Could some electronics guru please clarify the following ? An LED is a diode, so the maximum voltage drop through it should be approximately 0.7 V. Recently, I was casually going over some LED driver design related Web pages, which stated that typically the LED voltage drop is around
3.3 - 3.5 V ? Could someone please point out how this is possible ? Am I missing something important ?
Yes, "bandgap".
~0.7V is for silicon diodes. Other materials have other voltages. For example, germanium diodes are (were) ~0.2V.
LED junctions are made from materials with high bandgaps, tending to increase with decreasing wavelength. So infrared LEDs are ~1.7V say, red LEDs 2.2V, blue leds 3V, UV leds 4V etc.
-- John Devereux
-- http://en.wikipedia.org/wiki/Band_gap#List_of_band_gaps
Kids these days. Look up "germanium diode".
Mark L. Fergerson
"panfilero"
** It does more.The
The FET & LED circuit connects to the TL072 all the time.
It indicates power is connected and max signal level by getting brighter.
... Phil
Because most audio design is nonsense.
John
The parallel resistor keeps the fet biased for conditions where the LED won't be conducting. I'm not really sure why they care for an indicator light.
My confidence level is not very high for this circuit. First of all, nobody good does 4 way connections. If they did, they would put a dot in the schematic.
Lots of AC coupling here for a circuit that isn't battery powered. BTW, I've bought a dBx compressor on ebay for probably less than this will cost you to build.
Your reply is incredibly unhelpful, John, even for you. Please dump your narcissistic attitude for a while and relax.
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