| ??? 03/17/09 15:37 Read: times |
#163533 - 10 mA??? I don't think so! Responding to: ???'s previous message |
David Prentice said:
Assuming that your ULN2803 has all eight darlingtons conducting, this allows 1.25mA through each LED.
You can parallel some port pins, but from the data sheet, there is still a limit of 25mA for the whole port. The SGS data sheet says, "...Each darlington features a peak load current rating of 600mA (500mA continuous)..." I've often used this device sinking 50 mA per output for longer than 1-second at a time, and with a duty cycle of 40% or so with no ill-effect. It will warm up ... since it drops some voltage (Vce) at a that current-per-darlington and produces a proportional amount of heat. You may of course be using an 8051 with enhanced output sink ratings. If you are not, then I predict some blue smoke. I doubt it will be "blue smoke" but it is likely to fail. The current flowing through the GND pin of the '2803, will be the sum of all the collector (output) currents. If the device that drives that pin is incapable of the (maximally 4 A) current flowing through the 8 collecotors, the voltage at the GND pin will rise, if the sink path is resistive as it would be with a MOSFET driver. This applies to the MOSFET output on an 805x, and that's not capable of sinking much current at all. David Let's try to encourage the O/P to read the datasheets and not rely on "smoke-testing" and speculation. RE |
