Didier Juges wrote: > They are not, but system designers, as far as I can tell, have overcome > this problem by providing local filtering/decoupling/regulation at the > most sensitive points and therefore do not require the entire power > budget to a system to be low noise. > > Most of our power supplies (we only make custom military supplies) have > many outputs (one we make right now has 34 outputs, all independently > regulated with floating grounds), sometimes several outputs of the same > voltage, so that the customer can isolate various sections of the > system, and provide as much filtering at the point of load as needed for > each subsystem. Also, being a 100% military house, few customers call > our supplies affordable :-) > > For instance, on the 5370, a lot of the power is used to drive logic > circuits, TTL and ECL. For the most parts, these are not very sensitive > to noise, certainly not as much as the OCXO, the VCOs and the input > comparators, which probably (I have not checked the manual yet) run from > a different voltage. > > Modern high integration chips have advanced power/thermal management > functions which turn off parts of the chip when not in use. This results > in very severe load transients. Often, the noise (periodic and random > deviation, PARD) on the 5V, 3V and lower rails is driven by the very > fast load transients of the logic chips more than by the switcher > itself. A specification we are reviewing right now has a load change > requirement from 55 to 110A on a 3V rail in less than 1uS at the end of > a 56 inches bus bar. With that kind of load transient, the ripple does > not matter much compared to the transient response through the bus bar, > even assuming a perfect power supply with infinite output capacitance. > > Didier > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Didier Thanks for the info. As far as the 5370 is concerned the triggered phase lock oscillators, their loads and everything before them will be quite sensitive to power supply noise and glitches. The count chain devices thereafter should be somewhat less sensitive. Supply voltages are -15V, -5.2V, +5V, +15V. There is only one regulator for each voltage. Fuses are 1.5A for +15V and -15V, 7A for -5.2V and 5V. Input board uses +15V, -15V, +%V, -5.2V. Both -5.2V and +5V have on board LC filtering. Frequency reference assembly uses +15V and -5.2V with on board LC filtering Interpolator assembly uses -5.2V, +15V, -15V each with onboard LC fitering. Arming assembly uses all 4 voltages. If the on board LC filtering proves inadequate it will be difficult to retrofit better filters as the power supplies are often on internal planes. Extra filtering will probably need to be located at the supply. Bruce