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Applying GaN transistor as a replacement of SiC rectifier
Applying GaN transistor as a replacement of SiC rectifier
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Old 20th February 2018, 12:36 PM   #1
Bunpei is offline Bunpei  Japan
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Default Applying GaN transistor as a replacement of SiC rectifier

Kazuo Ozawa and Bunpei are collaborating in a new application of GaN transistor as a replacement of SiC rectifiers for power supplies used in digital audio devices. They think this is a novel approach and worth sharing on this forum.

For these years, Kazuo has made his efforts mainly on improving Salas Reflektor type and Taylor Follower type regulators. Recently, he applied GaN transistor, GS66502B of GaN Systems as a replacement of SiC MOSFET, C3M0280090 of CREE and obtained a satisfactory result.
http://john.asablo.jp/blog/img/2016/12/19/458cae.png
http://john.asablo.jp/blog/img/2017/01/17/460d69.jpg

On the other hand, Bunpei has tried such SiC rectifiers as manufactured by CREE, Rohm, Infineon. His latest favor was Infineon G6. He read Kazuo's blog post and thought, "Is there any GaN rectifier? That must be interesting."
There was a hint on a technical presentation given by Sanghyeon Park and Juan Rivas-Davila.
https://superlab.stanford.edu/poster..._Sanghyeon.pdf
They said, "Tying the gate to the source makes GaN transistor behave like a diode.". Bunpei's first attempt was not successful because the GaN transistor got very hot in his environment. He asked Kazuo to apply GS66502B with his custom board especially designed for cooling.

At the beginning of this month, Kazuo reported his first result on his blog page in Japanese,
GaN Transistorをダイオードとして使う: Konちゃんの虫眼鏡
expressing his very good comments on the new rectifiers. He applied the GaN transistors in PSU of full-wave rectification for an OCXO master clock generator.

Bunpei immediately purchased GS61008T, which has a thermal pad on its top , and followed Kazuo's approach. Bunpei applied the rectifiers to PSU of full-wave rectification with both 4 diodes type and 2 diodes type. Those PSUs are used for Chiaki's SDTrans384 SD memory card transport, ES9038PRO Dual Mono DAC and NDK DuCULoN OCXO master clock generator.
Bunpei's impressions for the new GaN rectifiers were very similar to those given by Kazuo. Both of them felt something very new and remarkable in the improvement of resultant sound quality. "It's a kind of quantum leap!"

Kazuo and Bunpei hope that DIY audiophiles on this forum will confirm their claim is not any bluff and will have a happy music.

You can easily purchase those GaN transistors, products of GaN Systems via Mouser. For cooling, Kazuo designed a special circuit board and Bunpei soldered a small piece of copper plate on the thermal pad of the GaN chip.
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Old 20th February 2018, 04:21 PM   #2
MorbidFractal is offline MorbidFractal
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It is a bit hard to decipher what they think is going on...

Quote:
Originally Posted by Bunpei View Post
Bunpei's impressions for the new GaN rectifiers were very similar to those given by Kazuo. Both of them felt something very new and remarkable in the improvement of resultant sound quality. "It's a kind of quantum leap!"

Kazuo and Bunpei hope that DIY audiophiles on this forum will confirm their claim is not any bluff and will have a happy music.
Language similar to the above is not very helpful... Then again I am probably not in a position to comment.

Otherwise let's all race out and buy these things to try them out.

https://www.mouser.com/ds/2/692/GS61...319-913415.pdf

https://www.wolfspeed.com/media/down...3M0280090D.pdf

Data Sheet for the GS61008T indicates 0 reverse recovered charge implying no minority carriers in the device.

Accordingly there is no quoted reverse recovery time, Trr. However device capacitance and their associated charges still exists. Otherwise the device appears to not have a parasitic Body Source diode.

Data Sheet for the C3M0280090D quotes figures for recovered charge and therefore includes figures for reverse recovery time. This is in addition to device capacitances and their associated charges under given conditions. The device does have a parasitic Body Source diode.

https://superlab.stanford.edu/poster..._Sanghyeon.pdf

Amongst other repetitive things the Author seems to be having problems with Simulation not matching Reality in respect of power losses. A wet finger may suggest that the model is inaccurate... everyone moans about simulation in respect of such anomalies.

Picture from the GS61008T data sheet attached.

It might be pertinent from the right side graph of Ids vs Vgs that the 'channel' does not become conductive until Vgs hits about 2V.

Looking at the left side graph of Isd vs Vsd the Vgs = 0V curve only begins to show conduction as Vds rises to 2V. The Vgs = -2V only begins to show conduction as Vds rises to 4V. The same offset.

This is the forward conduction drop of the equivalent diode but it is not a diode...

This might be the reason why simulation does not follow reality. Does the model include such effects?

Going off the wall if you tie gate to source and then reverse bias the device what happens internally when it is conducting in the reverse mode?

Second Picture is a poor representation of what might be happening internally.

VINT is a voltage drop across the internal Source with the Gate tied to the package source. With Zero volts external the internal drop is negative with respect to the Gate and.... the device turns on.

The above might be rubbish but in terms of how it sounds...

Are Schottky diodes, majority carrier devices sonically as good as the above proposal?

Perhaps Bunpei can try them out and report back.
Attached Images
File Type: png Screenshot at 2018-02-20 16:28:10.png (84.1 KB, 798 views)
File Type: png Screenshot at 2018-02-20 16:50:39.png (6.4 KB, 808 views)
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Old 20th February 2018, 08:57 PM   #3
Bunpei is offline Bunpei  Japan
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Hi, MorbidFractal!

I appreciated your comments very much!

Quote:
Originally Posted by MorbidFractal View Post
Going off the wall if you tie gate to source and then reverse bias the device what happens internally when it is conducting in the reverse mode?
This explanation might be helpful.
"Does the GaN enhancement mode HEMT have a body diode? How do the reverse conduction characterisitcs compare with Sillicon MOSFET?"
GaN FAQs | GaN Systems

Bunpei
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Old 20th February 2018, 10:59 PM   #4
sSound is offline sSound
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I've used GaN HEMT in RF/Microwave applications, they have higher mobility than regular Si, and higher breakdown voltage than GaAs, however CREE GaN transistors tend to be very expensive (do you have a cheap source?)
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Old 21st February 2018, 12:40 AM   #5
Bunpei is offline Bunpei  Japan
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At Mouser, an unit price of GS61008T for Qty. 1 is USD 7.60. It is not cheap. I think worth paying, however.
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Old 21st February 2018, 01:08 AM   #6
sSound is offline sSound
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Quote:
Originally Posted by Bunpei View Post
At Mouser, an unit price of GS61008T for Qty. 1 is USD 7.60. It is not cheap. I think worth paying, however.
Not bad, usually RF HEMTs are around 60-100 USD, 7.60 is not bad at all.
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Old 21st February 2018, 07:19 AM   #7
Bunpei is offline Bunpei  Japan
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This picture shows one of Bunpeiís applications.
Two GaN transistors are used for ďa full-wave rectifier with two diodes and center-tap transformer configuration.
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File Type: jpg 506554E0-3E2F-46FC-876F-46E184EC8263.jpg (966.0 KB, 753 views)
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Old 21st February 2018, 10:07 PM   #8
Bunpei is offline Bunpei  Japan
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The second pictue shows four GaN Transistors are used for 4-diode rectifier (bridge) configuration in the left side part. The right side part shows a conventional SiC diode set with Infineon Gen6 products.
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Old 1st March 2018, 12:54 PM   #9
Kazuo Ozawa is offline Kazuo Ozawa  Japan
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As Bunpei precisely reports, my first interest for GaN started from the study of Taylor Follower type Regulator. When I replaced MTP3055VL with GS66502B for
shunt on the regulator, I found great improvement. Then I decided to apply this GaN to Power amplifier particularly the Amazing Circlotron.

In reference to Amazing Circlotron I made one modification which is adding cascode to the first stage. (1st picture)
On 2nd picture shows you how to implement GaN on a heat sink, Gan is beneath a small aluminum panel.
Also, you can see the modified Amazing Circlotron which I made on 3rd picture.

The sound of this amp made excites me. I used to use some bipolar transistors, MOSFETs, and tubes for final stage until then, I guess GaN is best of all and have no need to choose other items anymore IMO.

There are two challenges.
First one is the green board of GaN is too small to satisfy maximum consumption of heat. Then I made the board made of aluminum substrate (4th picture).
The second one is to change rectifiers to GaNs which I use Infineon G5 SiC diodes now.

Until this late spring, I will report next modified amp with GaN.
Attached Images
File Type: jpg 4.jpg (88.9 KB, 649 views)
File Type: jpg 3.jpg (105.7 KB, 266 views)
File Type: jpg 2.jpg (262.1 KB, 238 views)
File Type: jpg 1.jpg (16.7 KB, 240 views)
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Old 15th March 2018, 11:37 AM   #10
pdcaceo is offline pdcaceo  Hong Kong
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Dear Kazuo Ozawa ,


Any update on this GaN project?


look forward to see it.
__________________
Wilson
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