Power Multiplexer Switchover with Soft-Start MOSFET Control
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Solution Overview
Problem
Power multiplexers often exhibit undesirable channel switchover behaviors, such as large inrush currents, reverse currents, and output voltage drop, due to immediate switching between input power supplies, which can cause circuit damage and instability.
Innovation Solution
The power multiplexer circuit employs a switch circuit with MOSFETs arranged in a back-to-back topology, using drivers and pull-downs to manage inrush currents and a soft-start amplifier to control the output voltage ramp rate, along with diode amplifiers and boost comparators to stabilize the output voltage during switchover operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If immediate switching between input power supplies is used, then channel switchover speed is improved, but large inrush currents and reverse currents are generated causing circuit damage
Solution Approach 1:
The patent applies preliminary action by gradually increasing the output voltage through a soft-start amplifier before completing the channel switchover. The method involves: (1) detecting when the output voltage exceeds a first threshold voltage during switchover, (2) in response to the detection, increasing a gate voltage to turn on a MOSFET, and (3) turning on the MOSFET to connect the input power supply to the output. This staged approach prevents immediate full-power switching that causes inrush currents, while still achieving relatively fast switchover once the voltage threshold is reached.
2Speed
If immediate switching between input power supplies is used, then channel switchover speed is improved, but output voltage drop and instability occur
Solution Approach 1:
The patent implements preliminary action by establishing a staged voltage transition sequence. The controller first allows the output voltage to rise to a first threshold level through the soft-start amplifier, then activates the MOSFET to complete the connection. This ensures the output voltage stabilizes progressively rather than dropping during transition, maintaining stability while achieving fast final switchover.
Solution Approach 2:
The patent employs feedback by continuously monitoring the output voltage during switchover operations. The controller detects when the output voltage exceeds the first threshold voltage and uses this feedback signal to trigger the MOSFET activation. This closed-loop control ensures the switchover occurs at the optimal moment, preventing voltage drops and maintaining output stability throughout the transition.
3Stability of the object's composition
If soft-start amplifier with voltage threshold detection is used, then output voltage stability is improved, but switchover time increases
Solution Approach 1:
The patent applies parameter changes by using a fixed first threshold voltage level (e.g., 90-95% of target voltage) that optimizes the balance between stability and speed. The soft-start amplifier increases voltage at a controlled rate until this threshold is reached, then the MOSFET provides immediate full-power connection. This parameter optimization ensures the majority of voltage establishment occurs rapidly through the MOSFET, minimizing total switchover time while maintaining stability during the critical transition phase.
Data Source
AI summary
Channel switchover power multiplexer circuits, and methods of operating the same are disclosed. An example power multiplexer a first transistor coupled to a first input, a second transistor coupled to the first transistor to couple a first voltage at the first input to an output, a third transistor coupled to a second input, a fourth transistor coupled to the third transistor to couple a second voltage at the second input to the output, a diode amplifier to provide a third voltage to a gate of the first transistor to block a reverse current, and a soft-start amplifier to provide a fourth voltage to a gate of the fourth transistor to turn on (with adjustable VOUT ramp rate) the fourth transistor with a constant ramp rate.