Design Approach for a Self-Oscillating Resonant Converter Operating in High Frequency for LED Applications

In this paper, a design approach for the self-oscillating command circuit (SOCC) as a driver for a resonant converter operating in high frequency for LED applications is proposed. This proposal, conceived from the proposed methodologies, contemplates the influence of the Cascode gallium nitride (GaN) FET input and output capacitances, making it relevant to higher switching frequencies, where such parasitic elements lead to increased errors. In conjunction with higher efficiency levels, series resonant inverters like the zero-voltage switching half-bridge are known to have potentially reduced size on its reactive components when operated at higher frequencies, resulting in smaller and lighter systems. Combined to the 'simplicity and low cost of the SOCC, these advantages translate into a simple and cost-effective high-power-density application. The self-oscillating resonant converter (SORC) accurate design is based upon the describing function method as a linearization tool and the extended Nyquist stability criterion that evaluates whether or not the system can oscillate around given predicted frequency. Practical input capacitance measurement data for different silicon MOSFETs and a Cascode GaN FET are compared and considered in order to obtain a high-frequency design approach for an SORC. Simulation and experimental results for an SORC with Cascode GaN FET operating at 1 MHz for a 10-W LED are shown based on the design procedure described.