Switch-Node Boost Inductor Protection Against Current Runaway
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Solution Overview
Problem
Existing fly-back converters in USB-PD power supplies face issues with inductor current runaway and efficiency loss due to improper boost-switch operation, requiring additional pins and increased die-size for sensing, which complicates the primary IC and increases quiescent currents.
Innovation Solution
A boost converter system that senses input voltage through a switch node without additional pins, using a comparator to control the boost-switch based on reference voltages to prevent current runaway and optimize efficiency, ensuring stable power supply to the primary IC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional pins and sensing circuitry are added to detect input voltage and control boost-switch operation, then inductor current runaway is prevented, but device complexity and die-size increase
Solution Approach 1:
The existing BSW pin, originally designed for a single function, is made multi-functional by using it both as a switching node connection and as an input voltage sensing point. This allows the system to detect VIN and control the boost-switch without adding dedicated sensing pins, thereby preventing inductor current runaway while maintaining simple device structure.
Solution Approach 2:
The system uses its own internal switching node (BSW pin) to provide the sensing function rather than requiring external sensing circuitry. The existing voltage switching behavior at the BSW pin is leveraged to derive input voltage information, making the system self-sufficient for protection without external assistance or additional components.
2Reliability
If additional sensing circuitry is added to monitor input voltage, then boost-inductor damage is prevented, but quiescent currents increase
Solution Approach 1:
The system uses the natural voltage switching at the BSW pin during normal operation to provide sensing information. No separate sensing circuitry is activated, meaning no additional quiescent current is drawn for protection functions. The existing switching activity serves dual purposes: power switching and voltage sensing.
Solution Approach 2:
The sensing function is extracted from the normal switching operation rather than being added as a separate function. By detecting voltage levels during the existing switching cycles, the system obtains protection information without the overhead of dedicated sensing circuits that would consume additional quiescent power.
3Power
If boost-switch is continuously operated to maintain supply voltage, then power delivery is improved, but inductor current runaway occurs when input voltage is high
Solution Approach 1:
The system implements voltage-level feedback by monitoring the BSW pin voltage and comparing it against predefined thresholds. When VIN exceeds a certain level, the feedback mechanism detects this through the BSW voltage characteristics and automatically adjusts or disables boost-switch operation, preventing inductor current runaway while maintaining optimal power delivery under normal conditions.
Solution Approach 2:
The boost-switch operation is made dynamic rather than continuous. The system adapts the switching behavior based on real-time input voltage conditions detected through the BSW pin, enabling continuous operation when VIN is appropriate and disabling operation when VIN is too high, thereby preventing harmful current runaway while maintaining power delivery efficiency.
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
The solution effectively prevents boost-inductor damage and maintains efficiency by dynamically controlling the boost-switch operation, reducing the need for additional pins and complexity in the primary side controller.
Implementation Method 1
A boost converter system that senses input voltage through a switch node without additional pins, using a comparator to control the boost-switch based on reference voltages
Implementation Method 2
A first end or terminal of the boost-inductor 130 is coupled to the auxiliary winding 132 through a low pass filter 136 formed by a capacitor and a diode, and a second end or terminal is coupled to the BSW-pin. The second terminal of the boost-inductor 130 is further coupled to a voltage supply-pin (Vcc-pin) in the primary IC 118 through a diode 138
Data Source
AI summary
Systems and methods are provided to supply a voltage (Vcc) to a primary IC in a switch-mode-power-supply following startup. Briefly, an input voltage (VIN) coupled through a boost-inductor to a switch-pin of the IC is sensed by isolating a DC component (VDC_BSW) of the voltage and checking if VIN is greater than a minimum VIN (VIN_MIN) by comparing VDC_BSW to a starting reference voltage (VREF_START) in the IC. If VDC_BSW is greater than VREF_START, a boost-switch in the IC through which the switch-pin is coupled to ground is cycled on and off to alternately store and discharge energy in the boost-inductor, boosting Vcc. Thereafter, VIN is checked against a maximum input voltage by comparing VDC_BSW to a reference voltage (VREF), greater than VREF_START, and if VDC_BSW is greater than VREF, boost is turned off by turning off and ceasing to cycle the boost-switch, protecting the boost-inductor from current runaway.