Switching Converter Control Circuit for Current Mode Operation
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Solution Overview
Problem
The existing DC/DC converters face challenges in configuring a duty controller as a modulator of a current mode due to the voltage-dependent nature of the voltage feedback, making it difficult to perform current mode control effectively while providing overcurrent protection.
Innovation Solution
A control circuit is introduced that includes a sample hold circuit, a variable amplifier with gain adjustment based on the output voltage, a duty controller generating pulse modulation signals, and an overcurrent protection circuit, allowing for current mode control using differential voltages and ensuring overcurrent protection through current detection signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage feedback is used for control, then output voltage stabilization is achieved, but current mode control cannot be performed due to voltage dependency
Solution Approach 1:
The feedback signal is segmented into two independent components: voltage feedback (VFB) for output voltage stabilization and current feedback (VCS) for current mode control. This segmentation allows each feedback path to perform its specific function independently without interference, resolving the contradiction between voltage stabilization and current mode control capability
Solution Approach 2:
The detection resistor RCS acts as an intermediary element that converts coil current into a voltage signal (VCS) that can be processed by the duty controller. This intermediary transformation enables current mode control by providing a current-proportional voltage signal that is independent of output voltage, while voltage feedback continues to handle voltage stabilization separately
2Reliability
If overcurrent protection is added to DC/DC converter, then safety is improved, but device complexity increases due to additional external circuits
Solution Approach 1:
The overcurrent protection function is merged with the existing duty controller by utilizing the current feedback signal VCS from the detection resistor RCS. The duty controller integrates both voltage feedback (VFB) and current feedback (VCS) processing, combining overcurrent protection and voltage control in a single integrated circuit rather than requiring separate external protection circuits
Solution Approach 2:
The duty controller is designed with multi-functionality to handle both voltage feedback processing for output stabilization and current feedback processing for overcurrent protection. This universal design allows a single controller to perform multiple functions that would traditionally require separate circuits, reducing overall device complexity while maintaining comprehensive protection
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 configuration enables current mode control and overcurrent protection by generating a differential voltage dependent only on the coil current, independent of the output voltage, thereby enhancing the operational flexibility and safety of the DC/DC converter.
Implementation Method 1
The DC/DC converter includes an output circuit and a control circuit. The output circuit includes a switching transistor, a detection resistor, a transformer, a rectifying diode, and an output capacitor
Implementation Method 2
The switching transistor and the detection resistor form a current loop with a primary coil of the transformer. The rectifying diode and the output capacitor are connected to a secondary coil of the transformer
Implementation Method 3
The rectifying diode and the output capacitor are connected to a secondary coil of the transformer
Implementation Method 4
The rectifying diode and the output capacitor are connected to a secondary coil of the transformer
Data Source
AI summary
A control circuit used in a switching converter having a coil, a switching transistor, and a detection resistor, includes: a current detection terminal configured to receive a detection voltage obtained by superimposing a voltage detection signal on a current detection signal; a sample hold circuit configured to sample-hold the detection voltage in an OFF period of the switching transistor to generate a sample hold voltage; a variable amplifier configured to amplify a difference between the sample hold voltage and the detection voltage; a duty controller configured to generate a pulse modulation signal; a driver configured to control the switching transistor based on the pulse modulation signal; and an overcurrent protection circuit configured to compare the detection voltage with a predetermined threshold voltage and change the pulse modulation signal to an OFF level of a switching transistor when the detection voltage is identical to the predetermined threshold voltage.