Background: A company had developed technology to enable visual disorders to be corrected by using a laser to actually modify the radius of curvature of the cornea. Product Resources was engaged to design and build a power supply to provide 75 kilovolt, 80 joule pulses at a rate of 30 to 100 pulses per second to power a new, more powerful laser.

Project: Starting with a concept that eliminated all semiconductors from the high voltage circuit, Product Resources engineered and built a working prototype of the power supply. The design concept was first modeled using circuit simulation software to verify and test the engineering calculations. The energy levels in the circuit were so high as to be capable of exploding any component which failed to function perfectly, so all final tuning had to be done using the computer before the prototype was actually run at full power. As a result, the power supply ran its first time exactly as designed. The power supply functions by charging an energy storage capacitor to 1400 volts in less than 5 milliseconds from a 200 volt DC reservoir supply. This required Product Resources to design a series switching regulator which employs four 1000 volt MOSFET transistors in series, switching at 50 kHz. The energy storage capacitor is discharged by a thyristor into the primary of a specially designed, step up, pulse transformer that charges an output capacitor with 80 joules of energy at a secondary voltage of 75 kilovolts. The laser is switched at the precise instant the output capacitor achieves maximum voltage. The prototype was delivered to the customer on schedule and within budget. Product Resources is working on a production version.

Technologies: power MOSFET switching at high voltages, thyristor switching with very high di/dt, pulse transformers, energy storage capacitors, copper bussbars, kilowatt linear power supplies, transistor logic circuits, fiber optic logic communications

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