MOSFET Supply Voltage Selector With Near-Zero Quiescent Current
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Solution Overview
Problem
Existing voltage selector circuits suffer from high steady-state quiescent currents and voltage dropout, particularly when selecting between supply voltages from different sources, such as batteries and adaptors, leading to inefficient power management.
Innovation Solution
A circuit comprising a comparator and biasing circuits to generate difference signals for selectively configuring power switches, ensuring quiescent current is drawn only from the chosen supply and minimizing voltage dropout, using P-MOSFETs and N-MOSFETs with pull-up and pull-down resistors to manage voltage selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a comparator-based voltage selector is used to select between supply voltages, then voltage selection capability is improved, but quiescent current consumption increases
Solution Approach 1:
The patent employs a clocked comparator that operates periodically rather than continuously. The comparator is enabled only during specific clock cycles when voltage comparison is needed, while remaining disabled during other cycles to minimize quiescent current draw. This periodic operation maintains voltage selection capability while dramatically reducing steady-state power consumption.
Solution Approach 2:
The patent introduces dynamic control of the comparator through clock signals and enable/disable mechanisms. The comparator's operational state transitions between active and inactive based on system requirements, allowing the circuit to adapt its power consumption levels dynamically while maintaining voltage selection functionality when needed.
2Device complexity
If diodes are used in voltage selector circuit, then circuit simplicity is improved, but voltage dropout increases
Solution Approach 1:
The patent replaces the passive diode-based voltage selection mechanism with an active MOSFET-based switching system controlled by a comparator. Instead of relying on diode forward voltage drops to determine selection, the system uses active switches that can be fully turned on to minimize resistance and voltage drop, thereby eliminating the energy loss associated with diode voltage drops while maintaining circuit functionality.
Solution Approach 2:
The patent changes the operational parameters of the voltage selection circuit by using MOSFETs with controllable on-resistance instead of fixed diode characteristics. By controlling the gate voltage of MOSFETs, the circuit can achieve very low on-resistance states, dramatically reducing voltage dropout compared to diode-based solutions while maintaining the ability to select between different voltage supplies.
3Use of energy by moving object
If back-to-back PMOS transistors are used for voltage selection, then quiescent current is reduced, but current delivery capability deteriorates when voltages are close
Solution Approach 1:
The patent introduces a comparator as an intermediary device that actively determines which voltage source should be selected. Instead of relying on the passive behavior of back-to-back PMOS transistors, the comparator actively compares voltages and controls the switching of MOSFETs, ensuring proper current delivery capability even when input voltages are very close together, while maintaining low quiescent current through controlled operation.
Data Source
AI summary
A circuit for selecting a maximum supply voltage from a first voltage source and a second voltage source is disclosed. The circuit comprises a comparator for comparing the first voltage and the second voltage. Based on the comparison, a first bias signal and a second bias signal are generated for biasing the gate terminals of a first power switch and a second power switch respectively. The first power switch and the second power switch are biased such that the maximum voltage among the first voltage and the second voltage appear at an output node.