2002 they were neither reliable nor cost-effective and could not be used for commercial purposes. Both of these technologies can significantly increase power density and switching speed. Figure 1 shows a 1 kW power factor correction (PFC) power supply, which can reach 156 W per cubic inch-twice that of super junction silicon chips and ten times that of 10 years ago.
Figure 1 A 99% efficient 1kW GaN-based continuous current mode (CCM) totem pole power factor correction (PFC) converter reference design using a 1 kW universal AC input power supply
Automotive applications are increasing the demand for internal power supplies and electronic equipment in vehicles. In 2002, it was only a dream to be able to switch the power supply above the AM radio frequency band (2.2 MHz). In 2018, not only can we switch on the AM band, but we can switch in a smaller and more efficient way. Some of Texas Instruments’ latest integrated field effect transistor (FET) converters have switching frequencies higher than 6 MHz. Advances in semiconductor technology and packaging have made these improvements possible. Figure 2 shows how the power density of an integrated FET converter expands in typical linear bipolar complementary metal oxide semiconductor (BiCMOS) technology as feature size decreases.
Semiconductor packaging also plays an important role in shrinking size and higher frequency switching. The parasitic loss in the package can limit the reasonable switching speed of the switching power supply. The typical package previously used single bond wires to connect silicon to the lead frame pins. Now we can directly connect the copper metal layer to the package or printed circuit board. This type of package can reduce parasitic inductance and stray capacitance, thereby achieving better Fast conversion time. At the same time, thermal management has also been improved, which is important when increasing power density.
Figure 2 Development of typical linear BiCMOS technology
Notebook adapters (external adapters) are usually called “bricks”. I looked for it, found one, and decided to weigh it-up to 1.35 pounds! Figure 3 compares the dimensions of the 2002 notebook adapter (1.35 pounds) and the 2018 notebook adapter (0.39 pounds) with real bricks (3.25 pounds). Over time, the reduction in size is amazing.
Figure 3 Comparison of notebook adapter sizes
By increasing efficiency, increasing switching frequency and improving thermal management, size can be reduced. But without technological breakthroughs, it is difficult to achieve all three improvements:
・ Resonant topologies, such as active clamp flyback and inductance, inductance and capacitance.
・ Multi-level converter.
・ Wide band gap devices such as GaN and SiC.
・ Secondary rectification and resonance.
The power density of the 2002 power adapter is about 5 W/in3. Although impressive at the time, if the size is smaller, it can be easily carried when traveling. Figure 4 shows the growth of adapter power density in the past few years. These measurements relate to commercially available 65-W adapters.
Figure 4 65-W adapter size and power density improvement
I am excited about the changes and improvements in the power supply industry over the past few years. The situation is very optimistic now, although I can not predict whether they will get better, but it is worth waiting for us.
About the Author:
Robert Taylor is an applications manager for Texas Instruments.
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