Adaptive Start-Up Control Circuit for High-Impedance Power Sources
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Solution Overview
Problem
Existing switched mode power supply (SMPS) systems experience undervoltage conditions during start-up due to fixed frequency and duty cycle operations, particularly when using power sources with high internal resistance, leading to potential system shutdowns.
Innovation Solution
An adaptive start-up control circuit that monitors input voltage ripple and adjusts the off-time (Toff) of the power converter based on the power source's impedance, using a filter, voltage-to-current conversion, and a comparator to control the power transistors, thereby reducing the average input current and mitigating voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed frequency and duty cycle operations are used during start-up, then the SMPS can operate with simple control circuitry, but undervoltage conditions occur when using power sources with high internal resistance
Solution Approach 1:
The patent implements dynamic adjustment of the off-time (Toff) period based on detected voltage ripple characteristics. The control circuit modifies Toff adaptively during start-up to account for power source impedance variations, transitioning from fixed to dynamic control to prevent undervoltage conditions while maintaining operational reliability.
Solution Approach 2:
The patent incorporates a feedback mechanism that detects voltage ripple at the input of the power converter and uses this information to adjust the off-time period. The ripple detector monitors voltage variations and feeds this information back to the control circuit, which then modifies Toff accordingly to mitigate voltage drops and ensure reliable start-up.
2Productivity
If the power converter draws high input current during start-up, then the system can initialize quickly, but voltage drops occur in power sources with high internal resistance
Solution Approach 1:
The patent introduces a periodic off-time (Toff) period in the switching cycle during start-up, creating a pulsating rather than continuous current draw. This periodic action allows the power source to recover between pulses, reducing average current stress and mitigating voltage drops while still achieving necessary initialization current peaks.
Solution Approach 2:
The patent dynamically changes the off-time parameter (Toff) based on detected voltage ripple and power source characteristics. By adjusting Toff as a variable parameter rather than using a fixed value, the system optimizes the balance between input current magnitude and voltage drop prevention, adapting to different power source impedances during start-up.
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 adaptive control circuit mitigates voltage drops in power sources with high internal resistance, preventing undervoltage conditions and ensuring stable operation of the SMPS and connected loads.
Implementation Method 1
The filter has a first VIN input and a filter output and is configured to provide a filtered signal in which transient oscillations of VIN are attenuated
Implementation Method 2
The voltage-to-current conversion circuit is configured to provide a signal having a current value representative of a voltage differential between the filtered signal and VIN
Implementation Method 3
The capacitor is coupled between the current output and ground terminal and is configured to integrate a current provided at the current output to form a capacitor voltage
Implementation Method 4
The comparator is configured to compare the capacitor voltage to Vref to provide a comparison result
Data Source
AI summary
In some examples, an apparatus includes a filter, a voltage-to-current conversion circuit, a first current source, a second current source, a capacitor, a comparator, and a buffer. The filter has a first input voltage (VIN) input and a filter output. The voltage-to-current conversion circuit has a first input, a second VIN input, and a current output, the first input coupled to the filter output. The first current source is coupled between the current output and ground terminal. The second current source is coupled between a power terminal and the current output. The capacitor is coupled between the current output and ground terminal. The comparator has a comparator output, a comparator input, and a reference voltage (Vref) input, the comparator input coupled to the current output. The buffer has a buffer input and a buffer output, the buffer input coupled to the comparator output.