Power Designs 2005 precision power source- article - Page 1
Forum section: electronics / repair

author: cdev
author_rank: Super Contributor
timestamp: January 07, 2017, 08:47:31 pm
content: When surfing the web I stumbled acrossthis article on the Power Designs 2005that discusses it and embeds a schematic. I thought some people here might find it useful at some point.

author: saturation
author_rank: Super Contributor
timestamp: January 08, 2017, 03:25:12 pm
content: Details from the archives:https://www.eevblog.com/forum/chat/what-is-a-good-power-supply/msg101788/#msg101788

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 10, 2017, 02:47:30 pm
content: I now own one of these and a couple of the HP precision supplies, but am curious what purpose they serve. I understand the low noise part, but why would you ever care if your supply was set at 5.015 volts instead of 5.016? It is clumsy and unreliable as a calibration reference and I haven't thought of another purpose.The market seems to say my assessment is correct, as this company is out of business and the market is not filled with replacements.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 10, 2017, 07:38:16 pm
content: This is really old design - from days when digital (or other high resolution) voltmeters where still rare and expensive. With such an accurate source one could dial in the voltage instead of measure the actual voltage with an independent meter. So they had there application - but today it is enough if you get an accurate reading of the actual voltage. Even that is not that important any more as more an more circuits have voltage regulation build in.Some of the better quality digital controlled lab supplies are an adequate replacement - though noise might be higher now in many cases.

author: sync
author_rank: Frequent Contributor
timestamp: January 10, 2017, 08:06:25 pm
content: Quote from: CatalinaWOW on January 10, 2017, 02:47:30 pmFrom the HP 6113A manual. 0.1% is good enough for calibrating 1% analog meters.

author: saturation
author_rank: Super Contributor
timestamp: January 12, 2017, 06:28:41 pm
content: Precision supplies were most popular when analog signals were the principle control signals in all analog designs. Today, precision supplies are a niche item, I think Keithley devices are a common name in this area. They are not intended as calibration sources.A reason to get old precision models [ HP or Power Designs] today instead of just any linear DC supply is that they were made to higher stability, tolerance, and lower noise, than just your ordinary linear supply. Because what they are was not widely known, they are sold fairly cheaply, too.The best models are from the 1970s, as they are their most accurate and lowest cost.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 12, 2017, 10:08:59 pm
content: Thanks for the responses, but I guess I still don't "get it".Kleinstein, I understand the convenience aspect, but that presumes you have some need for four or more digit precision in setting a power supply voltage.Saturation, I date from the days of analog computing. Worked with guys on very large simulations with dozens of op amps, multipliers and the like. Calibration and set up was a big deal, but it was far easier to generate traceability with voltmeters and the like. In terms of control signals in delivered product I would be stunned if designs were shipped that required four digit supply accuracy for proper function.The kind of use cases I have thought of (and discarded) are things like design verification (my widget works on 5 volts +/- 10% and here is the proof). But then a supply accurate to 1 % would be adequate, and even then traceability would be easier in general for a voltmeter. The voltmeter can be used for many things, you don't have to pay for separate calibration. The same thing applies to the design verification end of control signals in analog circuits. It is easier to sweep a voltage while observing the response and noticing the behavior change than it is to step through a large number of voltages and see which ones work. If there is hysteresis in the response you can't even use the half interval method to reduce the number of steps.Possibly there are applications in chemistry where activation potentials can be sensitive to voltage, or something, but nothing I have heard or thought of gives that face plant "well of course" moment.

author: saturation
author_rank: Super Contributor
timestamp: January 13, 2017, 12:30:22 am
content: The 6114 and other precision supplies were strictly design and experiment instruments, to proxy say for the output of sensors, thermocouples, photocells, solar cells, emulate control voltages for move servos or stepper motors, etc., in the old all analog days. Naturally, you can still use it as an ordinary power supply. However, today you'll see the 6114 or others mentioned in experiments requiring high stability supplies or precision to remove the supply as a cause for any variation in experimental results or make very small adjustments; some examples from our library.http://lss.fnal.gov/archive/2014/pub/fermilab-pub-14-522-ppd.pdfHere's the HP Journal write up for the supply back in 1972.http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1972-11.pdf

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 13, 2017, 01:00:00 am
content: Quote from: CatalinaWOW on January 10, 2017, 02:47:30 pmCuz they look awesome?

author: mmagin
author_rank: Frequent Contributor
timestamp: January 13, 2017, 01:06:58 am
content: I think it's easier to see why these were made but no longer exist -- Today a lot of what people did with these they'd just use an SMU for the same things.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 13, 2017, 05:18:53 am
content: Quote from: saturation on January 13, 2017, 12:30:22 amThis quote from the journal article answers my question"Substantial current is needed at precisely known voltages in a number of applications. Among these are calibration and performance evaluation of positioning servos, memory excitation, and a-to-d converter tests. Also included are TTL threshold and other semiconductor tests where it may be expedient to test several devices in parallel."Or saying a different way - Supplying test signals to low impedance devices.I have reached the "well of course" stage in my understanding. Mostly a matter of getting the words "power supply" out of my mind. Thanks to all for your comments.