JP2003264316A - Led control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily charge the luminance gradient of an LED and to make possible to set maximum luminance. <P>SOLUTION: An output current from a constant current circuit 10 is charged by a capacity-variable circuit 12 varied by luminance gradient select data depending on the capacity of the circuit to produce a voltage which is inputted to a comparator 13. A voltage of a triangular wave outputted from a triangular wave oscillator 11 is compared with a voltage produced by charging, and a signal of 'H' state is delivered to an AND circuit 16 if the voltage produced by charging is higher. A comparator 15 delivers the signal of 'H' state to the AND circuit 16 until the count of a 4 bit counter 14 matches maximum luminance set data. The AND circuit 16 produces the logical product of output signals from the comparators 13 and 15 and delivers it to an MOSFET Q1. The MOSFET Q1 flickers an LED 17 depending on an output signal from the AND circuit 16. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED control circuit for blinking an LED, and more particularly to an LED control circuit for changing a brightness gradient of an LED.

[0002]

2. Description of the Related Art Some of today's electronic devices such as mobile phones and video cameras are equipped with LEDs (Light-Emitting-Diodes) as means for transmitting various information to a user. For example, a key of a mobile phone is caused to blink by an LED to notify a user of a specific state (battery exhaustion, etc.).
In order to improve the quality, there is an electronic device equipped with such an LED, in which the brightness at the start and end of the blinking of the LED is gradually made brighter and gradually darkened to make it blink like a firefly. .

FIG. 10 shows an example of a conventional LED control circuit. The LED control circuit shown in the figure has resistors R12 and R1.
3, capacitor C2, LED30, transistor Tr1
Composed of and.

The resistor R12 is connected between the IN terminal to which a signal is input and the base of the npn-type transistor Tr1. The capacitor C2 is connected between the base of the transistor Tr1 and the ground. The cathode of the LED 30 is connected to the collector of the transistor Tr1 and LE
The anode of D30 is connected to the power source Vcc via the resistor R13.
Are connected.

If the forward voltage of the LED 30 is about 2V to 3.5V, the voltage of the power source Vcc needs to be about 4V. L
Resistor R13 for limiting the current to the ED30
Depends on the forward current of the LED 30, but is about several mA to several tens mA.
A resistance value is selected that limits

The resistance value of the resistor R12 and the capacitance value of the capacitor C2 are such that a sufficient current can be supplied to the base of the transistor Tr1 and the LED 30 changes a desired brightness depending on the time constant of the resistor R12 and the capacitor C2. To be selected.

The operation of the conventional LED control circuit will be described below. When a signal that changes from the “L” state to the “H” state or the “L” state within the blinking cycle is input to the IN terminal by the control signal of the CPU or the like, the time constant of the resistor R12 and the capacitor C2 causes the transistor Tr1 to operate. Base current changes slowly. As a result, the brightness of the LED 30 has a brightness gradient and blinks gently. here,
The "L" state is 0V, and the "H" state is the power supply voltage of the CPU, which is about 2V to 5V.

[0008]

By the way, the conventional LE
In the D control circuit, the blinking cycle can be easily changed by changing the cycle of the signal input to the IN terminal. However, in order to change the brightness gradient, the resistor R12 and the capacitor C2 must be replaced to change the time constant,
There was a problem that it could not be changed easily.

The present invention has been made in view of the above points, and it is possible to easily change the brightness gradient.
It is an object to provide an ED control circuit.

[0010]

According to the present invention, in order to solve the above problems, an LED control circuit for controlling blinking of an LED outputs an output voltage in which a rising rate and a falling rate of the voltage are changed according to selection data. Voltage output unit, a triangular wave oscillator that outputs a triangular wave voltage, a voltage comparator that outputs a brightness gradient control pulse signal when the output voltage is greater than the triangular wave voltage, and a switching that drives an LED by the brightness gradient control pulse signal. An LED control circuit is provided, which comprises:

According to such an LED control circuit, the rising rate and the falling rate of the output voltage can be changed according to the selection data.
When the output voltage is higher than the triangular wave voltage output from the triangular wave oscillator, the brightness gradient control pulse signal is output. Therefore, the brightness gradient of the LED is changed by changing the selection data.

Further, according to the present invention, in the LED control circuit for controlling the blinking of the LED, when the cycle of the binary counter and the count value of the binary counter is performed a number of times corresponding to the selection data, the count value is counted. A counter unit that counts up and counts down, a count comparator that outputs a brightness gradient control pulse signal until the count value of the binary counter and the count value of the counter unit match, and an LED according to the brightness gradient control pulse signal. And a switching element that drives the LED.

According to such an LED control circuit, when the count value of the binary counter and the count value of the binary counter are cycled a number of times corresponding to the selection data, the counter counts up and down. Since the brightness gradient control pulse signal is output until the count value of the unit matches, the LE can be changed by changing the selection data.
Change the brightness gradient of D.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of an LED control circuit according to a first embodiment of the present invention.

The LED control circuit shown in the figure is a constant current circuit 1
0, triangular wave oscillator 11, variable capacitance circuit 12, comparator 1
3, 15, 4 bit counter 14, AND circuit 16, L
ED17, MOSFET (Metal Oxide Semiconductor F
The field effect transistor Q1 and the resistor R1.

The constant current circuit 10 receives a pulse signal, discharges the constant current at the rising edge of the input pulse signal, and absorbs the constant current at the falling edge of the input pulse signal. The constant current circuit 10 charges and discharges a capacitor (details described later) included in the variable capacitance circuit 12 by discharging and sucking a constant current.

The triangular wave oscillator 11 outputs a triangular wave voltage to the negative terminal of the comparator 13. The variable capacitance circuit 12 has four
Luminance gradient selection data, which is bit digital data, is input, and the capacitance is changed according to the input luminance gradient selection data. 2A and 2B are examples of a specific circuit diagram of the variable capacity circuit. FIG. 2A is a circuit diagram of a capacity multiplication circuit, and FIG.

The capacitance doubling circuit shown in FIG. 2A includes an operational amplifier Z1, a resistor Rc connected between the negative terminal and the output terminal of the operational amplifier Z1, a positive terminal of the operational amplifier Z1, and an output terminal. Ra and Rb connected in series to
And a capacitor Ca connected between the positive terminal of the operational amplifier Z1 and the ground. In the capacitance doubling circuit shown in FIG. 2A, the capacitance generated at the terminal P0 is (the resistance value of the resistor Ra / the resistance value of the resistor Rb) × the capacitance value of the capacitor Ca.

The capacitance variable circuit 12 shown in FIG. 2B has an operational amplifier 12a, resistors R2 to R10, a capacitor C1,
It is composed of analog switches 12b and 12c. The resistor R2 is connected between the negative terminal and the output terminal of the operational amplifier 12a. One ends of the resistors R3 to R6 are connected to the operational amplifier 1
It is connected in parallel to the output terminal of 2a and the other end is connected to the analog switch 12b. Analog switch 12b
Is connected to a terminal P1 connected to the comparator 13. One ends of the resistors R7 to R10 are connected to the analog switch 12c connected to the positive terminal of the operational amplifier 12a, and the other ends are connected to the terminal P1. The resistors R3 to R6 and the resistors R7 to R10 are selected so as to have different resistance values.

The capacitor C1 is connected between the positive terminal of the operational amplifier 12a and the ground. Analog switch 1
2b and 12c each have four switches inside, and 4b
The switch is opened / closed according to the brightness gradient selection data which is the digital data of it. According to the 4-bit digital data, each of the open / close patterns of the analog switches 12b and 12c has 15 patterns except the pattern in which all the switches are opened.

Here, it is assumed that the analog switch 12b closes the switch to which the resistor R3 is connected and the analog switch 12c closes the switch to which the resistor R7 is connected according to the brightness gradient selection data. Here, if the resistance value of the resistor R3 is 1 kΩ, the resistance value of the resistor R7 is 1 MΩ, and the capacitance of the capacitor C1 is 0.001 μF, the terminal P
The capacitance generated at 1 is 10 μF from the relationship of (resistance value of resistor R3 / resistance value of resistor R7) × capacitance value of capacitor C1.

The resistors R3 to R6 and the resistors R7 to R10 are connected to resistors having different resistance values, and the switches of the analog switches 12b and 12c are switched by the brightness gradient selection data which is 4-bit digital data. , 15 patterns of capacitance values can be obtained. The brightness gradient selection data is sent from, for example, a CPU.

The comparator 13 shown in FIG. 1 compares the voltage input to the negative terminal with the voltage input to the positive terminal, and when the voltage input to the positive terminal is larger than the voltage input to the negative terminal. , 'H' state PWM (Pulse Width Modul
ation) Output the output signal.

The 4-bit counter 14 performs binary 4-digit counting in synchronization with the input clock CLK. Four
The bit counter 14 outputs the counted value to the comparator 15. The 4-bit counter 14 counts at a frequency sufficiently higher than the frequency of the triangular wave output from the triangular wave oscillator 11.

The comparator 15 receives the maximum brightness setting data, which is 4-bit digital data, and the count value counted by the 4-bit counter 14. Comparator 15
Outputs the PWM output signal in the “H” state until the count value of the 4-bit counter 14 matches the value of the input maximum brightness setting data, and then outputs the signal in the “L” state. The maximum brightness setting data is sent from, for example, a CPU.

The AND circuit 16 includes a comparator 13 and a comparator 1.
The logical product of the PWM output signals output from 5 is obtained, and the result is output to the MOSFET Q1. MOSFET Q1
Is an N-channel MOSFET, which inputs the signal output from the AND circuit 16 from the gate to turn on / off between the drain and the source.

One end of the resistor R1 is connected to the power supply Vdd, and the other end is connected to the anode of the LED 17. LE
The cathode of D17 is connected to the drain of MOSFET Q1. The source of MOSFET Q1 is connected to ground.

In the LED 17, a current flows when the drain and the source of the MOSFET Q1 are turned on to emit light. The operation of the LED control circuit according to the first embodiment will be described below.

First, the constant current circuit 10 and the triangular wave oscillator 1
1, the operation of the capacitance variable circuit 12 and the comparator 13 will be described. FIG. 3 is a diagram showing a voltage waveform, where (a) is
Voltage waveform of pulse signal input to constant current circuit, (b)
FIG. 4A is a diagram showing a voltage waveform input to the comparator, and FIG. 7C is a diagram showing a voltage waveform output from the comparator.

As shown in FIG. 3A, the constant current circuit 10 outputs a constant current when the input pulse signal transits from the'L 'state to the'H' state. Since the current output from the constant current circuit 10 is charged by the variable capacity circuit 12, the voltage generated at the positive terminal of the comparator 13 is as shown in FIG.
As shown by the waveform A1 in (b), it gradually rises.

A triangular wave voltage is input from the triangular wave oscillator 11 to the negative terminal of the comparator 13 as shown by the waveform A2 in FIG. 3 (b). The comparator 13 compares the triangular wave voltage input to the negative terminal with the voltage input to the positive terminal. When the voltage input to the positive terminal is higher than the voltage of the triangular wave input to the negative terminal, that is, when the voltage of the waveform A1 is higher than the voltage of the waveform A2, the comparator 13 outputs
As shown in FIG. 3C, a PWM output signal in which the pulse width in the'H 'state gradually increases is output.

On the contrary, when the pulse signal input to the constant current circuit 10 transits from the “H” state to the “L” state, the constant current circuit 10 discharges the electric charge charged in the variable capacitance circuit 12. Inhale the current. As a result, the voltage input to the positive terminal of the comparator 13 gradually decreases, and the comparator 13 gradually reduces the “H” state to PWM.
Output the output signal.

Here, it is assumed that the signal output from the comparator 15 is always in the "H" state. Since the MOSFET Q1 is driven by the PWM output signal shown in FIG. 3C, the brightness of the LED 17 gradually becomes bright from the rise of the pulse signal input to the constant current circuit 10 to the'H 'state. Further, the pulse signal input to the constant current circuit 10 gradually becomes dark from the fall to the “L” state. Thus, from the comparator 13 via the AND circuit 16, the MO
A PWM output signal for turning on / off the SFET Q1 and gradually making the LED brighter or darker is output.

Next, the 4-bit counter 14 and the comparator 1
5 and the operation of the AND circuit 16 will be described. Four
The bit counter 14 performs binary 4-digit counting in synchronization with the input clock CLK. The count value of the 4-bit counter 14 is input to the comparator 15.

The comparator 15 has a maximum brightness setting data, which is 4-bit digital data, and a 4-bit counter 14.
The count value that is being counted by is input. Comparator 1
5 outputs the signal in the “H” state until the count value of the 4-bit counter 14 matches the value of the maximum brightness setting data, and then outputs the signal in the “L” state. afterwards,
The count value of the 4-bit counter 14 is saturated and becomes' 111.
When it becomes 1 and the count value returns to "0000", the comparator 15 outputs the "H" state again. Since the maximum brightness setting data is 4-bit data, there are 15 levels of "H".
A PWM output signal having a range of states can be output.

The AND circuit 16 takes the logical product of the PWM output signal output from the comparator 13 for giving the LED 17 a brightness gradient and the PWM output signal output from the comparator 15. FIG. 4 shows the PWM output from the AND circuit.
In the figure which explains an output signal, (a) is maximum brightness setting data '0001', (b) is maximum brightness setting data '0010', (c) is maximum brightness setting data. Shows the state when it is '0011'.

The maximum brightness setting data "0001" causes the comparator 15 to output the PWM output signal having the "H" state of the minimum width among the PWM output signals having the width of the "H" state of 15 steps. As shown in FIG. 4A, the comparator 13
A PWM output signal SA1 outputted from the comparator 15 and a PWM output signal SA3 outputted from the comparator 15 which is the logical product of the PWM output signal SA2 having the minimum width'H 'state are
It is output from the ND circuit 16.

The maximum brightness setting data '0010' is the PW having the second minimum width'H 'state of the PWM output signal from the comparator 15 having the width of 15'H' state.
The M output signal is output. As shown in FIG. 4B, the logical product of the PWM output signal SB1 output from the comparator 13 and the PWM output signal SB2 having the second minimum width'H 'state output from the comparator 15 is calculated. The taken PWM output signal SB3 is output from the AND circuit 16.

The maximum brightness setting data '0011' is the PW having the third minimum width'H 'state from the comparator 15 in the PWM output signal having the width of 15'H' state.
The M output signal is output. As shown in FIG. 4C, the logical product of the PWM output signal SC1 output from the comparator 13 and the PWM output signal SC2 output from the comparator 15 having the third minimum width'H 'state is calculated. The taken PWM output signal SC3 is output from the AND circuit 16.

In this way, P output from the comparator 15
The maximum brightness can be changed by changing the width of the'H 'state of the WM output signal, and the logical product of the PWM output signal output from the comparator 13 can be used to change the brightness gradient and the maximum brightness. Can be changed.

Next, variable brightness gradient of the LED 17 and maximum brightness setting will be described. First, the variable brightness gradient will be described. In order to change the brightness gradient of the LED 17, the capacity of the capacity variable circuit 12 is changed by the brightness gradient selection data of 4 bits. For example, the capacitance varying circuit 12 and the data bus of the CPU are connected, and the capacitance of the capacitance varying circuit 12 can be varied by a program.

The brightness gradient selection data changes the capacitance of the capacitance variable circuit 12 by switching the analog switches 12b and 12c shown in FIG. By changing the capacitance of the capacitance variable circuit 12, the waveform A1 shown in FIG.
Of the PWM output signal shown in FIG. 3C changes the width of the “H” state. By this, LED1
The brightness gradient of 7 is changed.

5A and 5B are explanatory views for explaining the change of the brightness gradient and the maximum brightness. FIG. 5A shows a pulse signal input to the constant current circuit, and FIG. 5B shows the change of the brightness gradient. Figure,
(C) is a figure which shows the change of the maximum brightness.

That is, the constant current circuit 1 shown in FIG.
The brightness of the LED 17 gradually increases as the pulse signal input to 0 rises to the'H 'state.
By changing the capacitance value of the capacitance variable circuit 12 according to the brightness gradient selection data, the brightness gradient of the LED 17 is
It can be changed as shown in FIG.

Similarly, even when the pulse signal of the constant current circuit 10 transits from the “H” state to the “L” state,
The brightness gradient of the LED 17 is changed by changing the capacitance value of the capacitance changing circuit 12 according to the brightness gradient selection data.

Next, the maximum brightness setting will be described. L
To change the maximum brightness of the ED 17, the maximum brightness setting data is changed. For example, the comparator 15 and the data bus of the CPU are connected, and the maximum brightness setting data can be changed by a program. The comparator 15 outputs the PWM output signal in the “H” state until the count value of the 4-bit counter 14 matches the value of the maximum brightness setting data.

That is, the constant current circuit 1 shown in FIG.
As the pulse signal input to 0 rises to the'H 'state, the brightness of the LED 17 gradually increases as shown in FIG. 5 (c). Depending on the maximum brightness setting data,
The maximum value of the brightness of the LED 17 is fixed, and the maximum brightness of the LED 17 can be changed by changing the maximum brightness setting data.

As described above, by changing the brightness gradient selection data and the maximum brightness setting data, the brightness gradient and the maximum brightness of the LED can be easily changed. In the above description, the brightness gradient selection data and the maximum brightness setting data are 4-bit data, but they are not limited to this. Increase or decrease the number of resistors of the capacitance variable circuit 12, or
By increasing or decreasing the number of digits of the 4-bit counter 14,
It may be controlled by data other than bit.

Further, the constant current circuit 10 and the triangular wave oscillator 1
1, the capacity variable circuit 12, the comparators 13 and 15, the 4-bit counter 14, and the AND circuit 16 may be integrated as a monolithic semiconductor circuit. Thereby, the number of parts can be reduced.

Further, in the above description, the capacitance variable circuit 12
The gradient of the voltage input to the comparator 13 is changed by changing the capacitance of the
The constant current value of the constant current circuit 10 may be switched by selection data or the like to change the brightness gradient of the LED 17.

Next, a second embodiment of the present invention will be described. FIG. 6 is an LE according to the second embodiment of the present invention.
It is a circuit diagram of a D control circuit. The LED control circuit shown in the figure includes a 6-bit counter 20 and a clock-select circuit 2.
1, 6-bit up / down counter 22, comparator 23,
25, 4 bit counter 24, AND circuit 26, LED
27, a MOSFET Q2, and a resistor R11.

The 6-bit counter 20 is synchronized with the input clock CLKA and is binary 6-digit (CLK shown in FIG. 6).
6, CLK5, ..., CLK1 is 1 from 6 digits of binary 6 digits
Corresponds to a digit. ) Count. The 6-bit counter 20 outputs the counted value to the comparator 23. In addition, the 6-bit counter 20 displays the 6th digit (CLK
6) is output to the clock-select circuit 21.

The clock-select circuit 21 has 4 bits.
And the sixth digit of the binary 6-digit count value output from the 6-bit counter 20.
The clock-select circuit 21 divides the sixth digit of the binary 6-digit count value output from the 6-bit counter 20 as a reference clock according to the value of the input brightness gradient selection data, and outputs the select clock. To do.

If the brightness gradient selection data is "0000", the clock-select circuit 21 outputs the reference clock, which is the sixth digit of the binary six-digit count value, as the select clock. If the brightness gradient selection data is "0001", a clock obtained by dividing the reference clock by two is output as the select clock. Similarly, up to '1111', a clock obtained by dividing the reference clock by 16 is output as a select clock. FIG. 7 shows a select clock (a reference clock and a select clock obtained by dividing the reference clock by 2, 3, 16) output from the clock-select circuit.
The clock-select circuit 21 outputs a select clock obtained by dividing the reference clock as shown in FIG. 7 according to the brightness gradient selection data.

Here, one cycle of the reference clock is 6 bi
This is the same as the cycle in which the t counter 20 counts from 0 to 63. The reference clock is 6 of the 6-bit counter 20.
The digit changes from "0" to "1", and then becomes "0", which is one cycle.

The 6-bit up / down counter 22 receives the pulse signal and the select clock output from the clock-select circuit 21. The 6-bit up / down counter 22 is synchronized with the select clock at the rising edge of the input pulse signal and is binary 6 digits (CT shown in FIG. 6).
6, CT5, ..., CT1 correspond to 6 to 1 digits of binary 6 digits. ) Count-up is started, and at the falling edge of the input pulse signal, binary 6 is synchronized with the select clock.
Start the digit countdown. The 6-bit up / down counter 22 outputs the count value to the comparator 23.

The comparator 23 is a 2-bit counter of the 6-bit counter 20.
The 6-digit decimal count value and the 6-bit up / down counter 22 count value are input. The comparator 23 has 6 bits
Until the count value of the counter 20 and the count value of the 6-bit up / down counter 22 match, P in the “H” state
Output the WM output signal. FIG. 8 is a specific circuit diagram of the comparator 23. The comparator 23 includes Ex-OR circuits Z2 to Z2.
It has a Z7, a NOR circuit Z8, an AND circuit Z9, and an RS-FF circuit Z10.

Terminals a1 to a of the Ex-OR circuits Z2 to Z7
6, each digit of the 6-bit counter 20 (CLK1, CL
K2, ..., CLK6) are input. Ex-OR circuit Z
The digits (CT1, CT2, ..., CT6) of the 6-bit up / down counter 22 are input to the terminals b1 to b6 of 2 to Z7. As a result, until the count value of the 6-bit counter 20 and the count value of the 6-bit up / down counter 22 match, the'H 'state is output from any of the Ex-OR circuits Z2 to Z7, and the NOR circuit Z8 is
Output'L 'state. If the count values match, Ex
The “L” state is output from all of the OR circuits Z2 to Z7, and the NOR circuit Z8 outputs the “H” state.

The RS-FF circuit Z10 is a NOR circuit Z8.
Input the output of as a set signal. NOR circuit Z8
Until the count value of the 6-bit counter 20 and the count value of the 6-bit up / down counter 22 match.
The "L" state is output and the RS-FF circuit Z10 outputs "H".
The PWM output signal of the state is output. When the count values match, the NOR circuit Z8 outputs the "H" state and RS-
The FF circuit Z10 outputs the PWM output signal in the'L 'state.

The count value of the 6-bit counter 20 is "6".
When it becomes 3 '(' 111111 '), the AND circuit Z9
Outputs the'H 'state, and the PW of the RS-FF circuit Z10
The M output signal is reset to the'H 'state.

That is, the comparator 23 includes the count value of the 6-bit counter 20 and the 6-bit up / down counter 2
PWM in'H 'state until the count value of 2 matches
The output signal is output, and then the PWM output signal in the “L” state is output. The comparator 23 outputs the “H” state again when the count value of the 6-bit counter 20 becomes “111111”.

The 4-bit counter 24 starts binary 4-digit counting in synchronization with the input clock CLKB and outputs the count value to the comparator 25. Comparator 25,
AND circuit 26, MOSFET Q2, resistor R11, LE
D27 is the comparator 15 according to the first embodiment, AND
Since the circuit 16, the MOSFET Q1, the resistor R1, and the LED 17 are the same as those of the circuit 16, the description thereof is omitted.

The operation of the LED control circuit according to the second embodiment will be described below. First, the operations of the 6-bit counter 20, the clock-select circuit 21, the 6-bit up / down counter 22, and the comparator 23 will be described.

The 6-bit counter 20 outputs a binary 6-digit count value synchronized with the input clock CLKA to the comparator 23. Simultaneously with this output, the sixth digit of the binary six digits is input to the clock-select circuit 21 as the reference clock.

The clock-select circuit 21 outputs the reference clock and the select clock obtained by dividing the reference clock to the 6-bit up / down counter 22 according to the brightness gradient selection data.

The 6-bit up / down counter 22 starts counting 6 binary digits in synchronization with the select clock at the same time as the rising edge of the input pulse signal, and outputs it to the comparator 23.

The comparator 23 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 and the count value of the 6-bit up / down counter 22 match. FIG. 9 is a diagram showing a PWM output signal waveform output from the comparator. FIG. 9A shows a case where the reference clock is output to the 6-bit up / down counter as a select clock, and FIG. When the divided select clock is output to the 6-bit up / down counter, (c) shows the PWM output signal waveform when the select clock obtained by dividing the reference clock by 3 is output to the 6-bit up / down counter.

When the reference clock is selected and output as the select clock by the clock-select circuit 21, the 6-bit up / down counter 22 counts up the count value in synchronization with the reference clock, as shown in FIG. 9A. I will do it. That is, in the 6-bit up / down counter 22, the 6-bit counter 20 sets the count value to 0.
Every time 63 counts are made, the count value is incremented by "1".

Here, the 6-bit up / down counter 2
The count value of 2 is set to "1"("000001").
The RS-FF circuit Z10, until the count value of the 6-bit counter 20 becomes "1"('000001'),
It outputs the PWM output signal in the “H” state. When the count value of the 6-bit counter 20 exceeds "1"("000001"), the PWM output signal in the "L" state is output. Furthermore, when the 6-bit counter 20 continues counting and the count value becomes '63'('111111'), a reset signal is output from the AND circuit Z9 and the RS-FF circuit Z
10 outputs the PWM output signal in the'H 'state.

Next, a 6-bit up / down counter 2
The value of 2 is counted up to '2'('000010'), and the RS-FF circuit Z10 operates as a 6-bit counter 20.
The PWM output signal in the “H” state is output until the count value of “2” (“000010”).

In this way, every time the 6-bit counter 20 counts the count value from "0" to "63", 6-bit counter 20
A PWM output signal having a pulse width T, 2T, 3T, 4T, ... Proportional to the count value of the it up / down counter 22 is output.

When a clock obtained by dividing the reference clock by 2 in the clock-select circuit 21 is selected and output as the select clock, as shown in FIG. 9B, 6 bi
The t up / down counter 22 counts up the count value in synchronization with the clock obtained by dividing the reference clock by two. That is, 6-bit up / down counter 2
2 indicates that the 6-bit counter 20 counts 0 to 63
Each time it repeats, the count value is incremented by "1".

Here, the 6-bit up / down counter 2
The value of 2 is set to '1'('000001'). RS-F
The F circuit Z10 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 becomes “1” (“000001”). When the count value of the 6-bit counter 20 exceeds "1"("000001"), the PWM output signal in the "L" state is output. Furthermore, 6b
The it counter 20 continues counting, and the count value is' 6.
When it becomes 3 '(' 111111 '), a reset signal is output from the AND circuit Z9, and the RS-FF circuit Z10 is
It outputs the PWM output signal in the “H” state.

The value of the 6-bit up / down counter 22 remains "1"("000001") and RS-FF.
The circuit Z10 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 becomes “1” (“000001”). After that, RS-FF circuit Z
10 outputs the PWM output signal in the'L 'state. RS
The FF circuit Z10 is reset when the count value of the 6-bit counter 20 becomes' 63 '(' 111111 '), and outputs the PWM output signal in the'H' state.

Next, the 6-bit up / down counter 2
The value of 2 is counted up to '2'('000010'), and the RS-FF circuit Z10 operates as a 6-bit counter 20.
The PWM output signal in the “H” state is output until the count value of “2” (“000010”).

In this way, the 6-bit counter 20
Every time "0" to "63" is repeated twice, the 6-bit up / down counter 22 increments the count value by "1". Then, every time the 6-bit counter 20 counts the count value from “0” to “63”, 6-bit counter 20
A PWM output signal having a pulse width T, T, 2T, 2T, ... Proportional to the count value of the up / down counter 22 is output.

When a clock obtained by dividing the reference clock by 3 in the clock-select circuit 21 is selected and output as the select clock, as shown in FIG. 9C, 6bi
The t up / down counter 22 counts up the count value in synchronization with the clock obtained by dividing the reference clock by three. That is, 6-bit up / down counter 2
2, the 6-bit counter 20 increments the count value by "1" each time the count of "0" to "63" is repeated three times.

Here, the 6-bit up / down counter 2
The value of 2 is "1"('000001'). RS-F
The F circuit Z10 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 becomes “1” (“000001”). When the count value of the 6-bit counter 20 exceeds "1"("000001"), the PWM output signal in the "L" state is output. Furthermore, 6b
The it counter 20 continues counting, and the count value is' 6.
When it becomes 3 '(' 111111 '), a reset signal is output from the AND circuit Z9, and the RS-FF circuit Z10 is
It outputs the PWM output signal in the “H” state.

The value of the 6-bit up / down counter 22 remains "1"("000001") and RS-FF
The circuit Z10 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 becomes “1” (“000001”), and then the RS-FF circuit Z1.
0 outputs the PWM output signal in the'L 'state. RS-
The FF circuit Z10 is reset when the count value of the 6-bit counter 20 becomes' 63 '(' 111111 '), and outputs the PWM output signal in the'H' state.

The above operation is further performed by the 6-bit counter 20.
Repeats until it counts "0" to "63". Next, the value of the 6-bit up / down counter 22 is "2".
It is counted up to ('000010') and RS-F
The F circuit Z10 outputs the PWM output signal in the “H” state until the count value of the 6-bit counter 20 becomes “2” (“000010”).

In this way, the 6-bit counter 20
Every time “0” to “63” is repeated three times, the 6-bit up / down counter 22 increments the count value by “1”. Then, every time the 6-bit counter 20 counts the count value from “0” to “63”, 6-bit counter 20
A PWM output signal having a pulse width T, T, T, 2T, ... Proportional to the count value of the up / down counter 22 is output.

Similarly, when the frequency division of the reference clock is increased, the PWM output signals having the same pulse width are repeatedly output by the number proportional to the frequency division. When the pulse signal input to the 6-bit up / down counter transits from the “H” state to the “L” state, the 6-bit up / down counter counts down the count value. Comparator 2
3 is a PWM having a pulse width proportional to the count value of the 6-bit up / down counter 22 being counted down.
Output the output signal. That is, the PWM output signal whose pulse width is gradually shortened is output, and the brightness of the LED 27 is gradually decreased.

Regarding the operations of the 4-bit counter 24, the comparator 25, and the AND circuit 26, the 4-bit counter 14, the comparator 15, and the comparator 15 described in the first embodiment,
The operation is the same as that of the AND circuit 16. The comparator 25 outputs a PWM output signal in the'H 'state that is proportional to the maximum brightness setting data. The AND circuit 26 outputs the PWM output signal output from the comparator 23 and the PW output from the comparator 23.
The logical product of the M output signals is calculated and output to the MOSFET Q2. The MOSFET Q2 turns on / off between the drain and the source according to the PWM output signal to blink the LED 27.

As described above, by changing the brightness gradient selection data and the maximum brightness setting data, the brightness gradient and the maximum brightness of the LED can be easily changed. In addition, since all are controlled by digital data, it is possible to prevent deterioration of blinking quality due to deterioration of parts such as capacitors.

Further, instead of controlling the interval at which the'H 'state of the PWM output signal is output, the PWM is output at a constant cycle.
Since the “H” state of the output signal is output and the width thereof is made variable, the flicker of the LED 27 can be prevented.

In the above description, the brightness gradient selection data and the maximum brightness setting data are 4-bit data, but they are not limited to these. In addition, the 6-bit counter 20 and the 6-bit up / down counter 22 are also 6-bit
The counter is not limited to t.

The 6-bit counter 20 and the clock-
Select circuit 21, 6-bit up / down counter 2
2, comparators 23, 25, 4 bit counter 24, and
The AND circuit 26 may be integrated as a monolithic semiconductor circuit. Thereby, the number of parts can be reduced.

[0088]

As described above, according to the present invention, the rising rate and the falling rate of the output voltage are changed according to the selection data,
Since the brightness gradient control pulse signal is output when the output voltage is higher than the triangular wave voltage output from the triangular wave oscillator, the brightness gradient of the LED can be changed by changing the selection data, and the brightness gradient of the LED can be easily changed. You can

Further, according to the present invention, when the count value of the binary counter and the count value of the binary counter are cycled a number of times corresponding to the selection data, the count value of the counter section for counting up and down. Since the brightness gradient control pulse signal is output until and match, the brightness gradient of the LED can be changed by changing the selection data, and the brightness gradient of the LED can be easily changed.

[Brief description of drawings]

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

2A and 2B are specific circuit diagrams of a variable capacitance circuit, in which FIG. 2A is a capacitance doubler circuit diagram, and FIG. 2B is a specific circuit diagram of the variable capacitance circuit.

FIG. 3 is a diagram showing voltage waveforms, where (a) is a voltage waveform of a pulse signal input to a constant current circuit, (b) is a voltage waveform input to a comparator, and (c) is a voltage output from the comparator. It is a figure which shows a waveform.

FIG. 4 is a diagram for explaining a PWM output signal output from an AND circuit, in which (a) shows that the maximum luminance setting data is' 000.
When the value is 1 ', the maximum brightness setting data is (001) in (b).
When the value is 0 ', the maximum brightness setting data is (001) in (c).
It is a figure which shows the state at the time of 1 '.

5A and 5B are explanatory diagrams for explaining the variation of the luminance gradient and the maximum luminance, FIG. 5A is a diagram showing a pulse signal input to the constant current circuit, FIG. 5B is a diagram showing variation of the luminance gradient, and FIG. FIG. 4 is a diagram showing a change in maximum brightness.

FIG. 6 is a circuit diagram of an LED control circuit according to a second embodiment of the present invention.

FIG. 7 is a select clock output from a clock-select circuit (reference clock and reference clock are 2, 3, 1
It is a figure which shows the select clock divided by 6.

FIG. 8 is a specific circuit diagram of the comparator 23.

FIG. 9 is a diagram showing a PWM output signal waveform output from a comparator, where FIG. 9A shows a case where a reference clock is output as a select clock to a 6-bit up / down counter.
(B) is a case where a select clock obtained by dividing the reference clock by 2 is output as a 6-bit up / down counter, (c)
Is 6bi for the select clock, which is the reference clock divided by 3.
PWM when t up / down counter is output
It is a figure which shows an output signal waveform.

FIG. 10 is an example of a conventional LED control circuit.

[Explanation of symbols]

10 constant current circuit 11 Triangular wave oscillator 12 capacity variable circuit 12a operational amplifier 12b, 12c Analog switch 13,15 Comparator 14,24 4-bit counter 16,26, Z9 AND circuit 17,27 LED 20 6-bit counter 21 Clock-select circuit 22 6-bit up / down counter 23,25 comparator Q1, Q2 MOSFET R1 to R11 resistance C1 capacitor Z2-Z7 Ex-OR circuit Z8 NOR circuit Z10 RS-FF circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jun Yabuzaki             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Hisayoshi Usui             Saitama Prefecture Kodama-gun Kamikawa-cho Otomoto character No. 300 Toyohara             18 Inside Saitama NEC Corporation F-term (reference) 5F041 BB13 BB26

Claims (11)

[Claims] 1. An LED control circuit for controlling blinking of an LED, comprising: a voltage output section for outputting an output voltage in which a rising rate and a falling rate of the voltage are varied according to selection data; a triangular wave oscillator for outputting a triangular wave voltage; An LED control circuit comprising: a voltage comparator that outputs a brightness gradient control pulse signal when the output voltage is higher than the triangular wave voltage; and a switching element that drives an LED by the brightness gradient control pulse signal. 2. The constant voltage circuit for supplying a constant current according to a control signal, and the capacity variable according to the selection data to charge and discharge the constant current output from the constant current circuit. 2. The LED control circuit according to claim 1, further comprising: a capacitance variable circuit that varies a rising rate and a falling rate of the voltage. 3. The capacitance variable circuit has a capacitance multiplication circuit, and varies a resistance value between an output terminal and a positive electrode terminal of an amplifier of the capacitance multiplication circuit according to the selection data to vary the capacitance. The LED control circuit according to claim 2, wherein: 4. A plurality of resistors and an analog switch that opens and closes a switch according to the selection data are connected between the output terminal and the positive electrode terminal, and the resistance value is a combination of the plurality of resistors when the switch is opened and closed. 4. The LED control circuit according to claim 3, wherein the LED control circuit is variable by changing. 5. A pulse output circuit which outputs a maximum brightness control pulse signal of a constant cycle having a pulse width according to setting data, and a logical product operation of the brightness gradient control pulse signal and the maximum brightness control pulse signal. 2. The LED according to claim 1, further comprising: a logical product circuit that outputs the result of the logical product operation to the switching element.
Control circuit. 6. The pulse output circuit includes a binary counter, and a count comparison circuit that outputs a predetermined voltage until the count value of the binary counter reaches the value of the setting data to generate the maximum brightness control pulse signal. The LED control circuit according to claim 5, further comprising: 7. An LED control circuit for controlling blinking of an LED, wherein a binary counter and a count value of the binary counter are counted up and down when a cycle corresponding to selected data is performed. A counter unit, a count comparator that outputs a brightness gradient control pulse signal until the count value of the binary counter and the count value of the counter unit match, and switching that drives an LED according to the brightness gradient control pulse signal. An LED control circuit comprising: an element. 8. The clock selection circuit, wherein the counter section outputs a reference clock using the most significant bit of the binary counter as a clock and a clock obtained by dividing the reference clock according to the selection data, and the clock select circuit. The LED control device according to claim 7, further comprising: a binary up / down counter that starts the count-up and the count-down in synchronization with a clock output from a circuit according to a control signal. 9. The counter comparator detects whether or not the count value of the binary counter and the count value of the counter unit match, and all the bits of the binary counter have the same value. When a reset signal is output, a reset circuit that outputs a reset signal is input, and the reset signal is input to output a predetermined voltage. 8. The LED control circuit according to claim 7, further comprising: a flip-flop circuit that outputs the predetermined voltage until it is detected that the brightness gradient control pulse signal is generated. 10. A pulse output circuit for outputting a maximum brightness control pulse signal of a constant cycle having a pulse width according to setting data, and a logical product operation of the brightness gradient control pulse signal and the maximum brightness control pulse signal. 8. The LED according to claim 7, further comprising: a logical product circuit that outputs the result of the logical product operation to the switching element.
Control circuit. 11. The pulse output circuit outputs a maximum brightness control binary counter and a predetermined voltage until the count value of the maximum brightness control binary counter reaches the value of the setting data. 11. The LED control circuit according to claim 10, further comprising: a maximum brightness control count comparator that generates a signal.