HV class D?

Nevod · 18th October 2011, 05:59 AM

Again, I've been thinking about using class D for driving ESL panels. I've understood why it is not possible to just use transformer, and using synchronous rectifier, which anyways needs HV switches, seems to be pointless - if you already have HV switches, you can just make an amp.

So I've stumbled upon the HV SiC JFETs and read some app notes regarding using them in cascode configuration with MOSFETs as lower device and JFET as higher device in HV SMPS. As such, is it possible to use such a device as an output stage switch in a class D amp? I don't see why it couldn't be, but I may not be right.

Also, there would have to be at least several changes made for the amp to work with ESL and corresponding high voltage, hence, high EMI: each module would have to be shielded and grounded, cables to the panels should also be shielded. Instead of LC filter, I suppose, just an inductor in series with output should be used, so there would be no oscillation.

geraldfryjr · 06:13 AM

I think it can be done using at least a +/- 2kv supply .
I know of a link for a 1 kw 1500v switching supply that can give you some idea's.

here it is ,

http://w5jgv.com/hv-ps1/

jer

Nevod · 18th October 2011, 06:21 AM

Don't think such a thing would have high switching frequency.. I was thinking about something more moderate, perhaps for driving headphones, with +-500v supply.

But the link is very interesting, thanks!

geraldfryjr · 18th October 2011, 06:25 AM

Yes I think it is very possible as the outputs are filtered back into a dc voltage any how.

jer

geraldfryjr · 18th October 2011, 06:39 AM

I did build a PWM circuit with that in mind but right now it is on the back burner somewhere.

So far it has a TTL output and produces 0v to 5v as well as a very clean sine wave and square waves as well.
I even ran music through it as a test.
I was shocked as to how well it worked.
I had not figured out how to drive FET's until much later,so I never finished it.
I was using a very high switching frequency as well some where in the 100khz to 300khz range.
I just used a large air core inductor that I had made that was laying around for the output filter.
It was for a small tesla coil wrapped with some #30 magnet wire on a 2"dia X 2.5" long form.
It was fun and pretty neat, as well as I still have it.

jer

marce · 18th October 2011, 11:24 AM

Easier to use lower voltage and transformer on output, saftey and EMC are two concerns with HV designs.

Nevod · 18th October 2011, 12:45 PM

marce,
Transformers change the sound, and interact with ESL. There are already direct-drive amplifiers for ESL headphones, but I'd like to know if a comparably sounding class D is possible.

18th October 2011, 05:59 AM	#1
Nevod diyAudio Member Join Date: Nov 2007	HV class D? Again, I've been thinking about using class D for driving ESL panels. I've understood why it is not possible to just use transformer, and using synchronous rectifier, which anyways needs HV switches, seems to be pointless - if you already have HV switches, you can just make an amp. So I've stumbled upon the HV SiC JFETs and read some app notes regarding using them in cascode configuration with MOSFETs as lower device and JFET as higher device in HV SMPS. As such, is it possible to use such a device as an output stage switch in a class D amp? I don't see why it couldn't be, but I may not be right. Also, there would have to be at least several changes made for the amp to work with ESL and corresponding high voltage, hence, high EMI: each module would have to be shielded and grounded, cables to the panels should also be shielded. Instead of LC filter, I suppose, just an inductor in series with output should be used, so there would be no oscillation.

18th October 2011, 06:07 AM	#2
geraldfryjr diyAudio Member Join Date: Feb 2008 Location: Jackson,michigan	I think it can be done using at least a +/- 2kv supply . I know of a link for a 1 kw 1500v switching supply that can give you some idea's. here it is , http://w5jgv.com/hv-ps1/ jer Last edited by geraldfryjr; 18th October 2011 at 06:13 AM.

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18th October 2011, 06:21 AM	#3
Nevod diyAudio Member Join Date: Nov 2007	Don't think such a thing would have high switching frequency.. I was thinking about something more moderate, perhaps for driving headphones, with +-500v supply. But the link is very interesting, thanks!

18th October 2011, 06:25 AM	#4
geraldfryjr diyAudio Member Join Date: Feb 2008 Location: Jackson,michigan	Yes I think it is very possible as the outputs are filtered back into a dc voltage any how. jer

18th October 2011, 06:39 AM	#5
geraldfryjr diyAudio Member Join Date: Feb 2008 Location: Jackson,michigan	I did build a PWM circuit with that in mind but right now it is on the back burner somewhere. So far it has a TTL output and produces 0v to 5v as well as a very clean sine wave and square waves as well. I even ran music through it as a test. I was shocked as to how well it worked. I had not figured out how to drive FET's until much later,so I never finished it. I was using a very high switching frequency as well some where in the 100khz to 300khz range. I just used a large air core inductor that I had made that was laying around for the output filter. It was for a small tesla coil wrapped with some #30 magnet wire on a 2"dia X 2.5" long form. It was fun and pretty neat, as well as I still have it. jer

18th October 2011, 11:24 AM	#6
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	Easier to use lower voltage and transformer on output, saftey and EMC are two concerns with HV designs.

18th October 2011, 12:45 PM	#7
Nevod diyAudio Member Join Date: Nov 2007	marce, Transformers change the sound, and interact with ESL. There are already direct-drive amplifiers for ESL headphones, but I'd like to know if a comparably sounding class D is possible.

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