@Lawrence -- yes, one must utilize that a 100 ohm resistor was used in the output circuit for the 2nd and 3rd test series. I will be working on trying to build a higher-output DUT; but if you have another prototype, I would be glad to test it! So far, prototype A is our best DUT... @all: No answer as to how the output LED an be so bright... I don't have a solution either. The question stands: PhysicsProf: Now here's the question -- the input LED is noticeably dimmer with 0.75V in, but the output LED remains VERY bright. Now, the input power RMS according to the scope analysis is 160 micro-watts... that's 0.16 mW. And the current in the output circuit determined by the output resistor (100 ohms) is something like 1.33mV/100ohms =13.3 microamps, which is not much at all for lighting the LED.
Now that bright output LED is running at less than 2.3 volts (2.3 V rms across the output including LED and 100-ohm R) with a current of about 13 MICROamps. How in the world does it light up so brightly?? [/b] My colleague John at the University has a PhD and a great deal of electronics experience -- and he was puzzled by the brightness of the output LED given the input power -- and the output power. So he hooked up a light detector to get a quick look at the LED signal -- on channel 2 (so ignore the power calculation in the attachments below). The first is with the white LED provided by Lawrence. We noted that this has a phosphor which extends the light output, so we replaced this with a fast-response red LED, and obtained the second plot. With the red LED, it is clear that the light output is in synch with the jump in output voltage -- no surprise there. Then back to the white LED, but with the red LED in parallel -- but with reversed direction. Guess what, BOTH white and red light up in this case! the RED faintly... but shows that there is a back EMF in the output circuit to light the reversed red LED.... More fun. Still the mystery remains, how the white LED can glow so brightly under these conditions, such low power input.
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