Oscillation-free, short-circuit protection circuit
AssigneeFairchild Semiconductor Corporation
InventorsJames R. Kuo, Timothy G. Moran
Life of this patent
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Abstract
A line driver circuit capable of operating at high speeds. The output transistor, an emitter connected to an output terminal, has a special feedback capacitor connected to its base. The feedback capacitor helps pull the output terminal high to increase the switching speed of the line driver circuit. Special current injection and removal techniques are used to speed the switching times of the PNP current supply transistors. The line driver circuit also has special circuitry to limit the output current from exceeding certain limits and for keeping the line driver circuit from overheating.
Claims20
In a circuit having an output terminal for connection to a signal line, and an output transistor having an emitter terminal connected to said output terminal, a base terminal connected to two sources of current, and a collector terminal connected to a first voltage supply, said circuit comprising:
- a first current sensing transistor coupled to said output transistor collector terminal in such a way that said first current sensing transistor is turned on when current through said output transistor collector terminal exceeds a first limit,
- a second current sensing transistor coupled to said output transistor collector terminal in such a way that said second sensing transistor is turned on when current through said output transistor collector terminal exceeds a second limit,
- means responsive to said first and second sensing transistors so that one of said two current sources of current to said output transistor base terminal is turned off when both first and second sensing transistors are turned on whereby the current through said output transistor is reduced.
A circuit for limiting the current through a transistor, said transistor being responsive to a plurality of transistor control means, the amount of current through said transistor being proportional to the number of transistor control means turned on, said circuit comprising:
- a first current sensing transistor responsive to said current in such a way that said first current sensing transistor is turned on when said current exceeds a first limit,
- a second current sensing transistor responsive to said current in such a way that said second current sensing transistor is turned on when said current exceeds a second limit, said second limit being greater than said first limit, and
- means responsive to said first and second current sensing transistors for turning off at least one of said transistor control means, so that said current is limited in proportion to the number of said transistor control means remaining turned on.
A temperature sensing circuit in an integrated circuit comprising:
- means for generating a current proportional to temperature,
- a latch responsive to said current, said latch setting itself into one state when said current exceeds a first predetermined amount and resetting itself into a second state when said current drops below a second predetermined amount below said first predetermined amount,
- a transistor, said transistor being responsive to a plurality of transistor control means, the amount of current through said transistor being proportional to the number of transistor control means turned on, and
- means responsive to said latch for turning off at least one of said transistor control means when said latch is set and turning on said one transistor control means when said latch is reset,
- whereby the amount of current through said transistor is reduced when a predetermined temperature is exceeded, said current reduction remaining until the temperature is below said predetermined temperature.
Dependencies are inferred from the claim text.