AC/DC Converter Transient Response via Secondary COT Control
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Solution Overview
Problem
Traditional AC/DC converters face limitations in power density due to large transformer and capacitor sizes, slow transient response, and high electromagnetic interference (EMI) noise, especially at high voltages, which complicates the design of compact and efficient chargers for portable devices.
Innovation Solution
The implementation of a secondary side constant-on-time (COT) control scheme with a comparator-based feedback loop on the secondary side of the transformer, allowing for higher switching frequencies up to 150 kHz, reduced transformer turns, and MOSFET flip-chip packaging on a single die paddle for improved thermal dissipation and EMI reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional PWM control fly-back AC/DC converter is used, then the converter can operate with basic components, but the transformer and capacitor sizes are large, limiting power density
Solution Approach 1:
The patent changes the control parameter from traditional PWM with bandwidth limited to one-tenth of switching frequency to COT control with bandwidth up to one-fifth of switching frequency. This parameter change enables higher switching frequencies (up to 150 kHz), which directly reduces transformer and capacitor sizes while increasing power density to exceed 0.5 W/cc.
Solution Approach 2:
The patent implements dynamic control through COT (Constant On-Time) methodology where the on-time of the main switch is dynamically adjusted based on load conditions. This dynamic approach allows the system to operate efficiently across varying loads with smaller magnetic components, achieving high power density without requiring oversized transformers and capacitors.
2Speed
If traditional PWM control is used, then the control circuit is simple, but the transient response is slow due to narrow control bandwidth
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors the output voltage and adjusts the main switch on-time accordingly. The COT control uses a feedback loop that compares the actual output with the desired output and dynamically adjusts the switching parameters, achieving fast transient response while maintaining controlled complexity through integrated control logic.
Solution Approach 2:
The COT control methodology performs preliminary action by pre-setting the on-time of the main switch based on expected load conditions. This preliminary timing adjustment allows the system to respond faster to load transients without requiring complex real-time calculations, balancing speed and complexity effectively.
3Temperature
If high voltage drain lead with large area is used for cooling, then thermal dissipation is improved, but EMI noise increases due to high dv/dt
Solution Approach 1:
The patent segments the drain lead into multiple smaller connections rather than using a single large-area lead. This segmentation reduces the loop area for high dv/dt signals, thereby minimizing EMI noise generation while still providing adequate thermal dissipation through distributed connection points to the copper pad.
Solution Approach 2:
The patent applies different qualities to different parts of the drain connection: the area close to the MOSFET drain has optimized geometry for EMI reduction with smaller effective loop area, while the overall connection maintains sufficient thermal contact area for heat dissipation. This local quality differentiation resolves the contradiction between EMI and thermal requirements.
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 enables a compact charger design with enhanced power density exceeding 0.5 W/CC, reduced component size, improved thermal performance, and minimized EMI, while maintaining stable output voltage during load transitions.
Implementation Method 1
A transformer TX1 transfers energy received from a primary side source to a secondary side to power a load
Implementation Method 2
The exposed surface of the die paddle is directly attached to a conductive area of the PCB for heat dissipation
Data Source
AI summary
A charger comprises a housing, a first multi-layer printed circuit board (PCB), a second multi-layer PCB, and a third multi-layer PCB. The first PCB comprises at least a portion of a primary side circuit. The second PCB comprises at least a portion of a secondary side circuit. The third PCB is perpendicular to the first PCB and the second PCB. An isolation coupling element is disposed on the third PCB. The isolation coupling element comprises a multi-layer PCB. The first PCB comprises a high voltage (HV) semiconductor package. A surface of a die paddle of the HV semiconductor package is exposed from a molding encapsulation of the HV semiconductor package.