PWM Soft-Start Circuit for Capacitive Inrush Current Limiting
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Solution Overview
Problem
Existing soft-start circuits require large metal-oxide semiconductor (MOS) transistors with a large safe operating area, leading to increased layout area and costs due to the need for current limiting and protection against infinite current spikes during power-on in capacitive loads.
Innovation Solution
A soft-start circuit configuration that includes a controller, switch unit, free-wheeling unit, energy storage unit, and energy release unit, allowing for reduced requirements on the switch unit, enabling the use of smaller components and reducing the overall size and cost of the circuit by operating in a pulse width modulation mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOS transistor with a large safe operating area is used to implement current limiting soft-start, then the soft-start function is achieved, but the package size is large and layout area increases
Solution Approach 1:
The patent divides the soft-start function into two separate stages: a first soft-start stage using a first MOS transistor and a second soft-start stage using a second MOS transistor. This segmentation allows each transistor to be optimized for its specific function, with the first transistor handling initial current limiting and the second transistor taking over for continued soft-start, thereby reducing the size requirements for individual components while maintaining overall reliability.
Solution Approach 2:
The patent implements periodic switching between two MOS transistors in different time periods. The first MOS transistor operates during an initial time period for primary current limiting, then switches to the second MOS transistor for continued soft-start operation. This periodic action allows the system to achieve comprehensive soft-start protection while using smaller, more compact transistor components.
2Reliability
If a MOS transistor with a large safe operating area is selected for current limiting, then soft-start is achieved, but the package size increases and costs increase
Solution Approach 1:
The patent segments the current limiting function across two different MOS transistors operating in different time periods. The first MOS transistor handles initial current limiting with moderate specifications, while the second MOS transistor continues the soft-start process. This segmentation eliminates the need for a single oversized transistor, reducing component costs and manufacturing complexity while maintaining adequate current limiting capability throughout the soft-start process.
Solution Approach 2:
The patent employs two MOS transistors with relatively modest specifications rather than one expensive, high-capacity transistor. By using multiple smaller, more economical components in sequence, the system achieves the same protective function at lower overall cost, making the design more economically viable for mass production.
3Reliability
If a MOS transistor with a large safe operating area is used, then soft-start is achieved, but the size occupied by the entire soft-start circuit increases
Solution Approach 1:
The patent divides the soft-start protection function into two sequential stages using separate MOS transistors. The first MOS transistor provides initial current limiting during an early time period, then the second MOS transistor continues the soft-start process. This segmentation allows each transistor to be smaller in size since they share the protective function over time, reducing the total volume occupied by the soft-start circuit compared to using a single large transistor.
Solution Approach 2:
The patent implements time-based periodic switching between two MOS transistors to provide continuous soft-start protection. The first transistor operates during an initial time period, then the second transistor takes over for subsequent operation. This periodic action enables the use of smaller transistor components while maintaining comprehensive protection, thereby reducing the overall circuit footprint and volume.
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 solution effectively reduces the size and cost of the soft-start circuit and power supply device while ensuring safe and controlled power supply to capacitive loads, improving safety and reducing electromagnetic interference.
Implementation Method 1
In a first time period, the controller is configured to control the switch unit to be on, so that the power module charges the energy storage unit through the energy release unit. In a second time period, the controller is configured to control the switch unit to be off, so that the energy release unit discharges the energy storage unit through the free-wheeling unit.
Data Source
AI summary
This application provides a soft-start circuit, a control method thereof, and a power supply device. The soft-start circuit includes a controller, a switch unit, a free-wheeling unit, an energy storage unit, and an energy release unit. In a first time period, the controller is configured to control the switch unit to be on, so that the power module charges the energy storage unit through the energy release unit. In a second time period, the controller is configured to control the switch unit to be off, so that the energy release unit discharges the energy storage unit through the free-wheeling unit. The first time period and the second time period are one operating cycle. According to embodiments of this application, a soft-start function can be implemented. In addition, a smaller size is occupied, and costs are reduced.