Browse Prior Art Database

Card Selectable Current Limit

IP.com Disclosure Number: IPCOM000087249D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Kress, JE: AUTHOR

Abstract

Current limits of secondary loads (or the total primary current) are allowed to be set to a level only slightly higher than an installed feature load, thus reducing the fire hazard that exists if the limit is set internal to the supply at a level above that of the maximum feature load current. Heretofore, an adjustable limit has been provided that requires set up after manufacture or after a change in features at the customer's location. In the arrangement described the current limit can be raised or lowered simply by inserting or removing the cards, drawing the currents that necessitate a change in the limit.

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Card Selectable Current Limit

Current limits of secondary loads (or the total primary current) are allowed to be set to a level only slightly higher than an installed feature load, thus reducing the fire hazard that exists if the limit is set internal to the supply at a level above that of the maximum feature load current. Heretofore, an adjustable limit has been provided that requires set up after manufacture or after a change in features at the customer's location. In the arrangement described the current limit can be raised or lowered simply by inserting or removing the cards, drawing the currents that necessitate a change in the limit.

In the figure, I is the current needing a limit (which may be on the primary or secondary side of isolation). VI is a voltage directly proportional to the current. R1 is a resistor in the power supply. R2, R3 and RN are card-mounted resistors. V REF is a reference voltage, and C is a comparator.

V REF and VI/I set the minimum feature current limit to

(Image Omitted)

If a feature card-carrying resistor R2 is installed, then the additional current allowed is Delta I = Imin R1/R2. For example, if R1 = 1 kOmega, and R2 = 5 kOmega, then DeltaI = 15 A X 1 kOmega /5 kOmega = 3 A. The total current allowed is 18 amperes.

Similarly, if another feature card-carrying resistor R3 is installed, the additional current allowed is Delta I = Imin R1/R3. Thus if R3 = 7.5 kOmega, then Delta I = 15 A X 1 kOmega /7.5 kOmega = 2 A and the total curr...