Why Choose Active ORing Instead of a Traditional Diode?

December 1, 2011
By

Chester Firek

An interview with Chester Firek, Senior Product Marketing Manager for the Vicor Cool-ORing family of Active ORing  power management solutions. The discussion covers the advantages and challenges of Active ORing over traditional diode solutions. There’s also a white paper and Cool-ORing family product matrix at the end of the post.

Q:  In one sentence how would you describe the Cool-ORing products?

A:  Cool-ORing is a complete family of high-performance power management solutions designed to replace either ORing diodes or other conventional Active ORing devices to increase efficiency, improve power density, and add flexibility to a redundant power system. 

Q:  What are the advantages of an Active ORing versus a traditional diode solution?

A:  I definitely can’t do that in one sentence! 

In its simplest form, an ORing device is a diode that protects the system against an input power source fault condition.  A diode allows current to flow in one direction only, thus isolating the fault from the redundant bus, allowing the system to continue to run from the remaining redundant power sources.  In an active ORing solution the ORing diode is replaced with a combination of a power MOSFET and a controller IC.

The critical benefit in the active solution are 10x reduction in power dissipation

For the diode the power dissipation is based on the forward voltage drop across the diode multiplied by the current.  In the active solution the MOSFET has a very low on-state resistance characteristic, RDS(on) that when multiplied by the square of the current through the device determines the power loss. 

As an example, for a 20A application, a zener diode with a .45V forward voltage drop could dissipate as much as 9 Watts of power, while a MOSFET with a 2mOHM RDS on would dissipate only 0.8W, a more than 10x reduction in power loss. 

Q:  That’s definitely impressive.  Are there any other measurements that we should consider? 

A:  Key performance metrics are speed (including early fault detection), accuracy and lowest possible RDS(on).  Accuracy and response times are characteristics of the ORing controller, and RDS(on) is dependent on the MOSFET selection.

Q:  Why is earlier fault detection important? 

A:  Quite simply because this sets the trigger for the response time. In this critical role Cool-ORing products are able to monitor and detect a fault at lower voltages levels than most competitive solutions and on average can provide more than twice the accuracy of most competitive devices.

But don’t forget that once a fault is detected the response time is critical. This ultimately determines the magnitude and duration of reverse currents and can mean the difference between a damaged system and a safe disconnect of a failed supply. Cool-ORing can provide up to 25% faster response as compared to competitive solutions.

Q:  What products are included in the Cool-ORing family?

A:  We offer a complete family of Active ORing solutions, including discrete active ORing controllers as well as full-function system-in-package solutions with high-speed integrated low on-state resistance MOSFETs, in high-density thermally enhanced LGA packages that reduce the power footprint.

Cool-ORing products meet the requirements of end voltage systems at 5V and below as well as the standard intermediate bus voltages of 9.6V, 12V and +/- 48V. This supports a variety of configurations and provides you with the flexibility to develop the redundant power system that meets your specific needs.

For more information read the white paper, “Active ORing Solutions in Redundant Power System Architectures

For more information about the Cool-ORing family go to the Product Matrix on our web site.

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2 Responses to:
Why Choose Active ORing Instead of a Traditional Diode?

  1. Istvan Vojtko on January 9, 2012 at 4:08 AM

    That’s definitely impressive:

    “a zener diode with a .45V forward voltage”
    “a MOSFET with a 2nohm RDS”

    Best regards,

    Steve

    • Chester Firek on January 9, 2012 at 12:46 PM

      Hello Steve, thanks for reading my post. As I’m sure you probably realized the mention of a 2 nano ohms MOSFET was an error, it was incorrectly transcribed and should have read 2 milli Ohms. Although Picor does offer a 360 micro Ohm RDS(on) MOSFET, the PI5101, which I believe is the lowest RDS(on) MOSFET available. Thanks again! Chester

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