So you believe that heat disappears once it gets to the case? I'm talking about the real theta_JA in the real system, not the marketing number. You can't usefully write equations containing marketing numbers.
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
hobbs at electrooptical dot net
http://electrooptical.net
You're missing the point. I'll address the math on Sunday+ ...Jim Thompson
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| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Maybe, but I don't think that I am. The two dice are not meaningfully coupled thermally--the lead frames are completely isolated, and the plastic isn't much better at heat conduction than air is.
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
hobbs at electrooptical dot net
http://electrooptical.net
There's a speed vs. accuracy tradeoff, though. Slowish mirrors made with quick op amps are great, but trying to make a fast, accurate mirror that way is surprisingly difficult, mostly because the op amp needs a big input error to reach maximum slew.
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
hobbs at electrooptical dot net
http://electrooptical.net
One interesting possibility is to let the current mirror mostly do its own thing, but use an op amp to null out the average error in the emitter circuit via a voltage divider. Hmm, might be useful.
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
hobbs at electrooptical dot net
http://electrooptical.net
There are better ways, think charge pumps used in PFD's. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
In a built-up circuit? I can see it in an IC, provided the switching frequency is sufficiently far out of band. (There's a trick used in high power audio amps, to equalize the supplies: you ground one end of an inductor, and switch the other end from VCC to VEE. Any DC imbalance goes away magically, and the switcher doesn't have to supply the whole load.)
My interest is primarily in making accurate replicas of photocurrents for use in bandaging nonlinearities elsewhere in the system, e.g. Figure
12 of
formatting link
. So switching noise is a no-no. (As I say to myself over and over, there's SMPS quiet and then there's instrument quiet.)
I've been working for awhile, on and off, to make a noise canceller good to an honest 70 dB from DC to 10 MHz. The analogue accuracy and noise requirements are pretty stringent, and it has to work over about a
1000:1 photocurrent range. The combination makes it very interesting. Even with gussied-up mirrors, it needs three automatic tweaks per photodiode--R_ee' at DC, and AC tweaks of j omega and omega**2.
It simulates great, and I have some PDs that by my measurements should be adequate, but we'll see when the boards are done. My beautiful PCB hunchback and opera singer got chucked in the deep end on that one--over
200 parts, all connected to each other. She learned to swim pretty well, and is now doing her first client work. The analogue board will go out to fab later this month.
Hopefully Firmware Hunchback and I can get the CPU board done soon, and it'll be a product this year. (I'm like butter spread over too much bread at the moment.)
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
hobbs at electrooptical dot net
http://electrooptical.net
I rarely do "built-up" circuits, though that kind of project is in the works.
Have fun ;-) ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Since the collector and emitter are swapped (right?), it's possible that the transistor could "just work", depending on the circuit.
See this electronics.stackexchange.com question:
formatting link
"Q: What will happen if for a BJT transistor it's Emitter terminal is treated as collector and collector as Emitter in a common Emitter amplifier circuit?"
"A: (Short Answer) It will work but will have a lower ? (beta)"
Perhaps the circuit can work with a lower beta. Or, if not, perhaps some component values can be modified to aid that.
"Low saturation" transistors (usually switching types in the 20-100Vceo,
1-10A range) have surprisingly good inverted hFE, especially in regards to the spice models, which almost unanimously give erroneous fractional BR parameters (presumably, to improve modeling of the forward region only). Veb is still limited though.
(Whose flight to LAX via DTW got cancelled this afternoon.)
--
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
hobbs at electrooptical dot net
http://electrooptical.net
Yep. The circuit did work... only it was marginal on breakdown. Problem was solved by eliminating need for PNP. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
There are a few transistors around that have high Vebo. For example,
2SA1252/2SC3134 (PNP/NPN), which are guaranteed to 15V.
If I had any, I'd measure the reverse beta.
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
I seem to remember stories of stuff that stopped working because the reverse beta dropped over time, it could then magically be fixed by touchin g the transistor with a lit cigarette (or soldering iron) the heating restoring the beta
Not sure if the "164" was forward or reverse, or at what voltage.
...Since it's reversed hFE, should it be hEF? ;-)
These I think are obsolete now (the baggie is also empty, oh noes!), but I imagine the newer ones (PBSS303NX,115, etc.) have similar behavior. Haven't measured more, haven't needed the behavior either.
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