DC/DC Converter Frequency Stabilization via Detection Transistor Feedback
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Solution Overview
Problem
Fixed ON time control DC/DC converters face challenges in noise resistance due to variations in switching frequency, leading to electromagnetic interference (EMI) noise and reduced noise resistance properties, especially when multiple converters operate together.
Innovation Solution
Incorporating a detection transistor and a level shifter within the DC/DC converter circuit to adjust the ON duty ratio based on the ON resistance of the high-side transistor, and using feedback resistors integrated into the circuit to stabilize the operating frequency and improve noise resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed ON time control is used to simplify circuit configuration and reduce power consumption, then switching frequency varies under light loads, but this causes electromagnetic interference noise and reduced noise resistance properties
Solution Approach 1:
The patent introduces a feedback mechanism where the switching frequency is detected and fed back to the control circuit. The control circuit adjusts the ON time of the switching element based on the detected frequency to maintain frequency stability. This feedback loop eliminates the frequency variation problem while keeping the fixed ON time control structure, thereby resolving the contradiction between simplified circuit configuration and electromagnetic interference reduction.
Solution Approach 2:
The patent makes the ON time dynamic by adjusting it based on the detected switching frequency. Although the basic structure uses fixed ON time control, the ON time is dynamically modified through the feedback mechanism to compensate for frequency variations. This dynamic adjustment maintains frequency stability without requiring a completely different control architecture, thus resolving the contradiction between simplicity and noise resistance.
2Loss of energy
If multiple DC/DC converters operate together with variable switching frequencies, then power consumption is reduced under light loads, but frequency variations cause mutual electromagnetic interference
Solution Approach 1:
The patent implements a feedback mechanism that detects the switching frequency and feeds it back to the control circuit. The control circuit dynamically adjusts the ON time based on the detected frequency to maintain frequency stability. This allows multiple converters to operate at stable, coordinated frequencies, eliminating mutual electromagnetic interference while preserving the energy-saving benefits of fixed ON time control under light loads.
Solution Approach 2:
The patent changes the ON time parameter dynamically based on the detected switching frequency. By adjusting this key parameter in response to frequency variations, the system maintains stable operating frequencies across multiple converters, preventing electromagnetic interference while keeping power consumption low under light load conditions.
3Stability of the object's composition
If ON time is reduced as input voltage increases to maintain constant switching frequency, then frequency stability is improved, but circuit complexity increases due to additional control components
Solution Approach 1:
The patent uses a feedback mechanism where the switching frequency is detected and fed back to the control circuit. The control circuit adjusts the ON time based on the detected frequency to maintain frequency stability. This feedback-based approach achieves frequency stability without requiring complex predictive control algorithms or multiple sensors, thus resolving the contradiction between frequency stability and circuit complexity.
Solution Approach 2:
The control circuit automatically adjusts the ON time based on feedback from the detected switching frequency without requiring external intervention or complex control logic. The system self-regulates to maintain frequency stability, achieving the desired performance with minimal additional complexity.
Data Source
AI summary
A DC/DC converter 10 has a high-side transistor QH as a switching element and a low-side transistor QL as a synchronous rectifier element. A first primary electrode D and secondary primary electrode S of the high-side transistor QH are connected to an input voltage VIN and an external terminal T1, respectively. A detection transistor QD is provided in a row with the high-side transistor QH, and the ON voltage of the high-side transistor QH when ON is output as detection voltage VQD from the detection transistor QD. The output detection voltage VQD is added to a feedback voltage VFB1 by an adder CB, and inputted to a comparator CMP1. The ON period of a one-shot pulse PS1 outputted from the comparator CMP1 is regulated so as to be in direct proportion to the sum of the detection voltage VQD and the feedback voltage VFB1.