Bipolar Startup Transformer Circuit for Low-Voltage TEG Charging
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Solution Overview
Problem
Thermoelectric generators (TEGs) produce low output voltages, making it challenging for boost converters to start up from a de-energized state due to switch threshold voltages exceeding the TEG output, leading to increased costs and complexity with existing solutions like batteries or multiple transformers.
Innovation Solution
A boost converter circuit with a single transformer that operates as a self-starting oscillator using a bipolar startup stage and multiplexes into a flyback converter mode, enabling startup from low positive or negative input voltages and achieving bipolar operation through flux commutation, reducing circuit complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a battery is incorporated to operate switches during startup, then the startup capability from low voltage is improved, but the cost and complexity of circuit integration increase
Solution Approach 1:
The patent extracts and removes the battery component from the startup mechanism, replacing it with a capacitor-based solution. The capacitor is charged during normal operation and discharged to provide the necessary voltage boost for startup, eliminating the need for external battery power sources while maintaining reliable startup capability from low voltages.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the TEG and the boost converter switches. This capacitor acts as a mediator that accumulates energy during normal operation and releases it during startup to overcome the threshold voltage requirement, replacing the direct battery connection and reducing overall system complexity.
2Adaptability or versatility
If multiple transformers are used for bipolar operation, then the capability to support both polarities is improved, but the cost and complexity of circuit implementation increase
Solution Approach 1:
The patent designs a single transformer that can operate with both positive and negative input voltages from the TEG. The boost converter circuit is configured to automatically adapt its operation based on the input polarity, allowing one transformer to perform the function that would traditionally require two separate transformers, thereby reducing complexity while maintaining bipolar versatility.
Solution Approach 2:
The patent implements dynamic switching control that adapts the circuit operation based on the input voltage polarity. The control logic dynamically adjusts the switching sequences and transformer connections to accommodate either positive or negative input from the TEG, enabling a single static transformer to achieve bipolar operation through dynamic control rather than requiring multiple fixed transformers.
3Loss of energy
If the TEG output voltage is as low as 50 mV, then the efficiency of thermal energy harvesting is improved, but the ability to start up the boost converter deteriorates due to switch threshold voltages
Solution Approach 1:
The patent implements a preliminary charging phase where a capacitor is charged to the required threshold voltage before the boost converter switches are activated. This preliminary action ensures that when startup is initiated, the capacitor can immediately provide the necessary voltage boost to overcome the switch threshold requirements, enabling reliable startup even when the TEG output is as low as 50 mV during normal operation.
Solution Approach 2:
The patent introduces a capacitor as an intermediary voltage boosting element between the low-voltage TEG output and the high-threshold switches. This capacitor mediates the voltage transition by accumulating charge and releasing it in a controlled manner to bridge the voltage gap, allowing the switches to turn on reliably without requiring the TEG to directly provide high voltage during startup.
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 and cost-effective self-starting from low input voltages, achieving stable output voltages for powering CMOS circuits without the need for external power sources or multiple transformers, while maintaining efficiency and reducing complexity.
Implementation Method 1
a transformer configured with a primary winding and a secondary winding that are driven from a voltage supplied by a thermoelectric generator (TEG)
Implementation Method 2
Thermoelectric generators (TEGs) can be employed for thermal energy harvesting and are capable of powering downstream electronic circuits from the TEG
Data Source
AI summary
A circuit includes a transformer configured with a primary winding and a secondary winding that are driven from a voltage supplied by a thermoelectric generator (TEG). The circuit includes a bipolar startup stage (BSS) coupled to the transformer to generate an intermediate voltage. The BSS includes a first transistor device coupled in series with the primary winding of the transformer to form an oscillator circuit with an inductance of the secondary winding when the voltage supplied by the TEG is positive. A second transistor device coupled to the secondary winding of the transformer enables the oscillator circuit to oscillate when the voltage supplied by the TEG is negative. After startup, a flyback converter stage can be enabled from the intermediate voltage to generate a boosted regulated output voltage.