Flyback Converter Temperature Compensation via PTAT Feedback
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Solution Overview
Problem
Existing isolated flyback converters using primary side sensing and an output diode face challenges in temperature compensation, requiring an iterative process to select optimal scaling and temperature compensation resistors, which is tedious and non-optimized.
Innovation Solution
A temperature compensation technique that uses a proportional-to-absolute temperature voltage source connected to the feedback loop via a temperature compensation resistor, allowing the selection of optimal resistor values without iterative processes by ensuring no current through the resistor at room temperature, thus not affecting the output voltage initially.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a temperature compensation resistor is added to the feedback loop to compensate for diode voltage drop changes with temperature, then the output voltage stability over temperature is improved, but the complexity of resistor selection increases due to requiring iterative optimization
Solution Approach 1:
The patent applies preliminary action by designing the temperature compensation circuit to automatically establish the correct relationship between the temperature compensation resistor and scaling resistor through the initial power-on state. When the converter first powers on at room temperature, the PTAT voltage source produces zero current through the temperature compensation resistor, allowing the feedback loop to initially set the output voltage using only the scaling resistor. This preliminary configuration eliminates the need for iterative optimization, as the circuit self-configures during normal operation.
2Measurement precision
If iterative optimization process is used to select optimal resistor values, then the temperature compensation accuracy is improved, but the time and effort required for design increases
Solution Approach 1:
The patent implements self-service by designing a circuit that automatically determines the optimal resistor values without requiring manual iterative optimization. The PTAT voltage source and temperature compensation resistor are configured to self-adjust based on the operating temperature and output voltage requirements. During initial power-on at room temperature, the circuit naturally establishes the correct feedback relationship, eliminating the need for time-consuming iterative design processes while maintaining high temperature compensation accuracy.
3Reliability
If a temperature compensation circuit is implemented to offset diode voltage drop changes, then the output voltage regulation is improved across temperature ranges, but the circuit complexity increases
Solution Approach 1:
The patent applies merging by integrating the temperature compensation function directly into the existing feedback loop without adding separate complex compensation circuits. The PTAT voltage source and temperature compensation resistor are combined with the feedback network, allowing the same feedback mechanism that regulates output voltage to also compensate for temperature-induced diode voltage drops. This unified approach improves voltage regulation across temperature ranges while minimizing additional circuit complexity.
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 method simplifies the selection of optimal resistor values, improving temperature stability of the output voltage without affecting the initial output voltage setting, thereby enhancing the converter's performance across varying temperatures.
Implementation Method 1
A voltage source generating a proportional-to-absolute temperature voltage VPTAT is connected to the VFB node of a feedback loop in the converter
Implementation Method 2
The circuit 14 detects the voltage at the drain of MOSFET MPOWER during the discharge cycle (MOSFET MPOWER is off). The drain voltage is related to the winding ratio of L1 and L2, and the voltage across winding L2 is the output voltage Vout plus the voltage drop across the diode D
Data Source
Figure 1~2
Figure 3~6
Figure 7~9
AI summary
An isolated flyback converter having a temperature compensation (TC) circuit (30) uses primary side sensing and an output diode (D), the output diode having a variable voltage drop related to its temperature. A feedback voltage V FB , proportional to the output voltage V OUT , in a feedback loop is compared to a fixed reference voltage V REF for setting a duty cycle of a power switch, wherein V FB is caused to approximately equal V REF . The TC circuit has a voltage source (32) configured to generate a proportional-to-absolute-temperature voltage V PTAT , wherein V PTAT is at approximately V REF at a calibration temperature To and rises as a temperature exceeds To. The voltage source is connected to the V FB node via a TC resistor R TC , so that at To no current flows through R TC . Therefore, the selection of the optimal R TC does not affect the selection of a scaling resistance for generating V FB . The current through R TC at elevated temperatures compensates V OUT .