SEPIC Converter Overvoltage Protection via Parallel Varistor and Capacitor
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Solution Overview
Problem
DC-DC converters with converter capacitors in the active current path, such as SEPIC and CUK converters, face challenges in diverting overvoltage pulses, leading to high voltage buildup and potential damage to transistors and diodes, as traditional varistors require large, expensive components and may not prevent voltage overshoot.
Innovation Solution
Incorporating a voltage-dependent element, such as a varistor, TVS diode, or spark gap in parallel with the converter capacitor to divert high potentials to ground, allowing the storage capacitor to absorb overvoltage energy, reducing the burden on the varistor and protecting the converter components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a varistor is installed at the input to divert overvoltage pulses, then overvoltage protection is provided, but the varistor must be designed to dissipate the entire overvoltage pulse as heat, requiring a large, expensive, and bulky component
Solution Approach 1:
The patent divides the overvoltage protection function into two segments: the varistor (now smaller) handles initial overvoltage diversion, while the storage capacitor absorbs the remaining overvoltage energy. This segmentation allows the varistor to be much smaller since it no longer needs to dissipate the entire pulse alone.
Solution Approach 2:
The storage capacitor acts as an intermediary element between the varistor and the converter circuit. It receives the overvoltage energy diverted by the varistor and absorbs it, preventing the varistor from needing to handle the full energy dissipation burden.
2Reliability
If a varistor is installed at the input to divert overvoltage pulses, then overvoltage protection is provided, but the high dU/dt of the overvoltage pulse causes voltage overshoot within the circuit that can destroy the converter transistor
Solution Approach 1:
The storage capacitor is positioned in parallel with the converter transistor to provide beforehand cushioning. When overvoltage occurs, the capacitor absorbs the voltage surge before it can damage the transistor, protecting it from the harmful effects of rapid voltage changes.
3Adaptability or versatility
If a SEPIC or CUK converter is used with a converter capacitor in the current path, then the converter can generate output voltages both smaller and larger than input voltage, but incoming overvoltage pulses cannot be diverted into the storage capacitor
Solution Approach 1:
The patent merges the overvoltage protection function with the existing storage capacitor in the SEPIC or CUK converter circuit. By connecting the storage capacitor in parallel with the converter transistor, the same capacitor serves both its original function and as an overvoltage absorption element.
4Adaptability or versatility
If the converter capacitor is connected in the active converter current path, then the converter topology can generate variable output voltages, but overvoltage pulses cause high voltage buildup at the converter transistor
Solution Approach 1:
The storage capacitor acts as an intermediary protective element between the overvoltage pulse source and the converter transistor. It absorbs the excess voltage energy, preventing it from reaching and damaging the transistor while allowing the converter to maintain its variable output voltage capability.
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 configuration effectively limits voltage across the converter transistor, reduces the size and cost of varistors, and prevents damage from rapid voltage changes, making the circuit more efficient and robust against overvoltage pulses.
Implementation Method 1
a voltage-dependent element, such as a varistor, TVS diode, or spark gap in parallel with the converter capacitor to divert high potentials to ground
Implementation Method 2
allowing the storage capacitor to absorb overvoltage energy, reducing the burden on the varistor and protecting the converter components
Data Source
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AI summary
The invention relates to a circuit arrangement for converting voltages, said arrangement having a DC voltage converter comprising a converter capacitor located in the active converter current path, a voltage-dependent element being connected in parallel to the converter capacitor.