Constant On-Time PWM Converter Control Circuit for Transient Response
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Solution Overview
Problem
Constant on-time PWM switching converters experience increased switching frequency and reduced efficiency during load transients, leading to slower response times and higher switching losses due to the rapid triggering of on-time and off-time cycles without adequate time for recovery.
Innovation Solution
A control circuit and method that prolongs the on-time during load transients, allowing for a variable on-time that is longer than the constant on-time, but not exceeding a predetermined maximum, to decrease switching frequency and switching losses, while ensuring efficient recovery of output voltage and improved transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the constant on-time PWM control method is used, then the converter operates efficiently in steady state, but the switching frequency increases excessively during load transients causing higher switching losses
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed constant on-time control to a dynamic variable on-time control during load transients. The control circuit detects load transient conditions and dynamically adjusts the on-time duration to be longer than the constant on-time, which reduces the switching frequency during transients and thereby reduces switching losses while maintaining the ability to recover output voltage efficiently.
2Loss of time
If the constant on-time is used, then the control is simple, but the recovery time for output voltage is prolonged during load transients
Solution Approach 1:
The patent implements feedback by monitoring the output voltage and detecting load transient conditions. When a load transient is detected, the control circuit activates a different on-time generation path that provides a longer on-time duration, enabling faster recovery of the output voltage. This feedback mechanism allows the system to adapt its on-time based on operating conditions without requiring complex external control.
Solution Approach 2:
The patent prepares for load transients by having multiple on-time generation paths ready in advance. When a transient condition is detected, the system switches to a pre-configured longer on-time path, allowing immediate action to extend the on-time and speed up voltage recovery without needing to calculate or adjust parameters in real-time during the transient event.
3Productivity
If the minimum off-time is fixed, then the control is straightforward, but the switching frequency cannot be reduced during transients
Solution Approach 1:
The patent segments the on-time control into multiple independent generation paths: one for constant on-time operation and another for variable extended on-time operation. Each path has its own on-time generation circuitry, allowing the system to select between them based on load conditions. This segmentation enables flexible switching frequency control during transients while keeping each individual control path relatively simple.
Data Source
AI summary
A control circuit provides a control signal for a constant on-time PWM switching converter to produce an output voltage, such that the converter operates with a constant on-time at a first state and operates with a variable on-time at a second state, so as to decrease the switching frequency and thereby the switching loss, to increase the efficiency of the converter, to improve the transient response, and to reduce the recovery time of the output voltage.