JPS63142392A - Light emitting diode array head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This light emission relates to a light emitting diode (hereinafter referred to as LID) array head used as a printing light source of a printer, and particularly to its driving method.

[Conventional technology]

FIG. 3 is a block diagram showing a conventional LED array head disclosed in, for example, Japanese Unexamined Patent Publication No. 59-184680. In the figure, 1 is a hybrid integrated circuit that constructs the drive section, 2 is a drive integrated circuit, 1a is a resistor Ra,
This is a current distribution circuit consisting of Rb and transistors Qll to Qln. The hybrid integrated circuit 1 is constituted by the drive integrated circuit 2 and the current distribution circuit 1a. Further, 3 is a hybrid integrated circuit that constructs the head part, and 41 to 4m are each n LED elements 4.
are formed with m LED chips, RT1 to RTnm are m x n printed film resistors connected to each of the LED elements 4 of each LED chip 41 to 4m, 5 is 0 distribution lines,
6 is m common lines. One of each of the LED chips 41 to 4m is connected to the distribution line 5 in parallel via the LED stacker conductor 4 plate resistors RT1-RTnm on the total amount side, and the common line 6 is connected to each one of the LED chips 41 to 4m in parallel. LED chips 41-4
m of n LED chips 41 are connected together, and the hybrid integrated circuit section 3 is connected to these LED chips 41.
~4m, a printed film resistance RTl~RTnm, a distribution line 5, and a common line 6. Further Q21~Q
2m is a transistor as a switching element for selectively controlling current supply to the LED chips 41-4m, 71-7m is an amplifier circuit, and 8 is a decoder circuit.

FIG. 4 is a block diagram showing the configuration of the drive integrated circuit 2, and in the figure, 2a is a buffer circuit;
b is a decoder circuit, 2C is a primary latch circuit consisting of n bistable flip-flops, 2d is a secondary latch circuit also consisting of n bistable flip-flops, and 2e is a buffer output circuit.

Next, the operation will be explained. FIG. 5 is a timing chart showing the operation. As shown in the figure, when the clear signal of F2 is applied to the primary latch circuit 2C, all n-bit data that was previously latched is reset. Next, when the enable signal of the decoder circuit 2bKFi is applied, the decoder output obtained by converting the input C is sequentially applied to the primary latch circuit 2C to select a bistable flip-flop in units of k bits. At the same time, k-bit parallel data Dp is amplified by the buffer circuit 2a and sequentially inputted to the selected bistable 7 lip-flop, and at the same time, the strobe signals fsx, f5z ~ of F3 are amplified by the buffer circuit 2a.
In synchronization with fsz (t=n/k), all n bits of data dil to din are latched by the primary latch circuit 2C. Next, when time T1 has elapsed, the clear signal of F4 is applied to the secondary latch circuit 2d, and all n-bit data previously latched is reset. Immediately thereafter, when the strobe signal f51 of F5 is applied, in synchronization with this, the n bits of data stored in the primary latch circuit are moved as they are and stored in the secondary latch circuit 2d. At this time, the data in the primary latch circuit 2C is immediately reset by the clear signal F2 after time F2, and the data signals of the next group are latched.

The data DP of the secondary latch circuit 2d is the next clear signal f.
It is held until 52 is added, and the buffer output circuit 28K
m is gone. At this time, first, the decoder circuit 8 which selectively drives the transistor Q21 via the amplifier circuit 71 converts the input G in order to operate the LED chip 41. Transistor Q21 has n-bit LED drive current Ii1~
Since Iin flows at the same time, it must be a large current transistor, and the propagation delay time during switching is TPHL *
It is necessary to set the pulse width and time of the out enable signal B in consideration of TPLH. In the same way,
The pulse time TI4 for the output enable of the buffer output 2e must also be set within the drive time F5 of the transistor Q21 to drive the current distribution circuit 1a.

As described above, data is transferred in units of n bits of data, and the LED chips 41 to 4m are shifted and driven every time F2, thereby causing all the LED elements 4 to emit light. by the way,
LED drive current Ii1~ generated from current distribution circuit 1a
In*m is adjusted by the current value in order to equalize the variation in the amount of light emitted from the LED element 4, so the printed film resistor RTl-R
The purpose is achieved by connecting Tnm in series corresponding to the LED element 4 and trimming the function using, for example, a laser so that the current reaches a specified amount of light emission.

[Problems that light emission attempts to solve]

Conventional LED array heads are configured as described above, so in order to eliminate variations in the light emission output of each LED element, trimming is performed using a printed film resistor laser connected in series to the LED elements. , for example 2
Since it is necessary to perform this on each IED element weighing 000 to 4000 g, it takes a long time to reheat it, resulting in low manufacturing efficiency and an expensive head. multiple leds
Since current is supplied to element 4, the LED to be driven
The number of elements 4 varies depending on the input signal, transistor Q
The collector current of 21 to Q2m is not constant, and transistors have a basic characteristic that VCE varies somewhat depending on the magnitude of the collector current.
Since the collector voltages of the transistors Q21 to Q2m vary depending on the number of D elements 4, the voltage applied to the LED elements 4 varies, and the light emitting output of each LED element 40 is not constant, resulting in a blurred printed image. There was a problem in that it caused density unevenness.

This light emission was made in order to solve the problems mentioned above, and the aim is to always keep the light emission output of each LED element constant and to obtain an inexpensive LED array head that can obtain high-quality printed images. .

[Means for solving problems]

In this LED array head for light emission, each of the plurality of constant current drive circuits is connected to the LED of each of the plurality of LED chips.
In addition to being connected to the LED chip, a switching element is provided corresponding to a plurality of LED chips.

[For production]

The LED element for this light emission is driven by a constant current drive circuit with a predetermined current value, and even if the collector current of the transistor of the switching element fluctuates, it maintains a constant light emission output and prevents density unevenness in the printed image of the printer. do.

〔Example〕

An example of this light emission will be described below with reference to the drawings. 1st
In the figure [,4.4,~4m,5,6.

Since Q21 to Q2m are the same as those given the same reference numerals in FIG. 3, their explanation will be omitted. Further, 9 is a hybrid integrated circuit constructing a driving section, and 10 is light emission data D corresponding to each LED element 4 of the LED chips 41 to 4m.
n-bit shift register with latches, 11,1
2.13 is a correction data set of 3 bits each prepared for correcting the light emission output of each of the LEDs 4;
H2, H.

14 is an AND circuit that performs a logical product of the strobe signal S for setting the light emission time and the light emission data D, and 15 is n constant current drive circuits. The hybrid integrated circuit 9 includes these shift registers 10.
11 to 13, an AND circuit, and a constant current drive circuit 15.

Further, 16 is a current control circuit, 17 to 20 are four current amplification circuits connected in parallel, 21 is a comparison circuit, and R is a conversion resistor. Therefore, the output current is converted into a voltage by a conversion resistor R and detected, this voltage value is compared with a reference voltage by a comparison circuit 21, and a control signal is input to the current control circuit 16. In addition, this constant current drive circuit 15 includes each LED.
One each of chips 41 to 4m, LED on the total amount side
Element 4 is connected in parallel, and transistors Q21 to
The LED element 4 is caused to emit light by controlling one of Q2m to be conductive. Here, four current increase circuits 17
~20 output current values, e.g. 8mA, 4mA+, respectively
If it is set to 2mA + 1mA and the current value is controlled using the latter three current amplifier circuits 1B and 19.20, 8m
p, to 15 mA, eight steps of correction are possible for each 1 mA. Correction data H1, H2, H for each LED element 4
3 can be set to be uniform by measuring the light emission output of the LED element 4 in advance, and is stored in the ROM (not shown here).

Next, the operation will be explained. FIG. 2 is a timing chart for explaining the operation, and T5 in the figure is one period for driving m LED chips 4. T6 indicates a time for storing the light emission data D and correction data H1, H2, H3 in the shift register 10 or 11-13, and T7 indicates a time for driving one LED chip 4.

First, in order to drive the LED chip 41, light emission data D and correction data H1 and H according to the LED chip 4 and K are
2 and H3 are input to shift registers 10° and 11 to 13, respectively. When the input is completed, each data is latched, a strobe S is inputted, and the transistor Q21 is made conductive for a time T7 equivalent to the strobe S.

At this time, each constant current drive circuit 15 has correction data Hl,
Current amplification circuit 17 ~ which outputs current by H2 and H3
20 to correct the output current value, LED step 4,
According to the light emission data D, each of the LED elements 4 can emit light with approximately the same magnitude of light emission output.

During the period until the driving of the LED chip 41 is finished, the light emission data D and correction data H1, H2, 13 of the LED chip 4□ to be driven next are inputted, and when the driving is finished, the data is latte and the above-mentioned Similarly, the KLED chip 42 is driven. Thereafter, in the same manner, the LED element 4 is driven m times until the LED step reaches 4 m, and one cycle indicated by T5 in FIG. 2 is completed.

[Effect of luminescence]

As described above, according to this light emission, a switching element is provided corresponding to a plurality of LED chips, and each of a plurality of constant current drive circuits is connected to the LED element of each of a plurality of LED chips. Since the element is driven by a constant current drive circuit at a predetermined current value, it is possible to maintain a constant light emitting output even if the collector current of the transistor of the switching element fluctuates, thereby preventing density unevenness in the printed image of the printer. There is an effect that can be done.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an LED array head according to an embodiment of this light emission, Fig. 2 is a timing chart for explaining its operation, Fig. 3 is a block diagram showing a conventional LED array head, and Fig. 4 is a block diagram showing a conventional LED array head. The figure is a block diagram showing the drive integrated circuit, and FIG. 5 is a timing chart for explaining the operation of the conventional LED array head. 4 is an LED element, 4 to 4 are LED chips, 9 is a drive unit (hybrid integrated circuit), 15 is a constant current drive unit, 11
, 12.13 is a storage means (shift register), Q2□~
Q2m is a switching element (transistor). In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Country (Vα((j LL

Claims (2)

[Claims] (1) In a light-emitting diode array head in which a plurality of light-emitting diode chips each formed of a plurality of light-emitting diode elements are arranged, a drive section having a plurality of constant-current drive circuits is provided, and each of the constant-current drive circuits is A light emitting diode array head comprising a switching element connected to the light emitting diode element of each of the plurality of light emitting diode chips and controlling current supply to the light emitting diode element for each light emitting diode chip. (2) the drive section includes the plurality of constant current drive sections and a storage means for storing output current control data, and the output current control data is sequentially replaced in the storage means according to the light emitting diode element to be driven; 2. The light emitting diode array head according to claim 1, wherein said constant current drive section is controlled by said output current control data.