Short circuit protection circuit
AssigneeInternational Business Machines Corporation
InventorJu-Hi J. Hong
Life of this patent
Estimating the term…
Abstract
A protection circuit is provided in which the output voltage is sensed and the output device is shut-off for protection when the output voltage falls below a predetermined trip voltage. The monolithic integrated circuit includes a voltage shifting circuit for transferring the output voltage to a biasing circuit which biases a switching circuit which turns the line driver off, when an overload or short circuit causes a voltage drop below a predetermined trip voltage. The protection circuit is disabled during start-up or signal rise time by splitting the input signal into two separate paths in which the signals have different delays. The shorter delay allowing the input signal to rise and to appear on the output line before the longer delay input signal rises enabling the protection circuit.
Claims7
A short circuit protection circuit for a line driver comprising:
- an output transistor having an emitter output for connection between a source and a load and developing an output voltage;
- a first bias resistor connected between the source and the base of said output transistor;
- a switching transistor connected between the base of said output transistor and the load for switching the bias of said output transistor for on and off operation thereof;
- a voltage tracking transistor coupled across the load and connected to the base of said switching transistor;
- a second bias resistor connected between the source and the base of said switching transistor for developing a voltage thereacross which is a function of the output voltage and which is used to bias said switching transistor;
- a first and second inverting transistor for providing an input signal in parallel at the base of said switching transistor and at the base of said output transistor, respectively, said first inverting transistor providing a later input signal response at the base of said switching transistor than the signal response at the base of said output transistor thereby disabling said protection circuit during low voltage portions of the output signal rise time.
Dependencies are inferred from the claim text.