Variable On-Resistance Switch for Short-Circuit Detection in Power Supplies
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Solution Overview
Problem
Conventional isolated switching power supplies, particularly in vehicles, face safety issues due to potential short-circuit abnormalities that can lead to excessive primary current flow, potentially damaging semiconductor devices before fuses can intervene, especially in high-power applications.
Innovation Solution
A semiconductor device with a switch terminal, ground terminal, and a detection circuit that monitors switch voltage to detect short-circuit abnormalities, switching to a higher on-resistance value during detection periods and forcibly stopping the pulse-drive if an abnormality is detected, using parallel transistors and comparators to generate detection signals based on threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the output switch uses a low on-resistance value for continuous operation, then power consumption and heating are reduced, but the device cannot detect short-circuit abnormalities in the switch terminal
Solution Approach 1:
The patent applies dynamics by making the on-resistance of the output switch variable rather than fixed. The controller dynamically switches between a first on-resistance value (low) during normal operation and a second on-resistance value (high) during detection periods, allowing the device to optimize power consumption during continuous operation while enabling short-circuit detection when needed.
Solution Approach 2:
The patent implements periodic action by introducing detection periods during which the output switch is set to the high on-resistance value to detect short-circuit abnormalities. These detection periods occur intermittently rather than continuously, allowing the device to maintain low power consumption during normal operation while periodically checking for faults.
2Reliability
If the output switch uses a high on-resistance value for short-circuit detection, then short-circuit abnormalities can be detected, but power consumption and heating increase during detection
Solution Approach 1:
The patent limits the use of high on-resistance value to specific detection periods rather than continuous operation. The controller switches to the high on-resistance value only when needed for detection, thereby minimizing power consumption and heating while maintaining effective short-circuit detection capability.
3Reliability
If fuse protection is used for excessive current, then device protection is provided, but damage occurs before the fuse can intervene in high-power applications
Solution Approach 1:
The patent implements preliminary action by actively monitoring the switch terminal voltage to detect short-circuit abnormalities before excessive current can cause damage. The detection circuit continuously checks for abnormal voltage levels, and the controller can respond by adjusting the output switch resistance or stopping pulse drive, preventing damage before it occurs rather than relying on passive fuse protection.
Solution Approach 2:
The patent uses feedback by having the detection circuit monitor the switch terminal voltage and provide information to the controller. Based on this feedback, the controller can detect short-circuit abnormalities and take appropriate protective actions, creating a closed-loop protection system that responds quickly to abnormal conditions.
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
Enhances safety by reducing power consumption and heating in the output switch during short-circuit conditions, preventing damage from excessive primary current and ensuring the semiconductor device operates safely by cutting off excessive current.
Implementation Method 1
an output switch connected between the switch terminal and the ground terminal and configured to be switchable between a first on-resistance value and a second on-resistance value higher than the first on-resistance value
Implementation Method 2
the detection circuit includes a comparator configured to generate a detection signal by comparing the switch voltage or a voltage corresponding thereto with a predetermined threshold voltage
Data Source
AI summary
There is provided a semiconductor device that includes a switch terminal; a ground terminal; an output switch connected between the switch terminal and the ground terminal and configured to be switchable between a first on-resistance value and a second on-resistance value higher than the first on-resistance value; a detection circuit configured to detect a short-circuit abnormality of the switch terminal by monitoring a switch voltage that appears at the switch terminal in a predetermined detection period; and a controller configured to perform a pulse-drive of the output switch by setting the output switch to the second on-resistance value in the detection period, continuously perform the pulse-drive of the output switch by setting the output switch to the first on-resistance value if the short-circuit abnormality of the switch terminal is not detected, and forcibly stop the pulse-drive of the output switch if the short-circuit abnormality of the switch terminal is detected.