To measure transistor characteristics using the NANO-R4 board ( see "Transistor Curve-Tracer") , a constant-current source for the base current with the following characteristics is required:

-  Range from 2 µA to 4000 µA in increments of at least 1 µA
-  Switchable from positive currents (for n-type devices) to negative currents (for p-type devices).
-  Switchable from current (base current) to voltage (gate voltage) for field-effect transistors 

Unlike my previous projects with isolated current sources—I  had to use  DC/DC converter for the power supply and isolators (e.g. ADUM.....) for the SPI/I2C bus—I made it here  without these specialized and more expensive components.

Except for the 5V voltage reference (e.g., ZRB500), the I2C DAC MCP4725, and an electronic switch (e.g., TLP2222A),  I only need an inexpensive dual op-amp (e.g., TL072) for voltage inversion with a gain of +/- 1  [1] and for voltage-to-current conversion (Negative Impedance Converter (“NIC”) [2] ). 

With this design, I also only need one electronic switch (TLP222 or similar) instead of the usual four.

The switching from current to voltage for FETs (using a resistor) hasn’t been implemented here yet, and only maximum gate voltages of +/- 4V can be generated;

for that, an additional op-amp is needed.

The Current Source can use not only for the Curve-tracer.

The linearity is very good; the accuracy above 20 µA is better than 1%, and it can be further improved, for example, by using higher-precision resistors in the inverter and the “NIC".

Power consumption is very low; overall, the Curvetracer consumes less than 0.5 W (with a relatively dim display and small collector currents), allowing for extended operation on a single 18650 battery. 

 

The current source alone consumes less than 0.1 W, in contrast to the isolated constant-current source, which consumes approximately 1 W. 

[1] https://gusbertianalog.com/opamp-with-gain-switch/
[2] https://www.elektroniktutor.de/analogverstaerker/ui_konv.html