US 4,431,134 AGranted

Digital thermostat with protection against power interruption

AssigneeMicroComm Corporation

InventorsDonald B. Hendricks, Austin R. Larson

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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.

Claims11

Dependent claims

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.

7 more elements

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.

9 more elements

Dependencies are inferred from the claim text.