Low Dropout Regulator Over Current Protection Circuit
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Solution Overview
Problem
Conventional over current protection circuits for low dropout regulators increase voltage dropout and aggravate heat dissipation issues, degrading the performance of the regulator and potentially damaging it.
Innovation Solution
The proposed over current protection circuit incorporates a sense transistor, sense resistor, operational amplifier, and first transistor to sense and control the current through the power transistor, maintaining low dropout voltage and minimizing heat dissipation by using a current-mirror circuit and carefully designed resistor configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional over current protection circuit with a resistor connected to the supply voltage is used, then over current protection is achieved, but the voltage dropout increases significantly and heat dissipation is aggravated
Solution Approach 1:
The current sensing function is segmented from the main power path. A separate sense transistor is used to detect the current flowing through the power transistor, allowing the protection circuit to operate independently without adding significant resistance to the main current path, thus avoiding increased voltage dropout and heat dissipation.
Solution Approach 2:
A sense transistor is introduced as an intermediary element to sense the current flowing through the power transistor. This intermediary component allows the protection circuit to monitor current without directly affecting the main power transmission path, preventing the voltage dropout and heat dissipation problems caused by placing a sensing resistor in the main current path.
2Measurement precision
If the voltage across the sensing resistor is made high to improve sensing accuracy, then measurement precision is improved, but the voltage dropout increases and contradicts the low dropout function
Solution Approach 1:
The sensing mechanism changes from direct voltage measurement across a resistor in the main current path to sensing the voltage drop across a separate sense transistor. This parameter change allows accurate current sensing while maintaining the low dropout characteristic of the regulator, as the sense transistor operates in a separate circuit path.
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 effectively prevents damage from over current while maintaining low dropout voltage and reducing heat dissipation, ensuring the low dropout regulator's performance and reliability.
Implementation Method 1
The operational amplifier is configured to output a control signal according to the voltage across the sense resistor and a reference voltage
Implementation Method 2
The sense transistor is configured to sense the current flowing through the power transistor
Implementation Method 3
The first transistor is configured to control the power transistor according to the control signal
Data Source
AI summary
An over current protection circuit for low dropout regulator comprises a sense transistor, a sense resistor, an operational amplifier and a first transistor. The sense transistor senses the current flowing through the power transistor. The sense resistor is coupled to the sense transistor and shares the same current flowing through the sense transistor. The operational amplifier outputs a control signal according to the voltage across the sense resistor and a reference voltage. The first transistor controls the power transistor according to the control signal.