Lateral Bipolar Transistor Overvoltage Protection Circuit
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Solution Overview
Problem
Conventional overvoltage protection methods, such as diodes, face challenges in effectively protecting electronic circuits from both positive and negative voltage transients due to their inherent resistive characteristics and polarity-dependent responses, which can lead to prolonged discharge times and higher peak voltages during inductive events.
Innovation Solution
A lateral bipolar transistor-based overvoltage protection device is designed to switch into a low impedance state independently of discharge polarity, utilizing symmetric N-type doping and punch-through mechanisms, and incorporating a silicon-controlled rectifier (SCR) configuration for rapid and asymmetric response, with a switch-off circuit to revert to a high impedance state once the threat is mitigated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes are used for overvoltage protection, then protection against voltage transients is provided, but the diodes conduct at forward bias voltage (typically 0.7V) which may cause false triggering when supply voltages fall outside supply rail voltage
Solution Approach 1:
The patent changes the triggering parameter from a fixed diode forward voltage (0.7V) to a configurable voltage threshold determined by a voltage divider network (R1, R2) and Zener diode breakdown voltage. This allows the protection threshold to be independently set above the supply voltage, preventing false triggering while maintaining reliable protection.
Solution Approach 2:
The patent introduces an intermediary voltage divider network and Zener diode between the protected node and the clamping diodes. This intermediary structure detects overvoltage conditions at a higher threshold voltage and only triggers the clamping action when the threshold is exceeded, eliminating false triggering from normal supply voltage variations.
2Reliability
If diodes are used for overvoltage protection, then protection is provided, but the resistive current-voltage characteristic causes prolonged discharge time and higher peak voltages
Solution Approach 1:
The patent changes the electrical characteristic of the protection device from resistive (diodes) to active switching (MOSFETs). The MOSFETs operate in saturation region during normal conditions with very high impedance, then switch to triode region during overvoltage events with very low on-resistance, enabling rapid discharge and reducing peak voltages.
Solution Approach 2:
The patent makes the protection device dynamic by using MOSFETs that can rapidly transition between high-impedance (off) and low-impedance (on) states. This dynamic switching capability allows the device to respond quickly to overvoltage events, conducting discharge rapidly and reducing the duration of protective action compared to static resistive diodes.
3Adaptability or versatility
If symmetric N-type doping is used for polarity-independent protection, then both positive and negative voltage transients are protected, but the device complexity increases compared to single-polarity protection
Solution Approach 1:
The patent uses symmetric N-type doping regions (first and second N-type regions with substantially equal doping concentrations) to create a balanced structure that responds equally to both positive and negative voltage transients. This symmetric design achieves polarity independence while maintaining manufacturing simplicity through consistent doping processes.
Solution Approach 2:
The patent creates a universal protection device that handles both positive and negative overvoltage events with a single integrated structure. The symmetric N-type regions enable the same physical structure to protect against voltage transients of either polarity, eliminating the need for separate protection circuits for each polarity.
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 robust, polarity-independent overvoltage protection with rapid response and controlled foldback voltage, effectively managing both positive and negative voltage transients, reducing peak voltages and ensuring efficient discharge of electrostatic events.
Implementation Method 1
when the conduction is to be triggered by punch-through mechanisms, then the distances between PN boundaries of the first and second N-type regions with the first P-type region, respectively, and internal punch through structures in the N-type regions should be about the same for each of the first and second N-type regions
Implementation Method 2
the overvoltage protection device is arranged to temporarily latch on in response to an overvoltage condition
Data Source
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AI summary
An overvoltage protection device in combination with a filter, the overvoltage protection device having a first node for connection to a node to be protected (8), a second node (9) for connection to a discharge node; and a control node (79); and wherein the filter comprises at least one of: (a) a capacitor (620, 630, 640) connected between the first node and the discharge node; (b) a capacitor (620a, 630a) connected between the control node and the discharge node; or (c) an inductor (650) in series connection with the first node. In some embodiments, the overvoltage protection device can include an NPN semiconductor structure including: first (40) and second (50) N-type regions and a first P-type region (60); wherein one of the N-type regions is connected to a terminal, conductor or node (8) that is to be protected against an overvoltage event, and the other one of the N-type regions is connected to a reference, and wherein a field plate (70) in electrical contact with the first P-type region overlaps with but is isolated from portions of the N-type regions.