Driven switch body. (what about greater than one bootstrap)

I don't understand the drawing. Where does the Q9 BF862 JFET's source current go?

This is a version they sent me to check--Q6 is the tail current source for Q9, but it's drawn upside down. (My output is paper schematics plus BOMs, so their layout guy did the schematic capture.)

Cheers

Phil Hobbs

I had to change K1 to a 9-V coil part, because it didn't pull in reliably with a 12 V coil. Otherwise it worked fine. I still have one someplace.

Cheers

Phil Hobbs

Normally a TIA's output voltage is relative to the summing-junction return, FGND in this case, but here it's relative to FGND - Vgs of the JFET, where Vgs is a poorly-defined value. But you added a 2nd BF862 to match, trying to bias to Vgs=0 (for Idss = 10 to 25mA). Was this a design where you only needed to know relative output changes?

FGND is "floating ground". The probe tip has to have a bias voltage (AC and /or DC), and the simplest approach was to float the whole front end.

Cheers

Phil Hobbs