JPH0444532B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a control device for a heater such as a jar rice cooker, and particularly relates to control when the heater overheats due to malfunction of electronic components or usage environment (high humidity). .

<Prior Art> FIG. 3 is a circuit diagram of a conventional microcomputer (hereinafter referred to as microcomputer)-equipped jar rice cooker. In this circuit, the rice cooking heating method is controlled by the rice cooking relay 32 from the microcomputer 31 in the control section 30.
is controlled, and thereby the rice cooking heater 33
Heat it up. By the way, a malfunction has occurred in which the electronic components of the control unit 30 malfunction, causing the rice cooking relay 32 to latch on, causing the rice cooking heater 33 to be continuously energized and damaging the rice cooker. The energization is affected by the following three factors.

1 The microcomputer output terminal 31a is latched in the ON state due to the intrusion of static electricity or noise, and the rice cooking relay 32 is turned ON regardless of the program.

2 Due to condensation or the like between the emitter and collector of the rice-cooking relay driving transistor 34, a short circuit occurs, and the rice-cooking relay 32 turns on regardless of the base potential.

3 Turns ON regardless of coil voltage due to welding of rice cooking relay 32. These are caused by partial destruction of the microcomputer 31 and problems in the circuit, and even if the rice cooking relay control output terminal 31a of the microcomputer 31 is programmed to be reset, the continuous energization state cannot be stopped.

In such a situation, temperature control is not possible. In other words, since the rice cooker relay 32 cannot be turned off, the heater continues to heat up until the overtemperature rise prevention device is activated (temperature fuse 35 is cut off), eventually causing damage to the rice cooker, such as melting the top lid. In addition, 36 in the figure is an inner pot switch, 37 is a power supply circuit,
38 is a transformer.

<Objective> In view of the above, an object of the present invention is to provide a heater control device that can prevent continuous heating even when normal control is no longer possible.

<Example> Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3. The heater control device according to the present invention energizes the electric heater 1 as the heating means of the heating circuit A. A current detection circuit 5 that detects the current flowing through the heater 1, comprising a drive relay 2 to control, a drive circuit 3 to drive the drive relay 2, and a control circuit 4 to output a control signal to the drive circuit 3.
and a malfunction prevention circuit 6 that turns off the heating circuit A when the drive relay 2 malfunctions,
The control circuit 4 has a function of outputting a heating circuit cutoff signal to the malfunction prevention circuit 6 based on the output signal of the current detection circuit 5.

FIG. 1 is an electrical circuit diagram of the heater, in which the heating circuit A is connected to an AC power source 7, and the control circuit 4 is connected to the AC power source 7 via a transformer 8 and a power source circuit 10.

The control circuit 4 is a general one-chip microcomputer, which has a program ROM, data RAM, ALU, etc. inside, and is driven by a reference clock oscillator, and has an output terminal for driving the drive circuit 3. 4a and an output terminal 4b for controlling the malfunction prevention circuit 6,
It also has an input terminal 4c into which a voltage signal from the current detection circuit 5 is input. The control circuit 4 also has a function of converting an analog signal input from the input terminal 4c into a digital signal and outputting the digital signal.

The drive circuit 3 includes a first transistor 11, whose base side is connected to the output terminal 4a of the control circuit 4, whose collector side is connected to the relay coil 2a of the drive relay 2, and whose emitter side is connected to the relay coil 2a of the drive relay 2. is connected to the positive side of the power supply circuit 10.

The malfunction prevention circuit 6 includes a second transistor 1
2 and a heating circuit cutoff relay 13, the base side of the second transistor 12 is connected to the output terminal 4b of the control circuit 4, the collector side is connected to the relay coil 13a of the cutoff relay 13, and the emitter side is connected to the power supply circuit. Connected to the positive side of 10. Further, the cutoff relay 13 for preventing malfunction is composed of a relay coil 13a and a relay contact 13b.

The control circuit 4 has a function of outputting an ON signal to the first transistor 11 during normal heating, and outputting an OFF signal to the first transistor 11 when a certain value is reached by an input signal from a temperature sensor, etc. The two transistors 12 are provided with a function of outputting an ON signal and an OFF signal in the event of a malfunction.

Further, the drive relay 2 includes a relay coil 2a and a relay contact 2b. The heating circuit A is formed by connecting the drive relay 2, the relay contacts 2b and 13b of the cutoff relay 13, and the rice cooking heater 1 in series.

The current detection circuit 5 includes a current detector (current transformer) CT interposed in the heating circuit A, and a diode D3 and a capacitor C1 that convert the output voltage of the detector CT into a DC voltage. One end is connected to the input terminal 4c of the control circuit 4.

In addition, in the figure, R1, R2, R3, R4, R5, R
6 is a resistor, D1, D2, D3 are diodes, 15
1 is an inner pot switch, and 16 is a temperature fuse.

Next, the control program of the control device will be explained based on the flowchart of FIG. 2. First, the control circuit 4 determines the set temperature TS, inputs a temperature signal from a temperature sensor (thermistor) not shown,
Heating control is performed by comparing the two. For example, if the measured temperature TE is higher than the set temperature TS, a signal to turn off the drive relay 2 is output from the output terminal 4a,
Turn off the transistor 11 of the drive circuit 3, demagnetize the relay coil 2b, and turn off the relay contact 2a.
Then, turn off heater 1.

If the measured temperature TE is lower than the set temperature TS, a signal is output from the output terminal 4a to turn on the transistor 11, and the drive relay 2 is turned on to turn on the heater 1.
Turn on.

In this way, when the rice cooking relay control output terminal 4a of the control circuit 4 is in the OFF state under normal conditions,
Since the drive relay 2 is OFF, no current flows to the rice cooking heater 1, and nothing is output to the current detector CT.

However, even though a command to turn off the drive relay 2 has been issued in the program processing for some reason, when current flows through the rice cooker heater 1, a voltage is output to the current detector CT.

Utilizing this characteristic, subsequent processing will be explained based on the flowchart of FIG. After detecting the current flowing through the rice cooking heater 1, converting it into a DC voltage,
Furthermore, A/D conversion is performed inside the control circuit 4, and the data at this time is stored. To control the drive relay 2, just look at the drive relay flag SRYf. If the flag is set, this is a command to turn the drive relay 2 ON, so return to main control. If the flag is reset, the command is to turn the relay OFF, so the next step is Proceed to judgment. If the condition is normal, drive relay 2
If it is OFF, nothing will be output to the current detector CT, so the A/D converted value of the current flowing through rice cooker heater 1.
VCT=O and returns to main control.

If current flows through the rice cooking heater 1 for some reason, VCT>O, and the process proceeds to the next continuous heating prevention routine. Here, a signal is output to turn off the cutoff relay 13 for preventing continuous heating,
Processing to stop the rice cooking heater 1 is performed. In this case, the second transistor 12 is turned off by the relay OFF signal of the output terminal 4b of the control circuit 4, and the cutoff relay 1
3 is turned OFF to cut off the heating circuit A and cut off the power supply to the rice cooking heater 1.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, instead of the rice cooker as in the above embodiment, the heater may be a microwave oven or an electromagnetic cooker. In this case, the heating means will each consist of a magnetron and a heating coil.

<Effects> As is clear from the above description, according to the present invention, if the electronic components malfunction or the drive relay cannot be controlled due to the usage environment (high humidity environment, etc.), for example, the normal control circuit Even if the output terminal for driving the drive relay is latched in the ON state, or the relay drive transistor becomes ON due to destruction or condensation, and the drive relay cannot be controlled from the control circuit, heat that should not flow will be generated. By detecting the current flowing through the means with a current detector, malfunctions can be quickly detected and a malfunction prevention circuit can be activated, so as soon as a malfunction begins, heating will stop and a part of the main body will melt. It is possible to prevent the product from heating up to a certain level, thereby eliminating the anxiety caused to the user.

In addition, by providing two relays that control energization to the heating circuit, even if the drive relay malfunctions, the cutoff relay can reliably shut off the heating circuit, allowing normal heating control and control when an abnormality is detected. Compared to the case where one relay is used for both purposes, safety can be improved.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a heater showing an embodiment of the present invention, FIG. 2 is a control flowchart of the same, and FIG. 3 is an electric circuit diagram of a conventional heater. A: heating circuit, 1: heater, 2: drive relay,
3: Drive circuit, 4: Control circuit, 5: Current detection circuit, 6: Malfunction prevention circuit, 8: Transformer, 10:
Power supply circuit, 11: first transistor, 12: second transistor, 13: cutoff relay.

Claims (1)

[Claims] 1. A drive relay that controls energization of the heating means of the heating circuit, a drive circuit that drives the drive relay, and a control circuit that outputs a control signal to the drive circuit,
A current detection circuit that detects the current flowing through the heating means, and a malfunction prevention circuit that turns off the heating circuit when the drive relay malfunctions are provided, and the malfunction prevention circuit is configured to cut off the current supply to the heating means intermittently. It consists of a relay and a switching element that turns on and off the cutoff relay, the relay contact of the drive relay and the relay contact of the cutoff relay are connected in series, and the control circuit controls the drive relay according to the heating temperature during normal heating. A control device for a heater, comprising means for turning on and off the switching element and turning on the switching element when a malfunction is detected by an output signal of the current detection circuit.