currentcurrent-limitingmaximum-ratingsoperational-amplifieroutput
Im looking to drive an LED, but am not sure if i should use an op-amp or bjt configured as a switch. Is it possible for an op-amp to source roughly 10mA; the current needed to drive an LED in series with a resistor?
If this depends on the type of op-amp, then how would I go about figuring out the maximum current an op-amp could source?
You most probably don't have a LED 'with a maximum voltage of 2V when powered from a 5GV source', but a LED that is rated for a maximum of 20 mA.
Components that have a low resistance, and particularly ones that approximately drop the same voltage over a wide current range, are rated for a maximum current, not a maximum voltage.
For most components, voltage and current have a fixed relation that can be found in their datasheet. In most cases it is their product (power P = V * I) through power dissipation that causes a temperature rise above what the integrated circuit material is rated and causes it to fail. The maximum could be expressed in either power or voltage. But when component and temperature variations can cause the same voltage to cause widely different currents, it makes more sense to express the maximum as a current. OTOH, if above a certain voltage breakdown will occur, but the breakdown current is not easy to specify, it makes more sense to express the maximum as a voltage.
Summary: the maximum is generally expressed in the unit that is (for the components at hand) most stable.
EDIT - IGNORE C1 - unfortunately this is the only circuit that I could find with the Rout component shown within the feedback loop so, please ignore C1 - it is not meant to be there.
This technique is used (with care) a fair amount: -
Ignore C1 and just analyse how much current the op-amp can supply to a load in the place of C1. If the maximum output of the op-amp is (say) 4 volts (+/-5 volts supply), there can be no more than 53mA delivered into a short circuit.
On normal loads, the op-amp has to work a bit harder because the 75 ohm forms a potential divider BUT, the good side is the feedback loop compensates for this.
Best Answer
Usually we're concerned with how much loading can be put on the output and still have it function properly. The output swing specification will be at a specific load resistance, usually load is between the output and ground on both dual and single-supply op-amps. For example, the dual-supply OP-07:
You can see that over the whole temperature range with +/-15 supplies it is guaranteed to have a swing of +/-11V with a 2K load, meaning that it can supply +/-5.5mA. If the supplies are different then the current may be different.
If you're primarily interested in short-circuit maximum current, that is not always specified, though some op-amps do have numbers. For example, the ubiquitous LM324:
As you can see, it guarantees (at 25°C) the output short circuit current won't exceed 60mA, but it's only guaranteed to source or sink 5 or 10mA. Also note that the LM324 has a (nominal) 50uA current sink on the output so if you ask it to sink more than some tens of uA the output will no longer get that close to the negative rail. If the load is a resistor to the negative rail, the issue does not arise.
In general the minimum guaranteed current (for it to work properly) is going to be much smaller than the maximum guaranteed short-circuit current (if they even give a number for the latter).