JP2007208109A - Led control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED control circuit which alleviates a load on a CPU and adjusts the brightness and brightness gradient of an LED in a free and complicated manner. <P>SOLUTION: Data signals in periods A, B, C, and D are inputted to a DAC circuit 12, in which a period A maintains a minimum output voltage, a period B switches the minimum output voltage to a maximum output voltage with a data signal of a count circuit 11 corresponding to an input clock, a period C maintains the maximum output voltage, and a period D switches the maximum output voltage to a minimum output voltage with a data signal of the count circuit 11. The count circuit 11 repeats counting in the increasing order of the period A, period B, period C, and period D (e.g., counting voltage up and down between the preset minimum and maximum and repeating that counting in a preset number of times). Each period can be changed by selecting and adjusting a clock cycle separately for each operation at a clock selection circuit 10, which enables a complicated variation in a brightness gradient in an increase and decrease of the brightness of the LED. A power voltage supplied to the DAC circuit 12 is supplied from a power supply circuit 13 based on maximum brightness setting data, thus allowing a change in the maximum brightness of the LED. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control circuit for blinking or lighting an LED (Light Emitting Diode), and more particularly to an LED control circuit capable of adjusting the luminance gradient and maximum luminance of an LED.

  In recent years, there are many electronic devices equipped with LEDs such as mobile phones. The LED plays a role of transmitting information in a blinking or lighting manner, and the blinking operation is also used for decoration. For this reason, there is a need for an LED control circuit that enables more free and complex LED brightness gradient and brightness adjustment.

  As a conventional LED control circuit, a PWM type LED control circuit can be cited. FIG. 3 is a block diagram showing a conventional LED control circuit based on the PWM method. As shown in FIG. 3, the data output from the CPU 1 and set in the drive current setting decoder 2 is compared with the actual output voltage in the PWM circuit 3. The comparison result is applied to the gate terminal of the transistor (FET) 5 of the LED driver 4 as a gate control pulse. The transistor 5 is connected so that a current flows through the LED 7 when it is turned on. By adjusting the on / off ratio of the transistor 5, the brightness gradient and brightness adjustment of the LED 7 can be set with a high degree of freedom.

Examples of such PWM type LED control circuits include LED control circuits such as Patent Document 1 and Patent Document 2. The LED control circuit of Patent Document 1 uses a variable capacitance circuit for adjusting the luminance gradient. Patent Document 2 discloses an LED control circuit that uses a counter to adjust the on / off ratio.
JP 2003-264316 A JP 2004-205669 A

  However, in the PWM type LED control circuit having such a configuration, for example, when it is desired to blink the LED so that the firefly shines by continuously changing the load current set value, the set value data is sequentially sent from the CPU to the PWM circuit. Need to continue. For this reason, there has been a problem that as the method of blinking or lighting the LED becomes more complicated, the burden on the CPU increases.

  The present invention is directed to solving the problems of the background art, and provides an LED control circuit that can reduce the burden on the CPU and can adjust the brightness gradient and brightness of LEDs more freely and complexly. Objective.

  In order to achieve the above object, an LED control circuit according to claim 1 of the present invention includes a clock selection circuit that selects and outputs a predetermined clock based on first input data, and a predetermined clock according to the clock. A count circuit that generates a data signal, a DAC (Digital Analog Converter) circuit that inputs a data signal and outputs a voltage corresponding to the input, and a current drive circuit that passes a current corresponding to the output of the DAC circuit to the LED It is characterized by having.

  In addition, the power supply circuit for supplying a power supply voltage based on the second input data to the DAC circuit is provided, the first input data is data for setting the brightness gradient of the LED, and the second input data is the maximum of the LED. It is data for setting brightness.

  The power supply circuit has the same configuration as that of the DAC circuit according to claim 1, the second input data is input instead of the data signal, and the count circuit has a minimum output of the DAC circuit in the first period. The output of the DAC circuit sequentially increases from the minimum value to the maximum value in the second period, the output of the DAC circuit becomes the maximum value in the third period, and the output of the DAC circuit increases from the maximum value in the fourth period. Generating a data signal that sequentially decreases to the minimum value, and the clock selection circuit selects a clock used in the first to fourth periods from a plurality of types of clocks according to the first input data, and outputs the selected clock to the count circuit; The current driving circuit includes a transistor connected in series with the LED, a current detector that detects a current flowing through the LED, and a control terminal of the transistor so that the output of the current detector is equal to the output of the DAC circuit. Characterized by comprising an amplifier circuit which outputs a signal to.

  According to the above configuration, the control time in the CPU software can be shortened, and the LED current can be controlled based on the luminance gradient and the input data for luminance adjustment when the LED is blinking or lighting.

  According to the present invention, the control time of the CPU software is short, and the LED current can be controlled with a high degree of freedom in setting the brightness gradient and brightness adjustment when the LED is blinking or lighting.

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

  FIG. 1 is a configuration diagram of an LED control circuit according to an embodiment of the present invention. In FIG. 1, as in the conventional example shown in FIG. 3, reference numeral 7 denotes an LED, which is connected in series with the transistor 5. Reference numeral 9 denotes a first reference voltage source that supplies a power supply voltage to the LED 7. A clock selection circuit 10 selects and outputs a predetermined clock based on the luminance gradient setting data from the CPU. A count circuit 11 outputs a data signal according to the input clock. A DAC circuit 12 receives a data signal from the count circuit 11 and outputs a power supply voltage based on the input data signal. Reference numeral 13 denotes a power supply circuit. For example, a power supply voltage based on the maximum luminance setting data input from the CPU is output and supplied to the DAC circuit 12 with the same configuration as the DAC circuit 12 described above. Reference numeral 14 denotes a current driving circuit, which includes an operational amplifier 18 and a transistor 5. Reference numeral 16 denotes a current detector composed of a resistor, which detects a current flowing through the transistor 5. The operational amplifier 18 receives the output voltage of the DAC circuit 12 and the voltage detected by the current detector 16 and outputs a voltage to the gate terminal of the transistor 5. Reference numeral 19 denotes a second reference voltage source that supplies a power supply voltage to the power supply circuit 13.

  FIG. 2 is an operation waveform diagram showing the LED current by the LED control circuit in the present embodiment shown in FIG. The operation of the LED control circuit shown in FIG. 1 will be described below with reference to FIG.

  Further, as a control drive of the LED shown in FIG. 2, a period A during which the minimum output voltage is held, and a maximum output voltage that is carried by 1 bit from the minimum output voltage based on the data signal output from the count circuit 11 by the input clock. Period B (for example, [0,0,0] → [0,0,1] →... [1,1,0] → [1,1,1] in the case of a 3-bit DAC circuit) And a period C during which the maximum output voltage is held, and an operation of switching down to the minimum output voltage by dropping by 1 bit from the maximum output voltage based on the data signal of the count circuit 11 (for example, in the case of a 3-bit DAC circuit [1 , 1, 1] → [1, 1, 0] →... [0, 0, 1] → [0, 0, 0]).

  As the data signal input to the DAC circuit 12 in FIG. 1, the count circuit 11 sets the above four operations in the order of period A → period B → period C → period D (for example, from the set minimum value). Count up or down between the maximum values, and repeat this count a set number of times). Further, the operation times of the period A, the period B, the period C, and the period D are determined by the clock period, and by preparing several types of clocks having different periods, the clock selection circuit 10 causes the period A, the period B, The clock cycle can be individually selected in each operation of period C and period D. By doing in this way, it becomes possible to change each operation time of the period A, the period B, the period C, and the period D freely, and the brightness | luminance gradient of a raise and fall of LED brightness can be changed complicatedly.

  Further, the power supply voltage supplied to the DAC circuit 12 is supplied as an output voltage based on the maximum brightness setting data by the power supply circuit 13, so that the maximum output voltage of the DAC circuit 12, that is, the LED maximum brightness can be freely changed. It becomes.

  As described above, the adjustment of the LED current by the LED control circuit according to the present embodiment is managed by the count circuit 11. Therefore, once the maximum luminance setting and the luminance gradient setting are made, the LED driving is performed by inputting the start bit. The CPU does not need to send the LED setting data until the operation set in the count circuit 11 is completed after starting the operation, and the load on the CPU is remarkably reduced as compared with the conventional PWM method. As a result, it is possible to realize control of blinking or lighting of the LED with a light burden on the CPU and a high degree of freedom.

  The LED control circuit according to the present invention has a short control time in the CPU software, and can control the LED current with a high degree of freedom in setting the brightness gradient and the brightness adjustment in the blinking or lighting of the LED. This is useful as a control circuit for adjustment.

The block diagram of the LED control circuit in embodiment of this invention Operation waveform diagram showing LED current by LED control circuit of this embodiment Configuration diagram of conventional LED control circuit

Explanation of symbols

1 CPU
2 Drive current setting decoder 3 PWM circuit 4 LED driver 5 Transistor 7 LED
9, 19 Reference voltage source 10 Clock selection circuit 11 Count circuit 12 DAC circuit 13 Power supply circuit 14 Current drive circuit 16 Current detector 18 Operational amplifier

Claims (7)

  A clock selection circuit that selects and outputs a predetermined clock based on the first input data, a count circuit that generates a predetermined data signal according to the clock, and the data signal are input, and a voltage corresponding to the input is set. An LED control circuit comprising: a DAC circuit for outputting; and a current driving circuit for causing a current corresponding to the output of the DAC circuit to flow through the LED.   2. The LED control circuit according to claim 1, further comprising a power supply circuit that supplies a power supply voltage based on second input data to the DAC circuit.   2. The LED control circuit according to claim 1, wherein the first input data is data for setting a luminance gradient of the LED.   3. The LED control circuit according to claim 2, wherein the second input data is data for setting a maximum luminance of the LED.   5. The LED control circuit according to claim 2, wherein the power supply circuit has the same configuration as that of the DAC circuit according to claim 1 and inputs second input data instead of a data signal. In the count circuit, the output of the DAC circuit has a minimum value in the first period, the output of the DAC circuit sequentially increases from the minimum value to the maximum value in the second period, and the output of the DAC circuit in the third period. Generates a data signal in which the output of the DAC circuit decreases sequentially from the maximum value to the minimum value in the fourth period,
2. The LED according to claim 1, wherein the clock selection circuit selects a clock used in the first to fourth periods from a plurality of types of clocks according to first input data, and outputs the clock to the count circuit. Control circuit.   The current drive circuit includes a transistor connected in series with the LED, a current detector that detects a current flowing through the LED, and a control terminal of the transistor so that the output of the current detector is equal to the output of the DAC circuit. The LED control circuit according to claim 1, further comprising an amplifier circuit that outputs a signal.

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