Switching Regulator Current Measurement Circuit
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Solution Overview
Problem
Measuring current in switching regulators is challenging due to transient voltages and currents produced by high-speed switching actions, which complicates accurate current measurement.
Innovation Solution
A current measurement circuit is implemented in switching regulators, comprising a switching transistor, a current measurement circuit with differential inputs, an analog-to-digital converter, and a voltage averaging circuit, along with switches that emulate the current through the switching transistor by coupling and decoupling terminals based on the transistor's on/off states, allowing for accurate measurement of average current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed switching action is used in the switching regulator, then power conversion efficiency and response speed are improved, but transient voltages and currents are produced that complicate accurate current measurement
Solution Approach 1:
The measurement circuit performs preliminary integration of voltage across the switching transistor during the on-state, accumulating charge that represents the time-integral of current. This preliminary action occurs before the transistor turns off, capturing the current information while the switching action is happening, thereby enabling accurate measurement despite the transient conditions
Solution Approach 2:
An intermediary measurement circuit is introduced between the switching transistor and the measurement instrumentation. This circuit includes integration elements (capacitors) and switching elements that mediate the measurement process by converting the difficult-to-measure instantaneous current into an integrable voltage signal, thereby enabling accurate current measurement without directly interfacing with the high-speed switching node
2Reliability
If current measurement is performed during switching transistor on-state, then real-time current information is obtained, but transient switching voltages interfere with measurement accuracy
Solution Approach 1:
The measurement circuit extracts only the relevant voltage information across the switching transistor during the on-state, separating the measurement function from the switching function. By using differential measurement and integration, the circuit extracts the current-related voltage component while rejecting the transient switching artifacts, thereby achieving accurate real-time current monitoring
Solution Approach 2:
The transient switching voltages and the inherent on-resistance voltage drop are converted into beneficial measurement signals. The voltage across the transistor during conduction, which includes both the transient component and the resistive drop, is integrated over time to produce a signal proportional to the average current. The transient nature actually helps by ensuring the measurement is taken during the active conduction period when current is flowing
Data Source
AI summary
Features and advantages of the present disclosure include a switching regulator and current measurement circuit. In one embodiment, a switching transistor in the switching regulator has a first voltage on a first terminal and a switching voltage on a second terminal. A current measurement circuit has first and second input terminals. A first switch couples the second terminal of the switching transistor to the first terminal of the current measurement circuit when the switching transistor is on, where the second input terminal of the current measurement circuit is coupled to the first terminal of the switching transistor and measurement(s) may be taken. When the switching transistor is off, the first and second input terminals of the current measurement circuit are coupled together, and measurements emulate zero current through the switching transistor.