Has any one ever applied oven heated diodes in a circuit to keep the Vf down to a minimum?
I remember years ago I was tossing this idea around in my head but didn't have the resources to experiment with this idea.
Thinking a glass type package may live longer.
Jamie
Vf goes down but Rs goes up. Most diodes have a crossover temperature where the Vf vs If tempco is zero. That can be quite low, like 10 mA, for some small schottky diodes.
Try low-barrier schottkies maybe, before going to the trouble of heating them.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
On a sunny day (Wed, 19 Jun 2013 17:51:21 -0400) it happened Jamie wrote in :
Schottky, Germanium...
Probably not worth the trouble, what with the availability of Schottky and back diodes, or for normal speeds, comparators and FET bridges.
I did once know a guy who, against my advice, insisted on using a breakpoint amplifier made with diodes. He eventually had to put the diodes in a crystal oven to make it work acceptably. Talk about an exercise in turd-polishing.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
The first closed-loop controller that I designed (I must have been 19 or 20 then) had a feedforward nonlinear breakpoint thing, 709 opamps and diodes and such. It approximately mapped the throttle lever position into steam valve position open-loop so that the PID stuff could be disabled if necessary (like in case of a broken tach) and was also be constrained in its range of influence (to limit catastrophic runaways.) Worked fine, 32,000 horsepower.
Signal swing was +-10 volts so a little diode TC didn't matter.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
A lot of NIM bin systems used the +/- 24V power supplies to good effect; with the right op amps, and higher signal voltages, the diode breakpoint thing is very well behaved.
Modern design with +5V single supplies is just NOT well behaved, and (IMHO) low voltage analog design is like playing tennis wearing a straitjacket. White straitjacket, of course.
Single-supply analog is a nuisance, but there are some great RRIO opamps around now. You can do some nonlinear breakpoint things by just letting opamps rail.
My latest fave is AD8565, a really remarkable part.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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I got chucked in the deep end on my first engineering job too, but not quite like that.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
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The "deep end" is the best place to learn. In fact I thrive on "impossible" specifications, and topics I have not a clue about when I take on the job. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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I love to cook with wine. Sometimes I even put it in the food.
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I was turning a trimpot and nearly rippled the LASH ship off the dock at Avondale Shipyards. I got it up to 60 RPM, about half speed. A ship's engineer ran over and shut me down. I could have dumped some gangways into the Mississippi and killed a few guys.
Lately I do things that don't have such consequences.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
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I'm having trouble visualizing the "feedforward nonlinear breakpoint thing" inside an error driven closed feedback loop- usually the feedforward would adjust a parameter to stabilize the loop dynamics which would otherwise va ry widely as a function of some other input.
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inside an error driven closed feedback loop- usually the feedforward would adjust a parameter to stabilize the loop dynamics which would otherwise vary widely as a function of some other input.
I meant that the basic forward direction was throttle pot, nonlinear fungen, valve positioner, no RPM feedback.
Off to the side was the shaft tachometer, error amp, PID controller thing that summed into the fungen output. It had a limited range of influence, about 20% of steam valve travel, and "RPM feedback" could be shut off if there were any problems. Properly trimmed, actual RPMs followed the throttle setting pretty well, but sluggish.
The steam valve was a 3-stage thing, itself very nonlinear by design, because a ship's speed is nonlinear on shaft horsepower. It was a low pressure hydraulic servo, powered by lube oil from a gravity tank at deck level.
I'd never done a control system before. I sumulated it on a PDP-8 in Focal, plotted transient response sideways on a roll-paper teletype at 10 cps and hand-colored the curves. We showed it to the owners' consultant, a crusty old marine Chief Engineer, and he said "that's just the way an experienced operator would work the valves by hand" so we got the job.
Ships are mostly diesels nowadays, because they are much easier to maintain. Steam plants are really, really complex.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
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inside an error driven closed feedback loop- usually the feedforward would adjust a parameter to stabilize the loop dynamics which would otherwise vary widely as a function of some other input.
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aoperator
regulating steam generators are no problem, the secret is in the (D) parameter of the PID loop. :)
Jamie
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