LED CCS questions...

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#2
Hi,
by steep do you mean less voltage change for a wide range of operating current?

If you are looking for a voltage reference then you want little change in voltage, provided the temperature coefficient does not get significantly worse.
 
#5
In Doug Self's discrete preamp article, I read that the tempco of a LED is very close to that of a BJT. To check this, I rigged up a test circuit comprising a transistor ccs, biased with a red LED. I monitored the current with my meter whilst heating the assembly with a hairdryer. If both the transistor and LED were heated equally, there was little change in current. If either was heated more than the other, the change was significant. This experiment was crude, but it showed that an LED biased ccs is good enough for me.
 
#8
Isn't the function of the diode (Red or Green LED or just 1N4148) in the CCS to provide a voltage drop with which to bias a transistor? If that's the case, isn't the issure the stability of the voltage drop rather than the current?

I seem to recall from an experience trying to get a CCS / LTP to do what I wanted, where I was scrathing my head and making the repeated measurement to try to fathom things, hat the only thing measurement that always came out the same was the thedrop across a red LED. Hot, cold or luke warm. However, if you swapped out for a different PN from as different mfg -- then you would get a change.
 
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