Power Supply Device Bootstrap Control for Light Load Efficiency
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Solution Overview
Problem
Conventional low-power consumption switching regulators face challenges in reducing power consumption, particularly at light load states due to internal consumption currents, and existing methods to reduce input current through feedback of output voltage are hindered by startup and protection issues.
Innovation Solution
A power supply device incorporating an output transistor, feedback voltage generation, soft start voltage generation, error amplifier, oscillator, slope voltage generation, comparator, PWM pulse generation, on-time fixed pulse generation, and a selector to control the output transistor based on load conditions, switching between PWM and on-time fixed modes to optimize power efficiency and reduce internal consumption currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the output voltage Vout is fed back to drive the control circuit, then the input current Iin is reduced, but the control circuit cannot operate during startup or abnormal protection
Solution Approach 1:
The patent introduces an intermediary voltage generation circuit that creates a bootstrap voltage Vbb by charging a capacitor Cboot through a resistor Rboot during the switching cycle. This bootstrap voltage serves as a mediator to power the control circuit during normal operation, while allowing the output voltage feedback to drive the control circuit during light load conditions. The intermediary mechanism resolves the contradiction by providing an alternative power source that enables control circuit operation when direct feedback would fail.
Solution Approach 2:
The patent dynamically switches between different power supply modes for the control circuit. During heavy load conditions, the control circuit is powered by the output voltage feedback to minimize input current. During light load or startup conditions, the control circuit switches to being powered by the bootstrap voltage. This dynamic adaptation resolves the contradiction by optimizing the power source selection based on operating conditions.
2Loss of energy
If the internal consumption current Icc is reduced for light load operation, then power efficiency improves, but the control circuit cannot maintain operation
Solution Approach 1:
The patent employs periodic action through the bootstrap capacitor charging mechanism. The capacitor Cboot is charged periodically during each switching cycle through resistor Rboot, creating a periodic voltage supply that sustains the control circuit operation. This periodic energy transfer allows the control circuit to maintain operation even when average power consumption is reduced for light load efficiency.
3Loss of energy
If switching regulator is used instead of LDO, then power efficiency is improved, but internal consumption current increases at light load
Solution Approach 1:
The patent changes the operational parameters of the switching regulator by implementing a bootstrap-based control circuit power supply that allows the regulator to operate in a modified mode during light load conditions. The bootstrap voltage enables the control circuit to function with reduced input current, effectively changing the operating point parameters to achieve both high efficiency and low internal consumption current simultaneously.
Data Source
AI summary
A power supply device includes: a comparator that compares an error voltage and a slope voltage to generate a comparison signal; a PWM pulse generation portion that generates a PWM pulse based on a clock signal and the comparison signal; an on-time fixed pulse generation portion that uses the comparison signal as a trigger to generate an on-time fixed pulse where an on-time and an on-time number are constant; a one shot pulse generation portion that generates once, when a soft start voltage exceeds a predetermined threshold voltage, a one shot pulse where the on-time and the on-time number are constant; and a selector that selects any one of the PWM pulse, the on-time fixed pulse and the one shot pulse.