Power Switch Temperature Estimation Using Body Diode Voltage
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Solution Overview
Problem
Existing power converter systems face challenges in accurately estimating the temperature of power switches without dedicated sensors, leading to potential overtemperature conditions being detected too late, and existing methods require significant operational time to determine initial temperature or current levels.
Innovation Solution
A system that uses a standard diode as a temperature sensor by sampling the voltage across the body diode of a power switch, applying a test pulse to generate a test current, and repeating the process multiple times to determine an initial temperature estimation, which can then be used for shunt-less current measurement during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated temperature sensor is used to measure power switch temperature, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The body diode of the power switch itself is used as the temperature sensing element. The diode's forward voltage drop characteristics are measured to determine the junction temperature, eliminating the need for separate temperature sensors. The power switch's own body diode serves the dual purpose of power conversion and temperature sensing.
Solution Approach 2:
The body diode performs multiple functions: it provides the freewheeling path for inductive loads during normal operation and simultaneously serves as the temperature sensing element. This multi-functional approach eliminates dedicated temperature sensors while maintaining measurement capability.
2Device complexity
If an external temperature sensor is used to estimate power switch temperature, then device complexity is reduced, but measurement accuracy deteriorates due to temperature differences between sensor and switch die
Solution Approach 1:
The temperature measurement is performed directly at the power switch junction using its own body diode, eliminating the temperature gradient issue between separate sensors and the switch die. The measurement occurs at the exact location where temperature information is needed.
3Measurement precision
If current sensor is used to measure current for temperature estimation, then current measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The body diode's forward voltage drop is measured to infer both current and temperature information. The diode itself serves as the sensing element, eliminating the need for separate current sensors. The voltage measurement across the diode provides sufficient information for both current and temperature estimation.
4Device complexity
If Singh method is used for sensorless current sensing, then device complexity is reduced, but productivity decreases due to significant operational time required before accurate temperature or current determination
Solution Approach 1:
The system performs preliminary characterization of the body diode's forward voltage drop characteristics during manufacturing or initial setup, storing these characteristics for later use. This preliminary action enables rapid temperature and current determination during operation without requiring extended warm-up or calibration periods.
Solution Approach 2:
The system applies a test pulse that exceeds normal operating conditions to quickly characterize the body diode's behavior. By using a stronger, shorter test pulse, the system obtains sufficient characterization data rapidly without requiring prolonged operation under normal conditions.
5Device complexity
If Singh method is used for temperature estimation, then device complexity is reduced, but reliability decreases because overtemperature conditions are detected too late after system has been operating at excessive temperature
Solution Approach 1:
The system characterizes the body diode's voltage-temperature characteristics in advance and implements real-time monitoring during operation. This preliminary characterization enables immediate detection of temperature excursions without delay, improving reliability by detecting overtemperature conditions as they develop rather than after prolonged operation.
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
Enables quick and accurate determination of power switch temperature and current without the need for current or temperature sensors, reducing costs and errors associated with external sensor measurements.
Implementation Method 1
the voltage drop over the power switch while turned on during normal operation
Implementation Method 2
the temperature changes across the resistance of the power switch can be estimated using the body diode temperature estimation
Implementation Method 3
A test pulse is applied to one of the power switches to drive a test current through the inductive load
Data Source
AI summary
A system for a power switch of a multiphase power converter coupled to an inductive load including a test controller, a voltage sampling circuit, a processing circuit, and a converter. A test pulse is applied to power switches of the converter to generate a test current through the inductive load, which forward biases a body diode of a power switch during a freewheel portion after the test pulse is completed. The voltage across the body diode is sampled during the freewheel portion, and the voltage samples are converted to a voltage value and a slope value. The voltage and slope values are converted to an estimated temperature value based on a characterization of the inductive load and the body diode. The conversion may be performed by a lookup table that stores an estimated temperature value for each unique combination of the voltage and slope values.