Drive Circuit Inhibits Self-Turn-On in Parallel Switches
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Solution Overview
Problem
Conventional drive circuits for switches connected in parallel face issues with self-turn-on due to differing threshold voltages, leading to erroneous switching states, particularly when electric charge is supplied through parasitic capacitance, causing switches to turn on despite being intended to remain off.
Innovation Solution
A drive circuit configuration where each switch has an electrical path connecting its second main terminal or a negative voltage supply to the main control terminal, with impedance settings ensuring the potential difference increase due to parasitic capacitance remains below the threshold voltage, and the impedance of the path for the switch with the lowest threshold voltage is set lower than others, preventing self-turn-on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switches with different threshold voltages are connected in parallel, then the system can handle varying current requirements, but self-turn-on occurs due to parasitic capacitance causing erroneous switching states
Solution Approach 1:
A discharge path is introduced as an intermediary element between the control terminal and the second main terminal of each switch. This discharge path includes a discharge element (resistor, diode, or transistor) that provides a controlled route for dissipating electric charge accumulated in the parasitic capacitance, preventing the charge from causing erroneous turn-on while maintaining the ability to handle varying current requirements through parallel connection of switches with different threshold voltages
Solution Approach 2:
The invention changes the electrical parameters of the discharge path (resistance, conductance, or switching characteristics) to match the specific threshold voltage and parasitic capacitance characteristics of each switch. By adjusting these parameters, the discharge path effectively controls the potential difference across the control terminal, ensuring it remains below the threshold voltage during off-state while allowing the parallel switch configuration to maintain adaptability
2Reliability
If the impedance of the electrical path is increased to reduce charge flow through parasitic capacitance, then self-turn-on is prevented, but the switching speed and response time deteriorate
Solution Approach 1:
The discharge path incorporates a dynamic element (transistor or diode) that changes its electrical characteristics based on the switching state. During turn-off, the discharge element provides a low-impedance path to rapidly discharge parasitic capacitance and prevent self-turn-on. During turn-on, the discharge element becomes high-impedance or is bypassed, allowing fast charging of the gate capacitance without restriction, thus maintaining high switching speed while ensuring reliable off-state
Solution Approach 2:
The discharge path is designed to act in advance during the turn-off transition, rapidly removing charge from the parasitic capacitance before it can accumulate to dangerous levels. This preliminary discharge action prevents the potential difference from reaching the threshold voltage, while the same discharge path does not interfere with the subsequent turn-on operation, maintaining both reliability and speed
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 inhibits self-turn-on in switches with varying threshold voltages, ensuring accurate on and off states by managing the potential difference across the control terminal, thereby enhancing the reliability of parallel-connected switch systems.
Implementation Method 1
electric charge flowing into the electrical path through a parasitic capacitance of the driven switch
Implementation Method 2
The impedance of each of the electrical paths is set so that the potential difference increased by electric charge flowing into the electrical path
Data Source
AI summary
A drive circuit drives driven switches connected in parallel with one another. The driven switches each include first, second main, and main control terminals. When a potential difference of the main control terminal with respect to the second main terminal becomes greater than or equal to a threshold voltage, the flow of current between the first and second main terminals is permitted. At least two driven switches have different threshold voltages. The drive circuit includes, for each driven switch, an electrical path electrically connecting the second main terminal or a negative voltage supply, which is at a negative voltage lower than the potential of the second main terminal, to the main control terminal. The impedance of each of the electrical paths is set so the potential difference increased by electric charge flowing into the electrical path through a parasitic capacitance of the driven switch becomes less than the threshold voltage.