NTC Resistor Network for Temperature-Compensated DCR Current Sensing
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Solution Overview
Problem
The inductor direct current resistance (DCR) in DC-to-DC converters varies with temperature, affecting current measurement accuracy and introducing time constant mismatches that lead to control errors in switching regulators, causing distorted waveforms and sampling delays.
Innovation Solution
A DC-to-DC converter with a temperature-compensated inductor DCR dynamic current sensing system, using a resistor network with a negative temperature coefficient (NTC) coupled with a current sensing capacitor to match the time constant of the inductor, ensuring accurate current measurement across a range of temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a parallel RC current detection circuit is used to measure inductor current, then current measurement is achieved, but time constant mismatching occurs due to inductor DCR value changes over temperature range
Solution Approach 1:
The patent applies parameter changes by using a resistor network with negative temperature coefficient (NTC) that changes its resistance value with temperature to compensate for the inductor's DCR changes. The NTC resistor network is configured to have its resistance decrease as temperature increases, counteracting the increase in inductor DCR, thereby maintaining matched time constants across the operating temperature range and eliminating control errors.
2Adaptability or versatility
If inductor DCR varies with temperature, then temperature adaptability is achieved, but current measurement accuracy deteriorates
Solution Approach 1:
The patent converts the harmful effect of inductor DCR variation with temperature into a beneficial compensation mechanism. By using an NTC resistor network whose resistance decreases with temperature increase, the circuit exploits the temperature dependence to counterbalance the inductor's DCR increase, transforming the temperature-induced error source into a self-compensating system that maintains accurate current measurement across temperatures.
3Device complexity
If time constant matching is not maintained, then device complexity is reduced, but control precision deteriorates
Solution Approach 1:
The patent introduces an intermediary element - the NTC resistor network - that mediates between the inductor's temperature-varying DCR and the RC detection circuit's time constant. This intermediary component automatically adjusts its resistance with temperature to maintain time constant matching, providing continuous compensation without requiring complex control algorithms or additional active components.
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 solution maintains matched time constants and improves current measurement accuracy, reducing control errors and ensuring stable operation of switching regulators over varying temperatures.
Implementation Method 1
a resistor network having a negative temperature coefficient (NTC) is coupled to the inductor and the current sensing capacitor
Implementation Method 2
a current sensing capacitor coupled to the inductor, wherein a voltage across the current sensing capacitor is substantially proportional to a current through the inductor
Data Source
AI summary
A resister network having a negative temperature coefficient (NTC) may be utilized to create a temperature compensated equivalent resistance “R” for a current sensing RC network used in measuring inductor current of a DC-to-DC converter or a general switching regulator that needs to use inductor current as a control signal. The NTC resistor of the RC network effectively compensates for the positive temperature coefficient of the switching regulator inductor's inherent DC resistance (DCR). Keeping the time constants of the RC network and the switching regulator inductor substantially matched improves operation of cycle by cycle based control modes such as peak current sensing by the switching regulator controller in performing peak current control for the DC-to-DC converter.