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Question, How can I turn On an LED powered by 2 AA Batteries Switched on from a low voltage .15v from a small Genorator? When the wind blows The small Generator has a propeller and I would like to send a signal to turn on the The LED that is powered by 2AA batteries. The generator Is not powerful enough to light the LED on it's own for this application. It is a model of a wind turbine for demonstration purpous so it will not produce enough power on its own to light up anything. Thank you for your help

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marked as duplicate by laptop2d, Community Feb 3 '17 at 16:46

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    \$\begingroup\$ Why are there so many 0.15 generator questions!? \$\endgroup\$ – Bradman175 Jan 31 '17 at 7:03
  • \$\begingroup\$ Because the question is not answered. The generator is acting as a resistor and feeding volts to the gate so I kept clarifying \$\endgroup\$ – Randy Severino Jan 31 '17 at 7:41
  • \$\begingroup\$ Its a good idea to do some research before asking 1)there are many similar questions 2) this site is mostly about electrical engineering design, meaning that you come up with a design, and when your stuck we give you help. Post a schematic of what you have tried 3) If your first question got closed, it needs some work, reopen the first question. If it doesn't get reopened that means its off topic and posting a simmilar question probably will get closed also \$\endgroup\$ – laptop2d Feb 1 '17 at 17:16
  • \$\begingroup\$ Some of those answers did not work. They caused the generator to pulling current like a motor and started spinning. \$\endgroup\$ – Randy Severino Feb 3 '17 at 16:45
  • \$\begingroup\$ analogsystemsrf solved the question correctly. Great job. \$\endgroup\$ – Randy Severino Feb 3 '17 at 16:47
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Connect the generator to Emitter of some NPN transistor (small signal is fine). Connect the collector to 100 ohm resistor, other lead of resistor to LED's cathode (bar of the bar+arrow symbol), LED's anode to +3 volts.

Now the key: use 2 resistors to bias the NPN transistor's base to 0.5 volts; figure 100microAmp drain on the battery at all times, unless you include a switch. We want 0.5 volts across the bottom resistor, 2.5 volts across the top resistor. A good way to view resistors, to design without a chululator, is express the current as Ohms/Volt; our 100uA is 10,000 ohms per volt. Thus we need 5Kohm from base to GND/RTN/-Battery, and 25,000 from base to VDD/+Battery. If you don't have exactly those, use 4.7Kohm and 24Kohm.

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  • \$\begingroup\$ Wow. thanks, I hope it does not make the Generator Turn like a motor when it is connected to the Emitter? You know what I mean? Would a Mosfet be better? thank you. \$\endgroup\$ – Randy Severino Jan 31 '17 at 7:38
  • \$\begingroup\$ The delta-Vin is 150 milliVolts. A silicon junction (the EB) will at room temperature increase the current by 10:1 for every 58 milliVolts increase in Vbe. You should expect nearly 1,000X increase in current; there will be some idling current. \$\endgroup\$ – analogsystemsrf Feb 3 '17 at 15:30

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