Switching Control Circuit Terminal Merging for Soft Start and Power Limiting
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Solution Overview
Problem
In switching power supply apparatuses, the increasing number of functions in switching control ICs leads to an increase in the number of terminals, resulting in larger IC packages and higher unit costs, while limiting the number of terminals restricts the functions provided, necessitating multiple types of ICs and increasing manufacturing and management complexity.
Innovation Solution
A switching control circuit with a soft start terminal that uses a soft start controller and a maximum on-pulse period limiting device, incorporating a voltage-period conversion circuit and a constant current circuit, allows for the integration of soft start and power limiting functions using a single terminal, reducing the number of terminals and IC size while maintaining functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of functions in switching control IC is increased, then the capability and functionality are improved, but the number of terminals increases, leading to larger IC package size and higher unit cost
Solution Approach 1:
The patent combines the soft start function and power limiting function into a single terminal (terminal 20). The soft start controller and maximum on-pulse period limiting device share this terminal, allowing both functions to be controlled through a single interface point. This merging of functions reduces the total number of terminals required on the IC package.
Solution Approach 2:
Terminal 20 serves multiple purposes: it is used for soft start control during initialization and for power limiting during normal operation. The single terminal provides universal control for both soft start and power limiting functions, eliminating the need for separate dedicated terminals for each function.
2Adaptability or versatility
If the number of terminals in switching control IC is increased, then more functions can be provided, but the unit cost of the IC increases
Solution Approach 1:
The patent merges the control interfaces for soft start and power limiting into a single terminal, reducing the total terminal count. Fewer terminals mean simpler packaging and lower manufacturing costs per unit.
Solution Approach 2:
By making terminal 20 a multi-functional terminal that handles both soft start and power limiting, the IC can provide more functions without proportionally increasing the terminal count, thereby controlling unit cost.
3Area of stationary object
If the number of terminals is limited, then the IC size and cost are reduced, but the provided functions are limited, necessitating multiple types of ICs
Solution Approach 1:
The patent combines multiple control functions into a single terminal interface, allowing the IC to provide both soft start and power limiting functions without requiring additional terminals. This enables feature-rich ICs with compact packaging.
Solution Approach 2:
Terminal 20 is designed as a universal control terminal that can perform both soft start control and power limiting. This multi-functionality allows a single IC type to serve multiple application needs, reducing the variety of IC types required.
Data Source
AI summary
In a switching control circuit, a length of a soft start period is set by a time constant of an external circuit that is connected to a soft start terminal of a switching control IC. After a voltage of the soft start terminal has reached a predetermined voltage at the termination of the soft start period, the on-pulse period of a first switching device is limited by a maximum value. When a Zener diode is connected between the soft start terminal and ground, the upper limit voltage of the soft start terminal is a Zener voltage and, hence, the maximum on-pulse period is limited by this voltage. As a result, the switching control circuit and a switching power supply apparatus, which have a soft start function and a power limiting function, are reduced in size and cost by limiting the number of terminals.