n00b part help?

[ian87]

trying to mod an MT-2 according to some info i received from Arn C. (thanks!), but i cannot for the life of me fiigure out this here part:

"R2:      10kohm -> Semitec CRD E102 (source follower load)
(Semitec CRD E102: Current Regulative Diode, 1.0mA, replaceable by JFETs of similar Idss values)"

anyone know of a workalike for this, or can someone at least point me in a direction? i can find ZERO info on this thang.

thanks much!

ian

[mikeb]

Just wanted  to say I can't help you at all, sorry.   (but at least you know someone cares)...

Mike

[Peter Snowberg]

One thing that makes it hard to find info about these things is that they're called by a bunch of different names. The names "constant current diode" and "constant current regulator" (CCR) are a little more common.

Several companies make these buggers, but you can also make one yourself using an N-channel JFET and a resistor. Simply connect the gate to the source with a resistor and there you go.... instant current regulator... to use it connect the gate as the cathode and the drain as the anode. You might want to start with a 10K pot, but that's just a random number I'm throwing out. The actual value will depend on the JFET.

For testing, hook up a 9V battery in series with a 1K resistor and the JFET and a good meter set for current measuring. You can then adjust the pot until you get 1.0mA on the meter.

For an example, check out the schematic here: http://www.forsselltech.com/JFET%20Opamp.PDF Q3 and Q4 are both N-channel JFETs used in this manner. Here's something maybe even a little better... an actual CCR datasheet http://www.vishay.com/docs/70195/70195.pdf

I hope that helps.

Take care,
-Peter

[ian87]

thanks, peter, for the info, and thanks mikeB for the love!