Power Supply Temperature Rise Test
Keywords: Contact-based measurement; Data Acquisition System (DAQ)
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In the research, design, and production of power supplies (PSUs), temperature rise testing is a critical process to ensure product performance, service life, and safety. Elevated temperature has multiple and serious impacts on a power supply, including degradation of performance and stability, accelerated damage to components and reduced lifetime, as well as potential safety hazards. Therefore, temperature rise testing is a standard and indispensable item in qualification and validation testing, playing a vital role in ensuring long-term, reliable operation of the PSU.
The primary objective of a temperature rise test is to measure the temperature variation of the product and its key components to determine whether temperatures exceed allowable limits and comply with relevant safety standards. For power supplies, the importance of thermal management is reflected in the following aspects:
1. Ensuring operational stability and efficiency: Whether due to an increase in ambient temperature or heat generated internally during operation, temperature variations directly affect the stability and efficiency of a power supply. Elevated ambient temperature can significantly degrade PSU performance by reducing the stability of internal electronic components. Excessive temperature leads to lower operating efficiency and reduced stability.
Figure 1: Derating Curve
Refer to : https://commons.wikimedia.org/wiki/User:Arnulf_zu_Linden
2. Extending component service life: Elevated temperatures significantly shorten component lifetime. Overheating can alter the physical properties of internal materials (such as thermal expansion or electrolyte leakage) or directly damage components, thereby reducing overall reliability. Therefore, controlling internal temperature is essential to ensuring the long-term reliability of a power supply.
3. Preventing potential safety hazards: Temperature rise testing is a key indicator in evaluating the safety performance of electrical and electronic products. Prolonged operation at high temperatures may degrade the performance of insulating materials, leading to insulation failure, loosening of mechanical connections, and potentially severe safety hazards such as electric shock, burn injuries, or fire.
In accordance with the M-CRPS regulation requirements, during heat dissipation characteristics analysis, thermocouples shall be installed on at least the top 10 critical components for temperature measurement. The following are the key components subject to focused monitoring:
1. Power semiconductor devices – The primary sources of heat generation, with a direct impact on product lifetime. Examples include silicon FETs, gallium nitride (GaN) devices, silicon carbide (SiC) devices, DrMOS, POL ICs, and diodes.
2. Magnetic components – Excessive temperature in the magnetic core or windings can lead to insulation breakdown or magnetic saturation. Examples include transformers and inductors.
3. Capacitors – Key lifetime-limiting components. Capacitors are considered limited-lifetime components, such as high-voltage bulk storage capacitors, aluminum liquid electrolytic capacitors, aluminum polymer capacitors, as well as MLCCs and X/Y safety capacitors.
4. Printed circuit boards (PCBs) and connectors
- PCB surface: Particular attention should be paid to areas populated with surface-mount (SMD) power devices. During testing, it must be ensured that the PCB temperature remains below the glass transition temperature (Tg) of the laminate material (e.g., for FR-4 with Tg = 130 °C, the operating temperature should be maintained below 120 °C).
- Power connectors: Monitor the temperature rise of both the metallic contacts and the plastic housing to ensure that, under large-current conditions, surface contact temperatures do not exceed the limits specified by applicable safety standards.
5. Other safety and protection-related components
- Line fuses: Verify that under normal and repeated transient conditions, temperature rise does not cause unintended fuse blowing.
- Metal Oxide Varistors (MOVs): As surge protection components, ensure that their power dissipation and temperature under static operation remain within safe limits.
- Optocouplers: Used for circuit isolation; their maximum operating temperature must comply with derating standards.
Note: Before performing precise temperature measurements, it is recommended to first use a thermal imaging camera to scan the top and sides of the power supply to identify the actual hotspots. Thermocouples can then be accurately attached to these critical areas for precise measurement.
Figure 2: Thermocouple placement for a 185 mm × 60 mm form factor
Refer to : Open Compute Project M-CRPS Version 1.05.00 RC5
Principle and Implementation of Contact-Based Measurement
Temperature rise testing is based on thermodynamic principles, evaluating heat generation by measuring the temperature changes of components. Among various measurement methods, contact-based measurement is a fundamental approach that is both direct and precise:
1. Measurement tools: Contact-based measurement primarily uses sensors such as thermocouples or thermistors.
2. Measurement method: These sensors must be in direct contact with the component surface to accurately measure temperature.
3. Measurement preparation: Before formal measurement, the sample unit should be checked for integrity and placed in a controlled environment (ambient temperature 23 °C ± 2 °C, relative humidity 50 %RH to 90 %RH) for at least 10 hours to allow the surface temperature to stabilize and reach equilibrium with the room temperature.
Figure 3: Common Thermocouple Types and Their Temperature Ranges
Application of Data Acquisition Systems in Temperature Rise Testing
While thermocouples measure the temperature at specific points, data loggers continuously and reliably record multi-point data, allowing engineers to monitor the complete temperature profile over time.
In power supply temperature rise testing, the use of a data acquisition system and the data recording process are critical:
1. Continuous monitoring and data feedback: During operation at rated load, engineers must use sensors such as thermocouples or thermistors to continuously monitor temperature/temperature rise at each measurement point. The data logger ensures that these readings are accurately and continuously recorded.
2. Comprehensive parameter recording: To fully evaluate the performance of the power supply, the data acquisition system should not only record the temperature/temperature rise at all measurement points but also simultaneously measure and log operational electrical parameters, including:
- Voltage
- Current
- Input Power
- Output Voltage
- Output Current
- Output Power
3. Observation and analysis of curves: The long-term data recorded by the data acquisition system allows engineers to observe whether the temperature curve changes at each test point are normal. By analyzing these curves, engineers can determine whether the temperature rise has reached a stable state and assess whether the product design is thermally sound.
4. Abnormal Event Handling and Traceability: If the DUT exhibits abnormal behavior during testing—such as noises, sparks, vibrations, or activation of over-temperature protection—the data acquisition system can immediately save the current readings. This enables engineers to halt the test promptly and perform root-cause analysis and corrective actions.
In summary, during power supply temperature rise testing, contact-based measurement provides the actual surface temperature of components, while the data acquisition system delivers continuous time-resolved recordings along with corresponding electrical performance data. Together, they form the essential foundation for ensuring the accuracy and reliability of temperature rise test results.
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