Fast Magnetic Reduction/Reestablishment Supply

SPICE modeling current waveform for the notch supply showing constant current level followed by fast fall time and subsequent rise back to constant level.

For a customer, EHT designed and built a power supply to drive magnetic field coils. The coil current profile needed to rise to a flat top, then drop to near zero, and finally re-establish at the same flat top value. EHT engineers designed an IGBT-based solution to accomplish this task. Initial work was performed in SPICE modeling to identify faults, design inductance values, and evaluate the required PWM frequency. The figure shows the current waveform from the SPICE model.

Testing data showing current profile with a 5 kA flat top.

Once the supply was designed, EHT engineers rapidly constructed a proof-of-concept on the bench top to validate the model. The current profile from this test is shown in the figure. The flat top is maintained at 5 kA using a PWM switch operating at 500 kHz. The supply was capable of quickly reducing and reestablishing the magnetic field (rise/fall times were independently fiber-optically controlled). This solution was then delivered to a customer.