Type III compensated voltage mode line feedforward synchronously rectified boost converter for driving Class D audio H-bridge to deliver 7 W peak power into an 8 omega speaker

Authors: YAVUZ KILIÇ

Abstract: In this paper, a circuit topology for a synchronously rectified boost converter aimed to act as a power supply for a Class D H-bridge that would deliver up to 7 W peak power into an 8 Omega speaker is presented. The design is implemented in a submicron BCD process technology. Some of the challenges in this design are as follows. The first challenge was to optimise the design such that it would not cause on-chip power dissipation levels that would go beyond acceptable levels for Wafer Level Chip Scale Package (WLCSP), which is a commonly used package for space constrained applications in portable spaces. To address this issue, a Class G mode of operation to deliver multiple boost voltage levels has been proposed. Second, due to the chosen submicron BCD process lacking some devices such as zener diodes to clamp maximum voltages that active device gate-source and/or drain-source terminals in case of transient or normal operating conditions of the circuit, new ways of circuit implementation techniques have been come up with to prevent active devices from being damaged. One more important issue for handheld applications is that it is imperative to choose a small form factor (height and footprint) external inductor, which can also stand up to 4 A for this particular design. The new trend in small footprint power inductors is to use an iron powder core to keep the inductance constant. This creates a new problem with these types of inductors, whereby the series resistance of the inductor would increase with the frequency, which will increase the inductor AC core losses at switching frequencies of the switching converter. Trade-offs between total harmonic distortion plus noise and boosted voltage levels are also studied.

Keywords: Boost converter, DC-DC converter, voltage mode, line feedforward, pulse width modulation, synchronous rectification, Class D, Class G, audio, BCD, inductor

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