Switching power supply, also known as switching power supply, switching converter, is a high-frequency power conversion device, is a kind of power supply. The switching transistors used in the switching power supply of civil fusion are mostly switched between the fully open mode and the fully closed mode, both of which have the characteristics of low dissipation. The switching between the two modes will have higher dissipation, but the time is very short, so the switching power supply of civil fusion can save energy and produce less waste heat. The high conversion efficiency of the switching power supply is one of its advantages, and the switching power supply has high working frequency. It can also use small size and light weight transformer, and the switching power supply will be light. Civil fusion switching power supply products are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting and other fields.
As an important part of switching power supply, the stress test of power semiconductor device is also the most important. Let’s share the related content in the following small class. Many switching power supply test is high quality and harsh, especially the switching power supply below.
Stress measurement of power semiconductor devices
Power semiconductor devices mainly include: DC main power transistor, output rectifier diode, power factor correction main power transistor, power factor correction rectifier diode, power factor correction four level diode, etc. The correct use of these power semiconductor devices is an important guarantee of power supply reliability. In order to ensure the reasonable use of power devices, reasonable current, voltage and junction temperature derating should be considered. Therefore, the following aspects should be paid attention to in the test:
A. Meet the requirements of voltage derating; B. Meet the current derating requirements.
A. Test the VDS voltage waveform of power semiconductor device under the worst condition to determine the maximum voltage and maximum peak voltage. Due to the high voltage of VDS, the maximum voltage peak frequency can reach 30-40mhz. When the voltage peak is less than 300V (the general rated voltage is 300, the bandwidth is 100m or 50m, and the test waveform is not distorted), the original probe of ordinary oscilloscope can be used. When the voltage peak is greater than 300V, the test result of the high voltage passive probe shall prevail (the bandwidth is 100m), and the test waveform shall not be distorted. The bandwidth of active high voltage probe is narrow, generally 20MHz, and it is easy to deform, so it is not recommended.
The voltage stress test mainly tests the voltage stress under dynamic condition (because the voltage stress under steady state is small). The specific test conditions are as follows:
(1) The input voltage is the highest voltage. Test device in no-load, full load, current limiting state, no-load to current limiting (output voltage about 50V), no-load to deep current limiting (output voltage less than 40V), (all load jump conditions are: jump time 5ms, TR, TF are 1a, corresponding to 20us), no-load voltage stress short-circuit state. Change the input voltage and repeat the above test under the minimum input voltage and rated input voltage. Record the maximum stress of the test, record the waveform of over standard voltage.
(2) When the module is in the floating charge state, the monitoring changes the module to even charge. At this time, due to the inconsistency of the rising speed of the module voltage, the module with fast rising voltage instantly bears too high power. At the same time, the module can not be short-circuit retracted (the voltage is higher than the short-circuit retraction point), which is due to the large stress of the module, Ken may cause excessive stress in the device. Specific simulation methods: for example, when testing 25A (or 50A module), use 100A module and 25A module (or 50A module) in parallel, and then with 100A load, adjust the output voltage of 100A module to 43a, and the voltage of 25A (or 50a) module to 42V. At this time, 25A (or 50a) module can’t output with load, suddenly adjust the voltage of 25A (or 50a) module to 58V, At this time, the voltage of 25A (or 50a) module rises to make it bear 100A load instantaneously, and the voltage stress of the tube at this time is tested.
(3) When the input voltage jumps between the maximum voltage and the minimum voltage (the jump time is 20ms), test the output no-load, full load, current limiting state, no-load full load jump, no-load to current limiting (the output voltage is about 50V), no-load to deep current limiting (the output voltage is less than 40V), (all load jump conditions are: jump time 5ms, TR and TF 1a, corresponding to 20us), Voltage stress of the device from no-load to short-circuit.
For 100A module, the cabinet can be used to simulate the above phenomenon. The main purpose is to make the module bear a large load instantaneously without allowing the module to retract, so as to test the voltage stress at this time. According to the actual circuit, the maximum voltage stress of each module can be analyzed and tested.
B. Current stress test
The worst-case current waveform of power devices is tested to determine the maximum working current and peak current. The specific test conditions are as follows:
(1) The input voltage is the lowest and the output voltage is the highest. Under the conditions of full load, current limiting, no-load full load jump, no-load to current limiting (output voltage is about 50V), no-load to deep current limiting (output voltage is less than 40V), (all load jump conditions are: jump time 5ms, TR and TF are 1a, corresponding to 20us), no-load to short circuit, the current stress of the device.
(2) The maximum voltage and minimum voltage of input voltage jump (jump time 201ms), respectively test the output full load, current limiting, no-load full load jump, no-load current limiting (output voltage about 50V), no-load to deep current limiting (output voltage less than 40V), (all load jump conditions are: jump time 5ms, TR and TF are 1a, corresponding to 20us), no-load short circuit device current stress.
According to the actual circuit analysis and test, the maximum rated current is calculated respectively.
(1) For voltage stress, in all cases, if the maximum VDS measured is less than the rated working voltage of the device, it is qualified; If the maximum VDS measured is greater than the rated working voltage of the device, the project team can issue the report on excessive use of the device for specific equipment certification, and the device is qualified, otherwise it is unqualified.
(2) For current stress, under various conditions, if the maximum current measured is less than the rated working current of the device, it is qualified; If the maximum current measured is greater than the rated working current of the device, the project team can issue the device overuse report for specific device certification, which is qualified, otherwise it is unqualified.
The above is the experience of stress testing of power semiconductor devices of switching power supply shared by small class today.
Editor in charge ajx