Symmetrical Output Switch-Mode Power Supply Using Current Mirrors
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Solution Overview
Problem
Conventional switched-mode power supplies for mobile devices suffer from low efficiency and short battery life due to significant energy losses in charge pumps, requiring multiple components and a large silicon surface area, resulting in limited playback time and increased costs.
Innovation Solution
A voltage regulating device with a power stage and control circuit that uses a single inductor and two capacitors to generate symmetrical regulated DC voltages, achieving an efficiency of at least 80% by adopting specific configurations and minimizing energy in the inductor, thus reducing the number of passive components and silicon surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional switched-mode power supply with charge pump is used to generate symmetrical voltages, then the audio amplifier can be powered, but the energy efficiency is only about 75% with significant energy losses in the charge pump
Solution Approach 1:
The patent inverts the conventional charge pump approach by using a current mirror circuit that mirrors currents instead of pumping voltages. The first and second current mirrors generate symmetrical output currents from a single input current, eliminating the voltage pumping losses that limit efficiency to 75% in conventional designs.
Solution Approach 2:
The patent replaces the mechanical charge pump mechanism with an electrical current mirror system. Instead of using switches and capacitors to physically pump voltage (mechanical action), the invention uses transistor-based current mirrors to replicate and invert currents electronically, achieving higher efficiency.
2Area of stationary object
If a charge pump is used to generate negative voltage from positive voltage, then symmetrical voltages can be provided to the audio amplifier, but five condensers, an inductor, and connections occupying a silicon surface area of 0.42 mm2 are required
Solution Approach 1:
The patent merges multiple functions into the current mirror circuitry. The same transistors that perform current mirroring also generate both positive and negative output currents, eliminating the need for separate charge pump components like five condensers and an inductor, reducing silicon area to 0.05 mm2.
Solution Approach 2:
The current mirror circuit serves multiple functions simultaneously: it generates symmetrical output currents, provides current buffering, and enables voltage amplification. This multi-functionality eliminates the need for dedicated passive components, reducing both component count and silicon footprint.
3Duration of action of moving object
If a conventional power supply setup is used, then the audio amplifier can operate, but the playing time is limited to 30 to 70 hours due to energy losses
Solution Approach 1:
The patent employs feedback mechanisms through the current mirror configuration that automatically adjusts output currents to match input current references. This feedback control ensures minimal energy dissipation and maintains high efficiency, extending battery life from 30-70 hours to over 100 hours.
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 extends battery life to about 100 hours, reduces component costs, and minimizes the silicon surface area, while maintaining high energy efficiency and symmetrical voltage generation.
Implementation Method 1
The power stage comprises an inductor between a first node and a second node
Implementation Method 2
a first capacitor between a node at a reference potential and a second switch coupled to the first node; a second capacitor between a node at the reference potential and a third switch coupled to the second node
Data Source
AI summary
The invention relates to a switched-mode power supply delivering a first (VPOS) and a second (VNEG) voltage which are symmetrical. It comprises a power stage (30) comprising an inductor (L), and switches (A, B, C, D, E) controlled by control signals. It also comprises a control circuit (34), coupled to the power stage (30), that is able to produce error signals (Verr1, Verr2) as a function of the difference between a reference voltage (Vref) and the first (VPOS) and second (VNEG) voltages. The power supply comprises a synchronization circuit (38), coupled to the power stage (30) and to the control circuit (34), for generating the control signals in a manner that applies a control strategy adapted to minimize error signals, maintain a non-zero amount of energy in the inductor (L), and maintain the absolute value of the first (VPOS) and second (VNEG) voltages at substantially equal values.