Controller for ORing field effect transistor

Abstract

An ORing element for use in a power supply and / or power system. The ORing element may include a field effect transistor (FET), a first bi-polar transistor and a second bi-polar transistor. The FET may be electrically connected between an input and an output. The first bipolar transistor may have an emitter electrically connected to the source of the FET and a collector electrically connected to a gate of the FET. The second bi-polar transistor may be diode connected, with its emitter electrically connected to its base. The emitter of the second bi-polar transistor may also be electrically connected to the base of the first bi-polar transistor. The collector of the second bi-polar transistor may be electrically connected to the drain of the FET.

Description

BACKGROUND[0001]The structure of many electrical power systems includes multiple power modules joined in parallel by a common power bus. ORing circuit elements are typically included between the power supply module's output and the power bus to prevent a failure of one power supply module from drawing down the power bus and leading to a complete failure of the power system. There are several common ORing element designs, each having certain disadvantages.[0002]One common ORing element is a simple diode placed in series between a power supply module's output and the power bus. When the output voltage of the power supply module is sufficiently greater than the voltage at the power bus, the diode is forward-biased, allowing current to flow from the power supply module to the power bus. If, however, the output of the power supply module drops below the output of the power bus, then the diode will be reverse biased. When the diode is reverse biased, the power supply module is essentially...

AI Technical Summary

Benefits of technology

[0023]While several embodiments of the invention have been described, it should be apparent that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the present invention. For example, the values of various components may be varied. Also various components (e.g., resistors, filtering capacitors, etc.) may be added or removed to the circuits. The present description is therefore intended to cover all such modifications, alterations and adaptations without departing from the scope and spirit of the present invention as defined by the appended claims.

Problems solved by technology

An ideal diode would be an ideal ORing element but real diodes have significant forward drop voltages and for many applications the associated power dissipation makes the use of simple diodes unattractive.

Comparator circuits used to control FET-based ORing elements have disadvantages that stem from the fact that real comparators have finite offset voltages associated with their input circuitry.

The offset voltage means that there will always be some error in setting (or determining) the threshold voltage at which the control function will turn the FET on or off.