Switching Converter Hysteresis Control for Stable Fixed Frequency
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Solution Overview
Problem
Fixed frequency peak current control in switching converters results in a minimum ON time period for the main switch, leading to increased output voltage ripple and instability due to inherent control circuit delays.
Innovation Solution
A controller with a hysteresis generating circuit and switching control circuit that adjusts upper and lower hysteresis limits based on output voltage and frequency, allowing smooth transitions between modes to stabilize output voltage and maintain constant switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fixed frequency peak current control is used, then switching frequency is maintained, but output voltage ripple increases and stability deteriorates when input voltage increases
Solution Approach 1:
The patent implements dynamic switching between two control modes: peak current control mode and hysteresis control mode. The controller dynamically selects the appropriate mode based on operating conditions, allowing the system to adapt to varying input voltages and maintain both frequency stability and voltage regulation performance
Solution Approach 2:
The patent changes the control parameter from fixed frequency to variable frequency with hysteresis bandwidth adjustment. By dynamically adjusting the hysteresis bandwidth parameter based on operating conditions, the system maintains stability across different input voltage ranges while preventing the main switch ON time from reaching minimum limits
2Speed
If main switch ON time period decreases to minimum, then switching frequency increases, but output voltage goes up and large ripple arises
Solution Approach 1:
The patent applies preliminary anti-action by using hysteresis control to prevent the main switch ON time from decreasing to the minimum period. The hysteresis mechanism anticipates the problem of excessive frequency increase and voltage ripple by adjusting the switching threshold in advance, thereby preventing the adverse effect before it occurs
Solution Approach 2:
The patent introduces an intermediary control mechanism (hysteresis control circuit) that mediates between the peak current control and the main switch operation. This intermediary layer adjusts the switching thresholds dynamically, preventing direct coupling between input voltage changes and main switch ON time, thus avoiding excessive frequency increase and voltage ripple
Data Source
AI summary
A controller for a switching converter has a hysteresis generating circuit to provide an upper hysteresis limit and a lower hysteresis limit based on an output voltage, a switching control circuit for providing a switching control signal, and a frequency locking circuit for adjusting one of the upper hysteresis limit and the lower hysteresis limit based on the switching control signal and a clock signal. When the switching converter is in a first mode, a main switch of the switching converter is turned ON by comparing a current sense signal representative of a current flowing through the main switch with the lower hysteresis limit, and is turned OFF by comparing the current sense signal with the upper hysteresis limit. When the switching converter is in a second mode, the main switch is turned ON based on the clock signal, and is turned OFF based on the current sense signal.