Insulated metal substrate (IMS) printed circuit boards (PCBs) are an attractive alternative to conventional FR4-based PCBs and power modules due to their good thermal performance, low cost, and compatibility with the reflow soldering processes. In this thesis, the dielectric performance of IMS PCBs is characterised to validate their use in high-voltage power electronic applications and ensure that an acceptable lifetime and reliability can be reached. In particular, the high-frequency degradation of the dielectric is investigated.

The IMS dielectric was characterised using breakdown tests with various voltage waveforms and frequencies to closely approximate their use-case in power electronic converters. Two high-voltage generators were designed and realised to generate high-frequency square-wave and sinusoidal waveforms. In addition, diagnostic tests were performed to identify the effect of electrical ageing on the dielectric properties.

he designed high-voltage test sources allowed for ramp breakdown and lifetime tests up to 100 kHz and 10 kVpk. These tests showed that the dielectric degrades extremely fast under high-frequency voltage stress, most likely due to localised high partial discharge activity and electrical treeing. As a result, no reasonable lifetime can be expected when operating above the discharge inception voltage. For thick dielectrics (>100 µm), surface discharges are the dominant degradation mechanism with an inception voltage of 2.4 kVpk. The maximum nominal voltage should be limited to approximately 1.5 kVpk to ensure the reliable operation of the IMS PCBs.

The effectiveness of ultraviolet (UV) irradiation for disinfection has been well-known for more than a century. Recent advances in light­-emitting diode (LED) technology have brought UV LEDs to the consumer market. These offer many advantages over traditional gas­-discharge lamps, allowing UV radiation to be generated with higher reliability in a much smaller form factor. In this thesis, the design of a portable battery­-powered sterilizer based on UV LEDs is described. The sterilizer is intended for the sterilization of personal items such as mobile phones, face masks, and keys.

The design of the sterilizer consisted of two parts: the LED array and the LED driver. For their design, a model­-based approach was taken to ensure high performance and low cost. For the LED array, a radiometric model was developed and applied in an optimization procedure. The design of the LED driver was based on an analytical loss model in MATLAB and LTspice simulations.

The UV LED array provides a radiant power of 113 mW to the disinfection area, resulting in an irradiation dose of 195 μW/cm2. This allows for more than 99.9% disinfection in less than 15 min. The LED driver is a boost converter operating at 750 kHz in the discontinuous conduction mode. This converter supplies the array with a nominal input power of 4.3 W at a simulated efficiency of 91%.

The design of the LED driver is verified with a prototype. Measurements show efficiencies around 83% at 4.1 W output power. Incorporating several improvements over the prototype, efficiencies between 85–87% can be expected for the LED driver in the sterilizer.