JPS63168986A - Electric hot plate controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control device for an electric hot plate for home use, which has a plurality of heaters and selectively switches one of them for use. It is related to.

BACKGROUND OF THE INVENTION Conventionally, an electric hot plate, as shown in FIG.
The temperature of the shibrate is detected by a temperature detection means such as a bimetal thermometer (page 12), and the temperature of the plate is controlled by mechanically opening and closing the contacts. In addition, the heaters 2 and 3 arranged as shown in FIG.
It was designed so that the power could be switched on and off.

On the other hand, in recent years, with improvements in electronic technology, electric hot plates equipped with a temperature control device that combines an electronic circuit and a negative characteristic thermistor have been considered in order to improve control temperature. Each of the heaters is selectively switched using a relay to generate heat individually. An example of such a configuration is shown in FIG.

As shown in FIG. 3, relay contacts 4 and 6 are connected in series to the heaters 2 and 3, and the first relay contact 4 is controlled to open and close by energizing a relay coil 7 through a transistor 6.
The second relay contact 5 is controlled to open and close by energizing a relay coil 9 using a transistor 8.

16 is a selection circuit for selectively using one of the heaters, which can be selected using the input switch 17. 18 is a temperature control circuit that controls the temperature of the thermistor with respect to the reference voltage. Temperature control is performed by changing the voltage across both ends, and the control temperature can be made variable by externally changing the reference voltage.

Note that 10.11 in the figure generates a DC voltage for driving the relay across the capacitor 12 using a resistor and a diode.

Similarly, the DC resistors and diode capacitors 13, 14, and 15 provide power for the control circuits 16, 17, and 18.

Problems to be Solved by the Invention However, in the configuration as shown in FIG.
There was a problem in that the heaters 2 and 3 were energized at the same time during welding. Each of these heaters 2 and 3 has a capacity of about 12A, and when both are energized at the same time, it is 24A.
If the current is too large, the power supply wires will generate heat, creating a risk of fire or other danger.

The present invention takes the above-mentioned conventional problems into consideration and attempts to improve safety by preventing the two heaters from being energized at the same time.

Means for Solving the Problems In order to solve the above problems, the present invention provides that one of the relay contacts connected in series to the heater that opens and closes in the relay drive circuit has an open side contact. The series circuit of the relay contact on the other side and the heater is connected to the power source via this open side contact.

Effect of the Invention According to the present invention, when a relay having an open side contact is closed, it always disconnects the other relay from the power supply. Only the heater will be energized.

Example FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In Figure 1, 2 and 3 are heaters, and 6'\-
7 are connected to relay contacts 4 and 6, respectively. The series circuit of the relay contact 5 and the heater 3 is connected to the other relay contact 4.
It is connected between the open side contact (4-NC) and the power supply.

Therefore, when relay contact 4 is not operated and closed, the series circuit of relay contact 5 and heater 3 is connected to the power supply, and when relay contact 4 is operated and closed, relay contact 6 and heater 3 are connected to the power supply. The series circuit of is disconnected from the power supply.

The relay contacts 4 are controlled to open and close by a relay coil 7, and the relay coil 7 is driven by a transistor 6. Further, the relay contacts 6 are controlled to open and close by a relay coil 9, and the relay coil 9 is driven by a transistor 8. Note that 10.
11 is a diode and a resistor, which generates a DC voltage across the capacitor 12 for the relay coil. Same (13,1
4° 16 is a resistor, diode, and capacitor, and serves as a power supply circuit for the relay selection circuit 16 and the temperature control circuit 18. 17 is a switch which is input to the relay selection circuit 16 to select which of the heaters 2 and 3 is energized (61.-). Reference numeral 19 denotes a temperature sensor, and when a predetermined temperature is reached, the output of the temperature control circuit 18 turns off one of the transistors 6 and 8, opens a relay contact, and stops energizing the heater.

20 is a temperature fuse that cuts off the power when the temperature rises abnormally.

With the above configuration, temperature control is normally performed by energizing one of the heaters, but in the unlikely event that a contact welding failure occurs, for example, if contact 5 is welded, the selection circuit 16 will switch on the heater. When 2 is selected and the contact 4 is closed, the contact 5 and the heater 3 are disconnected from the power supply and are not energized at the same time. The same applies to the case of a failure in which the contact point 4 remains closed.

Therefore, it is possible to prevent a large current from generating heat and causing a fire or the like.

Effects of the Invention As is clear from the description of the embodiments described above, the present invention provides a hot plate in which a plurality of heaters are selectively energized to generate heat, and one heater is connected to the other through the open side contact of relay contact 7 of one heater. Since the heaters and relay contacts are connected in a series circuit, each heater is not energized and generates heat at the same time, increasing safety.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing the configuration of an embodiment of the present invention, FIGS. 2a and 2b are a circuit diagram and top view of a conventional example, and FIG. 3 is a circuit diagram showing a conventional example. 2.3...Heater, 4,6...Relay contact, 6.8...Transistor (relay drive circuit), 7゜9...Relay coil .

Claims (1)

[Claims] It has a plurality of heaters connected to a power supply, a relay contact connected in series to each heater, a relay drive circuit, and a heater selection circuit for selectively using each heater, and one relay contact A control device for an electric hot plate, characterized in that a series circuit of a heater and a heater is connected to a power source via an open contact of another relay.