Output Stage Protection Circuit Using Dynamic Gate Voltage Clamping
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Solution Overview
Problem
Existing protection circuits for output stages in audio systems are inadequate in preventing over-currents, which can cause damage due to sustained high current levels during short conditions, as they rely on fixed current limits that are higher than normal operating currents.
Innovation Solution
A protection circuit comprising PMOS and NMOS transistors with a voltage clamping mechanism using series-connected transistors and switches to clamp gate voltages, allowing for fold-back control modes to prevent excessive current and resume normal operation by selectively coupling supply voltages to nodes between transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes are used as voltage clamping devices to pull down current to a fixed value, then the current is limited to a fixed value, but the limited current is larger than normal operating current and sustains in the output stage during short conditions causing damage
Solution Approach 1:
The patent implements dynamic current limiting by using transistors (Q1, Q2) and switches (S1, S2) that actively adjust the current limit based on operating conditions. Unlike fixed diode clamping, the transistor-based circuit can dynamically reduce the current limit during fault conditions through feedback mechanisms, preventing sustained high current flow that would cause overheating and damage to the output stage.
2Ease of operation
If a fixed current limit is used during normal operation, then the circuit operates normally, but during short conditions the fixed limit remains too high and causes overheating
Solution Approach 1:
The patent employs feedback mechanisms where the status of switches S1 and S2 provides information about operating conditions. During normal operation, the feedback maintains appropriate current levels. During short conditions, the feedback triggers a response that reduces the current limit, thereby controlling heat generation while maintaining normal operation during healthy conditions.
3Volume of moving object
If the output stage is designed for small size to reduce heat resistance, then the device is compact, but it becomes more vulnerable to damage from over-current and heat
Solution Approach 1:
The patent implements preliminary protective action by placing the voltage clamping circuit with transistors Q1, Q2 and switches S1, S2 before the output stage. This preliminary protection mechanism detects and responds to over-current conditions before they can cause damage to the compact output stage, allowing the device to maintain small size while preserving reliability through proactive current limiting.
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
Effectively prevents damage from over-currents by reducing current flow through transistors during malfunctions and resumes normal operation once the fault is resolved, ensuring the output stage's integrity and functionality.
Implementation Method 1
the first transistor and the second transistor are arranged to clamp a gate voltage of the PMOS of the output stage and are connected in series between the first supply voltage and a gate terminal of the PMOS
Implementation Method 2
the first switch is coupled to the first supply voltage and a node between the first transistor and the second transistor, and the first switch is arranged to selectively couple the first supply voltage to the node between the first transistor and the second transistor
Data Source
AI summary
A semiconductor device including: an output stage, including a PMOS, an NMOS and an output terminal, wherein a source terminal of the PMOS is connected to a first supply voltage, a drain terminal of the PMOS is connected to a drain terminal of the NMOS and the output terminal, a source terminal of the NMOS is connected to a second supply voltage, and the output terminal outputs an output signal; and a protection circuit, including a first voltage clamping circuit, including a first transistor, a second transistor and a first switch, wherein the first transistor and the second transistor are for clamping a gate voltage of the PMOS of the output stage and are connected in series, the first switch is coupled to the first supply voltage and a node between the first transistor and the second transistor for selectively coupling the first supply voltage to the node.