MOSFET Protection Circuit Using Voltage-Dependent Capacitive Clamping
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Solution Overview
Problem
Insulated gate transistor devices, such as MOSFETs, face the issue of unintentionally switching on due to capacitive coupling between the load path and drive input, leading to voltage spikes that can cause erroneous switching.
Innovation Solution
An electronic circuit with a protection circuit that includes a second transistor device and a voltage-dependent capacitor connected between the load path of the first transistor device and the drive node of the second transistor device, which forms a capacitive voltage divider to maintain the first transistor in the off-state by reducing the drive voltage and preventing voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor device is switched off, then the voltage across the load path increases, but the capacitive coupling causes voltage spikes at the gate node that erroneously switch the transistor on
Solution Approach 1:
The patent introduces a protection circuit as an intermediary between the load path and the gate node. This protection circuit includes a capacitor that couples the load path to the gate node, acting as a mediator to manage the voltage transitions and prevent harmful voltage spikes from directly affecting the gate node during switching operations
Solution Approach 2:
The patent utilizes a capacitor with voltage-dependent capacitance that changes its electrical parameters dynamically. The capacitance value is selected to provide appropriate coupling at different voltage levels, allowing the circuit to maintain reliable off-state operation while accommodating the voltage increases across the load path during switching
2Object-affected harmful factors
If the capacitance of the coupling capacitor is increased, then the voltage spike at the gate node is reduced, but the drive voltage control becomes less effective
Solution Approach 1:
The patent employs a capacitor whose capacitance is not fixed but varies with voltage conditions. This dynamic characteristic allows the capacitor to provide different coupling effects at different operating points - providing stronger coupling when voltage spikes are problematic and reducing coupling when precise drive voltage control is needed
Solution Approach 2:
By selecting a capacitor with voltage-dependent capacitance, the patent changes the electrical parameter of the coupling element based on operating conditions. This allows the circuit to automatically adjust the coupling strength to prevent voltage spikes while maintaining effective drive voltage control across different 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
Effectively prevents the first transistor from unintentionally switching on by managing the capacitive coupling and voltage spikes, ensuring reliable operation by maintaining the transistor in the off-state during rapid voltage increases across the load path.
Implementation Method 1
a capacitor (3) coupled between the load path (D1-S1) of the first transistor device (1) and the first drive node (G2) of the second transistor device (2), wherein a capacitance of the capacitor (3) is voltage dependent such that the capacitance decreases as a voltage across the capacitor (3) increases
Implementation Method 2
the load path is capacitively coupled with the drive input. In a MOSFET, for example, a drain node, which is part of the load path, is capacitively coupled with the gate node, which is part of the drive input
Implementation Method 3
which forms a capacitive voltage divider to maintain the first transistor in the off-state by reducing the drive voltage and preventing voltage spikes
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An electronic circuit and a method are disclosed. The electronic circuit includes: a first transistor device (1) comprising a first drive node (G1), a second drive node (S1), and a load path (D 1-S 1); and a protection circuit (5) coupled to the first and second drive nodes (G1, S1) and the load path (D1-S1) of the first transistor device (1). The protection circuit (5) includes a second transistor device (2) having a first drive node (G2), a second drive node (S2), and a load path (D2-S2) connected between the first and second drive nodes (G1, S 1) of the first transistor device (1), and a capacitor (3) coupled between the load path (D1-S1) of the first transistor device (1) and the first drive node (G2) of the second transistor device (2). A capacitance of the capacitor (3) is voltage dependent such that the capacitance decreases as a voltage (V3) across the capacitor (3) increases.