Current Control Strategies for Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Two Switched-Mode Converters to Achieve Optimal Power Allocation

Abstract

Switch-linear hybrid (SLH) envelope tracking (ET) power supply is one of the mainstream structures for achieving both high efficiency and high bandwidth. When tracking a high bandwidth envelope signal, the overall efficiency of SLH ET power supply with the single switched-mode converter is limited. This paper adopts two switched-mode converters with different tracking bandwidths instead of the single switched-mode converter. The switched-mode converter with low tracking bandwidth is called slow switched-mode converter (SSMC), which aims for providing the low-frequency load current components with low slew rate; while the switched-mode converter with high tracking bandwidth is called fast switched-mode converter (FSMC), which copes with the high-frequency load current components with high slew rate. The rest load current components are processed by the linear amplifier. The class-A linear amplifier is employed for reducing the complexity of the circuits, which works as a voltage regulator that does not sink the load current. The SSMC provides the majority of the load current with low switching frequency. Thus, the switching loss of the SSMC is not high. The FSMC is operated at high switching frequency but provides the minority of the load current, and thus the switching loss of the FSMC is not high. The valley-point current control and peak current control with critical continuous current mode are proposed for the SSMC and FSMC, respectively, achieving the desired power allocation among the SSMC, FSMC, and the linear amplifier. Finally, a prototype is fabricated in the lab aiming for tracking a 10-MHz envelope signal and 20-W average output power. Experimental results are provided to verify the effectiveness of the proposed configuration and its current control strategies. The efficiency of the proposed SLH power supply is 77.0%, a 4.5% efficiency improvement compared with the SLH ET power supply with the single switched-mode converter.