LED control device and control method of LED control device

The present application claims priority under 35 U.S.C. § 365 to PCT/JP2017/003098, filed on Jan. 30, 2017, the disclosure of which are incorporated herein by reference.

The present invention relates to an LED control device and a control method of an LED control device.

LED control devices for controlling the brightness of two (a plurality of) LED devices have been known (for example, see JP 2015-041588 A).

Such conventional LED control devices include, for example, a smoothing circuit that outputs a reference signal obtained by smoothing a PWM light controlling signal, and a control unit that controls a plurality of switching elements for controlling an LED current flowing through each of the LED device based on the reference signal.

The control unit uses a voltage detected by a detection resistor, through which the current flowing through each switching element also flows, to control the LED current flowing through each of the two LED devices to have a value according to the reference signal.

If the two PWM light controlling signals have substantially the same frequency and duty ratio, the operational frequencies of the two switching elements controlled based on the PWM light controlling signals may be synchronized.

The synchronized operational frequencies of the two switching elements affect the detection of the voltage at each switching element. This causes a problem in that the control unit may fail to control each switching element in a desired manner, and thus fail to supply a predefined LED current to the two LED devices.

Problem to be Solved by the Invention

The object of the present invention therefore is to provide an LED control device in which the operational frequencies of two switching elements configured to control two LED devices with PWM light controlling signals suitable for the respective LED devices are prevented from being synchronized so that a desired control operation may be performed on each of the switching elements to supply a predefined LED current to each of the two LED devices.

Solution to Problem

An LED control device according to an embodiment in an aspect of the present invention is an LED control device configured to control LED devices, including:

a first terminal to which a first electrode of a battery is connected, and a first node of a first LED device and a first node of a second LED device are connected;

a second terminal to which a second electrode of the battery is connected;

a first switching element connected between a second node of the first LED device and the second terminal to control a current flowing through the first LED device;

a first detection resistor through which at least a part of a current flowing through the first switching element flows;

a first integration circuit configured to output a first reference signal REF 1 obtained by integrating a first PWM light controlling signal defining a dimming ratio of the first LED device;

a first control unit configured to control an operation of the first switching element by a first control signal based on a relationship between a first reference value obtained from the first reference signal and a first detection voltage value of the first detection resistor;

a second switching element connected between a second node of the second LED device and the second terminal, and configured to control a current flowing through the second LED device;

a second detection resistor through which at least a part of a current flowing through the second switching element flows;

a second integration circuit configured to integrate a second PWM light controlling signal defining a dimming ratio of the second LED device to output a second reference signal REF 2 ; and

a second control unit configured to control an operation of the second switching element by a second control signal based on a relationship between a second reference value obtained from the second reference signal and a second detection voltage value at the second detection resistor,

wherein

the first integration circuit changes the first reference signal to be different from the second reference signal in one cycle of the first PWM light controlling signal, and

the first control unit controls, in the one cycle of the first PWM light controlling signal, the first switching element by the first control signal at a first operational frequency for turning on and off the first switching element, the first operational frequency being different from a second operational frequency for turning on and off the second switching element.

The LED control device further includes:

a first capacitor having one end that is connected to the first terminal, and another end that is connected to the second node of the first LED device;

a first coil having one end that is connected to the other end of the first capacitor;

a first diode having a cathode that is connected to the first terminal, and an anode that is connected to another end of the first coil;

a second capacitor having one end that is connected to the first terminal, and another end that is connected to the second node of the second LED device;

a second coil having one end that is connected to the other end of the second capacitor; and

a second diode having a cathode that is connected to the first terminal, and an anode that is connected to another end of the second coil,

wherein

the first switching element has one end that is connected to the other end of the first coil,

the first detection resistor has one end that is connected to another end of the first switching element, and another end that is connected to the second terminal,

the second switching element has one end that is connected to the other end of the second coil, and

the second detection resistor has one end that is connected to another end of the second switching element, and another end that is connected to the second terminal.

In the LED control device,

when the first PWM light controlling signal and the second PWM light controlling signal are in synchronization with each other,

the first integration circuit integrates the first PWM light controlling signal to output the first reference signal, which is a triangular wave, in the one cycle of the first PWM light controlling signal, and

the second integration circuit integrates the second PWM light controlling signal to output the second reference signal, which is a constant DC voltage, in the one cycle of the second PWM light controlling signal.

In the LED control device,

the first control unit changes the first operational frequency by the first control signal in the one cycle of the first PWM light controlling signal, and

the second control unit controls the second operational frequency to be a constant DC voltage by the second control signal in the one cycle of the second PWM light controlling signal.

In the LED control device,

the first control unit turns on the first switching element and then turns off the first switching element when the first detection voltage value of the first detection resistor reaches the first reference value of the first reference signal, and, after turning off the first switching element, turns on the first switching element when a current flowing through the first diode becomes zero, and

the second control unit turns on the second switching element and then turns off the second switching element when the second detection voltage value of the second detection resistor reaches the second reference value of the second reference signal, and after tuning off the second switching element, turns on the second switching element when a current flowing through the second diode becomes zero.

In the LED control device,

the first integration circuit includes:

a first integration resistor connected between a first signal input terminal, to which the first PWM light controlling signal is supplied, and a first signal output terminal, from which the first reference signal is outputted; and

a first integration capacitor connected between the first signal output terminal and the second terminal, and

the second integration circuit includes:

a second integration resistor connected between a second signal input terminal, to which the second PWM light controlling signal is supplied, and a second signal output terminal, from which the second reference signal is outputted; and

a second integration capacitor connected between the first signal output terminal and the second terminal,

and

the second integration capacitor has a capacitance that is greater than a capacitance of the first integration capacitor.

In the LED control device,

the capacitance of the second integration capacitor is set so that the first reference signal corresponds to a constant DC voltage in the one cycle of the first PWM light controlling signal, and

the capacitance of the first integration capacitor is set so that the first reference signal corresponds to a triangular wave in the one cycle of the first PWM light controlling signal.

In the LED control device,

the first switching element is a first MOS transistor having a drain that is connected to the other end of the first coil, a source that is connected to the one end of the first detection resistor, and a gate to which the first control signal is inputted, and

the second switching element is a second MOS transistor having a drain that is connected to the other end of the second coil, a source that is connected to the one end of the second detection resistor, and a gate to which the second control signal is inputted.

In the LED control device,

the first control unit detects the first detection voltage value based on a potential difference between the one end of the first detection resistor and the second terminal, and

the second control unit detects the second detection voltage value based on a potential difference between the one end of the second detection resistor and the second terminal,

and

the second detection resistor has a resistance value that is equal to a resistance value of the first detection resistor.

In the LED control device,

the first control unit detects a voltage at the one end of the first coil and a voltage at the other end of the first coil, and determines that the current flowing through the first diode is zero when the voltage at the one end of the first coil becomes equal to or less than the voltage at the other end of the first coil, and turns on the first switching element, and

the second control unit detects a voltage at the one end of the second coil and a voltage at the other end of the second coil, and determines that the current flowing through the second diode is zero when the voltage at the one end of the second coil is equal to or less than the voltage at the other end of the second coil, and turns on the second switching element.

The LED control device is mounted on a two-wheel vehicle, and

the first LED device and the second LED device are head lamps, tail lamps, or indicators of the two-wheel vehicle.

In the LED control device,

the second integration resistor has a resistance value that is equal to a resistance value of the first integration resistor.

In the LED control device,

the first LED device emits light with a color that is different from a color of light emitted from the second LED device.

The LED control device further includes

a microcomputer configured to output the first PWM light controlling signal and the second PWM light controlling signal based on a command signal commanding the first LED device and the second LED device to emit light, the command signal being inputted from outside.

In a control method of an LED control device according to an embodiment in an aspect of the present invention, the LED control device including:

a first terminal to which a first electrode of a battery is connected, and a first node of a first LED device and a first node of a second LED device are connected;

a second terminal to which a second electrode of the battery is connected;

a first switching element connected between a second node of the first LED device and the second terminal to control a current flowing through the first LED device;

a first detection resistor through which at least a part of a current flowing through the first switching element flows;

a first integration circuit configured to output a first reference signal REF 1 obtained by integrating a first PWM light controlling signal defining a dimming ratio of the first LED device;

a first control unit configured to control an operation of the first switching element by a first control signal based on a relationship between a first reference value obtained from the first reference signal and a first detection voltage value of the first detection resistor;

a second switching element connected between a second node of the second LED device and the second terminal, and configured to control a current flowing through the second LED device;

a second detection resistor through which at least a part of a current flowing through the second switching element flows;

a second integration circuit configured to integrate a second PWM light controlling signal defining a dimming ratio of the second LED device to output a second reference signal REF 2 ; and

a second control unit configured to control an operation of the second switching element by a second control signal based on a relationship between a second reference value obtained from the second reference signal and a second detection voltage value at the second detection resistor,

the method includes:

changing, by the first integration circuit, the first reference signal to be different from the second reference signal in one cycle of the first PWM light controlling signal; and

controlling the first switching element by the first control unit by means of the first control signal at a first operational frequency for turning on and off the first switching element that is different from a second operational frequency for turning on and off the second switching element in the one cycle of the first PWM light controlling signal.

Effect of the Invention

An LED control device in an aspect of the present invention is an LED control device configured to control LED devices, including:

a first terminal TS to which a first electrode of a battery Vi is connected, and a first node of a first LED device and a first node of a second LED device are connected;

a second terminal to which a second electrode of the battery Vi is connected;

a first switching element connected between a second node of the first LED device and the second terminal to control a current flowing through the first LED device;

a first detection resistor through which at least a part of a current flowing through the first switching element flows;

a first integration circuit configured to output a first reference signal obtained by integrating a first PWM light controlling signal defining a dimming ratio of the first LED device;

a first control unit configured to control an operation of the first switching element by a first control signal based on a relationship between a first reference value obtained from the first reference signal and a first detection voltage value of the first detection resistor;

a second switching element connected between a second node of the second LED device and the second terminal, and configured to control a current flowing through the second LED device;

a second detection resistor through which at least a part of a current flowing through the second switching element flows;

a second integration circuit configured to integrate (smooth) a second PWM light controlling signal defining a dimming ratio of the second LED device to output a second reference signal REF 2 ; and

a second control unit configured to control an operation of the second switching element by a second control signal based on a relationship between a second reference value obtained from the second reference signal and a second detection voltage value at the second detection resistor.

The first integration circuit changes the first reference signal to be different from the second reference signal in one cycle of the first PWM light controlling signal, and the first control unit controls, in the one cycle of the first PWM light controlling signal, the first switching element by the first control signal at a first operational frequency for turning on and off the first switching element, the first operational frequency being different from a second operational frequency for turning on and off the second switching element.

As a result, the first reference signal changes to be different from the second reference signal, and the first switching element is controlled by the first control signal at the first operational frequency for turning on and off the first switching element, the first switching element being different from the second operational frequency for turning on and off the second switching element, in the one cycle of the first PWM light controlling signal.

Thus, in the LED control device according to the present invention, the operational frequencies of the two switching elements that control the two LED devices by corresponding PWM light controlling signals are prevented from synchronizing, so that a desired control operation may be performed on the respective switching elements to supply predefined LED currents to the two LED devices.

FIG. 1 is a diagram illustrating an example of a configuration of an LED control device 100 according to a first embodiment in an aspect of the present invention.

FIG. 2 is a diagram illustrating an example of operation waveforms of the LED control device 100 according to the first embodiment shown in FIG. 1 .

FIG. 3 is a diagram illustrating an example of conventional operation waveforms.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment]

FIG. 1 is a diagram illustrating an example of a configuration of an LED control device 100 according to a first embodiment in an aspect of the present invention.

As shown in FIG. 1 , the LED control device 100 controls a first LED device X 1 and a second LED device X 2 in response to a command signal S by a voltage supplied from a battery Vi.

The first LED device X 1 includes, for example, one LED element or a plurality of LED elements connected in series as shown in FIG. 1 . Similarly, the second LED device X 2 includes one LED element or a plurality of LED elements connected in series.

The color of light emitted from the first LED device X 1 (the wavelength of the output light) is set to be different from the color of light emitted from the second LED device (the wavelength of the output light). The dimming ratio of the first LED device X 1 and the dimming ratio of the second LED device X 2 are controlled independently of each other in this manner. This results in a synthesized light having a predefined tone.

The first and second LED devices X 1 and X 2 are used in, for example, lighting devices of consumer electronics. The LED control device may also be used in two-wheel vehicles. In this case, the first and second LED devices X 1 and X 2 are used in any of the head lamps, the tail lamps, and indicators of the two-wheel vehicles.

As shown in FIG. 1 for example, the LED control device 100 includes a microcomputer M, a first terminal (power supply terminal) TS, a second terminal (ground terminal) TG, a first switching element SW 1 , a first detection resistor R 1 , a first capacitor C 1 , a first coil L 1 , a first diode D 1 , a first detection node A 1 , a first integration circuit Z 1 , a first control unit CON 1 , a second switching element SW 2 , a second detection resistor R 2 , a second capacitor C 2 , a second coil L 2 , a second diode D 2 , a second detection node A 2 , a second integration circuit Z 2 , and a second control unit CON 2 . The LED control device 100 may also include the battery Vi and the first and second LED devices X 1 and X 2 .

The microcomputer M is configured to output a first PWM light controlling signal PWM 1 and a second PWM light controlling signal PWM 2 in response to the command signal S, which is inputted from outside to command the first and second LED devices X 1 and X 2 to emit light. The command signal S is inputted manually by a user (not shown), for example, to the microcomputer M.

The first terminal TS is connected to a first electrode (positive electrode) of the battery Vi. The first terminal TS is also connected to a first node (anode) X 1 a of the first LED device X 1 and a first node (anode) X 2 a of the second LED device X 2 .

The second terminal (ground terminal) TG is connected to a second electrode (negative electrode) of the battery Vi and grounded.

The first capacitor C 1 has one end that is connected to the first terminal TS, and the other terminal that is connected to a second node (cathode) X 1 k of the first LED device X 1 .

The first coil L 1 has one end L 1 a that is connected to the other end of the first capacitor C 1 .

The first diode D 1 has a cathode that is connected to the first terminal TS, and an anode that is connected to the other end L 1 b of the first coil L 1 .

The first switching element SW 1 is connected between the second node (cathode) X 1 k of the first LED device X 1 and the second terminal TG.

As shown in FIG. 1 , for example, the first switching element SW 1 is a first MOS transistor having one end (drain) that is connected to the other end of the first coil L 1 , another end (source) that is connected to one end (first detection node A 1 ) of the first detection resistor R 1 , and a gate to which a first control signal Gate 1 is inputted.

The first switching element SW 1 is configured to control a current flowing through the first LED device X 1 in response to the first control signal Gate 1 .

The first detection resistor R 1 is connected between the first detection node A 1 and the second terminal TG. The first detection resistor R 1 has the one end that is connected to the other end (first detection node A 1 ) of the first switching element SW 1 , and the other end that is connected to the second terminal TG, as shown in FIG. 1 .

At least part of the current flowing through the first switching element SW 1 (in the example of FIG. 1 , all the current flowing through the first switching element SW 1 ) flows through the first detection resistor R 1 .

The second capacitor C 2 has one end that is connected to the first terminal TS, and the other end that is connected to the second node (cathode) X 2 k of the second LED device X 2 .

The second coil L 2 has one end L 2 a that is connected to the other end of the second capacitor C 2 .

The second diode D 2 has a cathode that is connected to the first terminal TS, and an anode that is connected to the other end L 2 b of the second coil L 2 .

The second switching element SW 2 is connected between the second node (cathode) X 2 k of the second LED device X 2 and the second terminal TG.

As shown in FIG. 1 , for example, the second switching element SW 2 is a second MOS transistor having one end (drain) that is connected to the other end of the second coil L 2 , another end (source) that is connected to one end (second detection node A 2 ) of the second detection resistor R 2 , and a gate to which a second control signal Gate 2 is inputted.

The second switching element SW 2 is configured to control a current flowing through the second LED device X 2 in response to the second control signal Gate 2 .

The second detection resistor R 2 is connected between the second detection node A 2 and the second terminal TG. As shown in FIG. 1 , for example, the second detection resistor R 2 has the one end that is connected to the other end (second detection node A 2 ) of the second switching element SW 2 , and the other end that is connected to the second terminal TG.

At least part of the current flowing through the second switching element SW 2 (in the example of FIG. 1 , all the current flowing through the second switching element SW 2 ) flows through the second detection resistor R 2 .

The resistance value of the second detection resistor R 2 is set to be equal to the resistance value of the first detection resistor R 1 .

The first integration circuit Z 1 is configured to output a first reference signal REF 1 obtained by integrating the first PWM light controlling signal PWM 1 defining the dimming ratio of the first LED device X 1 .

The first integration circuit Z 1 is configured to change the first reference signal REF 1 to be different from a second reference signal REF 2 outputted by the second integration circuit Z 2 in one cycle of the first PWM light controlling signal PWM 1 .

The first integration circuit Z 1 , for example, integrates the first PWM light controlling signal PWM 1 to output a first reference signal REF 1 which is a triangular wave corresponding to one cycle of the first PWM light controlling signal PWM 1 .

For example, the first integration circuit Z 1 includes a first integration resistor RZ 1 and a first integration capacitor CZ 1 as shown in FIG. 1 .

The first integration resistor RZ 1 is connected between a first signal input terminal TI 1 to which the first PWM light controlling signal PWM 1 is supplied and a first signal output terminal TO 1 from which the first reference signal REF 1 is outputted.

The first integration capacitor CZ 1 is connected between the first signal output terminal TO 1 and the second terminal TG.

With such a configuration, the first integration circuit Z 1 integrates the first PWM light controlling signal PWM 1 inputted to the first signal input terminal TI 1 to output the first reference signal REF 1 from the first signal output terminal TO 1 .

The second integration circuit Z 2 is configured to output a second reference signal REF 2 obtained by integrating (smoothing) the second PWM light controlling signal PWM 2 defining the dimming ratio of the second LED device X 2 .

The second integration circuit Z 2 is configured to integrate the second PWM light controlling signal PWM 2 to output the second reference signal REF 2 which is a constant DC voltage in one cycle of the second PWM light controlling signal PWM 2 .

The second integration circuit Z 2 includes, for example, a second integration resistor RZ 2 and a second integration capacitor CZ 2 , as shown in FIG. 1 .

The second integration resistor RZ 2 is connected between a second signal input terminal TI 2 to which the second PWM light controlling signal PWM 2 is supplied, and a second signal output terminal TO 2 from which the second reference signal REF 2 is outputted.

The second integration capacitor CZ 2 is connected between the second signal output terminal TO 2 and the second terminal TG.

The second integration circuit Z 2 is configured to integrate the second PWM light controlling signal PWM 2 inputted to the second signal input terminal TI 2 to output the second reference signal REF 2 from the second signal output terminal TO 2 .

The capacitance of the second integration capacitor CZ 2 is set to be greater than the capacitance of the first integration capacitor CZ 1 . In other words, the capacitance of the first integration capacitor CZ 1 is set to be lower than the capacitance of the second integration capacitor CZ 2 .

The resistance value of the second integration resistor RZ 2 is set to be equal to the resistance value of the first integration resistor RZ 1 .

A signal inputted to the second integration circuit Z 2 is smoothed more than a signal inputted to the first integration circuit Z 1 before being outputted.

Thus, the capacitance of the second integration capacitor CZ 2 is set so that the second reference signal REF 2 is a constant DC voltage during the one cycle of the second PWM light controlling signal PWM 2 . Furthermore, the capacitance of the first integration capacitor CZ 1 is set so that the first reference signal REF 1 has a triangular wave in one cycle of the first PWM light controlling signal PWM 1 .

Thus, as described above, the first integration circuit Z 1 changes the first reference signal REF 1 to be different from the second reference signal REF 2 in the one cycle of the first PWM light controlling signal PWM 1 .

The first control unit CON 1 is configured to control the operation of the first switching element SW 1 by means of the first control signal Gate 1 based on the relationship between a first reference value obtained on the basis of the first reference signal REF 1 and a first detection voltage value across the first detection resistor R 1 .

The first control unit CON 1 is configured to detect the first detection voltage value based on a potential difference between the one end (first detection node A 1 ) of the first detection resistor R 1 and the second terminal TG.

The first control unit CON 1 further is configured to detect a voltage at the one end L 1 a of the first coil L 1 and a voltage at the other end L 1 b of the first coil L 1 .

For example, the first control unit CON 1 is configured to turn on the first switching element SW 1 first, and to turn off the first switching element SW 1 when the first detection voltage value of the first detection resistor R 1 reaches the first reference value of the first reference signal REF 1 .

After turning off the first switching element SW 1 , the first control unit CON 1 turns on the first switching element SW 1 when the current flowing through the first diode D 1 becomes zero.

In more detail, after turning off the first switching element SW 1 , the first control unit CON 1 determines that the current flowing through the first diode D 1 is zero when the voltage at the one end L 1 a of the first coil L 1 becomes lower than the voltage at the other end L 1 b of the first coil L 1 , and turns on the first switching element SW 1 .

In particular, the first control unit CON 1 changes a first operational frequency of the first switching element SW 1 by the first control signal Gate 1 in the one cycle of the first PWM light controlling signal PWM 1 .

The first control unit CON 1 thus controls the first switching element SW 1 by the first control signal at the first operational frequency for turning on or off the first switching element SW 1 , the first operational frequency being different from a second operational frequency for turning on or off the second switching element SW 2 , in the one cycle of the first PWM light controlling signal PWM 1 .

The second control unit CON 2 is configured to control the operation of the second switching element SW 2 by the second control signal Gate 2 based on the relationship between a second reference value that is based on the second reference signal REF 2 and a second detection voltage value across the second detection resistor R 2 .

The second control unit CON 2 detects the second detection voltage value based on a potential difference between the one end (second detection node A 2 ) of the second detection resistor R 2 and the second terminal TG.

The second control unit CON 2 also detects the voltage at the one end L 2 a of the second coil L 2 and the voltage at the other end L 2 b of the second coil L 2 .

For example, the second control unit CON 2 turns on the second switching element SW 2 first, and turns off the second switching element SW 2 when the second detection voltage value at the second detection resistor R 2 reaches a second reference value of the second reference signal REF 2 .

After turning off the second switching element SW 2 , the second control unit CON 2 turns on the second switching element SW 2 when the current flowing through the second diode D 2 becomes zero.

In more detail, after turning off the second switching element SW 2 , the second control unit CON 2 determines that the current flowing through the second diode D 2 is zero when the voltage at the one end L 2 a of the second coil L 2 becomes lower than the voltage at the other end L 2 b of the second coil L 2 , and turns on the second switching element SW 2 .

In particular, the second control unit CON 2 controls the second operational frequency of the second switching element SW 2 to be at a constant value by the second control signal Gate 2 in the one cycle of the second PWM light controlling signal PWM 2 .

As a result, as described above, the first control unit CON 1 controls the first switching element SW 1 by the first control signal at the first operational frequency that is different from the constant second operational frequency in the one cycle of the first PWM light controlling signal PWM 1 .

As described above, the LED control device 100 controls the brightness of the first and second LED devices L 1 and L 2 in response to the first and second PWM light controlling signals PWM 1 and PWM 2 outputted from the microcomputer M in accordance with, for example, the operation of the user (the input of the command signal S).

An example of the operation of the LED control device 100 having the above configuration will then be described below. FIG. 2 is a diagram illustrating an example of operation waveforms of the LED control device 100 according to the first embodiment shown in FIG. 1 . FIG. 3 is a diagram illustrating an example of conventional operation waveforms. In the example of FIG. 3 , the LED control device 100 shown in FIG. 1 is operated according to the conventional operation waveforms. In the examples of FIGS. 2 and 3 , the first PWM light controlling signal PWM 1 and the second PWM light controlling signal PWM 2 are in synchronization with each other (with substantially the same frequency and duty ratio).

For example, in the conventional operation, if the two PWM light controlling signals PWM 1 and PWM 2 are in synchronization with each other (with substantially the same frequency and duty ratio), the operational frequencies (the frequencies of the first and second control signals Gate 1 and Gate 2 ) of the two switching elements SW 1 and SW 2 controlled based on these PWM light controlling signals are caused to be in synchronization with each other as shown in FIG. 3 .

The operations at the synchronized operational frequencies of the two switching elements affect the detection of the current flowing through each of the switching elements. As a result, the first and second control units CON 1 and CON 2 may fail to control the respective switching elements to operate in a desired manner, and fail to supply the predefined LED currents to the two LED devices.

In contrast, the LED control device 100 according to the first embodiment operates so that, when the first PWM light controlling signal PWM 1 and the second PWM light controlling signal PWM 2 are in synchronization with each other (with substantially the same frequency and duty ratio), the second integration circuit Z 2 integrates the second PWM light controlling signal PWM 2 to output the second reference signal REF 2 , which is a constant DC voltage in the one cycle of the second PWM light controlling signal PWM 2 , as shown in FIG. 2 .

At this time, the first integration circuit Z 1 changes the first reference signal REF 1 to be different from the second reference signal REF 2 outputted from the second integration circuit Z 2 in the one cycle of the first PWM light controlling signal PWM 1 .

In particular, in the example shown in FIG. 2 , the first integration circuit Z 1 integrates the first PWM light controlling signal PWM 1 to output the first reference signal REF 1 , which is a triangular wave in the one cycle of the first PWM light controlling signal PWM 1 . In the example of FIG. 2 , while the first PWM light controlling signal PWM 1 is in a “High” level, the first reference signal REF 1 is increased, and while the first PWM light controlling signal PWM 1 is in a “Low” level, the first reference signal REF 1 is decreased.

The second control unit CON 2 controls the operation of the second switching element SW 2 by means of the second control signal Gate 2 based on the relationship between the second reference value (⅕ of the second reference signal REF 2 ) obtained from the second reference signal REF 2 , which is a constant DC voltage, and the second detection voltage value (the voltage at the second detection node A 2 ) of the second detection resistor R 2 .

For example, the second control unit CON 2 turns on the second switching element SW 2 (by switching the second control signal Gate 2 to the “High” level) first, and turns off the second switching element SW 2 (by switching the second control signal Gate 2 to the “Low” level) when the second detection voltage value of the second detection resistor R 2 reaches the second reference value of the second reference signal REF 2 , which is ⅕*REF 2 .

After turning off the second switching element SW 2 (by switching the second control signal Gate 2 to the “Low” level), the second control unit CON 2 turns on the second switching element SW 2 when the current flowing through the second diode D 2 becomes zero.

The second control unit CON 2 thus controls the second operational frequency of the second switching element SW 2 to be constant by the second control signal Gate 2 in the one cycle of the second PWM light controlling signal PWM 2 .

On the other hand, the first control unit CON 1 controls the operation of the first switching element SW 1 by the first control signal Gate 1 based on the relationship between the first reference value (⅕ of the first reference signal REF 1 ) obtained from the first reference signal REF 1 that varies in the aforementioned manner and the first detection voltage value (the voltage at the first detection node A 1 ) of the first detection resistor R 1 .

For example, the first control unit CON 1 turns on the first switching element SW 1 (by switching the first control signal Gate 1 to the “High” level) first, and turns off the first switching element SW 1 (by switching the first control signal Gate 1 to the “Low” level) when the first detection voltage value of the first detection resistor R 1 reaches the first reference value of the first reference signal REF 1 , which is ⅕*REF 1 .

After turning off the first switching element SW 1 (by switching the first control signal Gate 1 to the “Low” level), the first control unit CON 1 turns on the first switching element SW 1 (by switching the first control signal Gate 1 to the “High” level) when the current flowing through the first diode D 1 becomes zero.

Thus, the first control unit CON 1 changes the first operational frequency of the first switching element SW 1 by the first control signal Gate 1 in the one cycle of the first PWM light controlling signal PWM 1 .

The first control unit CON 1 controls the first switching element SW 1 by the first control signal Gate 1 at the first operational frequency for turning on and off the first switching element SW 1 , which is different from the second operational frequency for turning on and off the second switching element SW 2 , in the one cycle of the first PWM light controlling signal PWM 1 .

As described above, the first reference signal REF 1 changes in a manner to be different from the second reference signal REF 2 (for example, if one is a triangular wave, the other is a constant DC voltage). As a result, the first switching element is controlled by the first control signal at the first operational frequency for turning on and off the first switching element, which is different from the second operational frequency for turning on and off the second switching element, in the one cycle of the first PWM light controlling signal PWM 1 .

As shown in FIG. 2 , the first operational frequency of the first switching element SW 1 changes in accordance with the change in the first reference signal REF 1 . Thus, the period of time during which the first operational frequency is in synchronization with the second operational frequency of the second switching element SW 2 does not continue for a long time.

The LED control device 100 therefore is capable of preventing the synchronization of the operational frequencies of the first and second switching elements SW 1 and SW 2 that control the first and second LED devices X 1 and X 2 based on the first and second PWM light controlling signals PWM 1 and PWM 2 each corresponding to one of the two LED devices X 1 and X 2 to perform a desired control operation on each of the switching elements. As a result, a predefined LED current may be supplied to each of the first and second LED devices X 1 and X 2 .

If the first and second reference signals REF 1 , REF 2 are different from each other, the operational frequencies of the first and second switching elements SW 1 and SW 2 do not synchronize. Therefore, the aforementioned problem is not caused.

Thus, in the LED control device 100 according to the first embodiment, each the first and second LED devices X 1 and X 2 is surely caused to emit light with a predefined dimming ratio in response to the command signal S inputted by the user.

As described above, an LED control device in an aspect of the present invention is an LED control device configured to control LED devices, including:

a first terminal (power supply terminal) TS to which a first electrode (positive electrode) of a battery Vi is connected, and a first node (anode) of a first LED device X 1 and a first node (anode) of a second LED device X 2 are connected;

a second terminal (ground terminal) to which a second electrode (negative electrode) of the battery Vi is connected;

a first switching element SW 1 connected between a second node (cathode) of the first LED device and the second terminal to control a current flowing through the first LED device;

a first detection resistor R 1 through which at least a part of a current flowing through the first switching element SW 1 flows;

a first integration circuit Z 1 configured to output a first reference signal REF 1 obtained by integrating a first PWM light controlling signal PWM 1 defining a dimming ratio of the first LED device;

a first control unit CON 1 configured to control an operation of the first switching element by a first control signal Gate 1 based on a relationship between a first reference value obtained from the first reference signal REF 1 and a first detection voltage value of the first detection resistor R 1 ;

a second switching element SW 2 connected between a second node (cathode) of the second LED device and the second terminal, and configured to control a current flowing through the second LED device;

a second detection resistor R 2 through which at least a part of a current flowing through the second switching element SW 2 flows;

a second integration circuit Z 2 configured to integrate (smooth) a second PWM light controlling signal PWM 2 defining a dimming ratio of the second LED device to output a second reference signal REF 2 ; and

a second control unit CON 2 configured to control an operation of the second switching element by a second control signal Gate 2 based on a relationship between a second reference value obtained from the second reference signal REF 2 and a second detection voltage value at the second detection resistor R 2 .

The first integration circuit changes the first reference signal REF 1 to be different from the second reference signal REF 2 in one cycle of the first PWM light controlling signal PWM 1 , and the first control unit controls, in the one cycle of the first PWM light controlling signal PWM 1 , the first switching element by the first control signal at a first operational frequency for turning on and off the first switching element, the first operational frequency being different from a second operational frequency for turning on and off the second switching element.

As a result, the first reference signal REF 1 changes to be different from the second reference signal REF 2 (for example, if one is a triangular wave, the other is a constant DC voltage), and the first switching element is controlled by the first control signal at the first operational frequency for turning on and off the first switching element, the first switching element being different from the second operational frequency for turning on and off the second switching element, in the one cycle of the first PWM light controlling signal PWM 1 .

Thus, in the LED control device according to the present invention, the operational frequencies of the two switching elements that control the two LED devices by corresponding PWM light controlling signals are prevented from synchronizing, so that a desired control operation may be performed on the respective switching elements to supply predefined LED currents to the two LED devices.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The embodiments may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The embodiments and their modifications are included in the scope and the subject matter of the invention, and at the same time included in the scope of the claimed inventions and their equivalents.

Although the MOS transistors are selected as the switching elements in the embodiment, bipolar transistors or other switching elements may also be selected.

100 : LED control device

M: microcomputer

TS: first terminal (power supply terminal)

TG: second terminal (ground terminal)

SW 1 : first switching element

C 1 : first capacitor

L 1 : first coil

D 1 : first diode

R 1 : first detection resistor

A 1 : first detection node

Z 1 : first integration circuit

CON 1 : first control unit

SW 2 : second switching element

C 2 : second capacitor

L 2 : second coil

D 2 : second diode

R 2 : second detection resistor

A 2 : second detection node

Z 2 : second integration circuit

CON 2 : second control unit

Vi: battery

X 1 : first LED device

X 2 : second LED device