Voltage Regulator Soft-Start Circuit Using Reference Voltage Ramp-Up
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Solution Overview
Problem
Voltage regulators experience excessive current flow during start-up due to rapid ramp-up of output voltage, which can damage the regulator or prevent output, and existing solutions either increase cost and space with external capacitors or occupy die area with integrated capacitors.
Innovation Solution
A soft-start circuit that uses a transistor with low threshold voltage, an inverter, and resistors to generate a reference voltage that ramps up at the same rate as the supply voltage, avoiding the need for capacitors and preventing overvoltage protection false triggers during start-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charging capacitor is provided as an external component to control the ramp-up rate, then the regulator can avoid excessive current flow, but the cost and space requirements are increased
Solution Approach 1:
The patent integrates the soft-start functionality directly into the voltage regulator circuit by utilizing the existing reference current generator and regulator components. The reference voltage naturally ramps up at the same rate as the supply voltage due to the operational amplifier's operation, eliminating the need for separate external capacitors while maintaining protection against excessive current flow.
Solution Approach 2:
The voltage regulator circuit uses its own internal reference current generator and operational amplifier to generate a ramping reference voltage that automatically controls the output voltage ramp-up rate. The circuit serves its own soft-start function without requiring external components, reducing both cost and space requirements.
2Reliability
If a charging capacitor is provided as an integrated circuit component to control the ramp-up rate, then the regulator can avoid excessive current flow, but the die area is increased
Solution Approach 1:
The patent integrates the soft-start functionality directly into the voltage regulator circuit by utilizing the existing reference current generator and regulator components. The reference voltage naturally ramps up at the same rate as the supply voltage due to the operational amplifier's operation, eliminating the need for separate external capacitors while maintaining protection against excessive current flow.
Solution Approach 2:
The voltage regulator circuit uses its own internal reference current generator and operational amplifier to generate a ramping reference voltage that automatically controls the output voltage ramp-up rate. The circuit serves its own soft-start function without requiring external components, reducing both cost and space requirements.
3Speed
If the regulator output voltage snaps up quickly to intermediate voltage, then the regulator responds faster, but the ESD clamp turns on and generates large currents that can damage the regulator
Solution Approach 1:
The patent implements a preliminary ramping phase where the reference voltage is generated to increase at the same rate as the supply voltage during start-up. This preliminary controlled ramping action occurs before the regulator reaches its final operating state, preventing the ESD clamp from turning on due to excessive voltage rise rate while maintaining eventual fast response capability.
Solution Approach 2:
The patent dynamically adjusts the reference voltage ramp-up rate to match the supply voltage ramp-up rate during start-up, then transitions to normal regulation operation. This dynamic control allows the system to adapt its response characteristics based on the operating phase, protecting against damage during start-up while maintaining fast response during normal 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
This approach allows for a slow and controlled ramp-up of the regulator voltage, achieving a sufficient time constant without capacitors, thus reducing the area required and preventing damage from excessive current flow.
Implementation Method 1
a transistor having a low threshold voltage that turns on initially during a start-up period when a supply voltage starts to ramp up
Implementation Method 2
if the regulator has a resistor-capacitor (RC) triggered electrostatic discharge (ESD) clamp on its load
Implementation Method 3
if the regulator snaps up faster than the RC time constant of the ESD clamp
Implementation Method 4
an inverter coupled between the reference current generator and the transistor; an output signal from the inverter is provided to a gate of the transistor
Data Source
AI summary
An improved start-up (soft-start) circuit for use with voltage regulators, and an improved regulator start-up methodology. For example, an apparatus includes a voltage regulator circuit and a start-up circuit operatively coupled to the voltage regulator circuit. The start-up circuit is configured to provide a current signal, during a start-up period, that generates a reference voltage at a reference input of the voltage regulator circuit such that the reference voltage ramps up at a rate substantially equal to a ramp-up rate of a supply voltage coupled to the start-up circuit and the voltage regulator circuit.