PlasmaSonic SSTC II Power Board

The 3MHz PlasmaSonic™ III SSTC

10.1MHz Resonator II Prototype

Introduction

After the very successful stereo audio modulation of the PlasmaSonic I and PlasmaSonic II systems, I realized there was only

one problem still plaguing the high quality audio reproduction of these systems. At the low frequencies I was running at, there

was considerable corona "hiss" and noise from the arc. For high quality audio, this "hiss" had to be eliminated. To get a quiet

arc, the operational frequency of the coil had to exceed 3MHz and ultimately run at around 10MHz or higher.

So I started to set out on building a full-bridge that could operate at 3MHz. After much research, I found that IXYS RF had a

family of switching power supply MOSFETs that were capable of operation up to 30MHz. I decided to use these and

quickly obtained some samples from my local IXYS represenative.

Originally, I was planning on developing a low-cost solid state plasma speaker (full range) system, however current consumer safety

regulations would prevent the PlasmaSonic III from ever becoming a marketed item.

At the time of development, most of this project was veiled in secrecy, however, now that I am no longer pursuing a commercial

avenue with this, I will post my full design as well as photos and some videos of its operation.

Click here for the DE475-501A IXYS RF Power MOSFET Datasheet

Primary Design

The primary coil was wound directly on top of the secondary coil using 12 AWG wire and 5-10 turns.

Secondary Design

(Dimensions in inches)

Secondary Specifications:

1.0" Diameter Polyethylene Coilform

4.0" Winding Length

32 AWG Magnet Wire

Approx. 400 Turns

Ls = 1.07mH (measured)

Fres = 3.1MHz (measured)

Secondary Specifications: (High Freq Commercial Prototype)

0.5" Diameter Polyethylene Coilform

3.0" Winding Length

32 AWG Magnet Wire

Approx. 350 Turns

Ls = 0.23 mH (measured)

Fres = 10.1 MHz (measured)

Resonant Switching

Because of the high frequency nature of this project, resonant switching to acquire ZVS switching was absolutely

necessary due to the high switching losses which would occur at 3MHz. However, at the conclusion of this project,

I never got far enough to successfully operate the full-bridge at ZVS. I attribute this to the reason of the very poor reliabilty

obtained at operation from up to 10MHz.

Gate Driver Design

At 3MHz, the most difficult part of the design was the gate drive circuit. To accomodate this, I came up with a unique design

that allowed a reservoir on the secondary side of the gate transformer to provide all the energy required to switch the MOSFET

on. This unique gate drive circuit worked extremely well and with the proper cores, was able to switch the full-bridge at over 10MHz.

However, at frequencies above 3MHz, conduction losses (and relatively slow rise-times and fall-times of the gate drive), the circuit

become unreliable, lasting only a few minutes before overheating.

Testing at above 10MHz

The final goal of this design was to utilize switching at over 10MHz which (shown by previous ion speaker creators) was COMPLETELY

silent. Operation above 3MHz was extremely silent, although some subharmonics at 10-20kHz could still be heard or at least seen with a

spectrum analyzer. Operation above 10MHz virtually eliminated this and put these subharmonics into the noise floor.

Maximum operation of this system was verified at about 10.1MHz using a very small 3.0" x 0.5" diameter coilform wound with 32 AWG

wire. However, operation did prove to be unreliable, although the arcs (about 3" long at CW actually appeared bright orange rather than the typical purple arcs we see normally)

Schematics and Electrical Design

The following schematics are for the 3MHz PlasmaSonic™ III SSTC Board (Requires Adobe Acrobat 5.0)

Click here for the Power Section Schematic

Click here for the Prototype Test Driver / Low Voltage Power Supply (LVPS) Schematic

Last modified June 20, 2004 10:43:21 PM