KR101053335B1 - LED driving circuit - Google Patents

Abstract

The present invention relates to a LED driving circuit, comprising: a plurality of first to n-th DC / DC converters supplying voltages to a plurality of first to n-th LED groups; Voltage detection including first to nth output voltage detectors 100-1 to 100-n for detecting output voltages of the plurality of first to nth DC / DC converters 10-1 to 10-n, respectively. Circuit unit 100; High voltage selection unit 200 for selecting the highest detection voltage (Vdmax) of the plurality of first to n-th detection voltage (Vd1 ~ Vdn) from each of the first to n-th output voltage detector (100-1 ~ 100-n) ); A comparator 300 comparing the highest detection voltage Vdmax selected by the high voltage selector 200 with a preset reference voltage Vref and outputting a switching signal according to the comparison result; And a comparator 300 connected between a common power line LCOM connected to a terminal of a common power supply voltage Vcc of the plurality of first to Nth DC / DC converters 10-1 to 10-n, and a ground. A switch 400 is provided to switch the on / off operation according to the switching signal from) and supply or cut off the common power supply voltage Vcc.

LED, drive, LCD display, backlight, overvoltage protection (OVP),

Description

LED driving circuit {LED DRIVING CIRCUIT}

The present invention relates to an LED driving circuit that can be applied to an LCD display device, and in particular, by implementing a dual protection structure of individual overvoltage protection and total overvoltage protection, LED driving circuit which can perform full overvoltage protection even in case of malfunction of individual overvoltage protection. It is about.

In general, most of the light source is configured by applying a Cold Cathode Flourscent Lamp (CCFL), but the development of products that adopt LED (Light Emitting Diode) as a new light source is being actively made. Unlike the CCFL's AC output, the LED applies DC output to the LED to adjust the brightness between the LEDs. In particular, in order to operate LEDs configured in series in this part, the voltage is adjusted accordingly. In order to adjust the LED driving voltage in this way, step-up and step-down converters are used.

For step-up converters, flyback or boost converters are used.

However, in the step-up converter, the output voltage is varied according to the state of the LED, so that the output may be output at a state higher than or equal to the reference voltage according to the abnormal state of the sensing portion, thereby destroying the peripheral device. Since this results in abnormal conditions due to product damage, these step-up converters include individual overvoltage protection, which shuts down the individual PWM control ICs to prevent damage to internal circuits and components in the event of an overvoltage. .

On the other hand, in the conventional step-up converter, the output voltage changes according to the duty of the gate of the FET so that the output voltage becomes a desired size. It is fed back by a feedback resistor to supply a constant current to the load, which changes the gate duty, which in turn affects the output voltage, which supplies a constant current to the load regardless of the load. In this case, a step-up converter generally has an OVP (Over Voltage Protection) function in order to protect the voltage, since a constant voltage for feeding back the integrated circuit is not supplied when the load is opened.

However, in the step-up converter that operates normally with a load, the output voltage is normally adjusted in accordance with the voltage detection, so that the overvoltage protection (OVP) circuit that operates when an abnormality occurs does not operate. In case that the existing OVP circuit is overlooked even if it is an abnormal state, when the load is opened, the voltage rapidly rises and the element breaks down and reaches an abnormal state.In this case, when the element is destroyed, It also has risks.

   That is, even in the case of including the individual overvoltage protection function in the stub-ep converter, when the resistance for detecting the overvoltage is shorted, since the detection voltage is low, it operates in a direction to continuously increase the output voltage, resulting in overvoltage. There is a problem.

The present invention has been proposed to solve the above problems of the prior art, the object of which is to implement a double protection structure of individual overvoltage protection and total overvoltage protection, it is possible to perform full overvoltage protection even in the event of malfunctioning individual overvoltage protection Therefore, the present invention provides an LED driving circuit which can more reliably prevent damage to internal circuits and components due to overvoltage.

A first technical aspect of the present invention for achieving the above object of the present invention, a plurality of first to n-th DC / DC converter for supplying a voltage to each of the plurality of first to n-th LED group; A voltage detection circuit unit including first to nth output voltage detectors detecting output voltages of the plurality of first to nth DC / DC converters; A high voltage selector which selects a highest detected voltage among a plurality of first to nth detected voltages from each of the first to nth output voltage detectors; A comparison unit comparing the highest detection voltage selected by the high voltage selection unit with a predetermined reference voltage and outputting a switching signal according to the comparison result; And a common power supply line connected to common power supply voltage terminals of the plurality of first to Nth DC / DC converters, and a ground, to be turned on / off according to a switching signal from the comparator, thereby to control the common power supply voltage. An LED drive circuit having a switch to supply or cut off is proposed.

Each of the plurality of first to nth DC / DC converters may include: a feedback circuit unit configured to detect a current flowing in a corresponding LED group among the plurality of first to nth LED groups; An overvoltage detection circuit unit detecting a driving voltage supplied to a corresponding LED group among the plurality of first to nth LED groups; And a step-up converter that adjusts the step-up of the driving voltage in a PWM manner based on the voltage from the feedback circuit unit and performs overvoltage protection according to the detected voltage from the overvoltage detection circuit unit.

Each of the first to n-th output voltage detectors may include a plurality of split resistors for dividing and detecting a driving voltage supplied to a corresponding LED group among the plurality of first to n-th LED groups.

The high voltage selector may include first to nth diodes for detecting detection voltages from the first to nth output voltage detectors; And a common connection node configured to commonly connect the plurality of cathodes of the first to nth diodes to select the highest detection voltage.

The comparison unit may include a non-inverting terminal receiving the detection voltage selected by the high voltage selecting unit, an inverting terminal receiving the preset reference voltage, and outputting a switching-on signal when the detection voltage is higher than the reference voltage. If the voltage is not higher than the reference voltage, it characterized in that the operational amplifier having an output terminal for outputting the switching off signal.

The switch includes an N-channel MOS transistor having a drain connected to a common power line connected to common power voltage terminals of the plurality of first to nth DC / DC converters, a source connected to ground, and a gate connected to an output terminal of the comparator. Characterized in that consisting of.

According to the present invention as described above, by implementing a dual protection structure of individual overvoltage protection and total overvoltage protection, it is possible to perform the overall overvoltage protection even in case of individual overvoltage protection malfunction, so that the internal circuit and component damage due to the overvoltage is more certain in advance. There is an effect that can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention is not limited to the embodiments described, and the embodiments of the present invention are used to assist in understanding the technical spirit of the present invention. In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

1 is a block diagram of an LED driving circuit according to the present invention.

Referring to FIG. 1, the LED driving circuit according to the present invention includes a plurality of first to n-th DC / DC converters 10-1 supplying a voltage to each of the first to n-th LED groups LEDG1 to LEDGn. First through n-th output voltage detectors 100-1 through 100-n for detecting output voltages of the first through n-th and the plurality of first through n-th DC / DC converters 10-1 through 10-n. The highest detection of the first to the n-th detection voltage (Vd1 ~ Vdn) from the voltage detection circuit unit 100 and the first to n-th output voltage detection unit (100-1 ~ 100-n) The high voltage selector 200 selecting the voltage Vdmax and the highest detection voltage Vdmax selected by the high voltage selector 200 and the preset reference voltage Vref are compared with each other, and the switching signal is determined according to the comparison result. A common power source connected to the comparator 300 for outputting the control unit 300 and the common power supply voltage Vcc of the plurality of first to Nth DC / DC converters 10-1 to 10-n through a limiting resistor RI; Connect between line (LCOM) and ground Air, by on / off operation according to a switching signal from the comparison unit 300, a switch 400 to the common power supply voltage (Vcc) supplied or cut off.

Here, the limiting resistor RI protects the switch 400 by proposing a high current and voltage by the power supply voltage Vcc.

In this case, each of the plurality of first to n-th DC / DC converters 10-1 to 10-n detects a current flowing in a corresponding LED group among the plurality of first to n-th LED groups LEDG1 to LEDGn. From the feedback circuit section 11, the overvoltage detection circuit section 12 for detecting a driving voltage supplied to the LED group among the plurality of first to n-th LED groups LEDG1 to LEDGn, and the feedback circuit section 11 from the feedback circuit section 11; And a step-up converter 13 that adjusts the step-up of the driving voltage in a PWM manner based on the voltage and performs overvoltage protection according to the detected voltage from the overvoltage detection circuit unit 12.

Each of the first to nth output voltage detection units 100-1 to 100-n divides and detects a driving voltage supplied to a corresponding LED group among the plurality of first to nth LED groups LEDG1 to LEDGn. It includes a plurality of split resistors.

For example, the first output voltage detection unit 100-1 may include a plurality of division resistors R1-1 and R1-2 for dividing and detecting a driving voltage supplied to the first LED group LEDG1. Can be.

The second output voltage detector 100-2 may include a plurality of split resistors R2-1 and R2-2 for dividing and detecting a driving voltage supplied to the second LED group LEDG2.

The n-th output voltage detector 100-n may include a plurality of split resistors Rn-1 and Rn-2 for dividing and detecting a driving voltage supplied to the n-th LED group LEDGn. .

The high voltage selector 200 may detect first to nth diodes D1 to Dn that detect detection voltages Vd1 to Vdn from the first to nth output voltage detectors 100-1 to 100-n, respectively. ) And a common connection node (NCOM) for connecting the plurality of cathodes of the first to nth diodes D1 to Dn to select the highest detection voltage Vdmax.

The comparison unit 300 may include a non-inverting terminal receiving the detection voltage selected by the high voltage selecting unit 200, an inverting terminal receiving the predetermined reference voltage, and switching on when the detection voltage is higher than the reference voltage. An operational amplifier (OPA) having an output terminal for outputting a signal and outputting a switching off signal when the detection voltage is not higher than a reference voltage.

The switch 400 may include a drain connected to a common power line LCOM connected to a common power supply voltage Vcc of the plurality of first to nth DC / DC converters 10-1 to 10-n, and a ground; And an N-channel MOS transistor having a source connected to the gate and a gate connected to the output terminal of the comparator 300.

Hereinafter, the operation and effects of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, the LED driving circuit of the present invention includes a plurality of first to n-th DC / DC converters 10 for supplying driving power required for each of the first to n-th LED groups LEDG1 to LEDGn. -1 to 10-n).

In this case, each of the plurality of first to nth DC / DC converters 10-1 to 10-n may include a feedback circuit unit 11, an overvoltage detection circuit unit 12, and a step-up converter 13. In this case, the feedback circuit unit 11 detects a current flowing in the corresponding LED group among the plurality of first to n-th LED groups LEDG1 to LEDGn and supplies a feedback voltage VFB to the step-up converter 13. Output, and adjust the current flowing in the LED group to be constant. The overvoltage detection circuit unit 12 detects a driving voltage supplied to the corresponding LED group among the plurality of first to nth LED groups LEDG1 to LEDGn to provide an overvoltage protection voltage VOVP to the step-up converter 13. Outputs

The step-up converter 13 adjusts the step-up of the drive voltage in a PWM manner based on the voltage from the feedback circuit section 11. If an overvoltage occurs during such step-up operation, overvoltage protection is performed based on the detected voltage from the overvoltage detection circuit section 12.

As described above, each of the plurality of first to n-th DC / DC converters 10-1 to 10-n individually performs overvoltage protection, and individually stops the operation of the internal circuit and the device when the overvoltage occurs. I can protect it. However, in the case where the resistor for detecting the overvoltage for the overvoltage protection is short-circuited, the problem of failing to perform the overvoltage protection is solved through the operation described below.

First, the voltage detecting circuit unit 100 of the present invention includes the first to nth output voltage detecting units 100-1 to 100-n and includes a plurality of first to nth DC / DC converters 10-1 to. 10-n) Detect each output voltage.

Specifically, each of the first to nth output voltage detection units 100-1 to 100-n divides a driving voltage supplied to a corresponding LED group among the plurality of first to nth LED groups LEDG1 to LEDGn. And a plurality of split resistors to be detected.

For example, the first output voltage detector 100-1 includes two split resistors R 1-1 and R 1-2 which divide a driving voltage supplied to the first LED group LEDG 1. The first detection voltage Vd1 is detected by the first connection node N1 of the two split resistors R1-1 and R1-2 and output to the high voltage selector 200. The second output voltage detector 100-2 includes two split resistors R2-1 and R2-2 for dividing a driving voltage supplied to the second LED group LEDG2. The second detection voltage Vd2 is detected by the second connection node N2 of the resistors R2-1 and R2-2 and output to the high voltage selector 200. The nth output voltage detector 100-n includes two split resistors Rn-1 and Rn-2 for dividing a driving voltage supplied to the nth LED group LEDGn. The nth detection voltage Vdn is detected by the nth connection node Nn of the division resistors Rn-1 and Rn-2 and output to the high voltage selector 200.

Next, the high voltage selector 200 may detect the highest detection voltage among the plurality of first to nth detection voltages Vd1 to Vdn from each of the first to nth output voltage detectors 100-1 to 100-n. Select (Vdmax).

Specifically, the high voltage selector 200 is configured to accurately detect the detection voltages Vd1 to Vdn from each of the first to nth output voltage detectors 100-1 to 100-n. n diodes D1 to Dn, wherein each of the first to nth diodes D1 to Dn may be formed from each of the first to nth output voltage detectors 100-1 to 100-n. A plurality of first to nth detection voltages Vd1 to Vdn are detected. Further, the highest detection voltage Vdmax among the first to nth detection voltages Vd1 to Vdn through a common connection node NCOM for commonly connecting a plurality of cathodes of the first to nth diodes D1 to Dn. ) Is selected and output to the comparator 300.

Next, the comparison unit 300 compares the highest detection voltage Vdmax selected by the high voltage selection unit 200 with a preset reference voltage Vref, and outputs a switching signal according to the comparison result.

Specifically, the operational amplifier OPA of the comparison unit 300 compares the detection voltage selected by the high voltage selector 200 through the non-inverting terminal with the preset reference voltage through the inverting terminal. If the detection voltage is higher than the reference voltage, the switching on signal is output to the switch 400 through the output terminal. If the detection voltage is not higher than the reference voltage, the switching off signal is output to the switch 400 through the output terminal.

Here, the reference voltage of the comparison unit 300 is set higher than the reference voltage for determining the individual overvoltage in each of the plurality of first to n-th DC / DC converters (10-1 to 10-n), LED, etc. It is set lower than the breakdown voltage of the device.

Next, the switch 400 is connected between the common power line LCOM connected to the terminal of the common power supply voltage Vcc of the plurality of first to Nth DC / DC converters 10-1 to 10-n and the ground. In connection, the on / off operation is performed according to the switching signal from the comparator 300 to supply or cut off the common power supply voltage Vcc.

Specifically, the N-channel MOS transistor (NMOS) of the switch 400 is turned on in response to the switching-on signal from the comparator 300 when an abnormal overvoltage occurs in which the highest detection voltage is higher than a reference voltage, and thus the common power supply voltage. (Vcc) is connected to ground to stop the plurality of first to n-th DC / DC converters 10-1 to 10-n to operate the first to n-th DC / DC converters 10-1 to 10. -n) the entire protection operation is performed.

On the contrary, the N-channel MOS transistor (NMOS) of the switch 400 is turned off according to the switching off signal from the comparator 300 when the peak detection voltage is not higher than the reference voltage, and thus the common power supply. The voltage Vcc is normally supplied to the plurality of first to n-th DC / DC converters 10-1 to 10-n, and thus the plurality of first to n-th DC / DC converters 10-1 to 10-n. ) Are in a state capable of operating normally.

In the present invention as described above, with each of the plurality of first to n-th DC / DC converters (10-1 to 10-n) each has an overvoltage protection function, by further implementing the overall overvoltage protection function, Solving the problems that can not be solved by the individual overvoltage protection alone, it is possible to improve the reliability of the overvoltage protection.

1 is a block diagram of an LED driving circuit according to the present invention.

Explanation of symbols on the main parts of the drawings

10-1 to 10-n: first to nth DC / DC converters 11: feedback circuit portion

12: overvoltage detection circuit 13: step-up converter

100: voltage detection circuit

100-1 to 100-n: first to nth output voltage detectors

200: high voltage selection unit 300: comparison unit

400: Switch Vd1 to Vdn: First to nth detection voltages

Vdmax: highest detection voltage D1 to Dn: first to nth diodes

NCOM: Common Connection Node OPA: Operational Amplifier

NMOS: N-channel MOS transistor

Claims (6)

delete A plurality of first to n-th DC / DC converters supplying voltages to the plurality of first to n-th LED groups, respectively; A voltage detection circuit unit including first to nth output voltage detectors detecting output voltages of the plurality of first to nth DC / DC converters; A high voltage selector which selects a highest detected voltage among a plurality of first to nth detected voltages from each of the first to nth output voltage detectors; A comparison unit comparing the highest detection voltage selected by the high voltage selection unit with a predetermined reference voltage and outputting a switching signal according to the comparison result; And A common power line connected to a common power supply voltage terminal of the plurality of first to Nth DC / DC converters and a ground, and on / off according to a switching signal from the comparator, to supply the common power supply voltage Or having a switch to cut off,       Each of the plurality of first to nth DC / DC converters includes: A feedback circuit unit for detecting a current flowing in a corresponding LED group among the plurality of first to n-th LED groups; An overvoltage detection circuit unit detecting a driving voltage supplied to a corresponding LED group among the plurality of first to nth LED groups; And A step-up converter that adjusts the step-up of the drive voltage in a PWM manner based on the voltage from the feedback circuit section and performs overvoltage protection according to the detected voltage from the overvoltage detection circuit section. LED driving circuit comprising a. The method of claim 2, wherein the first to n-th output voltage detector, And a plurality of division resistors for dividing and detecting a driving voltage supplied to a corresponding LED group among the plurality of first to n-th LED groups. The method of claim 3, wherein the high voltage selector, First to nth diodes for detecting detection voltages from the first to nth output voltage detectors; And A common connection node for connecting the plurality of cathodes of the first to nth diodes in common to select the highest detection voltage. LED driving circuit comprising a. The method of claim 4, wherein the comparison unit, A non-inverting terminal receiving the detection voltage selected by the high voltage selecting unit, an inverting terminal receiving the preset reference voltage, and outputting a switching-on signal when the detection voltage is higher than the reference voltage, wherein the detection voltage is a reference voltage. LED driving circuit comprising an operational amplifier having an output stage for outputting a switching off signal if not higher. The method of claim 5, wherein the switch, And an N-channel MOS transistor having a drain connected to a common power line connected to a common power voltage terminal of the plurality of first to nth DC / DC converters, a source connected to ground, and a gate connected to an output terminal of the comparator. LED drive circuit.

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