The Circuit Diagrams


I have done a lot of searching for SSTC's, and haven't found any who use this method, even specifically searching for this idea.

The Control Unit


The selector switch is double pole, one pole is shown, this is because I can't use a common ground as the amplifier return is mid level, and the interruptor uses the positive for one opto connection.
The umbilical includes a fibre optic cable which uses the middle pin of the connector as a guide.
There are 2 amplifiers, one is used to trigger the optics, the other is optionally used as a monitor for speaker or headphones, the one i used for the optics has a poential divide for 'speaker return' but the opto is connected instead.

Relay Control

Very simply this is controlled from the control panel's 'main' switch, this is everythinng that is connected to the umbilical, there are also LED's, but these are for illumination of the coil only.

The Driver


Starting with an oscillator module to generate the 129KHz square wave, this feeds into a TC4428 gate drive ic which outputs opposing cycles, most other sstc's use this to drive a low voltage H bridge and isolating transformer, the way my design differs is that it's driving 4 opto isolators, the signal is then inverted to interface to the mosfets in the H bridge directly, no need for other items in the chain, though it does need a special power supply.
Just to note, there is a BNC connector on the base, along with a 10 turn potentiometer, the BNC is for connecting a frequency meter and/or scope, the latter is to check the mark-space ratio of the square wave is at 1:1

Power Supply


This looks a bit intimidating, but my design is based on a toroidal transformer with extra windings, this can easily be done with 2 small transformers, each with 2 windings of about 9volts, this will give 4 12volt supplies when rectified, 3 supplies for the driver circuit, the other for the oscillator and gate drive ic, plus the fan.

H Bridge


Nothing special here, the outputs from the drive are connected to the appropriate gates.

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Alternate H Bridge and gate drive


Instead of using the power supply above, this is an idea i had, if you ignore the mosfets for a moment, each side has 2 simple supplies in series, each with a dropper resistor, diode and capacitor, with a zener to limit the voltage.
The capacitors should hold the voltage long enough when the associated mosfet is turned on to supply the isolation circuit.
You would only need 1 12volt supply for the oscillator/driver/fan
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