JPH03112514A - Control circuit of electric cooker - Google Patents

Abstract

PURPOSE:To realize an electric cooker having a high accuracy clock function not influenced by the change of external condition by providing a temperature control means for supplying an electric current to a resistance to keep the temperature of ambient atmosphere of a crystal vibrator constant when the detected temperature of a temperature sensor is less than a preset temperature. CONSTITUTION:A microcomputer 1 is adapted to divide the vibration output of a crystal vibrator 18 to calculate the time and display the current time on LCD 16 in addition to boiling rice according to a program written in ROM. At the time of rice boiling by a timer, the time is inverse-operated in order to complete boiling rice at the reserved time to start boiling rice. A temperature control circuit 22 turns on a transistor 21 to make a resistance 20 generate heat when the ambient temperature of the crystal vibrator 18 detected by a temperature sensor 19 is lower than the preset temperature (60 deg.C which is the highest temperature near the substrate during boiling rice), and other wise, the circuit stops heat generation of the resistance 20 to keep the ambient temperature of the crystal vibrator 18 substantially constant, so as to restrain the fluctuation of vibration frequency due to a temperature change of the crystal vibrator 18.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a control circuit for electric cooking appliances such as jar rice cookers and bread makers with clock functions used in general households.

BACKGROUND OF THE INVENTION In recent years, electric cookers that have a clock function and can set the cooking start time have been manufactured. In the control circuits of these electric cooking appliances with a clock function, a crystal oscillation circuit is formed on a printed circuit board, and the oscillation output is frequency-divided to drive the clock.

Problems to be Solved by the Invention However, the oscillation frequency of a crystal oscillation circuit has a quadratic temperature characteristic as shown in Figure 4, and the clock may go awry due to temperature changes due to seasons, day and night, or temperature rises due to cooking heating. There was a problem with putting it away.

The present invention solves the above-mentioned conventional problems, and aims to provide a control circuit for an electric cooker that has a highly accurate clock function that is not affected by changes in external conditions. be.

Means for Solving the Problems In order to solve the above problems, the control circuit of the electric cooker of the present invention includes a temperature sensor and a crystal oscillation near the crystal oscillation used for clocks, cooking time settings, etc. A resistor for heating the atmosphere is installed, and if the temperature detected by the temperature sensor is below a set temperature, temperature control means is provided for controlling the temperature of the atmosphere around the crystal oscillator by supplying current to the resistor to keep the ambient temperature of the crystal oscillator constant. It is something that

Effect With the above configuration, if the ambient temperature of the crystal oscillator is lower than the set temperature, the temperature regulating means supplies current to the resistor, the resistor generates heat, and raises the ambient temperature, and if the ambient temperature is higher than the set temperature, the temperature regulating means is activated. Means 1'□ does not supply current to the resistor and is naturally cooled, so that the ambient temperature of the crystal oscillator is kept almost constant, and the crystal oscillator oscillates at almost one point on the temperature characteristic curve of the oscillation frequency. As a result, the clock
becomes less erratic.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 2 is a partially cutaway front view of a jar rice cooker according to an embodiment of the present invention. In FIG. 2, 1 is an inner pot, 2 is a heater for heating the inner pot 1, and 3 is a circuit board.

FIG. 1 is a circuit diagram of the control circuit of the rice jar rice cooker, which is wired on the circuit board 3. In Figure 1, b-Y2
is connected to an AC power source via the contact 11a of the relay 11 and supplied with current. The power supply circuit 13 is connected to the AC power supply 12 to generate an AC power supply, has a ROM, and is a one-chip microcomputer (hereinafter referred to as "one-chip microcomputer") that performs a series of rice cooking operations, timer rice cooking operations, and clock operations according to programs written in the ROM. (referred to as a microcomputer) 14. 15
16 is an LCD that is connected to the microcomputer 14 and displays the cooking status and current time; 17 is a first switch that receives the signal from the microcomputer 14 and drives the relay 11; This is a transistor. A crystal oscillator 18 forms an internal circuit of the microcomputer 14 and a crystal oscillator circuit, and a temperature sensor 19 for detecting the ambient temperature of the crystal oscillator 18 is located near the crystal oscillator 18. A resistor 20 is installed to raise the ambient temperature of the oscillator 18 by generating heat, and a current is supplied to this resistor 20 from the power supply circuit 13 via a second transistor 21 . 22 is a temperature control circuit that drives the second transistor 21, which includes a resistor 23 connected to the power supply circuit 13 via the temperature sensor 19, and a temperature control circuit that drives the second transistor 21;
A series circuit of resistors 24 and 25 connected to 3 and resistor 23
and a ratio device 26 whose input terminals are connected to the connection point of the temperature sensor 19 and the connection point of the resistors 24 and 25, and compares the output voltage of the temperature sensor 19 and the reference voltage at the connection point of the resistors 24 and 25. Then, in order to keep the output voltage of the temperature sensor 19 constant, the second transistor 21 is controlled on and off to adjust the current supply to the resistor 20, and the crystal oscillator 18 located near the temperature sensor 19 Adjust the temperature so that the ambient temperature remains constant.

FIG. 3 shows a cross-sectional view of the vicinity of the crystal oscillator 18, in which a temperature sensor 19 and a resistor 20 are arranged side by side with the crystal oscillator 18 at the center, and these are all installed in a case 27, and the inside is thermally conductive. It is filled with resin 28 which has excellent properties.

Next, the operation in the above configuration will be explained.

In addition to cooking rice according to the program written in the ROM, the microcomputer 14 calculates the time by dividing the oscillation output of the crystal oscillator 18, and displays the current time on the LCD 1B. Also, when cooking rice with a timer, the time is counted backwards and the rice cooking is started so that the rice cooking is completed at the reserved time.

The temperature control circuit 22 turns on the second transistor 21 when the ambient temperature of the crystal oscillator 18 detected by the temperature sensor 19 is lower than the set temperature (in this embodiment, 60° C., which is the maximum temperature near the substrate during rice cooking). to generate heat in the resistor 20,
If this is not the case, the heat generation of the resistor 20 is stopped, the ambient temperature of the crystal oscillator 18 is kept almost constant, and the crystal oscillator 18 is
Fluctuations in oscillation frequency due to temperature fluctuations can be suppressed.

Effects of the Invention As described above, according to the control circuit for an electric cooker of the present invention, it is possible to realize an electric cooker with a clock function that does not go out of order due to temperature changes during the season, day and night, or temperature increases due to cooking. This is very advantageous in practice.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a control circuit of a jar rice cooker according to an embodiment of the present invention, and Fig. 2 is a partially cutaway front view of the same jar rice cooker.
Fig. 3 is an enlarged sectional view of the vicinity of the crystal oscillator, and Fig. 4 is a temperature characteristic diagram of the crystal oscillation circuit.
Power supply circuit, 14... Microcomputer, 18... Crystal oscillator, 19... Temperature sensor, 20... Resistor, 21...
Second transistor, 22...temperature adjustment circuit.

Claims (1)

[Claims] 1. a crystal oscillator used for clocks and cooking time settings, a resistor installed to heat the atmosphere near the crystal oscillator, a temperature sensor installed near the crystal oscillator, and a temperature sensor installed near the crystal oscillator; A control circuit for an electric cooking appliance, comprising: temperature adjusting means for supplying current to the resistor to keep the ambient temperature of the crystal oscillator constant if the temperature detected by the sensor is equal to or lower than the set temperature.