1、Lessons Learned Entry: 0603Lesson Info:a71 Lesson Number: 0603a71 Lesson Date: 1998-10-22a71 Submitting Organization: JPLa71 Submitted by: C. Stell/D. OberhettingerSubject: DC-DC Converter Applications (1995) Abstract: Several JPL flight projects obtained low cost, commercial quality, hybrid DC-DC p
2、ower converters from a single vendor that proved unsuitable in some intended applications. Hybrid power supplies are complicated and difficult to analyze. Worst Case Analysis (WCA) techniques, if applied to just the hybrid, may not be sufficient to identify application sensitivities to external inte
3、rfaces, and/or to identify non-linear interactions that may occur within the hybrid.Description of Driving Event: Several JPL flight projects obtained low cost, commercial quality, hybrid DC-DC power converters from a single vendor which proved unsuitable in some intended applications. The sensitivi
4、ty of this family of converters to load, ground, and input/output power conditions was not evident in the vendor documentation. Specific DC-DC power converter design limitations involved several different failure mechanisms including:1. Use of a sync circuit external to the converter frequently coup
5、led noise into the internal pulse width modulator (PWM), keeping the power FET (field effect transistor) saturated, which led to its eventual failure. Reference (1)2. Imbedded electromagnetic interference (EMI) filters in most of these converter designs lacked a damping resistor; the resulting insta
6、bility kept the FET saturated until it failed. Reference (2)3. The startup capabilities of these converters were insufficient for the Mars Pathfinder (MPF) mission worst case cold temperature.4. Slow input voltage rise time resulted in failure of the converter to turn on due to PWM regulator latch-u
7、p.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A JPL tiger team was able to resolve these problems through external and/or internal design changes with significant schedule and budget impact. Also see Reference (3) for related vendor issues.Additi
8、onal Keyword(s): Parts ProcurementReference(s):1. JPL Problem/Failure Analysis Reports (PFARs) No. 6419, 6978, and 69502. GSFC Failure Analysis Report (FAR) No. FA781263. “Commercial Electronic Parts Supplier Evaluation,“ JPL Lesson Learned No. 9-121.4. C. B. Stell, “Off the Shelf Power Converter Un
9、it Electrical Performance Evaluation, Jet Propulsion Laboratory, February 2, 1998.Lesson(s) Learned: Hybrid power supplies are complicated and difficult to analyze. Worst Case Analysis (WCA) techniques, if applied to just the hybrid, may not be sufficient to identify application sensitivities to ext
10、ernal interfaces, and/or to identify non-linear interactions that may occur within the hybrid.Recommendation(s): The following activities are recommended to verify the suitability of a hybrid power supply application:1. Involve a power supply engineer in the selection, application, analysis, and tes
11、t of hybrid power supplies.2. Conduct worst case analysis on all hybrid power supply applications including internal and external circuitry. Utilize the suppliers specification limits, the users environment (line, filter, load, temperature, radiation, life) with appropriate margin, and the internal
12、part manufacturers tolerances. Retain the results of WCA computer modeling for analysis of future applications.3. Conduct parts stress analysis (PSA) assuming worst case conditions. This permits future users of the power supply to merely update the analysis if warranted by changes in the converter d
13、esign or changes in worst case conditions.4. Conduct thermal analysis, including minimum heat sink bond area. Assume worst case conditions and document the results for future updates as needed.5. Thoroughly test power supplies considering: a72 Output voltage regulationa72 Efficiencya72 Standby power
14、 consumptiona72 Output voltage ripplea72 Output voltage turn-on overshootProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a72 Input voltage variationa72 Input inrush currenta72 Load current transient responsea72 Load current transient cross regulation
15、a72 Input common mode currenta72 Differential input currentEvidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & Processesa71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1998-10-28a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
