Current Sensing Circuit with Voltage Follower and Current Mirror
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Solution Overview
Problem
Current sensing circuits in DC/DC converters face inaccuracies due to process-dependent internal resistive elements and stability issues with regular voltage amplifiers, particularly in highly accurate applications.
Innovation Solution
A circuit comprising a first resistor, a second resistor, a voltage follower, and a current mirror, where the first resistor converts current to a voltage drop, and the voltage follower and current mirror provide a sensing current proportional to the original current, using external resistors to enhance accuracy and stability by allowing user-adjustable gain and temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If internal resistive elements are used for current sensing, then the circuit complexity is reduced, but the measurement precision deteriorates due to process-dependency and thermal coefficient mismatches
Solution Approach 1:
The patent introduces an external sense resistor as an intermediary element to convert current to voltage, and a voltage follower as a mediator to buffer and transfer the voltage signal without loading effects. This intermediary approach isolates the sensing function from the process-dependent internal resistive elements, achieving high precision current measurement while maintaining circuit simplicity.
2Measurement precision
If regular voltage amplifiers are used to enlarge the voltage signal, then the measurement precision is improved, but the stability of the current sensing circuit deteriorates
Solution Approach 1:
The voltage follower configuration provides unity gain feedback that maintains signal integrity without the stability issues of regular voltage amplifiers. The feedback mechanism ensures that the output voltage follows the input voltage exactly, providing both signal amplification capability and circuit stability simultaneously.
3Measurement precision
If external resistors are used to improve sensing accuracy, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The external sense resistor serves multiple functions: it converts current to voltage for sensing, provides a known reference value for calculations, and enables temperature compensation. The voltage follower also performs multiple roles including buffering, signal transfer, and impedance matching. This multi-functionality reduces the need for additional components, offsetting the complexity increase from using external resistors.
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 solution achieves accurate and stable current sensing, enabling applications such as over current protection, load line control, and current monitoring with improved power efficiency and reduced thermal drift.
Implementation Method 1
The first resistor converts a current flowing through the first resistor to a voltage drop between positive and negative sides of the first resistor
Implementation Method 2
The voltage follower is coupled to the positive side of the first resistor via a non-inverting terminal, and coupled to the negative side of the first resistor through the second resistor via an inverting terminal to cause a voltage at the inverting terminal to follow a voltage at the non-inverting terminal
Implementation Method 3
The current mirror is coupled to the voltage follower to provide a sensing current proportional to the current flowing through the first resistor
Data Source
AI summary
A circuit includes a first resistor, a second resistor, a voltage follower and a current mirror. The first resistor converts a current flowing through the first resistor to a voltage drop between positive and negative sides of the first resistor. The second resistor is coupled to the negative side of the first resistor. The voltage follower is coupled to the positive side of the first resistor via a non-inverting terminal, and coupled to the negative side of the first resistor through the second resistor via an inverting terminal to cause a voltage at the inverting terminal to follow a voltage at the non-inverting terminal. The current mirror is coupled to the voltage follower to provide a sensing current proportional to the current flowing through the first resistor.