High reliability in DC-DC converters for space must meet certain standards for electrical and environmental performance as well as defined quality requirements. The differences between these reliability grades can be subtle and can be concealed with clever marketing. The product literature must be studied carefully, and questions must be asked, to determine exactly what the product is, and, equally important, what it is not. Basic elements to investigate are: temperature rating, hermeticity, military specification compliance and a rigorous environmental qualification. The ultimate test of reliability beyond that is official qualification and certification by the US Department of Defense.
Space level hybrid DC-DC Converters, radiation tolerant or radiation hardened, are also governed by MIL-PRF-38534. The manufacturer should have a radiation hardness assurance plan certified by DLA to MIL-PRF-38534 Appendix G. Space level DC-DC converters are available on SMDs and are typically procured to Class K.
Typical characteristics of space grade DC-DC converters include:
Total Ionizing Dose (TID) radiation
For low earth orbits or where the DC-DC converter is adequately shielded, a 30 krad(Si) guarantee is often sufficient. For higher orbits or longer missions, a 100 krad(Si) guarantee may be required. TID performance should be verified by the manufacturer with component test data or guarantees, worst case analysis, and test data on the complete converter. Additional test margin can sometimes be substituted for analysis.
Enhanced Low Dose Rate Sensitivity (ELDRS)
TID testing is normally performed at high dose rates to shorten test time and reduce test cost. Testing at lower dose rates, closer to those seen in actual space environments, has shown increased sensitivity to radiation in some components, especially bipolar technologies. Modern space programs will almost certainly have an ELDRS requirement. Older DC-DC converter designs may not have an ELDRS guarantee, so be sure to inquire about this. ELDRS performance is proven through testing and analysis.
Single Event Effects (SEE)
Single event effects are caused by energetic particles which interact with