Timeline for Transistor as switch in variable voltage environment
Current License: CC BY-SA 3.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 3, 2015 at 17:06 | vote | accept | kolosy | ||
| Oct 5, 2013 at 5:08 | comment | added | Russell McMahon♦ | @kolosy all the answer you need is in my answer. Your question is too distributed to be sure what you really want. IF you can tolerate say 0.05V lower than battery Vmin then a MOSFET can be made to work. But, can you tolerate this. Who can say. You don't. Use a MOSFET. And look at my Rb sizing fo a bipolar. Smaller Rb is OK. And note that Vast_bipolar is NOT usually 0.7V, except by fluke - it may be 0.05V say through 1V+ deep-ending on situation. Use a MOSFET. Use a MOSFET. | |
| Oct 4, 2013 at 20:05 | comment | added | kolosy | sorry, but all the detail is there, including what raw vin looks like, what the load on the sensor is, etc. i appreciate your answer, but the question was can a transistor (bjt, specifically) work in an environment where Vc looks like it does here. You answered the "if not, then what" part, but not the original question. | |
| Oct 4, 2013 at 14:22 | comment | added | Russell McMahon♦ | More and better data allows instant answers without multiple passes. | |
| Oct 4, 2013 at 14:13 | comment | added | Russell McMahon♦ | @kolosy It would be better if you slightly refined your question. Saying things like "that's essentially the problem" means we MAY get "that's" right and may not. IF say V_LiFePO4_minimum minus a truly tiny amount - say 50 mV, is enough then just use a MOSFET of suitable low Rdson and it will work. If "Raw Vin" is higher and always available you should say so and say what it is. A linear regulator may well do a fine job when fed from Raw_Vin. You say sensor is 7 mA load. What other loads are there? What is sensor max allowed or desired voltage in your application? | |
| Oct 3, 2013 at 16:25 | comment | added | kolosy | that's essentially the problem. the alternative is to run off of the raw Vin for the whole circuit, which can vary quite a bit, hence the original question. | |
| Oct 3, 2013 at 6:29 | history | answered | Russell McMahon♦ | CC BY-SA 3.0 |