3.13.2 Power Supply Protections

Multiple short-circuit protection circuits are built into this system. Starting from the AC side, there is a mains-side fuse for the commercial-grade AC-DC power supply. If the main power supply ever faults, this fuse will trip. This provides additional protection for the system in the event of water ingress or other unexpected conditions.

Continuing on the DC side, there is a fuse on each of the power inputs to the main board. The Peltier side (HV Domain 2) uses a user-replaceable 3AG fuse while the digital logic side (HV Domain 1) uses a board-mount SMD fuse. Different fuses were selected because the Peltier module consumes a lot of current with current spikes, while the digital logic side should never see such large transients. It is expected that if the logic side fuse trips, something failed catastrophically, thus requiring the board to be repaired before it could be used again.

Next, Positive Temperature Coefficient (PTC) self-resetting fuses were added to each of the fan headers on the board. This ensures that if a fan short-circuits, the +12V rail will also not be shorted. Another protection for the +12V rail is from the MCP1754S linear regulator. This linear regulator contains short-circuit protection with current-foldback limiting. The last power protection on the board are two PTCs on the +5V and +12V outputs to the display board. This ensures that if the connector is short circuited, the current is limited.