SMPS Power Controller Sampling for Inductance Variation Compensation
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Solution Overview
Problem
Switching-mode power supplies (SMPS) face inaccuracies in over current protection (OCP) and over power protection (OPP) due to inductance variation in inductive devices, leading to uncertainties in triggering these protections, which can result in incorrect peak current-sense signal readings.
Innovation Solution
The SMPS employs a power controller that samples the current-sense signal during a predetermined sampling time independent of the inductance and input voltage, and uses an adjustment time to compensate for inductance variations, allowing for accurate modification of OCP and OPP triggering conditions by isolating the inductance-related information from the input voltage, thereby ensuring output ratings are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current-sense signal is used directly for OCP and OPP detection, then the protection mechanism responds quickly, but the peak current reading becomes inaccurate due to signal propagation delay and inductance variation
Solution Approach 1:
The patent applies preliminary action by sampling the current-sense signal at a predetermined time point before the expected peak occurs. The sampling time is calculated based on known parameters (input voltage, inductance, and a predetermined current value) to predict when the peak will occur. By sampling beforehand and holding this sample value, the system obtains an accurate representation of the peak current without being affected by signal propagation delays or inductance variations that would occur if sampling happened at or after the peak.
2Ease of manufacture
If inductance variation is tolerated in mass production, then manufacturing cost is reduced, but the OCP and OPP triggering conditions become inaccurate and uncertain
Solution Approach 1:
The patent implements feedback by using the sampled current-sense signal value to dynamically adjust and determine the peak current reading. Instead of relying on a fixed or nominal inductance value, the system samples the actual current at a calculated time point and holds this value as the representative peak current. This feedback mechanism compensates for inductance variations, allowing the OCP and OPP thresholds to be accurately determined despite manufacturing tolerances in the inductance of the inductive device.
3Device complexity
If the sampling time is made independent of inductance and input voltage, then the control logic is simplified, but the ability to track actual peak current under varying conditions is reduced
Solution Approach 1:
The patent resolves this contradiction by calculating the sampling time in advance based on the relationship between input voltage, inductance, and a predetermined current value. The sampling time is determined by the formula derived from the inductor current equation, allowing the system to sample at the optimal moment before the peak occurs. This preliminary calculation approach maintains measurement precision across varying conditions while keeping the control logic relatively simple, as the sampling time is determined once per switching cycle based on measurable parameters.
Data Source
AI summary
A power supply control method capable of compensating inductance variation of an inductive device in a power supply. The power supply has a power switch controlling a winding current through the inductive device, and converts an input voltage into an output voltage. A sampling time is provided within an ON time of the power switch. The sampling time has a length substantially independent from the ON time, the input voltage, and an inductance of the inductive device. A current-sense signal, a representative of the winding current, is sampled to hold a sample voltage after the sampling time. The power switch is controller in response to the sample voltage so as to make the output voltage comply with an output rating.