The present invention discloses a method of controlling electrical current or voltage to be supplied to the heated glass pane found on refrigerator. A control circuit capable of performing the mentioned method is disclosed as well. BACKGROUND OF THE INVENTION

Heated glass panes have been used in commercial refrigeration doors for many years to avoid formation of fog on the glass surface owing to the temperature differences occurred in between the internal and external environment. Considering that glass is an insulating material by itself, the glass surface has to be coated with a layer ofconductive material, more precisely a resistive material, in order to conduct the electric and generate sufficient heat to avoid vapor condensation. The temperature of the glass pane is preferably above dew point temperature of the surrounding ambient air to prevent fogging onto the glass pane. Generally, coatings used in glass pane of refrigerator are known as Transparent Conductive Oxides (TCOs). The three mostcommonly employed TCOs materials are Fluorine-doped Tin Oxide, Indium-Tin Oxide, and thin stacks of sliver oxides and metallic silver. Relying on the thickness of the coating material and type of coating material as well as size of the glass pane, an electric current of specified amount has to be supplied in order to maintain the glass pane temperature while not overheating the glass pane at the same time. Consideringthat main electric supply always has higher voltage than the voltage actually needed for heating the glass pane, the refrigerator normally includes a circuit to conduct a process for stepping down the voltage. With recent advances in glass coatings and electronic control technology, numerous approaches have been described in attempt to bring down the cost to fabricate the voltage step-down circuit and improve energyefficiency of the refrigerator. For example United States patent application no. 5959816 describes a voltage regulating circuit utilized for controlling supplied voltage to glass panes on a refrigerator. The described voltage regulating circuit particularly uses a sensing circuit to detect abnormalities in output voltage and prompt the circuit control element to 5interfere the voltage to be supplied thereof for voltage regulation. Further, real-time temperature and/or humidity sensing means are employed in both United States patent application no. 4260876 and 4870252 to facilitate periodical control over the voltage to be supplied to the glass pane. By precisely control the supplied voltage according to the environmental variation, these inventions aim to conserve and reduce amount of Oelectric energy supplied to the refrigerator.

Apart from regulating the supplied voltage accord to the temperature fluctuation in the surrounding environment, it is possible too regulating the voltage following other influential factors. For example, a simple voltage regulating mechanism can be 5devised to facilitate the refrigerator to adaptably use varied line voltages of different countries, with slight adjustment, to heat the glass panes without the need of using transformer to step-down the line voltage first.

SUMMARY OF THE INVENTION

0The present invention aims to provide a control circuit programmed to proportionally regulate supplied voltage to heated glass pane in a refrigerator. More specifically, the disclosed invention employs a TRIAC to carry out the voltage stepping down process in the refrigerator coupling to the programmable control circuit. 5An other object of the present invention is to offer control circuit, possessing voltage stepping-down capabilities for heated glass panes, which can be manufactured at relatively lower price without using transformers.

Still, an object of the disclosed invention is to offer a simple voltage stepping-down0mechanisms facilitating the line voltage to be regulated to a much smaller range fitting glass panes prepared in different sizes. Another object of the present invention is to offer a method for stepping-down the voltage from the supply line without using transformers. The disclosed method is applicable with simple adjustment to match great range of line voltage available in 5many countries.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention includes a control circuit capable of proportionally supplying electrical current from an alternate lOcurrent power supply to a glass pane coated with transparent conductive oxides on refrigerator comprising a triode for alternating current (TRIAC) electrically gating the voltage to be supplied to the glass pane; and a micro-controller configured to fire an electrical pulse to the TRIAC after a pre-determined delayed duration once detecting zero crossing of each phase of the alternate current; wherein the TRIAC allows

15electrical current conduction at each phase of the alternate current to the glass pane upon receiving the electrical pulse and the total electrical current supplied to the glass pane is inversely related to the pre-determined delayed duration. More preferably, five locations of jumpers are employed in the present invention to be used to set the voltage level to be supplied to the glass panes. Specifically, setting in these jumpers in

20conjunction with the micro-controller will determine conduction angle of the electrical current. Thus, the amount of the voltage supplied to the glass panes is based on the predetermined setting of the jumpers.

In another aspect, the disclosed control circuit further comprises a direct current 25power supply to power the micro-controller. More preferably, the direct current power supply is a capacitive transformerless power supply.

In further aspect, the zero detecting in the disclosed invention is performed using an internal comparator at Neutral line interfaced with a resistor. The interfaced resistor 30can significantly influence the duration of the delay thus the amount of voltage to be finally supplied to the heated glass. Another embodiment of the present invention involves a method of proportionally supplying electrical current from an alternate current power supply to a glass pane coated with transparent conductive oxides on refrigerator comprising providing a alternate current to the glass pane through a TRIAC of a control circuit; detecting zero crossing of each phase of the alternate current by the control circuit; and firing an electrical pulse from a micro-controller of the control circuit to the TRIAC to permit conduction of the electrical current to the glass pane after a predetermined delayed duration upon detecting the zero crossing; wherein the predetermined delayed duration is inversely related to the total electrical current supplied to the glass pane.

Similarly, the disclosed method employs a direct current power supply to power the micro-controller. Preferably, the direct current power supply is a capacitive transformerless power supply. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic diagram of one embodiment of the disclosed invention;

Figure 2 shows a schematic diagram of the capacitive transformerless power supply circuit;

Figure 3 shows cross-sectional view of the heated glass pane in general;

Figure 4 shows possible Triac conduction angle of the disclosed circuit; and

Figure 5 is a graph showing various phase angle of the Triac for the heated glass pane.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the present invention may be embodied in other specific forms and is not limited to the sole embodiment described herein. However modification and equivalents of the disclosed concepts such as those which readily occur to one skilled in the art are intended to be included within the scope of the claims which are appended thereto.

According to one preferred embodiment of the present invention, as shown in 5 schematic circuit diagram, a control circuit capable of proportionally supplying electrical current from an alternate current power supply to a glass pane coated with transparent conductive oxides on refrigerator is disclosed. The disclosed control circuit comprises a triode for alternating current (TRIAC) electrically gating the voltage to be supplied to the glass pane; and a micro-controller configured to fire an Oelectrical pulse to the TRIAC after a pre-determined delayed duration once detecting zero crossing of each phase of the alternate current; wherein the TRIAC allows electrical current conduction at each phase of the alternate current to the glass pane upon receiving the electrical pulse and the total electrical current supplied to the glass pane is inversely related to the pre-determined delayed duration. The amount of the5delay will be based on the predetermined setting of the jumpers. It was found by the inventors of the present invention that combination of TRIAC and the zero crossing detection enables the disclosed circuit to precisely regulate or down-step the voltage to the desired level matching the available surface and thickness of the glass pane. Figure 3 illustrates standard establishment of common heated glass pane in0refrigerator. Considering that alternating current generally used in supplied line electricity shifts between phases from time to time, the present invention utilizes zero- crossing of the supplied alternating current as an automated signal to prompt the disclosed circuit to initiate the voltage control mechanisms programmed in the circuit in accord with the phases or half wave of the electric current. Using this intrinsic5property of the alternating current, the disclosed circuit ensures the regulating mechanisms is activated in each phase of the alternating current irregardless of the frequency of the supplied electricity in different countries therefore facilitating manufacture of refrigerator equipped with the disclosed control circuit. OMore preferably, five locations of jumpers are employed in the present invention to be used to set the voltage level to be supplied to the glass panes. Specifically, setting in these jumpers in conjunction with the micro-controller will determine conduction angle of the electrical current. Thus, the amount of the voltage supplied to the glass panes is based on the predetermined setting of the jumpers. Referring to Figure 1, five set of jumpers connected to five resistors in series forming a voltage divider that divide a PIC supply voltage to five levels. The PIC will read the voltage level based 5on the position of the jumper and will produce the delay according to the required TRIAC output voltage.

TRIAC in the present invention serves as the port to gate flow of electric current towards the glass panes and the current conduction is allowed only following l Oactivation of the TRIAC. It is important to be noted that the TRIAC permits only the electrical current to pass through to the glass pane upon receiving the electrical pulse fired by the micro-controller. The electrical pulse triggers activation of the TRIAC while the timing to fire the electrical pulse is crucial in the disclosed invention to determine the amount of voltage supplied to the glass pane. Specifically, the amount

15of the voltage to be supplied to the glass panes is directly accorded to the duration available to conduct the electrical current through the TRIAC. The point at the half wave or one of the phases of the alternating current which the electric conduction in the TRIAC began is known as conduction angle, Θ, of the TRIAC. More specifically, the voltage to be supplied across the heating surface of the glass pane in the disclosed

20invention is regulated by controlling the conduction angle of the TRIAC. As illustrated in figure 4, the relationship in between the conduction angle, the output voltage, the ampere of conducted current (AVG) and the watt of power output (RMS) is shown. The length of pre-determined delayed duration thus decides the conduction angle of the TRIAC and the amount of voltage to be supplied across the glass panes

25according to the conduction angle thereof.

Considering that line voltage can be varied among countries in terms of power and frequency. Preferably, the disclosed circuit of the present invention facilitates regulation of supplied line voltage of various amplitude and frequency in the 30produced refrigerator through a simple yet reliable mechanism. Knowing the voltage and frequency as well as sheet resistance of the glass panes, the conduction angle for acquiring the preferred voltage can be calculated using formulation shown in the following,

0.— sin 2« I

T( s) ^■ * roue) max I 7 KAiS) max ~

— sin 2a T ²

= ¹ T( ss.) ^I L

¹ P (OUT ^' )) ¹ ' P ((OUT)nwL. P, (out) max.

where

IT(AV) : Rectified Mean Current

IT(AV) max : Maximum Rectified Mean Current

IT (max) : Peak Current

IT(RMS) : RMS Current

IT(RMS) max : Maximum RMS Current

P(OUT) - : Output Power

P(OUT) max : Maximum Output Power

RL : Resistive Load

a : Conduction Angle

Consequently, the disclosed circuit, through adjusting the length of pre-determined delayed duration of firing the electrical pulse, can exploit the conduction angle to regulate the exact electrical current or voltage supplied to the glass panes. In turn, themicro-controller incorporated to the disclosed circuit features to be programmable to fire the electrical pulse at any occasion after the zero crossing of the electrical current in relative to the compared neutral line. The length of pre-determined delayed duration directly affect the supplied voltage to the heated glass panes. Pursuant to another preferred embodiment, the zero detecting in the disclosed circuit is performed using an internal comparator at Neutral line interfaced with a resistor. For example, microcontroller pic 12f675 can be used in one embodiment of the 5present invention which has one analog comparator embedded inside and is useful in interfacing with analog signal. Analog comparator works by comparing two analog signal and generate a signal on the output to indicate which signal is larger. In this embodiment employing pic 12f675, the comparator output signal is represented with logic '0' or T. Pins GPO and GP1 of 12f675 can be used as the inputs of the lOcomparator. There is also an on-chip Comparator Voltage Reference that can be applied as an input of the comparator. In addition, the comparator output can be read directly from the 12f675 special register called CMCON register. For detecting the zero crossing of the sinusoid AC voltage, the disclosed invention needs the comparator module. Preferably, one I/O pin of the microcontroller is connected to the

15 AC voltage. This signal is then compared with the on-chip Comparator Voltage Reference which is set to 0 volt. The comparator output is read directly from the internal CMCON register. Output changes from '0' to T indicates a zero crossing from negative cycle to positive cycle of the AC signal and changes from T to '0' indicates a zero crossing from positive cycle to negative cycle of the AC signal. These 0output changes are used as the base of the switching algorithm to control the heater in one of the embodiments.

To ensure smooth operation of the micro-controller without subjected to fluctuation in the alternating current of the supplied line, the disclosed circuit uses a direct current 5power supply to power the micro-controller in one of the preferred embodiments. More preferably, the direct current power supply is a capacitive transformerless power supply. Utilization of transformless power supply renders the equipped refrigerators to be manufactured at much lower price and capacitive power supply requires relatively smaller space for installation also. Nonetheless, the capacitive 0transformerless power supply is charged by the alternating current of the supply line and possible embodiment of the capacitive transformerless power supply ishown in figure 2. In respect to another embodiment, a method of proportionally supplying electrical current from an alternate current power supply to a glass pane coated with transparent conductive oxides on refrigerator is disclosed. The method comprises the steps of 5providing a alternate current to the glass pane through a TRIAC of a control circuit; detecting zero crossing of each phase of the alternate current by the control circuit; and firing an electrical pulse from a micro-controller of the control circuit to the TRIAC to permit conduction of the electrical current to the glass pane after a predetermined delayed duration upon detecting the zero crossing; wherein the (predetermined delayed duration is inversely related to the total electrical current supplied to the glass pane.

A method of claim 5 further comprising a direct current power supply to power the micro-controller.

5

As in setting forth, TRIAC in the disclosed method serves as the port to gate flow of electric current towards the glass panes and the current conduction is allowed only following activation of the TRIAC. The electrical pulse triggers activation of the TRIAC while the timing to fire the electrical pulse is crucial in the disclosed invention0to determine the amount of voltage supplied to the glass pane. Specifically, the amount of the voltage to be supplied to the glass panes is directly accorded to the duration available to conduct the electrical current through the TRIAC. The point at the half wave or one of the phases of the alternating current which the electric conduction in the TRIAC began is known as conduction angle, Θ, of the TRIAC.5More specifically, the voltage to be supplied across the heating surface of the glass pane in the disclosed invention is regulated by controlling the conduction angle of the TRIAC. The length of pre-determined delayed duration thus decides the conduction angle of the TRIAC and the amount of voltage to be supplied across the glass panes according to the conduction angle thereof. Referring to figure 5, the TRIAC shows0different phase angle in terms of current and voltage prior and after its activation by the micro-controller. The power being channeled to the heat glass panes equals to the total current pass through the TRIAC at each phase or half wave. Further, the disclosed method preferably regulates the conduction angle to control the exact amount of electrical current or voltage being supplied to the glass panes, particularly through adjusting the length of pre-determined delayed duration of firing 5the electrical pulse. More preferably, the micro-controller incorporated to the circuit features to be programmable to fire the electrical pulse at any occasion after the zero crossing of the electrical current in relative to the compared neutral line. In the disclosed method, the length of pre-determined delayed duration directly affect the supplied voltage to the heated glass panes. Moreover, the steps of detecting zero lOcrossing in the disclosed is performed using an internal comparator at Neutral line interfaced with a resistor within the circuit.

Preferably, the operation of the micro-controller is powered by a standalone power supply without subjected to fluctuation in the alternating current from the supplied 151ine. More specifically, the disclosed method uses a direct current power supply to power the micro-controller in one of the preferred embodiments. More preferably, the direct current power supply is a capacitive transformerless power supply. Still, the capacitive transformerless power supply is charged by the alternating current of the supply line.

20

The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in 25the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.