Freewheeling Step-Down Converter with Diode Clamp
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Solution Overview
Problem
Conventional Buck and synchronous Buck converters face inefficiencies due to rectifier switching and conduction losses, shoot-through conduction, stored charge, high dV/dt, voltage overshoot, noise, and high gate drive losses, particularly during light-load operations where inductor current becomes discontinuous, leading to poor regulation and efficiency.
Innovation Solution
A freewheeling step-down converter topology that includes a high-side MOSFET, an inductor, and an output capacitor connected in series, with a freewheeling clamp comprising a diode and a freewheeling MOSFET in parallel, and break-before-make circuitry to control the gates of both MOSFETs, allowing for reduced diode recovery stress and improved efficiency by diverting diode recovery current to the output capacitor and load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional Buck converter uses a rectifier diode for synchronous rectification, then efficiency is improved during heavy-load operations, but diode recovery stress, voltage overshoot, and noise increase during light-load operations
Solution Approach 1:
The patent introduces a freewheeling diode as an intermediary component connected in parallel with the rectifier diode. This freewheeling diode provides an alternative current path during the rectifier diode's recovery period, thereby reducing the recovery stress and voltage overshoot while maintaining efficiency benefits during both heavy and light-load operations
Solution Approach 2:
The patent changes the operating parameters by controlling the timing and conduction state of the freewheeling diode through PWM control. By adjusting the duty cycle and switching timing, the system optimizes the balance between utilizing the rectifier diode for efficiency during heavy loads and protecting against recovery stress during light loads
2Object-affected harmful factors
If a conventional Buck converter operates in discontinuous conduction mode during light-load operations, then component stress is reduced, but regulation precision and efficiency deteriorate
Solution Approach 1:
The patent ensures continuous inductor current flow by introducing the freewheeling diode that maintains current circulation during light-load operations. This prevents discontinuous conduction mode while keeping component stress low, thereby maintaining both regulation precision and efficiency across all load conditions
Solution Approach 2:
The freewheeling diode serves multiple functions: it provides a current path during rectifier recovery, maintains continuous conduction during light loads, and prevents inductor current reversal. This multi-functionality allows the system to maintain precision and efficiency while reducing component stress simultaneously
3Reliability
If a synchronous Buck converter uses break-before-make circuitry to prevent shoot-through, then reliability is improved, but gate drive losses and switching complexity increase
Solution Approach 1:
The patent employs intrinsic body diodes of the MOSFETs as freewheeling paths during shoot-through prevention intervals. This self-service approach eliminates the need for external freewheeling diodes and complex gate drive timing circuits, reducing overall system complexity while maintaining reliability
Solution Approach 2:
The patent merges the shoot-through prevention function with the rectifier diode function by utilizing the intrinsic body diode of the low-side MOSFET. This consolidation eliminates separate components and simplifies the gate drive circuitry while maintaining reliable operation
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 freewheeling step-down converter experiences softer diode recovery, reduced noise, and improved efficiency by maintaining inductor current during light-load operations, enhancing regulation and reducing gate drive losses, while eliminating discontinuous inductor current and current reversal issues.
Implementation Method 1
The operation of a DC/DC inductive switching converter is based on the simple principle that the current in an inductor (coil or transformer) cannot be changed instantly, and that an inductor will produce an opposing voltage to resist any change in its current
Implementation Method 2
an output capacitor is placed across the output terminal of the switching regulator circuit. Together the inductor and the output capacitor form a 'low-pass' filter able to prevent most of the MOSFETs' switching noise before it reaches the load
Implementation Method 3
A freewheeling clamp comprising a freewheeling diode and freewheeling MOSFET is connected in parallel with the inductor
Implementation Method 4
By using one or more transistors switching at a high frequency to repeatedly magnetize and de-magnetize an inductor, the inductor can be used to step-up or step-down the converter's input voltage
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 2C
AI summary
A freewheeling DC/DC step-down converter includes a high-side MOSFHT, an inductor and an output capacitor connected between the input voltage and ground. A freewheeling clamp, which includes a freewheeling MOSFET and diode, is connected across the inductor. When the high-side MOSFET is turned off, a current circulates through the inductor and freewheeling clamp rather than to ground, improving the efficiency of the converter. The converter has softer diode recovery and less voltage overshoot and noise than conventional Buck converters and features unique benefits during light-load conditions.