Soft-Start Device Smooth Switching Without External Capacitors
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Solution Overview
Problem
Existing soft-start devices face challenges in controlling the switching time point, leading to discontinuous surges and instability, and require external large capacitors to prolong the soft-start time, increasing cost and integration difficulties.
Innovation Solution
A soft-start device utilizing a soft switching circuit and an attenuation circuit to achieve smooth switching and prolonged soft-start time without additional pins or external capacitors, using a current source, transistors, and an amplifier with an attenuation circuit to gradually increase the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch is used to switch back to closed loop when ramp voltage approaches fixed voltage source value, then soft-start mechanism ends and system restores to normal operation, but switching time point is hard to control causing discontinuous surges and system instability
Solution Approach 1:
The patent introduces a third transistor as an intermediary component between the first and second transistors. This third transistor acts as a buffer that smoothly transitions the switching process, preventing direct abrupt switching between open and closed loops. The intermediary transistor ensures continuous current flow while enabling the transition, thereby eliminating discontinuous surges and improving system stability without making switching time point control difficult.
2Reliability
If current source is made small and capacitor is made large to prolong soft-start time, then power supply voltage rises more gradually avoiding circuit damage, but additional pin and externally connected large capacitor are required increasing cost and integration difficulty
Solution Approach 1:
The patent merges the soft-start timing function with the existing transistor circuit structure. Instead of using a separate external capacitor connected through an additional pin, the invention utilizes the inherent capacitance and resistance characteristics of the integrated transistor network to achieve the desired soft-start time constant. This integration approach eliminates the need for external components while maintaining circuit protection functionality.
Solution Approach 2:
The patent enables the circuit to generate its own soft-start timing characteristics using internal components. The transistor network self-regulates the voltage rise rate through its inherent electrical properties, eliminating the need for external timing components. The circuit serves its own timing function, reducing device complexity and integration requirements while maintaining reliable circuit protection during power-on.
Data Source
AI summary
A soft-start device including a current source, a first transistor, and a second transistor is described. The first transistor is coupled to the current source, and an amount of current conducted by the first transistor is determined according to a voltage. The second transistor is also coupled to the current source, and an amount of current conducted by the second transistor is determined according to a fixed bias. An initial voltage value of the voltage is smaller than a voltage value of the fixed bias. However, after a soft start, the voltage value of the first voltage is increased gradually to be larger than the voltage value of the fixed bias, such that the soft start may be implemented smoothly.