Method and apparatus for power supply switching with logic integrity protection

• US 5,790,873 A
• Filed: 07/23/1996
• Issued: 08/04/1998
• Est. Priority Date: 07/23/1996
• Status: Expired due to Term

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Standard Microsystems Corporation (Microchip Technology Incorporated)
• Inventors: Wahler, Richard E., Popper, Jay D.
• Primary Examiner(s): Ray, Gopal C.
• Application Number:
  US08/685,376
• Time in Patent Office: 742 Days
• Field of Search: 395/750.06, 395/750.08, 395/750.01, 395/182.12, 364/707, 364/492, 307/66, 365/226, 365/229
• US Class Current: 713/300
• CPC Class Codes: G06F 1/26 Power supply means, e.g. regulation thereof for memories G11C
• CPC Class Codes: H02J 9/005 using a power saving mode for copiers G03G15/5004
• CPC Class Codes: H02J 9/06 with automatic change-over , e.g. UPS systems
• CPC Class Codes: Y02B 70/30 Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
• CPC Class Codes: Y04S 20/20 End-user application control systems

Abstract

A method and apparatus for providing power management functions in a computer or other electronic system which includes a primary power supply, a trickle power supply and a battery back-up power supply. A power management circuit includes a storage element which stores an indication of the current turn-on or turn-off condition of the primary power supply. The power management circuit also includes a group of logic gates which process signals which are supplied to the storage element under normal operating conditions to control the turn-on or turn-off condition of the primary power supply. The power management circuit senses when the trickle supply is deactivated due to a line power failure or the like, and subsequently switches the power supply inputs of the storage element and certain of the logic gates from the trickle supply to the battery back-up supply. A blocking signal is generated which prevents those signals which require the trickle supply for logic integrity from being applied to the storage element. In this manner, only signals which do not require the trickle supply for logic integrity are applied to the storage element while the trickle supply is deactivated.

Claims

1. A method of switching power supplies in an electronic system including a primary power supply, a trickle power supply and a battery back-up power supply, the method including the steps of:

monitoring the voltage of the trickle power supply; and

switching power supply inputs of a first group of logic gates in a power management circuit from the trickle power supply to the battery back-up power supply if the trickle supply voltage falls below the back-up supply voltage by a predetermined amount, wherein the first group of logic gates process signals which determine a turn-on or turn-off condition of the primary power supply, and wherein the condition of said primary power supply is maintained.

2. The method of claim 1 further including the steps of:

generating a blocking signal if the trickle supply voltage falls below the back-up supply voltage by a predetermined amount; and

applying the blocking signal to signal inputs of a second group of logic gates which process signals which depend on the trickle power supply for logic integrity.

3. The method of claim 2 wherein the first and second groups of logic gates include at least one gate in common.

4. The method of claim 1 wherein the step of switching power supply inputs further includes the step of switching the power supply input of a storage element which stores an indicator of whether the primary power supply was in a turn-on or a turn-off condition at a time when the trickle supply voltage falls below the back-up supply voltage by a predetermined amount.

5. The method of claim 4 wherein the storage element stores a one-bit indicator which has one value if the primary power supply is in a turn-on condition and another value if the primary power supply is in a turn-off condition.

6. The method of claim 1 wherein the step of switching power supply inputs further includes the step of switching the power supply input of a logic gate which processes a user-programmed alarm signal.

7. The method of claim 1 wherein the step of switching power supply inputs further includes the step of switching the power supply input of a logic gate which processes a power on reset signal for the trickle supply.

8. The method of claim 1 wherein the step of switching power supply inputs further includes the step of switching the power supply input of a logic gate which processes a power on reset signal for the battery back-up supply.

9. An apparatus for switching power supplies in an electronic system including a primary power supply, a trickle power supply and a battery back-up power supply, the apparatus comprising:

a storage element which stores an indication as to whether the primary power supply is in a turn-on condition or a turn-off condition;

a group of logic gates having inputs connected to receive signals which determine a turn-on or turn-off condition of the primary power supply, and outputs coupled to inputs of the storage element; and

a control circuit having inputs connected to receive outputs of the trickle power supply and the battery back-up power supply, wherein the control circuit is operative to monitor the voltage of the trickle power supply and to switch power supply inputs of the group of logic gates from the trickle supply to the battery back-up power supply if the trickle supply voltage falls below the back-up supply voltage by a predetermined amount to maintain the condition of said primary power supply.

10. The apparatus of claim 9 wherein the control circuit is further operative to generate a blocking signal if the trickle supply voltage falls below the back-up supply voltage by a predetermined amount, wherein the blocking signal is applied to signal inputs of a second group of logic gates which process signals which depend on the trickle power supply for logic integrity.

11. The apparatus of claim 10 wherein the first and second groups of logic gates include at least one gate in common.

12. The apparatus of claim 9 wherein the control circuit is operative to switch a power supply input of the storage element from the trickle supply to the battery back-up power supply if the trickle supply voltage falls below the back-up supply voltage by a predetermined amount.

13. The apparatus of claim 9 wherein the storage element stores a one-bit indicator which has one value if the primary power supply is in a turn-on condition and another value if the primary power supply is in a turn-off condition.

14. The apparatus of claim 9 wherein the control circuit is further operative to switch the power supply input of a logic gate which processes a user-programmed alarm signal.

15. The apparatus of claim 9 wherein the control circuit is further operative to switch the power supply input of a logic gate which processes a power on reset signal for the trickle supply.

16. The apparatus of claim 9 wherein the control circuit is further operative to switch the power supply input of a logic gate which processes a power on reset signal for the battery back-up supply.

17. An apparatus for switching power supplies in an electronic system including a primary power supply, a trickle power supply and a battery back-up power supply, the apparatus comprising:

a storage element which stores an indication as to whether the primary power supply is in a turn-on condition or a turn-off condition; and

a control circuit having inputs connected to receive outputs of the trickle power supply and the battery back-up power supply, a first output corresponding to a first signal indicative of whether the trickle supply voltage has been turned off, and a second output corresponding to the trickle supply if the trickle supply is turned on and corresponding to the battery back-up supply if the trickle supply is turned off;

wherein the first output of the control circuit is coupled to an enable input of a logic gate which is operative to supply the indication to be stored in the storage element, and the second output is coupled to a power supply input of the storage element for maintaining the condition of said primary power supply.

18. The apparatus of claim 17 wherein the control circuit further includes:

a comparator having a first input coupled to the trickle supply and a second input coupled to the battery back-up supply; and

a switchable voltage divider coupled between the first input of the comparator and a circuit potential, the switchable voltage divider operative to apply a voltage division to the voltage applied to the first input of the comparator in response to a transition in the first signal at the first output of the control circuit.

19. The apparatus of claim 18 wherein the switchable voltage divider includes at least one field effect transistor having a gate coupled to the first output of the control circuit.

20. The apparatus of claim 17 wherein the control circuit further includes:

a comparator having a first input coupled to the trickle supply and a second input coupled to the battery back-up supply; and

a group of logic gates coupled between an output of the comparator and the first output of the control circuit, wherein at least a subset of the group of logic gates include power supply inputs coupled to the second output of the control circuit.