Boost Converter Pre-Charge Current Control
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Solution Overview
Problem
Boost converters in portable electronic devices often stress components and operate at suboptimal efficiency due to high pre-charge currents when converting battery voltage to higher output voltages for loads, leading to potential damage and inefficiency.
Innovation Solution
A boost converter design that includes an inductor with a first and second terminal, where a first FET isolates the second terminal from the ground and a second FET periodically isolates it from the output, controlled by a controller to manage pre-charge current through a pre-charging mode, reducing stress on components and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boost converter directly powers a load requiring voltage greater than battery voltage, then the load can be powered, but component stress increases and efficiency decreases
Solution Approach 1:
The patent applies preliminary action by implementing a pre-charge mode that activates before the boost converter operates in normal switching mode. During this preliminary phase, the converter delivers limited current to gradually charge the output capacitor, preventing the high inrush current that would otherwise stress components when the load is first connected or after undervoltage lockout recovery.
Solution Approach 2:
The patent implements dynamics by dynamically switching between two operational modes: pre-charge mode and switching mode. The controller monitors output voltage and transitions between modes based on real-time conditions. In pre-charge mode, the high-side FET is periodically pulsed to deliver controlled current, while in switching mode, normal boost operation resumes. This dynamic adaptation resolves the contradiction by adjusting operation based on load and voltage conditions.
2Speed
If a boost converter operates with high pre-charge current, then the load can be quickly powered, but operational efficiency decreases
Solution Approach 1:
The pre-charge mode serves as a preliminary action phase that prepares the output capacitor before full-power operation. By controlling the high-side FET with periodic pulsing during this phase, the system delivers just enough current to raise the output voltage to a threshold level, avoiding the energy waste of delivering full pre-charge current while still enabling relatively quick load power-up.
Solution Approach 2:
The patent applies periodic action by pulsing the high-side FET at controlled intervals during pre-charge mode. Instead of continuously delivering maximum current, the FET is activated in periodic bursts, allowing the output capacitor to charge in steps. This periodic charging approach achieves adequate power-up speed while significantly reducing average current and energy loss compared to continuous high-current charging.
3Loss of time
If a boost converter provides high pre-charge current to quickly charge the output capacitor, then the load can be powered faster, but component lifespan decreases
Solution Approach 1:
The pre-charge mode implements preliminary action by performing a controlled, limited-duration charging phase before normal operation. This preliminary charging to a threshold voltage (rather than full voltage) reduces the time components are exposed to high stress conditions while still achieving functional power-up of the load, thereby extending component lifespan without excessive delay.
Solution Approach 2:
The system dynamically adjusts its operation through mode switching. During pre-charge mode, the controller applies a gentler charging regimen with periodic FET pulsing that reduces stress on capacitors and other components. Once the output voltage reaches the threshold, the system transitions to switching mode. This dynamic approach balances power-up speed with component protection, extending lifespan by avoiding prolonged exposure to high-stress conditions.
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 limits pre-charge current, reducing component stress and improving efficiency by transitioning from pre-charging to switching mode as the output voltage reaches a predetermined level, thereby extending the lifespan of converter components and enhancing operational efficiency.
Implementation Method 1
an inductor comprising a first terminal and a second terminal, where the first terminal is coupled to an input terminal of the boost converter
Implementation Method 2
a first field effect transistor (FET) configured to selectively isolate a second terminal of the inductor from a ground reference, a second FET configured to selectively isolate the second terminal of the inductor from an output terminal of the boost converter
Data Source
AI summary
Method and apparatus is disclosed for providing a controlled pre-charging current for capacitive loads coupled to a boost converter. For at least some embodiments, the boost converter may include a high-side field effect transistor (FET) and a low-side FET. The boost converter may provide the pre-charge current by periodically enabling the high-side FET while the low-side FET is maintained in an off state. The high-side FET may be enabled by a square-wave signal. The pre-charge current may be delivered until the output voltage of the boost converter exceeds a reference voltage. After the output voltage exceeds the reference voltage, the boost converter may transition to a normal (switching) operation.