Semiconductor Circuit Soft Turn-Off for Automotive Ignition
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Solution Overview
Problem
The existing soft turn-off operation in ignition devices for automotive internal combustion engines is influenced by temperature characteristics of the power switch, leading to variable soft turn-off times and potential abnormal combustion issues like backfire or knocking.
Innovation Solution
A semiconductor integrated circuit is designed with a soft turn-off circuit that receives a control signal to gradually drop a reference voltage, a current sensing circuit to monitor the current, and a drive circuit to limit the current based on the sensed voltage, ensuring a consistent soft turn-off time irrespective of temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a variable resistor is connected to the gate terminal of the power switch to perform soft turn-off operation, then the current flowing through the power switch can be gradually turned off, but the soft turn-off operation time varies depending on the temperature characteristics of the power switch
Solution Approach 1:
The patent introduces a feedback mechanism where the drive circuit monitors the actual current flowing through the power switch and adjusts the gate voltage accordingly. The drive circuit outputs a drive signal that limits the current based on feedback from the current flowing through the power switch, ensuring the soft turn-off operation time remains consistent regardless of temperature variations in the variable resistor.
Solution Approach 2:
The patent dynamically changes the drive signal parameters (voltage and current limits) based on real-time monitoring of the power switch current. The drive circuit adjusts these parameters during the soft turn-off operation to maintain a consistent turn-off time, compensating for temperature-induced variations in the variable resistor's characteristics.
2Reliability
If the ignitor turns off the power switch independently from the engine control unit, then the power switch protection function is achieved, but the ignition timing may be disrupted causing abnormal combustion
Solution Approach 1:
The patent implements a dynamic control mechanism where the drive circuit continuously monitors both the control signal from the engine control unit and the actual current state of the power switch. This dynamic monitoring allows the system to coordinate the protection function with the ignition timing requirements, preventing disruptions to the combustion process while still protecting the power switch.
Solution Approach 2:
The drive circuit uses feedback from both the control signal and the power switch current state to make real-time decisions about when to turn off the power switch. This dual feedback mechanism ensures that the protection function is activated only when appropriate, maintaining accurate ignition timing while still providing necessary protection against overcurrent conditions.
Data Source
AI summary
A semiconductor integrated circuit for controlling a power switch in accordance with a control signal, which is at one of a first level and a second level for respectively turning on and off the power switch. The semiconductor integrated circuit includes a control circuit configured to receive the control signal to thereby output a reference voltage, a value of which gradually drops from a predetermined value when the received control signal remains at the first level for a predetermined time, a current sensing circuit configured to sense a current flowing through the power switch, and a drive circuit configured to receive the control signal and the reference voltage to thereby output a drive signal, the drive signal limiting the current flowing through the power switch in accordance with the reference voltage and a sense voltage corresponding to the current sensed by the current sensing circuit.