Highly Integrated ZVS Flyback Converter ICs With Pulse Transformer to Optimize USB Power Delivery for Fast-Charging Mobile Devices

Abstract

Flyback converter with USB power delivery is widely used for fast-charging mobile devices. However, conventional solutions have issues such as lower efficiency, higher cost, a large number of external components, and lower loop gain bandwidth. In this article, a high-efficiency zero-voltage switching (ZVS) flyback converter with primary-and secondary-side control ICs is proposed to solve the aforementioned issues with high integration level. The proposed control replaces optocoupler to achieve ZVS and secondary-side-regulation (SSR) by a pulse transformer. The ICs further integrate the USB power delivery (PD) controller and the constant voltage (CV)/constant current (CC) loop compensation to reduce external components. The proposed control and small-signal model are illustrated and verified by the experiment. The control ICs were fabricated in a 180-nm BCD process. The implemented 20-V/3-A/60-W USB PD flyback converter achieved 93.5% maximum efficiency using Si power switches. The feasibility of the proposed converter is verified by a thorough test of programmable power supply (PPS) with various CC/CV levels and load/line transients. Index Terms-Converter, constant voltage (CV)/constant current (CC), fast-charging, flyback converter, pulse transformer, USB power delivery (PD), zero-voltage switching (ZVS). I. INTRODUCTION U SB power delivery (PD) supporting up to 100 W (20 V/5 A) has become a popular standard for mobile devices' fast-charging solution [1]-[3]. An adapter with the USB-PD specification has the advantage of supplying various devices with a single converter. For example, the converter with the input from the grid can provide a 5-V dc output voltage for cellphone load and a 19-V dc output voltage for laptop computer load. Thus, the carrying adaptors and corresponding electronic trash can be reduced. Moreover, the extended specification of USB PD includes a programmable power supply (PPS) which is suitable for fast-charging mobile devices.

New Fixed-Frequency Digital Control to Improve the Light-Load Efficiency of an Isolated Regulated Converter

“…C S reflects to the secondary side and resonates with L O . The V ds(S) and I Lo expressions of this stage are shown in Equation (10).…”

“…The threshold voltage requires high precision. (2) Detecting the zero current of the inductor current by a ZCD (zero-cross detector) circuit and turning off the freewheeling switch [9][10][11]. (3) Using the voltage-second balance method [6,12,13].…”

A high-efficiency active clamped flyback AC-DC converter using an integrated digital isolator in isolated communication

“…But the precision of PSS will be compromised by parasitic resistance and the voltage drop brought on by leakage inductance [11]. In [12,13,14,15], a magnetic isolation circuit is applied in place of an optocoupler, output of the error amplifier or control signal can be sent to the controller through the microtransformer integrated on chip, which offers an opportunity to reduce the volume of the system. However, as reported in [16], compared with the capacitor-coupled isolator, the inductor-coupled isolator is more sensitive to external electromagnetic interference and less cost effective.…”