Power Supply IC Timing Correction for High Power Factor
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Solution Overview
Problem
Existing power factor correction circuits face challenges in reducing switching loss while maintaining a high power factor, as turning on a transistor after a predetermined time period since the inductor current reaches zero can lead to negative inductor currents, deteriorating the power factor.
Innovation Solution
An integrated circuit is designed to control the switching of a transistor in a power supply circuit, using a delay circuit to generate a delayed on-signal and a correction circuit to adjust the command values based on the time period and ratio, ensuring the transistor is turned on for a longer time period to compensate for negative inductor currents, thereby correcting the power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the transistor is turned on after a predetermined time period since the inductor current reaches zero, then switching loss is reduced, but the power factor deteriorates due to negative inductor current
Solution Approach 1:
The integrated circuit performs preliminary detection of when the inductor current reaches zero and pre-calculates the optimal turn-on timing, then applies a predetermined delay to this detected timing. This preliminary action allows the system to anticipate the optimal switching moment rather than reacting after the delay has already occurred, thereby reducing switching loss while preventing excessive negative current.
Solution Approach 2:
The system continuously monitors the inductor current and uses this feedback information to dynamically adjust the turn-on timing of the transistor. By comparing the actual current waveform with the desired waveform, the control circuit optimizes the switching timing to minimize both switching loss and negative current duration, resolving the contradiction between these two parameters.
2Productivity
If the transistor is turned on for a longer time period to compensate for negative inductor current, then the power factor is improved, but switching loss increases
Solution Approach 1:
The system dynamically adjusts the transistor on-time based on real-time detection of the inductor current waveform and the calculated negative current duration. Rather than using a fixed extended on-time, the control circuit optimizes the duty cycle dynamically to achieve the minimum necessary conduction time to cancel negative current while minimizing switching losses. This dynamic adjustment resolves the contradiction by finding the optimal balance point.
Solution Approach 2:
The system changes the switching parameters (turn-on timing and on-duration) based on the detected operating conditions and calculated negative current characteristics. By continuously optimizing these parameters rather than using fixed values, the system achieves improved power factor correction while minimizing the increase in switching loss, effectively resolving the contradiction between these two performance parameters.
Data Source
AI summary
An integrated circuit for a power supply circuit, including: a first command value output circuit outputting a first command value to turn on a transistor of the power supply circuit for a first time period; an on signal output circuit outputting an on signal to turn on the transistor; a delay circuit delaying the on signal by a predetermined time period; a correction circuit correcting the first command value, to output a second command value to turn on the transistor for a second time period; and a driver circuit turning on and off the transistor based respectively on the delayed on-signal and the second command value. The correction circuit corrects the first command value based on the predetermined time period and a ratio between the second time period and another time period from when the transistor is turned off to when an inductor current of the power supply circuit reaches a predetermined value.