JP2019103289A - Power supply device and light irradiation system including the same - Google Patents

Abstract

To provide a power supply device connected to a light irradiation device including a light-emitting diode achieving accurate dimming without depending on a reference voltage error.SOLUTION: A power supply device 1 comprises a DCDC converter 2, a detection resistor R1, an instruction voltage generation unit 3, a comparator U2, a power supply unit 4, and a phase compensation unit 5. When a detection voltage Vsen is larger than an instruction voltage Vsp, the comparator U2 generates a high-level feedback voltage Vfb. When the detection voltage Vsen is smaller than the instruction vole Vsp, the comparator generates a low-level feedback voltage Vfb. When the feedback voltage Vfb is larger than an internal reference voltage, the DCDC comparator 2 decreases a driving current If of a light-emitting diode D1. When the feedback voltage Vfb is smaller than the reference voltage, the DCDC converter increases the driving current If.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power supply device that dims a light emitting diode using a DCDC converter.

  Patent Document 1 generates a drive current according to a light adjustment control signal having a level according to a target luminance of a light emitting element, and supplies a current driver to the light emitting element, a voltage drop of the current driver and a predetermined reference voltage. An error amplifier that amplifies an error and generates a feedback voltage, a pulse width modulator that adjusts the duty ratio of a gate pulse signal according to the feedback voltage, and a control characteristic that defines the relationship between the dimming control signal and the frequency of the gate pulse signal And a frequency control unit that causes the pulse width modulator to generate a gate pulse signal of a frequency according to the current dimming control signal.

  Patent Document 2 is based on an error amplifier which outputs an error amount between a detection voltage indicating a current value flowing in an LED array and a reference voltage K times (K = constant) to a PWM control circuit unit and an output signal of the error amplifier. And a PWM control circuit for outputting a PWM signal for supplying a direct current corresponding to the dimming level to the LED array by controlling on / off of the transistor.

JP, 2014-103001, A JP, 2015-225770, A

  However, Patent Document 1 relates to the reference voltage, as described in paragraph [0046], the error amplifier drops the voltage of the current driver, that is, the error between the lowest voltage among the voltages of the LED terminals and the predetermined reference voltage. There is only a description of amplification, and there is no description of the error of the reference voltage itself. Therefore, Patent Document 1 can not generate the problem of accurately dimming the light emitting diode without depending on the error of the reference voltage.

  In Patent Document 1, an error between a voltage drop of a current driver and a predetermined reference voltage is generated as a feedback voltage, and a feedback voltage is generated based on an error between a dimming control signal and a voltage drop of the current driver. The basic configuration is different from the present invention because it is not.

  In Patent Document 2, the amount of error between the detected voltage and the reference voltage is multiplied by K and output to the PWM control circuit unit. However, this reference voltage is a dimming voltage and not a DCDC converter reference voltage. Therefore, Patent Document 2 does not disclose the error of the reference voltage assumed by the present application.

  An object of the present invention is to provide a power supply device that dims a light emitting diode with high accuracy without depending on the error of the reference voltage of the DCDC converter.

The power supply device according to one aspect of the present invention is
Connected to a light emitting device having a light emitting diode (D1),
A DCDC converter (2) that generates a drive current for the light emitting diode (D1) by comparing the feedback voltage (Vfb) with a predetermined reference voltage (Vref), and a drive current (If) flowing through the light emitting diode (D1) Detection voltage (Vsen), a variable voltage section (31) generating an indication voltage (Vsp) for dimming the light emitting diode (D1), and a detection voltage (Vsen) And a comparator (U2) that generates a feedback voltage (Vfb) based on the command voltage (Vsp) and inputs it to the DCDC converter (2), the detection voltage (Vsen) is a command voltage When it is larger than (Vsp), a high level feedback voltage (Vfb) is generated, and the detection voltage (Vsen) becomes an instruction voltage (V). If smaller than p), a low level feedback voltage (Vfb) is generated, and if the feedback voltage (Vfb) is greater than the reference voltage (Vref), the DCDC converter (2) generates the drive current (If) of the light emitting diode (D1). ), And if the feedback voltage (Vfb) is smaller than the reference voltage (Vref), the drive current (If) is increased.

  According to this aspect, when the detection voltage (Vsen)> the command voltage (Vsp), the feedback voltage (Vfb) of high level is output from the comparator (U2), and thus the driving current (If) becomes Vfb> Vref. Decreases and the detection voltage (Vsen) decreases. The above is repeated, and the detection voltage (Vsen) is made equal to the command voltage (Vsp).

  On the other hand, when the detection voltage (Vsen) <the command voltage (Vsp), the low level feedback voltage (Vfb) is output from the comparator (U2), and the drive current (If) increases as Vfb <Vref. The detection voltage (Vsen) increases. The above is repeated, and the detection voltage (Vsen) is made equal to the command voltage (Vsp).

  Thus, the drive current (If) is controlled such that the detection voltage (Vsen) matches the command voltage (Vsp), and the drive current (If) is controlled to a value corresponding to the dimming level indicated by the command voltage. .

  Here, determination of presence / absence of coincidence between the command voltage (Vsp) and the detection voltage (Vsen) is executed by the comparator (U2), and the reference voltage (Vref) does not intervene. The detection voltage (Vsen) and the command voltage (Vsp) can be made to match precisely without dependency. As a result, accurate light control can be realized.

  In the above aspect, the comparator (U2) has a non-inverting input terminal (+) to which the detection voltage (Vsen) is input, an inverting input terminal (-) to which the instruction voltage (Vsp) is input, and a feedback voltage (Vfb) The power supply apparatus includes a first resistor (R5) connected between the inverting input terminal (-) and the variable voltage unit (31), an inverting input terminal (-), and an output terminal. And a second resistor (R7) and a capacitor (C5) provided therebetween.

  When the detected voltage changes rapidly, the capacitor (C5) functions and the gain of the comparator (U2) can be limited to a value determined by the ratio of the second resistor (R7) to the first resistor (R5). Abrupt change of Vfb) can be prevented, and loss reduction can be achieved.

  In the above aspect, the power supply device includes a third resistor (RA) connected between the anode of the light emitting diode (D1) and the feedback terminal of the DCDC converter (2), the feedback terminal, and the output terminal of the comparator (U2). And a fourth resistor (RB) connected between them.

  By providing these resistors (RA, RB), it is possible to prevent the problem that the output voltage from the DCDC converter (2) is not stable and the output voltage can not be controlled within a predetermined range. Thus, for example, the output voltage from the DCDC converter (2) can be set when the light emitting diode (D1) is in the open state due to a failure, and can be distinguished from the output voltage at the normal time. It is possible to detect

  According to the present invention, it is possible to accurately match the detection voltage and the instruction voltage without depending on the error of the reference voltage, so it is possible to realize the light adjustment with high accuracy.

It is a circuit diagram of the power supply device concerning a comparative example of the present invention. It is a circuit diagram of a power supply unit concerning an embodiment of the invention. It is a block diagram which shows the function structure of DCDC converter IC. FIG. 6 is a circuit diagram of a power supply device according to Embodiment 2 of the present invention.

(Process leading to the present invention)
As a conventional power supply device, there is one which supplies a constant drive current to a light emitting diode using a general DC-DC converter IC.

  In such a DC-DC converter IC, the reference voltage has an error of, for example, ± 1%. In this case, in the conventional power supply device in which the DCDC converter IC is incorporated, an error current of ± 0.01 A occurs when the maximum value of the drive current of the light emitting diode is 1A. In the conventional power supply, this error current is constant regardless of the drive current. Therefore, in the conventional power supply device, when the drive current is decreased for dimming, the ratio of the error current to the drive current is increased, and there is a problem that the light emitting diode can not be accurately dimmed.

  The details will be described below. FIG. 1 is a circuit diagram of a power supply device 100 according to a comparative example of the present invention. The power supply device 100 includes a DC / DC converter IC, an inductor L100, a detection resistor R100, and an adder A100, and is connected to the light emitting diode D100. The power supply Vcc is supplied to the anode of the DCDC converter IC and the light emitting diode D100.

  The adder A100 is an analog adder, adds the detection voltage Vsen and the instruction voltage Vsp in an analog manner, generates a feedback voltage Vfb, and outputs the feedback voltage Vfb to the DC-DC converter IC. The detection voltage Vsen is a detection voltage indicating the current value of the drive current If flowing to the light emitting diode D100. The instruction voltage Vsp is an instruction voltage for specifying the dimming level of the light emitting diode D100, and is instructed by the user, for example.

  The DCDC converter IC compares the feedback voltage Vfb input from the feedback terminal T100 with the predetermined reference voltage Vref, determines the duty ratio of the PWM signal so that the feedback voltage Vfb matches the reference voltage Vref, and the DCDC converter IC The built-in switch is turned on and off to generate an output voltage Vo, which is output from an output terminal T200. The inductor L100 smoothes the output voltage Vo to generate a drive current If of the light emitting diode D100. Since the reference voltage Vref is fixed regardless of the dimming level, to dim the light emitting diode D100, the drive current If is a current value corresponding to the dimming level, and the feedback voltage output from the adder A100 The instruction voltage Vsp may be determined such that Vfb is the same as the reference voltage Vref.

  The detection voltage Vsen is represented by Vsen = If × R100. Further, the feedback voltage Vfb is adjusted to be Vfb = Vref by the instruction voltage Vsp, and the adder A100 outputs the calculation result of Vsen + Vsp as Vfb, and therefore, it is expressed as Vsen = Vref−Vsp. Therefore, If × R100 = Vref−Vsp holds, the following equation (A) is obtained.

  If = (Vref-Vsp) / R100 (A)

  Here, it is assumed that R100 = 0.1Ω and Vref = 0.1V. In this case, it can be understood from equation (A) that in order to flow the drive current If of 1 A, V sp = 0 V may be set. Further, in order to flow the drive current If of 0.1 A, it is understood from the equation (A) that Vsp may be set to 0.09 V. Further, it can be understood from the equation (A) that Vsp = 0.099 V should be set in order to flow the drive current If of 0.001 A. Thus, assuming that 1 A is the maximum value of the drive current If, by adjusting the command voltage Vsp, the drive current If is adjusted to 1/10, 1/100, etc., and the dimming level is 1/10, It can be 1/100.

  By the way, in a general DC-DC converter IC, the reference voltage Vref generally has a predetermined error. Here, assuming that the error is plus or minus 1%, the reference voltage Vref has an error of plus or minus 0.001 V, so that Vref is 0.1 = 0.001 V.

  Therefore, when Vref = 0.1 ± 0.001 V and R100 = 0.1 Ω are substituted into the equation (A), the following equation (B) is obtained.

  If = (0.1 ± 0.001-Vsp) / 0.1 ... (B)

  As can be seen from this equation, the value of the error current with respect to the drive current If is ± 0.01 A (= 0.001 / 0.1) regardless of the dimming level. Therefore, when If = 1A, the ratio of the error to the drive current If is only ± 1%, but if If = 0.1A, the ratio of the error to the drive current If is ± 10%. When = 0.01 A, the ratio of the error to the drive current If reaches even ± 100%.

  Furthermore, since the output of the adder A100 also has a constant error, this error is superimposed on the error of the reference voltage Vref, and the ratio of the error to the drive current If further increases.

  As described above, in the power supply apparatus 100, the ratio of the error to the drive current If increases as the drive current If decreases. Therefore, there is a problem that light adjustment with low gradation can not be performed with high accuracy. In particular, the light source may be required to have a dimming level of, for example, about 100 steps, in inspection applications such as irradiating light to inspect scratches on a product or in UV curing applications in which a resin is cured by ultraviolet light. The power supply apparatus 100 can not meet this request.

  The present invention has been made in view of such a problem, and it is an object of the present invention to provide a power supply device capable of achieving accurate light adjustment by accurately matching a detection voltage and an instruction voltage without depending on an error of a reference voltage. It is.

Embodiment 1
Hereinafter, the power supply device 1 according to the embodiment of the present invention will be described. FIG. 2 is a circuit diagram of the power supply device 1 according to the embodiment of the present invention. The power supply device 1 includes a DCDC converter 2, a detection resistor R1, an instruction voltage generation unit 3, a comparator U2, a power supply unit 4, and a phase compensation unit 5, and includes, for example, a light emitting diode D1 for emitting visible light or ultraviolet light. It is connected to the light irradiation device 6. A light irradiation system 7 is configured by the power supply device 1 and the light irradiation device 6.

  The power supply unit 4 is configured of, for example, a power supply circuit that generates an input voltage Vin which is a DC voltage of a fixed level. The power supply unit 4 has a positive terminal connected to the PVin pin and SVin pin of the DC-DC converter IC 21 and a negative terminal connected to ground. The input voltage Vin is used as a drive voltage of the power supply device 1 input to the DC-DC converter IC21, the comparator U2, the operational amplifier U3, and the like.

  The DCDC converter 2 generates the drive current If of the light emitting diode D1 by comparing the feedback voltage Vfb output from the comparator U2 with the predetermined reference voltage Vref.

  The DCDC converter 2 includes a DCDC converter IC (integrated circuit) 21, capacitors C1, C3 and C4, and resistors R3 and R4. The DCDC converter IC 21 includes an SW pin, a PVin pin, an SVin pin, an Ith pin, an SHDN / Rt pin, an SGND pin, a PGND pin, and an FB pin.

  The SW pin is connected to the light emitting diode D1 through the inductor L1, and to the capacitor C4 through the inductor L1, and outputs the output voltage Vo of the DC-DC converter IC21. One end of the capacitor C4 is connected to the connection point K1 of the inductor L1 and the light emitting diode D1, and the other end is grounded. The PVin pin is a main power supply pin and receives an input voltage Vin. The SVin pin is a signal power supply pin and receives an input voltage Vin. The Ith pin is a pin for determining the reference voltage Vref. The Ith pin is grounded via a resistor R4 and a capacitor C1. The SHDN / Rt pin is a pin for determining the oscillation frequency of the oscillator provided in the DC-DC converter IC21. The SHDN / Rt pin is grounded via a resistor R3. The SGND pin is a main power supply ground pin for grounding the main power supply. The PGND pin is a signal power ground pin for grounding the signal power.

  One end of the capacitor C3 is connected to the connection point K2 of the plus terminal of the power supply unit 4 and the SVin pin, and the other end is grounded, and the input voltage Vin is stabilized.

  The inductor L1 is connected to the SW pin and, together with the capacitor C4, smoothes the output voltage Vo to generate a drive current If.

  The light emitting diode D1 has an anode connected to the connection point K1, a cathode connected to the connection point K3, and emits light by the drive current If. The connection point K3 is a connection point between the cathode of the light emitting diode D1 and one end of the detection resistor R1.

  One end of the detection resistor R1 is connected to the connection point K3, and the other end is grounded. The detection resistor R1 generates a detection voltage Vsen (= If · R1) indicating the value of the drive current If, and outputs the detection voltage Vsen to the non-inverting input terminal (+) of the comparator U2.

  The command voltage generation unit 3 includes a variable voltage unit 31 and an operational amplifier U3. The variable voltage unit 31 is configured of, for example, a variable voltage circuit that changes the instruction voltage Vsp in accordance with the dimming level instructed by the user. Here, the instruction voltage generation unit 3 is connected to an operation unit (not shown) that receives a light adjustment instruction from the user. The variable voltage unit 31 generates the command voltage Vsp so that the command voltage Vsp increases linearly, for example, as the dimming level instructed by the user increases.

  In the operational amplifier U3, the inverting input terminal (-) is connected to the output terminal, the positive terminal of the variable voltage unit 31 is connected to the non-inverting input terminal (+), the input voltage Vin is input to the positive side power supply terminal The power supply terminal is grounded and constitutes a voltage follower. Thereby, the command voltage Vsp is stabilized.

  In the comparator U2, the inverting input terminal (-) is connected to the connection point K4 of the resistor R5 and the resistor R7, and the instruction voltage Vsp is input. The non-inverting input terminal (+) of the comparator U2 is connected to the connection point K3, and the detection voltage Vsen is input. In the comparator U2, the input voltage Vin is input to the positive side power supply terminal, and the negative side power supply terminal is grounded. Furthermore, the output terminal of the comparator U2 is connected to the FB pin.

  The comparator U2 outputs the feedback voltage Vfb at a low level when the instruction voltage Vsp is larger than the detection voltage Vsen (Vsp> Vsen), and the high level when the instruction voltage Vsp is smaller than the detection voltage Vsen (Vsp <Vsen) Outputs the feedback voltage Vfb of The feedback voltage Vfb is input to the FB pin.

  The phase compensation unit 5 includes resistors R5 and R7 and a capacitor C5. One end of the resistor R5 is connected to the output terminal of the operational amplifier U3, and the other end is connected to the connection point K4. One end of the resistor R7 is connected to the connection point K4, and the other end is connected to the FB pin via the capacitor C5.

  When the detection voltage Vsen changes rapidly, the capacitor C5 functions to limit the gain of the comparator U2 to a value determined by the ratio of the resistor R7 to the resistor R5. As a result, it is possible to prevent the rapid change of the feedback voltage Vfb, and to reduce the loss of the power supply device 1.

  FIG. 3 is a block diagram showing a functional configuration of the DCDC converter IC21. The DCDC converter IC 21 includes a reference voltage generation unit 211, a PWM signal generation unit 212, a switch SW, and a diode 213. The reference voltage generation unit 211 generates a reference voltage Vref according to the values of the resistor R4 and the capacitor C1 connected to the Ith pin. In the present embodiment, it is assumed that the reference voltage Vref has an error of, for example, ± 1%, that is, 0.001 V at 0.1V. The error value of 1% is an example.

  The PWM signal generation unit 212 adjusts the duty ratio of the PWM signal supplied to the switch SW so that the feedback voltage Vfb matches the reference voltage Vref. In detail, when the feedback voltage Vfb is larger than the reference voltage Vref (Vfb> Vref), the PWM signal generation unit 212 reduces the duty ratio of the PWM signal supplied to the switch SW by a predetermined level to reduce the drive current If Let On the other hand, when the feedback voltage Vfb is smaller than the reference voltage Vref (Vfb <Vref), the PWM signal generation unit 212 increases the duty ratio of the PWM signal by a predetermined level to increase the drive current If. Furthermore, when the feedback voltage Vfb matches the reference voltage Vref, the PWM signal generation unit 212 maintains the duty ratio of the PWM signal at the current value. The PWM signal generation unit 212 includes an oscillator, and the frequency of the PWM signal is determined according to the oscillation frequency of the oscillator.

  The switch SW is formed of, for example, a switching element formed of a transistor such as a MOSFET or a bipolar transistor, and is turned on / off according to the PWM signal generated by the PWM signal generation unit 212. One terminal of the switch SW is connected to the capacitor C3 via the PVin pin, and an input voltage Vin is input. The switch SW has the other terminal connected to, for example, the cathode of the diode 213, and is connected to the inductor L1 via the SW pin. Further, the switch SW has a control terminal input with a PWM signal. In the diode 213, the cathode is connected to the other terminal of the switch SW, and the anode is grounded.

  When the switch SW is turned on, energy is charged to the inductor L1 by the input voltage Vin, and when the switch SW is turned off, the energy charged to the inductor L1 is discharged. By repeating this, the DC drive current If is supplied to the light emitting diode D1.

  Next, the operation of the power supply device 1 will be described. The reference voltage Vref is set to an intermediate value between the feedback voltage Vfb (Hi) and the feedback voltage Vfb (Lo).

  When the detection voltage Vsen is larger than the command voltage Vsp (Vsen> Vsp), the feedback voltage Vfb (Hi) of high level is output from the comparator U2, so that Vfb (Hi)> Vref. As a result, the DCDC converter IC 21 decreases the duty ratio of the PWM signal by a predetermined level to reduce the drive current If. As a result, the drive current If decreases, and the detection voltage Vsen (= If · R1) decreases with the decrease. The above is repeated, and the drive current If gradually decreases, and the detection voltage Vsen gradually decreases with the decrease, and eventually, the detection voltage Vsen matches the command voltage Vsp.

  On the other hand, when the detection voltage Vsen is smaller than the command voltage Vsp (Vsen <Vsp), the low-level feedback voltage Vfb (Lo) is output from the comparator U2, so Vfb (Lo) <Vref. Thus, the DCDC converter IC 21 increases the duty ratio of the PWM signal by a predetermined level to increase the drive current If. As a result, the drive current If increases, and the detection voltage Vsen (= If · R1) increases with the increase. The above is repeated, and the drive current If gradually increases, and the detection voltage Vsen gradually increases with the increase, and eventually, the detection voltage Vsen matches the command voltage Vsp.

  Thus, the drive current If is controlled such that the detection voltage Vsen matches the command voltage Vsp, and the light emitting diode D1 is dimmed at the dimming level indicated by the command voltage Vsp.

  Here, the determination as to whether the instruction voltage Vsp matches the detection voltage Vsen is performed by the comparator U2, and the reference voltage Vref is not present. Therefore, the detection voltage Vsen and the command voltage Vsp can be accurately matched without depending on the error of the reference voltage Vref. As a result, even if the drive current If is decreased to output light of low gradation from the light emitting diode D1, the ratio of the error of the reference voltage Vref to the drive current If does not increase, and light adjustment with high accuracy Can be realized.

Second Embodiment
FIG. 4 is a circuit diagram of a power supply device 1A according to a second embodiment of the present invention. In the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The difference between FIG. 4 and FIG. 2 is that resistors RA and RB are added.

  The resistor RA is connected between the anode of the light emitting diode D1 and the FB pin. The resistor RB is connected between the FB pin and the output terminal of the comparator U2. The resistors RA and RB are provided to prevent the problem that the output voltage Vo from the DC-DC converter IC 21 is not stabilized and the output voltage Vo can not be controlled within a predetermined range. As a result, for example, the output voltage Vo from the DCDC converter IC 21 can be set when the light emitting diode D1 is broken into an open state, and can be distinguished from the output voltage Vo in the normal state. It becomes possible.

  The present invention can adopt the following modifications.

  (1) In FIG. 2 and FIG. 4, the phase compensation unit 5 may be omitted.

  (2) In FIG. 2, FIG. 4, although the light emitting diode D1 was one, this is an example and the several light emitting diode D1 may be provided. In this case, the plurality of light emitting diodes D1 may be connected in series or in parallel. Alternatively, a plurality of series circuits each including a plurality of light emitting diodes D1 connected in series may be connected in parallel.

  (3) In FIG. 2 and FIG. 4, the DCDC converter IC 21 is not limited to a general one (commercially available), and may be configured by one originally developed by the inventor. Moreover, although the DCDC converter 2 is comprised by integrated DCDC converter IC21, you may be comprised by the circuit which is not integrated.

1,1A Power supply unit 2 DCDC converter 21 DCDC converter IC
31 Variable voltage part D1 Light emitting diode If Drive current R1 Detection resistance Vfb Feedback voltage Vref Reference voltage Vsen Detection voltage Vsp Instruction voltage

Claims (4)

What is claimed is: 1. A power supply connected to a light emitting device having a light emitting diode, comprising:
A DCDC converter generating a drive current of the light emitting diode by comparing a feedback voltage with a predetermined reference voltage;
A detection resistor that detects a drive current flowing through the light emitting diode and generates a detection voltage;
A variable voltage unit that generates an instruction voltage for dimming the light emitting diode;
And a comparator that generates a feedback voltage based on the detection voltage and the indication voltage, and inputs the feedback voltage to the DCDC converter.
The comparator generates the feedback voltage of high level when the detection voltage is larger than the indication voltage, and generates the feedback voltage of low level when the detection voltage is smaller than the indication voltage.
The DC-DC converter reduces the drive current of the light emitting diode when the feedback voltage is larger than the reference voltage, and raises the drive current when the feedback voltage is smaller than the reference voltage. The comparator includes a non-inverting input terminal to which the detected voltage is input, an inverting input terminal to which the instruction voltage is input, and an output terminal to output the feedback voltage.
A first resistor connected between the inverting input terminal and the variable voltage unit;
The power supply device according to claim 1, further comprising a second resistor and a capacitor provided between the inverting input terminal and the output terminal. A third resistor connected between the anode of the light emitting diode and the feedback terminal of the DCDC converter;
The power supply device according to claim 1, further comprising a fourth resistor connected between the feedback terminal and the output terminal of the comparator. A light emitting device having a light emitting diode;
The light irradiation system provided with the power supply device in any one of Claims 1-3.

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