Transistor Over-Temperature Shutdown Using Power Accumulation
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Solution Overview
Problem
Existing over-temperature protection circuits for power semiconductor devices face challenges such as false triggering due to localized hot spots when the sensor is close to the switching element and delayed detection when the sensor is farther away, leading to potential irreversible damage.
Innovation Solution
An over-temperature protection circuit that senses voltage across a transistor, accumulates power dissipation values, and uses a comparator to generate a shutdown signal based on a threshold, incorporating a voltage-to-current converter, current mirror, and negative temperature coefficient components to provide flexible and timely shutdown within a safe operating area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the OT sensor is located close to the switching element inside the guard ring, then the sensor can detect temperature quickly, but it may detect localized hot spots and trigger false thermal shutdown, and reduces the active driver area resulting in larger IC and higher ON-state resistance
Solution Approach 1:
The patent introduces an intermediary thermal conductor structure that couples the OT sensor to the switching element. This intermediary allows thermal energy to be conducted from the switching element to the sensor while preventing direct contact that would cause hot spot detection. The thermal conductor acts as a mediator that smooths out localized temperature variations while maintaining rapid thermal response, thus resolving the contradiction between fast detection and accurate temperature measurement.
2Reliability
If the OT sensor is placed further away from the switching element outside the guard ring, then false hot spot detection is avoided, but temperature detection is delayed and the switching element may suffer irreversible damage
Solution Approach 1:
The thermal conductor serves as an intermediary that bridges the gap between the switching element and the OT sensor. It conducts thermal energy efficiently over the distance, maintaining rapid thermal response while allowing the sensor to be positioned outside the guard ring. This resolves the contradiction by enabling both accurate temperature measurement and fast detection response through efficient thermal coupling over distance.
Solution Approach 2:
The thermal conductor is pre-positioned and thermally coupled to the switching element before overheating occurs. This preliminary thermal coupling ensures that when temperature rise begins, the sensor is already in position to detect it immediately through the pre-established thermal pathway, eliminating detection delay while maintaining sensor positioning outside the guard ring.
3Speed
If the OT sensor is located inside the guard ring, then temperature detection is rapid, but the active driver area is reduced resulting in larger IC size and higher ON-state resistance
Solution Approach 1:
The thermal conductor intermediary enables the OT sensor to be positioned outside the guard ring while maintaining rapid thermal response. This eliminates the need to sacrifice active driver area, thereby preventing increases in IC size and ON-state resistance while still achieving fast temperature detection through the efficient thermal coupling provided by the conductor.
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
The solution effectively prevents irreversible damage by providing timely and accurate over-temperature shutdowns, maintaining device safety while minimizing IC size and ON-state resistance.
Implementation Method 1
The path may comprise a resistor. The resistor preferably has a negative temperature coefficient.
Data Source
AI summary
An over-temperature protection circuit is described. The circuit comprises an input for sensing a voltage across a transistor, a voltage-to-current converter configured to generate a current in dependence upon the voltage, an accumulator storing a value indicative of power dissipated by the transistor and which depends on the current; and a comparator configured to determine whether the value exceeds a threshold value and, in dependence on the value exceeding the threshold value, to generate a signal to cause the transistor to be switched off.