Digital thermostat with protection against power interruption

• US 4,431,134 A
• Filed: 11/08/1982
• Issued: 02/14/1984
• Est. Priority Date: 11/08/1982
• Status: Expired due to Fees

• Current Assignee: Calabria Joseph, Wargo Peter
• Original Assignee: Microcom (HP Inc.)
• Inventors: Hendricks, Donald B., Larson, Austin R.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US06/439,776
• Time in Patent Office: 463 Days
• Field of Search: 365/228, 365/229, 364/844, 307/39, 165/12, 236/46 R
• US Class Current: 236/46.00R
• CPC Class Codes: G05D 23/1917 using digital means
• CPC Class Codes: G06F 1/30 Means for acting in the event of power-supply failure or interruption, e.g. power-supply fluctuations for resetting only G06F1/24

Abstract

A microcomputer controlled digital thermostat is powered by supply voltage derived from a large capacitance (e.g. 3.3 farad) voltage supply capacitor. The voltage supply capacitor is normally charged by an AC voltage which is derived from the furnace and which is rectified by a full wave rectifier bridge. Time and temperature data are stored in read/write RAM storage. The microcomputer controls operation of the thermostat as a function of sensed temperature and the stored time and temperature data. A voltage sensing circuit senses the supply voltage from the voltage supply capacitor and prevents the supply voltage from being provided to the microcomputer and other portions of the thermostat control circuitry when a prolonged interruption of AC power causes the supply voltage to decrease to a predetermined value. The supply voltage continues to be supplied to the read/write RAM to retain the stored time and temperature data. When AC power is restored, and the voltage supply capacitor is recharged, the digital thermostat is ready to resume operation without requiring the user to re-enter all of the stored time and temperature data. The capacitance of the voltage supply capacitor is sufficiently large to allow the capacitor to supply the current needed to retain the stored time and temperature data in the RAM through prolonged power interruptions without the need for a backup battery.

Claims

1. A temperature control apparatus comprising:

terminal means for connection to a source of AC power;

rectifier means connected to the terminal means for rectifying the AC power to produce a DC charging current;

a voltage supply terminal;

voltage supply capacitor means for providing a DC supply voltage at the voltage supply terminal, the voltage supply capacitor means being charged by the DC charging current;

read/write storage means connected to the voltage supply terminal and powered solely by the DC supply voltage for storing time and temperature data, the read/write storage means being capable of retaining the time and temperature data so long as the DC supply voltage at the voltage supply terminal exceeds a first predetermined value;

temperature sensing means for sensing temperature;

control circuit means powered solely by the DC supply voltage for providiing temperature control signals as a function of the sensed temperature and the stored time and temperature data;

switching means connected between the voltage supply terminal and the control circuit means for supplying the DC supply voltage to the control circuit means to power the control circuit means when in a first state and for preventing the control circuit means from receiving the DC supply voltage when in a second state, the switching means having the first and second states as a function of a power control signal; and

voltage sensing means for sensing the DC supply voltage of the voltage supply terminal and providing the power control signal as a function of the sensed DC supply voltage, the power control signal causing the switching means to have the second state when the DC supply voltage is less than a second, higher predetermined value.

2. The temperature control apparatus of claim 1 wherein the voltage supply capacitor means has a capacitance which is sufficiently high to allow current to be supplied from the voltage supply capacitor means to the read/write memory means to retain the time and temperature data for a period of at least twenty-four hours before the DC supply voltage at the voltage supply terminal decreases from the second predetermined value to the first predetermined value.

3. The temperature control aparatus of claim 2 wherein the capacitance of the voltage supply capacitor means is greater than 1 farad.

4. The temperature control apparatus of claim 3 wherein the capacitance of the voltage supply capacitor means is between about 3 farad and about 4 farad.

5. The temperature control apparatus of claim 1 wherein the temperature sensing means is powered by the DC supply voltage through the switching means and produces a temperature signal indicative of the sensed temperature, and wherein the control circuit means receives the temperature signal and provides the temperature control signals as a function of the temperature signal.

6. The temperature control apparatus of claim 5 wherein the control circuit means comprises:

programmed computer means for providing the temperature control signals as a function of a stored program, the temperature signal, and the stored time and temperature data; and

real time circuit means connected between the switching means and the computer means for disconnecting the computer means from the DC supply voltage during periods of inactivity of the computer means.

7. The temperature control apparatus of claim 6 wherin the computer means signals the real time circuit means each time that the computer means is about to enter a period of inactivity, and wherein the real time circuit means disconnects the computer means from the DC supply voltage for a selected time interval in response thereto.

8. The temperature control apparatus of claim 6 wherein the real time circuit means is also connected between the switching means and the temperature sensing means and disconnects the temperature sensing means from the DC supply voltage during periods of inactivity of the computer means.

9. A temperature control apparatus comprising:

terminal means for connection to a source of AC power;

rectifier means connected to the terminal means for rectifying the AC power to produce a DC charging current;

voltage supply capacitor means for providing a DC supply voltage, the voltage supply capacitor means being charged by the DC charging current;

read/write storage means being powered by the DC supply voltage for storing time and temperature data, the read/write storage means being capable of retaining the time and temperature data so long as the DC supply voltage exceeds a first predetermined value;

temperature sensing means powered by the DC supply voltage for sensing temperature and providing a temperature signal indicative of sensed temperature;

control circuit means powered by the DC supply voltage for providing temperature control signals as a function of the temperature signal and the stored time and temperature data;

wherein the control circuit means comprises;

programmed computer means for providing the temperature control signals as a function of a stored program, the temperature signal, and the stored time and temperature data; and

real time circuit means for disconnecting the computer means from the DC supply voltage during periods of inactivity of the computer means; and

voltage sensing means for sensing the DC supply voltage, the voltage sensing means disconnecting the control circuit means from the DC supply voltage when the DC supply voltage is less than a second, higher predetermined value.

10. The temperature control apparatus of claim 9 wherein the computer means signals the real time circuit means each time that the computer means is about to enter a period of inactivity, and wherein the real time circuit means disconnects the computer means from the DC supply voltage for a selected time interval in response thereto.

11. The temperature control apparatus of claim 9 wherein the real time circuit means also disconnects the temperature sensing means from the DC supply voltage during periods of inactivity of the computer means.