Power Converter Soft-Start Control via Dynamic On-Time Adjustment
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Solution Overview
Problem
Conventional resonant circuits in electronic apparatuses face issues with soft-start control, leading to voltage stress on switching elements, limited applicability to diode rectifier circuits, and increased cost due to high power density requirements.
Innovation Solution
An electronic apparatus with a converting circuit and a control circuit that compares feedback signals with target voltages to generate error voltages, outputting driving signals during startup based on error voltage thresholds, adjusting frequency accordingly to manage voltage stress and reduce complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional soft-start control using both PFM and PWM is adopted, then the resonant circuit can start up, but voltage stress on switching elements increases and energy loss occurs
Solution Approach 1:
The patent applies dynamics by making the switching element's on-time variable during startup. The control circuit dynamically adjusts the on-time based on feedback voltage levels, transitioning from longer on-times at low voltages to shorter on-times as voltage increases. This dynamic adjustment prevents fixed high voltage stress while enabling controlled startup, resolving the contradiction between reliable soft-start and voltage stress reduction.
Solution Approach 2:
The patent changes the timing parameter (on-time) of the switching element during the startup process. By varying the on-time duration based on the feedback voltage threshold comparisons, the system adapts the operating parameters to reduce voltage stress during critical startup phases while maintaining control reliability. This parameter change approach directly addresses the voltage stress issue during soft-start.
2Reliability
If phase shift control of output rectifier circuit is adopted, then soft-start can be achieved, but it is only applicable to synchronous rectification circuits and increases device complexity
Solution Approach 1:
The patent extracts the soft-start control function from the output rectifier circuit phase shift method and relocates it to the primary side control circuit. By taking out the phase shift requirement from the rectifier circuit and implementing equivalent control through primary side timing adjustment, the solution eliminates the need for complex synchronous rectification circuitry while maintaining soft-start functionality, thus reducing overall device complexity.
Solution Approach 2:
The patent creates a universal control approach that works with both diode rectifier circuits and synchronous rectifier circuits. The primary side control method using feedback voltage threshold comparison and dynamic on-time adjustment is applicable to various rectifier types, making the soft-start control universal rather than limited to synchronous rectification only. This multi-functionality reduces the need for circuit-specific control designs.
3Power
If additional circuits are added to meet high power density requirements, then power density increases, but the cost of electronic apparatus greatly increases
Solution Approach 1:
The patent implements self-service by using the existing feedback circuitry and voltage sampling nodes to control the switching element timing. The control circuit utilizes the feedback voltage itself (without additional sensing circuits) to determine when to adjust the on-time, making the existing circuitry serve dual purposes: power conversion feedback and startup control. This eliminates the need for additional dedicated control circuits, reducing manufacturing cost while maintaining power density.
Data Source
AI summary
An electronic apparatus includes a converting circuit and a first control circuit. The converting circuit converts an input voltage to an output voltage. The first control circuit compares a feedback signal representing the output voltage with a target voltage to generate an error voltage. When the electronic apparatus is on a starting-up status and the error voltage is not greater than a threshold voltage, the first control circuit outputs a first driving signal to drive the converting circuit according to the error voltage. When the electronic apparatus is on a starting-up status and the error voltage is greater than the threshold voltage, the first control circuit stops outputting the first driving signal. A frequency of the first driving signal is determined according to the error voltage.