Adaptive IGBT Soft Turn-On Circuit for Shorter Ignition Delay
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Solution Overview
Problem
Power switching devices, such as IGBTs, experience significant turn-on delays during the soft turn-on process, leading to reduced maximum charging current and energy storage, which can result in poor ignition sparks due to manufacturing process spreads and temperature variations, making accurate ignition spark control challenging.
Innovation Solution
A self-adaptive control circuit for power switching devices that includes pre-charging means to set a pre-charging value below the threshold voltage, using a buffer with a gain lower than 1, and an auxiliary MOSFET to sense and adjust the threshold value, allowing for reduced turn-on delay without overshoots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a direct turn-on current is applied to the gate terminal to achieve soft turn-on, then the incremental ratio of voltage across the primary winding is reduced (avoiding overshoot), but the turn-on delay increases significantly
Solution Approach 1:
The gate terminal is pre-charged to a voltage close to the threshold voltage before the turn-on current is applied. This preliminary action reduces the turn-on delay by starting the gate voltage closer to the switching threshold, while the soft turn-on current is then applied to maintain low dv/dt without causing overshoot.
Solution Approach 2:
The pre-charging voltage is dynamically adjusted to be close to the threshold voltage rather than using a fixed low value. This dynamic adjustment allows the system to optimize between turn-on delay and overshoot prevention by adapting the initial gate voltage to the specific device characteristics and operating conditions.
2Loss of time
If a low pre-charging voltage is applied to reduce turn-on delay, then the delay is reduced, but the IGBT may turn on unintentionally due to manufacturing spreads and temperature variations
Solution Approach 1:
The system uses feedback from the transformer primary voltage to dynamically adjust the pre-charging voltage. When the primary voltage indicates approaching threshold conditions, the pre-charging voltage is adjusted accordingly. This feedback mechanism allows the pre-charging voltage to be high enough to reduce delay but low enough to prevent unintentional turn-on, adapting to manufacturing spreads and temperature variations.
Solution Approach 2:
The pre-charging voltage parameter is changed from a fixed low value to a dynamically adjustable value close to the threshold voltage. This parameter change allows optimization of turn-on delay while maintaining reliability by adapting to device-specific threshold voltages that vary due to manufacturing spreads and temperature effects.
3Productivity
If the turn-on delay is reduced, then the maximum charging current and energy storage increase, but control accuracy over ignition spark generation decreases
Solution Approach 1:
The control system uses feedback from the transformer primary voltage to precisely control the timing and magnitude of the turn-on signal. This feedback enables accurate control of ignition spark generation while maintaining reduced turn-on delay, as the system can precisely determine when to apply the turn-on current based on real-time voltage conditions.
Solution Approach 2:
The system dynamically adjusts the pre-charging voltage and turn-on current timing based on real-time operating conditions. This dynamic control allows optimization of charging current while maintaining precise control accuracy for ignition spark generation, adapting to varying loads and operating states.
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 reduces turn-on delay and maintains a low incremental ratio of voltage across the primary winding, ensuring accurate and efficient ignition spark generation independent of manufacturing process spreads and temperature variations.
Implementation Method 1
The pre-charging means includes means for sensing an indication of the threshold value; further means is used for setting the pre-charging value according to the sensed threshold value
Implementation Method 2
using a buffer with a gain lower than 1
Implementation Method 3
the IGBT is firstly turned on by applying a suitable voltage to its gate terminal. As a result, the IGBT passes from an off (blocking) state—wherein a collector-emitter voltage thereof is about equal to a voltage provided by an automotive battery (typically 12V, with respect to a reference or ground voltage)—to an on state—wherein the same collector-emitter voltage reaches a saturation voltage (such as lower than 1V)
Implementation Method 4
When the IGBT is turned off so as to cause an abrupt cut of the charging current. Consequently, an extra-voltage appears across the primary winding; this generates a very high voltage at each secondary winding (of the order of some thousands of volts), which high voltage causes the generation of the ignition spark
Data Source
AI summary
An embodiment of a control circuit is proposed for turning on a power switching device, the switching device turning on in response to a control signal exceeding a threshold value. The control circuit includes pre-charging means for providing the control signal at a pre-charging value not reaching the threshold value, and soft turn-on means for gradually increasing the control signal from the pre-charging value to a turn-on value exceeding the threshold value; the pre-charging means includes means for sensing an indication of the threshold value, and means for setting the pre-charging value according to the sensed threshold value.