Does anyone know what this diode is for? [SOLVED] - Page 1
Forum section: electronics / projects

author: DiligentMinds.com
author_rank: Newbie
timestamp: November 07, 2012, 02:41:12 am
content: .

author: w2aew
author_rank: Super Contributor
timestamp: November 07, 2012, 04:45:14 am
content: My first thought would be that it is used as part of temperature compensation. The tempo of the NPN b-e junction somewhat compensates for the Zener tempo. Perhaps the diode is helping to minimize variations in the opamp q-point vs. temperature.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: November 07, 2012, 05:19:36 am
content: I'd say it is supplying the power to the LTZ1000 block.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 07, 2012, 05:39:13 am
content: the blurb from linear tech says:QuoteApart from seeing that, I cant help.

author: elal1862
author_rank: Newbie
timestamp: November 07, 2012, 11:22:22 am
content: My best guess would be: To prevent the opamp's output from sinking current.Having a source/sink voltage source sounds nice, but they can have some serious stability issues.So the diode is (most likely) there to prevent instability -or even oscillation- under certain load conditions.

author: w2aew
author_rank: Super Contributor
timestamp: November 07, 2012, 03:01:25 pm
content: Quote from: DiligentMinds.com on November 07, 2012, 05:18:41 amI still suspect it's part of fine temperature compensation. Even though its inside the feedback loop, it will have a small influence on the opamp's output voltage vs. temperature, thus have a very small influence on the input voltage difference, and therefore on the input bias currents vs. temperature. Note that the input bias current changes vs. temperature might not be included in the LTSpice model.

author: muvideo
author_rank: Frequent Contributor
timestamp: November 08, 2012, 01:51:26 am
content: Hello, while waiting for Linear's answer I give my thought.Probably is useful to startup correctly the reference,upon startup both opamp inputs are zero, so dependingon the unit's input offset, the out will try to go either up,following starting the reference, or down locking it.The diode will keep the opamp without feedback untilthe out will not forward-bias the diode, so it will amplifythe noise on inputs with a gain of few million times.So basically it's waiting that the noise will steer the outthe correct way (up) to start the reference.Disclaimer: here is late, so I could have written strangeor plainly wrong thingsSo I asked also advice also on volt-nuts mailing list,they are the ones on these sort of things.Fabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: November 08, 2012, 10:51:42 am
content: Quote from: DiligentMinds.com on November 08, 2012, 05:54:45 amNot bad from a non EEBy the way that's all the best I'm happy to win on a friendly forum,the problem is when that is all my employer wants to pay,and is becoming too frequent here latelyFabio.

author: ecat
author_rank: Frequent Contributor
timestamp: November 08, 2012, 05:02:06 pm
content: I do know this much,Albert Einstein:He graduated from high school at the age of 17 and enrolled at the Swiss Federal Polytechnic School in Zurich. Albert graduated in 1900 with a degree in physics.Bill Gates:A dumpster diver, bullshitter and to all intents a thief - allegedly.Nikola Tesla:Earned degrees in physics, mathematics, and mechanical and electrical engineering from the Austrian Polytechnic Institute... Before he moved to the US and became famous?

author: muvideo
author_rank: Frequent Contributor
timestamp: November 08, 2012, 05:08:06 pm
content: Quote from: DiligentMinds.com on November 08, 2012, 03:46:35 pmSo it's even worse, I have a degree (ME), so no hope for me, I'm doomed...

author: free_electron
author_rank: Super Contributor
timestamp: November 08, 2012, 05:30:28 pm
content: you know how einstein was always bad at maths ? well, i'm even worse !

author: ecat
author_rank: Frequent Contributor
timestamp: November 08, 2012, 06:33:50 pm
content: Quote from: DiligentMinds.com on November 08, 2012, 06:02:45 pmI'll give you the Tesla history, I had a vague memory there was some complication. Still, I'd bet money he would have passedEinstein: I thought his lack of any degreewasthe 'popular opinion', which is why I jumped in - A recent T.V. program went out of its way to make this point. Could have been a mathematics and physics teaching diploma?

author: ecat
author_rank: Frequent Contributor
timestamp: November 08, 2012, 08:09:44 pm
content: Quote from: DiligentMinds.com on November 08, 2012, 06:49:01 pmMost definitely, but this was the BBCQuote from: DiligentMinds.com on November 08, 2012, 06:49:01 pmNo, you're ok. At the end of the day all we can do is wave our willies in the direction of that which we each believe to be the most credible source while skirting the issue of Norma Jeane jollies.Quote from: DiligentMinds.com on November 08, 2012, 06:49:01 pmditto