Re: 7K mainframes common-mode input range?


The only documentation that I am aware of which discusses the power
and current limits of the 7000 power supplies is the Tektronix one
which discusses the 7704A, 7904, and 76xx power supplies:

Some plug-ins converted a higher voltage supply to a lower one to
provide enough current. 7D15 uses a switching power supply to convert
-15 volts to -5.2 volts for ECL. The 7D01 uses an inverter to convert
the +15 and -15 volt supplies to -4.8 and -2.0 volts for ECL. I think
someone mentioned here that it was so power constrained, that they
used a slightly lower voltage. The -2.0 volts is used specifically
for ECL termination also saving power so they must have been

On Wed, 27 Dec 2017 17:13:52 -0800, you wrote:

Yup, that's what I have - the PECL output bias currents go through the dropping Zener/R networks and then larger resistors all the way down to the -15V supply. They act more as constant current sources, and may even improve the speed by keeping the quiescent emitter currents nearly the same in both states, but the main function is to pull enough current while not being so low in R that the 50 ohm environment is hard to achieve. The outputs are Schottky-clamped in case things get out of hand with the -15V termination. As you can imagine, it's not power-efficient at all, but only needed at certain spots, so not too bad overall - wouldn't want to do all the outputs with such loads.

Speaking of power, it is my understanding that the +/-15V and +5V supplies are rated up to 500 mA each - but not all at the same time of course - as long as total (single-wide) plug-in power is less than 16.5W. Does anyone have info or advice to the contrary? I don't think I'll have anything near the maximums, but do need to run a 1 GHz PLO at 130 mA from -15V, plus two or three of these high power ECL shifter/terminations up to 40 mA per set. The +15V needs maybe 200 mA for amplifiers, while the +5V will run all the PECL Vcc, maybe 400 mA or so. I'm picturing less than 10W for the major items, leaving a few for miscellaneous.


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