TECH TALK

Power Bugs
Power bugs (also called taps or just ”bugs”) are probably the most common method used to connect power to backplanes.  Bugs mount on the rear side of the backplane and provide a screw to fasten a ring terminal or bus bar.  They are rated up to 22 amps per connection.  Typically, there are one or more bugs for each voltage (+12V, -12V, 3.3V, and 5V) and ground.

Plug-in Power Connector
CompactPCI and VME64X backplanes can accommodate plug-in power supplies.  A 38-pin or 47-pin Positronic power connector compliant to the PICMG 2.11 specification is installed on the front side of the backplane. Dual Positronic connectors are required for redundant power applications.

Power Nuts
Power nuts are mounted on the front side of the backplane.  A screw threaded into the nut from the rear secures a ring terminal.  6/32 PEM nuts are rated at 42 amps per connection.  These sometimes are selected over a screw stud or power bug due to their low profile.

Screw Studs
The M4 screw stud (also called a lug) is another termination option.  Rated at 18 amps each, these are small enough to be installed between slots to save space.  They secure ring terminals and are commonly used to connect chassis ground.

Screw Studs

Fastons
Fastons accompany other power connectors to allow additional power while taking minimal space.  The 6.35mm (0.25") blades are rated at 12 amps each.  They are often used to connect +12 volt input supplies. 

Faston Spade

ATX Power Connector
A standard for PCI systems, ATX supplies have been adopted by CompactPCI systems for cost savings.  The standard 20-pin Molex ATX connector is mounted on the rear side of the backplane to directly connect an ATX power supply.

Bus Bar

Bus Bar
Bus bars provide a convenient way to attach bulky power cables to the backplane.  This method distributes large amounts of power efficiently and simplifies wiring.  Bus bars are mounted to the backplane using screw studs or power bugs.  They are not as common as other fasteners described above.

Bus bars are often found in VMEbus systems to carry +5 volts and ground.  They commonly mount between J1 and J2 in a VMEbus system.  For VME64X, they are installed in a 1U space below J2, meaning the VME64X backplane must be 7U high.  Bus bars are rated up to 125 amps for a 21 slot backplane.