Track Regulator Soft-Start Circuit Using Feedback Current Injection
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Solution Overview
Problem
Implementing a soft-start function in track regulators to prevent inrush current and overshoot voltage during startup is challenging, especially in 5V range applications, due to limitations in N-channel input amplifiers and feedback loops, leading to potential damage and high costs when using digital-to-analog converters for multiple regulators.
Innovation Solution
A cost-effective soft-start solution for track regulators is achieved by using a feedback resistor in combination with a variable current generator, which generates a linear downward current ramp to control the output voltage ramp-up during startup, avoiding inrush current and overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital-to-analog converter is used to implement soft-start function in track regulators, then the soft-start function can be achieved to limit inrush current and overshoot voltage, but the cost and area increase significantly
Solution Approach 1:
The patent extracts the soft-start control function from the error amplifier and implements it separately through a dedicated control circuit that generates a time-varying reference voltage. This separation allows the soft-start function to be achieved without requiring expensive digital-to-analog converters, as the control circuit uses simpler components like resistors, capacitors, and transistors to generate the required voltage ramp.
Solution Approach 2:
The patent replaces the expensive digital-to-analog converter with a cost-effective analog control circuit that uses readily available, low-cost components. The control circuit generates the soft-start reference voltage using a network of resistors, capacitors, and transistors, eliminating the need for expensive digital conversion hardware while achieving the same soft-start effect.
2Ease of operation
If the feedback loop is made effective only when output voltage is higher than certain voltage, then the N-channel input amplifier can operate within its input range, but inrush current and overshoot voltage cannot be controlled during startup
Solution Approach 1:
The patent implements preliminary action by generating a time-varying reference voltage before the regulator reaches its normal operating state. The control circuit activates during startup to generate a reference voltage that ramps from zero to its final value, controlling the output voltage slope before the feedback loop becomes fully effective. This preliminary control prevents inrush current and overshoot voltage during the critical startup phase when the feedback loop is not yet operational.
Data Source
AI summary
A track regulator circuit includes an input terminal for receiving an input signal, an output stage with an output terminal for applying an output signal to a load, an error amplifier coupled to the input terminal, and a feedback resistor between the output terminal and the error amplifier for transferring to the error amplifier a feedback signal indicative of the output signal. The error amplifier is configured for driving the output stage as a function of the difference between the input signal and the output signal so that the output signal tracks the input signal. The circuit includes a current generator coupled to the feedback resistor for injecting into the feedback resistor a soft-start current to unbalance the error amplifier, with the intensity of the soft-start current gradually ramping down to zero.