How things in power electronics have changed

Article By : Robert Taylor

The market for power electronics has seen huge growth due to some incredible advancements in the power-supply field.

I started at Texas Instruments (TI) in 2002; since that time, the market for power electronics more than quadrupled, at a compound annual growth rate of ~8%. This huge growth is due to some incredible advancements in the power-supply field.

Some of the topics that I’ll discuss in this article would have seemed impossible back in 2002. For example, one of my first projects was a two-phase converter for a low-voltage high-current processor application. The input voltage was 12V with an output of 1V at 40 A. The power stages each operated at 250 kHz, giving an output ripple of 500 kHz. I remember not being able to test the supply with a traditional electronic load because the voltage was too low. Needing to quickly get some testing done, I used a large 1-m strip of copper to achieve the equivalent resistance for loading the supply. When I turned on the power supply, the loop of copper actually twisted, as it was hanging because of the electric field.

The most recent specification that our team received for this type of supply was 1V at 550 A! This design is a 12-phase power supply, with advanced techniques for current sharing and transient response. We now have an entire lab bench full of specialized equipment for testing. Application-specific processors are getting more and more power hungry, as consumers demand more from the internet and cloud.

Another exciting technology advance is the increased use of wide-band-gap devices such as gallium nitride (GaN) and silicon carbide (SiC). GaN and SiC have both been around for a while, but in 2002 neither were reliable or cost-effective enough for commercial use. Both technologies enable great increases in power density and switching speeds. Figure 1 shows a 1-kW power-factor-correction (PFC) power supply that is able to achieve 156 W per cubic inch – an improvement of 2× over super-junction silicon and a 10× improvement from 10 years ago.

Figure 1 99% efficient 1kW GaN-based continuous current mode totem-pole PFC converter reference design with a 1-kW universal AC input power supply

Automotive applications are increasing the demand on power supplies and electronics inside vehicles. In 2002, it was only a dream to be able to switch your power supply above the AM radio band (2.2 MHz). In 2018, not only can we switch well above the AM band, but we can do it in a smaller and more efficient way. Some of TI’s latest integrated field-effect transistor (FET) converters switch at greater than 6 MHz. These improvements are made possible by advances in semiconductor technology as well as packaging. Figure 2 shows how power density for integrated FET converters has scaled in typical linear bipolar complementary metal-oxide semiconductor (BiCMOS) technology as feature size decreased.

 Figure 2 Advances in typical linear BiCMOS technology vs. time

Semiconductor packaging also plays a large role regarding shrink size and switching at higher frequencies. Parasitic losses from the package can limit how fast switching power supplies can reasonably switch. Typical packaging previously used single-bond wires to connect the silicon to the lead frame pins. Now we are able to connect copper metal layers directly to the package or PCB. This type of packaging decreases parasitic inductance and stray capacitance to enable faster transition times. Thermal management also improves, which is important when increasing power density.

Notebook adapters (external adapters) are often referred to as bricks. I dug around and found the first one I had and decided to weigh it – 1.35 lbs! Figure 3 compares the sizes of an actual brick (3.25 lbs), a notebook adapter from 2002 (1.35 lbs), and a notebook adapter from 2018 (0.39 lbs). The size reduction vs. time is amazing.

Figure 3 Comparison of notebook adapter sizes

This size reduction is made possible by increased efficiency, increased switching frequency, and improved thermal management. It is very difficult to achieve all three improvements without technical breakthroughs like:

  • Resonant topologies like active clamp flyback and inductor-inductor-capacitor
  • Multilevel converters
  • Wide-band-gap devices like GaN and SiC
  • Secondary rectification and resonance

The power-supply adapter from 2002 has a power density of ~5 W/in3. While impressive at the time, it is much nicer to have something smaller when traveling. Figure 4 shows how adapter power density has increased over the past few years. These measurements are of commercially available 65-W adapters.

Figure 4 Improvements in 65-W adapter size and power density

I am excited by the changes and improvements over the past years in the power-supply industry. Things are really going pretty well right now, and while I cannot imagine them getting any better, I guess we will have to wait and see.

Robert Taylor is an Applications Manager at Texas Instruments.

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