Pulse Transformer Design
Pulse Transformers are a special type of transformer that are designed to pass through square wave pulses, rather than a oscillating/RF frequency. They must have low stray ("leakage") inductance and stray capacitance to achieve clean, flat-top pulses. My experience with pulse transformer design is in the regime of high-voltage (1kV-50kV), nanosecond (5ns-1us) pulses. As a result of the high-voltage involved, a critical aspect of the designs is respecting standoffs to high voltage, both to prevent arcing as well as corona discharge (~70V/mil).
The dominant design parameters in pulse transformer design are:
- Primary-side winding style
- Wire gauge, insulation material and thickness,
- Number of series and parallel turns
- Spacing from the core
- Secondary-side winding style (same considerations as before, but adding on high-voltage standoff issues to
- Those above
- High-voltage standoff from primary side and surrounding components
- Minimum load
I was involved in the design of the pulse transformer at the core of EHT's nanosecond pulser technology which is now a provisional patent, filed in 2015. The dominant IP in this patent relates to the specific range of values of stray inductance and capacitance achieved, and the methods we developed to accomplish those values.
Provisional - High Voltage Transformer
Co-inventor with Eagle Harbor Technologies
Filed November 30, 2015
Serial No: 62/260,821
Pulse transformer circuit diagram including all sources of stray capacitance and inductance
In the file section below, I've included several reference documents that describe the behavior of pulse transformer, discuss optimization, and give estimates of values for stray C and L. I've kept them private until I can verify there is no IP included.
Knopfel Magnetic Inductance.pdf — Verified Inductance Formulas for Standard Conductor Geometries