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RIS-797, programmable isolated current-source charge-pulser

Started by Winfield Hill December 28, 2019
 The RIS-797 project is for an isolated, programmable
 current-source charge-pulser, using the op-amp MOSFET
 techniques analyzed in x-Chapters 4x.26.  This uses
 four 0.5pF isolator channels to run an I2C DAC and
 the current-source, including a range switch.  Total
 output node capacitance to ground = 5pF, mostly due
 to DC-DC power-supply module.  Two-terminal floating
 current sources can be used either as source or sink.
 DC-leakage is expected to be zero, up to several kV.

 See file RIS-797_isolated_charge_5pF-capacitance,
 in the DropBox folder:

https://www.dropbox.com/sh/tcmiahzzughadfk/AABtgFDy01cuTDWDRjujP6jva?dl=1


-- 
 Thanks,
    - Win
Winfield Hill wrote...
> > The RIS-797 project is for an isolated, programmable > current-source charge-pulser, using the op-amp MOSFET > techniques analyzed in x-Chapters 4x.26. This uses > four 0.5pF isolator channels to run an I2C DAC and > the current-source, including a range switch. Total > output node capacitance to ground = 5pF, mostly due > to DC-DC power-supply module. Two-terminal floating > current sources can be used either as source or sink. > DC-leakage is expected to be zero, up to several kV. > > See file RIS-797_isolated_charge_5pF-capacitance, > in the DropBox folder: > >https://www.dropbox.com/sh/tcmiahzzughadfk/AABtgFDy01cuTDWDRjujP6jva?dl=1
The technique can be used for currents ranging from nA to hundreds of amps. Once you connect a terminal to a supply or ground, the output capacitance of the current source will depend on the Coss of MOSFET Q2 (plus extra 5pF, but NOT if used as a current sink). For example, a 600-volt AO3162 has Coss only 0.45pF. Table 4x.5 has HV MOSFETs with Coss from 6.9 to 20pF. The 100V 515W 400A-capable HUF75652G has Coss 2345pF. We're talking about a four-order-of-magnitude range. The voltage compliance range of the CS is equal to the supply voltage, minus about 12V. The response speed to load changes is very fast, because the Q2 cascode transistor is largely independent of Vds. The response speed to programming changes can also be very fast, usually in the MHz region, except the suggested 12-bit MCP4921 DAC settling time is 4.5us. The RIS-792 posts (and files) discussed test-fixture boards (mobo plus three daughters) meant for quick evaluation of various component combinations. These will also be available with free shipping, as soon as we order more. Maybe a RIS-797 PCB will come later. -- Thanks, - Win