I am trying to drive an IR LED, but even with a transistor it looks dim (through the phone camera).
To eliminate all variables (unreliable Vin pin on ESP, unreliable 3.3V pin, defect transistor) I mounted it on a breadboard and attached a 5v power supply to it.
5V, 220 Ohms resistor, 1,2V forward voltage: LED still looks pretty dim, but 17mA check out
So I tried a 10 Ohms resistor, but to no avail. The LED looks brighter, but is still very dim and it draws 35mAs. Weird. as there should technically be ~300mA.
To crosscheck this I attached a normal red LED (I know that a 10 Ohms resistor ist way too small and would burn out the LED), but it shines bright and draws.... 20mAs.
Am I missing a huge fundamental concept of electrical engineering here or what is happening?
You can't see the actual infrared,. There can be visible light but that's not what an IR LED optimized for.
Something is limiting the current and the voltage is dropping (or something is wrong with your measurement). With 5V applied and 1.2V across the LED, that leaves 3.8V across the resistor, and 3.8V/10 Ohms is 380mA. That's Ohm's Law... Physics and a law of nature (with man-made units-of-measure).
Check if the 5V is "holding up".
P.S. I've seen some "impossible" things before but you've got to believe the physics. The last time I had something unexplainable it was an intermittent connection and although seemingly repeatable, the intermittent connection was why two different tests/measurements didn't agree.
Is to check the data sheet and obey the ratings. For typical LEDs, it is 20 mA max.
Please post a schematic, with pins, parts and connections clearly labeled.
I was checking the resistor again and saw that I read the value wrong (the blue metal oxide resistors are sometimes hard to read for me) and it was a 100Ohms resistor, so the ~34mA checks out.
Mea culpa.
I used to time to read about the workings of transistors and learned that they have a fixed Ic current based on the supplied base current.
The LED now shines bright (even in the phone cam) and is able to reach a receiver further away.
Now I am afraid that I got it working through sheer luck and not because I used the specs correctly.
Looking at e.g. 0.1mA Ib it hits two curves (Ic 1mA and 10mA) and my theory starts to crumble.
In the book I am reading there was an example graph for a BJT I could get behind.
Uce is fixed and the Ic is dependant on the supplied Ib, but I can't find such a graph in the datasheet I linked.
What am I missing?^
And what is with cases in the diagram above where the values are something different than 1,10,150 or 500mA?
Yes, regular bipolar transistors are "current amplifiers". But in practical circuits they are more-often used as voltage amplifiers or as a "switch". The hfe (current gain) varies from part-to-part so linear amplifiers need to take that into account also.
In digital circuits, transistors are used as switches. They are usually "off" with zero (or near-zero) base-emitter current and near-zero collector-emitter current.
Or they are "on" and "saturated" with the collector-emitter current limited by something else (like a resistor in series with an LED). To saturate a transistor, you'll typically feed-in about 0 times as much base-emitter current as required. i.e. If the transistor has an hfe of 100, you'd need to 10mA to get 1A through the emitter-collector, and load. But, you might supply 100mA to the base "saturating" it and getting the maximum current through it, limited by the load resistance.
There can be visible light but that's not what an IR LED optimized for.
