MOSFET Power Switch Circuit for Portable Devices
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Solution Overview
Problem
Conventional USB charge and power supply circuits for portable electronic devices face issues such as inability to automatically stop battery charging when supplying power to the system load, high standby power consumption, and leakage current due to Schottky diodes, which result in heating and inefficiency.
Innovation Solution
A charge and power supply circuit with a control unit that uses MOSFET switches and a Schottky diode to manage power flow, automatically switching between USB charge, standby, battery supply, and USB supply modes based on input voltage detection, minimizing power consumption and preventing reverse current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky diode is used in the USB charge and power supply circuit, then the circuit can provide power supply function, but the reverse current of the Schottky diode causes large leakage current and heating
Solution Approach 1:
The patent extracts the problematic Schottky diode from the circuit and replaces it with MOSFETs that have negligible reverse current. The control unit manages the MOSFET switching to provide power supply function without the leakage current issue inherent to Schottky diodes.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by using MOSFETs with different characteristics (negligible reverse current) compared to Schottky diodes. This parameter change eliminates the leakage current problem while maintaining power supply capability.
2Reliability
If the USB charge circuit charges the rechargeable battery during standby state, then the battery can be charged, but the circuit consumes excessive power during standby
Solution Approach 1:
The patent implements dynamic switching between different operational modes (USB charge mode, standby mode, battery supply mode, USB supply mode) based on real-time detection of USB connection status and battery charge state. The control unit dynamically adjusts circuit configuration to minimize standby power consumption while maintaining charging capability when needed.
Solution Approach 2:
The control unit continuously detects the USB connection status and battery charge state, then provides feedback control signals to the MOSFETs to switch between operational modes. This feedback mechanism ensures the circuit automatically transitions to low-power standby mode when appropriate, reducing standby power consumption.
3Reliability
If the conventional USB charge circuit is used as an independent charger, then the battery can be charged, but the circuit cannot directly supply USB power to the system load
Solution Approach 1:
The patent designs a universal power management circuit that can perform multiple functions: USB charging, standby power management, battery supply, and direct USB power supply to system load. The control unit and MOSFETs work together to enable the circuit to adapt to different operational requirements, providing both charging and power supply capabilities.
4Power
If most current flows through the Schottky diode during power supply, then the circuit can function, but the Schottky diode heats up and dissipates power
Solution Approach 1:
The patent removes the Schottky diode from the current path and replaces it with MOSFETs that have much lower conduction losses. This extraction eliminates the heating problem while maintaining the power supply function, as MOSFETs can handle the current with minimal voltage drop and power dissipation.
Data Source
AI summary
A charge and power supply circuit includes: a first switch coupled between a first node and a positive terminal of a battery; a second switch coupled between a USB connector and one of the first node and a second node; a third switch coupled to a load in series between the first and second nodes; and a control unit controlling the switches. In a USB charge mode, an input voltage from the USB connector is permitted to charge the battery via the conducting first and second switches. In a battery supply mode, the battery is permitted to supply a battery voltage to the load via the conducting first and third switches. In a USB supply mode, the input voltage is permitted to be supplied to the load via the conducting second and third switches.