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A digital hybrid current mode (HCM) control technique which combines peak current and average current mode (ACM) control methods is studied. The proposed controller consists of three control loops, an analogue fast current loop, a digital slow current loop and an outer voltage loop. For the control method, both continuous and discrete-time models are built. Similarly, a continuous-time model for ACM control is provided for comparison. For both control techniques, a compensator design method is proposed. The control methods are implemented on a 6 W synchronous buck converter with a mixed-signal ARM-based microcontroller. Controller models are verified with the frequency response measurements of the inner and outer loops. In digital HCM control, higher DC gain and phase margin is achieved with the same gain margin compared to digital ACM control. Furthermore, the transient responses of the systems are analysed. When the outer voltage loop is open, 30% faster dynamic response is measured by the digital HCM method. With voltage compensation, comparable dynamic response on the output voltage is achieved without inductor current overshooting by the digital HCM control.

Laser Diodes are the essential components for development of high power laser systems. To operate these devices, highly efficient and high power density, compact, current regulated switching converters are necessary. In this paper, Gallium Nitride (GaN) based synchronous buck converters are studied for the application of laser diode driver. For this purpose, two synchronous buck converters one with Si-based the other one with GaN-based are designed, simulated, tested and compared. With the application of GaN-based semiconductors, 96.6% efficiency and 9.1 W/cm 3 power density is achieved for 11A, 28V load at 700 kHz operating frequency.

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The three-level flying capacitor (3LFC) buck converter has the potential to provide better efficiency and higher power density as compared to the traditional buck converter. However, due to the flying capacitor's instability issues, control is challenging. In this paper, the digital hybrid current mode (DHCM) control method, which combines the average and peak current mode control techniques, is modified and implemented to a 3LFC buck converter. For flying capacitor (FC) voltage balancing, a novel asymmetric slope compensation (ASC) technique is presented. The proposed ASC technique achieves FC voltage balancing by adjusting the slope compensation of the two switching pairs asymmetrically, and therefore is applicable to any type of digital peak current mode control (PCM) method. The ASC technique for DHCM control of the 3LFC buck converter is verified in simulations and experimentally with an ARMbased mixed-signal microcontroller on a 250-kHz, 24-V input, and 35-W/4-A output prototype. The overall control method enables the implementation of the 3LFC buck converter for accurate and fast current regulation, and therefore is especially advantageous for LED and laser diode driver applications.