JP2001188498A - LED driver - Google Patents

Abstract

(57) [Problem] To reduce the data transfer time with a simple configuration and eliminate the need for a data holding latch circuit when sequentially transmitting light emission data to a plurality of shift registers, thereby providing a drive circuit structure for a multi-pixel display device. Provided is an LED driver capable of simplifying and shifting a light emission timing for each shift register to reduce a rush current. SOLUTION: In an LED driver which connects a plurality of LED drivers each having a shift register composed of a plurality of bits and sequentially transmits light emission data to a shift register of each driver, an enable signal ENIN is input together with the light emission data. The shift register is configured to capture the light emission data DIN in response to the input of the enable signal, capture the light emission data of a predetermined bit, and then output the enable signal together with the light emission data to the next shift register.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an LED driver. More specifically, the present invention relates to an LED driver in which a plurality of LED drivers are connected and light emission data is transferred to a shift register of each driver to emit light.

[0002]

2. Description of the Related Art In a display device or the like using an LED, an LED driver is used to drive and control the LED according to data to be displayed.

FIG. 3 shows a conventional L driver using an LED driver.
FIG. 3 is a schematic configuration diagram of an ED data transfer circuit. This drive circuit is obtained by connecting a plurality of LED drivers each including a plurality of bits of a shift register 11, and each shift register 11 includes a plurality of flip-flops 1 corresponding to the number of bits.
0 is connected in series. Each shift register 11
In addition to the clock signal CLK, the light emission data signal D
IN is input. Each shift register 11 transfers the light emission data signal to the shift register of the next LED driver. Each LED driver outputs an LED drive signal corresponding to light emission data from a driver output terminal (not shown) to cause the LED to emit light.

[0004]

However, in such a configuration in which the shift registers 11 are simply connected in series and the emission data are sequentially transferred to transmit the emission data signal, a long data transfer time is required. That is, if the number of bits of each shift register 11 is n and M shift registers 11 are connected, and if the clock cycle is t, the data transfer time becomes nMt, which is longer in proportion to M. Become. Therefore, when a large number of drivers (shift registers 11) are connected to a display device having a large number of pixels,
This data transfer time is a factor that restricts the screen display frequency (refresh rate).

Further, when the data transfer time is long, each driver needs to maintain the light emission at that time, and each shift register keeps operating until the light emission data signal is transferred to all the drivers. The operation time becomes long, and a circuit for latching each bit of each shift register and a latch pulse for controlling the circuit are required.

FIG. 4 is a block diagram of a conventional LED driver having such a latch circuit. In the circuit of FIG. 4, the light emission data signal is input from the SERIAL-IN terminal and output from the SERIAL-OUT terminal. This light emission data signal is input to the FF circuit 12 constituting each bit of the shift register together with the clock signal from the CLOCK terminal. The latch pulse is input from the LATCH terminal,
In accordance with H ”and“ L ”, the data of the shift register is passed or held via the latch circuit 13. OUT0 to OUT7
Is an 8-bit driver output terminal, and transistor 1
4 is a constant current output terminal of the open collector via the terminal 4.

In the above-mentioned conventional LED driver, especially when a plurality of LED drivers are connected, the shift register of each driver is operated until the data signal is transmitted to all the drivers. A latch circuit and a latch pulse for driving the latch circuit are required, which complicates the circuit configuration. Also, the light emission data signal is sequentially transferred to each shift register while being held by the latch circuit,
After the light emission data is taken into all the shift registers, the LEDs corresponding to the respective shift registers are made to emit light at the same time, so that the rush current at the start of light emission becomes large, the power supply capacity must be increased, and the EMC (Electromagneti
c Compatibility) It is necessary to sufficiently consider electromagnetic interference as a countermeasure, and the structure of the entire circuit becomes more complicated and larger.

The present invention has been made in consideration of the above-mentioned prior art, and has a simple structure to reduce the data transfer time and eliminate the need for a data holding latch circuit for sequentially transmitting light emission data to a plurality of shift registers. It is an object of the present invention to provide an LED driver capable of simplifying a drive circuit structure of a pixel display device and reducing a rush current by shifting a light emission timing for each shift register.

[0009]

In order to achieve the above object, according to the present invention, a plurality of LED drivers each having a plurality of bits of a shift register are connected, and light emission data is sequentially transferred to each driver's shift register. LED
In the driver, an enable signal is input together with the light emission data, and each shift register captures the light emission data in response to the input of the enable signal, and after capturing the light emission data of a predetermined bit, shifts the enable signal together with the light emission data to the next shift. There is provided an LED driver characterized by being configured to output to a register.

According to this configuration, the shift register of each driver takes in the light emission data corresponding to the driver in response to the input of the enable signal, and outputs the enable signal and the light emission data signal to the shift register of the driver at the subsequent stage. As a result, the shift register of the subsequent driver takes in the emission data corresponding to the driver, and similarly outputs an enable signal and an emission data signal to the next shift register of the subsequent driver. In this way, by sequentially transmitting the light emission data signal in a daisy chain type token passing format using the enable signal as a token, the shift register of each driver operates only for a time during which the enable signal is input and captures the light emission data. After the enable signal is output to the shift register of the next stage, the operation is not required, so that the data transfer time is shortened, and there is no need to hold the data until all the emission data is taken into the shift register of the connected driver. Thus, the need for a latch circuit is eliminated.

In a preferred configuration example, light emission is started by using the enable signal as a trigger.

According to this configuration, since the LED of the driver is started to emit light by using the enable signal as a trigger during the token period when the enable signal is input, the LED emission start time of each driver can be shifted, and the rush current can be reduced. The size can be reduced, and EMC measures can be reduced.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an LED driver according to an embodiment of the present invention.

In this example, a plurality of LED drivers a,
It is an example of a drive circuit of an LED display device in which b, c,... are connected. Each of the LED drivers a, b, c,... Has the same configuration, and only the LED driver a is illustrated. Each LED driver has a plurality of flip-flops 1 corresponding to a plurality of bits.
It has a shift register consisting of zeros. The light-emitting data signal DIN is input to each flip-flop 10, and a signal line for a clock signal CLK and an enable input signal ENIN is connected via a gate circuit 19. Each LED driver has a clock input terminal 24, a light emission data input terminal 22, an enable signal input terminal 23,
Light emission data output terminal 25, enable signal output terminal 26
Is formed. Each LED driver fetches a light emission parameter corresponding to the driver from DIN during a token period as described later, and simultaneously outputs the L
Input to ED driver.

FIG. 2 is a time chart showing the operation of the circuit of FIG. Enable input signal ENI of each driver
As shown in (A), (B) and (C), only during the period when N is “H”, the internal shift register operates to capture the light emission parameters. (A), (B), and (C) are the enable signal levels at the ENIN terminal 23 of each of the LED drivers a, b, and c. For example, when the enable signal (A) of the LED driver a becomes “H”, n “H” level signals (a1 to a) corresponding to the bit number n are obtained from the light emission signal DIN.
Since the enable signal is set to “H” until n) is counted by the counter 21 (FIG. 1) and n emission parameters are fetched, all the luminescence parameters assigned to the shift register of the LED driver a have been fetched. Then, the enable input signal is set to "L" to end the token. When the enable input signal is set to "L", the enable output signal ENOUT is set to "H", and the enable output signal ENOUT is set to the next LE.
It is assumed that the enable input signal (B) of the D driver b. Accordingly, the token period of the next-stage LED driver b is started, and the light-emitting parameters corresponding to the bit number n are fetched in the same manner as the preceding-stage driver a.

As described above, the enable input signal ENIN
Is used as a token of the driver, and by sequentially transferring the token to a driver at a subsequent stage, all the LED drivers connected in order can capture light emission data. In this scheme,
Regardless of the number M of LED drivers, the operation time of the shift register of each driver is n · t (n: number of bits, t:
Clock period), and does not become constant and long even if the number of drivers increases. Therefore, even if the operation of the shift register is stopped and the light emission is stopped, the refresh rate is not reduced, and a latch for holding the data of the shift register is not required.

Further, in this token method, after the emission parameter is determined, it is not necessary to wait for the emission parameter transfer time to another driver. Therefore, after the enable input signal falls to "L", the emission is performed for each driver. Can be started. By starting light emission at different timings for each driver by using the enable signal as a trigger in this way, an inrush current can be reduced and EMC measures can be reduced as compared with a conventional configuration in which light emission is started simultaneously.

[0018]

As described above, according to the present invention, the shift register receives the enable signal by sequentially transmitting the light-emitting data signal in the daisy-chain type token passing format using the enable signal as a token. It does not need to be operated after operating for a certain period of time to capture the light emission data and output the enable signal to the next stage shift register, so the data transfer time is reduced, and the data is transferred until the light emission data is captured by all shift registers. Need not be held, and a latch circuit is not required, so that the circuit configuration of the multi-pixel display device can be simplified.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an LED driver according to an embodiment of the present invention.

FIG. 2 is a time chart of the circuit of FIG. 1;

FIG. 3 is a schematic configuration diagram of a conventional LED driver.

FIG. 4 is a circuit configuration diagram of another conventional LED driver.

[Explanation of symbols]

10, 12: flip-flop, 11, 15, 17: shift register, 13, 16, 18: latch circuit, 14:
Transistor, 19: gate circuit, 20: amplifier, 2
1: counter, 22 to 26: terminal, 27 to 30: light emission data signal

Claims (2)

[Claims] An LED driver for connecting a plurality of LED drivers each having a shift register composed of a plurality of bits, and sequentially transmitting light emission data to a shift register of each driver. The shift register is configured to capture light emission data in response to the input of the enable signal, and after capturing light emission data of a predetermined bit, output the enable signal together with the light emission data to a next shift register. driver. 2. The LED driver according to claim 1, wherein light emission is started by using the enable signal as a trigger.