JP5420384B2 - Constant current power supply - Google Patents

Description

  The present invention relates to a constant current power supply device.

  Conventionally, there is a constant current power supply device as a power source that outputs a constant current. This constant current power supply device is used, for example, for lighting a light emitting diode (see, for example, Patent Document 1).

[Configuration of Constant Current Power Supply Device 100]
FIG. 5 is a circuit diagram of a constant current power supply device 100 according to a conventional example. The constant current power supply device 100 supplies constant current to a plurality of light emitting diodes LED1 to LEDn (n is an integer satisfying n ≧ 3) connected in series by using AC power input from the AC power supply Vin. The constant current power supply device 100 includes a rectifying unit RF, a diode D1, a capacitor C1, an inductor L, a switch element Q1 composed of an N-channel MOSFET, a resistor R1, a comparator CMP, a DC power supply Vref, A clock generation unit CLK and a flip-flop FF.

  Both ends of the AC power source Vin are connected to the two input terminals of the rectifying unit RF. A cathode of the diode D1, one electrode of the capacitor C1, and an anode of the light emitting diode LED1 are connected to the first output terminal of the rectifying unit RF. The other electrode of the capacitor C1 and one end of the inductor L are connected to the cathode of the light emitting diode LEDn. The other end of the inductor L is connected to the anode of the diode D1 and the drain of the switch element Q1.

  The second output terminal of the rectifying unit RF corresponding to the reference potential point of the constant current power supply device 100 is connected to the source of the switch element Q1 via the resistor R1, and the inverting input terminal of the comparator CMP is connected. Is done. The non-inverting input terminal of the comparator CMP is connected to the positive electrode of the DC power supply Vref, and the negative electrode of the DC power supply Vref is grounded.

  The reset terminal of the flip-flop FF is connected to the output terminal of the comparator CMP. The clock generation unit CLK is connected to the set terminal of the flip-flop FF, and the gate of the switch element Q1 is connected to the output terminal of the flip-flop FF.

[Operation of Constant Current Power Supply Device 100]
The constant current power supply device 100 having the above configuration performs constant current control by controlling the switch element Q1 according to the drain current of the switch element Q1.

  Specifically, when the switch element Q1 is turned on, the AC power supplied from the AC power source Vin is rectified by the rectifying unit RF, and the DC power based on the second output terminal is supplied from the first output terminal. Output. The direct current output from the first output terminal of the rectifying unit RF is transmitted through the light emitting diodes LED1 to LEDn, one end to the other end of the inductor L, the switch element Q1, and the resistor R1. It flows to the second output terminal. According to this, since a current flows through the light emitting diodes LED1 to LEDn, the light emitting diodes LED1 to LEDn are turned on. Further, when current flows from one end of the inductor L to the other end, energy is stored in the inductor L.

  The current flowing through the switching element Q1, that is, the drain current of the switching element Q1, is converted into a voltage by flowing through the resistor R1 and input to the inverting input terminal of the comparator CMP. Here, during the period in which the switch element Q1 is in the on state, the current flowing from one end of the inductor L to the other end increases as time elapses. Further, during the period in which the switch element Q1 is in the ON state, the drain current of the switch element Q1 is equal to the current flowing from one end of the inductor L to the other end. The voltage input to the inverting input terminal of the comparator CMP increases as the drain current of the switch element Q1 increases. As described above, during the period in which the switch element Q1 is in the ON state, the voltage input to the inverting input terminal of the comparator CMP becomes higher as time passes.

  When the voltage input to the inverting input terminal of the comparator CMP becomes equal to or higher than the voltage output from the positive electrode of the DC power supply Vref, the comparator CMP outputs an H level voltage. On the other hand, when the voltage input to the inverting input terminal of the comparator CMP becomes less than the voltage output from the positive electrode of the DC power supply Vref, the comparator CMP outputs an L level voltage.

  For this reason, when the voltage input to the inverting input terminal of the comparator CMP increases as time elapses and becomes equal to the voltage output from the positive electrode of the DC power supply Vref, the comparator CMP outputs an H level voltage. . Then, the flip-flop FF to which the H level voltage is input outputs an L level gate signal, and the switch element Q1 to which the L level gate signal is input is turned off.

  When the switch element Q1 is turned off, current flows in the order from one end of the inductor L to the other end, the diode D1, and the light emitting diodes LED1 to LEDn due to the energy stored in the inductor L during the period in which the switch element Q1 is on. The light emitting diodes LED1 to LEDn are turned on. The energy stored in the inductor L during the period when the switch element Q1 is in the ON state decreases as the current flows in the order described above, and the current flowing in the order described above is stored in the inductor L during the period when the switch element Q1 is in the ON state. Decreases as the energy consumed decreases. For this reason, when the switch element Q1 is turned off, the current flowing from one end of the inductor L to the other end decreases as time elapses.

  When the switch element Q1 is turned off, the drain current of the switch element Q1 becomes “0”, so that “0” is input to the inverting input terminal of the comparator CMP. For this reason, since the voltage input to the inverting input terminal of the comparator CMP is less than the voltage output from the positive electrode of the DC power supply Vref, the comparator CMP outputs an L level voltage. Then, the flip-flop FF to which the L level voltage is input outputs an H level gate signal at the rise of the clock signal, which is a periodic signal output from the clock generation unit CLK, and the H level gate signal is input. The switch element Q1 to be turned on is turned on.

  Note that the current flowing through the light emitting diodes LED1 to LEDn is smoothed by the capacitor C1.

As described above, the constant current power supply device 100 compares the voltage of the positive electrode of the DC power supply Vref, that is, a predetermined constant voltage with the voltage converted from the drain current of the switch element Q1, and compares the result. The switch element Q1 is controlled according to the above. Therefore, as shown in FIGS. 6 and 7, the peak value of the voltage at the inverting input terminal of the comparator CMP (see VNEG _CMP in FIGS. 6 and 7) to which the voltage converted version of the drain current of the switch element Q1 is input. Is a constant value equal to the voltage at the non-inverting input terminal of the comparator CMP to which a constant voltage is input (see VPOS _CMP in FIGS. 6 and 7).

FIG. 6 is a first timing chart of the constant current power supply device 100. VOUT _RF indicates a voltage output from the first output terminal of the rectifying unit RF, and IOUT _RF indicates a current output from the first output terminal of the rectifying unit RF. VNEG _CMP indicates the voltage of the inverting input terminal of the comparator _CMP , and VPOS _CMP indicates the voltage of the non-inverting input terminal of the comparator CMP. I _LED indicates a current flowing through each of the light emitting diodes LED1 to LEDn.

FIG. 7 is a partially enlarged view of FIG. 6 showing the relationship between the voltage VNEG CMP at the inverting input terminal of the comparator _CMP and the voltage VPOS _{CMP at} the non-inverting input terminal of the comparator CMP.

As described above, the peak value of the voltage VNEG _CMP at the inverting input terminal of the comparator CMP is a constant value equal to the voltage VPOS _CMP at the non-inverting input terminal of the comparator CMP. Therefore, the constant current power supply device 100 narrows the ON width of the switch element Q1 as the voltage VOUT _RF output from the first output terminal of the rectifying unit RF increases in order to continue supplying a constant current to the supply destination. Thus, the duty ratio of the switch element Q1 is reduced. Therefore, as shown in FIG. 6, as the voltage VOUT _RF output from the first output terminal of the rectifier unit RF increases, the current IOUT _RF output from the first output terminal of the rectifier unit RF decreases. ing.

JP 2005-116572 A

As described above, the peak value of the voltage at the inverting input terminal of the comparator CMP is a constant value equal to the voltage at the non-inverting input terminal of the comparator CMP. Here, since the voltage at the inverting input terminal of the comparator CMP is equal to the voltage conversion of the drain current of the switch element Q1, the peak value of the drain current of the switch element Q1 (see ID _Q1 in FIG. 8) is also shown in FIG. As shown in FIG.

FIG. 8 is a second timing chart of the constant current power supply device 100. More specifically, FIG. 8A is a timing chart of the constant current power supply device 100 at a constant load, and FIG. 8B is a lighter load than that of FIG. 8A. It is a timing chart of the constant current power supply device 100 at the time of load. Here, the light load means that, for example, the number of the plurality of light emitting diodes LED1 to LEDn connected in series decreases, or the rising voltage of each of the light emitting diodes LED1 to LEDn decreases. ID _Q1 indicates the drain current of the switch element Q1. I _L indicates the current flowing from one end of the inductor L to the other end, AVE_I _L indicates the average value of the current _{I L} which flows from one end of the inductor L to the other end.

As the load becomes lighter, the increase rate per unit time of the drain current ID _Q1 of the switch element Q1 increases. Therefore, the slope of the drain current ID _Q1 of the switch element Q1 in the period from time t16 to t17 in FIG. 8B is the drain of the switch element Q1 in the period from time t11 to t12 in FIG. It is larger than the slope of the current ID _Q1 .

Here, the drain current _{ID Q1} of the switching element Q1 is equal to the current _{I L} which flows from one end of the inductor L to the other end. Therefore, the inclination of the end current flowing through the other end of _{I L} of the inductor L during the period from time t16~t17 in (b) of FIG. 8 also, the inductor in the period up to the time t11~t12 in (a) of FIG. 8 compared with the slope of the current I _L flowing from L end of the other end, it is larger. As a result, in FIG. 8 (a) and (b) the average value of the current _{I L} which flows from one end of the inductor L to the other end AVE_I _L away error occurs in the supply to each of the light emitting diode LED1~LEDn An error occurs in the constant current.

As described above, in the constant current power supply device 100, the increase rate per unit time of the drain current ID _Q1 of the switch element Q1 changes according to the fluctuation of the load, and as a result, the constant current supplied to the load is changed. In some cases, variations may occur.

  In view of the above-described problems, an object of the present invention is to provide a constant current power supply device that can suppress variations in constant current supplied to a load.

The present invention proposes the following items in order to solve the above-described problems.
(1) The present invention is a constant current power supply device that supplies a constant current to a load, wherein the current that flows through the load is input to an input terminal, and the current that converts the current that flows through the switch element into a voltage The voltage conversion means, the voltage converted by the current-voltage conversion means and a predetermined voltage are compared, and the control means for controlling the switch element according to the comparison result; and the current-voltage conversion means Proposing a constant current power supply device comprising: a correcting means for correcting either one of the converted voltage and the predetermined voltage according to the ON width of the switch element. ing.

  According to the present invention, a constant current power supply device that supplies a constant current to a load, a switch element in which the current that flows through the load is input to the input terminal, and a current-voltage conversion unit that converts the current flowing through the switch element into voltage Control means and correction means were provided. Then, the control unit compares the voltage converted by the current-voltage conversion unit with a predetermined voltage, and controls the switch element according to the comparison result. In addition, the correction means corrects either the voltage converted by the current-voltage conversion means or a predetermined voltage according to the ON width of the switch element.

  For this reason, it is possible to adjust the control of the switch element by correcting the voltage converted by the current-voltage conversion means or the predetermined voltage in accordance with the ON width of the switch element that changes according to the change of the load. Therefore, it is possible to suppress variation in the constant current supplied to the load.

  (2) In the constant current power supply device according to (1), the control unit is connected in series between an input terminal of the constant current power supply device and a reference potential point of the constant current power supply device. The first resistor and the second resistor, the voltage converted by the current-voltage conversion means, and the voltage at the connection point between the first resistor and the second resistor are compared, and the switch is selected according to the comparison result. Switch element control means for controlling the element, wherein the correction means corrects a voltage at a connection point between the first resistance and the second resistance in accordance with an ON width of the switch element. A constant current power supply device is proposed.

  According to this invention, the first resistance, the second resistance, and the switch element control means are provided in the control means. The first resistor and the second resistor were connected in series, and were provided between the input terminal of the constant current power supply device and the reference potential point of the constant current power supply device. The switch element control means compares the voltage converted by the current-voltage conversion means with the voltage at the connection point between the first resistor and the second resistor, and controls the switch element according to the comparison result. It was decided.

  Therefore, on / off of the switch element is controlled by the switch element control means, and the voltage converted by the current-voltage conversion means, that is, the switch element flows as the voltage at the connection point between the first resistor and the second resistor increases. A voltage-converted current can be increased. Here, the voltage at the connection point of the first resistor and the second resistor changes in the same manner as the input voltage input to the input terminal of the constant current power supply device, and the current flowing through the switch element is the current flowing through the switch element. It changes in the same way as voltage conversion. As described above, as the input voltage input to the input terminal of the constant current power supply device increases, the input current input to the input terminal of the constant current power supply device can be increased. Therefore, the power factor of the constant current power supply device can be improved.

  According to the above-described invention, the correction means corrects the voltage at the connection point between the first resistor and the second resistor in accordance with the ON width of the switch element. For this reason, the control of the switch element can be adjusted according to the ON width of the switch element that changes in accordance with the variation of the load. Therefore, the same effect as described above can be achieved.

  (3) In the constant current power supply device according to (2), the correction unit may calculate a correction value corresponding to an ON width of the switch element as a voltage at a connection point between the first resistor and the second resistor. And the correction value is set larger as the ON width of the switch element becomes wider, and the switch element control means is configured such that the voltage converted by the current-voltage conversion means is the first resistance and the second resistance. The switch element is turned off when a voltage at a connection point with a resistor is exceeded, and the switch element is turned on after a predetermined time has elapsed since the switch element was turned off. A constant current power supply is proposed.

  According to this invention, when the voltage converted by the switch element control means by the current-voltage conversion means becomes equal to or higher than the voltage at the connection point between the first resistor and the second resistor, the switch element is turned off, When a predetermined time elapses after the switch is turned off, the switch element is turned on. For this reason, an effect similar to the above can be produced by turning on and off the switch element.

  Further, according to the above-described invention, the correction means adds a correction value corresponding to the ON width of the switch element to the voltage at the connection point between the first resistor and the second resistor, and also adds the correction value to the switch element. The larger the on width, the larger the setting. For this reason, the control of the switch element can be adjusted according to the ON width of the switch element that changes in accordance with the variation of the load. Therefore, the same effect as described above can be achieved.

  According to the present invention, variation in the constant current supplied to the load can be suppressed.

It is a circuit diagram of the constant current power supply device concerning one embodiment of the present invention. It is a 1st timing chart of the said constant current power supply device. It is the elements on larger scale of the said 1st timing chart. It is a 2nd timing chart of the said constant current power supply device. It is a circuit diagram of the constant current power supply device which concerns on a prior art example. It is a 1st timing chart of the said constant current power supply device. It is the elements on larger scale of the said 1st timing chart. It is a 2nd timing chart of the said constant current power supply device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the constituent elements in the following embodiments can be appropriately replaced with existing constituent elements, and various variations including combinations with other existing constituent elements are possible. Accordingly, the description of the following embodiments does not limit the contents of the invention described in the claims.

[Configuration of Constant Current Power Supply Device 1]
FIG. 1 is a circuit diagram of a constant current power supply device 1 according to an embodiment of the present invention. The constant current power supply device 1 is provided in the constant current power supply device 100 and the connection of the inverting input terminal and the non-inverting input terminal of the comparator CMP with the constant current power supply device 100 according to the conventional example shown in FIG. The difference is that the DC power supply Vref is not provided, and that the resistors R2, R3, R4, R5 and the capacitor C2 that are not provided in the constant current power supply device 100 are provided. In the constant current power supply device 1, the same components as those of the constant current power supply device 100 are denoted by the same reference numerals, and the description thereof is omitted.

  The resistor R2 and the resistor R3 are connected in series, the first output terminal of the rectifying unit RF is connected to one end of the resistor R2, and the reference potential point of the constant current power supply device 1 is connected to the other end of the resistor R3. Is connected to the second output terminal of the rectifying unit RF. A connection point between the other end of the resistor R2 and one end of the resistor R3 is connected to the non-inverting input terminal of the comparator CMP. A connection point between the source of the switch element Q1 and the resistor R1 is connected to the inverting input terminal of the comparator CMP.

  The resistor R5 and the capacitor C2 are connected in series. One end of the resistor R5 is connected to the gate of the switch element Q1, and the other electrode of the capacitor C2 is connected to the second output terminal of the rectifying unit RF. The The other end of the resistor R5 and one electrode of the capacitor C2 are connected to the non-inverting input terminal of the comparator CMP via the resistor R4.

[Operation of Constant Current Power Supply Device 1]
The constant current power supply device 1 having the above configuration controls the switching element Q1 in accordance with the drain current of the switching element Q1 and the voltage output from the first output terminal of the rectifying unit RF, so that the constant current power supply apparatus 1 has a constant current. Perform current control. Furthermore, the constant current power supply device 1 finely adjusts the control of the switch element Q1 described above according to the ON width of the switch element Q1.

  Specifically, the voltage output from the first output terminal of the rectifying unit RF is divided by the resistors R2 and R3 and input to the non-inverting input terminal of the comparator CMP. The gate voltage of the switch element Q1 is charged to the capacitor C2 via the resistor R5, and the voltage across the capacitor C2 is input to the non-inverting input terminal of the comparator CMP via the resistor R4. For this reason, the voltage at the non-inverting input terminal of the comparator CMP is obtained by dividing the voltage output from the first output terminal of the rectifying unit RF by the resistors R2 and R3, and the gate voltage of the switch element Q1. It is equal to the sum of the voltages across the terminals of the capacitor C2 that changes accordingly (hereinafter referred to as the “total voltage”).

  Here, since the voltage output from the first output terminal of the rectifying unit RF is sufficiently larger than the gate voltage of the switching element Q1, the voltage output from the first output terminal of the rectifying unit RF is set as a resistance. The voltage divided by R2 and resistor R3 is sufficiently larger than the voltage across the capacitor C2 that changes according to the gate voltage of the switch element Q1. Therefore, it can be said that the voltage output from the first output terminal of the rectifying unit RF divided by the resistor R2 and the resistor R3 is corrected by the voltage across the capacitor C2.

  The drain current of the switch element Q1 is converted into a voltage by flowing through the resistor R1, and is input to the inverting input terminal of the comparator CMP. Therefore, the voltage at the inverting input terminal of the comparator CMP is equal to the voltage converted from the drain current of the switch element Q1.

  When the voltage converted from the drain current of the switch element Q1 exceeds the total voltage, the comparator CMP outputs an H level voltage, the flip-flop FF outputs an L level gate signal, and the switch element Q1 is turned off. It becomes a state. On the other hand, when the voltage converted from the drain current of the switch element Q1 becomes less than the total voltage, the comparator CMP outputs an L level voltage, and at the rise of the clock signal output from the clock generation unit CLK, the flip-flop FF An H level gate signal is output, and the switch element Q1 is turned on.

  As described above, the constant current power supply device 1 compares the sum of the voltage obtained by converting the drain current of the switch element Q1 with the total voltage as described above, and controls the switch element according to the comparison result.

Here, the total voltage is a terminal of the capacitor C2 that changes according to the gate voltage of the switch element Q1 to the voltage output from the first output terminal of the rectifier RF divided by the resistor R2 and the resistor R3. This is the sum of the inter-voltages. As described above, the voltage output from the first output terminal of the rectifying unit RF is sufficiently larger than the gate voltage of the switch element Q1. For this reason, a total voltage changes similarly to the voltage output from the 1st output terminal of rectification part RF. Specifically, if the voltage output from the first output terminal of the rectifying unit RF changes in a sine wave shape, the divided input voltage also changes in a sine wave shape. Therefore, as shown in FIG. 2, the peak value of the voltage at the inverting input terminal of the comparator CMP (see VNEG _CMP in FIGS. 2 and 3) to which the voltage converted version of the drain current of the switch element Q1 is input is The voltage is equal to the voltage at the non-inverting input terminal of the comparator CMP (see VPOS _CMP in FIGS. 2 and 3) to which a voltage that changes similarly to the voltage output from the first output terminal of the rectifying unit RF is input. .

FIG. 2 is a first timing chart of the constant current power supply device 1. FIG. 3 shows a voltage VNEG _{CMP at} the inverting input terminal of the comparator _CMP and a voltage VPOS _{CMP at} the non-inverting input terminal of the comparator CMP. It is the elements on larger scale of FIG. 2 which show a relationship.

As described above, the peak value of the voltage VNEG _CMP at the inverting input terminal of the comparator _CMP is equal to the voltage VPOS _CMP at the non-inverting input terminal of the comparator CMP. The voltage VPOS CMP at the non-inverting input terminal of the comparator _CMP is obtained by dividing the voltage output from the first output terminal of the rectifying unit RF by the resistor R2 and the resistor R3, and the gate voltage of the switch element Q1. It is equal to the sum of the inter-terminal voltages of the capacitor C2 that changes in response to the above, and changes in the same manner as the voltage VOUT _RF output from the first output terminal of the rectifying unit RF as described above. For this reason, the peak value of the voltage VNEG _CMP at the inverting input terminal of the comparator CMP changes in the same manner as the voltage VOUT _RF output from the first output terminal of the rectifying unit RF.

FIG. 4 is a second timing chart of the constant current power supply device 1. More specifically, FIG. 4A is a timing chart of the constant current power supply device 1 at a constant load, and FIG. 4B is a light load that is lighter than that of FIG. It is a timing chart of the constant current power supply device 1 at the time of load. VGS _Q1 indicates a gate-source voltage of the switch element Q1, and V _C2 indicates a voltage between terminals of the capacitor C2.

The constant current power supply device 1 narrows the ON width of the switch element Q1 as the load becomes lighter in order to continue supplying a constant current. Since the capacitor C2 is charged by the gate voltage of the switch element Q1, the inter-terminal voltage V _C2 of the capacitor C2 becomes higher as the ON width of the switch element Q1 becomes wider. Thus, the terminal voltage V _C2 of the capacitor C2, as the load increases, the higher.

When the terminal voltage _{V C2} of the capacitor C2 increases, the voltage _{VPOS CMP} voltage _{VPOS CMP} of the non-inverting input terminal of the comparator CMP becomes high, as a result, the peak value of the voltage _{VNEG CMP} of the inverting input terminal of the comparator CMP growing. For this reason, the peak value of the drain current ID _Q1 of the switch element Q1 increases.

If the peak value of the drain current ID _Q1 of the switching element Q1 is increased, the peak value of the current I _L which flows from one end of the inductor L to the other is also increased, resulting in current flowing from one end of the inductor L to the other end I _L average AVE_I _L is increased.

  According to the above constant current power supply device 1, the following effects can be obtained.

In the constant current power supply device 100 according to the conventional example shown in FIG. 5, as shown in FIG. 6, as the voltage VOUT _RF output from the first output terminal of the rectifier unit RF increases, Since the current IOUT _RF output from the output terminal 1 decreases, the power factor sometimes deteriorates.

On the other hand, the constant current power supply device 1 changes the voltage output from the first output terminal of the rectifying unit RF to the voltage divided by the resistor R2 and the resistor R3 according to the gate voltage of the switch element Q1. The sum of the inter-terminal voltages of the capacitor C2 to be processed is compared with the voltage converted from the drain current of the switch element Q1, and the switch element is controlled according to the comparison result. Therefore, the peak value of the voltage VNEG _CMP at the inverting input terminal of the comparator CMP to which the voltage converted from the drain current of the switch element Q1 is input is the voltage VOUT output from the first output terminal of the rectifying unit RF. It changes in the same way as _RF . Here, since the drain current of the switch element Q1 is substantially equal to the current output from the first output terminal of the rectifying unit RF, the current output from the first output terminal of the rectifying unit RF is the current of the rectifying unit RF. The voltage changes in the same manner as the voltage VOUT _RF output from the first output terminal. Therefore, the power factor of the constant current power supply device 1 can be improved as compared with the power factor of a conventional constant current power supply device such as the constant current power supply device 100.

Further, the constant current power supply unit 100 according to the prior art shown in FIG. 5, as shown in FIG. 8, the average value AVE_I _L of the current I _L which flows from one end of the inductor L to the other end, as the load becomes lighter It was getting bigger.

On the other hand, the constant current power supply device 1 corrects the voltage output from the first output terminal of the rectifying unit RF by dividing the voltage by the resistor R2 and the resistor R3 with the voltage across the capacitor C2. According to this, as the load is increased, it is possible to increase the average value AVE_I _L of the current I _L flowing from one end to the other end of the inductor L. For this reason, the constant current power supply device 1 can suppress variation in the constant current supplied to the load, that is, the constant current supplied to each of the light emitting diodes LED1 to LEDn.

  Further, by adjusting the resistance ratio between the resistor R2 and the resistor R3, the timing at which the comparator CMP outputs the L level voltage can be adjusted, and the ON width of the switch element Q1 can be adjusted.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1,100; Constant current power supply device C1, C2; Capacitor CLK; Clock generation part CMP; Comparator D1; Diode FF; Flip-flop L; Inductor LED1-LEDn; Light emitting diode Q1; Switch element R1-R5; Part

Claims (1)

A constant current power supply device for supplying a constant current to a load,
A switch element in which the current flowing through the load is input to an input terminal;
Current-voltage conversion means for converting the current flowing in the switch element into a voltage;
A first resistor and a second resistor connected in series between an input terminal of the constant current power supply device and a reference potential point of the constant current power supply device;
Switch element control means for comparing the voltage converted by the current-voltage conversion means with the voltage at the connection point between the first resistor and the second resistor and controlling the switch element according to the comparison result; ,
Correction means for adding a correction value corresponding to the ON width of the switch element to a voltage at a connection point between the first resistor and the second resistor ;
The correction means sets the correction value to be larger as the ON width of the switch element becomes wider,
The switch element control means includes
When the voltage converted by the current-voltage conversion means is equal to or higher than the voltage at the connection point between the first resistor and the second resistor, the switch element is turned off,
The constant current power supply apparatus , wherein the switch element is turned on when a voltage converted by the current-voltage conversion means becomes less than a voltage at a connection point between the first resistor and the second resistor .

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