1. Technical Field
Embodiments of the present disclosure relate to light source driving devices, and particularly to a light source driving device with a fault detecting function.
2. Description of Related Art
The benchmark voltage often uses a fixed bias voltage. However, the lamp status feedback signal often varies according to a lamp brightness control signal or a surrounding temperature. Because the voltage level comparison circuit 50 compares the varied lamp status feedback signal to the benchmark voltage of a fixed bias voltage, unreliable detection of faults may occur. Therefore, the light source driving device cannot exactly determine whether the light source 10 is nonfunctional.
The power stage circuit 300 converts an external electrical signal to an alternating current (AC) signal. The transformer circuit 200 is connected between the power stage circuit 300 and the light source 100 to convert the AC signal to a high voltage electrical signal adapted to drive the light source 100.
The fault detecting circuit 500 detects whether the light source 100 is nonfunctional and outputs a fault signal upon the condition that the light source 100 is nonfunctional. The control circuit 400 is connected between the fault detecting circuit 500 and the power stage 300 to output a control signal to the power stage circuit 300 based on the fault signal.
In one embodiment, the fault detecting circuit 500 includes a voltage level comparison circuit 530 and a variable-benchmark voltage circuit 540. The voltage level comparison circuit 530 has a first input to receive a lamp status feedback signal, a second input, and an output to output the fault signal.
The variable-benchmark voltage circuit 540 is connected to the second input of the voltage level comparison circuit 530 to provide a variable-benchmark voltage signal according to a lamp brightness control signal and a surrounding temperature of the light source 100. In one embodiment, the variable-benchmark voltage circuit 540 includes a first adding resistor R1, a second adding resistor R2, a temperature detecting circuit 510, and a signal processing circuit 520.
The temperature detecting circuit 510 detects the surrounding temperature of the light source 100, and transforms the surrounding temperature to a first voltage signal V1. The signal processing circuit 520 transforms the lamp brightness control signal to a second voltage signal V2. In one embodiment, the lamp brightness control signal includes controlling current flowing through lamps, dimming duties, and so on.
The first adding resistor R1 is connected between the temperature detecting circuit 510 and the second input of the voltage level comparison circuit 530. The second adding resistor R2 is connected between the signal processing circuit 520 and the second input of the voltage level comparison circuit 530. In one embodiment, the first adding resistor R1 and the second adding resistor R2 are structured and arranged to add the first voltage signal V1 and the second voltage signal V2 to acquire the variable-benchmark voltage signal.
The voltage level comparison circuit 530 respectively receives the lamp status feedback signal and the variable-benchmark voltage signal via the first input and the second input of the voltage level comparison circuit 530, and checks whether a difference between the lamp status feedback signal and the variable-benchmark voltage signal is within a predefined range. The voltage level comparison circuit 530 compares the difference between the lamp status feedback signal and the variable-benchmark signal with the predefined range so as to determine whether the light source 100 is nonfunctional, and to output a fault signal to the control circuit 400 upon the condition that the light source 100 is nonfunctional. In one embodiment, the voltage level comparison circuit 530 outputs the fault signal to the control circuit 400 to turn off the power stage circuit 300 upon the condition that the difference between the lamp status feedback signal and the variable-benchmark voltage signal is not within the predefined range. The voltage level comparison circuit 530 does not output the fault signal upon the condition that the difference between the lamp status feedback signal and the variable-benchmark voltage signal is within the predefined range. In practical applications, the predefined range can be defined according to different requirements. In one example, the predefined range may be 0.5V.
The fault detecting circuit 500 may further includes a first voltage dividing resistor R3 and a second voltage dividing resistor R4 connected in series between a reference voltage source Vcc and a ground. A common node of the first voltage dividing resistor R3 and the second voltage dividing resistor R4 is connected to the second input of the voltage level comparison circuit 530 to slightly adjust the variable-benchmark voltage signal.
The variable voltage circuit 512 includes a temperature sensitive resistor Rt and a third voltage dividing resistor R5 connected in series between the reference voltage source Vcc and the ground to divide the reference voltage source Vcc to transform the surrounding temperature to the first voltage signal V1. In one embodiment, the first voltage signal V1 is a direct current (DC) voltage signal.
A non-inverting input of the first operational amplifier 511 is connected to a common node of the temperature sensitive resistor Rt and the third voltage dividing resistor R5, and an inverting input of the first operational amplifier 511 is connected to an output of the first operational amplifier 511. Thus, an output voltage of the first operational amplifier 511 is substantially equal to an input voltage of the first operational amplifier 511, both being V1. Accordingly, the first operational amplifier 511 obtains effective isolation between the output voltage and the input voltage of the first operational amplifier 511. In one embodiment, the first operational amplifier 511 is a voltage follower. An input impedance of the first operational amplifier 511 is very high, and an output impedance of the first operational amplifier 511 is very low.
An inverting input of the second operational amplifier 521 receives a reference voltage signal, and a non-inverting input of the second operational amplifier 521 receives the lamp brightness control signal. The second operational amplifier 521 compares the reference voltage signal with the lamp brightness control signal to output a high-low voltage level signal. In one embodiment, the second operational amplifier 521 is a voltage comparator.
The filtering circuit 522 is connected to an output of the second operational amplifier 521 to transform the high-low voltage level signal to the second voltage signal V2.
A non-inverting input of the third operational amplifier 523 is connected to the filtering circuit 522, and an inverting input of the third operational amplifier 523 is connected to an output of the third operational amplifier 523. Thus, an output voltage of the third operational amplifier 523 is substantially equal to an input voltage of the third operational amplifier 523, both being V2. Accordingly, the third operational amplifier 523 obtains effective isolation between the output voltage and the input voltage of the third operational amplifier 523. In one embodiment, the third operational amplifier 523 is a voltage follower. An input impedance of the third operational amplifier 523 is very high, and an output impedance of the third operational amplifier 523 is very low.
The signal processing circuit 520 may further include a voltage divider 524 connected to the inverting input of the second operational amplifier 521. The voltage divider 524 divides the reference voltage source Vcc to output the reference voltage signal to the inverting input of the second operational amplifier 521. In one embodiment, the voltage divider 524 includes a fourth voltage dividing resistor R6 and a fifth voltage dividing resistor R7 connected in series between two ends of the reference voltage source Vcc. A common node of the fourth voltage dividing resistor R6 and the fifth voltage dividing resistor R7 is connected to the inverting input of the second operational amplifier 521 to output the reference voltage signal to the inverting input of the second operational amplifier 521.
In one embodiment, the filtering circuit 522 includes a first filtering resistor R8, a second filtering resistor R9, a first filtering capacitor C1, and a second filtering capacitor C2.
The first filtering resistor R8 and the second filtering resistor R9 are connected in series between the output of the second operational amplifier 521 and the non-inverting input of the third operational amplifier 523. The first filtering capacitor C1 is connected between a common node of the first filtering resistor R8 and the second filtering resistor R9 and the ground. The second filtering capacitor C2 is connected between the non-inverting input of the third operational amplifier 523 and the ground. A common node of the second filtering capacitor C2 and the second filtering resistor R9 outputs the second voltage signal V2 to the non-inverting input of the third operational amplifier 523.
Thus, the lamp status feedback signal varies according to the lamp brightness control signal and the surrounding temperature of the light source 100. The fault detecting circuit 500 dynamically adjusts the variable-benchmark voltage signal inputted to the voltage level comparison circuit 530 according to the lamp brightness control signal and the surrounding temperature. Then, the voltage level comparison circuit 530 compares the varied lamp status feedback signal to the dynamically adjusted variable-benchmark voltage signal, which leads to reliable detection of faults. Therefore, the light source driving device 90 determines whether the light source 100 is nonfunctional with a high reliability.
While various embodiments and methods of the present disclosure have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present disclosure should not be limited by the above-described embodiments, but should be defined only in accordance with the following claims and their equivalents.
Number | Date | Country | Kind |
---|---|---|---|
2009 1 0105117 | Jan 2009 | CN | national |
Number | Name | Date | Kind |
---|---|---|---|
5485059 | Yamashita et al. | Jan 1996 | A |
6285139 | Ghanem | Sep 2001 | B1 |
7276862 | Kim et al. | Oct 2007 | B2 |
7372217 | Tsai et al. | May 2008 | B2 |
20030122508 | Yang et al. | Jul 2003 | A1 |
20070090774 | Ger et al. | Apr 2007 | A1 |
20090273286 | Veskovic et al. | Nov 2009 | A1 |
20100019694 | Chen et al. | Jan 2010 | A1 |
Number | Date | Country |
---|---|---|
101105603 | Jan 2008 | CN |
Number | Date | Country | |
---|---|---|---|
20100181918 A1 | Jul 2010 | US |