Limiting Current Circuit With Delay Unit For Short Circuit Protection
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Solution Overview
Problem
Existing limiting current circuits are inadequate in protecting enhancement MOSFETs from rapid increases in load current during short circuits, as the discharge mechanism is too slow, leading to prolonged exposure to high currents and potential damage.
Innovation Solution
A limiting current circuit with output short circuit protection, comprising an external voltage source, a driving transistor, a voltage control resistor, a voltage control transistor, and a delay unit, which extends the internal resistance periods of these components to manage and limit currents effectively during short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge mechanism is used to limit load current when a predefined current level is exceeded, then the load current can be limited, but the discharge is too slow to protect the enhancement MOSFET from rapid current rises during short circuits
Solution Approach 1:
The patent introduces a delay unit that proactively manages the discharge timing of the parasitic capacitance. Instead of passive discharge, the delay unit actively controls when discharge occurs, ensuring that during rapid short circuit conditions, the discharge is delayed until the overcurrent condition is confirmed, thereby providing faster protective action for the enhancement MOSFET.
Solution Approach 2:
The delay unit acts as an intermediary between the current sensing mechanism and the discharge path. It mediates the control signal to the discharge transistor, introducing a controlled time delay that allows the circuit to distinguish between transient current spikes and genuine short circuit conditions, thereby improving the speed and accuracy of the protection response.
2Speed
If the discharge current is increased to speed up protection, then the response time improves, but the circuit complexity and potential for false triggering increase
Solution Approach 1:
The delay unit serves as an intermediary control element that manages the discharge process without requiring complex circuit modifications. It provides a simple yet effective mechanism to control discharge timing, avoiding the need for complex feedback loops or multiple sensing circuits that would increase overall system complexity.
Solution Approach 2:
The patent utilizes the inherent parasitic capacitance of the discharge transistor as a timing element. By changing the operational parameters (voltage levels, resistance values) of the delay unit, the circuit achieves adjustable protection response times without adding complex active components, thereby maintaining circuit simplicity while improving protection speed.
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 effectively limits output currents during short circuits, reducing the risk of damage to the circuit by managing internal resistances and parasitic capacitance, thereby protecting the circuit from excessive current exposure.
Implementation Method 1
The voltage control transistor has an internal resistance and a parasitic capacitance
Implementation Method 2
The voltage control transistor has an internal resistance and a parasitic capacitance. The delay unit makes the internal resistance of the voltage control transistor is less than the internal resistance of the driving transistor when the load is shorted
Data Source
AI summary
A limiting current circuit that has output short circuit protection is connected to an external voltage source and comprises an output terminal, an input current unit, a driving transistor, a voltage control resistor, a voltage control transistor and a delay unit. The output terminal is connected to a load and has an output current. The driving transistor has an internal resistance, a drain current and a gate voltage. The voltage control resistor has a resistor voltage. The voltage control transistor has an internal resistance and a parasitic capacitance. The delay unit makes the resistor voltage charging the parasitic capacitance to extend the period of lower internal resistance of the voltage control transistor and the period of higher internal resistance of the driving transistor, makes the internal resistance of the voltage control transistor is less than the internal resistance of the driving transistor when the load is shorted.