Power Supplies: What’s next?

This article develops a vision of the future from the history of power supplies. You will learn why efficiency is important, what influences the lifetime of power supplies and how Software Defined Power enables you to save development costs.

What are power supplies?

Power supplies convert the unregulated voltage of the grid into a consumer-specific form. Typically this is a voltage, but in LED drivers it can also be current. Some niches require a high frequency output to emit microwaves.

Power Supply History

Originally a power supply was an iron core transformer with bridge rectifier. In the beginning tube rectifiers (from ~1920) were used for this purpose, which were then replaced by selenium, gallium and finally silicon diodes (from ~1960).

Power supplies were gradually made much more compact (in the consumer sector in the 2000s) by using high frequency transformers instead of 50 Hz transformers. This was made possible by transistors that allowed high switching voltages. The new switching frequencies in 100kHz made significantly more compact power supplies possible. At the same time, the integration progressed significantly. At first, controls were only built with operational amplifiers. Gradually, semiconductor manufacturers integrated the technology into ICs. This trend will continue in the future.

Digital technology will also continue to assert itself. The first semiconductor manufacturers are already offering digital flyback controllers. Currently, however, they still lack the computing capacity.

What drives innovation?

Innovations in switching power supplies have been based to 80 % on advances in semiconductor technology in recent years. On the one hand the integration by means of semiconductors. So there are ICs, which allow the secondary side rectification with Lov-Voltage-Mosfets. The diode voltage drop of 0.7V can be reduced significantly. But also SiC and GaN power supplies will make their contribution, especially due to their improved component characteristics. Faster switching frequencies, in the MHz range, will make power supplies shrink even further. Also super-compact power supplies based on GaN will be found in the consumer sector in the future.

Digitization also offers new opportunities, especially the fact that microcontrollers with high computing power are available for a few euros. This offers the user better data accessibility. The developer can use the measured variables to build up high-performance controls.

But there are also innovations on the circuit technology basis. Meanwhile, there are also topologies that do without the mains rectifier. Or resonant switching topologies avoid switching losses. New technologies also make it possible to simply build bidirectional power supplies.

Efficiency – (Not) A figure for quality?

The conversion efficiency AC-DC also improved significantly. Initial efficiencies increased from 60 % to values of now typical 95 %. But what is the efficiency gain? Reduced electricity costs of course, CO2 savings: of course. But the main advantage for the user is that less heat is generated: Heat that is not generated does not have to be dissipated. But why is that important? Because the warmer a power supply unit, the shorter its service life. That’s why efficiency was often used as a quality criterion for durability in the past. But this is thought too simply. Electrolytic capacitors are particularly sensitive here. Although there are different quality classes, they are still responsible for a large number of device failures. Puls GmbH in Munich, a manufacturer of top-hat rail power supplies, shows in an application note as early as 2012 that the electrolytic capacitor is a frequent cause of failure in their power supplies. A special cooling concept was developed to reduce this disadvantage [1]. However, most power supply manufacturers do not make any precise predictions about service life.

Therefore it is obvious to optimize the disadvantage “Elko”. Modern digital control technology makes it possible to build power supplies based on film capacitors only. The Karlsruhe Institute of Technology (KIT) has presented a special control algorithm for this purpose [2].

Die Digitalisierung als Möglichmacher

Another megatrend will be to collect more data and evaluate it. The first major manufacturers have already taken up this technology trend and want to give users new insights by using the data. An example of this is the ProTop power supplies from Weidmüller [3]. However, many other manufacturers also offer these similar technologies. The obvious thing to do now is to develop algorithms to use and automatically evaluate this data.

But at this point one should not stop, but start. By using processors it is also possible to build up highly dynamic controls. Therefore, it is obvious to use explicit digital controls instead of digital control loops. This way loop-shaping can be used to design the exact system behavior and to specify the eigenvalues of the control. With exact system competence for demanding applications, one can build up eigenvalue controllers that enable highly dynamic step responses. Rise times in <<1mSec are possible.

Most power supplies are also optimized for only one operating point. Here digital power supplies can allow to cover a wide output range. This can be observed already with solar inverters, which offer 98% efficiency over a wide load range.

Digital defined Power as a chance

The market for power supplies is cost-driven. Therefore, it will continue to be important in the future to offer new technologies at affordable prices. However, the development and, depending on the standard, the required certification effort is considerable. It would therefore be obvious to offer hardware as basic equipment which can then be adapted by means of software. Similar to the component strategy in the automotive industry: One component – many possibilities!

For example, you have a hardware platform with an AC-DC unit that can be used for both voltage and current control. On the one hand, a power supply unit could be used as a top hat rail power supply, but on the other hand it could also be used as a LED driver. This way a variety of solutions can be covered on the basis of a common hardware platform.

Halbleiter als strategische Komponente

In the future, new processor generations such as RISC-V will also offer many opportunities to obtain even more computing power at favorable conditions. Already now a modern MCU has more computing power than my first computer. Therefore we can expect many exciting innovations in the coming years. Maybe soon there will be MCUs with integrated gate drivers?

Alternatively, it is conceivable that volume manufacturers of power supplies will develop their own ICs. Here there are movements such as OpenRoad, which will make it possible to implement even smaller quantities economically.

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