Protection Switch Turn-Off Circuit for Fast Overvoltage Disconnect
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Solution Overview
Problem
Existing protection switches in electrical systems face challenges in efficiently managing high voltage conditions, as they often require large size to minimize impedance and fast turn-off times, while also needing to prevent overvoltage damage to load circuits.
Innovation Solution
A high voltage protection switch circuit is designed with a level shift circuit, comparator, and bipolar transistors to monitor and quickly disconnect the power transistor from the load when the supply voltage exceeds a limit, using a clamped supply voltage to ensure safe operation and fast discharging of capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the protection switch is made large to provide low switch impedance, then power dissipation is reduced, but the gate to drain and gate to source capacitance increases making fast turn-off difficult
Solution Approach 1:
A bootstrap circuit is introduced as an intermediary mechanism to charge the gate capacitance during normal operation and rapidly discharge it during overvoltage events. The bootstrap circuit includes a capacitor that stores charge and a transistor that controls discharge, enabling fast turn-off without requiring the protection switch itself to be small.
Solution Approach 2:
The gate capacitance is pre-charged during normal operation through the bootstrap circuit, preparing the protection switch for rapid turn-off. When overvoltage occurs, the pre-charged capacitor immediately discharges through a dedicated path, achieving fast turn-off without waiting for external control signals.
2Power
If the protection switch is made large to accommodate load current, then current carrying capacity is improved, but the device size and impedance increase
Solution Approach 1:
The protection switch functionality is segmented into two parts: a large power switch for current carrying and a small control switch for turn-off control. The control switch is driven by the bootstrap circuit, allowing the power switch to be optimized for current capacity while the control mechanism handles the switching action.
Solution Approach 2:
The bootstrap circuit acts as an intermediary that enables the large protection switch to be controlled rapidly without requiring the control signal to directly drive the large gate capacitance. The bootstrap transistor mediates between the control logic and the power switch gate.
3Speed
If the gate capacitance is quickly discharged to achieve fast turn-off, then protection speed is improved, but additional circuit complexity is required
Solution Approach 1:
The bootstrap circuit is self-regulating and automatically charges and discharges based on the state of the protection switch. During normal operation, it charges the capacitor; during overvoltage, it automatically discharges to turn off the switch, requiring no external control logic beyond the overvoltage detection threshold.
Solution Approach 2:
The bootstrap circuit combines the turn-off function with the existing overvoltage detection mechanism. The same voltage threshold that triggers overvoltage protection also triggers the bootstrap discharge, merging two functions into a single integrated 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
This solution provides efficient and rapid disconnection of the power transistor during overvoltage conditions, protecting the load circuit while maintaining low power consumption and scalability for various voltage ranges.
Implementation Method 1
the protection switch generally has large gate to drain and gate to source capacitance to be quickly discharged in order to turn the protection switch off in a short amount of time
Data Source
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AI summary
A switch circuit (108) includes: a power transistor (110) having a source coupled to a supply terminal (104), a drain coupled to an output terminal (106), and a gate (131); a bipolar transistor (130) having a collector coupled to the supply terminal (104), an emitter coupled to the gate (131) of the power transistor (110), and a base (132); a bias circuit (133) to control an emitter current of the bipolar transistor (130); and a resistor (138) coupled between the supply terminal (104) and the base (132). A control circuit (139) receives a current at a current input to turn the bipolar transistor (130) on responsive to a control input (128) being in a first state, and ceases receiving the current at the current input to reduce a gate- source voltage of the power transistor (110) responsive to the control input (128) being in a different second state.