LDO Power Supply Circuitry for Fast Load-Transient Voltage Control
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Solution Overview
Problem
Low Drop Out (LDO) power supply circuits experience delays in responding to rapid changes in load current, leading to unstable output voltage due to internal circuit delays, causing the output voltage to rise excessively despite reduced load current.
Innovation Solution
The power supply circuitry incorporates a first transistor, feedback circuit, first and second differential amplifier circuits, and control circuits, including a high-pass filter differentiation circuit and current limiting resistor, to rapidly detect and respond to changes in load current, stabilizing the output voltage and preventing excessive voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional LDO feedback circuit is used, then the output voltage is stabilized under normal load conditions, but the response speed is slow when load current changes rapidly
Solution Approach 1:
The feedback circuit is divided into two parallel paths: a main feedback path for normal operation and a rapid response path activated during transient conditions. This segmentation allows the circuit to handle different operating conditions with optimized characteristics for each path.
Solution Approach 2:
The circuit dynamically switches between different feedback mechanisms based on operating conditions. During transient load changes, the rapid response path with differentiated feedback is activated to provide fast correction, while under normal conditions the conventional feedback path maintains stable regulation.
2Reliability
If the feedback response is delayed, then the circuit operates stably under normal conditions, but the output voltage rises excessively when load current is reduced rapidly
Solution Approach 1:
The differentiation circuit performs preliminary detection of load current changes before the conventional feedback can respond. By detecting the rate of change of load current, the circuit prepares corrective action in advance, preventing the output voltage from rising excessively during transient conditions.
Solution Approach 2:
A differentiated feedback signal is introduced to provide leading-edge information about load current changes. This feedback mechanism generates a control signal proportional to the rate of change of load current, enabling the circuit to anticipate and counteract voltage deviations before they fully develop.
3Ease of operation
If the LDO continues making output current flow during load current reduction, then the feedback mechanism operates, but the output voltage exceeds the prescribed value
Solution Approach 1:
The circuit applies preliminary counter-action by generating a control signal that opposes the tendency of output voltage to rise during transient conditions. The differentiation circuit detects the rapid decrease in load current and produces a corrective signal that reduces the output transistor drive current in advance, preventing voltage overshoot.
Solution Approach 2:
The circuit changes the control parameter from simple voltage feedback to differentiated current feedback during transient conditions. By using the derivative of the load current as a control parameter, the circuit achieves more precise control over the output voltage during rapid transitions, maintaining both precision and stability.
Data Source
AI summary
A power supply circuitry includes a first transistor, a feedback circuit, a first differential amplifier circuit, a second differential amplifier circuit, and a first control circuit. The first transistor outputs a power supply voltage based on a drive signal. The feedback circuit generates a feedback voltage of the power supply voltage. The first differential amplifier circuit amplifies a difference between the feedback voltage and a reference voltage, and outputs the drive signal. The second differential amplifier circuit amplifies a difference between the reference voltage and the feedback voltage. The first control circuit detects a change in the power supply voltage by using a differentiation circuit and controls the power supply voltage based on an output of the second differential amplifier circuit.