What's a good medium-power opamp? I need to source/sink at least 60 mA, with say +-7.5 volt supplies, and swing +-6 maybe. No particular requirements otherwise.
I suppose I could boost a cheap SOT-23 opamp with a couple of cheap SOT-23 emitter followers....
v+ | c \\ +----Rb---b npn \\ | e \\ | | \\---------+----Rx----+------- / | | / | e / +----Rb---b pnp c | v-
but a single part would be nice; I have to do this 16 times on a smallish board.
John
Your suggested approach is probably the least fraught with possible stability problems.
But when I need lots of near-rail-to-rail swing I put resistors in the VCC and VEE lines and add the transistors there (e.g., base to VCC pin, emitter to rail, collector to output point... if you don't need rail-to-rail, tie OpAmp output to collectors).
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
Single:
Slower dual:
-- Regards, John Popelish
The 8272 looks good, especially so since I'll be essentially driving a bypassed power rail, and it doesn't mind capacitive loads. It's $1.30 at 1K, but it would save me a lot of parts, 16 times. Boosting a small opamp into a bypassed load would add, say, 7 more parts.
16 x 7 = 112!John
Like this....
v+ | v+ R | | e \VCC----------------------b pnp \ c \ | \--------------------+-------OUTPUT / | / c /VEE---------------------b npn | e R | | v- v-
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
Yeah, that's neat but harder to analyze for stability. One would
*really* have to trust the Spice models, or test the heck out of it.I can imagine way too many oscillation modes!
We recently did something similar, using opamp supply currents to drive transistors sort of like that, but current-mirror mode, to turn the opamp into a fairly precise current source. The sim we did didn't work at all, apparently because the opamp model doesn't actually pull current from the rails!
John
If you tie "Output" back to the OpAmp out it resolves to just a compound follower.
Spice models can be treacherous, which is why I roll so many of my own.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
You can't use a regular amp with biased npn/pnp into the rail and then sum the 16 others into its input?
Why not? I once had to cram over 50 parts onto the size of a standard
40c postage stamp. Now wait, that'll be 41c soon. 0201, SC75, oh what fun to debug.-- Regards, Joerg http://www.analogconsultants.com/
If I had trusted SPICE every time many of my design would not exist today. Can't remember the last time I fired up SPICE. Some time last year I guess.
-- Regards, Joerg http://www.analogconsultants.com/
But you aren't building a very complex structure from individual devices. My chip designs are almost always way over 1000 devices.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
True. However, some designs are, let's say, highly unorthodox. For example SPICE often isn't very useful when you have to use the saturation behavior of a custom-mix ferrite as a design parameter. Or in detecting and handling mode jumps of a laser diode. Or mapping sound wave reflections from a biopsy needle in a diseased area of human tissue.
-- Regards, Joerg http://www.analogconsultants.com/
It sounds like, pretty soon, you and Jim are going to have to collaborate -- your scales of construction are constantly converging!
Tim
-- Deep Fryer: A very philosophical monk. Website @
Anybody got decent models for ferrite beads?
John
[snip]
I seem to recall seeing one... maybe Google ?:-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
=A0|
=A0c
=A0c
=A0|
The supply voltage is lower than you want - absolute maximum +/-6.5V - and the guaranteed output current is only 50mA, but it has a surprisingly potent output stage.
-- Bill Sloman, Nijmegen
For pure frequency domain stuff, yes:
However, saturation is another matter. I've not seen much there that I could really use. In the end you have to design a circuit that can find the onset and slope and auto-calibrate. Ferrites are like a pasta dish. When Giuseppe cooks it tastes different than when Antonio is the chef.
-- Regards, Joerg http://www.analogconsultants.com/
ad826 is close I think, and dual
-Lasse
Have you looked at the audio headphone or speaker drivers? National makes dozens. If they are stereo, you only need to do it 8X.
Tam
Check out if an audio amp might fit. For example, one version of the LM386 goes to 18V single supply if you really need 15V total:
Those are really cheap, well under 50c in qties.
[...]-- Regards, Joerg http://www.analogconsultants.com/
-- Doesn't sound like much of a trade to me... ;)
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.