There are normally-closed SSRs that have depletion fets inside, but they could fry form too much power.
Ixys is making self-protecting SSRs that can be used as both switches and current limiters.
I recently designed a 32-channel VME SSR board. We measure the voltage drop across the switching mosfets plus a small padder resistor, and run some FPGA code to protect the switches. The diffamp is the interesting part.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Thanks Phil, I had to go look up 'my' specs on a laser drive. (Copied from Jan Hall years ago.) I quoted
Answer to ligo noise
GH
which doesn't quite do what you want, but it's interesting.
I am at both ends of the spectrum. Some projects require top performance regardless of cost. Some are low-qty and NRE matters much more than BOM cost. With others every penny is turned around and the cost calculation has four digits or more after the decimal. Milli-Cents. See-sawing between projects with pricey LTC parts and projects where a LM324 already costs too much is fun.
Once I was ridiculed here when mentioning that I occasionally use 5%,
10% and 20% resistors. On one such project the client asked me to provide a list of max tolerance relaxation for all resistors. This effort cost 1/4 billed hour and the client had that fully amortized in less than three months.-- Regards, Joerg http://www.analogconsultants.com/
In saturation, yes.
I like to do this, when I'm feeling discrete, and short on voltage:
Obviously, it will have R1 + Rds(on) resistance in saturation (that's voltage saturation, not FET current saturation, to be perfectly pedantic).
Don't know if that's competitive to your 7 cent LM339, or whatever it was.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Just general principles. Schottky rectifiers aren't known for low reverse leakage, and the metal shape definition presumably involves a wet etching process.
There are references in LL101 Schottky diode data to 'guard ring', a technique to limit surface fields which transport dirt. I suspect contamination in diode leakage, as a matter of course (and there's some VERY nice low-leakage specs on JFET gates to bolster my preference for subsurface junctions). The same culprit would move a reference by a few millivolts.
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If you confined the switched currents to within a very small footprint abov e ground plane you may be able to get away with one.
My 1996 millidegree controller - which used a switcher to control the curre nt through the Peltier - ended up being turned into a laser diode temperatu re controller. One of my co-authors - Paul Buggs - did it, and I'm still in contact with him (after a fashion) and could ask what he actually did.
He was the guy who briefly reinstated the development prototypes linear Pel tier feed to establish that switching driver wasn't injecting any noise int o the original temperature controller.
-- Bill Sloman, Sydney
everse leakage,
There aren't a lot of wet etches done in IC processes anymore--RIE is essen tially universal. There are still reasons to prefer buried structures, most ly having to to do with surface states, and I have no data about the stabil ity of V_f in Schottky barriers.
Cheers
Phil Hobbs
The CPUs and display are worth more than that.
Den torsdag den 7. december 2017 kl. 02.27.25 UTC+1 skrev snipped-for-privacy@notreal.com:
"Worth" ?? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
It's what you learn, after you know it all, that counts.
worth noun Definition of worth
1 a : monetary value - farmhouse and lands of little worth
"Worth" is in the eye of the delusional consumer. Value is in the eyes of the bean counters. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
It's what you learn, after you know it all, that counts.
Wrong.
Worth is in the eye of both the seller and buyer. Since we're talking about BOM cost, the consumer has nothing to do with it. Cost and price are only loosely correlated (only in that price is usually greater than cost). "Value" and "worth" are exactly the same thing. In this case, quite obviously the components are worth what they cost (because the transaction happened).
Thanks.
The offset of the discrete diff pair will likely be a problem in this case, though--I'm trying to keep the burden down to 250 mV or less, with accuracy of a couple of percent, so +-5 mV is about what I can tolerate.
The MC33078/9 is pretty hard to beat for this sort of job--it's 20 times as fast as the LM324/358 and almost as cheap, at the price of more bias current (300 nA-ish).
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
Easy, just get one of those matched--oh... Easy, just do it monolithic, you need 10k+ of these right?... :^)
That doesn't go to the rails, though..?!
324 won't go to +V rail either; do you have further-out rails available to run the opamp from?Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
I have +12 and +5. The previous version was all +12, but this one has to be shrunk down a lot, so thermal management is an issue.
I need +12 for the laser driver because I want it to be sub-Poissonian (i.e. have less than full shot noise) out to 125 mA. That requires a lot of voltage drop across the sense resistor.
Cheers
Phil Hobbs
5V is nice for TEC's. I tend to pick them undersized, with big heat sinks, so that it's hard to melt them when run full bore as heaters. I guess that limits the minimum temp. I'll then add thermal limits to the drive circuit.
Hmm, I've got a laser diode drive with a 60 C limit. (that's the max temp on the LD spec sheet, I run it under the max current so should be able to raise the temp. That would let me pull more lasers to 795nm. (Lasers typically run at 780 nm, the other half of rubidium's 'doublet'. Tuning laserheads at >60C calls for 'cooks' fingers, hot stuff :^)
George H.
Even "consultants" that say "pay me 2 bitcoin and I will restore your data"?
-- This email has not been checked by half-arsed antivirus software
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