Linear bench power supply

I had some Amazon.com gift cash available, and I became frustrated with my second switching bench power supply in a year giving up the ghost on me, so I tried buying a linear power supply, this one:

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I've only really owned switching bench supplies as bench space is at a premium for me at the moment and I liked how much voltage and current one could cram into a small package.

With this one, when I adjust the voltage up and down through certain points, I can hear mechanical relays clacking, I'm assuming they're switching in and out the taps on the big-ass main transformer. Clack, click, clunk.

I'm a little concerned about these relays failing over time if Im often changing the supply voltage up and down - any experience with this?

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Reply to
bitrex
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Well, if it moves, it wears out. You ought to get 1E5 clunks out of even a crappy relay, if it isn't switching too much current. I typically adjust th e supply quite seldom, so unless it was in an ATE setup or something, I pro bably wouldn't worry.

For bench use, I commend my favourite 75W solution: a random laptop brick p owering a 150 kHs Simple Switcher buck converter, followed by a cap multipl ier. For the positive side, you can put the cap multiplier inside the regul ation loop (using split feedback). On the negative side, you have to put in a diff amp, but either way you can get ripple way below your average linea r's.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

I have the older analog-meter version of that supply and it's been working fine for years. The relays don't clack very often.

At that Amazon price, you could keep a couple of spares around.

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$1260. But it has GPIB, whatever that is. Some ancient HP minicomputer interface, apparently.

Reply to
John Larkin

We resell the Mastech bench supply... now changed name to Volteq. I haven't heard any complaints about the relays failing. I guess it will depend in part on the quality of the relay.

George H.

Reply to
George Herold

If I remember right, the Fluke 410 10kV power supply had a couple of relays. Up and down several times a day for the duration of several PhD runs. Even survived a good dusting from a dry chemical fire extinguisher - I gave it a wash and bake (probably due for that anyway - chemistry lab).

I remember an HP high current supply that clacked it's way up and down as well. When we ordered a new version, the relays had been replaced by an SCR pre-regulator.

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Grizzly H.
Reply to
mixed nuts

So to get ~20v max, you might have a 12v brick, a variable buck converter with a 2v dropout, and a x2 cap multiplier? Can a variable buck go down to 0v output?

Reply to
Tom Del Rosso

That was called HPIB at the time, at least by them.

Reply to
Tom Del Rosso

Yeah. I read the original design specs, which seemed to be in some txtra-terrestrial language. The state charts were astonishing.

It took me a while to figure out that they used the word "signal" to mean "ttl logic level on a wire."

Does anybody still use this?

Reply to
John Larkin

Sure. With a Prologix GPIB-Ethernet adapter, it's a breeze.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

I do, although not entirely happily. For a long time, I dreamt of instruments with a real network connection. The sad thing is that we have that today, but nobody dares using it for fear of getting their expensive instrument hacked! And don't talk to me about the idiotic choice of OS most instrument makers made! Grrr!

Jeroen Belleman

Reply to
jeroen Belleman

Cap multiplier = RC lowpass with an emitter follower hung on it.

If you need more voltage, start with two laptop bricks in series, use a fancier converter, or float the laptop brick's output and use the inverting buck topology. (You can make an arbitrary positive voltage that way, in principle.)

You can use the free AC at the switch pin and make a voltage doubler out of it, which actually works really well, but you need huge caps if you want any serious current out of it.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Also in some large organisations, anything with an ethernet port or a PC in it allows the IT department to make rules about what you can do with it.

One place, they wanted to install some sort of company spyware on all of the computers in the labs, including ones doing real time control. They even bought a linux version of the spyware to run on my linux machine controlling an experiment. I suggested that if I wanted to avoid any extra latency or the need to upgrade the PC hardware due to running the spyware then perhaps I needed to change over the instrument control PC to a raspberry pi or some other architecture (since they did not yet have a version of the spyware that runs on those), but then they decided to let me leave it alone without the spyware.

Reply to
Chris Jones

Our test benches are all migrating to Python and Ethernet. We add a second Ethernet interface to each test computer so that none of the test traffic is on the company network. We use red Ethernet cables for the local nets.

I just finished designing our new "universal" test set, Ethernet based, with 272 DPDT relays. We'll hang a DVM, counter, and SMU on that same Ethernet. Maybe a scope, too.

The performance/price of Ethernet is thousands of times better than GPIB.

Reply to
John Larkin

IEEE-488 For hobby stuff, it's the interface used on 30 year old test equipment. The National Instruments PC cards are rather expensive.

The specification is horribly complex, but you typically don't need

99.9% of it. Many instruments talk in text strings. A simple parallel port interface can be made to work on one instrument at a time. I built a little PIC processor serial to IEEE-488 converter that just buffers text strings back and forth. Modern computers don't have serial ports, but serial via USB and serial via Bluetooth are cheap. Obviously, I don't need speed.
Reply to
mike

Only time I worried about it was in the rare case where the output voltage was right at the relay trip point and the current varied widely. It would click, click, click. I wouldn't run it long like that. Small change in voltage fixed it. Seems like some hysteresis would have fixed it...not sure how many supplies have that problem.

Reply to
mike

And Tektronix.

Reply to
jurb6006

Not sure what you mean by "at the time". GPIB was still sold and in use just five years ago. It is one of those very long lived interfaces like RS-232 or PC-104. I think it may finally be pretty much dead. The protocol is duplicated in some instrumentation bus I seem to recall though.

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Rick
Reply to
rickman

It is an IEEE standard, 488.1 for physical connections and 488.2 for command protocol.

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-TV
Reply to
Tauno Voipio

But what else can "signal" mean in a digital communications link? CMOS logic level or RS232 logic level?

Reply to
Tom Del Rosso

Well, at the time HP made test equipment!

They called it HPIB as if they invented it. I saw a datasheet for the TI chipset, and at least they didn't call it TIIB.

Reply to
Tom Del Rosso

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