Synchronous Rectifier Startup Control for Boost Converter Stability
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Solution Overview
Problem
Conventional step-up switching power supply devices experience unstable output voltage and increased coil current at startup due to leakage currents and inrush currents, which are not effectively managed by existing overcurrent protection mechanisms.
Innovation Solution
A step-up switching power supply device with synchronous rectification, featuring transistors P2a and P2b connected in parallel between the back gate and source of transistor P1, allowing controlled ON resistance adjustment and mask control of the pulse signal to reduce leakage currents, and variable overcurrent limit threshold based on comparison signals to manage inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If transistors P1 and P2 are increased in size to handle higher current capacities, then the current handling capability is improved, but the coil current increases abruptly at startup leading to unstable output voltage
Solution Approach 1:
The patent applies dynamics by making the ON resistance of the current path adjustable rather than fixed. Transistor P2 is controlled to have different resistance states: high resistance during startup to limit inrush current, and low resistance during normal operation to allow full current capacity. This dynamic adjustment resolves the contradiction between handling high current and maintaining stable startup behavior.
Solution Approach 2:
The patent changes the resistance parameter of the current path dynamically. By controlling transistor P2's ON resistance to be high during startup and low during normal operation, the system adapts its electrical characteristics to different operational phases. This parameter change allows the system to handle both startup stability and high current requirements effectively.
2Loss of energy
If transistor P2 is maintained always in an on state to cut off leakage current paths, then leakage current is reduced, but inrush current at startup increases causing unstable output voltage
Solution Approach 1:
The patent makes transistor P2's state dynamic rather than static. During startup, P2 is turned off (high resistance) to prevent excessive inrush current. During normal operation, P2 is turned on (low resistance) to block leakage current paths. This dynamic state change resolves the contradiction between preventing leakage and avoiding inrush current.
Solution Approach 2:
The patent applies periodic action by changing transistor P2's state based on operational phase. The transistor is off during startup phase and on during normal operation phase, creating a time-dependent control strategy that addresses different requirements at different times in the operational cycle.
3Ease of operation
If overcurrent protection mechanism is used to manage current, then current control is improved, but it cannot effectively manage inrush currents and peak coil currents at startup
Solution Approach 1:
The patent applies preliminary action by controlling transistor P2's resistance before the main switching operation begins. By setting P2 to high resistance during startup, the system preemptively limits inrush current before it can cause instability. This preliminary control action prevents the harmful effect rather than reacting to it afterward.
Solution Approach 2:
Transistor P2 acts as an intermediary element between the power supply and the load. It mediates the current flow by providing different resistance levels at different times, smoothing out the transition during startup and blocking leakage during normal operation. This intermediary function enhances both current control and startup reliability.
Data Source
AI summary
A step-up switching power supply device with synchronous rectification includes a first switch that is turned on at startup of the device and a second switch that is turned on when an output voltage reaches an input voltage, the first and seconds switches being connected in parallel between the back gate and the source of a synchronous rectifier transistor.