Flyback Converter Control Circuit for Output Voltage Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Primary-controlled flyback converters face issues with inaccurate sense voltages due to shortened demagnetizing times when input voltage drops to a valley, leading to deviations in output voltage, especially when using a constant on time control scheme.
Innovation Solution
A control circuit that includes a current sense circuit, a voltage sense circuit, and a control signal generator, which switches between constant on time and peak current modes based on current thresholds and adjusts blanking time according to the current sense signal to maintain accurate voltage sensing and control of the power switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a constant on time control scheme is used, then the power conversion efficiency is improved, but the output voltage accuracy deteriorates when input voltage drops to valley
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant on-time control scheme to a dynamic control scheme that adapts the on-time duration based on real-time current sensing. The controller extends the on-time when primary current decreases (low input voltage conditions) to ensure sufficient demagnetizing time, thereby maintaining accurate output voltage regulation while preserving power conversion efficiency across varying input conditions.
Solution Approach 2:
The patent changes the control parameter (on-time duration) dynamically based on the primary current level. When the primary current falls below a threshold indicating low input voltage, the controller increases the on-time to guarantee minimum demagnetizing time. This parameter adaptation resolves the contradiction by maintaining both efficiency and voltage accuracy under varying operating conditions.
2Productivity
If the demagnetizing time is shortened due to low input voltage, then the switching frequency increases, but the sense voltage accuracy deteriorates
Solution Approach 1:
The patent applies preliminary anti-action by proactively extending the on-time before the demagnetizing time becomes insufficient. The controller monitors primary current and, upon detecting levels below a threshold (indicating impending demagnetizing time shortage), it preemptively increases the on-time to ensure the demagnetizing process completes adequately, preventing sense voltage inaccuracies before they occur.
Solution Approach 2:
The patent implements feedback by continuously sensing the primary current and using this information to adjust the on-time duration. The current sense circuit provides real-time feedback to the controller, which modulates the switching duty cycle to maintain adequate demagnetizing time, thereby preserving sense voltage accuracy while adapting to input voltage variations.
3Measurement precision
If the on time is extended to maintain demagnetizing time, then the output voltage accuracy is improved, but the power conversion efficiency decreases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the on-time duration based on actual operating conditions rather than using a fixed extended time. The controller increases on-time only when necessary (when primary current indicates low input voltage requiring longer demagnetizing), and maintains normal on-time when conditions permit, thereby achieving voltage accuracy without unnecessary efficiency penalties.
Solution Approach 2:
The patent uses dynamics to create an adaptive control system that responds to real-time current conditions. Rather than statically extending on-time for all conditions, the system dynamically modulates on-time duration to match actual demagnetizing requirements, optimizing both voltage accuracy and power conversion efficiency across different operating points.
Data Source
AI summary
In one embodiment, a control circuit configured to control a power stage circuit of a primary-controlled flyback converter, can include: (i) a current sense circuit that generates a current sense signal by sampling a primary current; (ii) a voltage sense circuit that generates a voltage sense signal by sampling an auxiliary voltage after a blanking time has elapsed; (iii) a control signal generator that generates a switch control signal according to the voltage sense signal and the current sense signal; and (iv) the switch control signal being configured to control a power switch of the power stage circuit, where the switch control signal is active during a constant on time.