Power Supply Switching Circuit Isolation and Reverse Current Protection
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Solution Overview
Problem
Existing power supply switching circuits face challenges in ensuring isolation between multiple power supplies, leading to potential damage from reverse current and excessive voltage, especially in smaller node fabrication processes where high-voltage devices are not readily available, resulting in increased size and cost when using off-chip switches.
Innovation Solution
A power supply switching circuit comprising a first and second switch pair, each with a switch control circuit that uses differential current sources to generate control signals, ensuring only one power supply is connected to the output node at a time, and utilizing p-channel LD-MOSFETs or other suitable switches with intrinsic body diodes configured to prevent reverse current flow and handle high voltages within smaller process nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If off-chip high-voltage switches are used to handle power supply switching in small node fabrication processes, then the voltage handling capability is improved, but the device size and cost increase
Solution Approach 1:
The power supply switching circuit is divided into multiple switch pairs, where each switch pair handles a specific power supply connection. This segmentation allows the use of lower-voltage switches in each segment while collectively handling higher voltage through proper configuration and control
Solution Approach 2:
The patent introduces intermediate control circuits and body diodes as mediators that enable standard low-voltage switches to safely handle high-voltage power supplies. The body diodes act as natural voltage blockers, and the control circuits coordinate switching to prevent voltage exceedance across any single switch
2Reliability
If multiple power supplies are connected in parallel without isolation, then the system reliability is improved, but reverse current damage occurs
Solution Approach 1:
The circuit employs switch pairs with body diodes configured to preemptively block reverse current flow before it can cause damage. The switches are controlled to open before reverse current can develop, and the body diodes provide inherent reverse-current protection by conducting in the forward direction only
Solution Approach 2:
The body diodes inherent in MOSFET switches serve as natural intermediaries that prevent reverse current from flowing back into power supplies. These diodes are strategically positioned in each switch pair to block reverse current paths while allowing forward current flow during normal operation
3Ease of manufacture
If switches with breakdown voltage rating smaller than power supply voltage are used, then smaller process nodes can be utilized, but voltage exceedance may damage the switches
Solution Approach 1:
The control circuitry preemptively opens the switches before voltage conditions could exceed the switch breakdown ratings. The differential current control mechanism ensures switches transition to off-state before harmful voltage levels can develop across them
Solution Approach 2:
The body diodes and control circuits act as intermediaries that protect the switches from exceeding their voltage ratings. The body diodes provide inherent voltage blocking capability, while the differential current control system monitors and regulates switch operation to maintain voltages within safe limits
Data Source
AI summary
Disclosed is a power supply switching circuit comprising: a first switch pair configured to selectively connect a first power supply node to an output node; a second switch pair configured to selectively connect a second power supply node to the output node; and a switch control circuit configured to: respectively control first and second switches of the first switch pair by a first control signal and a second control signal; respectively control first and second switches of the second switch pair by a third control signal and a fourth control signal; and selectively connect one of the first power supply node or the second power supply node to the output node by at least one of (a) the first and second control signals or (b) the third and fourth control signals. At least one of the second control signal or the fourth control signal is powered via the output node.