DC Current Sensing Using Current Transformer and Estimator
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Solution Overview
Problem
Existing DC/DC converters require additional current sensors to determine output current, increasing complexity, size, weight, and power dissipation due to the inability of embedded current transformers to measure output current directly.
Innovation Solution
A current estimator module that uses a transistor current sensor and a duty cycle-based calculation to estimate the DC/DC converter's output current, eliminating the need for a second current sensor by applying the formula Iout = Iin * D, where Iin is the input current and D is the duty cycle, utilizing an inverting amplifier and integrator circuit to condition and process the signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a second DC current sensor (Hall Effect sensor or current sensing shunt) is added to measure output current, then measurement precision of output current is improved, but device complexity increases
Solution Approach 1:
The patent creates a mathematical model (copy) of the output current based on the relationship between input current and duty cycle. Instead of directly measuring output current with a physical sensor, the system calculates it using the formula Iout = Iin × D, where Iin is measured by the existing CT and D is the controlled duty cycle parameter. This virtual copy eliminates the need for a second physical sensor.
Solution Approach 2:
The patent introduces the duty cycle parameter D as an intermediary that links the measurable input current to the desired output current measurement. By using the known relationship Iout = Iin × D, the duty cycle serves as a mediator that allows indirect determination of output current without direct sensing, resolving the contradiction between measurement accuracy and system complexity.
2Measurement precision
If a second DC current sensor is added, then output current measurement capability is improved, but size increases
Solution Approach 1:
The patent replaces the physical presence of a second current sensor with a computational model. The output current is obtained through calculation (Iout = Iin × D) rather than physical measurement, eliminating the space requirements for additional sensors and their mounting structures, thereby reducing overall converter size.
3Measurement precision
If a current sensing shunt is used, then output current measurement is improved, but power dissipation increases
Solution Approach 1:
The patent uses a mathematical calculation to obtain output current information instead of forcing current through a resistive shunt. This virtual measurement approach eliminates the I²R losses inherent in shunt-based sensing, as no additional current path or resistive element is introduced into the power circuit.
4Measurement precision
If additional current sensors are added, then output current measurement capability is improved, but weight increases
Solution Approach 1:
The patent eliminates the need for a second physical current sensor by creating a virtual measurement through calculation. The output current is derived from the existing input current measurement and the duty cycle parameter, removing the weight of additional sensors, cables, and mounting hardware from the system.
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 solution simplifies the DC/DC converter design by accurately estimating output current without additional sensors, reducing size, weight, and power dissipation while maintaining operational control.
Implementation Method 1
A transistor current sensor, such as a current transformer, measures an instantaneous current passing through the transistor
Implementation Method 2
An inverting amplifier conditions the sensed current signal
Implementation Method 3
an inverting integrator that outputs an approximation of a time averaged value of an entire period of the converter cycle
Data Source
Figure 1~2
Figure 3~5B
AI summary
A DC/DC converter includes an internal transistor 30 and a current sensor 40 that is operable to sense a current passing through the transistor. The DC/DC converter 10 also includes an output current estimator module 44 that estimates the output current based on the sensed transistor current.