Constant-Voltage Circuit Soft Start Inrush Current Control
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Solution Overview
Problem
Constant-voltage circuit devices face issues with high inrush currents at startup, leading to potential power source voltage drops and device malfunctions, which are not effectively addressed by existing solutions that either increase power source capacity or consumption, or introduce noise with soft start functions.
Innovation Solution
A constant-voltage circuit device incorporating a soft start circuit with a capacitor and current control unit that gradually increases the reference voltage at startup, restricting inrush current and preventing output voltage overshoot, while maintaining low electrical consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power source capacity is increased to handle inrush current, then the inrush current problem is solved, but the device cost and size increase
Solution Approach 1:
The patent applies preliminary action by pre-charging the output capacitor through a dedicated charge current path before the main power switch is activated. This is achieved by using a first switch connected in parallel with the main power switch and controlled by a control signal that enables pre-charging phase. The output capacitor is charged to a predetermined voltage level before the main power switch turns on, which prevents excessive inrush current when the main switch activates.
2Reliability
If a soft start function is introduced to restrict inrush current, then the inrush current is limited, but noise is generated and electrical consumption increases
Solution Approach 1:
The patent segments the power switch into two distinct components: a main power switch for normal operation and a first switch for pre-charging. This segmentation allows independent control of the pre-charging function. The first switch is controlled by a dedicated control signal that activates only during startup to charge the output capacitor, then turns off. This eliminates the need for continuous soft-start control circuits that generate noise and consume power, while still achieving effective inrush current restriction.
3Reliability
If the output capacitor capacity is increased to reduce inrush current duration, then the inrush current time is reduced, but the device size and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-charging the output capacitor to a predetermined voltage level before the main power switch activates. This is controlled by a control signal that enables a first switch to charge the capacitor in advance. By setting the predetermined voltage appropriately, the patent reduces the voltage difference that needs to be charged when the main switch turns on, thereby reducing inrush current duration without requiring an oversized capacitor.
4Productivity
If the limit current is increased to allow faster charging, then the charging speed increases, but the inrush current becomes excessively high
Solution Approach 1:
The patent applies preliminary action by performing the charging operation in two distinct phases: a pre-charging phase where the first switch charges the output capacitor to a predetermined voltage level, and a main operation phase where the main power switch provides limited current. The control signal coordinates these phases by activating the first switch before the main switch and deactivating it when pre-charging is complete. This eliminates the conflict between fast charging and inrush current limitation by separating the high-current pre-charge function from the limited-current main operation.
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 restricts inrush currents, prevents output voltage overshoot, and ensures stable startup without increasing power consumption or introducing noise, thereby enhancing the reliability and efficiency of the constant-voltage circuit.
Implementation Method 1
a capacitor for soft start that is charged at startup
Data Source
AI summary
A constant-voltage circuit converts a voltage input to an input terminal and outputs a predetermined constant voltage from an output terminal. The constant-voltage circuit includes an output transistor to output an electrical current to the output terminal in response to a control signal, a reference voltage circuit to generate a predetermined reference voltage, a control circuit to adjust a voltage proportional to the output voltage output from the output terminal to the reference voltage output from the reference voltage circuit by controlling the output transistor and a soft start circuit including a capacitor for soft start that is charged at start-up and a current control unit to control an electrical current supplied to the reference voltage circuit. The current control unit adjusts the reference voltage to a voltage determined by the capacitor for soft start at the start-up until the reference voltage reaches a desired voltage.