PWM Switch Control for Low-Side Body Diode Emulation
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Solution Overview
Problem
In power converter applications, especially in discontinuous conduction mode, it is inefficient to maintain fully synchronous operation or completely turn off the low-side switch using FET body diodes for rectification, necessitating a solution to emulate body diode conduction.
Innovation Solution
A circuit that includes a pulse-width modulator (PWM) circuit generating complementary PWM signals, an AND gate, and multiplexers to control the low-side drive signal, forcing it to an inactive state based on a predetermined condition, while also driving a high-side switch to manage the load effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fully synchronous operation is maintained in discontinuous conduction mode, then power conversion efficiency is improved, but device complexity increases due to the need for additional control circuitry
Solution Approach 1:
The patent implements dynamic control of the low-side switch by transitioning between synchronous operation and body diode conduction based on the conduction mode detection. The control circuit dynamically adjusts the drive signal to the low-side switch, enabling it to operate synchronously during continuous conduction mode and turn off during discontinuous conduction mode, thereby optimizing efficiency across different operating conditions without requiring overly complex fixed control circuitry
Solution Approach 2:
The patent changes the operational parameters of the low-side switch based on detected conduction mode. During continuous conduction mode, the low-side switch operates with synchronous rectification parameters, while during discontinuous conduction mode, the control circuit modifies the drive signal parameters to allow body diode conduction, effectively adapting the switch behavior to match optimal efficiency requirements for each operating regime
2Device complexity
If the low-side switch is completely turned off using FET body diodes for rectification, then device complexity is reduced, but power conversion efficiency deteriorates in continuous conduction mode
Solution Approach 1:
The control circuit dynamically determines the conduction mode (continuous or discontinuous) and adjusts the low-side switch operation accordingly. During continuous conduction mode, the low-side switch is kept on for synchronous rectification to maintain high efficiency. During discontinuous conduction mode, the switch is turned off to allow body diode conduction, simplifying control while maintaining efficiency. This dynamic adaptation resolves the contradiction between simplicity and efficiency
Solution Approach 2:
The low-side switch is designed to serve multiple functions: synchronous rectification during continuous conduction mode and being turned off for body diode conduction during discontinuous conduction mode. The control circuit provides universal control capability that adapts to different operating conditions, allowing a single switch design to fulfill both efficiency requirements without requiring separate control circuits for each mode
Data Source
AI summary
A device includes a PWM circuit to generate a complementary PWM signal comprised of a positive polarity PWM signal and a negative polarity PWM signal. The positive polarity signal may drive a high-side switch. A trigger multiplexer may take as input the negative polarity PWM signal and may force an output based on a predetermined condition, the predetermined condition including but not limited to the maximum on-time of a low-side switch. The output of the trigger multiplexer may drive a low-side switch. The high-side switch and the low-side switch may drive a load.