Crowbar Latch for Intrinsically Safe Voltage Limiting
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Solution Overview
Problem
Existing voltage shunt devices for intrinsically safe systems face challenges in power dissipation, particularly in small enclosures, as they generate excessive heat during fault conditions, and require costly and sensitive components to manage voltage tolerances effectively.
Innovation Solution
A voltage crowbar device that latches across the voltage limiter in response to sensed current rather than voltage, reducing power dissipation by diverting current through the crowbar and using normal tolerance components, thereby reducing sensitivity and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zeners are used for voltage limitation in fault condition, then voltage clamping is achieved, but power dissipation becomes considerable and heat generation becomes difficult to dissipate
Solution Approach 1:
A crowbar device is introduced as an intermediary component between the input voltage source and the zener voltage limiter. The crowbar detects when input voltage exceeds a threshold and activates a latching short circuit across the zener, diverting excess current away from the zener. This mediator mechanism allows the zener to maintain its voltage clamping function while the crowbar handles the power dissipation of excess current, solving the contradiction between reliable voltage protection and excessive power loss.
2Loss of energy
If voltage crowbar device is used to reduce power dissipation, then power loss is reduced, but device complexity increases due to additional components
Solution Approach 1:
The crowbar device operates autonomously through self-latching mechanism. When the input voltage exceeds the threshold, the crowbar automatically activates and latches on, creating a short circuit across the zener without requiring external control signals or additional active components. The latching mechanism maintains the protective state as long as the fault condition persists, and automatically resets when the input voltage returns to normal levels. This self-service operation minimizes the need for additional control circuitry, reducing the complexity increase that would otherwise result from the crowbar addition.
3Ease of manufacture
If normal tolerance components are used instead of precise voltage sensing, then component costs are reduced, but voltage tolerance control becomes less precise
Solution Approach 1:
The invention replaces voltage-based sensing (electrical measurement) with current-based sensing. The crowbar device monitors current flow through the zener and activates when current exceeds a threshold corresponding to the maximum safe power dissipation. This substitution allows the use of simple current-sensing resistors and comparators with normal tolerances instead of precision voltage reference circuits and high-precision voltage comparators. The current-based approach achieves adequate protection precision while dramatically reducing component cost and complexity.
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 approach effectively reduces power dissipation and increases the available output voltage while maintaining safety, with improved reliability and reduced component costs due to the use of current sensing, which has broader tolerances and is less sensitive to voltage spikes.
Implementation Method 1
the crowbar device is arranged to latch responsive to a current sensed in the barrier device
Implementation Method 2
reducing power dissipation by diverting current through the crowbar
Implementation Method 3
a latching short circuit is fired across the zener
Data Source
AI summary
An electronic barrier device, includes an Isolating Barrier or a Zener Barrier, with a voltage limiter or voltage shunt such as at least one zener device for voltage limitation in a circuit during a fault condition. The barrier device includes a crowbar device arranged to latch across the at least one voltage shunt device to reduce power dissipation in the at least one voltage shunt device in the circuit fault condition. The crowbar device is arranged to latch responsive to a change in a current flowing in the barrier device.