Current Limiting Circuit Parasitic Device Prevention
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Solution Overview
Problem
Existing power supply circuits with current limiting circuits fail to provide desired current-to-voltage characteristics due to parasitic devices being turned on, which disrupt the intended output characteristics.
Innovation Solution
Incorporating a resistor between the base and emitter of a second transistor in the control current generating circuit, which raises the potential at the base above a predetermined level, ensuring that the control current decreases as the current through a second transistor increases, thereby preventing the parasitic device from being activated and maintaining desired output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiting circuit is implemented using a transistor-based control mechanism, then the output current can be regulated, but parasitic devices may be activated which disrupt the intended output characteristics
Solution Approach 1:
The patent introduces a diode as an intermediary component between the control transistor base and emitter. This diode acts as a mediator that establishes a predetermined voltage threshold, preventing the base-emitter voltage from reaching levels that would activate parasitic devices while still allowing proper current limiting functionality. The diode's forward voltage drop serves as a protective barrier against parasitic activation.
Solution Approach 2:
The patent modifies the electrical parameters of the control current generating circuit by introducing a voltage threshold through the diode. This parameter change ensures that the base potential of the control transistor is constrained to remain below a critical level, thereby preventing parasitic device turn-on while maintaining the ability to regulate output current through normal operation of the control transistor.
2Ease of operation
If the base potential of the control transistor is allowed to vary freely for current control, then current regulation is achieved, but the parasitic device turns on disrupting output characteristics
Solution Approach 1:
The patent applies preliminary action by pre-establishing a voltage threshold through the diode before the parasitic device can be activated. This preliminary voltage barrier is in place before any potential parasitic turn-on condition can occur, preventing the harmful effect while allowing the control transistor to operate within safe voltage ranges for current regulation.
Solution Approach 2:
The diode serves as an intermediary that decouples the direct relationship between control transistor base potential and parasitic device activation. By introducing this intermediate component with a fixed voltage drop, the circuit allows base potential to vary for current control while the diode ensures the potential never reaches the critical level that would turn on parasitic devices.
Data Source
AI summary
A current limiting circuit for limiting an output current in response to a control current includes a detection circuit to detect a detection voltage responsive to an output voltage, and a control current generating circuit to generate a control current responsive to the detection voltage, wherein the control current generating circuit includes a first transistor through which the control current flows, a second transistor that becomes conductive upon a voltage responsive to an amount of the control current being greater than a predetermined voltage above the detection voltage, and a resistor connecting between a base and an emitter of the second transistor to raise a potential at the base of the second transistor above a predetermined level, wherein the amount of the control current flowing through the first transistor decreases as an amount of a current flowing through the second transistor increases.