Patent ID: 8922139

Claim:
A driver circuit configured to provide electrical energy at a drive voltage at an output of the driver circuit wherein the electrical energy at the drive voltage is derived from electrical energy at an input voltage at an input of the driver circuit, the driver circuit comprising: a power converter configured to convert the electrical energy at the input voltage into electrical energy at the drive voltage; a controller configured to control the power converter such that the power converter provides the electrical energy at the drive voltage; wherein the controller is configured to stop operation subsequent to an interruption of electrical energy provided at the input of the driver circuit, and resume operation subsequent to the provision of electrical energy at the input of the driver circuit; and a timing circuit coupled to the controller, wherein a timing voltage at the timing circuit decays with a pre-determined time constant if not maintained; and wherein the controller is configured to maintain the timing voltage at or above a first voltage level when the controller is in operation, determine an indication of a residual level of the timing voltage when the controller resumes operation after an interruption of electrical energy provided at the input of the driver circuit, and determine an indication of the duration of the interruption of electrical energy provided at the input of the driver circuit based on the first voltage level, the pre-determined time constant, and an indication of the residual level of the timing voltage.