Pseudo-Constant-On-Time Power Converter Control Circuit
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Solution Overview
Problem
In power converters with pseudo-constant-on-time (PCOT) control, the small amplitude of the ramp compensation signal can lead to an unstable system due to its dependence on the duty cycle, which varies with output voltage variations.
Innovation Solution
A control circuit for power converters that includes an on-time generating circuit, a ramp compensation circuit, a ramp regulating circuit, and a comparison circuit, where the ramp compensation signal amplitude is proportional to 1−D and the ramp regulating signal amplitude is proportional to D, ensuring a constant amplitude sum signal that is independent of the duty cycle, stabilizing the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCOT control is applied to keep switching frequency constant, then switching frequency stability is improved, but ramp compensation signal amplitude becomes dependent on duty cycle causing system instability
Solution Approach 1:
The ramp compensation signal is segmented into two separate signals: a first ramp compensation signal with amplitude proportional to (1-D) and a second ramp compensation signal with amplitude proportional to D. This segmentation allows independent control of each signal's amplitude characteristics, resolving the issue where a single ramp compensation signal's amplitude varies with duty cycle and causes instability.
Solution Approach 2:
The invention changes the amplitude parameters of the two ramp compensation signals dynamically based on duty cycle D. The first signal's amplitude is set proportional to (1-D) while the second signal's amplitude is set proportional to D. This parameter change strategy ensures that the combined compensation effect remains stable across varying duty cycles, solving the stability problem in PCOT control.
2Adaptability or versatility
If duty cycle varies with output voltage, then power converter adaptability is improved, but ramp compensation signal amplitude varies causing instability
Solution Approach 1:
The invention introduces dynamic adjustment mechanisms where the amplitudes of the two ramp compensation signals are continuously adapted based on the current duty cycle D. As duty cycle varies with output voltage, the first ramp compensation signal amplitude dynamically changes proportionally to (1-D) and the second signal amplitude dynamically changes proportionally to D. This dynamic adaptation maintains system stability while allowing full adaptability to output voltage variations.
Data Source
AI summary
A control circuit for controlling a switching circuit is disclosed. The control circuit has a ramp compensation circuit, a ramp regulating circuit and a comparison circuit. The ramp compensation circuit generates a ramp compensation signal with the amplitude proportional to the difference between 1 and the duty cycle of a main switch of the switching circuit. The ramp regulating circuit generates a ramp regulating signal with the amplitude proportional to the duty cycle of the main switch. The comparison circuit compares a reference signal with the sum of the ramp compensation signal, the ramp regulating signal and a feedback signal representative of an output voltage of the switching circuit, so as to provide a comparison result to control the switching circuit.