bcarso
Well-known member
Jens, where does the 20mA per LED come from (or is that for two of them)? I understand the worst-case 14mA per pair of 6.81k's per mic. Then you have a 1.7-3.6V LED depending on color, and a 10k resistor to 48V, so you will have no more than about 4.6mA per LED. So I get (4.6 + 4.6 +14 + 14) mA, or 37.2mA total not counting any other loads including the regulator voltage setting divider and the regulator operating current.
You mentioned 3 LEDs in the beginning of the thread, but I assume the third one can be run from a lower voltage.
It's just the inefficiency of the low-volt LED run from 48V that I was lamenting---not that you have much choice when that's your starting voltage (actually, one thing you could do would build a reg-per-mic circuit with the LED in series with the reg output going to the two 6.81k's, with feedback around the LED so that it didn't impair regulation. Then when the light was on you would know that the mic was not only being supplied voltage, but that it was drawing current as well. This would require a slightly higher unreg voltage to compensate for the LED drop though).
Anyway, no harm in making the supply handle 70mA.
I think you will have fun with discrete or hybrid (hybrid here meaning a combo of discretes and ICs) votage regulators, but again the three-term devices may be fine for the application.
You mentioned 3 LEDs in the beginning of the thread, but I assume the third one can be run from a lower voltage.
It's just the inefficiency of the low-volt LED run from 48V that I was lamenting---not that you have much choice when that's your starting voltage (actually, one thing you could do would build a reg-per-mic circuit with the LED in series with the reg output going to the two 6.81k's, with feedback around the LED so that it didn't impair regulation. Then when the light was on you would know that the mic was not only being supplied voltage, but that it was drawing current as well. This would require a slightly higher unreg voltage to compensate for the LED drop though).
Anyway, no harm in making the supply handle 70mA.
I think you will have fun with discrete or hybrid (hybrid here meaning a combo of discretes and ICs) votage regulators, but again the three-term devices may be fine for the application.
