Author: Wang Zhongliang

Why do we measure the temperature rise of products?

The parts that can be touched when the product is working may cause personal injury if the temperature is too high; and the high temperature inside the device will also affect the performance of the product, and even lead to a decrease in the insulation level or increase the mechanical instability of the product.Therefore, in the process of product design, the temperature rise experiment is an important step that needs to be considered to ensure that the product can work safely and stably!

The method of measuring temperature rise can be divided into two categories: non-contact type and contact type according to the different temperature measuring instruments.

non-contact measurement

It can measure the temperature displayed on the outside of the measured object, and the real temperature can only be obtained by correcting the surface emissivity of the measured problem, and the measurement method is affected by the distance between the measured object and the instrument and the water vapor, smoke, etc. on the radiation channel. The influence of other media such as dust, so the measurement accuracy is low. The methods we often use in daily life include spectral temperature measurement technology, holographic interference temperature measurement technology, CCD-based three-primary color temperature measurement technology, and infrared radiation temperature measurement technology as shown in Figure 1 below:

5 minutes to learn the temperature rise test, reading this article is enough

Figure 1. Non-contact infrared thermal imager

contact measurement

Contact thermometer temperature probes generally have two types: thermocouples and thermal resistances:

ThermocoupleThe working principle is based on the Seeback effect. Two conductors with different components are connected to form a loop. If the temperature of the two connection ends is different, a physical phenomenon of thermal current is generated in the loop. This phenomenon is used to measure the temperature.

Thermal resistanceThe measurement principle is to measure the temperature according to the characteristic that the resistance itself also changes when the temperature changes.

In the contact test method, the temperature measuring element is directly in contact with the measured medium, and the temperature of the measured object is directly measured, so it is simple, reliable and high in measurement accuracy. Often used as shown in Figure 2:

5 minutes to learn the temperature rise test, reading this article is enough

5 minutes to learn the temperature rise test, reading this article is enough

Figure 2. A dedicated thermometer with a single function

The temperature rise test of the product is also an important part of the safety requirements, so how can we achieve economical and convenient measurement when designing a product?

MOSFETs and diodes in switching power supplies will generate switching losses, conduction losses, inductance losses, including coil losses, core losses, and losses caused by capacitance, etc. These losses are ultimately manifested in the form of heat, and overheating will reduce component performance. Losses increase, so it is important to understand where the unwanted power is lost.

Next, we use the desktop multimeter and its optional scan card function to conduct a temperature rise test experiment on the components of a 150W switching power supply:

Purpose

Test the temperature rise of power components when the power module is in a specific operating environment, voltage, frequency and load conditions.

equipment

(1). AC power supply, providing switching power supply with different voltages and currents

(2). Electronic load to make the AC converter work in different power states

(3). SDM3065X / desktop multimeter, used to record temperature data and draw the curve of temperature change with time with the EasyDMM multimeter host computer software on the PC side:

(4). Scan card and K-type thermocouple are used to collect temperature data, as shown in the figure below:

5 minutes to learn the temperature rise test, reading this article is enough

Figure 3. Data acquisition card with thermocouple connected

(5). Thermocouple glue and high temperature tape, high temperature tape is used to fix the thermocouple, and then use the thermocouple glue to fix the thermocouple to the part to be tested:

5 minutes to learn the temperature rise test, reading this article is enough

Figure 4. High temperature adhesive tape and thermocouple adhesive

Test Conditions

Input normal working voltage AC LINE 220V, frequency 50HZ, output load LOAD and ambient temperature 25℃.

Testing process

(1). According to the circuit conditions, first determine the components to be tested for temperature rise (switching MOSFET, switching transformer, primary rectifier filter capacitor, secondary rectifier tube, filter capacitor, filter Inductor), and then use thermocouple glue to close the temperature rise line Paste the determined components, as shown below

5 minutes to learn the temperature rise test, reading this article is enough

Figure 5. Components and thermocouples that need to be tested for temperature rise

(2) The thermocouples need to be numbered first, so that the temperature corresponding to each channel can be distinguished on the instrument. When the machine is not turned on, the ambient temperature can be seen to be 27°C, as shown in the figure:

5 minutes to learn the temperature rise test, reading this article is enough

Figure 6. Desktop multimeter SDM3065X with data acquisition card installed

(3). Set the test conditions according to the specifications

Change the input voltage of the switching power supply, turn it on again, and set the test conditions, as shown in Table 1

5 minutes to learn the temperature rise test, reading this article is enough

Table 1: Output Condition Settings

(4). Using the scanning card function of the SDM3065X multimeter and the easyDMM host computer software on the PC, record the temperature data of the key components of the switching power supply for 35 minutes and the full load for 25 minutes, as well as the temperature trend diagram of the components, as shown in Figure 7&8&9 :

5 minutes to learn the temperature rise test, reading this article is enough

Figure 7. Temperature trend graph measured at room temperature of 27°C

5 minutes to learn the temperature rise test, reading this article is enough

Figure 8. Temperature trend of 80W components with half-load output

5 minutes to learn the temperature rise test, reading this article is enough

Figure 9. Temperature trend of 150W components with half-load output

Precautions when experimenting

(1). The temperature rise line coupling point should be close to the component test point as much as possible, and the temperature rise line (thermocouple) wiring should try to avoid affecting the heat dissipation of the component under test.

(2). The tested samples should simulate their actual work or placement status in the system.

(3). For products without fans, the influence of the large flow of outside air on it should be avoided as much as possible during the test.

If there are no special requirements, you can follow the component temperature standards on the supplier’s parameter table. Generally speaking:

The maximum temperature of MOSFET&diode does not exceed 125℃, the maximum resistance is 150℃, the maximum capacitance is 105℃, and the maximum temperature of transformer is 155℃.

Note! The reference given above is the highest value. Some standards require derating, and general applications will not reach such a high value. Compare the measured temperature value with the relevant standard safety value. The temperature value of the device must be less than the device specification. safe value on .

The analysis of the test results is as follows in Table 2:

5 minutes to learn the temperature rise test, reading this article is enough

Table 2. Analysis of temperature test results

In summary, the temperature rise test of the product can accurately analyze the temperature condition of the product when it is working, and what kind of load state the components in the internal circuit are in, so as to help engineers analyze the areas that need to be improved in the design: including the use of components Is it appropriate, whether the layout is reasonable, whether the heat dissipation design is reliable, etc. With the help of SDM3065X for temperature test, the temperature change process of key components can be seen more intuitively and effectively, thus helping engineers to design better products!

5 minutes to learn the temperature rise test, reading this article is enough

About Dingyang

SIGLENT is a company specializing in general electronic test and measurement instruments and related solutions.

Since the launch of the first digital oscilloscope product in 2005, Dingyang Technology has been the fastest growing digital oscilloscope manufacturer in the world for more than 10 years. After years of development, Dingyang products have expanded to digital oscilloscopes, handheld oscilloscopes, function/arbitrary waveform generators, spectrum analyzers, desktop multimeters, DC power supplies and other general test and measurement instrument products. In 2007, Dingyang established a global strategic partnership with LeCroy, a leader in high-end oscilloscopes. In 2011, Dingyang developed into a leading digital oscilloscope manufacturer in China. In 2014, Dingyang released China’s first smart oscilloscope SDS3000 series, leading the trend of “one per hand” laboratory using oscilloscopes to transition from functional oscilloscopes to smart oscilloscopes. In 2017, Dingyang released the SDG6000X series of pulse/arbitrary waveform generators that broke the monopoly of the industry and broke through domestic technical bottlenecks in many parameters, with an output bandwidth of up to 500MHz. At present, Dingyang has established branches in Cleveland, USA and Hamburg, Germany, and its products are exported to more than 70 countries around the world. SIGLENT is gradually becoming a world-renowned brand of testing and measuring instruments.

About Dingyang Hardware Design and Testing Think Tank

Dingyang Hardware Design and Testing Think Tank (abbreviated as Dingyang Hardware Think Tank) is led by Shenzhen Dingyang Technology Co., Ltd. and founded.

Dingyang Hardware Think Tank takes advantage of the situation, advocates the concept of “connection-sharing-collaboration-creation”, holds high the banner of volunteer service, believes that the Internet is the base of “love”, and believes that people have the desire to share from the heart.

Dingyang Hardware Think Tank selects the seven most common problems in the hardware field: power supply, clock, DDR, low-speed bus, high-speed bus, EMC, test and measurement to focus on. Look for the “best-in-class” issues to discuss, organize experts to answer questions on the “best-in-class” issues, and turn the valuable knowledge and experience accumulated by hardware masters into public wealth, benefiting more hardware people.

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