Low cost microcomputer power supply with power on reset and low voltage inhibit functionality

• US 5,760,625 A
• Filed: 10/03/1995
• Issued: 06/02/1998
• Est. Priority Date: 10/03/1995
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Macks, Harold Ryan
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): KIM, JUNG H
• Application Number:
  US08/538,491
• Time in Patent Office: 973 Days
• Field of Search: 327/142, 327/143, 327/198, 327/538, 327/540, 327/584, 327/580, 323/311
• US Class Current: 327/198
• CPC Class Codes: G06F 1/24 Resetting means
• CPC Class Codes: G06F 1/305 in the event of power-supply fluctuations

Abstract

A low cost, less complex microcomputer power supply circuit with temperature stability and low current consumption in which a single voltage regulating element is used to provide the supply voltage, power-on reset (POR) and low voltage inhibitor (LVI) functions to the microcomputer (12). In an exemplary embodiment, the power supply circuit (10) includes a regulating circuit with a zener diode (30) that is conductive when the voltage level of the DC source (14) is above a threshold value and nonconductive when the voltage level of the DC source (14) is below a threshold value. The regulator circuit provides a regulated supply voltage to the microcomputer from the DC source (14). The regulator circuit also provides a regulation signal, whose state depends on the conductivity of the zener diode (30), to a reset circuit. The reset circuit of the power supply circuit is responsive to the regulation signal for providing a reset signal to the microcomputer (12). The state of the reset signal similarly depends upon the conductivity of the zener diode (30). Accordingly, when the zener diode (30) is nonconductive, operation of the microcomputer (12) is inhibited. Alternatively, when the zener diode (30) is conductive, operation of the microcomputer (12) is enabled. In one embodiment, the power supply (10) further includes a time delay circuit (28, 32 and 34) for delaying initialization of the microcomputer to a known operating state until the DC source voltage rises above the threshold value for a period of time.

Claims

1. A circuit for coupling power from a DC source to a microcomputer and for resetting the microcomputer when the voltage level of the DC source rises above a threshold level, comprising:

a regulator circuit including a zener diode having a conductive state when the voltage level of the DC source is above a threshold value and a non conductive state when the voltage level of the DC source is below said threshold value that is dependent upon the zener voltage of said zener diode;

said regulator circuit coupled to the DC source for providing a regulated supply voltage to the microcomputer;

said regulator circuit also providing a regulation signal having a first state when said zener diode is operating in said conductive state and a second state when said zener diode is operating in said nonconductive state; and

means responsive to said regulation signal for providing a reset signal to the microcomputer, said reset signal having a first state when said zener diode is operating in said conductive state and a second state when said zener diode is operating in said non conductive state, wherein said zener diode controls the level of said regulated supply voltage.

2. A circuit as in claim 1 further comprising delay means coupled to said regulator circuit for delaying provision of said reset signal to the microcomputer for a predetermined period of time.

3. A circuit for providing regulated power to a microcomputer from a DC source, inhibiting operation of the microcomputer when the voltage supplied by the DC source drops below a predetermined threshold value above a ground potential, and resetting the microcomputer when the voltage supplied by the DC source raises above the predetermined threshold value, comprising:

a transistor having a collector, a base and an emitter, said collector coupled to the DC source, and said emitter coupled to a supply voltage terminal of the microcomputer;

a zener diode coupled to said base of said transistor; and

ground said zener diode having a conductive state and a non conductive state;

reset circuitry responsive to said zener diode for applying a reset signal to a reset terminal of the microcomputer when the zener diode is in said conductive state and to inhibit said reset signal to said reset terminal when said zener diode is in said non conductive state.

4. A circuit as in claim 3 further comprising a time delay triggered when said zener diode enters said conductive state, said time delay delaying application of said reset signal by said reset circuitry at the reset terminal of the microcomputer for a predetermined period of time.

5. A circuit for providing regulated power to a microcomputer from a DC source, inhibiting operation of the microcomputer when voltage supplied by the DC source drops below a predetermined threshold value above a ground potential, and resetting the microcomputer at a reset terminal when the voltage supplied by the DC source is below the predetermined threshold value comprising:

a first transistor having a collector, a base and an emitter, said collector coupled to the DC source, and said emitter coupled to a supply voltage terminal of the microcomputer;

a voltage divider comprising a first resistor, a zener diode having an anode and a cathode, and a second resistor, wherein said first resistor is connected between the collector and base of said first transistor, said cathode of said zener diode is connected to said base and said first resistor, and said second resistor is connected between said anode of said zener diode and ground potential;

said zener diode having a conductive state when the voltage at its cathode is above a predetermined threshold and a non-conducing state when the voltage at its cathode is below said predetermined threshold;

said zener diode of said voltage divider causing said first transistor to regulate the voltage applied to said supply voltage terminal when said zener diode is in its conducting state and to inhibit the application of regulated voltage to said supply voltage terminal when said zener diode is in its non-conducting state;

reset circuitry coupled to said zener diode and being responsive to said zener diode being in its conducting and nonconducting states for applying a reset signal to said reset terminal when said zener diode is in its non-conducting state.