Multiphase Power Supply Current Sensing with Shared Amplifier
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Solution Overview
Problem
Multiphase switching power supplies face challenges in achieving accurate and identical current sensing across phases, leading to signal-to-noise ratio issues, power losses, and increased cost and size due to the need for separate amplifiers for each phase.
Innovation Solution
A multiphase switching power supply uses an RC network to emulate inductor current, separating DC and AC components, and employs a single differential amplifier for all phases, with a sample and hold circuit to ensure identical amplification, reducing switching noise and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate amplifiers are used for each phase to amplify DC components, then current sensing accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the DC component amplification function into a single shared amplifier that serves all phases. The AC and DC separation circuit combines multiple phase signals, extracts DC components, and feeds them to one amplifier, eliminating the need for separate amplifiers per phase while maintaining sensing accuracy through precise AC-DC separation
Solution Approach 2:
The patent segments the current sensing signal into AC and DC components using an AC-DC separation circuit. This segmentation allows the DC components to be processed by a shared amplifier while AC components are handled separately, enabling resource sharing without compromising measurement precision
2Measurement precision
If separate amplifiers are used for each phase, then current sensing accuracy is improved, but system size increases
Solution Approach 1:
The patent merges multiple DC amplification functions into a single amplifier circuit that serves all phases. By combining the AC-DC separation stage with a shared amplifier, the controller footprint is reduced while maintaining the ability to accurately sense current across all phases through the unified amplification path
3Loss of energy
If low value sense resistors are used, then power loss is reduced, but signal to noise ratio deteriorates
Solution Approach 1:
The patent introduces an intermediary AC-DC separation circuit that acts as a mediator between the sense resistor and the amplifier. This circuit separates AC and DC components, allowing the use of low-value sense resistors for reduced power loss while the separation circuit enhances the AC component signal and removes DC offset, thereby improving the effective signal-to-noise ratio
Solution Approach 2:
The patent changes the signal parameters by separating AC and DC components. The AC-DC separation circuit transforms the combined signal into distinct AC and DC paths, where the AC component is amplified with enhanced signal-to-noise ratio while the DC component is handled separately, allowing low-value resistors to be used without sacrificing measurement quality
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 enhances current balancing, reduces switching noise, and minimizes system size and cost by ensuring accurate and identical current sensing across all phases, improving signal-to-noise ratio and stability.
Implementation Method 1
emulate the inductor current using a resistor-capacitor network across the inductor, where the time constant of the RC network is the same as the inductor-DCR time constant so that RC=L/DCR. Accordingly, the ramping voltage across the capacitor will track the ramping current through the inductor.
Data Source
AI summary
In a multiphase, current mode controlled switching power supply, current through the inductors in the various phases is sensed to determine when to turn off the switching transistors. An AC current feedback path, sensing the ramping ripple current, is separate from the DC current path, sensing the lower frequency average current. A shared differential amplifier has its inputs multiplexed to receive only the DC component signals from all the phases. The gain of the amplifier is set so that the DC sense signal has the proper proportion to the AC sense signal. The output of the amplifier is sampled and held for each phase using a second multiplexer. The AC sense signal and the amplified DC sense signal, for each phase, are combined by a summing circuit. The composite sense signal is applied to a comparator for each phase to control the duty cycle of the associated switch.