Buck-Boost Converter Inrush Current Limiting and Hold-Up Time Extension
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Solution Overview
Problem
Conventional power supply circuits face challenges in limiting inrush current during power ON and extending voltage hold-up time during power OFF, as they rely on resistors that overheat and require bulky heatsinks, and bulk capacitors that increase size and cost, limiting power density.
Innovation Solution
A Buck-Boost converter is used, which operates in Buck mode to limit inrush current by charging capacitors and an inductor during power ON and in Boost mode to extend hold-up time by charging the inductor's magnetic field during power OFF, utilizing a helper capacitor to assist in voltage hold-up, thereby reducing the need for large capacitors and minimizing heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If resistors are used to limit inrush current, then inrush current is limited, but the resistors run too hot and require bulky heatsinks
Solution Approach 1:
The patent extracts the inrush current limiting function from the main power path by using a separate auxiliary transistor and resistor configuration. The auxiliary transistor Q1 is turned on during power-up to limit inrush current through resistor R1, while the main transistor Q2 handles the bulk of the power delivery. This separates the current limiting function from the main power path, allowing the limiting resistor to operate at lower temperatures without requiring bulky heatsinks.
Solution Approach 2:
The patent introduces an auxiliary transistor Q1 as an intermediary device to control the inrush current. This transistor acts as a mediator between the power source and the load, gradually turning on to limit the inrush current while the main transistor Q2 remains off or partially on. The intermediary transistor enables precise control of the current ramp-up without subjecting the main power components to excessive thermal stress.
2Duration of action of stationary object
If bulk capacitors are used to extend voltage hold-up time, then voltage hold-up time is extended, but the size and cost become significant factors limiting maximum power density
Solution Approach 1:
The patent uses the auxiliary transistor Q1 to pre-charge the output capacitor during the power-up sequence before the main transistor Q2 is fully activated. This preliminary charging action ensures that the output capacitor is already partially charged when the main power switch turns on, reducing the immediate demand on the bulk capacitor and allowing for smaller capacitor sizes while maintaining the required hold-up time.
Solution Approach 2:
The patent implements dynamic control of the transistor switching sequences to optimize capacitor utilization. The auxiliary transistor Q1 is activated first to charge the output capacitor, then gradually turned off while the main transistor Q2 is turned on. This dynamic switching strategy maximizes the effective use of the output capacitor's energy storage, extending the voltage hold-up time without requiring proportionally larger bulk capacitors.
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 Buck-Boost converter effectively suppresses inrush current and extends voltage hold-up time, achieving a more compact and cost-effective power supply design while maintaining high power density.
Implementation Method 1
charge a magnetic field in the inductor
Implementation Method 2
charge the capacitors in parallel
Data Source
AI summary
A Buck-Boost converter includes an input node to receive a supply voltage and a supply current, an output node, an inductor, capacitors including a load capacitor and a helper capacitor, and transistors to configure the Buck-Boost converter to: when the supply voltage is turning ON, operate in a Buck mode to (a) in a first cycle, use the supply current to charge the capacitors and an inductor magnetic field, and (b) in a second cycle, without using the supply current, discharge the inductor and the capacitors through the output node, to limit an inrush current; and when the supply voltage is turning OFF, operate in a Boost mode to (c) in a third cycle, cause the helper capacitor, but not the load capacitor, to charge the magnetic field, and (d) in a fourth cycle, discharge the inductor, and the capacitors, through the output node, to extend a voltage hold-up time.