In medium-voltage (MV) power electronic systems such as grid-connected converters, a compact, isolated, and reliable auxiliary power supply is critical for powering control logic, gate drivers, and sensing circuitry. This design uses a high- frequency flyback converter that prioritizes insulation strength and EMI performance. The converter is designed to operate from a 230 V AC input (rectified to ~325 V DC) and delivers a 24 V DC output at up to 30 W. The flyback topology is selected especially for its simplicity at low power levels and inherent galvanic isolation. A UCC28C42-Q1 current-mode PWM controller is used to drive the power MOSFET at a switching frequency of 100 kHz. This controller features primary-side sensing, eliminating the need for opto-couplers or secondary-side feedback circuits. This improves reliability, particularly beneficial in medium/high-voltage isolated systems. To handle voltage spikes from leakage inductance during switch turn-off, an RCD clamp circuit is placed across the primary switch. This limits peak voltage stress and minimizes radiated and conducted EMI. The flyback transformer uses a planar magnetic structure, offering the following benefits: (a) Reinforced isolation up to 30 kV, essential for use in MV converter; (b) Low inter-winding capacitance, reducing common-mode noise coupling; and (c) Compact and thermally efficient structure, using multilayer PCB windings for tight coupling and repeatability.

A tertiary winding is specifically included to power the UCC28C42-Q1 controller, allowing it to self-bias after initial start-up through a high-resistance bootstrap path or auxiliary circuitry. To suppress common-mode noise further, common-mode filters are incorporated at the input and output. These filters help attenuate common-mode currents generated due to high dV/dt switching and parasitic capacitive paths, thus ensuring compliance with EMI standards and protecting sensitive low-voltage circuits. Furthermore, an earth-connected shield is placed between the primary and secondary windings. This provides a low impedance path for the common-mode currents, which would otherwise entirely couple through the inter-winding capacitance between the primary and secondary. This work was done by Senthil Arumugam, Syed Rasheed, Rajvardhan Patil and Sagnik Banerjee under the guidance of Prof. Sandeep Anand.