NB/T 10297-2019Technical specification for derating of electronic components of AC-DC switching power supply (English PDF)

3.1 Electronic components

Components that make up a switching power supply, including resistors, capacitors, diodes, transistors, micro-integrated circuits, optoelectronic devices, magnetics Parts, connectors, printed circuit boards, wires, fuses, shells, etc.

3.2 Surface mount technology

It is a kind of surface mount components (also known as chip components) without leads (wires) or short leads (foot) mounted on the printed circuit board Circuit assembly technology that uses reflow soldering or dip soldering on the surface or on the surface of other substrates.

3.3 Pulse width modulation

Pulse width modulation is an analog control method, which modulates the bias of the transistor gate or base according to the change of the corresponding load.

The current switching regulator power supply output transistor or the change in the conduction time of the transistor, this method can make the output voltage of the power supply change when the working conditions change keep constant.

3.4 Thermal resistance Rth

The resistance that heat encounters on the heat flow channel, the ratio of the temperature difference on the heat flow channel to the power dissipation in the channel, reflects the medium or the inter-medium The heat transfer capacity indicates the temperature rise caused by 1 W power loss, in °C/W or K/W. Multiply the thermal power dissipation by the thermal resistance to get Obtain the temperature rise on the heat flow channel.

3.5 Magnetic saturation Bmax

When a magnetic material or a magnetized body is in a magnetized state, the magnetic flux per unit cross-sectional area is called the magnetic flux density, which varies with the magnetizing magnetic field.

When the magnetic field intensity continues to increase but the magnetic flux density no longer increases, the magnetic flux density is called magnetic saturation.

3.6 Derating

The stress that the component bears during use is lower than its rated value, so as to delay the degradation of its parameters and improve the reliability of use. Usually use Stress ratio and ambient temperature are expressed.

3.7 Rating

The maximum use stress value allowed by the component.

3.8 Stress

Electrical, thermal, and mechanical loads that affect the failure rate of components.

4.1 Resistance

See Table 1 for resistance derating requirements.

5.1 Device temperature test

5.1.1 The temperature test diagram is shown in Figure 1.

5.1.2 The requirements for the AC stabilized power supply for testing are as follows.

- Stability < 1%;

--Waveform distortion < 5%;

- Frequency change (< ±1) Hz.

5.1.3 Requirements for test load equipment

A programmable electronic load should be used. If the test product has multiple outputs, an integrated programmable multiple electronic load should be used.

5.1.4 The schematic diagram of the device temperature test location is shown in Figure 2 and Figure 3.

5.1.5 Calculation of core temperature (Tj) of power semiconductor

5.1.6 The temperature test requirements are as follows.

--The exposed metal part of the end of the thermocouple should not be too long, about 0.5 cm, and can not be screwed together to have multiple contact points, as shown in Figure 4 As shown, the metal end of the thermocouple should be in full contact with the device under test when pasting the thermocouple;

Figure 4 Schematic diagram of thermocouple --When you encounter a part with a heat shrinkable tube, you need to remove the tube, paste the component body and put it back on, and cut off the tube if necessary a part of;

--Transformers, PFC inductors and other devices covered with insulating skin, need to gently scrape off a small piece of the outer insulating skin until the paint is exposed Cover the wire, stick the temperature rise wire on the enameled wire;

--Record the temperature change curve of the device until the curve is stable and the temperature change is less than 2 degrees within 30 minutes.

5.2 Device voltage and current stress test

5.2.1 Test purpose

Verify that the maximum working voltage and current stress of the device meet the derating requirements to ensure that the device has sufficient design margin to improve Product reliability.

--Electronic load machine;

--AC power supply;

--Oscilloscope;

5.2.2 The required test equipment is as follows.

--Voltage probe, differential probe, current probe.

5.2.3 The test steps are as follows.

a) Ensure that the AC power supplied to the power supply under test is isolated separately and cannot share a power supply network with the test equipment.

b) The probe must be reset to zero before testing.

c) The bandwidth of the voltage stress test oscilloscope is set to full bandwidth, and the bandwidth of the current stress test oscilloscope can be set to 20 M.

d) Only one probe can be used to test one device at a time, and the device in the test circuit that is not directly connected to the ground must use a differential probe.

e) Test the stress of the device under various conditions (including minimum and maximum input voltage, power-on, power-off, output short circuit, etc.) Or abnormal conditions).

5.3 Device power loss test

5.3.1 Test purpose

Since only the surface temperature of the device can be tested, for power devices, the core temperature can be calculated by testing its power loss. Verify that the derating requirements are met.

5.3.2 MOS tube power loss

5.3.3 Diode power loss

5.3.4 Resistance loss power

5.4 Input surge current test

5.4.1 Test purpose

At the moment the power is turned on, the equivalent impedance of the input filter capacitor is almost zero. At this time, if there is no protection component on the AC input circuit, the input The current will reach hundreds of amperes, which may cause damage to the input circuit components.

5.4.2 The schematic diagram of surge current test is shown in Figure 5.

5.4.3 The test steps are as follows.

a) AC input is the maximum working input voltage of the power supply.

b) When the output is full, test the inrush current of the power supply under cold and warm conditions.

c) Calculate the corresponding energy (I2t) according to the shape of the surge current waveform.

5.5 USB socket test

5.5.1 USB female seat temperature rise test

Refers to the result of a separate test of the USB female socket unit under the same voltage, load and environmental conditions.

5.5.2 USB socket plug test

The test method is carried out in accordance with the provisions of 18.2 in JB/T 12148-2015.

5.6.1 Lightning resistance test

The test method is carried out in accordance with the provisions of GB/T 17626.5, the test level is set to common mode ±6 kV, differential mode ±6 kV, and the phases are respectively set. 0 degrees, 90 degree, 180 degree, 270 degree, each phase test 5 times, each time interval is 60 seconds, the equivalent output impedance setting of the signal generator, common mode The voltage test is 12 ohm, and the differential mode voltage test is 2 ohm. The output load requires a full-load test and a resistive load. The test process The oscilloscope is used to measure the impulse surge residual voltage of the rectifier bridge, electrolytic capacitor and other devices, and it should meet the requirements in Table 2 and Table 3.

5.6.2 Anti-ringing wave test

The test method is carried out in accordance with the provisions of GB/T 17626.12. Refer to the provisions in 5.6.1 for test levels and setting requirements.

Note: To prevent damage to the oscilloscope, it should be connected to the mains through an isolation transformer.

5.7 Lightning current immunity

The test method is carried out in accordance with YD/T 944, the AC-DC switching power supply input interface should be able to withstand a nominal value of 5 kA (8/20 µS)

The impulse test of the discharge current is carried out between the live wire to the ground wire, the neutral wire to the ground wire, and the live wire to the neutral wire. The impulse current test waveform The test is repeated 5 times with positive polarity and negative polarity each with an interval of 3 minutes. The output load requires a full load test and is a resistive load.

After the test, the performance of the switching power supply was normal and no component was damaged.

5.8 Shell temperature test

5.8.1 Switching power supply with fan

a) Test under the worst conditions (including input voltage, output load, ambient temperature, etc.)

b) The thermocouple paste position should include the area with the highest temperature of the switching power supply shell, and if necessary, use an infrared thermal imaging tester for analysis.

c) After the temperature curve is stable, the temperature change is less than 2 degrees within 30 minutes, and the temperature test data is recorded.

5.8.2 Switching power supply without fan

a) Test under the worst conditions (including input voltage, output load, ambient temperature, etc.)

b) The thermocouple sticking position should include the area with the highest temperature of the switching power supply shell, and if necessary, use an infrared thermal imaging tester for analysis.

c) The test should be carried out according to the product label upward and product label downward.

d) The test should be carried out in a closed environment without wind and natural convection.

e) After the temperature curve is stable, the temperature change is less than 2 degrees within 30 minutes, and the temperature test data is recorded.