Overcurrent Protection Circuit With Differential Voltage Detection
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Solution Overview
Problem
Existing overcurrent protection circuits tend to excessively restrict output current when the input voltage is high, even with small input/output voltage differences, and are affected by variations in resistance values, leading to inaccurate power detection and potential thermal damage to transistors.
Innovation Solution
An overcurrent protection circuit that includes a sense transistor, voltage-current converting circuit, current-voltage converting circuit, voltage detection circuit, and current limiting circuit, allowing for accurate detection of excessive power in the output transistor and precise limitation of output current based on the input/output voltage difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the related art overcurrent protection circuit limits the output current based on the current flowing through resistor 45 when the input voltage is high, then the voltage generated across resistor 42 reaches the threshold voltage of the inverter circuit, but the output current is excessively restricted even when the input/output voltage difference is small
Solution Approach 1:
The protection circuit is divided into multiple independent detection paths: one path detects output current through sense transistor 41 and resistor 42, another path detects input voltage through resistor 45, and a third path detects the voltage difference between input and output through differential pair transistors 21 and 22. Each path operates independently to provide comprehensive protection without excessive current restriction.
Solution Approach 2:
The circuit changes the detection parameter from solely current-based (resistor 45) to a combination of current-based and voltage-difference-based detection. By introducing differential pair transistors 21 and 22 that respond to the voltage difference between Vin and Vout, the circuit adjusts the protection threshold dynamically based on actual power dissipation conditions rather than input voltage alone.
2Device complexity
If the related art overcurrent protection circuit uses a fixed resistance value in resistor 45, then the circuit structure is simple, but the current limitation is affected by variations in the resistance value
Solution Approach 1:
The differential pair transistors 21 and 22 provide feedback about the actual voltage difference between input and output terminals. This feedback mechanism compensates for resistance value variations in resistor 45 by adjusting the protection threshold based on real-time voltage difference measurements, thereby maintaining accurate current limitation despite component tolerances.
Solution Approach 2:
The differential pair transistors 21 and 22 act as intermediaries between the input voltage detection and the current limitation control. They translate the voltage difference information into a control signal that modulates the protection threshold, indirectly compensating for resistance variations without requiring precision resistors.
3Reliability
If the overcurrent protection circuit accurately detects excessive power generated in the output transistor, then thermal damage is prevented, but the circuit requires multiple converting circuits and detection circuits
Solution Approach 1:
The circuit merges multiple detection functions into a unified protection mechanism. The differential pair transistors 21 and 22 simultaneously detect voltage difference and modulate the protection threshold, while the sense transistor 41 and resistor 42 continue to detect output current. These functions are combined at the control node of transistor 44 to achieve comprehensive power-based protection without requiring entirely separate circuit blocks.
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 enables precise limitation of output current, preventing thermal damage and excessive current restriction, while maintaining accurate power detection and reducing the impact of resistance variations.
Implementation Method 1
a sense transistor 121 configured to output a first sense current Is1 proportional to a current lout supplied from the output transistor 120
Implementation Method 2
a voltage-current converting circuit 122 connected between an input terminal and an output terminal of the output transistor 120, and configured to output a first current I1 proportional to a difference between a voltage Vin of the input terminal and a voltage Vout of the output terminal
Implementation Method 3
a first current-voltage converting circuit 123 configured to output a first voltage V1 proportional to the first current I1
Implementation Method 4
a voltage detection circuit 124 configured to detect the first voltage V1, and to output a second sense current Is2 proportional to the current lout supplied from the output transistor 120
Implementation Method 5
a second current-voltage converting circuit 125 having the first sense current Is1 and the second sense current Is2 flow therein, and configured to output a second voltage V2 proportional to a sum of the first sense current Is1 and the second sense current Is2
Implementation Method 6
a current limiting circuit 126 configured to limit the current lout supplied from the output transistor 120, based on a second voltage V2 supplied from the second current-voltage converting circuit 125
Data Source
AI summary
There is provided an overcurrent protection circuit having a sense transistor through which a first sense current proportional to an output current of an output transistor flows, a voltage-current converting circuit connected between an input terminal of the output transistor and an output terminal thereof, and configured to output a first current, a first current-voltage converting circuit configured to output a first voltage proportional to the first current, a voltage detection circuit configured to detect the first voltage and to output a second sense current based on the output current of the output transistor, a second current-voltage converting circuit through which the first sense current and the second sense current flow, and a current limiting circuit configured to limit the output current of the output transistor based on a second voltage supplied from the second current-voltage converting circuit.