Dimmer circuit and lighting apparatus using the same

This application claims the benefit of Taiwan application Serial No. 101138777, filed Oct. 19, 2012, the subject matter of which is incorporated herein by reference.

1. Field of the Invention

The invention relates in general to a dimmer circuit and a lighting apparatus using the same, and more particularly to a dimmer circuit used in light emitting diode (LED) and a lighting apparatus using the same.

2. Description of the Related Art

In recent years, LED has gradually replaced the incandescent lamps to save energy consumption. Although the I LED load is not a resistive load, the dimmer is still needed to adjust the bright/dark level of the LED.

According to a currently used method, a high-watt resistor is serially connected to the input end of the driving circuit of the LED. However, when the dimmer outputs a high conduction angle, the working current of LED increases, and the resistor ends up with more energy consumption.

The invention is directed to a dimmer circuit and a lighting apparatus using the same capable of improving energy loss at high conduction angle.

According to an embodiment of the present invention, a dimmer circuit is provided. The dimmer circuit comprises a dimmer, a rectifier, a sample-and-hold unit, an integral unit and a current holding circuit. The dimmer is coupled to an alternating current (AC) for modulating the AC into an AC light modulating signal. The AC light modulating signal contains multiple wave pulses each having an adjustable conduction angle. The rectifier couples the dimmer and the AC for converting the AC light modulating signal into a direct current (DC) light modulating signal having multiple positive wave pulses. The sample-and-hold unit is coupled to the rectifier for continuously sampling the positive wave pulses of the DC light modulating signal to obtain an average positive wave pulse. The integral unit is coupled to the sample-and-hold unit for integrating the average positive wave pulse to generate a DC voltage. One end of the current holding circuit is coupled to the sample-and-hold unit and the rectifier and the other end is coupled to the integral unit. The current holding circuit comprises a bleeder and a switch. The switch is coupled to the bleeder. The current holding circuit determines the on/off state of the switch according to a comparison between the DC voltage and a reference voltage, such that the DC light modulating signal passes through the bleeder or the switch.

According to another embodiment of the present invention, a lighting apparatus is provided. The lighting apparatus comprises a solid state lighting lamp and a dimmer circuit. The dimmer circuit is coupled to the solid state lighting lamp for adjusting the brightness of the solid state lighting lamp. The dimmer circuit comprises a dimmer, a rectifier, a sample-and-hold unit, an integral unit and a current holding circuit. The dimmer is coupled to an AC for modulating the AC into an AC light modulating signal. The AC light modulating signal contains multiple wave pulses each having an adjustable conduction angle. The rectifier couples the dimmer and the AC for converting the AC light modulating signal into a DC light modulating signal having multiple positive wave pulses. The sample-and-hold unit is coupled to the rectifier for continuously sampling the positive wave pulses of the DC light modulating signal to obtain an average positive wave pulse. The integral unit is coupled to the sample-and-hold unit for integrating the average positive wave pulse to generate a DC voltage. One end of the current holding circuit is coupled to the sample-and-hold unit and the rectifier, and the other end is coupled to the integral unit. The current holding circuit comprises a bleeder and a switch. The switch is coupled to the bleeder. The current holding circuit determines the on/off state of the switch according to a comparison between the DC voltage and a reference voltage, such that the DC light modulating signal passes through the bleeder or the switch.

The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings.

FIG. 1 shows a functional block diagram of a dimmer circuit according to an embodiment of the invention.

FIG. 1 shows a functional block diagram of a dimmer circuit according to an embodiment of the invention. The dimmer circuit 100 comprises a dimmer 110 , a rectifier 120 , a sample-and-hold unit 130 , an integral unit 140 and a current holding circuit 150 .

The dimmer 110 is coupled to an alternating current (AC) 200 for modulating the AC 200 into an AC light modulating signal S 1 . The AC light modulating signal S 1 contains multiple wave pulses each having an adjustable conduction angle A 1 .

The rectifier 120 is coupled to the dimmer 110 and the AC 200 for converting the AC light modulating signal S 1 into a direct current (DC) light modulating signal S 2 having multiple positive wave pulses. The DC light modulating signal S 2 can be transmitted to the driving circuit 400 , which further provides the DC light modulating signal S 2 to the solid state lighting lamp 300 . On the other hand, the DC light modulating signal S 2 can also be transmitted to the sample-and-hold unit 130 , such that the bleeder 152 or the switch 151 can be turned on. In the present example, the rectifier 120 is a full-wave rectifier, but the embodiment of the invention is not limited thereto.

The sample-and-hold unit 130 is coupled to the rectifier 120 for continuously sampling the positive wave pulses of the DC light modulating signal S 2 to obtain an average positive wave pulse. The sample-and-hold unit 130 further obtains a period T 1 and a conduction angle A 1 of the DC light modulating signal S 2 .

The integral unit 140 is coupled to the sample-and-hold unit 130 for integrating the average positive wave pulse according to the period T 1 and the conduction angle A 1 and obtaining an average value of the integral, that is, the DC voltage S 3 .

One end of the current holding circuit 150 is coupled to the sample-and-hold unit 130 and the rectifier 120 , and the other end is coupled to the integral unit 140 . The current holding circuit 150 comprises a bleeder 152 and a switch 151 . The bleeder 152 is a passive element or an active element, wherein the passive element is such as a resistor, and the active element is such as a metal oxide semiconductor (MOS) element. The switch 151 is an active element such as a metal oxide semiconductor element. The switch 151 is coupled to the bleeder 152 . In the present example, the bleeder 152 and the switch 151 are connected in parallel. In another example, the bleeder 152 and the switch 151 can be combined as one single element, such as a metal oxide semiconductor element.

The current holding circuit 150 determines whether the switch 151 is turned on or turned off according to a comparison between the DC voltage S 3 and a reference voltage, such that the DC light modulating signal S 2 passes through the bleeder 152 or the switch 151 . The value range of the reference voltage is between 2.25˜2.65V. The voltage range is a range of corresponding voltage values simulated or calculated according to a range of high conduction angle. In another embodiment, the reference voltage may have other voltage range.

In the present example, the current holding circuit 150 further comprises a comparison unit 153 coupled between the integral unit 140 and the switch 151 for comparing the DC voltage S 3 with the reference voltage. When the DC voltage S 3 is smaller than the reference voltage, the comparison unit 153 controls the switch 151 to be turned off, such that the DC light modulating signal S 2 passes through the bleeder 152 . In terms of one of the controlling methods, the comparison unit 153 may output a low level signal to the switch 151 , such that the switch 151 is turned off and the DC light modulating signal S 2 can only pass through the bleeder 152 . Conversely, when the DC voltage S 3 is larger than the reference voltage, the comparison unit 153 controls the switch 151 to be turned on, such that the DC light modulating signal S 2 passes through the switch 151 . In terms of one of the controlling methods, the comparison unit 153 may output a high level signal to the switch 151 , such that the switch 151 is turned on and the DC light modulating signal S 2 can pass through the switch 151 with lower impedance.

To summarize, when the dimmer 110 outputs a low conduction angle, the DC light modulating signal S 2 passes through the bleeder 152 to increase the holding current and improve the flickering phenomenon which occurs when the conduction angle is low. When the dimmer 110 outputs a high conduction angle, the DC light modulating signal S 2 passes through the switch 151 to improve or avoid energy loss which occurs when the DC light modulating signal S 2 passes through the bleeder 152 .

As indicated in FIG. 1 , the dimmer circuit 100 can be used in the field of illumination. For example, a lighting apparatus 10 comprises a dimmer circuit 100 , a solid state lighting lamp 300 and a driving circuit 400 . The dimmer circuit 100 is coupled to the solid state lighting lamp 300 for adjusting the brightness of the solid state lighting lamp 300 . The solid state lighting lamp 300 is such as various types of LED. The driving circuit 400 is coupled between the dimmer circuit 100 and the solid state lighting lamp 300 for receiving the DC light modulating signal S 2 from the rectifier 120 to drive the solid state lighting lamp 300 .

While the invention has been described by way of example and in terms of the preferred embodiment(s), it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.