Low Input Voltage Boost Converter With Peak Inductor Current Control
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Solution Overview
Problem
Low input voltage boost converters face challenges in accurately detecting and utilizing low input voltages due to offsets and mismatches, leading to inefficiencies and variance in peak inductor current, especially when harvesting energy from sources with small output voltages like thermoelectric generators with low thermal gradients.
Innovation Solution
A boost converter design with peak inductor current control and offset compensated zero detection, using a control scheme that maintains constant peak inductor current independently of input and output voltages, and employing duty cycled comparators for efficient energy harvesting from very low input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional boost converter design is used, then circuit simplicity is maintained, but offset errors and mismatches cause inaccurate voltage detection and control at very low input voltages
Solution Approach 1:
The patent applies preliminary action by performing offset cancellation before the main voltage detection and control operations. The offset compensation circuit pre-calculates and stores offset values that are then subtracted from subsequent measurements, ensuring accurate detection of very low input voltages without requiring complex real-time correction mechanisms throughout the circuit.
Solution Approach 2:
The patent introduces an intermediary offset compensation circuit that mediates between the raw comparator signals and the control logic. This intermediary component processes and corrects offset errors independently, allowing the main boost converter circuit to remain relatively simple while achieving high measurement precision through the intermediary's correction function.
2Loss of energy
If peak inductor current is allowed to vary with input voltage, then control circuit complexity is reduced, but conversion efficiency deteriorates at low input voltages
Solution Approach 1:
The patent implements feedback by continuously monitoring the inductor current and adjusting the duty cycle to maintain constant peak current regardless of input voltage variations. The control circuit uses feedback signals from the current sense resistor and voltage dividers to dynamically adjust switching parameters, ensuring optimal efficiency across the full input voltage range while managing complexity through systematic feedback loops.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the duty cycle and switching frequency based on input voltage levels to maintain constant peak inductor current. At very low input voltages, the control circuit modifies operating parameters including extending the on-time and adjusting the frequency to keep current constant, thereby maximizing efficiency without requiring overly complex circuit architecture.
3Use of energy by moving object
If duty cycled comparators are not used, then comparator accuracy is maintained, but power consumption increases significantly at low input voltages
Solution Approach 1:
The patent applies periodic action by duty cycling the comparators - activating them only during specific phases of the switching cycle when zero-crossing detection is required, rather than keeping them continuously active. This periodic operation dramatically reduces power consumption at low input voltages while maintaining detection accuracy by ensuring comparators are fresh and calibrated when needed.
Solution Approach 2:
The patent introduces dynamics by making comparator operation conditional and time-varying rather than static and continuous. The comparators are dynamically enabled and disabled based on switching phase requirements, allowing the system to adapt power consumption to actual detection needs. This dynamic approach maintains measurement precision during critical detection windows while minimizing overall power usage during non-critical periods.
Data Source
AI summary
The low input voltage boost converter with peak inductor current control and offset compensated zero detection provide a boost converter scheme to harvest energy from sources with small output voltages. Some embodiments described herein includes a thermoelectric boost converter that combines an IPEAK control scheme with offset compensation and duty cycled comparators to enable energy harvesting from TEG inputs as low as 5 mV to 10 mV, and the peak inductor current is independent to first order of the input voltage and output voltage. A control circuit can be configured to sample the input voltage (VIN) and then generate a pulse with a duration inversely proportional to VIN so as to control the boost converter switches such that a substantially constant peak inductor current is generated.