what is the range of acceptable current going into the base? why does it drop for a darlington?
did i mention that you are the man, unclejed?
did i mention that you are the man, unclejed?
because the current gain of a darlington is the beta of the first transistor multiplied by the beta of the second. so if the current gain of each transistor is 100, the total gain is 100*100, or 10,000. the only thing in a darlington that adds is the base-to-emitter voltage drop. because the gain is so much higher, the bias "knee" will be much sharper, so your bias adjustment will be more sensitive than it was for a single transistor
argh. sorry to keep buggin' you, but it appears i'm still doing it wrong. I can't even get the LED to light up with the darlington. unclejed, would you mind doing a refresh of the schematic with the values you think I need?
If you really want it small and stuff...
Seems to me that you might have a better go with using a comparator for this little project. For what it's worth:
A SOT-23-5 comparator: http://ww1.microchip.com/downloads/en/DeviceDoc/21696f.pdf. Have a look at pages 15-16 for how it works. 10uA of standby current, runs off 1.6-5.5V. 30mA output current will drive an LED directly.
And CHEAP!: Digi-Key - MCP6541RT-E/OTCT-ND (Manufacturer - MCP6541RT-E/OT)
Seems to me that you might have a better go with using a comparator for this little project. For what it's worth:
A SOT-23-5 comparator: http://ww1.microchip.com/downloads/en/DeviceDoc/21696f.pdf. Have a look at pages 15-16 for how it works. 10uA of standby current, runs off 1.6-5.5V. 30mA output current will drive an LED directly.
And CHEAP!: Digi-Key - MCP6541RT-E/OTCT-ND (Manufacturer - MCP6541RT-E/OT)
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