19-02-2018, 06:52 AM
The CCS is for a LTP, it also serves in a cathode follower. I've built the single tranny version just using the MJE340, but apparently this has a low Zout as the hFE of the 340 is low. So you plonk the smaller Q in to increase Zout. AFAIK Zout is basically Re x Q1 hFE x Q2 hFE - hoe (which I don't know how to find and isn't on datasheets) is low, so can apparantly be left out.
"the tempco of the LEDs or zener needs to have the same polarity as the BE junction. Otherwise it will makes things worse, not better. " Could you expand on this please Jeffrey, how is this calculated/solved?
As the application is for a valve circuit, precision isn't important. I keep meaning to have a play with the ring of two CCS, but am unsure how one figures out Zout and wouldn't a ring of two with added upper Q be better still?
Thanks for your help lads, Andy.
"the tempco of the LEDs or zener needs to have the same polarity as the BE junction. Otherwise it will makes things worse, not better. " Could you expand on this please Jeffrey, how is this calculated/solved?
As the application is for a valve circuit, precision isn't important. I keep meaning to have a play with the ring of two CCS, but am unsure how one figures out Zout and wouldn't a ring of two with added upper Q be better still?
Thanks for your help lads, Andy.
