Buck Converter CV CC Control Circuit
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Solution Overview
Problem
Non-isolated buck converters face challenges in providing both constant voltage (CV) and constant current (CC) control, as they are often limited to either CV or CC control, and are susceptible to changes in input line voltage.
Innovation Solution
A control circuit for a buck converter that includes a power switch, an input line voltage sampling circuit, and a constant-voltage (CV) and constant-current (CC) control module, which uses pulse-width-modulation (PWM) or pulse-frequency-modulation (PFM) to maintain a constant peak inductor current and output voltage, even when the input line voltage changes, by sampling the input line voltage and output voltage to determine a reference voltage for controlling the power switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If non-isolated buck converter uses conventional control, then circuit complexity is reduced, but ability to provide both constant voltage and constant current control deteriorates
Solution Approach 1:
The control circuit is designed to perform both constant voltage (CV) and constant current (CC) control functions within a single integrated system. The control module includes a voltage control unit that regulates output voltage and a current control unit that regulates output current, allowing the non-isolated buck converter to serve multiple control purposes without requiring separate circuits for each function.
2Device complexity
If non-isolated buck converter shares ground terminal, then device complexity is reduced, but output voltage stability deteriorates when input line voltage changes
Solution Approach 1:
An isolated control circuit is introduced as an intermediary component between the non-isolated power stages. This isolated control circuit receives feedback signals from the output stage through galvanic isolation, processes the feedback, and generates control signals for the power switch. The isolation barrier prevents input line voltage variations from directly affecting the output voltage, thereby maintaining stability while still allowing the simplified ground-sharing topology.
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 ensures that the buck converter maintains constant output current and voltage despite changes in the input line voltage, effectively addressing the limitations of conventional non-isolated power supplies by integrating both CV and CC control.
Implementation Method 1
Magnetic energy is stored in the inductance when the switch is turned on, and the energy is transferred to the output when the switch is turned off
Implementation Method 2
A switching mode controller rapidly switches a power transistor on and off with a variable duty cycle or variable frequency and provides an average output that is the desired output voltage
Data Source
AI summary
A control circuit is provided for a buck converter that includes at least an inductor coupled to an output of the buck converter. The control circuit includes a power switch configured for coupling to a line voltage and configured for charging the inductor, an input line voltage sampling circuit, and a constant-voltage (CV) and constant-current (CC) control module coupled to the power switch. During a charging period of the inductor, the CV and CC control module is configured to control the power switch to provide a constant output current by maintaining a constant peak inductor current, even when the input line voltage changes. During a discharging period of the inductor, the CV and CC control module is configured to monitor the sensed output voltage to control the power switch to provide a constant output voltage.