WO2009004520A1

WO2009004520A1 - Lighting and heating circuit and assembly, and a method for lighting and heating

Info

Publication number: WO2009004520A1
Application number: PCT/IB2008/052466
Authority: WO
Inventors: Kumar Arulandu; Marcel V. Somer
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-06-29
Filing date: 2008-06-23
Publication date: 2009-01-08
Also published as: TW200917897A

Abstract

A lighting and heating circuit has a load circuit, a power supply, and a control circuit. The load circuit has a light emitting diode, a heating resistor coupled in series with the light emitting diode, and an auxiliary diode coupled anti-parallel with the light emitting diode. The power supply supplies power to the load circuit, and produces current of a first polarity to cause the light emitting diode to conduct, and current of a second polarity to cause the auxiliary diode to conduct. The control circuit controls the power supply to produce a predetermined current of first polarity and a predetermined current of second polarity, to cause the light emitting diode to produce a predetermined light and to cause the heating resistor to produce a predetermined heat.

Description

Lighting and heating circuit and assembly, and a method for lighting and heating

FIELD OF THE INVENTION

The present invention relates to a lighting and heating circuit. The present invention further relates to a lighting and heating assembly, whereby an object such as a glass object may be heated. The present invention still further relates to a method for lighting and/or heating an object.

BACKGROUND OF THE INVENTION

JP 2001/61623 discloses a mirror provided with a number of LEDs disposed at a top end side of the mirror. Resistors included in a power supply circuit of the LEDs are affixed at the rear side of the mirror, and generate heat when the LEDs are powered, thus preventing moisture condensation on the mirror.

When the LEDs are dimmed by reducing the current fed to the LEDs, or when the LEDs are not powered, the amount of heat generated by the resistors decreases accordingly, and moisture condensation on the mirror may not be prevented to a satisfactory level, or not at all when the LEDs are not powered.

OBJECT OF THE INVENTION

It is desirable to provide an electrical circuit allowing both a lighting and a heating function, wherein these functions are controllable independently from each other to a suitable extent.

SUMMARY OF THE INVENTION

In an embodiment of a circuit according to the invention, a lighting and heating circuit is provided, the circuit comprising a load circuit, a power supply for supplying electrical power to the load circuit, and a control circuit for controlling the power supply. The load circuit comprises at least one light emitting diode, LED, at least one heating resistor coupled in series with the light emitting diode, and at least one auxiliary diode coupled anti- parallel with the light emitting diode. The power supply is configured to produce current of a first polarity to cause the light emitting diode to conduct, and to produce current of a second polarity to cause the auxiliary diode to conduct. The control circuit is configured to produce a predetermined current of first polarity and a predetermined current of second polarity, to cause the light emitting diode to produce a predetermined light and to cause the heating resistor to produce a predetermined heat. The power supply may be a voltage source or a current source. The current of first polarity may be generated by a current source, or a voltage source energizing the load circuit with a voltage having a first polarity, whereas the current of second polarity may be generated by a current source, or a voltage source energizing the load circuit with a voltage having a second polarity reverse to the first polarity. When a predetermined current of first polarity flows in the load circuit, this current flows through the LED and the heating resistor. As a result, the LED produces a predetermined light (such as light of a predetermined intensity and/or colour), and the heating resistor produces a predetermined heat. The LED may be dimmed, and by changing the current of first polarity, the light produced by the LED and the heat produced by the heating resistor changes accordingly.

When a predetermined current of second polarity flows in the load circuit, this current flows through the auxiliary diode and the heating resistor. As a result, the heating resistor produces a predetermined heat. By changing the current of second polarity, the heat produced by the heating resistor changes accordingly. Thus, by selecting the current of first polarity, the light generated by the LED is selected, and at least part of the heat generated by the heating resistor is selected. If it is desired to generate additional heat without changing the light produced by the LED (i.e. keeping the current of first polarity constant), then a suitable current of the second polarity may be selected to produce the additional heat in the heating resistor. In the latter situation, the current is an alternating current, where current of first polarity is alternated with current of second polarity.

In this specification, "heat" is generally equivalent to "heating power", expressed in J/s or W.

In an embodiment of the circuit according to the present invention, the control circuit controls the power supply to operate in pulse width modulation mode. Thus, an easy control of the amount of light and heat is provided depending on the pulse width and the amplitude of the current, both of which may vary. A frequency, or similarly a period, of the current pulses may be selected as needed in view of other requirements or restraints, such as to avoid flicker of the light, or range of control of the light and/or heat. The pulses may be rectangular, or have any other suitable shape. The load circuit may be energized by pulses of current of first polarity only, or by pulses of current of second polarity only, or by a combination of pulses of current of first and second polarity.

In an embodiment of the circuit according to the present invention, a pulse width of the current of first polarity is independent from a pulse width of the current of second polarity. The pulse width of the pulses of current of first polarity may differ, and may be controlled differently, from the pulses of current of second polarity.

Thus, the generation of light by the LED with the current of first polarity may be selected within a range from a minimum value zero at which the LED is off and the current of first polarity is zero, to a value or maximum value at which the LED is on and the current of first polarity is greater than zero or has a maximum value. During the generation of light by the LED with the current of first polarity, also heat is generated by the heating resistor. With regard to the current of first polarity, the amount of heat may range from a minimum value zero when the LED is off and the current of first polarity is zero, to a first maximum value when the LED is on and the current of first polarity is at a maximum.

With current of the second polarity reverse to the first polarity, no light is generated by the LED, since the LED blocks current of the second polarity, whereas the auxiliary diode does not block current of second polarity. However, the current of second polarity generates heat in the heating resistor. With regard to the current of second polarity, the amount of heat may range from a minimum value zero when the current of second polarity is zero, to a second maximum value when the current of second polarity is at a maximum.

When in a period of time both current of first polarity and current of second polarity flows in the load circuit, the amount of heat generated in the heating resistor firstly is determined by the amount of light to be generated by the LED (which amount of heat may be considered to have a minimum value). Secondly, in addition to the heat generated by the current of first polarity, heat may be generated by the current of second polarity in an amount from zero to said second maximum value, independently from the current of the first polarity or the heat generated thereby. In an embodiment of the circuit according to the present invention, a pulse width of the current of second polarity is selected such that a sum of power generated in the heating resistor as a result of the pulse width of the current of second polarity and power generated in the heating resistor as a result of a pulse width of the current of first polarity is substantially the same for varying pulse widths of the current of first polarity. Here, when it is assumed that a required heating power to be generated in the heating resistor may be fully provided by current of second polarity, the heating power generated in the heating resistor by a current of second polarity may be diminished to balance heating power generated in the heating resistor by a current of first polarity. In an embodiment of the circuit according to the present invention, the resistor is wire-shaped or ribbon-shaped. Wire-shaped or ribbon-shaped resistors provide a distributed heat generation, and may simplify a heating of a large area, and heat transfer thereto.

In an embodiment of the circuit according to the present invention, the auxiliary diode is a Zener diode. A Zener diode does not only provide the rectifying function useful for the present invention, but also an overvoltage protection for the LED.

In an embodiment of a lighting and heating assembly according to the present invention, there is provided: an object, at least one LED connected to the object, at least one resistor coupled in series with the light emitting diode and connected to the object for heating the object, and at least one auxiliary diode coupled anti-parallel with the light emitting diode. The assembly includes the load circuit as described above, where the LED may provide a lighting of the object, or a lighting of an environment of the object. The heating resistor provides a heating of the object.

In an embodiment of the assembly, the object at least partially is made of glass. Accordingly, a heating of the object by the heating resistor may prevent condensation to form on the surface of the glass object, or may have any other useful effect. The object may comprise a glass plate.

In an embodiment of the assembly, the object is a mirror. The heating resistor may be mounted at the back of the mirror, or may be provided in the mirror, e.g. in the form of thin wires. The LED may be used to throw light on a person being in front of the mirror.

In another embodiment of the assembly, the glass plate is a window, and the light emitting diode is integrated with the window. The window may be a car rear window, where the LED forms a braking light. The heating resistor may be provided in the window, e.g. in the form of thin wires. In an embodiment of a method of lighting, and heating an object, the method comprises: providing the load circuit, connecting the heating resistor to the object for heating the object; and supplying a predetermined current of a first polarity to the load circuit, thereby causing the light emitting diode to produce light and the heating resistor to produce heat. In an embodiment of a method of heating an object, the method comprises: providing the load circuit, connecting the heating resistor to the object for heating the object, and supplying a predetermined current of a second polarity to the load circuit, thereby causing the auxiliary diode to conduct and the heating resistor to produce heat. Both methods can be applied independently or in combination.

The claims and advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts a basic electrical circuit diagram of an embodiment of the invention used for lighting and heating of an object;

Figure 2 depicts a timing diagram of a current signal in the electrical circuit of Figure 1;

Figure 3 depicts a perspective view of an object provided with LEDs and resistors in an embodiment of the invention; and

Figure 4 depicts a perspective view of another object provided with LEDs and resistors in another embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLES

Figure 1 shows a power supply 10, such as a current supply, configured to supply a current I to a parallel circuit of an LED (Light Emitting Diode) 12 and a Zener diode 14 through a resistor 16. The LED 12, the Zener diode 14, and the resistor 16 form a load circuit.

Instead of one LED 12, in a practical embodiment a plurality of LEDs may be used, where the current I is fed to the plurality of LEDs. The LEDs may be of any suitable type, including e.g. OLED (Organic Light Emitting Diode).

The resistor 16, in a practical embodiment, may not be a concentrated element, but instead may comprise an element having a considerable extension in at least one dimension, e.g. in the form of a wire, a ribbon, a tape or a film. Several of these resistive elements may be connected in series and/or parallel.

The current I may have a first polarity to flow in a positive direction, and may have a second polarity, reverse to the first polarity, to flow in a negative direction. The current may be alternating. In at least one of said directions, the amplitude and time of the current flow may vary. The current may be rectangular pulse-shaped. The pulse width of the current may be modulated, where the modulation of current pulses in the positive direction may differ from the modulation of current pulses in the negative direction. For controlling the current I flowing in a positive and/or a negative direction, the power supply 10 is controlled by a control circuit 18. The control circuit 18 may comprise controls to control an on/off state of the LED 12 and an on/off state of the resistor 16, as well as controls to vary the current supplied to the LED 12 and the current supplied to the resistor 16. The control circuit 18 may be implemented in hardware, firmware, or software. The control circuit 18 may be provided with suitable actuators as known in the art.

When the current I flows in the positive direction, it flows through LED 12 causing the LED 12 to emit light. Zener diode 14 normally blocks current I flowing in the positive direction. Zener diode 14 would, however, in case the voltage across the LED 12 exceeds a predetermined threshold, conduct positive current, thus protecting the LED 12 against excessive voltages (ESD protection).

When the current I flows in the negative direction, it flows through the Zener diode 14, since LED 12 blocks current I flowing in the negative direction.

Figure 2 shows a time (t) diagram of current I of first polarity (flowing in the positive direction) alternating with current I of second polarity (flowing in the negative direction), as may be controlled by the control circuit 18. From time ti to time t₂, a current of first polarity and first amplitude Ii flows in the load circuit, in particular through LED 12, and resistor 16. Zener diode 14 blocks the current Ii in this time period. From time t₂ to time t3, no current flows in the load circuit. From time t3 to time U, a current of second polarity and second amplitude I₂ flows in the load circuit, in particular through Zener diode 14 and resistor 16. LED 12 blocks the current I₂ in this time period. From time U to time t₅, no current flows in the load circuit. At time t₅, one period of the current I is terminated, and a new period starts with a current of first polarity flowing through LED 12, and resistor 16, from time ts to time t₆. The width of the current pulse from ti to t₂, and/or its (absolute) amplitude, may differ from the width and/or (absolute) amplitude of the current pulse from t3 to U, or the current pulse from ts to U- Each of the time periods ti to t₂, t₂ to t3, t3 to U, and U to ts may be zero, thereby changing other time periods. At maximum, the current pulse of first or second polarity may have a duration of ti to ts, when the current pulse of the other polarity has a duration zero. The latter situation is equivalent to a direct current of first or second polarity, respectively. A heating power P generated by resistor 16 may be expressed as:

P = [Ii²*(t₂-t0 + I₂ ²*(t₄-t₃)]*R/(t₅-t₁)

where R is the resistance of resistor 16. From this expression, it can be easily seen that by selecting appropriate times t2, t3 and t4 in the control circuit 18, a predetermined constant heating power P may be set, while the current of first polarity flowing through the LED 12 may be varied. Also, a predetermined current of first polarity flowing through the LED 12 may be set, while the heating power P may be varied. Figure 3 illustrates an assembly including a mirror 30 in perspective rear view.

At the back of the mirror 30, a ribbon-like heating resistor 32 is mounted in a manner to transfer heat generated by the resistor 32 to the mirror 30 in at least an area thereof. LEDs 34 are mounted at the edges of the mirror 30. One or more auxiliary diodes (not shown in the Figure) are connected anti-parallel to the LEDs 34. Figure 4 illustrates an assembly including a car rear window 40, having a wire-like heating resistor 42 provided in or on the window 40. A plurality of red light emitting LEDs 44 are provided on or in the window 40 to function as a third braking light. One or more auxiliary diodes (not shown in the Figure) are connected anti-parallel to the LEDs 44. In the embodiment of Figure 4, and also in other embodiments, the resistor may comprise a (transparent) Indium Tin Oxide (ITO) coating or wire on or in the object.

Further, it is to noted that the auxiliary diode may be incorporated in the LED package. When using a large number of LEDs connected in series, the auxiliary diodes (when embodied as Zener diodes) also provide an extra reliability function. If one of the LEDs in the series connection would be broken down, thus representing an open circuit component, then the Zener diode will conduct. This will result in maintaining a proper functioning of the other LEDs in the series connection, despite the broken down LED in the series connection. Other possible applications of the present invention include shower cabinets, decoration panels, and showcases. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention.

The terms "a" or "an", as used herein, are defined as one or as more than one. The term plurality, as used herein, is defined as two or as more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term software, and the like as used herein, is defined as a sequence of instructions designed for execution on a computer system. A program, computer program, or software application may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution in a control circuit, on a controller or on a computer system.

Claims

CLAIMS:

1. A lighting and heating circuit comprising: a load circuit comprising: at least one light emitting diode, LED, at least one heating resistor coupled in series with the light emitting diode, and at least one auxiliary diode coupled anti-parallel with the light emitting diode; a power supply for supplying electrical power to the load circuit, the power supply being configured to produce current of a first polarity to cause the light emitting diode to conduct, and to produce current of a second polarity to cause the auxiliary diode to conduct; and a control circuit for controlling the power supply to produce a predetermined current of first polarity and a predetermined current of second polarity, to cause the light emitting diode to produce a predetermined light and to cause the heating resistor to produce a predetermined heat.

2. The circuit according to claim 1, wherein the control circuit controls the power supply to operate in pulse width modulation mode.

3. The circuit according to claim 2, wherein a pulse width of the current of first polarity is independent from a pulse width of the current of second polarity.

4. The circuit according to claim 2, wherein a pulse width of the current of second polarity is selected such that a sum of power generated in the heating resistor as a result of the pulse width of the current of second polarity and power generated in the heating resistor as a result of a pulse width of the current of first polarity is substantially the same for varying pulse widths of the current of first polarity.

5. The circuit according to any of the preceding claims, wherein the resistor is wire-shaped or ribbon-shaped.

6. The circuit according to any of the preceding claims, wherein the auxiliary diode is a Zener diode.

7. A lighting and heating assembly comprising: an object; at least one light emitting diode, LED, connected to the object; at least one resistor coupled in series with the light emitting diode and connected to the object for heating the object; and - at least one auxiliary diode coupled anti-parallel with the light emitting diode.

8. The assembly according to claim 7, wherein the object at least partially is made of glass.

9. The assembly according to claim 8, wherein the object comprises a glass plate.

10. The assembly according to claim 8 or 9, wherein the object is a mirror.

11. The assembly according to claim 9, wherein the glass plate is a window, and wherein the light emitting diode is integrated with the window.

12. A method of lighting, and heating an object, the method comprising: providing a load circuit comprising: at least one light emitting diode, LED, - at least one heating resistor coupled in series with the light emitting diode, and at least one auxiliary diode coupled anti-parallel with the light emitting diode; connecting the heating resistor to the object for heating the object; and - supplying a predetermined current of a first polarity to the load circuit, thereby causing the light emitting diode to produce light and the heating resistor to produce heat.

13. A method of heating an object, the method comprising: providing a load circuit comprising: at least one light emitting diode, LED, at least one heating resistor coupled in series with the light emitting diode, and at least one auxiliary diode coupled anti-parallel with the light emitting diode; connecting the heating resistor to the object for heating the object; and supplying a predetermined current of a second polarity to the load circuit, thereby causing the auxiliary diode to conduct and the heating resistor to produce heat.