KR20120070263A - Led string driving circuit - Google Patents

Abstract

PURPOSE: An LED string driving circuit is provided to easily detect the short of an LED in an LED string of a plurality of channels by detecting the highest voltage outputted from one common point in an extension circuit line. CONSTITUTION: A plurality of unit LED strings(S1 to Sn) are connected in parallel. A power source(210) supplies a voltage of each unit LED string. Each unit LED string comprises a serial connection circuit of N LEDs(D1 to Dn) and resistors(R21,R22,R23). A unit circuit comprises a serial circuit of diodes(D21,D22,D23) and resistors(R24,R25,R26).

Description

LED string driving circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LED) string driving circuit, and more particularly, to an LED string driving circuit capable of detecting a short state of an LED at one point with respect to an LED string of multiple channels.

In general, two methods are used to drive LEDs. One is to apply a constant voltage so that the current flows through the LED and output the light with the desired brightness. The other is to apply a constant current directly to the LED and output the light.

In general, there is no significant difference between a voltage driving method and a current driving method when driving one LED. However, when driving a plurality of LEDs simultaneously in a multi-channel (multi-channel) at the same time, the current deviation occurs even when driving at the same voltage due to the deviation of each LED, the brightness of each LED is different. Therefore, in the case of driving a plurality of LEDs in a multi-channel, it is common to use a constant current driving method rather than a constant voltage driving method. Especially when the brightness needs to be finely adjusted, the constant current driving method is used. When driving multiple LEDs, several channels are used for one driving chip. At this time, as the driving method of each channel, the constant current method is adopted as described above.

1 is a view showing an example of a conventional LED string driving circuit.

Referring to FIG. 1, a conventional LED string driving circuit supplies voltages to N unit LED strings S1, S2,... Sn, and parallel to each unit LED string S1, S2, .., Sn. It includes a power source 110. Each of the unit LED strings S1, S2, ..., Sn is composed of N LEDs D1, D2, ..., Dn and a series connection circuit of each of the resistors R10, R11, R12.

The conventional LED string driving circuit of the above configuration is driven by one power source 110, as shown. When one LED is shorted as in " V12 " of the n-th LED string Sn, the voltage of " V12 " rises above the voltage of " V11 ".

As described above, when the LED is shorted, the voltage applied to the resistors R10, R11, and R12 of each LED string S1, S2,. Therefore, in the conventional LED string driving circuit, a voltage sensing circuit (not shown) is separately provided for each channel (string) in order to detect the short circuit of the LED as described above, thereby increasing the cost. have.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described matters, and an object thereof is to provide an LED string driving circuit that can easily detect whether a LED is shorted at a single point with respect to LED strings of multiple channels. .

In order to achieve the above object, the LED string driving circuit according to the present invention,

N unit LED strings S1, S2, ..., Sn connected in parallel; And

It includes a power supply for supplying a voltage to each of the unit LED string (S1, S2, ..., Sn),

Each of the unit LED strings S1, S2, .., Sn is composed of a series connection circuit of N LEDs D1, D2, .., Dn and resistors R21, R22, and R23, respectively.

Each LED and each resistor directly connected to the resistors R21, R22, and R23 among the N LEDs D1, D2, .., and Dn of the unit LED strings S1, S2,. On the connection line between R21, R22, and R23, there is a feature in that the unit circuits composed of the series circuits of the diodes D21, D22, D23 and the resistors R24, R25, and R26 are respectively connected.

The resistors R24, R25, and R26 may be configured as one common resistor.

According to the present invention, a short circuit of LEDs with respect to the LED strings of the multiple channels is detected by detecting the highest voltage value outputted from one common point on the extension circuit line in which a general diode is additionally added to the LED strings of the multiple channels. short) can easily detect whether there is an advantage.

1 is a view showing an example of a conventional LED string driving circuit.
2 shows an LED string drive circuit according to the invention;
3 illustrates an LED string driving circuit according to another embodiment of the present invention.
4 is a view showing an operation simulation result when the LED is in a steady state in the LED string driving circuit of the present invention.
FIG. 5 is a view showing an operation simulation result when one LED of an arbitrary LED string is shorted in the LED string driving circuit of the present invention. FIG.
FIG. 6 is a diagram showing an operation simulation result when two LEDs of an arbitrary LED string are shorted in the LED string driving circuit of the present invention. FIG.

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

2 is a view showing an LED string driving circuit according to the present invention.

2, the LED string driving circuit according to the present invention includes N unit LED strings S1, S2, .., Sn connected in parallel; And a power supply 210 for supplying a voltage (for example, DC 10V) to each of the unit LED strings S1, S2, .., Sn.

Here, each of the unit LED strings S1, S2, .., Sn is composed of N LEDs D1, D2, .., Dn and a series connection circuit of the resistors R21, R22, and R23, respectively. .

In addition, of the LEDs D1, D2, .., Dn of the unit LED strings S1, S2,... Sn, each LED directly connected to the resistors R21, R22, R23, that is, 2, diodes D21, D22, D23 (where D21, D22, and D23 represent general diodes) on the connection line between the resistors R21, R22, and R23, respectively. And unit circuits composed of series circuits of resistors R24, R25, and R26 are connected respectively.

Here, the resistors R24, R25, and R26 may be configured as one common resistor R24, as shown in FIG.

Then, the operation of the LED string driving circuit according to the present invention having the above configuration will be briefly described.

Referring to FIG. 2, the LED string driving circuit according to the present invention includes N unit LED strings S1, S2,... Sn connected in parallel (for example, three unit LED strings S1, S2, S3) and any LED in the LED string (for example, the third string) of one of the three LEDs for each string (for example, the third LED from above) Is shorted, it is possible to detect the corresponding voltage at V4, thereby determining whether the LED in the string is short.

For example, when DC 10V power is applied to the LED string driving circuit of the present invention (assuming 0.7V drop per LED and general diode), 7.9V is set to V1 in the LED string S1 on the left side. In the middle of the LED string S2, 7.9V is sensed, and in the right LED string Sn, 8.6V is detected in V3.

At this time, the highest voltage among the above-mentioned voltages V1, V2, and V3 is detected at V4. That is, at V4, the voltage drop due to the respective general diodes D21, D22, and D23 at the voltage drop (7.9V, 7.9V, and 8.6V) caused by the LEDs in the LED strings S1, S2, and S3. 0.7V) value is further subtracted, so the left LED string S1: 7.9V-0.7V = 7.2V, the center LED string S2: 7.9V-0.7V = 7.2V, the right LED String (Sn): 7.9V is detected because the highest value of 8.6V-0.7V = 7.9V is 7.9V. Accordingly, by comparing the detected voltage value (7.9V) of V4 and the sensed voltage values of V1, V2, and V3, respectively, it is easy to know in which LED string a short of the LED has occurred.

Meanwhile, FIGS. 4 to 6 are diagrams illustrating an operation simulation result for each of a case in which the LED is in a normal state and a case in which the LED is short in the LED string driving circuit of the present invention.

First, referring to FIG. 4, this shows an operation simulation result when the LED is in a normal state. As shown, voltage detection values at V1, V2, and V3 are all constant at about 7.9 V, and V4 (yellow). It can be seen that the voltage detection value at is about 7.2V, which is 0.7 lower than the voltage detection value (7.9V) at V1, V2, and V3.

FIG. 5 is a diagram illustrating an operation simulation result when one LED of the third string Sn is shorted as described above. As illustrated, voltage detection values at V1 and V2 are 7.9 V, respectively. It can be seen that the voltage detection value at V3 is 8.6V, and the voltage detection value at V4 (yellow) is 7.9V, which is 0.7V lower than the voltage detection value (8.6V) at V3.

FIG. 6 shows an operation simulation result when two LEDs of the third string Sn are shorted. As illustrated, voltage detection values at V1 and V2 are 7.9 V, and voltage detection at V3. The value is 9.3V, and it can be seen that the voltage detection value at V4 (yellow) becomes 8.6V, which is 0.7V lower than the voltage detection value (9.3V) at V3.

As described above, the LED string driving circuit according to the present invention detects the highest voltage value output from one common point on the extension circuit line in which a general diode is additionally added to the LED strings of the multiple channels, respectively. With respect to the LED string of the LED has an advantage that can easily detect whether the short (Short).

As mentioned above, although the present invention has been described in detail with reference to the preferred embodiment, the present invention is not limited thereto, and it will be apparent to those skilled in the art that various changes and applications can be made without departing from the technical spirit of the present invention. Accordingly, the true scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of the same should be construed as being included in the scope of the present invention.

110,210: power supply S1, S2, .., Sn: unit LED string
D1, D2, .., Dn: LED D21, D22, D23: General Diode

Claims (2)

N unit LED strings S1, S2, ..., Sn connected in parallel; And
It includes a power supply for supplying a voltage to each of the unit LED string (S1, S2, ..., Sn),
Each of the unit LED strings S1, S2, .., Sn is composed of a series connection circuit of N LEDs D1, D2, .., Dn and resistors R21, R22, and R23, respectively.
Each LED and each resistor directly connected to the resistors R21, R22, and R23 among the N LEDs D1, D2, .., and Dn of the unit LED strings S1, S2,. An LED string drive circuit, to which a unit circuit composed of a series circuit of diodes (D21, D22, D23) and resistors (R24, R25, R26) is connected, respectively, on a connection line between (R21, R22, R23). The method of claim 1,
And the resistors (R24, R25, R26) consist of one common resistor.

Images