A stable DCV source up to 300V - Page 1
Forum section: electronics / general

author: BradC
author_rank: Super Contributor
timestamp: March 16, 2018, 02:33:43 am
content: G'day all,After recently acquiring a couple of nice 3478a to compliment my 3457a I've begun to do some comparative checks.One of them is for all intents and purposes almost bang on compared to the in-cal 3457a, and one reads consistently high (~50ppm). I'd like to be able to track/log drift for a while to see if it requires adjustment or is a deeper issue.I've been playing around with trying to get a vaguely stable DCV source for comparison and before I started to bodge up some Manhattan style madness I thought I might ask for advice.I tried using my basic Dick Smith 30V 2.5A linear psu through a large RC filter. That wanders all over the place. I reckon it moves 10 millivolts if I fart near it.My best result thus far has been to use a Tek PG506 on the 50V output into a divider comprised of 5 220k resistors in a 3/5 configuration. That allows me to put the PG into vari mode and get close enough to 30V. It's all over the place (relatively) with local condition variation and the weather here in Perth has been up and down over the last week, so getting any relatively stable comparison has been "fun". When I say all over the place, it has dropped 2.5mV over the time it has taken me to compose this post. That is related to a change in airflow in the room which has probably pulled half a degree C out of the PG in the last 20 minutes. Some of that is probably the divider also as it's swinging in the breeze, but it's part of the problem.As an aside, I have a 3 meters hooked up in parallel on DCV, and I plonked a 330uF cap across the input to see if it helped. With the impedance of the PG output and the extra half a meg of the divider it took hours to charge up and get stable, but I've been working on my GPIB interface again and found that sending a device reset to one of the 3478a caused a significant drop in the voltage across the cap (like half). Like something in the meter seems to be presenting a relatively low impedance during the reset cycle. Having been through the manual, I can't quite figure out what might be happening, but don't want to risk damage to the meter so I've removed the cap for now. Anyone ever seen something like that?Anyway, back on topic my plan was/is to just build a linear regulator based around a vaguely stable reference (~2.5-5v), chopper stabilized op-amp, some reasonably precision divider resistors and a PNP series pass transistor capable of delivering stable 300V & 30V outputs. I figured if I built a rudimentary oven around the ref/amp/divider it'd likely give me a more stable voltage to monitor/compare.Bear in mind it doesn't have to supply much current and absolute accuracy or long term drift is not a parameter. Being able to stay stable to a couple of hundred uV over an hour would be really nice, but I might be making that sound easier that it really is. I won't really know until I try I suppose.Is there a better approach? I've looked longingly at the Power Designs bench power supplies, but due to the weight postage is just too expensive to justify over here.

author: zhtoor
author_rank: Frequent Contributor
timestamp: March 16, 2018, 05:32:47 am
content: hello,use a string of 18650 (or other 3.7v common-cheap-chinese mobile phone batteries) followed bya resistive divider such as a rayleigh or a kvd divider. even a fixed resistor (stable) coupled with adecade resistance would do.i have tested the concept using a Muirhead D-801-D divider with a 6V / 3.7V battery, you can haveuV stable output for short time spans provided the temperature is reasonably constant.regards.-zia

author: BradC
author_rank: Super Contributor
timestamp: March 16, 2018, 05:35:50 am
content: Quote from: zhtoor on March 16, 2018, 05:32:47 amNow that's something that hadn't occurred to me.I have 48V of SLA sitting as a "backup of a backup", so I could relatively easily divide that down. That doens't easily lend itself to being extended to 300V though.

author: zhtoor
author_rank: Frequent Contributor
timestamp: March 16, 2018, 05:38:25 am
content: chinese mobile phone batteries are cheap, we can get one for usd 0.5 - usd 1 / piece.one hundred of those would be usd 50-100.pretty cheap and stable source (and re-chargeable too).regards.-zia

author: ap
author_rank: Frequent Contributor
timestamp: March 16, 2018, 06:22:11 am
content: What you need is not only high stability, but also low noise (differential and common mode). AN98 from Linear technology may be a starting point, I think there are some other ANs as well covering this. Using a good reference and a low ppm/K voltage divider (e.g. Caddock) together with a low drift OA should give you the voltage stability you need. Keep in mind, this voltage can be dangerous.

author: David Hess
author_rank: Super Contributor
timestamp: March 17, 2018, 01:30:35 pm
content: Reference noise gets multiplied by the output divider ratio. Drift is effectively low frequency noise. Filtering the reference is difficult to do without adding more drift but not impossible. I might also use several references in parallel or series to lower the noise compared to the reference voltage. See below about series stacking shunt voltage references.High close loop gain requires high open loop gain to maintain the same line and load regulation. Stacking references to produce a higher reference voltage will lower the closed loop gain for a given output voltage.Stacking 30 x 10 volt shunt references will yield 30 and 300 volts without additional errors from an amplifier and voltage divider. Stacking 3 x 10 volt shunt references will yield 30 volts and then a x10 amplifier can use an inexpensive precision 1:9 ratio standard resistor network.

author: BNElecEng
author_rank: Regular Contributor
timestamp: March 17, 2018, 02:40:07 pm
content: TI have an application note about stacking multiple REF50xx chips to achieve high voltage references:http://www.ti.com/lit/an/sbaa203/sbaa203.pdf

author: intabits
author_rank: Frequent Contributor
timestamp: July 05, 2018, 02:47:08 am
content: Sorry for the off-topic post, but where else would this go?From SBAA203.PDF (May 2013) p7:-"10000 REF5010 devices are used to build this device. This design probably hits the record of simultaneous use of TI parts in a single device."Not even close.IBM used TI transistors on their SMS cards, which were developed for the IBM 7030 aka "Stretch".https://en.wikipedia.org/wiki/File:IBM_7030_Stretch_circuit_board.jpghttps://en.wikipedia.org/wiki/File:IBM_7030-CNAM_22480-IMG_5115-gradient.jpgThis picture doesn't show the 33 feet of hardware behind this console!The 7030 used 170,000 transistors, probably most made by TI.So that "record" was beaten by a factor of 17, and 50 years!

author: Gyro
author_rank: Super Contributor
timestamp: July 05, 2018, 10:48:07 am
content: This thread resurfacing reminded me of a Youtube video that I saw, how to turn 9V batteries into an extremely lethal HV source. No soldering required! It might have some degree of short term stability and low noise at constant temperature, for a 300V stack at low current though.https://youtu.be/8hwLHdBTQ7s

author: TimFox
author_rank: Super Contributor
timestamp: July 08, 2018, 08:20:22 pm
content: Installing batteries in series up to a few hundred volts must be done carefully for personal safety reasons.Back in graduate school, when 300 V "B" batteries (Zn-C) were readily available, we put 10 in series to achieve 3000 V at low current.To avoid electrocution, we had the shop built a compartmented box out of acrylic plastic. The banana plugs connecting to the individual batteries were mounted on a cover panel that could be mated to the batteries simultaneously, with an appropriate safety cover over that panel.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 09, 2018, 12:10:08 am
content: Quote from: TimFox on July 08, 2018, 08:20:22 pmThis^^^^I have used a series string of 9V alkaline batteries (they're pretty cheap in bulk packs) as a source for comparing a 'unknown' 6.5 digit DMM against a trusted one. Not sure if that alone would be sufficient stability or low noise for meters in the 7.5-8.5 digit range. But I want to point out that I did so very, very carefully. And even when I was putting things aside and going to come back to them later in the day, I broke apart the string into <5 battery chunks before leaving it unattended.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 16, 2018, 12:14:43 am
content: Hi,I needed a supply to power vacuum tube noise diodes with a supply that has very low ripple and noise.The one below only has 120V output, but the circuit could be used up to 300V by adding more batteries and using a better reference and error op amp.I never tested stability, but noise is indeed very low (< 0.5mVRMS up to 100kHz).https://electronicprojectsforfun.wordpress.com/power-supplies/battery-operated-power-supplies/a-120v-40ma-battery-operated-power-supply/

author: james_s
author_rank: Super Contributor
timestamp: August 16, 2018, 01:43:27 am
content: I once got a bunch of lightly used 9V batteries that were changed out of the smoke alarms in a retirement home. At one point after the ones I hadn't used yet were starting to get old and leaky I chained a bunch of them together and lit a 240V 60W incandescent lamp and with a smaller string of batteries a 120V 75W bulb. It was weird to see line voltage lightbulbs brightly lit from batteries. I also recall striking an arc from a string of them, it was actually a little scary.

author: tkamiya
author_rank: Super Contributor
timestamp: August 31, 2018, 12:45:53 am
content: I saw that YouTube video and thought there is a tremendous amount of disrespect toward lethal power source. It's one thing to connect 10 or 20 but it is quite another to do 244 of them. In this configuration, any of the battery would need to withstand over 2KV of voltage, and encasement is simply not made for it. 9V battery can supply 500mA easily for short duration. That's more than enough to instantaneously kill.With any of them having low or high internal resistance, at any moment a few can open up. If this happens, there is a 2KV in an unknown location. Somewhere in video, the person makes a comment, some batteries are getting too hot to touch.I'm not against good natured fun and experimentation. But that's after taking necessary precautions and making preparations. Good thing the author lived to post the video....I didn't know those gator clip thing and thin gague wire could withstand that much voltage!