The simpler galvanostat consists of a high-voltage source producing a constant voltage
U with a resistor
R_{x} connected in series: in order to force an almost constant current through a load, this resistor shall be much higher than the load resistor R_{load}. As a matter of fact, the current
I through the load is given by : I = \frac{U}{R_x + R_{load}} and if R_x>>R_{load}, the current
I is approximately determined by
R_x as follows :I \cong \frac{U}{R_x} This simple realization requires rather high voltages (~100 V) to keep the load
current constant with sufficient approximation for all practical purposes. Therefore, more complex versions of galvanostats, using electronic amplifiers with
feedback and lower voltages, have been developed and produced. These instruments are capable to feed constant currents in the ranges from few
picoamperes (pA) to several
amperes (A); typical construction for use in the lower range of feed currents uses
operational amplifiers. == Example of application ==