3.5.1.3 Power Failure Detection

For safety reasons, it is important to detect a power failure on the Peltier side. There is a possibility that a wire comes loose, or the fuse blows on that section, both of which would disconnect the Pelter from power.

A standard approach for this problem would be to implement a voltage divider network and measure the input voltage to the Peltier plate. However, this would make the system unable to detect an open Peltier element, dead switching transistor or damaged current sense resistor. Additionally, this would require an additional I/O pin and add another point of failure.

Instead, the system uses the output of the current sense amplifier to detect a power failure. The amplified value is compared to a set point in a DAC. If the amplified value is below a low-level threshold, then the system considers this a power failure, and shuts down the Peltier circuit. The input to the current sense amplifier is protected by a current-limiting resistor on its input, with additional protection derived from its low-side position in the circuit.