A galvanostat (also known as amperostat) is a control and measuring device capable of keeping the current through an electrolytic cell in coulometric titrations constant, disregarding changes in the load itself.
Its main feature is its nearly "infinite" (i.e. extremely high in respect to common loads) internal resistance.
The designation "galvanostat" is mainly used in electrochemistry: this device differs from common constant current sources by its ability to supply and measure a wide range of currents (from picoamperes to amperes) of both polarities.
The galvanostat responds to changes in the resistance of the cell by varying its output potential: as Ohm's law shows,
{R}={U\overI}
Uc={Rv x Io}
Io
Uc
Rv
The simpler galvanostat consists of a high-voltage source producing a constant voltage
U
Rx
Rload
I
I=
U | |
Rx+Rload |
and if
Rx
Rload
I
Rx
I\cong
U | |
Rx |
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.
Galvanostatic deposition techniques can be used for some thin film deposition applications where there is no need to control morphology of the thin film.