Coaxial Bipolar High-Voltage Power Supply Design for Electrospinning

Core-shell and hollow nanofibers for drug delivery and filtration require perfectly concentric Taylor cones sustained by independent but precisely synchronized high-voltage supplies for the inner and outer solutions, typically +8 kV to +28 kV for the shell needle and –4 kV to –18 kV for the core needle. Coaxial bipolar systems must therefore maintain opposite-polarity voltages with differential stability better than ±28 V and reversal synchronization under 120 ms while monitoring individual solution currents at nanoampere resolution.

The dual supply uses two identical 240 kHz resonant converters operating from a common 48 V rail, one configured for positive output and one for negative, each driving its own 1:110 piezoelectric transformer and eight-stage Cockcroft-Walton multiplier encapsulated in solvent-resistant epoxy. Physical separation of 48 mm and triple mu-metal shielding prevent crosstalk below 18 V when one channel steps 12 kV.

Voltage synchronization is achieved by a master 80 MHz clock distributed via fiber optics; both converters lock switching phase to within ±8° and share a single 0.01 % reference, ensuring differential voltage remains within ±22 V across full temperature and load range. Individual needle currents are measured via capacitive pick-off rings with 1.8 nA resolution and used for closed-loop flow-rate correction in active feedback spinning systems.

Reversal for cleaning cycles is executed simultaneously: both converters ramp to zero in 68 ms, reverse drive phase, and reach opposite full voltage in an additional 94 ms with no measurable intermediate zero-crossing dwell that would collapse compound cones. A 400 ms reverse-polarity burst at 150 % amplitude burns off polymer residue without mechanical contact.

Safety incorporates dual independent arc detection: local per-channel collapse in <11 µs for events >180 nA/µs, and global shutdown only for simultaneous faults. Recovery implements staggered restart to prevent re-ignition of residual solvent vapor.

These coaxial bipolar supplies routinely produce 80–1800 nm core-shell fibers with shell thickness uniformity <6 % across 600 mm wide webs at collection speeds >280 m/min, enabling continuous production of phase-change microcapsules and high-efficiency hollow-fiber filtration media.