A sampling device samples a differential measuring voltage. The sampling device comprises a first holding device, a second holding device and a multiplexing circuit, which is configured to provide a differential sample of a sampled differential signal, derived from the differential measuring voltage by sampling with a first clock signal of a first clock rate, to the first holding device, at the occurrence of each HIGH-value of a second clock signal of a second clock rate being half of the first clock rate and provide a differential sample of the sample differential signal to the second holding device, at each LOW-value of the second clock signal. The sampling device comprises a reset device configured to reset the second holding device at or after each HIGH-value of the second clock signal and reset the first holding device at or after each LOW-value of the second clock signal.

A zero-crossing voltage detection circuit for detecting a phase voltage of a converter includes a comparator, a first transistor and a second transistor. The first transistor has a first base, a first collector and a first emitter. The first base couples with the first collector. The first emitter receives the phase voltage. The first collector provides a first voltage to a first terminal of the comparator. The second transistor has a second base, a second collector and a second emitter. The second base couples with the first base. The second base couples with the second collector. The second emitter receives a ground voltage. The second collector provides a second voltage to a second terminal of the comparator. The comparator compares the first voltage with the second voltage to generate a zero-crossing voltage signal.

A temperature measuring circuit includes: a first switch circuit configured to charge a capacitor upon receiving a first control signal and discharge the capacitor upon receiving a second control signal; a control circuit configured to set a control signal at a second control signal in response to an output voltage indicating that an inter-terminal voltage is higher than a first reference voltage, set the control signal at the first control signal in response to the output voltage indicating that the inter-terminal voltage is lower than a second reference voltage, and set the control signal at the second control signal in response to the output voltage indicating that the inter-terminal voltage is higher than a third reference voltage; a counter circuit configured to count a frequency of the control signal; and a temperature obtaining unit configured to obtain the temperature based on the frequency.