National LM317 or similar regulator can be used. Data sheet below

http://www.national.com/pf/LM/LM317.html

http://cache.national.com/ds/LM/LM117.pdf

Look on page 16 for a 1 amp current regulator circuit. Page 17 and 19 have
similar circuits for lower current. The "precision" circuit on p17 shows how
to make it adjustable. Remember that your load current flows through the
variable resistor, so make sure it has high enough power rating.

These circuits all assume that the load resistance is low enough that it
takes less than (Vin - Vdrop of Regulator - Vref ) volts across the load to
get the desired current. The LM317 needs about a 3V drop, and has a 1.2V
Reference voltage (which is dropped across the resistor). That leaves you
about 7.8V available at the load. Lower dropout regulators are available,
and most data sheets will show similar circuits.

Wilson


"daniel" wrote in message
...
is there a way of making a variable current supply with an output anywhere
form 0.1A to the maximum of the transformer but using a fixed voltage e.g
12V.

thanks