DC/DC Converter Control Circuit for Fast Voltage Transitions
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Solution Overview
Problem
DC/DC converters face challenges in reducing quiescent current while maintaining high-speed voltage changes, particularly during ramp-up and ramp-down operations, due to the limited charging/discharging speed of the error amplifier and the reverse polarity issue with feed forward capacitors.
Innovation Solution
A control circuit that combines feedback loop control with open loop control using an auxiliary circuit, which compares the feedback voltage with a ramp signal and sources or sinks an auxiliary current to enhance the voltage change speed without affecting stability, and includes a voltage source to adjust the reference voltage during these operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the operating current of the gm amplifier is reduced to suppress quiescent current, then power consumption is improved, but the charging/discharging speed of the capacitor is limited and the response speed of the error voltage becomes slow
Solution Approach 1:
The feed forward capacitor is charged in advance during normal operation to store energy. When voltage change is required, the stored charge is discharged to rapidly change the error voltage, providing preliminary action that enables fast response without increasing the gm amplifier's operating current during quiescent state.
Solution Approach 2:
The feed forward capacitor is periodically charged during normal operation and then discharged when voltage transition is needed. This periodic charging and discharging enables the system to maintain low quiescent current while providing high-speed response capability when required.
2Speed
If the operating current of the gm amplifier is increased to speed up voltage changes, then response speed is improved, but quiescent current increases
Solution Approach 1:
The feed forward capacitor is charged in advance during normal operation to store energy. When voltage change is required, the stored charge is discharged to rapidly change the error voltage, providing preliminary action that enables fast response without increasing the gm amplifier's operating current during quiescent state.
Solution Approach 2:
The feed forward capacitor acts as an intermediary energy storage element between the power supply and the gm amplifier output. It mediates the voltage change requirement by providing or absorbing charge as needed, enabling fast voltage transitions without requiring continuous high current from the gm amplifier, thus maintaining low quiescent current while achieving high voltage change speed when required.
Data Source
AI summary
A control circuit of a DC/DC converter includes: an error amplifier configured to generate an error voltage corresponding to an error between a feedback voltage based on an output voltage of the DC/DC converter and a reference voltage; a pulse modulator configured to generate a control pulse corresponding to the error voltage; and an auxiliary circuit configured to be enabled, when the output voltage of the DC/DC converter is decreased, to compare the feedback voltage with a ramp signal that decreases with time, and source or sink an auxiliary current to an output of the error amplifier according to a result of the comparison.