Soft-Start Switching Power Converter with Pulse-Frequency Modulation
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Solution Overview
Problem
Conventional flyback switching power converting apparatuses experience inrush currents during startup, which can damage components due to the sudden increase in primary side current.
Innovation Solution
A switching power converting apparatus comprising a voltage conversion module, a detecting unit, and a switching signal generating unit, where the detecting unit generates a detecting signal based on the output voltage and a reference voltage, and the switching signal generating unit adjusts the switching signal to gradually increase the secondary side current during startup, preventing inrush currents by controlling the switching frequency and duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the duty cycle of the PWM signal is maximized to raise output voltage quickly during startup, then the output voltage rises faster, but the primary side current becomes an inrush current that may damage the transistor
Solution Approach 1:
The patent applies preliminary action by generating a soft-start signal before normal operation to gradually increase the duty cycle from zero to maximum over a predetermined time period. This preliminary soft-start phase prevents inrush current by controlling the transistor to conduct gradually rather than immediately at full duty cycle, thus protecting the transistor while still achieving output voltage rise during startup.
2Reliability
If a soft-start mechanism is implemented to prevent inrush current, then component protection is improved, but the output voltage rising speed may be reduced
Solution Approach 1:
The patent applies dynamics by making the duty cycle adjustable and time-dependent rather than fixed. The duty cycle dynamically changes during startup from zero to maximum according to the soft-start signal, allowing the system to balance between protection and speed. After startup, the duty cycle can be adjusted based on output voltage feedback to maintain optimal performance, thus resolving the trade-off between protection and speed.
3Ease of operation
If pulse width modulation (PWM) is used to control the transistor, then the output voltage can be regulated, but inrush current occurs at startup when the duty cycle is maximum
Solution Approach 1:
The patent introduces a soft-start signal as an intermediary between the PWM control and the transistor gate. This soft-start signal acts as a mediator that gradually enables the PWM duty cycle rather than allowing immediate maximum duty cycle application. The soft-start signal thus mediates between the need for PWM-based voltage regulation and the need to prevent inrush current, allowing both functions to coexist by controlling the timing and rate of duty cycle application.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The apparatus is able to soft-start, avoiding inrush currents and ensuring stable output voltage by gradually increasing the secondary side current, thus protecting components and maintaining voltage stability.
Implementation Method 1
The voltage conversion module is operable, based on a switching signal having a switching frequency, to generate a secondary side current flowing through the first secondary winding of the transformer so as to output an output voltage associated with the secondary side current, and to generate a sensing voltage across the second secondary winding. The sensing voltage is associated with a winding turns ratio of the first secondary winding to the second secondary winding, and the output voltage.
Data Source
AI summary
A switching power converting apparatus includes a voltage conversion module, a detecting unit, and a switching signal generating unit. The voltage conversion module converts an input voltage into an output voltage associated with a secondary side current, which flows through a secondary winding of a transformer and is generated based on a switching signal. The detecting unit generates a detecting signal based on the output voltage and a predetermined reference voltage. The switching signal generating unit generates the switching signal based on the detecting signal and an adjusting signal so that the secondary side current is gradually increased during a start period of the switching power converting apparatus.