KR20090076330A - Light emitting devices and power supplies with time division multiple output DC-DC converters - Google Patents

Abstract

The present invention relates to a light emitting device and a power supply, and the technical problem to be solved is to drive a light emitting diode or a resistor in a time division multiple output method and a constant current driving method, and the output voltage of the DC-DC converter is a forward voltage of the light emitting diode To be determined by the sum or the sum of the voltages applied to the resistors.

To this end, for example, the present invention provides a DC-DC converter for boosting and outputting a DC voltage, a plurality of light emitting string parts connected in parallel to the DC-DC converter, and simultaneously connected to each light emitting string part, and controlling the DC-DC converter. And a plurality of switching elements for determining whether the light emitting string portion is turned on and off by the LED, and the DC-DC converter controls the plurality of switching elements by time division, so that the plurality of light emitting string portions emit light by time division. A light emitting device having a DC-DC converter is disclosed.

Description

LIGHT EMITTING DEVICE AND POWER SUPPLY HAVING TIME DIVISION MULTIPLE OUTPUT DC-DC CONVERTER}

The present invention relates to a light emitting device and a power supply having a time division multiple output DC-DC converter.

1, there is shown a circuit diagram of a light emitting device having a DC-DC converter according to the prior art.

As illustrated, a conventional light emitting device 100 '(for example, an LED backlight unit or an LED light) includes a DC-DC converter 110' for boosting and outputting an input voltage Vin, and the DC-DC converter. A plurality of light emitting diodes (LEDs) that receive an output voltage Vout of 110 ′ and emit light at a predetermined luminance, and feedback voltage information by the light emitting diodes (LED) is transmitted to the DC-DC converter 110 ′. It includes a resistor (R). Here, the inductor L for boosting the input voltage Vin and the zener diode ZD for preventing the inflow of the reverse voltage may be further connected to the DC-DC converter 110 ′.

The light emitting device of this type requires a high output voltage Vout (several tens of volts V) to light all of the plurality of light emitting diodes, which results in an expensive DC-DC converter. In addition, for local dimming of the backlight unit, the light emitting diode should be installed in a string unit, but a plurality of DC-DC converters are required to drive each string unit. That is, the need for a plurality of DC-DC converters has the disadvantage that the light emitting device is not only expensive but the wiring is complicated and the weight and volume are increased.

Meanwhile, in addition to the above-described method, a method of providing a light emitting diode in a string unit and connecting a switch to each string to control the PWM is also being studied. There is a disadvantage in that the voltage distribution applied to both ends of is also large. That is, since the remaining voltage is applied to both ends of the switching element at the output voltage from the DC-DC converter, and the remaining voltage is applied to both ends of the switching element, there is a problem that the efficiency is lowered and a considerable heat is generated in the switching element.

The present invention is to overcome the above-mentioned conventional problems, an object of the present invention is to drive a light emitting diode or a resistor in a time division multiple output method and a constant current drive method, and the output voltage of the DC-DC converter is the forward direction of the light emitting diode A light emitting device and a power supply having a time division multiple output DC-DC converter capable of automatically controlling the light emission state and suppressing heat generation such as a switch by being automatically determined by the sum of voltages or the sum of voltages applied to the resistance. To provide a device.

Another object of the present invention is to provide a light emitting device and a power supply having a time division multiple output DC-DC converter capable of local dimming by changing the brightness of the light emitting diode by PWM controlling the light emitting diode.

Another object of the present invention is to reduce costs by efficiently driving a plurality of string light emitting diodes or resistors using only one DC-DC converter.

In order to achieve the above object, a light emitting device having a time division multiple output DC-DC converter according to the present invention includes a DC-DC converter for boosting and outputting a DC voltage; A plurality of light emitting string parts connected in parallel to the DC-DC converter; And a plurality of switching elements connected to each of the light emitting string parts and determining whether the light emitting string parts are turned on and off by the control of the DC-DC converter. By controlling by time division, the said plurality of light emission string parts emit light by time division.

The DC-DC converter may turn on the plurality of switching elements at a constant frequency.

The DC-DC converter may turn on the plurality of switching elements sequentially.

The DC-DC converter may control the brightness of the light emitting string part by controlling the pulse width modulation (PWM) of the plurality of switching elements.

The DC-DC converter may turn on the plurality of switching elements by the same time, respectively.

The DC-DC converter may turn on the plurality of switching elements by different times.

The light emitting string part may be formed by connecting a plurality of light emitting diodes in series.

The switching element may be a field effect transistor whose gate voltage is controlled by the DC-DC converter.

A sensing resistor is connected to the light emitting string part to sense a current applied to the light emitting string part, and a current is applied to the node between the light emitting string part and the sensing resistor to convert the current applied to the light emitting string part into a voltage. The sensing wiring can be connected to feed back to the DC-DC converter.

The DC-DC converter may receive a voltage from the light emitting string part to reduce the output current when the voltage is higher than a predetermined reference voltage, and increase the output current when the voltage is smaller than the predetermined reference voltage.

The DC-DC converter may automatically set an output voltage by a sum of forward voltages of respective light emitting diodes forming the light emitting string part.

The current flowing through each of the light emitting string parts is always the same regardless of the output voltage of the DC-DC converter determined by each of the light emitting string parts.

The DC-DC converter may include a pulse width modulation (PWM) controller; A feedback voltage sensing unit receiving the voltage from the light emitting string unit and comparing the fed back voltage with a predetermined reference voltage and outputting the feedback voltage to the PWM controller; A gate driver which decreases an output current when the voltage fed back by the feedback voltage detector is higher than a predetermined reference voltage under control of the PWM controller, and increases an output current when the feedback voltage is smaller than a predetermined reference voltage; And a switch driver for controlling turn-on of the switching element in a predetermined order by the control of the PWM controller.

In addition, in order to achieve the above object, a power supply apparatus according to the present invention includes a DC-DC converter for boosting and outputting a DC voltage; At least one resistor string unit connected to the DC-DC converter; And a switching element connected to the resistance string unit and determining a current flow of the resistance string unit under control of the DC-DC converter, wherein the DC-DC converter controls the switching element by time division. The resistor string may be divided in time to allow a current to flow.

As described above, the light emitting device and the power supply apparatus having the time division multiple output DC-DC converter according to the present invention drive the light emitting diode or the resistor in the time division multiple output scheme and the constant current driving scheme, and also output the DC-DC converter. By automatically determining the voltage by the sum of the forward voltages of the light emitting diodes or the sum of the voltages applied to the resistors, not only the light emission state or the power supply state can be efficiently controlled, but also heat generation such as a switch can be suppressed.

In addition, the present invention enables local dimming by changing the brightness of a light emitting diode by PWM controlling the light emitting diode.

In addition, the present invention reduces costs by efficiently driving a plurality of string light emitting diodes or resistors using only one DC-DC converter.

In addition, the present invention can be sufficiently used as a general power supply device when using a resistor instead of a light emitting diode as described above.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that those skilled in the art may easily implement the present invention.

2 is a circuit diagram showing a light emitting device having a time division multiple output DC-DC converter according to the present invention.

As illustrated, the light emitting device 100 having the time division multiple output DC-DC converter according to the present invention includes a DC-DC converter 110, a plurality of light emitting string parts LS, and a plurality of switching elements S1,. S2, ..., Sn and sensing resistor Rs. Here, the DC-DC converter 110 may naturally be connected with an inductor L for voltage boosting and a zener diode ZD for preventing inflow of reverse current.

The DC-DC converter 110 includes an oscillator 111, a pulse width modulation (PWM) control unit 112, a feedback voltage detector 113, a reference voltage source 114, a gate driver 115, and a switch driver 116. And an overvoltage detector 117.

The oscillator 111 receives an input voltage Vin to provide a predetermined clock signal to the PWM controller 112 and the like.

The PWM controller 112 receives an external control signal CTL, a clock signal of the oscillator 111, a signal of the feedback voltage detector 113, and a signal of the overvoltage detector 117 to receive the gate driver 115. And the switch driver 116 are appropriately controlled.

The feedback voltage detector 113 has one end connected to the reference voltage source 114 to receive a reference voltage, and the other end node between the switching elements S1, S2,..., Sn and the sensing resistor Rs. The feedback voltage Vfb transmitted from the sensing wire SL connected to N is applied to output a predetermined signal to the PWM controller 112. In practice, the feedback voltage detector 113 may be a comparator having two input terminals and one output terminal. Of course, the reference voltage source 114 is connected to one of the two input terminals to apply the reference voltage Vref, and the sensing wire SL is connected to the other input terminal to receive the feedback voltage Vfb.

By such a configuration, when the feedback voltage is higher than the predetermined reference voltage, the PWM controller 112 controls the gate driver 115, that is, the switch S connected thereto, so that the output current of the DC-DC converter 110 is reduced. When the feedback voltage is smaller than the predetermined reference voltage, the gate driver 115, that is, the switch S connected thereto is controlled to increase the output current of the DC-DC converter 110. Therefore, a constant current determined by Vref / Rs flows through the light emitting string part LS. That is, the light emitting string part LS is driven with a constant current.

The gate driver 115 operates under the control of the PWM controller 112 and turns on or off the switch S connected thereto to output the energy stored in the inductor L at a predetermined voltage and a predetermined current. In practice, the gate driver 115 has a plurality of switches connected to and turned on and off, but the configuration and principle of transferring energy by turning on and off the inductor L and the switch S are well known to those skilled in the art. Details are omitted here.

The switch driver 116 also operates under the control of the PWM controller 112, and each switching element S1, S2,..., Sn is electrically connected to the switch driver 116. Therefore, the turn-on and turn-off of the switching elements S1, S2, ..., Sn are determined by the output signal of the switch driver 116. Here, although one wire is connected between the switch driver 116 and the switching elements S1, S2, ..., Sn, in practice, each of the switching elements S1, S2, ..., Sn Is connected to the switch driver 116 through an independent wiring.

The overvoltage detecting unit 117 notifies the PWM control unit 112 when the output voltage Vout of the DC-DC converter 110 exceeds a predetermined reference value, so that the overall voltage of the DC-DC converter 110 is increased. It serves to stop the operation.

The plurality of light emitting string parts LS are connected in parallel to receive an output voltage Vout from the DC-DC converter 110. In fact, as will be described below, the output voltage Vout of the DC-DC converter 110 is purely determined by the light emitting string part LS. The light emitting string part LS may include 10 to 30 light emitting diodes (LEDs) connected in series. However, the number of the series-connected light emitting diodes (LEDs) is not limited thereto.

The plurality of switching elements S1, S2,..., Sn are connected to ends of the light emitting string parts LS. The switching elements S1, S2,..., Sn may be any one selected from a common field effect transistor, a bipolar transistor, or an equivalent thereof, but are not limited thereto. Of course, the switching elements S1, S2, ..., Sn, for example, the gate electrode of the field effect transistor is electrically connected to the switch driver 116 of the DC-DC converter 110 through a wiring. .

The sensing resistor Rs is commonly connected between the ends of the switching elements S1, S2,..., And Sn and the ground terminal. A sensing line SL is connected between the switching elements S1, S2,..., Sn and the sensing resistor Rs, and the sensing line SL is fed back from the DC-DC converter 110. It is connected to the voltage sensing unit 113. By this configuration, the current I _LED flowing through the light emitting string part LS flows in the sensing resistor Rs. The current I _LED is converted into a voltage by the sensing resistor Rs and then transferred to the feedback voltage detector 113. That is, the current I _LED flowing in the light emitting string part LS is converted into the voltage Vfb and then transmitted to the feedback voltage detecting part 113.

As described above, the feedback voltage detecting unit 113 may reduce the output current I _LED through the DC-DC converter 110 when the feedback voltage Vfb is larger than the predetermined reference voltage Vref. The signal is transmitted to the PWM controller 112. In addition, the feedback voltage detector 113 may generate a signal for increasing the output current I _LED of the DC-DC converter 110 when the feedback voltage Vfb is smaller than the predetermined reference voltage Vref. The PWM controller 112 transmits the same.

Then, as described above, the PWM controller 112 controls the gate driver 115 and the switch S connected thereto so that the output current I _LED applied to the light emitting string part LS is reduced or increased. By controlling, the constant current I _LED always flows through each light emitting string part LS. That is, each of the light emitting string parts LS is driven with a constant current. Therefore, each light emitting string part LS always produces the same brightness.

On the other hand, the output voltage (Vout) of the DC-DC converter 110 is automatically set according to the characteristics of each light emitting string portion (LS). This is one of the features of the present invention. In general, it is known that the output voltage Vout of the DC-DC converter 110 should be mostly fixed. However, in the present invention, the output voltage Vout of the DC-DC converter 110 is automatically set according to the characteristics of each light emitting string part LS. As described above, each of the light emitting string parts LS is formed of a plurality of series-connected light emitting diodes (LEDs), and the light emitting diodes (LEDs) have a dispersion or error in the forward voltage Vf due to problems in the manufacturing process. In practice, the forward voltage Vf of the light emitting diode LED is approximately 3.5 ± 0.5V. Therefore, a total of 30 V is applied to the light emitting string part LS when all of the light emitting diodes LED constituting the light emitting string part LS are assumed to have a forward voltage Vf of 3 V and the number of series connected in series is ten. When the light emitting diodes LED forming the other light emitting string part LS are all assumed to have a forward voltage Vf of 4V and a number of 10 in series, a total of 40V is applied to the light emitting string part LS. . In other words, the output voltage Vout of the DC-DC converter 110 is automatically adjusted according to the forward voltage distribution of the LED. Further, as described above, no extra voltage is applied to the switching elements S1, S2, ..., Sn. Therefore, the heat generation problem of the switching elements S1, S2, ..., Sn can be solved.

In addition, as described above, even if the output voltage Vout of the DC-DC converter 110 according to the present invention is automatically adjusted for each light emitting string portion LS, the output current applied to the light emitting string portion LS ( Since the I _LED ) is constantly maintained at a constant current by the sensing resistor Rs and feedback control using the same, the luminance is always constant.

3 is a timing diagram of a switch with respect to the circuit diagram of FIG.

As illustrated, the PWM controller 112 of the DC-DC converter 110 controls the switch driver 116 to sequentially turn on the plurality of switching elements S1, S2,..., Sn connected thereto. Therefore, the plurality of light emitting string parts LS respectively connected to the switching elements S1, S2,..., Sn also emit light while being sequentially turned on. For example, when the switching element S1 is turned on, the switching elements S2 and Sn maintain a turn-off state. Therefore, only the light emitting string part LS connected to the switching element S1 emits light. In addition, when the switching element S2 is turned on, the switching elements S1 and Sn maintain the turn-off state. Therefore, only the light emission string part LS to which the switching element S2 is connected emits light. In this manner, all the switching elements S1, S2, ..., Sn are sequentially turned on, and the corresponding light emitting string part LS also emits light sequentially.

Here, the PWM controller 112 controls the luminance of all the light emitting string parts LS to be the same in time by allocating the same turn-on time of the plurality of switching elements S1, S2,..., And Sn. can do. In addition, the PWM controller 112 may change the luminance of the specific light emitting string part LS in time by allocating different turn-on times of the plurality of switching elements S1, S2,..., Sn. .

More specifically, the PWM controller 112 of the DC-DC converter 110 sets the switching elements S1, S2,..., Sn to different values using the switch driver 116. Width Modulation) allows the luminance of the light emitting string part LS to be changed. Accordingly, the present invention is easy to implement a local dimming technique applied to the backlight unit of the liquid crystal display.

On the other hand, in the present invention by turning on the switching elements (S1, S2, ..., Sn) with a cycle having a frequency of approximately 100Hz ~ 10kHz, even if the light emitting string portion LS emits light one by one, it is recognized by human eyesight Do not do it. If the turn-on frequency of the switching elements S1, S2,..., Sn is less than 100 Hz, flicker may occur in the light emitting device 100, but the control may be solved by controlling the frequency to 100 Hz or more.

4 is a graph showing a change in output voltage in a light emitting device having a time division multiple output DC-DC converter according to the present invention.

Assuming that the switching elements are S1, S2, ..., Sn, as shown in FIG. 4, the output voltage Vout applied to the light emitting string part LS assigned to each switch is different from each other. Has a value. For example, when the forward voltage of the light emitting string portion LS assigned to the switching element S1 is an average value, the output voltage Vout applied to the light emitting string portion LS has an average value, and the output string VLS of the light emitting string portion LS assigned to the switching element S2 has an average value. When the forward voltage is a minimum value, the output voltage Vout applied thereto has a minimum value, and when the forward voltage of the light emitting string portion LS assigned to the switching element Sn is a maximum value, the output voltage Vout applied thereto is It is the maximum value. As described above, according to the present invention, the output voltage Vout by the DC-DC converter 110 is not fixed but automatically adjusted according to the sum of the forward voltages of the light emitting string part LS to be turned on. Of course, even if the output voltage Vout is different for each light emitting string portion LS, the current I _LED flowing through the light emitting string portion LS is always kept constant by feedback control, thereby giving the same brightness. . In addition, according to the present invention, one cycle frequency of the switching elements S1 to Sn is controlled at approximately 100 Hz to 10 kHz, whereby the flickering phenomenon cannot be felt.

For reference, the output voltage Vout by the DC-DC converter 110 is expressed by the following equation.

Vout = Vref + n * Vf (LED)

Here, Vref is a predetermined reference voltage, n is the number of light emitting diodes, and Vf is a forward voltage of the light emitting diodes.

5 is a circuit diagram illustrating a power supply having a time division multiple output DC-DC converter according to the present invention. Since the power supply device 200 has substantially the same configuration as the above-described light emitting device 100, the description will be mainly given of differences.

As shown in FIG. 5, the present invention may be used as the power supply device 200 by connecting a resistor R to an output terminal of the DC-DC converter 110 instead of a light emitting diode.

A plurality of resistors R may be gathered to form one resistor string unit RS or a plurality of resistor string units RS may be connected in parallel. Of course, the resistors R may be provided separately or may be provided in a plurality connected in parallel. Substantially the resistor R means all electrical loads powered by the DC-DC converter 110.

In addition, a plurality of switching elements turned on or off by the switch driver 116 of the DC-DC converter 110 may also be provided in plural or one depending on the connection state of the resistor. In this manner, the present invention can be suitably used not only for light emitting devices but also for general power supply devices.

What has been described above is only one embodiment for implementing a light emitting device and a power supply device having a time division multiple output DC-DC converter according to the present invention, and the present invention is not limited to the above-described embodiment, As claimed in the claims, any person having ordinary skill in the art without departing from the gist of the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

1 is a circuit diagram showing a light emitting device having a DC-DC converter according to the prior art.

2 is a circuit diagram showing a light emitting device having a time division multiple output DC-DC converter according to the present invention.

3 is a timing diagram of a switch with respect to the circuit diagram of FIG.

4 is a graph showing a change in output voltage in a light emitting device having a time division multiple output DC-DC converter according to the present invention.

5 is a circuit diagram illustrating a power supply having a time division multiple output DC-DC converter according to the present invention.

<Description of Symbols for Main Parts of Drawings>

100; Light emitting device according to the present invention

110; DC-DC converter

111; Oscillator

112; PWM control

113; Feedback voltage detector

114; Reference voltage

115; Gate driver

116; Switch drive

117; Overvoltage Detector

Claims (14)

A DC-DC converter for boosting and outputting a DC voltage; A plurality of light emitting string parts connected in parallel to the DC-DC converter; And, A plurality of switching elements connected to each of the light emitting string parts and simultaneously determining whether the light emitting string parts are turned on and off by the control of the DC-DC converter; And the DC-DC converter controls the plurality of switching elements by time division, so that the plurality of light emitting string units emit light by time division. The method of claim 1, And the DC-DC converter sequentially turns on the plurality of switching elements. The method of claim 1, And said DC-DC converter turns on said plurality of switching elements at a constant cycle frequency. The method of claim 1, The DC-DC converter has a time division multiple output DC-DC converter, characterized in that the control of the plurality of switching elements PWM (Pulse Width Modulation) to control the brightness of each of the light emitting string portion. The method of claim 1, And the DC-DC converter turns on the plurality of switching elements by the same time, respectively. The light emitting device having a time division multiple output DC-DC converter. The method of claim 1, The DC-DC converter has a time division multiple output DC-DC converter, characterized in that to turn on the plurality of switching elements by a different time. The method of claim 1, The light emitting device having a time division multiple output DC-DC converter, characterized in that the plurality of light emitting diodes are connected in series. The method of claim 1, And the switching element is a field effect transistor whose gate voltage is controlled by the DC-DC converter. The method of claim 1, A sensing resistor is connected to the light emitting string part so as to sense a current applied to the light emitting string part. A time division multiple output DC-DC is connected to a node between the light emitting string unit and the sensing resistor to convert a current applied to the light emitting string unit into a voltage and feed it back to the DC-DC converter. A light emitting device having a converter. The method of claim 1, The DC-DC converter is When the voltage is fed back from the light emitting string part and the voltage is higher than a predetermined reference voltage, the output current is decreased. And the output current is increased when the voltage is smaller than a predetermined reference voltage. The method of claim 1, And the DC-DC converter is configured to automatically set the output voltage by the sum of the forward voltages of the light emitting diodes forming the light emitting string part. The method of claim 1, And the current flowing through each of the light emitting string parts is always the same regardless of the output voltage of the DC-DC converter determined by each of the light emitting string parts. The method of claim 1, The DC-DC converter is Pulse Width Modulation (PWM) control unit; A feedback voltage sensing unit receiving the voltage from the light emitting string unit and comparing the fed back voltage with a predetermined reference voltage and outputting the feedback voltage to the PWM controller; A gate driver which decreases an output current when the voltage fed back by the feedback voltage detector is higher than a predetermined reference voltage under control of the PWM controller, and increases an output current when the feedback voltage is smaller than a predetermined reference voltage; And, And a switch driver for controlling the turn-on of the switching element in a predetermined order by the control of the PWM control unit. A DC-DC converter for boosting and outputting a DC voltage; At least one resistor string unit connected to the DC-DC converter; And, A switching element connected to the resistance string unit and determining a current flow of the resistance string unit under control of the DC-DC converter, The DC-DC converter is a time division multiple output DC-DC converter, characterized in that the time is divided by controlling the switching element, so that the current flows through the resistance string portion.

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