JP7409209B2 - LED power supply device and LED dimming method - Google Patents

Description

The present invention relates to an LED power supply device and an LED dimming method that control an LED current flowing through an LED using an operational amplifier.

Generally, in an LED power supply device, the control voltage applied to the non-inverting input terminal of the operational amplifier 2 is changed by converting the LED current flowing through the LED into a voltage using a detection resistor and feeding back that value to the inverting input terminal of the operational amplifier 2. (For example, see Patent Document 1).

Japanese Patent Application Publication No. 2010-218969

However, the operational amplifier has an input offset voltage that is stochastically distributed in either positive polarity or negative polarity within the range specified in the data sheet. When the solid _line shown in FIG. 8(a) is the ideal characteristic (TYP), the LED current I with respect to the control voltage V _IN+ If there is variation up and down at the maximum value MAX) and the operational amplifier has a positive polarity input offset voltage, set the LED current I _LED to [0%] when the control voltage V _IN+ is set to 0 [mV]. I can't. Therefore, when the control voltage V _IN+ for a dimming signal such as a PWM signal is set as shown in FIG. 8(b), the LED current I _LED for the dimming signal also changes as shown by the dotted line in FIG. 8(c). There will be vertical variations within the input offset voltage distribution range for each device. This causes a problem in that when the operational amplifier has an input offset voltage of positive polarity, the LED current I _LED cannot be controlled to 0% even if the dimming signal is narrowed down to around 0%.

The present invention was made in view of such problems, and its purpose is to reduce _the LED current I to 0% by using a dimming signal even if the operational amplifier has a positive polarity input offset voltage. The object of the present invention is to provide an LED power supply device and an LED dimming method that can control the LED light intensity.

In order to achieve the above object, the LED power supply device and LED dimming method according to the present invention are configured as follows.
The LED power supply device of the present invention controls the LED current by feeding back the value of the LED current flowing through the LED to an inverting input terminal of an operational amplifier, and applying a control voltage based on a dimming signal to a non-inverting input terminal of the operational amplifier. The LED power supply device includes a bias circuit that biases an input offset voltage of the operational amplifier to the negative side by a bias voltage set to be higher than the maximum value of the input offset voltage on the positive side, and The present invention is characterized in that a value obtained by subtracting the input offset voltage is stored as offset correction data, and the characteristic of the control voltage with respect to the dimming signal is corrected in the positive direction of the control voltage by the amount of the offset correction data .
Further, in the LED dimming method of the present invention, the value of the LED current flowing through the LED is fed back to an inverting input terminal of an operational amplifier, and a control voltage based on a dimming signal is applied to a non-inverting input terminal of the operational amplifier to control the LED current. An LED dimming method in an LED power supply device for controlling an input offset voltage of the operational amplifier, wherein the LED power supply device controls an input offset voltage of the operational amplifier by a bias voltage set to be equal to or higher than the maximum value on the positive side of the input offset voltage. A bias circuit biased to the negative side is provided, the control voltage is set to 0 [mV] by inputting the dimming signal at the lowest level, and the measurement is performed with the inverting input terminal and the output terminal of the operational amplifier connected. The potential of the inverted input terminal is measured and stored as offset correction data, and the characteristic of the control voltage with respect to the dimming signal is corrected by the amount of the offset correction data in a positive direction of the control voltage. do.

The present invention has the advantage that even if the operational amplifier has a positive input offset voltage, the LED current can be controlled to 0% by the dimming signal.

1 is a circuit diagram showing the configuration of a first embodiment of an LED power supply device according to the present invention. 2 is a diagram for explaining a correction operation based on offset correction data by the microcomputer shown in FIG. 1. FIG. 2 is a circuit diagram showing a configuration of an input stage of the operational amplifier shown in FIG. 1. FIG. 2 is a diagram for explaining a correction operation based on power supply voltage correction data by the microcomputer shown in FIG. 1. FIG. It is a circuit diagram showing the composition of a 2nd embodiment of the LED power supply device concerning the present invention. It is a circuit diagram showing the composition of a 3rd embodiment of the LED power supply device concerning the present invention. It is a circuit diagram showing the composition of a 4th embodiment of the LED power supply device concerning the present invention. FIG. 3 is a diagram showing the relationship between a dimming signal, a control voltage, and an LED current in a conventional LED power supply device.

Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings.

(First embodiment)
Referring to FIG. 1, the LED power supply device of the first embodiment includes a _{DC power supply VDC} connected to the anode of LED1, an npn transistor Q1 connected in series between the cathode of LED1, and the ground terminal. It includes a detection resistor R1 and an LED control section 10 that controls an LED current _ILED based on a dimming signal.

The LED control unit 10 includes a microcomputer 11, a digital-to-analog converter (hereinafter referred to as DAC) 12, an operational amplifier 13, a bias circuit 14, a dimming signal input terminal D_IN and a correction data input terminal R of the microcomputer 11, and an operational amplifier 13. It has a non-inverting input terminal IN+, an inverting input terminal IN-, and an output terminal D_OUT.

The npn transistor Q1 has a collector connected to the cathode of the LED1, a base connected to the output terminal D_OUT, and an emitter connected to the ground terminal via the detection resistor R1.

The inverting input terminal IN- is connected to the connection point between the emitter of the npn transistor Q1 and the detection resistor R1, and receives a signal obtained by converting the LED current _ILED into a voltage by the detection resistor R1. As a result, the voltage at the output terminal D_OUT becomes V _IN- +V _be , the voltage V _IN- at the inverting input terminal IN- is fed back so that V _IN- = control voltage V _IN+ , and the LED current I _LED flowing through LED1 is controlled to be proportional to the control voltage V _IN+ .

The bias circuit 14 biases the input offset voltage of the operational amplifier 13 to the negative side by a bias voltage Vb set to be equal to or higher than the positive maximum value MAX of the input offset voltage of the operational amplifier 13. This is a circuit that always distributes the offset voltage on the negative polarity side.

Since the input offset voltage is always distributed on the negative polarity side by the bias circuit 14, the LED current I _LED with respect to the control voltage V _IN+ changes from the ideal characteristic (TYP) indicated by the solid line to the input indicated by the dotted line, as shown in FIG. 2(a). Even if variations occur up and down in the offset voltage distribution range (lower limit distribution MIN to upper limit distribution MAX), the LED current I _LED can be set to [0%] when the control voltage V _IN+ is set to 0 [mV]. .

Referring to FIG. 3, the input stage 20 of the operational amplifier 13 includes a constant current source 21, a differential pair 22 consisting of MOSFETs Q2 to Q5, and a current mirror circuit 23 consisting of MOSFETQ6 and MOSFETQ7, and an inverting input terminal IN-. The potential difference with the non-inverting input terminal IN+ is amplified and output as a voltage signal to the gain stage.

In the differential pair 22, the gate of MOSFETQ2 is connected to the inverting input terminal IN-, and the gate of MOSFETQ3 is connected to the non-inverting input terminal IN+. The constant current supplied from the constant current source 21 is directly supplied to the source of MOSFET Q5, whereas the constant current is supplied to the source of MOSFET Q4 via a bias resistor R2 functioning as a bias circuit 14. has been done. By setting the resistance value of the resistor R2 to an appropriate value, the input offset voltage of the operational amplifier 13 can always be distributed on the negative polarity side.

The microcomputer 11 is an information processing device that executes instructions written in a software program, and controls the dimming input from the dimming signal input terminal D_IN based on the ideal characteristics (TYP) of the control voltage V _IN+ with respect to the dimming signal. It outputs a digital signal for generating a control voltage V _IN+ according to the signal. The digital signal output from the microcomputer 11 is converted into a control voltage V _IN+ by the DAC 12 and applied to the non-inverting input terminal IN+.

The microcomputer 11 includes a memory 15 in which offset correction data is stored. The offset correction data is an input offset voltage that is biased to the minus side by the bias circuit 14 by more than the plus side maximum value MAX. Offset correction data measured at the time of shipment is input via the correction data input terminal R.

To measure the offset correction data, input a dimming signal of 0 [%], which is the lowest level, to the dimming signal input terminal D_IN to set the control voltage V _IN+ to 0 [mV], and connect the inverting input terminal IN- and the output. This is performed with the terminal D_OUT connected, and the potential of the inverting input terminal IN- is measured as offset correction data.

Note that the LED control unit 10 can be provided as a two-chip configuration of a microcomputer chip and an analog chip, housed in the same package. Further, the npn transistor Q1, the detection resistor R1, and the LED control section 10 may be housed and provided in the same package. In this case, in order to measure offset correction data, it is preferable to provide the inverting input terminal IN- and the output terminal D_OUT as external terminals.

The microcomputer 11 changes the ideal characteristic (TYP) of the control voltage V _IN+ with respect to the dimming signal to the positive direction of the control voltage V IN+ by the offset correction data stored in the memory 15, that is, the input _offset voltage biased by the bias circuit 14. Fix it. As a result, the ideal characteristic (TYP) and distribution range of the control voltage V _IN+ for the dimming signal shown in the actual situation and the dotted line in FIG. will be corrected in a positive direction by the value obtained by subtracting . Thereby, the LED current I with respect to the dimming signal The dimming characteristic of _{the LED} can be made close to ideal, as variations due to the input offset voltage are canceled out, as shown in FIG. 2(c).

Note that the upper limit of the control voltage V _IN+ is determined by the power supply voltage of the DAC 12, etc., and the power supply voltage of the DAC 12, etc. has variations. Therefore, the upper limit voltage of the control voltage V _IN+ is stored in the memory 15 as power supply voltage correction data, and the microcomputer 11 stores the characteristics of the control voltage V _IN+ for the dimming signal corrected based on the offset correction data as the power supply voltage correction data. Further modifications may be made based on this. Power supply voltage correction data measured at the time of shipment is input via the correction data input terminal R.

To measure the power supply voltage correction data, input the highest level dimming signal of 100% to the dimming signal input terminal D_IN, and connect the inverting input terminal IN- to any voltage (ground terminal, output terminal D_OUT, etc.). This is carried out in the connected state, and the potential of the non-inverting input terminal IN+ is measured as power supply voltage correction data.

As a result, as shown in FIG. 4(a), after the characteristics of the control voltage V _IN+ with respect to the dimming signal are corrected based on the offset correction data, as shown in FIG. Based on this, the upper limit and slope of the control voltage V _IN+ can be modified.

(Second embodiment)
Referring to FIG. 5, in the LED power supply device of the second embodiment, the LED control unit 10a is provided with a buffer 16, a low-pass filter consisting of a resistor R3, and a capacitor C1 instead of the DAC 12. There is no particular restriction on the configuration for generating the control voltage V _IN+ in this way.

(Third embodiment)
Referring to FIG. 6, in the LED power supply device of the third embodiment, an LED control section 10 is incorporated in a step-down chopper type switching power supply. The PWM generation section 30 generates a PWM signal with a duty ratio based on the control signal output from the output terminal D_OUT of the LED control section 10, and drives the switching element Q6 with the generated PWM signal. Thereby, the LED current I _LED is feedback-controlled to a value based on the dimming signal input from the dimming signal input terminal D_IN of the LED control section 10. As described above, the LED power supply device according to the present invention can be incorporated into various switching power supplies such as a step-up type and a buck-boost type.

(Fourth embodiment)
Referring to FIG. 7, the LED power supply device of the fourth embodiment is an LED drive device that converts AC input power into desired DC output power and supplies it to LED1, and is a connection point between LED1 and npn transistor Q1. The primary side control section 40 controls the DC output power to a predetermined value by controlling the MOSFET Q9 to turn on and off based on the feedback voltage.

Although constant voltage control is performed by the primary side control unit 40, a ripple voltage occurs in the voltage applied to the LED 1, so a ripple current also occurs in the LED current I _LED . Therefore, the LED control unit 10 reduces the ripple voltage and reduces the ripple current of the LED current I _LED . That is, the LED control unit 10 has a dimming function to control the LED current I _LED and a function to reduce the ripple current flowing through the LED 1. Thereby, the LED current I _LED can be controlled to around 0%, and the ripple current flowing through the LED 1 can be reduced, so that stable dimming with less flickering of the LED 1 can be performed.

As explained above, in this embodiment, the value of the LED current I flowing through _LED1 is fed back to the inverting input terminal IN- of the operational amplifier 13, and the control voltage based on the dimming signal is applied to the non-inverting input terminal IN+ of the operational amplifier 13. This is an LED power supply device that controls the LED current I _LED by applying V _IN+ , and the input offset voltage of the operational amplifier 13 is set to the negative side by the bias voltage Vb set to be greater than the positive side maximum value MAX of the input offset voltage. The present invention is characterized in that it includes a bias circuit 14 that applies a bias to.
With this configuration, even if the operational amplifier has a positive polarity input offset voltage, the LED current I _LED can be controlled to 0% by the dimming signal.

Furthermore, in this embodiment, the value obtained by subtracting the input offset voltage from the bias voltage Vb is stored in the memory 15 as offset correction data, and the characteristics of the control voltage V _IN+ with respect to the dimming signal are determined by adding the input offset voltage to the bias voltage _Vb. Correct the offset correction data in the direction.
With this configuration, variations due to the input offset voltage can be canceled out, and the dimming characteristics of _the LED current I in response to the dimming signal can be made close to ideal.

Furthermore, in this embodiment, the upper limit voltage of the control voltage V _IN+ is stored in the memory 15 as power supply voltage correction data, and the characteristics of the control voltage V _IN+ with respect to the dimming signal corrected based on the offset correction data are , correct the upper limit and slope of the control voltage V _IN+ based on the power supply voltage correction data.
With this configuration, the upper limit and slope of the control voltage V _IN+ with respect to the dimming signal can be corrected, and the dimming characteristics of the LED current I with respect to _the dimming signal can be made closer to the ideal.

Note that it is clear that the present invention is not limited to the above embodiments, and that the embodiments can be modified as appropriate within the scope of the technical idea of the present invention. Further, the number, position, shape, etc. of the above-mentioned constituent members are not limited to the above-mentioned embodiment, but can be set to a suitable number, position, shape, etc. for implementing the present invention. In addition, in each figure, the same code|symbol is attached to the same component.

1 LED
10, 10a LED control section 11 Microcomputer 12 DAC
13 Operational amplifier 14 Bias circuit 15 Memory 16 Buffer 20 Input stage 21 Constant current source 22 Differential pair 23 Current mirror circuit 30 PWM generation section 40 Primary side control section D_IN Dimming signal input terminal IN+ Non-inverting input terminal IN- Inverting input terminal D_OUT Control signal output terminal R Correction data input terminal R1 Detection resistor R2 Bias resistor R3 Resistor Q1 NPN transistor Q2, Q3, Q4, Q5, Q6, Q7 MOSFET
Q8, Q9 switching element

Claims (4)

An LED power supply device that controls the LED current by feeding back the value of an LED current flowing through the LED to an inverting input terminal of an operational amplifier, and applying a control voltage based on a dimming signal to a non-inverting input terminal of the operational amplifier,
comprising a bias circuit that biases the input offset voltage of the operational amplifier to the negative side by a bias voltage set to be higher than the maximum value of the input offset voltage on the positive side ;
A value obtained by subtracting the input offset voltage from the bias voltage is stored as offset correction data,
An LED power supply device characterized in that the characteristics of the control voltage with respect to the dimming signal are corrected in a positive direction of the control voltage by the amount of the offset correction data . storing an upper limit voltage of the control voltage as power supply voltage correction data;
2. An upper limit and a slope of the control voltage are corrected based on the power supply voltage correction data with respect to a characteristic of the control voltage for the dimming signal that has been corrected based on the offset correction data. LED power supply device. An LED dimming method in an LED power supply device, which controls the LED current by feeding back the value of the LED current flowing through the LED to an inverting input terminal of an operational amplifier and applying a control voltage based on a dimming signal to a non-inverting input terminal of the operational amplifier. And,
The LED power supply device includes a bias circuit that biases the input offset voltage of the operational amplifier to the negative side by a bias voltage set to be higher than the maximum value of the input offset voltage on the positive side,
Inputting the dimming signal at the lowest level to set the control voltage to 0 [mV], and offset-correcting the potential of the inverting input terminal measured with the inverting input terminal and output terminal of the operational amplifier connected. Measure and store it as data,
An LED dimming method, characterized in that the characteristics of the control voltage with respect to the dimming signal are corrected in a positive direction of the control voltage by the amount of the offset correction data. inputting the dimming signal at the highest level, measuring and storing the potential of the non-inverting input terminal as power supply voltage correction data with the inverting input terminal of the operational amplifier connected to an arbitrary voltage;
4. The upper limit and slope of the control voltage are corrected based on the power supply voltage correction data with respect to the characteristics of the control voltage for the dimming signal that have been corrected based on the offset correction data. LED dimming method.

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