TECH TALK

A journal of bus architecture tips & techniques

Choosing CompactPCI Power Supplies: Review of Plug-In

Four main types of power supplies are common in CompactPCI systems:  ATX, plug-in, open frame, and modular.  In a previous article, I reviewed one type: ATX.  Let’s discuss another power supply favorite:  plug-in supplies. 

Plug-in power supplies are popular because they can be easily removed, providing a simple means of service from the front panel. These supplies mount into the front of the enclosure and connect directly to the backplane.  You don’t have to deal with a wiring harness.  These features are critical for high availability systems requiring hot swapping of dual or N+1 redundant power supplies.  They are a great choice when a rear I/O card cage prevents a supply from being mounted in the back of the chassis. 

Plug-in power supplies are easily integrated into standard Eurocard (CompactPCI or VMEbus) enclosures. They use common dimensions:  3U or 6U high by 160 mm deep by one (4 HP) or two (8 HP) slots wide.  They range from 125W to 600W and accept both AC and DC inputs.    

CompactPCI plug-in power supplies conform to several electrical and mechanical specifications:

• PICMG CompactPCI 2.0 R 3.0.  Defines voltage distribution, tolerance, ripple, and capacitance.
  
  
• PICMG CompactPCI 2.11 R 1.0.  Defines electrical and mechanical interfaces and connector pins.
  
  
• IEEE 1101.10.  Defines front panel, EMI gasket, alignment pin, injector / extractor handle, and front panel keying.

Backplane connection
Plug-in power supplies connect to a standard 47-pin Positronics hot-pluggable power supply connector.  This connector usually is mounted vertically on the right side of the backplane or on a Power Interface Board (PIB).  Two Positronics connectors are provided for high outputs, redundancy, and N + 1 supplies.

The PIB is a separate board containing power circuitry for a backplane and Positronics power connector.  It is used to connect a plug-in supply to a standard backplane built with regular power taps.  PIBs are 3U or 6U in height and wide enough for single or dual power supply configurations.  They mount securely next to the backplane.  The AC or DC input is wired directly to the PIB, which provides a physical connection to the backplane for 3.3V, +5V, -12V, and +12V.

Cooling
Plug-in power supplies rely on the chassis manufacturer for cooling.  Their design allows air to be moved through them.  Since they can slide into the card cage to mount beside CompactPCI boards, they take advantage of the existing fan tray for cooling.  For horizontal chassis, plug-in supplies may mount to the left or right of the card cage.  In this setup, air is pushed through the boards and then, through the power supply.

Cost
Plug-in supplies cost significantly more than their ATX counterparts.  Be prepared to pay at least 100% more than an equivalent ATX supply.  This cost will be reflected in your chassis price.  Lower volume, a PIB (when necessary), and compliance to IEEE 1101.10 and other specifications contribute to the higher price.

Besides plug-in and ATX power supplies, two other power supply types can be specified in CompactPCI systems:  open frame and modular.  Look for articles about these supplies in the near future.

Back to TECH TALK