This circuit has been taken from a site that show how can we turn-on
an ultra-bright red led with radio-waves energy.
The radio-waves should create a voltage on the 1 wavelength antenna loop(the left square).
The darlington transistor should amplify the current and turn-on the led.
My questions are:
1)What is the minimum voltage that the antenna loop need to have in order to turn on the led?
I know that generaly there is ~1.4V(0.7VX2)voltage drop on the base-emitter of darlington pair,
so,it seems like the loop must produced at least 1.4V in order to turn it on,
but i am not sure.(maybe it might turn on on lower voltage?)
2)according to the circuit:at the moment that to loop will reach to the minimum voltage
that it can turn on the led,
Is the right transistor(second) will be on saturation state,while the left one(first) will be in active state?
or both are on active state?what are the hFE of each transistor?
Thanks in advance.