20-07-2011, 05:05 PM
The fifty times voltage-drop was new to me as well.
I've just started to use low-current (2mA) ones as it seemed ironic that I was fitting them to things to stop me from leaving them on and thereby draining the battery when in some cases the circuit itself didn't draw 20mA.
Rob's right about the voltages varying and I've always assumed 2.2 which seems close enough for any standard ones. If I've wanted to connect them to 3V I've always got away without a resistor.
These days it's easy to look at the data sheets and see just what they will stand and it's a simple matter to check with an ammeter that you aren't driving them too hard.
It isn't the end of the world if you do pop one. I blew a couple recently when trying to use a capacitor as a mains dropper; I ended up with a good old high-power 10K resistor and the LEDs are still working fine.
- Joe
I've just started to use low-current (2mA) ones as it seemed ironic that I was fitting them to things to stop me from leaving them on and thereby draining the battery when in some cases the circuit itself didn't draw 20mA.
Rob's right about the voltages varying and I've always assumed 2.2 which seems close enough for any standard ones. If I've wanted to connect them to 3V I've always got away without a resistor.
These days it's easy to look at the data sheets and see just what they will stand and it's a simple matter to check with an ammeter that you aren't driving them too hard.
It isn't the end of the world if you do pop one. I blew a couple recently when trying to use a capacitor as a mains dropper; I ended up with a good old high-power 10K resistor and the LEDs are still working fine.
- Joe
