leds as bias resistors

[pro_crip]

I have read here and there people talking about using hlmp-6000 leds instead of resistors, especially as a bias resistor. What are the guidelines for making such a swap, aside from: pull out resistor, swap in led? Or is it all as simple as that? Thanks.


Rich

[JC]

It will depend a lot on just what Voltage you are looking for.  IIRC, a forward-biased LED will drop in the neighborhood of 1.4-1.6 Volts.  If you need more, you will need to add resistance in series, or another diode or LED.  If you need less, you will need to make other arrangements.

You will also need to keep in mind how much current you expect to be traveling through the LED and avoid exceeding its forward current limit.

So, if you know the Voltage you are looking for and you know the current in the circuit you can figure it out.  It may be as simple as swapping the LED for the resistor or it may be a little more involved.

Of course, it is also necessary to keep in mind that the LED will need to be installed in the correct direction; a resistor is bi-directional, but an LED is not.

[2wo]

Well. It can be as simple as that But you need to check a few things. If you are looking to replace the cathode resistor in a simple gain stage. Measure the voltage across the resistor. Red LED’s bias at about 1.2-1.9 V, if the voltage across your resistor is close, say 10% or maybe a bit more and the current does not exceed what the LED can handle, your done. Or you can stack two 1.2V LED’s if you need 2.5V. From here it get’s a little more complicated but not much…John