Buck Regulator Active Diode Negative Current Discharge
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Buck power converters face inefficiencies due to inability to discharge excess energy when output voltage exceeds target voltage, requiring complex control systems to switch between PWM and PFM modes, and inefficiencies in low load conditions.
Innovation Solution
A buck power regulator design using a PMOS and NMOS transistor configuration with a zero crossing comparator and AND circuit to control 'negative' current flow, allowing proportional discharge of excess current through the NMOS transistor when output voltage rises too high, preventing normal ripple from triggering this discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the NMOS transistor is turned off once the inductor current reaches zero (active diode behavior), then power waste is reduced, but the converter cannot discharge excess energy when output voltage exceeds target voltage
Solution Approach 1:
The patent applies dynamics by making the NMOS transistor's off-voltage threshold variable rather than fixed. The threshold voltage is dynamically adjusted based on the difference between output voltage and target voltage. When output voltage exceeds target voltage, the threshold becomes more negative, allowing the NMOS to remain on and discharge excess energy. This dynamic adjustment resolves the contradiction by enabling overvoltage discharge capability while maintaining efficient operation under normal conditions.
2Productivity
If complex control systems are used to switch between PWM and PFM modes, then performance is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a single PFM control mode that can handle both normal operation and overvoltage conditions. The same PFM controller uses the voltage difference signal to dynamically adjust the NMOS threshold, eliminating the need for separate PWM and PFM control systems. This multi-functional approach maintains high performance while simplifying the overall control architecture.
3Adaptability or versatility
If the NMOS transistor remains on to allow negative current flow, then overvoltage discharge is enabled, but normal output ripple may cause unwanted current discharge
Solution Approach 1:
The patent applies parameter changes by using the voltage difference (Vout - Vtarget) as a dynamic parameter to adjust the NMOS threshold voltage. This creates a conditional response where the NMOS only allows significant negative current flow when the voltage difference indicates genuine overvoltage conditions. Normal ripple variations, which do not create sustained voltage differences, do not trigger unwanted discharge, thus maintaining reliability while enabling overvoltage protection.
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
Enables efficient operation in PFM mode by actively managing 'negative' current flow, maintaining high efficiency at low loads and preventing overvoltage buildup, thus simplifying control systems and improving overall performance.
Implementation Method 1
The buck converter stores energy into an inductor and provides an output voltage that is a result of the reluctance of the inductor to change current flowing in the inductor
Implementation Method 2
A node LX is formed at the connection between the NMOS and PMOS transistors. The LX node is also connected to an inductor L1, which is coupled to the output of the buck power regulator, and to a zero crossing comparator
Data Source
AI summary
An active diode formed within a buck power regulator with an NMOS transistor is connected to a PMOS transistor at a node that is further connected to the regulator output through an inductor. The active diode combines the NMOS transistor with circuitry to prevent conduction once the active diode passes a threshold voltage. Additional circuitry compares the output voltage to the target input voltage and varies the threshold voltage of the active diode such that the active diode can discharge excess current from the regulator each cycle until the output voltage is less than the target voltage.