Light source driving device

A light source driving device for driving a light source includes a power stage circuit, a transformer circuit, a control circuit, and a fault detecting circuit. The power stage circuit converts an external electrical signal to an alternating current (AC) signal. The transformer circuit is connected between the power stage circuit and the light source to convert the AC signal to a high voltage electrical signal adapted for driving the light source. The fault detecting circuit detects whether the light source is nonfunctional, and outputs a fault signal upon the condition that the light source is nonfunctional. The fault detecting circuit includes a voltage level comparison circuit and a variable-benchmark voltage circuit. The control circuit is connected between the fault detecting circuit and the power stage circuit to output a control signal to the power stage circuit based on the fault signal.

BACKGROUND

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

FIG. 4is a light source driving device with a fault detecting function. A power stage circuit30converts an external electrical signal to an alternating current (AC) signal. The AC signal is converted to a sine-wave signal to drive the light source10via a transformer circuit20. A control circuit40is connected to the power stage circuit30to control output of the power stage circuit30. A voltage level comparison circuit50is connected to the control circuit40to check whether a difference between a lamp status feedback signal and a benchmark voltage is within a predefined range so as to determine whether the light source10is nonfunctional and output a fault signal. The control circuit40turns off the output of the power stage circuit30based on the fault signal.

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 circuit50compares 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 source10is nonfunctional.

DETAILED DESCRIPTION

FIG. 1is a block diagram of one embodiment of a light source driving device90to drive a light source100in accordance with the present disclosure. In one embodiment, the light source driving device90includes a transformer circuit200, a power stage circuit300, a control circuit400, and a fault detecting circuit500. The light source driving device90has a fault detecting function. That is, the light source driving device90automatically turns off output of the power stage circuit300upon detecting that the light source100is nonfunctional. In one embodiment, the light source100includes a plurality of lamps, and nonfunctional operation of the light source100may include a broken lamp, a disconnection of a lamp, and so on.

The power stage circuit300converts an external electrical signal to an alternating current (AC) signal. The transformer circuit200is connected between the power stage circuit300and the light source100to convert the AC signal to a high voltage electrical signal adapted to drive the light source100.

The fault detecting circuit500detects whether the light source100is nonfunctional and outputs a fault signal upon the condition that the light source100is nonfunctional. The control circuit400is connected between the fault detecting circuit500and the power stage300to output a control signal to the power stage circuit300based on the fault signal.

In one embodiment, the fault detecting circuit500includes a voltage level comparison circuit530and a variable-benchmark voltage circuit540. The voltage level comparison circuit530has 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 circuit540is connected to the second input of the voltage level comparison circuit530to provide a variable-benchmark voltage signal according to a lamp brightness control signal and a surrounding temperature of the light source100. In one embodiment, the variable-benchmark voltage circuit540includes a first adding resistor R1, a second adding resistor R2, a temperature detecting circuit510, and a signal processing circuit520.

The temperature detecting circuit510detects the surrounding temperature of the light source100, and transforms the surrounding temperature to a first voltage signal V1. The signal processing circuit520transforms 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 R1is connected between the temperature detecting circuit510and the second input of the voltage level comparison circuit530. The second adding resistor R2is connected between the signal processing circuit520and the second input of the voltage level comparison circuit530. In one embodiment, the first adding resistor R1and the second adding resistor R2are structured and arranged to add the first voltage signal V1and the second voltage signal V2to acquire the variable-benchmark voltage signal.

The voltage level comparison circuit530respectively 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 circuit530, 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 circuit530compares the difference between the lamp status feedback signal and the variable-benchmark signal with the predefined range so as to determine whether the light source100is nonfunctional, and to output a fault signal to the control circuit400upon the condition that the light source100is nonfunctional. In one embodiment, the voltage level comparison circuit530outputs the fault signal to the control circuit400to turn off the power stage circuit300upon 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 circuit530does 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 circuit500may further includes a first voltage dividing resistor R3and a second voltage dividing resistor R4connected in series between a reference voltage source Vcc and a ground. A common node of the first voltage dividing resistor R3and the second voltage dividing resistor R4is connected to the second input of the voltage level comparison circuit530to slightly adjust the variable-benchmark voltage signal.

FIG. 2is a circuit diagram of one embodiment of the temperature detecting circuit510in accordance with the present disclosure. In one embodiment, the temperature detecting circuit510includes a first operational amplifier511and a variable voltage circuit512.

The variable voltage circuit512includes a temperature sensitive resistor Rt and a third voltage dividing resistor R5connected 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 V1is a direct current (DC) voltage signal.

A non-inverting input of the first operational amplifier511is 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 amplifier511is connected to an output of the first operational amplifier511. Thus, an output voltage of the first operational amplifier511is substantially equal to an input voltage of the first operational amplifier511, both being V1. Accordingly, the first operational amplifier511obtains effective isolation between the output voltage and the input voltage of the first operational amplifier511. In one embodiment, the first operational amplifier511is a voltage follower. An input impedance of the first operational amplifier511is very high, and an output impedance of the first operational amplifier511is very low.

FIG. 3is a circuit diagram of one embodiment of the signal processing circuit520in accordance with the present disclosure. In one embodiment, the signal processing circuit520includes a second operational amplifier521, a filtering circuit522, and a third operational amplifier523.

An inverting input of the second operational amplifier521receives a reference voltage signal, and a non-inverting input of the second operational amplifier521receives the lamp brightness control signal. The second operational amplifier521compares the reference voltage signal with the lamp brightness control signal to output a high-low voltage level signal. In one embodiment, the second operational amplifier521is a voltage comparator.

The filtering circuit522is connected to an output of the second operational amplifier521to transform the high-low voltage level signal to the second voltage signal V2.

A non-inverting input of the third operational amplifier523is connected to the filtering circuit522, and an inverting input of the third operational amplifier523is connected to an output of the third operational amplifier523. Thus, an output voltage of the third operational amplifier523is substantially equal to an input voltage of the third operational amplifier523, both being V2. Accordingly, the third operational amplifier523obtains effective isolation between the output voltage and the input voltage of the third operational amplifier523. In one embodiment, the third operational amplifier523is a voltage follower. An input impedance of the third operational amplifier523is very high, and an output impedance of the third operational amplifier523is very low.

The signal processing circuit520may further include a voltage divider524connected to the inverting input of the second operational amplifier521. The voltage divider524divides the reference voltage source Vcc to output the reference voltage signal to the inverting input of the second operational amplifier521. In one embodiment, the voltage divider524includes a fourth voltage dividing resistor R6and a fifth voltage dividing resistor R7connected in series between two ends of the reference voltage source Vcc. A common node of the fourth voltage dividing resistor R6and the fifth voltage dividing resistor R7is connected to the inverting input of the second operational amplifier521to output the reference voltage signal to the inverting input of the second operational amplifier521.

In one embodiment, the filtering circuit522includes 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 R8and the second filtering resistor R9are connected in series between the output of the second operational amplifier521and the non-inverting input of the third operational amplifier523. The first filtering capacitor C1is connected between a common node of the first filtering resistor R8and the second filtering resistor R9and the ground. The second filtering capacitor C2is connected between the non-inverting input of the third operational amplifier523and the ground. A common node of the second filtering capacitor C2and the second filtering resistor R9outputs the second voltage signal V2to the non-inverting input of the third operational amplifier523.

Thus, the lamp status feedback signal varies according to the lamp brightness control signal and the surrounding temperature of the light source100. The fault detecting circuit500dynamically adjusts the variable-benchmark voltage signal inputted to the voltage level comparison circuit530according to the lamp brightness control signal and the surrounding temperature. Then, the voltage level comparison circuit530compares 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 device90determines whether the light source100is 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.