Active Rectifier Dead-Time Control for Low-EMI Power Supplies
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Solution Overview
Problem
Existing power supplies with rectifiers face challenges in achieving high efficiency and reliability simultaneously, as improved efficiency often compromises reliability and vice versa, while also experiencing issues with total harmonic current distortion (iTHD) and electromagnetic interference (EMI).
Innovation Solution
The implementation of a rectifier circuit with transistors and adjustment circuits that control dead time between on-states, utilizing optocouplers to manage the gate-source voltage of transistors, allowing for automatic and adjustable dead time control, reducing component count and external control signals to enhance reliability and efficiency, and mitigate iTHD and EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional rectifier circuits with diode bridges are used, then the circuit structure is simple, but conversion efficiency is low and reliability is compromised
Solution Approach 1:
The patent replaces traditional diode bridge rectification with an active switching rectifier circuit using transistors (Q1-Q4) as electronic switches. This substitution enables precise control of switching timing through dead-time control circuits, optimizing the rectification process to achieve both high conversion efficiency and high reliability simultaneously by eliminating the inherent trade-off present in passive diode-based designs.
Solution Approach 2:
The patent introduces dynamic dead-time control mechanisms that adjust the off-time intervals between complementary transistor switches based on operating conditions. This dynamic adjustment optimizes the rectification process across varying loads and input voltages, maintaining peak efficiency while preventing shoot-through currents that would compromise reliability, thereby resolving the static limitations of traditional fixed-timing circuits.
2Loss of energy
If active switching elements are added to improve efficiency, then conversion efficiency increases, but device complexity and component count increase
Solution Approach 1:
The patent merges the dead-time control function directly into the gate drive circuits of the switching transistors. The emitter-coupled logic circuits generate complementary gate signals with built-in dead-time control, eliminating the need for separate external control circuits. This integration reduces overall device complexity while maintaining the efficiency benefits of active switching.
Solution Approach 2:
The switching circuit employs self-complementary gate drive generation where the state of one transistor automatically controls the gating of its complement through emitter-coupled logic. This self-service mechanism eliminates external control signals and reduces the burden on external control circuits, simplifying the overall system while preserving high efficiency operation.
3Reliability
If dead time control is implemented to improve reliability, then reliability increases, but generated EMI and harmonic distortion increase
Solution Approach 1:
The patent employs emitter-coupled logic circuits that dynamically adjust the dead-time parameter based on operating conditions. By optimizing the dead-time duration and timing characteristics, the circuit achieves reliable operation while minimizing the spectral content of switching transients. This parameter optimization reduces both EMI radiation and harmonic distortion in the output waveform.
Solution Approach 2:
The complementary gate drive generation uses inherent feedback through the emitter-coupled configuration, where the collector current of one transistor directly influences the base drive of its complement. This feedback mechanism ensures precise dead-time control that prevents excessive voltage spikes and current harmonics, reducing EMI and distortion while maintaining reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach maintains high efficiency and reliability while reducing iTHD and EMI, achieving cost-effective and reliable power conversion with fewer components and no external control signals, thereby improving overall performance.
Implementation Method 1
A power supply may include a rectifier circuit that performs the conversion using diode bridges and/or actively controlled switches
Implementation Method 2
power supplies that convert alternating current (AC) signals to direct current (DC) signals
Implementation Method 3
utilizing optocouplers to manage the gate-source voltage of transistors
Data Source
AI summary
A rectifier includes a first input and a second input that receive an unrectified signal, a first circuit portion including a first transistor coupled to the second input, a second circuit portion including a second transistor coupled to the first input, a third circuit portion including a third transistor coupled to the first input, a fourth circuit portion including a fourth transistor coupled to the second input. The first, second, third, and fourth circuit portions are operable to convert the unrectified signal into a rectified signal. The rectifier includes a first adjustment circuit coupled to a gate of the third transistor, and a second adjustment circuit coupled to a gate of the fourth transistor. The first adjustment circuit and the second adjustment circuit are configured to control a dead time between an on-state of the third transistor and an on-state of the fourth transistor.