Patent Application
20130264329
1. Field of Invention
The present invention relates to a temperature control circuit and more particularly to a temperature control circuit which can respectively control two heating devices, such as electric blankets and hot packs, by using simple elements.
2. Related Art
Heating devices such as hot packs are very popular in the market. The heating of a heater wire is interrupted automatically after it is heated up to a temperature preset by the user to ensure safety, so that the heating temperature of the heating device can be maintained within a preset range so that the heating device can be used as a hot compress and its safety can be ensured.
In order to control the temperature effectively, U.S. Pat. No. 5,861,610 employs a positive temperature coefficient (PTC) element as the sensing wire to sense the changes in temperature, and a heater wire for heating up and temperature control. These techniques have already been disclosed in U.S. Pat. Nos. 6,300,597, 6,310,322 and 6,768,086.
U.S. Pat. No. 7,180,037 discloses an invention employing a positive temperature coefficient (PTC) element or a negative temperature coefficient (NTC) element, and the main differences between it and the above-mentioned conventional techniques lie in that: U.S. Pat. No. 7,180,037 senses the zero cross signal generated by the response of zero crossing of AC power signals, and senses the zero cross signal generated by the response of zero crossing of phase-shift AC power signals generated by the change of resistance caused by the change of temperature by the positive temperature coefficient (PTC) element or the negative temperature coefficient (NTC) element. By measuring the phase-shift time of the two zero cross signals and until that the phase-shift time is increased to reach the phase-shift time preset by a controller, a control signal is output by the controller to render the circuit connected or interrupted. As a result, both heating up and temperature control are achieved.
The above-mentioned temperature control methods can achieve the effect of controlling temperature. Nevertheless, the above-mentioned temperature control methods can only heat up the heater wire of one heating device. The below problems will occur when the heater wires of two heating devices are heated up respectively:
1. The manufacturing cost is increased because the heating up of the two heater wires requires two sets of temperature control circuits.
2. If one switch is used for controlling the two heater wires, the two heater wires can only be heating up at the same time or stopped heating up at the same time. The heater wire of each of the two heating devices cannot be controlled separately.
3. When one switch is used for controlling the two heater wires and the two heating devices are placed at different locations, different temperatures will be sensed by two sensing wires and the controller will use a highest temperature for temperature control. Therefore, when one of the heater wires has reached a preset temperature and is stopped being heated up continuously; the heating up of the other heater wire, which has not reached a preset temperature, is also interrupted. As a result, the hot compress function of the two heating devices can not be used at the same time which is inconvenient for using.
In view of the above problems, a temperature control circuit of the present invention is disclosed to control two heating devices separately and can also save the manufacturing cost.
An object of the present invention is to provide a temperature control circuit for two heating devices. Two heater wires of the two heating devices can be heated up respectively by the positive half-period and negative half-period of alternating current. Sensing wires are used to sense the heating temperatures of the two heater wires respectively. When the heating temperatures of the two heater wires have reached preset temperatures, a controller is used to interrupt the heating up of the heater wires individually. Therefore, the hot compress effect of the two heating devices can be achieved, and two of the heating devices can be used at the same time or separately.
Another object of the present invention is to provide a temperature control circuit for two heating devices. By employing a disposition of a bi-directional thyristor and a plurality of diodes to control the heating wires of the two heating devices. Thereby, the elements are simplified and the manufacturing cost can be saved.
In order to achieve the above-mentioned objects, the present invention provides a temperature control circuit for two heating devices which comprise a first heating device and a second heating device. A first heater wire and a first sensing wire are disposed in the first heating device; a second heater wire and a second sensing wire are disposed in the second heating device. The first heater wire and the second heater wire are connected in parallel; the first sensing wire and the second sensing wire are connected in parallel. First ends of the first heater wire and the second heater wire as well as first ends of the first sensing wire and the second sensing wire are connected with a polarity of an alternating current power source. A temperature control circuit of the two heating devices comprises a bi-directional thyristor (TRIAC), a controller, a capacitor and four diodes. A first end of the bi-directional thyristor is connected to second ends of the first heater wire and the second heater wire. A second end of the bi-directional thyristor is connected to another polarity of the alternating current power source. The controller is connected with second ends of the first sensing wire and the second sensing wire. A first node is disposed between the controller and the second ends of the first sensing wire and the second sensing wire. The controller comprises a trigger circuit and the trigger circuit is connected with a gate of the bi-directional thyristor so that a controller switch can conduct the alternating current in two half-waves or one half-wave. The capacitor is coupled with the first node. A first end of the first diode is connected with the first end of the first sensing wire; a first end of the second diode is connected with the first end of the second sensing wire. The polarity of the first end of the second diode is different from that of the first end of the first diode. A second end of the third diode is connected with the second end of the first heater wire; a second end of the fourth diode is connected with the second end of the second heater wire. The polarity of the second end of the fourth diode is different from that of the second end of the third diode.
In implementation, the first sensing wire is a positive temperature coefficient (PTC) element or a negative temperature coefficient (NTC) element.
In implementation, a second node, a third node and a fourth node are disposed between the first end of the second heater wire and the polarity of the alternating current power source. The second end of the first diode is coupled with the second node; the first end of the first heater wire is coupled with the third node; and the second end of the second diode is coupled with the fourth node. A sixth node is disposed between the second end of the second sensing wire and the first node, and the second end of the first sensing wire is coupled with the sixth node.
In implementation, a fifth node is disposed between the fourth diode and the switch, and the first end of the third diode is coupled with the fifth node.
The present invention will become more fully understood by reference to the following detailed description thereof when read in conjunction with the attached drawings.
The temperature control circuit 1 comprises a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a bi-directional thyristor (TRIAC) 8, a controller 81 and a capacitor C.
A second end 12 of the first diode D1 is a negative pole and the second end 12 is coupled with the second node P2. A first end 11 of the first diode D1 is a positive pole and the first end 11 is connected with a first end 51 of the first sensing wire 5. A second end 22 of the second diode D2 is a positive pole and the second end 22 is coupled with the fourth node P4. A first end 21 of the second diode D2 is a negative pole and the first end 21 is connected with a first end 71 of the second sensing wire 7. A second end 44 of the fourth diode D4 is a negative pole and the second end 44 is connected with a second end 62 of the second heater wire 6. A first end 43 of the fourth diode D4 is a positive pole and the first end 43 is connected with a first positive polar end of the bi-directional thyristor 8. A fifth node P5 is disposed between the first end 43 of the fourth diode D4 and the first positive polar end of the bi-directional thyristor 8. A second positive polar end of the bi-directional thyristor 8 is connected with another polarity of the alternating current power source 9. The first end 41 of the first heater wire 4 is coupled with the third node P3. The second end 42 of the first heater wire 4 is connected with a second end 32 of the third diode D3. The second end 32 is a positive pole and the first end 31 of the third diode D3 is a negative pole. The first end 31 is coupled with the fifth node P5.
The controller 81 is connected with a second end 72 of the second sensing wire 7. A sixth node P6 and a first node P1 are disposed between the controller 81 and the second end 72 of the second sensing wire 7. A second end 52 of the first sensing wire 5 is coupled with the sixth node P6 and the capacitor C is coupled with the first node P1 so that the capacitor C as well as the first sensing wire 5 and the second sensing wire 7 form a resistor-capacitor (RC) circuit. The controller 81 comprises a trigger circuit 82 and the trigger circuit 82 is connected with the gate of the bi-directional thyristor 8.
Thereby, as shown in
When the temperatures of the first heater wire 4 and the second heater wire 6 increase, the temperatures of the first sensing wire 5 and the second sensing wire 7 increase. Because the first sensing wire 5 and the second sensing wire 7 as well as the capacitor C form the resistor-capacitor (RC) circuit, phase shifts are formed as shown in
When the temperature of the first heater wire 4 increases and based on the phase shift detected at the first node P1 which has reached a preset value, the controller 81 will control the bi-directional thyristor 8 to limit it from triggering negative half-period in order to stop the first heater wire 4 being heated up. When the temperature of the second heater wire 6 increases and based on the phase shift detected at the first node P1 which has reached a preset value, the controller 81 will control the bi-directional thyristor 8 to limit it from triggering positive half-period in order stop the second heater wire 6 being heated up.
Therefore, the present invention has the following advantages:
As a conclusion from the above disclosure, the objectives of the present invention can be achieved. The temperature control circuit for the two heating devices of the present invention not only can control the two heating devices individually for the convenience of usage, the elements are simplified and the manufacturing cost can be saved as well.
Although the embodiments of the present invention have been described in detail, many modifications and variations may be made by those skilled in the art from the teachings disclosed hereinabove. Therefore, it should be understood that any modification and variation equivalent to the spirit of the present invention be regarded to fall into the scope defined by the appended claims.
