It seem to me that the active NPN is the one with the higher base voltage, which corresponds to the input with the higher voltage. The other NPN is turned off regardless of whether its corresponding input is within the specified range or not, because its emitter is pulled high by the active NPN.
Sylvia.
You are right. If I'd been thinking harder when I posted that's what I woul d have said - I think. I must have let the fact that the input transistors are PNP's blind me to the fact that long-tailed pair involved are NPN's - t he input PNP's are just there for level-shifting and protection. They'd be lateral PNP's with a large emitter-base breakdown voltage and not much curr ent gain.
Sorry about that.
-- Bill Sloman, Sydney > The > other NPN is turned off regardless of whether its corresponding input is > within the specified range or not, because its emitter is pulled high by > the active NPN. > > Sylvia.
Sylvia, You are correct and Slowman is wrong (no surprise ;-)
Refer to the schematic in this Fairchild datasheet for a clearer view:
You don't "push" an emitter "down"... it turns OFF, it _is_ a diode after all.
I correctly described the situation two mornings ago in:
Message-ID: ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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 I was concentrating Sylvia's attention on the important transistors, I wasn't as wrong as most of the people who have posted in this thread. Fro m a pedagogic point of view my post - though wrong - was more useful than y our post of the 29th April 2015, which doesn't point out where the problem occurs, and strikes me as perfectly useless - though correct.
-- Bill Sloman, Sydney
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.