A switch controller (102, 702, 703) for at least one power switch (106, 702, 706), the switch controller comprising: a primary side comprising signal transmission circuitry to transmit signals representative of a desired driving of the at least one power switch; a secondary side isolated from the primary side and comprising signal reception circuitry to receive the signals representative of the desired driving and a drive signal generator (130, 630, 688) to generate a drive signal (148, 548, 648, 689, 748, 709) in response to and in accordance with valid signals received by the signal reception circuitry; and a signal transformer galvanically isolating the primary side from the secondary side but inductively coupling the signal transmission circuitry to the signal reception circuitry; wherein the secondary side signal reception circuitry further comprises a validation circuit (128, 628) to validate signals received by the signal reception circuitry, the switch controller being characterised in that the validation circuit comprises: a validation comparator (670, 671) to compare a parameter of the signals received by the signal reception circuitry with a validation criterion (660, 661), a timer to time a duration within a measurement period of time that the parameter of the signals received by the signal reception circuitry satisfies the validation criterion, wherein the measurement period of time is shorter than a time between 100 and 1000 nanoseconds, and a second comparator (678, 679) to compare the timed duration with a threshold duration and, in response to the timed duration exceeding the threshold duration, output to the drive signal generator signals (144, 146, 547, 549, 647, 649, 678, 679) indicative of the validity of particular signals received by the signal reception circuitry. a primary side comprising signal transmission circuitry to transmit signals representative of a desired driving of the at least one power switch; a secondary side isolated from the primary side and comprising signal reception circuitry to receive the signals representative of the desired driving and a drive signal generator (130, 630, 688) to generate a drive signal (148, 548, 648, 689, 748, 709) in response to and in accordance with valid signals received by the signal reception circuitry; and signal reception circuitry to receive the signals representative of the desired driving and a drive signal generator (130, 630, 688) to generate a drive signal (148, 548, 648, 689, 748, 709) in response to and in accordance with valid signals received by the signal reception circuitry; and a signal transformer galvanically isolating the primary side from the secondary side but inductively coupling the signal transmission circuitry to the signal reception circuitry; wherein the secondary side signal reception circuitry further comprises a validation circuit (128, 628) to validate signals received by the signal reception circuitry, the switch controller being characterised in that the validation circuit comprises: a validation comparator (670, 671) to compare a parameter of the signals received by the signal reception circuitry with a validation criterion (660, 661), a timer to time a duration within a measurement period of time that the parameter of the signals received by the signal reception circuitry satisfies the validation criterion, wherein the measurement period of time is shorter than a time between 100 and 1000 nanoseconds, and a second comparator (678, 679) to compare the timed duration with a threshold duration and, in response to the timed duration exceeding the threshold duration, output to the drive signal generator signals (144, 146, 547, 549, 647, 649, 678, 679) indicative of the validity of particular signals received by the signal reception circuitry. a validation comparator (670, 671) to compare a parameter of the signals received by the signal reception circuitry with a validation criterion (660, 661), a timer to time a duration within a measurement period of time that the parameter of the signals received by the signal reception circuitry satisfies the validation criterion, wherein the measurement period of time is shorter than a time between 100 and 1000 nanoseconds, and a second comparator (678, 679) to compare the timed duration with a threshold duration and, in response to the timed duration exceeding the threshold duration, output to the drive signal generator signals (144, 146, 547, 549, 647, 649, 678, 679) indicative of the validity of particular signals received by the signal reception circuitry.