Buck Regulator Load Release Overshoot Control
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Solution Overview
Problem
Buck regulators experience voltage overshoot during load release due to the inability to rapidly ramp down inductor current, leading to increased output capacitance requirements and power losses when using diode braking techniques.
Innovation Solution
A system and method that control the operation of a lower switching transistor using a comparator and PWM control circuit to rapidly reduce inductor current, employing diode braking only under specific conditions to minimize power losses and reduce output capacitance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the lower switching transistor is turned off during load release to rapidly reduce inductor current, then voltage overshoot is reduced, but power losses increase due to body diode forward drop
Solution Approach 1:
The patent dynamically controls the lower switching transistor to remain on during load release instead of turning it off. This maintains a low-impedance path for inductor current, allowing rapid current reduction without the body diode forward voltage drop that causes power losses. The dynamic aspect is that the transistor state is specifically maintained during the load release transition period rather than following conventional switching patterns.
Solution Approach 2:
The patent keeps the lower switching transistor in the on state during load release to maintain continuous current flow capability. This eliminates the interruption caused by turning the transistor off and using the body diode, thereby avoiding the associated power losses while still achieving rapid current reduction through controlled gate switching of the upper transistor.
2Speed
If the inductor current is rapidly ramped down during load release, then voltage overshoot is reduced, but the ability to do so is limited by the forward voltage drop across the body diode
Solution Approach 1:
The patent dynamically maintains the lower switching transistor in the on state during load release, creating a low-impedance path that enables much faster inductor current reduction compared to using the body diode. This dynamic control allows the current to ramp down rapidly without being limited by the body diode's forward voltage drop, thereby achieving both fast response and reduced overshoot.
3Object-affected harmful factors
If output capacitance is increased to absorb excess energy during load release, then voltage overshoot is reduced, but device area increases
Solution Approach 1:
The patent extracts the excess energy that would otherwise require large output capacitance by rapidly redirecting the inductor current through the controlled switching of the upper transistor. By maintaining the lower transistor on and using controlled upper transistor switching, the energy is dissipated or redirected more efficiently, reducing the burden on output capacitance and allowing for smaller capacitor selection.
Solution Approach 2:
The patent changes the operating parameters of the switching transistors during load release - specifically keeping the lower transistor on and controlling the upper transistor's duty cycle - to achieve rapid current reduction. This parameter change enables the system to handle load release without requiring increased output capacitance, thereby reducing the required capacitor area.
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
This approach effectively reduces voltage overshoot while maintaining efficiency by allowing negative current flow during load release, thereby reducing the required output capacitance and minimizing power losses.
Implementation Method 1
This causes a voltage drop across the body diode of the lower switching transistor 108 and the body diode forward drop results in increased reversed inductor voltage across the inductor 112.
Data Source
AI summary
A buck regulator comprises an upper switching transistor connected between a voltage input node and a phase node. A lower switching transistor is connected between the phase node and a ground node. An inductor is connected between the phase node and an output voltage node. Circuitry generates control signals to the upper switching transistor and the lower switching transistor responsive to the output voltage and a reference voltage. The control signals to the lower switching transistor selectively turn off the lower switching transistor responsive to a current direction through the lower switching transistor and an indication of whether a voltage error signal has been clamped at a selected level.