Low-Dropout Regulator Startup Circuit for Inrush Current Limiting
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Solution Overview
Problem
Low dropout voltage regulators face issues with inrush current during initial driving, which can damage the regulator and connected devices due to peak current charging the output capacitor, leading to potential malfunction or damage.
Innovation Solution
Incorporating an inrush preventer circuit with a determiner and limiter configuration that controls the gate voltage of the pass transistor using control signals, including an enable signal that is turned on during the initial driving period, to regulate the amplified voltage and prevent excessive inrush current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the LDO regulator directly charges the output capacitor during initial driving, then the output voltage can be quickly established, but excessive inrush current flows that can damage the regulator and connected devices
Solution Approach 1:
The inrush preventer circuit is activated before the main power switch is turned on. It pre-charges the output capacitor through a controlled current path, preventing the sudden inrush current that would occur if the capacitor were charged directly when the main switch closes. This preliminary action ensures the capacitor is partially or fully charged before full power is applied.
Solution Approach 2:
The inrush preventer circuit acts as an intermediary between the power input and the output capacitor. It provides a controlled current path through resistors and switches that limits the charging current to safe levels, mediating the energy transfer from the power source to the capacitor without allowing damaging peak currents.
2Reliability
If the inrush preventer circuit is activated during the entire operating period, then inrush current is continuously prevented, but the circuit complexity and power consumption increase
Solution Approach 1:
The inrush preventer circuit is designed to operate only during the initial startup period when the output capacitor needs charging. A control signal activates the preventer circuit at startup and deactivates it after a predetermined time interval or when the output voltage reaches a threshold level. This periodic operation provides protection when needed while minimizing unnecessary circuit activity and power consumption during normal operation.
3Speed
If the gate voltage of the pass transistor is directly controlled by the differential amplifier output, then the voltage regulation response is fast, but the initial current surge damages the circuit
Solution Approach 1:
Before the differential amplifier fully drives the pass transistor gate, the inrush preventer circuit is activated to pre-charge the output capacitor. This preliminary action reduces the voltage difference across the pass transistor when it fully conducts, thereby limiting the initial current surge while maintaining the fast response capability of the differential amplifier for subsequent regulation.
Solution Approach 2:
The inrush preventer circuit serves as an intermediary that temporarily shares the load current during startup. By providing an alternative current path through its resistors and switches, it mediates the current flow so that the pass transistor does not have to bear the full brunt of the capacitive charging current, protecting it from damage while allowing the differential amplifier to maintain control.
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 reduces the inrush current to one-third of its original value, allowing for stable output voltage and extended initial driving time, thereby protecting the low dropout voltage regulator and connected devices from damage.
Implementation Method 1
a differential amplifier configured to output an amplified voltage by comparing a feedback voltage with a reference voltage
Implementation Method 2
distribution resistors connected between the drain terminal and the ground terminal, configured to generate the feedback voltage
Implementation Method 3
a first transistor having a gate terminal connected to the gate terminal of the pass transistor, a source terminal connected to the power input voltage terminal, and a drain terminal connected to the first node, and configured to generate a first mirroring current of the amplified voltage
Data Source
AI summary
A low dropout voltage regulator includes a differential amplifier configured to output an amplified voltage by comparing a feedback voltage with a reference voltage, a pass transistor configured to receive a power input voltage into a source terminal, the amplified voltage into a gate terminal, and output an output voltage into a drain terminal, distribution resistors connected between the drain terminal and the ground terminal, configured to generate the feedback voltage, and an inrush preventer, connected in parallel between the differential amplifier and the pass transistor, and configured to output a regulated amplified voltage into the gate terminal according to a control signal, wherein the inrush preventer comprises a determiner configured to output an enable signal that is turned on during an initial driving period, and a limiter configured to output the regulated amplified voltage according to the enable signal.