Supply voltage monitoring apparatus

A supply voltage monitoring apparatus for use in monitoring a value of a supply voltage of an automotive vehicle, a circuit comprising:

• An analogue to digital converter (ADC) having an input for receiving an analogue voltage signal and an output for outputting a digital signal, and
• An input stage which connects the input of the ADC to a power supply at a point where the value of the supply voltage Vlink is to be measured, the input stage comprising:
• a potential divider having an upper resistance and a lower resistance, the two resistances connected in series to two nodes, a first node providing a connection to the supply voltage and a second node providing a connection to ground, the centre tap of the potential divider being connected to the input of the ADC,
• a switchable lower resistance which is connected in series with a switch between the centre tap of the potential divider and the ground, and
• a control circuit which is arranged to hold the switch open when the voltage at the centre tap is below a threshold value and to hold the switch closed when the voltage at the centre tap is above the threshold value.