current-sourcevoltage
I am just not sure that why in development labs, current sources are not as popular as voltage sources.
I have worked in different places, and they all have been using voltage sources.
I just want to find out why, in practice, voltage sources are much more popular than current sources. And, if there are applications that current sources are actually being used instead.
And what are the main advantages/disadvantages of using one vs. the other.
At some point if you want to have a current source that is fixed in uA, you need a primary voltage or current source. The mirror (as its name implies) just reflects a known current (maybe higher or lower if you parallel transistors (change transistor geometry) or introduce one or more emitter resistors, so then more like a magnifying mirror).
In an IC (and outside) you can servo all kinds of different current sources off a single reference current using weighted mirrors and such like, but you still need that current. Some ICs bring that node out to a pin, and you connect a resistor to Vcc or whatever so all the current mirrors in the chip are scaled by that current (which is more-or-less stable if Vcc >> 0.6V).
A voltage reference and a resistor is a kind of reference current (though note that the voltage of a current mirror input is not zero and changes at about -2mV/°C, so it won't be stable with temperature changes unless the voltage reference you use has a matching characteristic).
One way to get a voltage reference is to make a band-gap reference, which is naturally about 1.25V, but can be amplified to whatever voltage you like.
One IC that's worth studying is the TI (nee Burr-Brown) REF200, which has a representative schematic supplied on the datasheet. It has two two-terminal current 100uA +/- 0.5% source/sinks and a precision current mirror (full Wilson current mirror with emitter degeneration resistors). Also see AB165 , which covers a wide range of current sources.
IMPLEMENTATION AND APPLICATIONS OF CURRENT SOURCES AND CURRENT RECEIVERS
You will never get the ac and dc performance with the Wilson current mirror that the Howland current source can attain. Plus the Howland can sink and source current.
For the Wilson current pump, consider the mirroring BJT's constant current region - there is a voltage on the base set by the "other" BJT (that is acting like a diode) and you know that this sets a current into the base of both transistors - look how compliant the graph is - outside the saturation region. It's not really a good constant current source when Vce changes: -
The Howland current pump (on the other hand will have a compliance graph that is as flat as a pancake meaning you can swish Vce around and the collector current will remain really quite flat (dependent on resistor matching of course).
Best Answer
There are no advantages or disadvantages. Some devices require constant voltage. Some devices require constant current.
Majority of the DUTs** require constant voltage. That's why most of the bench top power supplies, which you have encountered in the labs, are constant voltage. Keep in mind that a descent lab power supplies have and adjustable max current threshold and 2 modes: constant voltage (CV) and constant current (CC). CC mode is activated automatically, when the DUT tries to pull more than the max current. Often, it's a sign of a problem, when a DUT wants to pull more current than expected.
Few DUTs require constant current. LEDs, for example. Often, a constant voltage supply powers a separate constant current circuit, which in turn powers a constant current DUT.
** DUT - device under test