What is MTBF and life cycle?

MTBF (Mean Time Between Failure) and Life Cycle are both indicators of reliability. MTBF can be calculated by two different methodologies, which are “part count” and “stress analysis”. The regulations, MIL-HDBK-217F Notice 2 and TELCORDIA SR/TR-332(Bellcore) are commonly used to calculate MTBF. MIL-HDBK-217F is a United States military standard, and TELCORDIA SR/TR-332(Bellcore) is a commercial regulation. The exact meaning of MTBF is, after continuously using the Power Supply for a certain amount of time, the average time that the probability of proper operation is down to 36.8%（e-1=0.368）. This MTBF means the probability of the product can continue the normal work after working continuously up to the calculated MTBF time is 36.8% (e-1=0.368). If the power adaptor is continuously used at double the MTBF time, the probability of proper operation becomes 13.5%（e-2=0.135）. Life Cycle is found by using the temperature rise of electrolytic capacitors under maximum operating temperature to estimate the approximate life of the Power Supplies. For example, RSP-750-12 MTBF=109.1K hours(25°C); electrolytic capacitor C110 Life Cycle=213K hours (Ta=50℃)