IGFET Inverse Voltage Protection via Protective Switch
Solution Overview
Problem
Insulated-gate field-effect transistors (IGFETs) with built-in Schottky diodes face protection issues due to inverse current flow through parasitic diodes when an inverse voltage is applied, leading to potential destruction of the IGFET or electric circuit.
Innovation Solution
The implementation of protective switch means, comprising first and second protective IGFETs that short-circuit the drain electrode with the gate electrode of the main IGFET, preventing inverse current flow by maintaining the potential of the gate electrode equal to or below that of the drain electrode, thus suppressing the reduction in breakdown voltage of the parasitic diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external diode is connected in series with the IGFET to block inverse current, then the IGFET is protected from inverse current damage, but power loss increases significantly and control of current becomes impossible when inverse voltage is applied
Solution Approach 1:
A protective IGFET is introduced as an intermediary device between the main IGFET and the external circuit. This protective transistor activates only when inverse voltage is detected, serving as a mediator that blocks harmful inverse current while allowing normal forward current to pass through the main IGFET without significant power loss.
Solution Approach 2:
The protective circuit dynamically responds to voltage polarity changes. When inverse voltage is applied, the protective IGFET turns on to block current; when forward voltage is applied, it turns off to allow current flow. This dynamic behavior enables protection only when needed, minimizing power loss during normal operation.
2Reliability
If an external diode is connected in series with the IGFET to block inverse current, then the IGFET is protected from inverse current damage, but the device complexity increases
Solution Approach 1:
The protective IGFET is integrated into the same semiconductor substrate as the main IGFET, merging two functions (protection and switching) into a single integrated device structure. This reduces the need for separate external components and simplifies the overall circuit implementation.
Solution Approach 2:
The protective IGFET serves multiple functions: it acts as a protection device during inverse voltage conditions, functions as a switching element, and integrates with the main IGFET to form a unified circuit. This multi-functionality reduces the need for additional dedicated protection components.
3Reliability
If the source electrode is in Schottky contact with the body region to form a built-in Schottky diode, then the inverse current blocking function is improved, but the breakdown voltage of the parasitic diode reduces when inverse voltage is applied
Solution Approach 1:
The protective IGFET acts as an intermediary that prevents the gate potential from rising above the drain potential during inverse voltage conditions. By controlling the gate potential through the protective transistor, the parasitic diode remains reverse-biased and maintains its breakdown voltage, while the Schottky diode still provides inverse current blocking.
Solution Approach 2:
The protective circuit provides feedback control by monitoring the voltage polarity and adjusting the gate potential accordingly. When inverse voltage is detected, the protective IGFET activates to clamp the gate potential, preventing the parasitic diode from becoming forward-biased and maintaining system reliability.
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
This solution effectively suppresses inverse current through the parasitic diode, protecting the main IGFET and load from damage by maintaining the breakdown voltage and reducing power loss, while providing a reverse blocking function with lower internal resistance compared to independent reverse blocking diodes.
Implementation Method 1
a source electrode being in Schottky contact with a body region
Implementation Method 2
forms a Schottky diode constituted of the source electrode and the body region, thereby the Schottky diode blocking an inverse current
Implementation Method 3
protective switch means, comprising first and second protective IGFETs that short-circuit the drain electrode with the gate electrode of the main IGFET, maintaining the potential of the gate electrode equal to or below that of the drain electrode
Implementation Method 4
another current path through a parasitic diode (a body diode or a inbuilt diode) based on a PN junction between the drain region and the body region
Implementation Method 5
the parasitic diode becomes in a forward bias state, thus causing current flow therethrough
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A switching device (10) has a main IGFET (11) having a Schottky barrier diode D3 for blocking an inverse current built therein, a protective switch means (12), and a protective switch control means (13). The protective switch means (12) is connected in between a drain electrode D and a gate electrode G of the main IGFET (11). The protective switch control means (13) turns on the protective switch means (12) when an inverse voltage is impressed to the main IGFET (ill). Thereby, the main IGFET (11) is protected from the inverse voltage.