Soft Start Circuit Clock-Driven Charging
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Solution Overview
Problem
Existing soft start circuits in power supply devices face challenges in achieving high-accuracy soft start times due to deviations caused by varying current flows when transistors are turned ON and OFF, leading to inconsistencies in capacitor charging.
Innovation Solution
A soft start circuit design incorporating a constant current source, PMOS transistors, and a capacitor, where the second transistor receives a clock signal and determines the current flow to the capacitor, ensuring consistent current delivery even when the transistor is ON or OFF, allowing for stable soft start voltage rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a capacitor with high capacitance value is used to obtain a soft start voltage that rises in a few milliseconds, then the soft start time can be controlled, but the circuit occupies a large area within an IC chip
Solution Approach 1:
The patent applies periodic action by using a clock signal to intermittently charge the capacitor through periodic switching of the transistor. Instead of continuous charging that would require a large capacitor, the capacitor is charged in periodic intervals, reducing the required capacitance value and IC chip area while maintaining the desired soft start time.
Solution Approach 2:
The patent changes the charging parameters by using intermittent charging with a clock signal instead of continuous charging. This parameter change allows the use of a smaller capacitor with lower capacitance value, thereby reducing the IC chip area occupation while achieving the same soft start time performance.
2Area of stationary object
If a capacitor is intermittently charged with a constant current using a clock signal to reduce the capacitor size, then the circuit scale is suppressed, but the operating point of the transistor differs when turned ON and OFF causing current deviation
Solution Approach 1:
The patent introduces an intermediary mechanism by using a current mirror circuit composed of transistors Q3 and Q4. This current mirror compensates for the operating point differences of the switching transistor Q2, ensuring that the charging current remains constant and accurate regardless of whether Q2 is in ON or OFF state, thereby achieving high-precision soft start time control.
Solution Approach 2:
The patent implements feedback through the current mirror configuration where the charging current is continuously adjusted based on the switching state. The current mirror provides feedback compensation that maintains a consistent charging current through the capacitor despite changes in the switching transistor's operating point, ensuring accurate soft start timing.
3Device complexity
If the transistor is turned OFF to stop the current as in Patent Document 1, then the circuit is simplified, but the operating point is not determined and desired current cannot flow consistently
Solution Approach 1:
The patent ensures continuity of useful action by maintaining current flow through the capacitor during both ON and OFF states of the switching transistor. The current mirror circuit continuously provides the charging current, ensuring that the useful action of charging the capacitor remains continuous and reliable, improving soft start time accuracy.
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
This design achieves high-accuracy soft start times by maintaining a consistent current flow and operation point, reducing errors and improving the accuracy of the soft start process.
Implementation Method 1
a capacitor connected between the second transistor and the ground terminal
Implementation Method 2
a constant current source, an output terminal which outputs a soft start voltage
Data Source
AI summary
To provide a soft start circuit capable of obtaining a high-accuracy soft start time. The soft start circuit is equipped with a constant current source, an output terminal which outputs a soft start voltage, a ground terminal, a first transistor which is connected between the constant current source and the ground terminal and has a gate and a drain both short-circuited, a second transistor which is connected between the constant current source and the output terminal and receives a clock signal at a gate thereof, and a capacitor connected between the second transistor and the ground terminal.