US 4,379,985 AGranted

Bipolar driver with illegal code detector

AssigneePitney Bowes Inc.

InventorVincent G. Coppola

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Abstract

A bipolar driver controls the operation of a reversible polarity load such as a motor. The driver links one terminal of the motor with either a positive or a negative potential power supply in response to processor command signals comprising a combination of logic levels appearing at a pair of driver input lines. The input lines are monitored to detect the presence of an illegal code combination which would otherwise function to simultaneously interconnect the load terminal with both positive and negative power supplies. The load terminal is linked to the power supplies by a separate power transistor for each power supply. Each power transistor is biased into conduction through a drive transistor. Upon detection of an illegal code, monitoring logic generates a signal which interrupts the emitter circuit of each of the drive transistors to inhibit both power transistors.

Claims12

Dependent claims

An interface for a processor, a reversible polarity load having two terminals the first of which terminals being tied to a substantially fixed reference level, and a pair of opposite polarity power supplies, the processor selectively transmitting one of several possible command signal codes to the interface, the signal codes designating different modes of operation of the load, the interface comprising:

a first power switch means, the first power switch means selectively interconnecting the second of said terminals of the load and the power supply of one polarity,
a second power switch means, the second switch means selectively interconnecting the second of said terminals and the power supply of opposite polarity,
means receiving each signal code and
(a) in response to a first signal code, forward biasing the first power switch means to interconnect the second of said terminals and the power supply of one polarity and reverse biasing the second power switch means such that the second of said terminals is not interconnected with the power supply of the opposite polarity,
(b) in response to a second signal code, reversing the first power switch means such that the second of said terminals is not interconnected to the power supply of one polarity and forward biasing the second power, switch means to interconnect the second of said terminals and the power supply of the opposite polarity, and
(c) in response to a third signal code, reverse biasing both power switch means such that the second of said terminals is not connected with either power supply,
the interface further comprising illegal signal code inhibit means, the inhibit means including monitoring means receiving the signal codes and in response to an invalid signal code which would otherwise function to forward bias both power switch means, inhibiting the operation of both of said power switch means.

4 more elements

Dependencies are inferred from the claim text.