Browse Prior Art Database

Fuser Overvoltage Protection Circuit

IP.com Disclosure Number: IPCOM000074837D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Van Cleave, GW: AUTHOR

Abstract

Overvoltage failure of a fuser regulating circuit, as described in U.S. Patent 3,532,855 is detected by transistor TA which is actuated upon regulating transistor T12 becoming reverse biased. In normal operation, the collector of regulating transistor T12 supplies current to a timing capacitor C4 whose rate of charge determines the firing time of a triac power control device, not shown. The current supplied to timing capacitor C4 by transistor T12 is determined by the voltage across capacitor C2. For example, if the fuser output voltage is too high, the voltage across capacitor C2 increases and causes the current supplied by transistor T12 to decrease. This, in turn, causes the conduction angle of the triac device to decrease if it is functioning normally.

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Fuser Overvoltage Protection Circuit

Overvoltage failure of a fuser regulating circuit, as described in U.S. Patent 3,532,855 is detected by transistor TA which is actuated upon regulating transistor T12 becoming reverse biased. In normal operation, the collector of regulating transistor T12 supplies current to a timing capacitor C4 whose rate of charge determines the firing time of a triac power control device, not shown. The current supplied to timing capacitor C4 by transistor T12 is determined by the voltage across capacitor C2. For example, if the fuser output voltage is too high, the voltage across capacitor C2 increases and causes the current supplied by transistor T12 to decrease. This, in turn, causes the conduction angle of the triac device to decrease if it is functioning normally. However, in the event of an output circuit failure such as the triac becoming shorted and conducting continuously, the transistor T12 will lose control. Therefore, the voltage across capacitor C2 will increase, trying to reduce, the triac firing angle until transistor T12 is cut off and further until it is reverse biased. This reverse biased condition is detected by transistor TA which becomes forward biased and turns on transistor TB. Transistor TB then supplies current to energize relay RY1, which removes AC power from the circuit to prevent a more serious failure.

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