“Some of Texas Instruments’ latest integrated field-effect transistor (FET) converters have switching frequencies above 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 scales in a typical linear bipolar complementary metal-oxide-semiconductor (BiCMOS) technology as feature size decreases.
Author: Robert Taylor
Robert Taylor is an applications manager at Texas Instruments.
I started working at Texas Instruments (TI) in 2002; the power electronics market as a whole has more than quadrupled since then, with a compound annual growth rate of around 8%. This huge growth has been fueled by some amazing advancements in the power supply space.
In this article I will review topics that seemed almost impossible in 2002. For example, one of my first projects was a two-phase converter for a low voltage, high current processor application: 12 V input, 1 V output, 40 A, both 250 kHz power stages, output ripple is 500 kHz. As I recall, it was not possible to test the power supply with a conventional Electronic load because the voltage was too low. To do some quick tests, I used a 1m copper tape to reach the equivalent resistance of the loaded power supply. And when I turn it on, the copper ring is actually twisted due to the electric field.
The latest spec from 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 techniques. We now have a complete set of test benches with specialized testing equipment. Application-specific processors are becoming more and more power-hungry as consumer demand for the Internet and the cloud increases.
Another exciting technological advance is the increased use of wide-bandgap devices such as gallium nitride (GaN) and silicon carbide (SiC). GaN and SiC have been around for a while, but were neither reliable nor cost-effective for commercial use in 2002. Both technologies can greatly improve power density and switching speed. Figure 1 shows a 1 kW power factor corrected (PFC) power supply capable of 156 W per cubic inch – a 2x improvement over superjunction silicon chips and a 10x improvement over 10 years ago.
Figure 1. 99% Efficient 1 kW GaN-Based Continuous Current Mode (CCM) Totem Pole Power Factor Correction (PFC) Converter Reference Design Using 1 kW Universal AC Input Power Supply
Automotive applications are increasing the demand for power supplies and electronics inside the vehicle. In 2002, being able to switch power above the AM radio band (2.2 MHz) was just a dream. In 2018, not only can we switch above the AM band, but we can switch in a smaller, more efficient way. Some of Texas Instruments’ latest integrated field-effect transistor (FET) converters have switching frequencies above 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 scales in a 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. Parasitic losses in the package can limit the speed at which a switching power supply can reasonably switch. A typical package previously used single bond wires to connect the silicon to the lead frame pins. Now we can connect the copper metal layer directly to the package or printed circuit board. This type of package reduces parasitic inductance and stray capacitance, resulting in better performance. 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
Laptop adapters (external adapters) are often referred to as “bricks”. I looked around, found one, and decided to weigh in – 1.35 pounds! Figure 3 compares the dimensions of a 2002 laptop adapter (1.35 lb) and a 2018 laptop adapter (0.39 lb) with a real brick (3.25 lb). The reduction in size over time is amazing.
Figure 3 Comparison of Notebook Adapter Dimensions
Size reduction can be achieved by increasing efficiency, increasing switching frequency, and improving thermal management. But without a technological breakthrough, it would be difficult to achieve all three improvements:
Resonant topologies such as active clamp flyback and Inductor inductor capacitors.
Wide bandgap devices such as GaN and SiC.
Secondary rectification and resonance.
The power density of the power adapter in 2002 was about 5 W/in3. While impressive at the time, the smaller size would have made it easy to carry while traveling. Figure 4 shows the increase in adapter power density over the past few years. These measurements relate to a commercially available 65-W adapter.
Figure 4 Improvements in 65-W adapter size and power density
I am heartened by the changes and improvements in the power industry over the past few years. Things are looking positive right now, and while I can’t predict if they’ll get better, it’s something to wait and see.