Patent ID: 7064552

Claim:
A device for determining an energy state of an energy storing device of a data carrier, in which a stabilized DC voltage for the supply of the data carrier is derived from an unstabilized DC voltage available at the energy storing device, comprising: an evaluation circuit connected to the energy storing device, said evaluation circuit comprising: an auxiliary capacitor having a first terminal and a second terminal, said second terminal being connected to ground, a measurement circuit connected to the first terminal of the auxiliary capacitor, measuring charging times of the auxiliary capacitor, an evaluation logic connected to an output of the measurement circuit, the evaluation logic determining a quantity describing the energy state of the energy storing device from the measured charging times of the auxiliary capacitor, and a current mirror arranged between the energy storing device and the measurement circuit, the current mirror having mutually parallel paths, wherein the first terminal of the auxiliary capacitor, the measurement circuit connected to the auxiliary capacitor, and the evaluation logic connected to the output of the measurement circuit are arranged in a first path of the mutually parallel paths and an ohmic resistor is arranged in a second path of the mutually parallel paths.