Power supply control for low voltage I2L circuits

A controlled current supply circuit for semiconductor circuitry, such as I L, which has an unscaled part (10) which remains continuously active and a scaled part (12) which, when not in a data processing mode requiring a high current can be operated at a much lower current so that the data therein is preserved and power is saved. Unless switching between low and higher currents is carefully controlled then there is a risk of data being lost. The present invention provides a current supply circuit (14) which in response to the generation of an on-signal or off-signal causes the current supply to the scaled logic (12) to increase or decrease in a number of steps, there being a sufficiently long time delay between steps to allow the scaled logic (12) to settle. The rate of increase or decrease of the injected current is such that there are smaller increments or decrements when the overall current is low causing the scaled logic (12) to be low and larger increments and decrements when the overall current is high causing the scaled logic (12) to be fast.