MOS Output Protection Circuit for Automation Equipment
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Solution Overview
Problem
Conventional protection systems for static output channels in automation equipment tend to trip and cut off electrical loads prematurely during the start phase, especially for capacitive or filament lamp loads, due to varying resistance and peak current fluctuations, leading to potential damage and the need for oversized switching devices.
Innovation Solution
An electronic control and protection system utilizing a MOS switching transistor, a limiting device with a bipolar transistor and voltage-drop element, and a cut-off device with a comparison and timer module to manage current thresholds and prevent premature cut-off, ensuring stable current stabilization and immunity to peak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cut-off current threshold is set to accommodate high inrush current (five times maximum current), then premature cut-off is avoided during start phase, but the switching device must be oversized to absorb the peak current without damage
Solution Approach 1:
The patent applies dynamics by implementing a time-dependent current threshold that is high only during the brief start phase and returns to normal levels afterward. This allows the switching device to tolerate peak inrush current temporarily without requiring permanent oversizing, as the device only needs to handle the high current for the limited duration of the start phase rather than continuously.
Solution Approach 2:
The patent applies beforehand cushioning by providing temporary current threshold adjustment during the start phase to cushion the impact of inrush current. The system prepares for the expected high current by setting a permissive threshold in advance, allowing the switching device to survive the initial peak without damage, after which normal protection levels are restored.
2Device complexity
If the cut-off current threshold is set to the nominal maximum current value, then the switching device can be sized appropriately, but the system becomes vulnerable to destruction from repeated peak currents during startup
Solution Approach 1:
The patent applies dynamics by implementing a time-dependent current threshold that adapts to different operational phases. During the start phase, the threshold is elevated to five times maximum current, allowing the properly sized switching device to operate without damage. After the start phase, the threshold returns to 1.25 times maximum current for normal protection. This dynamic adjustment ensures the switching device is neither oversized nor vulnerable to peak current damage.
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 system effectively limits peak currents during startup, preventing premature cut-off and reducing the need for oversized switching devices, while maintaining protection against overloads and short circuits, thus enhancing the reliability and efficiency of output channel control.
Implementation Method 1
a limiting device limiting the voltage at the terminals of said resistor to a predetermined maximum value
Implementation Method 2
the limiting device comprises a bipolar transistor, the emitter of which is connected to the source of the switching transistor and the collector of which is used to control the gate of the switching transistor
Implementation Method 3
the cut-off device comprises a comparison module between the base-emitter voltage of said bipolar transistor and a reference voltage
Implementation Method 4
the output of the comparison module being connected to a timer module, the output of which is connected to the gate of a cut-off MOS transistor
Implementation Method 5
a device for switching the electrical load comprising an MOS switching transistor, the source of which is connected to a positive voltage terminal via a resistor and the drain of which is connected to the load, the switching transistor being switchable between an on-state in which the load is connected to said resistor and an off-state
Data Source
AI summary
An electric control and protection system for an output channel of automation equipment, the output channel being capable of controlling an electrical load as a function of a control signal from the automation equipment, the control and protection system including: a device that switches the electrical load including an MOS switching transistor, a source of the MOS switching transistor being connected to a positive voltage terminal via a resistor and a drain of the MOS switching transistor being connected to the electrical load, the MOS switching transistor being switchable between an on-state in which the electrical load is connected to the resistor and an off-state.