Hybrid Capacitive-Inductive Voltage Converter for Low Ripple
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Solution Overview
Problem
Conventional inverting DC-DC voltage converters, such as the inverting buck-boost and Ćuk converters, fail to generate a negative output voltage with low ripple and fast transient response, often requiring additional post-regulators that reduce efficiency and increase cost.
Innovation Solution
A switched-mode voltage converter topology with a capacitive input stage and inductive output stage, utilizing a flying capacitor and a single inductor, generates a continuous output current and supports rapid transient response, allowing for the production of a negative output voltage with minimal ripple and reduced transistor voltage ratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional inverting buck-boost or Ćuk converter topologies are used, then negative output voltage can be generated, but output voltage ripple is high and transient response is slow
Solution Approach 1:
The converter is divided into two distinct stages: a charge pump input stage that generates an intermediate negative voltage, and a buck converter output stage that regulates the final negative output voltage. This segmentation allows each stage to be optimized independently, with the charge pump providing robust voltage inversion and the buck stage providing low-ripple regulation and fast transient response.
Solution Approach 2:
An intermediate negative voltage node is introduced between the charge pump and buck converter stages. This intermediary voltage serves as a stable input for the buck converter while being easily generated by the charge pump, enabling the system to achieve both high efficiency and low output ripple without requiring additional post-regulators.
2Reliability
If additional post-regulators are added to reduce output ripple, then output voltage stability improves, but system complexity and cost increase
Solution Approach 1:
The voltage inversion function and voltage regulation function are merged into a single integrated converter topology. The charge pump provides the inversion while the buck converter provides the regulation, eliminating the need for separate post-regulator stages and reducing overall system complexity.
Solution Approach 2:
The hybrid converter topology performs multiple functions simultaneously: voltage inversion, voltage regulation, and ripple reduction. This multi-functionality eliminates the need for additional dedicated post-regulator circuits, reducing both component count and system complexity while maintaining excellent output voltage stability.
3Power
If inverting buck-boost converter is used, then negative output voltage is generated, but both input and output currents are discontinuous causing high ripple and noise
Solution Approach 1:
The buck converter output stage ensures continuous inductor current flow to the output, eliminating the discontinuous current characteristics of the inverting buck-boost converter. This continuous current mode operation significantly reduces output voltage ripple and electromagnetic noise while maintaining efficient negative voltage generation.
4Reliability
If transistors are designed to withstand high voltages (VIN+|VOUT|), then voltage breakdown is prevented, but transistor size and chip area increase
Solution Approach 1:
The voltage stress is segmented and distributed across different transistor devices in the two-stage topology. The charge pump transistors only need to withstand the input voltage VIN, while the buck converter transistors only need to withstand the output voltage magnitude |VOUT|. This segmentation allows the use of smaller, more efficient transistors compared to the single high-voltage transistors required in conventional inverting buck-boost converters.
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 proposed topology achieves a negative output voltage with low ripple and high control bandwidth, reducing the need for additional regulators and minimizing chip area, thus enhancing efficiency and reducing costs while maintaining rapid transient response.
Implementation Method 1
a flying capacitor and a single inductor, generates a continuous output current
Implementation Method 2
an inductor is connected in series with the flying capacitor to the output terminal
Data Source
AI summary
An inverting buck voltage converter constructed of a switched-mode hybrid topology, with a capacitive input stage and an inductive output stage. The input stage operates as a charge pump to charge a flying capacitor connected in series with an inductor in the output stage. Clock circuitry generates first and second non-overlapping clock phases. In the second clock phase, the flying capacitor is charged to the input voltage, with a flying node between the flying capacitor and the output inductor connected at ground through a rectifier, while in the first clock phase, the flying capacitor supports the inductor current. The arrangement of the flying capacitor and inductor is such that the voltage appearing at the output terminal is inverted from the input voltage. Continuous output current is provided. Current limiting techniques protect the flying capacitor from overcurrent conditions.