Converter Current Sampling Circuit for Accurate Average Current Control
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Solution Overview
Problem
Existing power converter technologies face challenges in accurately measuring and regulating average currents in inductors, switches, and rectifiers across different converter topologies like boost, buck, and buck-boost, leading to inefficiencies in voltage conversion.
Innovation Solution
A circuit incorporating a voltage sensor, transconductance amplifiers, switches, a capacitive element, and a comparator, along with a sampling circuit, allows for precise measurement and regulation of average currents by sampling at the midpoint of conduction intervals, enabling efficient voltage conversion across various power converter topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If average current is measured by sampling at conventional points in the conduction interval, then the measurement can be implemented with simple circuitry, but the measurement precision is insufficient due to process and temperature variations
Solution Approach 1:
The circuit performs preliminary action by pre-charging the capacitive element during the entire conduction interval of the switch or rectifier, then discharges it during a separate sampling interval. This separates the measurement integration phase from the sampling phase, allowing accurate accumulation of current information before reading it out, thereby improving measurement precision without requiring complex real-time sampling circuitry.
Solution Approach 2:
The capacitive element acts as an intermediary that stores the integrated current information during the conduction interval and releases it during the sampling interval. This mediator allows the circuit to measure average current over the entire conduction period rather than at discrete points, improving measurement accuracy while keeping the sampling circuitry relatively simple.
2Measurement precision
If current sampling is performed continuously throughout the conduction interval, then measurement accuracy improves, but energy consumption increases
Solution Approach 1:
The circuit uses periodic action by charging the capacitive element continuously during the conduction interval and then discharging it periodically during a specific sampling window. This periodic charge-discharge cycle allows accurate integration of current over the full conduction period while limiting energy-consuming operations to brief sampling intervals, thereby reducing overall energy consumption compared to continuous sampling.
Solution Approach 2:
The capacitive element performs preliminary integration of the current signal during the entire conduction interval at low energy cost, then the accumulated information is read out in a brief high-energy sampling phase. This separates the low-energy integration process from the high-energy measurement process, optimizing the energy-efficiency tradeoff.
3Device complexity
If the sampling circuit measures instantaneous current values, then the circuit design is simpler, but the regulation accuracy of input or output current deteriorates
Solution Approach 1:
The capacitive element serves as an intermediary that integrates the instantaneous current values over the entire conduction interval, transforming them into an average current representation. This allows the simple instantaneous sampling circuit to effectively measure average current by accumulating information over time, maintaining circuit simplicity while achieving accurate current regulation.
Solution Approach 2:
The circuit performs preliminary integration of instantaneous current samples during the conduction interval before the final measurement is taken. This preliminary accumulation of current information allows the use of simple instantaneous sampling circuitry to achieve accurate average current measurement, resolving the contradiction between simplicity and precision.
Data Source
AI summary
In described examples, a circuit includes a voltage sensor that has an output, first and second transconductance amplifiers, first and second switches, a capacitive element, a comparator, and a sampling circuit. Each of the first and second transconductance amplifiers has a respective input, a respective output, and a respective transconductance. The first switch is coupled between the voltage sensor output and the first transconductance amplifier input. The second switch is coupled between the voltage sensor output and the second transconductance amplifier input. The capacitive element has a first terminal coupled to the respective outputs of the first and second transconductance amplifiers. The comparator has a respective input and a respective output. The comparator input is coupled to the respective outputs of the first and second transconductance amplifiers and to the first terminal of the capacitive element. The sampling circuit is coupled to the output of the comparator.