Semiconductor Switch Protection Circuit for Fast Short-Circuit Turn-Off
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Solution Overview
Problem
Existing protective circuits for semiconductor switches with gate drivers are complex, costly, and require significant space, failing to rapidly switch off the semiconductor switch during excessive power loss conditions such as short-circuits, which can lead to damage.
Innovation Solution
A protective circuit comprising a clamp diode, NPN and PNP bipolar transistors, capacitors, and resistors, forming a thyristor structure that can be fired to reduce gate voltage and short-circuit current, allowing for temporary or permanent switching off of the semiconductor switch without complex access to collector voltage or current monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage monitoring is performed using a high-voltage diode or operational power amplifier, then voltage detection is achieved, but the circuit becomes complex, costly, and requires significant space
Solution Approach 1:
The patent replaces expensive, complex high-voltage diodes and operational power amplifiers with a simple resistor divider network and standard operational amplifier that operates in a linear region. This substitution uses inexpensive, readily available components that reduce cost and complexity while maintaining the voltage detection function.
Solution Approach 2:
The patent creates a simplified analog model of the voltage monitoring function using a resistor divider that scales down the high voltage to a manageable level for the operational amplifier. This copying approach allows the system to monitor high voltage conditions without directly exposing sensitive components to high voltage stress.
2Measurement precision
If current monitoring is performed using a shunt or current transformer, then current detection is achieved, but the circuit requires significant space due to air gaps and creepage distances
Solution Approach 1:
The patent extracts the current sensing function from physical current transformers with large magnetic cores and air gaps, replacing it with an electrical measurement approach using a small shunt resistor and operational amplifier. This extraction eliminates the need for bulky magnetic components while preserving the current detection capability.
Solution Approach 2:
The patent replaces the mechanical/magnetic current transformer system with an electrical measurement system using Ohm's law. Instead of using magnetic field interactions requiring physical space for air gaps and creepage distances, the system uses voltage measurement across a small resistor to infer current, dramatically reducing space requirements.
3Reliability
If existing protective circuits are implemented, then some protection is provided, but the switch-off response is not sufficiently rapid and the circuit is complex and costly
Solution Approach 1:
The patent implements preliminary protection by continuously monitoring the voltage at the semiconductor switch using the operational amplifier circuit. The circuit is pre-configured with appropriate hysteresis and threshold levels so that when fault conditions are detected, the protection mechanism can immediately act to reduce the gate voltage and switch off the device, providing rapid response without requiring complex processing or multiple stages.
Solution Approach 2:
The patent employs negative feedback through the operational amplifier to continuously compare the actual voltage at the semiconductor switch against a reference threshold. This feedback mechanism ensures that any deviation indicating a fault condition is immediately detected and corrected by adjusting the gate voltage, providing rapid and reliable protection response.
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 provides a simple, low-cost, and space-efficient protection mechanism that effectively reduces short-circuit currents, enabling the semiconductor switch to withstand short-circuits longer and allowing for controlled switch-off, thus preventing damage.
Implementation Method 1
The protective circuit comprises a clamp diode, an NPN bipolar transistor, a PNP bipolar transistor, a capacitor and (at least) three resistors
Implementation Method 2
The collector of the NPN bipolar transistor is connected to the base of the PNP bipolar transistor. The base of the NPN bipolar transistor is connected to the collector of the PNP bipolar transistor
Implementation Method 3
The capacitor is connected in parallel with the base emitter path of the PNP bipolar transistor
Data Source
AI summary
A protective circuit for a semiconductor switch includes a clamp diode, an NPN bipolar transistor, a PNP bipolar transistor, a capacitor connected in parallel with the base-emitter path of the PNP bipolar transistor, and at least three resistors. The bipolar transistors are connected to a thyristor structure that is connected to the cathode of the clamp diode. A first resistor is connected in parallel with the base-emitter path of the NPN bipolar transistor. A first terminal of the second resistor is connected to the base of the PNP bipolar transistor. Either a third resistor is connected in parallel with the base-emitter path of the PNP bipolar transistor, or a first terminal of the third resistor is connected to the emitter of the PNP bipolar transistor and the second terminal of the third resistor is connected to the second terminal of the second resistor.