Switched-Mode Common-Mode Level Shifter for DC Saturation Control
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Solution Overview
Problem
Existing common-mode chokes are ineffective in shifting wideband DC differential signals across large AC or DC common-mode voltage differences due to saturation issues, especially in the presence of common-mode transients and severe disturbances.
Innovation Solution
A switched-mode level-shifter is employed, which commutates the common-mode voltage to reset the flux of the common-mode choke, allowing it to level shift differential signals between different DC common-mode voltages by using a common-mode inductive reactor with a switch that alternates between charging and resetting, driven by a chopping signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common-mode choke is used to level shift differential signals, then AC common-mode voltage can be shifted, but DC common-mode voltage causes core saturation and large inductive current flow
Solution Approach 1:
The patent applies periodic switching action to the common-mode choke through a bridge circuit that alternately connects and disconnects the choke from the common-mode voltage. This periodic action prevents continuous DC current flow that would cause saturation, while still allowing the choke to function as a level shifter for differential signals during the connected phases.
Solution Approach 2:
The patent transforms the static common-mode choke into a dynamic system by using switching elements (transistors or diodes) controlled by a pulse signal. The switching action dynamically adjusts the connection state of the choke, enabling it to handle both AC and DC common-mode voltages without saturation by periodically resetting the magnetic flux.
2Reliability
If a common-mode choke handles large DC common-mode voltage, then level shifting capability is improved, but inductive reactance vanishes at low frequency causing excessive current
Solution Approach 1:
The periodic switching of the bridge circuit creates time-varying inductive reactance that prevents excessive current flow. During the off-phase of the switching cycle, the inductive reactance is effectively removed, allowing the magnetic flux to reset. During the on-phase, the choke provides level shifting while the periodic nature limits average current consumption.
Solution Approach 2:
The bridge circuit acts as an intermediary between the common-mode voltage source and the common-mode choke. It mediates the connection by periodically connecting and disconnecting the choke, thereby controlling the current flow and preventing excessive power consumption while maintaining the level shifting function.
3Measurement precision
If a common-mode choke is used for wideband DC differential signals, then signal fidelity is improved, but common-mode transients cause saturation
Solution Approach 1:
The periodic switching action provides a mechanism to reset the magnetic flux before common-mode transients can cause saturation. The switching frequency is chosen to be high enough that the choke has time to demagnetize during the off-phase, preventing transient-induced saturation while maintaining signal fidelity during the on-phase.
Solution Approach 2:
The continuous periodic switching prepares the common-mode choke by regularly resetting its magnetic flux before transient disturbances occur. This preliminary action ensures the choke is always in a safe operating state with minimal stored energy, preventing transient-induced saturation.
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 approach enables the common-mode choke to accurately shift wideband DC differential signals across large voltage differences with exceptional fidelity, even in the presence of common-mode transients, and allows for faithful signal acquisition in severe disturbances, avoiding saturation and maintaining high accuracy and bandwidth.
Implementation Method 1
the inductive reactor when charged experiences a change of flux according to the applied voltage
Implementation Method 2
the inductive reactor when reset reverses the change of flux experienced thereby
Data Source
AI summary
A switched-mode level-shifter shifts a differential voltage superimposed on a common-mode voltage. In the level shifter, a common-mode inductive reactor has at least two windings, and at least one of the differential voltage and the common-mode voltage are applied to at least one of the windings of the reactor. A switch charges the inductive reactor when caused to be in a first state, where the inductive reactor when charged experiences a change of flux according to the applied voltage. The switch also actuates a reset of the charged inductive reactor when caused to be in a second state, where the inductive reactor when reset reverses the change of flux experienced thereby. A source of a chopping signal is provided to alternately drive the switch between the first and second states, where each of the first and second states is one of in and out of conduction.