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Number 2260 Application Note Burn-in Testing Techniques for Series Switching Power Supplies would be connected in parallel with the load resistance to mea- Introduction sure the power supply voltage. The load resistance is chosen to One of the consequences of the rapid growth of the telecommu- emulate the load resistances found in the final application, but nications, desktop computing, and network server markets is a may be chosen to reach full output capacity to perform burgeoning demand for switching power supplies and DC-to-DC stress testing. converters. While these power supplies are typically inexpensive, a high level of quality must be maintained through careful production testing. Monitor 110V or Power Supply Load 220V AC Input Voltage Highly accelerated stress screening (HASS) or "burn-in" Under Test R (3.3V - 48V) is a common production step for switching power supplies designed for computers and servers. Extended environmental testing is performed to ensure the product will continue to func- Figure 1. Monitoring the output of a switching power supply. tion properly over its entire service life. It is not uncommon to age and monitor thousands of power supplies at once. When designing this type of test system, the biggest challenge is deal- Output Cycling ing with the high number of channels the system must monitor To stress the power supplies being tested further, the output is and the test system surroundings. Large numbers of switching repeatedly turned on and off. If a device is destined to fail, the power supplies can produce tremendous amounts of electrical failure will generally occur when the output is cycled. To capture noise, which can reduce the test system's measurement perform- failure data, the output voltage of each power supply is measured ance significantly. during each time the output is turned on, as shown in Figure 2. After the output is cycled 15 to 20 times, the output is left on and the power supply is left to continue aging. While the out