Buck Converter Output Conduction Detection for Short-Circuit CCM Prevention
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Solution Overview
Problem
High voltage buck converters in automotive applications face issues with continuous current mode (CCM) operation due to slow recovery of the output conductor circuit, leading to inefficiencies and inability to prevent CCM operation in case of a short-circuited output, as the input side lacks visibility of the discharge period.
Innovation Solution
An integrated controller with an output conduction detector and bias self-supply circuit is implemented, allowing for direct sensing of output conduction through a bias transistor, using a bias diode and capacitor to detect freewheeling current, and a comparator to determine if the voltage exceeds a threshold, thereby preventing CCM operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If continuous current mode (CCM) operation is used in high voltage buck converters, then the converter can maintain stable operation, but the output conductor circuit recovery becomes slow and efficiency deteriorates
Solution Approach 1:
The patent implements preliminary detection of output conduction state through the bias supply circuit voltage monitoring. By detecting the voltage across the bias transistor before CCM operation fully develops, the system can preemptively switch to DCM mode, preventing the slow recovery and efficiency loss associated with CCM operation in high voltage buck converters.
2Measurement precision
If the input side controller monitors output parameters, then output regulation can be achieved, but the controller lacks visibility of the discharge period and cannot prevent CCM operation during short-circuit conditions
Solution Approach 1:
The patent introduces the bias supply circuit voltage as an intermediary parameter that indirectly reflects the output conduction state and discharge period conditions. By monitoring the voltage across the bias transistor (which is coupled to the output through the bias diode and capacitor), the controller gains visibility into the discharge period and can detect short-circuit conditions without directly measuring output current or voltage during the discharge phase.
3Duration of action of stationary object
If the output conductor circuit recovers slowly in CCM operation, then the converter can maintain continuous current flow, but the recovery time increases and performance deteriorates
Solution Approach 1:
The patent implements dynamic mode switching between CCM and DCM based on real-time monitoring of the bias supply circuit voltage. When the voltage indicates discharge period conditions or short-circuit scenarios, the controller dynamically transitions to DCM operation, which enables faster output conductor circuit recovery while maintaining adequate current flow through adjusted switching characteristics.
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
Enables efficient detection of output conduction, preventing CCM operation and improving the recovery of the output conductor circuit, enhancing the performance and efficiency of high voltage buck converters.
Implementation Method 1
a bias transistor having a gate coupled to receive the bias drive signal... wherein the bias transistor, responsive to the bias drive signal being asserted, conducts such that there is a voltage drop across the bias transistor
Implementation Method 2
an output conduction detector circuit coupled to a source and to a drain of the bias transistor, the output conduction detector circuit responsive to detecting the voltage drop to produce an output conduction signal
Data Source
AI summary
An integrated controller for a buck converter has an output conduction detector circuit that provides the input or high side of the controller with visibility of the discharge period and thereby prevents continuous current mode operation in case of a short-circuited output. The controller receives a feedback signal indicative of an output voltage of the buck converter and produces an input drive signal. A bias drive circuit receives the input drive signal and produces a bias drive signal. A bias supply circuit includes a bias transistor and and a bias diode. The bias drive transistor receives the bias drive signal. When the bias drive signal is asserted, the bias transistor conducts such that there is a voltage drop across the bias transistor. The output conduction detector circuit coupled to the bias transistor detects the voltage drop and produces an output conduction signal.