Comments on Rap Session 1 at APEC 2018

The Rap Sessions 1 last year concluded that “we have all the topologies we need” with flyback and LLC converter declared undisputed champions!? The same moderator and several returning panel members who adjudicated that last year changed this year their hats from topology to become either MAGNETICS or DEVICES experts!? With topologies declared dead on arrival, they invented an artificial contest for Rap Session 1 at this APEC 2018 entitled: BIGGEST IMPACT ON POWER CONVERSION: DEVICES OR MAGNETICS? This is like comparing Apples and Oranges! The only thing they have in common is that they are just components forced to operate at switching frequencies 100 times higher than needed!

UTILIZATION OF DEVICES AND FERRITE MATERIALS?

By doing so APEC 2018 conference managed to completely switch cause and effect in Power Electronics. Topology is a cause and components like switching devices, magnetics and capacitors are just mere consequences! They are the last one to be chosen based on the limitations imposed by switching methods and their topologies! Hence, bad topologies (most present ones!) do result mostly in bad use of all components! Now those device and magnetics “experts” wants us to believe otherwise that new devices and magnetics materials will fix any bad topology!? At APEC 2018 at Rap Session 1 they could not agree only on one thing: how high switching frequency must be, 2MHz or 20MHz! In fact, it was device manufacturers, first as power management companies for the past 50 years, and now the new kid on the block, GaN device manufacturers, who imposed 2MHz on ferrite manufacturers and now demand from them 10MHz ferrite material!? Note that the discussion in this first part is strictly referring to the use of ferrite materials for transformers and not for inductors. Inductors are covered in later Section with new Coreless Step-down Converter Topology.

Discussions at Rap Session:

1. We have all the ferrite we need... Magnetics 2MHz experts say!?

2. We need new ferrites for 10MHz operation...Device experts say!

Yet, both Device and Magnetics experts do not recognize each other’s fundamental flaws and how their exclusive focus on 10 MHz switching is completely misguided as further analyzed below.

HIGH FREQUENCY WARNING IN 1988

I have warned Power Electronics community 30 years ago against such “Safe at 10MHz switching speed” back in 1988. The attached cover of 1988 Power Technics magazine shows me running at speed of 500kHz with Integrated Magnetics Isolated Cuk converter topology and its prototype. What follows is another prototype based on Hybrid Switching Method and corresponding Isolated Topology operating at 50kHz (note the reduced running speed!). This is my second warning after 30 years.

While everyone went to 10 times higher switching frequencies of 5MHz I came down to 10 times lower switching frequency of 50kHz and my reduced running speed on attached revised version of the same drawing! Only 100-time difference but with bonus record 98% efficiency and still reduced size!

QUESTION TO DEVICE EXPERTS BY MAGNETICS EXPERTS

1. Utilization of devices?

Have you ever seen Magnetic expert question Device expert for its 1% device utilization at any switching frequency let alone 10MHz?

What is Device’s current, voltage and power ratings in actual topologies relative to their maximum capability! Please see enclosed drawing of buck converter used for 48V to 1V, 100A having 1% power utilization of its synchronous rectifier GaN device, or an “overkill” factor of 100!

2. Hard switching at 10MHz?

Did Magnetics expert ever ask Device experts why they are using hard switching at 10MHz (full square wave current of 100 A at turn-on and turn-off of the switch) instead of soft switching used even at 50kHz in proper topologies!

The device switching performance is likewise 100% dependent on topology and its ability to operate them at Zero Voltage (ZV), Zero Current (ZC) or both at both switching instances!

Why do device experts ignore topologies which are turning on and turning off synchronous rectifier switch at zero voltage and zero current? Then the switch does not even “know” it is switching since at critical switching instances it “sees” only zero current and zero voltage!

QUESTIONS TO MAGNETICS EXPERTS BY DEVICE EXPERTS

1. Ferrite material utilization?

Did Device experts ever ask Magnetics experts what their ferrite material utilization is (ratio of actual transformer flux density relative to its maximum flux capability)? Why is it only 0.1% for 2MHz optimized ferrite materials, or an “overkill” factor of 1000 to 1? Please see enclosed drawing of the ferrite properties of the PC200 material from TDK.

2. Size reduction with frequency increase?

Any size reduction with 40 times increased switching frequency?

Why device experts never asked magnetics experts why the size of transformer is staying the same despite the 40 times reduction of frequency from 2MHz to 50kHz?

While DEVICE and MAGNETICS experts are praising each other for their advanced 2MHz switching operation, let us turn to a lowly expert on Switching Methods and Topologies.

SWITCHING METHODS AND TOPOLOGIES EXPERT OPINION!

The above answers can only come from Topology experts which were sidelined last year. A more appropriate question to ask now is:

What Comes First: Switching Methods or Topologies?

It is an absence of the appropriate new optimum Switching Methods and their resulting consequence, various converter Topologies, which has stalled Power Electronics for last 70 years! We are now for the first time able to provide simultaneously optimum utilization of switching devices and best utilization of magnetic components with new Switching Methods, Resonance Scaling Method and related novel Topologies. The best yet, we DO NOT NEED 2MHz switching for size reduction as 100kHz works just fine!

MAGNETICS FOR INDUCTORS

How about ferrite cores used for inductors in converters like buck, boost and flyback. It was projected that 50MHz switching frequency would be needed to eliminate ferrite cores (see article in powerelectronics.com) This would not even reduce the magnetics size as the same cross section of the coil winding would be needed!? Yet, with right Switching Method and Topology, the ferrite core is not only eliminated at 50kHz but even reduced to short copper traces on PCB eliminating the need for windings.

CORELESS STEP-DOWN CONVERTER ELIMINATES CORES AND WINDINGS

One such converter is shown using new Storageless Switching Method and related novel Resonance Scaling Method. This drawing compares the buck converter with Coreless step-down DC-DC topology which eliminates magnetic cores and windings even at 50kHz but operates with duty ratio control and has one cycle transient response. The link to detailed powerlectronics.com article is at goo.gl/3N7qBp

BUCK CONVERTER RETIREMENT

While buck converter is used for last 70 years, now the times has come for its well-deserved retirement! Shown below is comparison buck converter with New Coreless Step-Down DC-DC. Both are regulating output DC voltage with simple PWM duty ratio modulation but with these crucial differences:

BUCK CONVERTER

1. Large ferrite core even at 20A DC load current.

2. Inferior transient response due to energy storage.

3. Eight buck modules needed in parallel to fix transient response.

4. Used exclusively to provide 12V to 2V, 100A eight module VRD.

5. Ten-billion-dollar industry relies exclusively on this “solution”!

CORELESS STEP-DOWN CONVERTER

1. Single IC chip with 4 GaN devices

2. One Cycle transient with single module.

3. No magnetics core at 50kHz.

4. No coil windings at 50kHz.

5. Two short copper traces of few mm each for two inductors.

6. Ultra-high efficiency of 99%.

7. No heat sinks needed.

8. First Power Supply on a Chip (PwrC) for 12V to 2V, 100A.

There are number of extensions including galvanic isolation with much reduced transformer size at 50kHz switching!

REAL ADVANTAGES OF GaN DEVICES

To dispel the notion that I am advocating to go from Transistors to Vacuum tubes, there is a great news for both GaN devices and ferrite materials when they are optimized for 50 kHz to 100kHz operation. Terrific low loss ferrite materials already exist with near 100% utilization. GaN manufacturers, however completely missed this with their ultra-high frequency direction! Yet, GaN devices true advantages are:

1. Planar technology enabling all devices and their interconnections can be implemented on a single chip.

2. Integrated drive circuitry on the same chip with power devices.

3. Making power switches and drive circuitry into an Integrated Power Circuit (IPC) for power processing like Integrated Circuits (IC) did for signal processing electronics.

4. Paralleling number of devices for much reduced conduction losses.

5. Scaling up to higher current and power taking advantage of five-times smaller size of devices compared to MOSFETs.

It does not take much to see that these GaN advantages will NOT be realized at 10MHz switching but will be much easier realized at 100 kHz switching with much improved efficiency and reduced size to boot!

Those GaN manufacturers who recognize first

the need to implement and optimize their devices with new System Technology will not only be well rewarded but will also make critical contribution to advancement of Power Electronics field.

CONCLUSION

Buck converter is bad even for a single module let alone for 8 modules in parallel! Thus, it should be abandoned in favor of modern solutions. This is just one of a number of “little box solutions!” which came owing to implementation of new Switching Methods and Resonance Scaling Method resulting in state-of-the-art novel Converter Topologies. The most important is that several solutions include also isolated converters with transformer size at 100kHz even smaller than 2 MHz present designs…Oh, and one more thing: your comments are very welcome!

In addition, those who want to collaborate on this path to Power Electronics for 22nd Century NOW feel free to contact me via email on cuk@teslaco.com.

Dr. Slobodan Cuk, formerly Professor at Caltech.

GaN EXPERT QUOTES

“Magnetics are catching up with higher frequencies possible with GaN.”

“GaN is not 10 times ahead of signal processing ICs. The problem is that silicon-based controller is not designed to operate at higher than 2-3 MHz. They could be, but the controller folks are lagging the GaN folks.”

“Yes, finally! There is also a need for higher speed digital control ICs for DC-DC conversion. GaN devices can be efficiently hard-switched at 10 MHz, but digital controller is usually limited to ~1 MHz.”