Patent ID: 9680382
Date: 2017-06-13
CPC Classifications: G01R,H02M

Claim:
1. A frequency determination circuit comprising: a positive crossing sense circuit coupled to sense a positive crossing of an input voltage coupled to be received from a dimmer circuit in response to the input voltage being greater than a first threshold voltage after a first threshold number of cycles has passed and after a zero crossing of the input voltage, wherein the zero crossing of the input voltage is detected in response to the input voltage being less than a second threshold voltage for a second threshold number of cycles; a validation circuit coupled to the positive crossing sense circuit to validate a previous zero crossing and the positive crossing of the input voltage after the positive crossing of the of the input voltage has occurred, wherein the validation circuit is coupled to sense an invalid previous zero crossing and positive crossing of the input voltage in response to sensing another zero crossing of the input voltage before an end of a third threshold number of cycles; and a measurement circuit coupled to the positive crossing sense circuit and the validation circuit to count a time between positive crossing pulses of the input voltage, wherein the measurement circuit includes a measurement counter coupled to a measurement register, wherein a measurement count of the measurement counter is coupled to be saved in the measurement register and wherein the measurement counter is coupled to be reset in response to each positive crossing pulse that is received from the positive crossing sense circuit, wherein an output signal of the measurement register is representative of a frequency of the input voltage.