JP4985870B1 - Constant current drive device and load drive device using the same - Google Patents

Abstract

When a current-driven load fluctuates or varies in its voltage drop due to the usage environment and individual variations, etc., even if a predetermined driving voltage is supplied to the load, it is caused by fluctuations in the voltage drop of the load. Therefore, the voltage at both ends of the current driving circuit is always affected and power loss or heat generation is caused.
A current flowing through a load is shunted with a first current driving circuit that serves as a first current path, and a second current path is shunted, and a second current path arranged in parallel with the first current driving circuit. Current is distributed to the current drive circuit 27, and heat generation is dispersed by the shunt current setting resistor 43 connected to the second current drive circuit 27, thereby suppressing heat generation in the current drive circuit and allowing a predetermined constant current to flow through the load. The configuration.
[Selection] Figure 1

Description

  The present invention relates to a constant current driving device that drives a load at a constant current and a load driving device using the constant current driving device. In particular, as one of application examples thereof, the present invention relates to a light emitting element driving device such as a light emitting diode (hereinafter referred to as LED) and a light emitting device.

  The device for driving the load at a constant current is not limited to the light emitting element driving device and the light emitting device.

  As a conventional load driving device, a configuration shown in FIG. 8 and FIG. 9 has been proposed for a light emitting element driving device and a light emitting device including light emitting elements such as LEDs (for example, see Patent Document 1).

  In FIG. 8, each of the light emitting element groups 10A, 10B, and 10C (generic name 10) is composed of a plurality of LED elements, for example, and the anodes of the light emitting element groups 10 are commonly connected, and current flows in the forward direction from the anode to the cathode. Are connected in series. A voltage VOUT generated by the voltage conversion unit 50 is supplied to each anode side of the light emitting element group 10. Further, current drive circuits 20A, 20B, and 20C (generic name 20) are connected to the respective cathode sides of the light emitting element groups 10 to drive each light emitting element group 10 with current.

  The connection points of the light emitting element groups 10A, 10B, and 10C and the current drive circuits 20A, 20B, and 20C are connected to the voltage drop detection circuits 30A, 30B, and 30C, and the detection result of the potential at each connection point is controlled. It is supplied to the signal generator 40. Since the voltage between the terminals of the light emitting element group 10 varies depending on the VF variation of LED elements, the drive current value, and the temperature characteristics, the potentials at the connection points are different. Therefore, the control signal generation unit 40 identifies the potential that has the largest voltage drop due to the forward voltage among the light emitting element groups 10A, 10B, and 10C, that is, the lowest potential among the connection points, and this potential is current driven. The voltage is fed back to the voltage conversion unit 50 so that the circuit 20 has a certain potential or more that can perform a desired operation, and the voltage VOUT generated by the voltage conversion unit 50 is adjusted. That is, by adjusting the voltage VOUT so that the voltage applied to the current drive circuit 20 that drives the light emitting element group 10 in which the inter-terminal voltage of the light emitting element group 10 becomes the maximum is the minimum voltage that can be driven, The power of the light emission driving device can be made necessary and optimum.

  FIG. 9 shows a conventional constant current driving device specifically showing one series of the light emitting element group 10 and the current driving circuit 20 in FIG.

  In the light emitting element group 10, N (N is an integer of 2 or more) LED elements 3 are connected in series, the drive power source 1 is connected to the anode side end Pa, the voltage VOUT is supplied, and the cathode side end Pc is connected to the cathode side end Pc. The current driving circuit 21 and the current setting resistor 23 are connected in series. The other end of the current setting resistor 23 is connected to the ground terminal 2. The current driving circuit 21 includes a driving MOS transistor 24 and an operational amplifier 25. The drain of the driving MOS transistor 24 is connected to the cathode side end Pc, and the source is connected to a node Ps which is one end of the current setting resistor 23. Is connected to the output of the operational amplifier 25. A current setting power supply 34 is connected to the non-inverting input of the operational amplifier 25, and the source of the driving MOS transistor 24 is connected to the inverting input. The operational amplifier 25 drives the driving MOS transistor 24 so that the voltage across the current setting resistor 23, that is, the potential of the source of the driving MOS transistor 24 is the same as the potential of the current setting power supply 34.

JP 2007-242477 A

  The conventional light emitting element driving device enables more efficient driving of the entire light emitting device including the light emitting element driving device, and the sum of the individual LED forward voltages VF constituting the light emitting element group is as follows. Consider that the voltage applied to each current drive circuit increases due to fluctuations caused by environmental changes such as temperature conditions, and voltage differences between light emitting element groups of multiple series due to individual variations. It has not been. That is, there is a problem that the voltage between the terminals of the current drive circuit other than the optimized series is large, the power consumption is large, and as a result, the heat generation of the chip is large. As a product trend of the light emitting element driving device, the number of series of the light emitting element group and the current driving circuit is increased, the number of series of LED elements constituting the light emitting element group is increased, the circuit scale is increased, The power supply voltage is increasing, and the problem becomes more prominent.

  The constant current drive device of the present invention has been made to solve such problems, and the present invention relates to power loss generated in each current drive circuit due to fluctuations in the voltage drop of the drive load and each of the power loss generated thereby. An object is to reduce heat generation in the current driving circuit.

A constant current driving apparatus for driving a load according to an embodiment of the present invention with a current has a first terminal connected to the other end of the load, one end connected to a first power supply, and a second power supply connected thereto, a second terminal connected to the other end of the current setting device for setting the current value of the current flowing to the load, one end is connected to the other end of the load or the current setting device a third terminal connected to the other end of the shunt current setting element, a first current driver circuit which is connected between the first terminal and the second terminal, the shunt setting element When one end is connected to the other end of the load, it is connected between the third terminal and the second terminal, and one end of the shunt setting element is connected to the other end of the current setting element. when connected, the second current driver times connected between said third terminal and said first terminal With the door, and is configured with a current flowing through the load to flow in shunt to the first current driver circuit and the second current driver circuit.

  The first current driving circuit includes a first operational amplifier and a first transistor, and the first transistor is connected so that a current flows between terminals of the first terminal and the second terminal, The control terminal of the first transistor is connected to the output of the first operational amplifier, the second terminal is connected to one input of the first operational amplifier, and the other terminal of the first operational amplifier is connected. The input includes a fourth terminal to which a current setting power source for setting a current value for flowing a current to the load is connected, and the second current driving circuit includes the first terminal or the second terminal And a switching element for controlling whether or not the current flows between the third terminal and a current dividing control circuit for controlling on / off of the switching element.

  According to the present invention, the current flowing through the load is shunted to the second current driving circuit, and a voltage drop is generated by the shunt current setting element connected in series with the second current driving circuit, so that heat generation can be absorbed. . As a result, an increase in the voltage applied to the first current drive circuit can be suppressed, and heat generated thereby can be suppressed. This makes it possible to increase the number of constant current drive devices configured on the same semiconductor substrate, increase the number of series of multiple drive loads, and increase the power supply voltage. A load can be mounted, and the system can be simplified.

1 is a circuit diagram showing a constant current driving device according to a first embodiment of the present invention. The circuit diagram which shows the constant current drive device concerning Embodiment 2 of this invention The circuit diagram which shows the constant current drive device concerning Embodiment 3 of this invention Circuit diagram showing a constant current driving apparatus according to Embodiment 4 of the present invention. Circuit diagram showing a constant current driving apparatus according to Embodiment 5 of the present invention. Circuit diagram showing a constant current driving apparatus according to Embodiment 6 of the present invention. Circuit diagram showing a constant current driving apparatus according to Embodiment 7 of the present invention. Configuration diagram showing a light emitting element driving device including a conventional constant current driving circuit Circuit diagram showing a constant current driving circuit in a conventional light emitting element driving device

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference symbols throughout all the drawings, and redundant description thereof is omitted.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration example of a constant current driving device for driving a load according to Embodiment 1 of the present invention. Here, one series of the light emitting element group and the current driving circuit is specifically shown.

  In FIG. 1, as a driving load, for example, an anode side end Pa of a light emitting element group 10 in which N (N is an integer of 2 or more) LED elements 3 are connected in series is connected to a driving power source 1 and supplied with a voltage VOUT. A constant current driving device 26 for driving the light emitting element group 10 and a current setting resistor 23 are connected in series to the cathode side end Pc, and one end of the current setting resistor 23 is connected to the ground terminal 2. The constant current drive device 26 connected between the cathode side end Pc and the node Ps which is the other end of the current setting resistor 23 is a first current drive that becomes a first current path of a current flowing through the light emitting element group 10. The circuit 21 and a second current drive circuit 27 that are arranged in parallel with the first current drive circuit 21 and shunt to form a second current path. The second current drive circuit 27 is connected in series with the shunt current setting resistor 43 at the connection point Pd, and is connected between the cathode side end Pc and the node Ps.

  The first current drive circuit 21 includes a drive MOS transistor 24 and an operational amplifier 25. The drain of the drive MOS transistor 24 is connected to the cathode side end Pc, the source is connected to the node Ps, and the output of the operational amplifier 25 is connected to the gate. It is connected. A current setting power supply 34 is connected to the non-inverting input of the operational amplifier 25, the setting voltage Vs is applied, and the source (node Ps) of the driving MOS transistor 24 is connected to the inverting input. The first current drive circuit 21 operates the operational amplifier 25 to drive the voltage across the current setting resistor 23, that is, the potential Vps of the node Ps to be the same as the set voltage Vs of the current setting power supply 34. The MOS transistor 24 is driven.

  The second current drive circuit 27 includes a drive MOS transistor 28 and a comparator 29. The drain of the drive MOS transistor 28 is connected to the cathode side end Pc via the shunt current setting resistor 43, and the source is connected to the node Ps. The output of the comparator 29 is connected to the gate. A non-inverted input of the comparator 29 is connected to a shunt current control power supply 35, to which a set voltage Vc is applied, and a cathode side end Pc is connected to an inverted input. When the potential Vpc at the cathode side end Pc is equal to or lower than the potential Vc of the shunt current control power source 35, the driving MOS transistor 28 is in an on state, a current flows through the second current driving circuit 27, and the potential Vpc becomes the potential Vc. If larger, the driving MOS transistor 28 is in an off state, and no current flows through the second current driving circuit 27.

  By providing the second current driving circuit 27 and shunting the current flowing through the light emitting element group 10 with the first current driving circuit 21, for example, a shunt current setting resistor 43 is provided outside the integrated circuit. By releasing the heat generation, there is an effect that power loss and heat generation in the first current drive circuit 21 and the second current drive circuit 27 can be suppressed.

  The second current drive circuit 27 is connected in series with the shunt current setting resistor 43 and is connected between the cathode side end Pc and the node Ps. However, the shunt current setting resistor 43 may be provided on the node Ps side. I do not care.

  Further, detailed operation will be described.

  The current flowing through the light emitting element group 10 is shunted to the first current driving circuit 21 and the second current driving circuit 27, joined again, and flows to the current setting resistor 23. If the current flowing through the light emitting element group 10 is ILED, the current flowing through the first current driving circuit 21 is Ictrl, the current flowing through the second current driving circuit 27 is Ibp, and the current flowing through the current setting resistor 23 is Irs, then The formula holds.

Irs = Ictrl + Ibp = ILED (1)
Further, under the condition that the driving MOS transistor 24 of the first current driving circuit 21 is operating, the operational amplifier 25 maintains the potential Vps of the node Ps at the set voltage Vs, while the current setting resistor 23 (the resistance value is changed). The drive MOS transistor 24 is feedback-controlled so that the current value flowing in the Rs) is constant at Irs = Vs / Rs. That is, at this time, the constant current ILED set as the predetermined drive current is expressed by the following equation.

ILED = Irs = Ictrl + Ibp = Vs / Rs (2)
In the first embodiment, the current ILED is set to a predetermined constant current by feedback control by the driving MOS transistor 24 and the operational amplifier 25, so that a current flows through the driving MOS transistor 24. It is a necessary operating condition. That is,
Ictrl> 0 (3)
Ibp <Vs / Rs (4)
It becomes.

Further, in order for the driving MOS transistor 24 to operate normally, the voltage Vx across the driving MOS transistor 24 (the voltage value is also assumed to be Vx) has a necessary minimum voltage of Vx = Vpc−Vps. Vmin. The minimum voltage Vmin is a value determined by the on-resistance of the driving MOS transistor 24 (the resistance value is Ron1) and a predetermined current ILED.
Vmin = Ron1 × ILED (5)
Is required.

In the second current drive circuit 27, when the resistance value of the on-resistance of the driving MOS transistor 28 is Ronb and the resistance value of the shunt current setting resistor 43 is Rd, the current Ibp flowing through the second current drive circuit 27 is ,
Ibp = (Vpc−Vps) / (Ronb + Rd) (6)
It becomes.

  The state where the current Ibp does not satisfy the formula (4) is that the sum of the forward voltages VF of the light emitting element group 10, that is, the both-end voltage VLED becomes lower than expected due to short-circuiting of the LED element 3. This indicates that the current Ibp flowing through the second current drive circuit 27 has increased from a predetermined value (Ibp> Vs / Rs) due to the increase in the potential Vpc of the terminal Pc.

  The potential Vc, which is the input of the comparator 29, is provided in order to stop an unnecessarily diversion operation in such an abnormal state. That is, it functions to prevent the abnormal current more than necessary due to the increase in the potential Vpc of the cathode side end Pc from being generated in the second current driving circuit 27 and the light emitting element group 10.

  In such an abnormal state, control for stopping the current drive to the first current drive circuit 21 may be provided. The embodiment will be described next.

(Embodiment 2)
FIG. 2 is a circuit diagram showing a configuration example of a constant current drive device 26A for driving a load according to the second embodiment of the present invention. The constant current drive device 26 according to the first embodiment has a first state in an abnormal state. The configuration for stopping the current drive of the current drive circuit 21 is added. Since the basic configuration is the same as that of the first embodiment, only the configuration of the difference will be described.

  2, the output of the comparator 29A in the second current drive circuit 27A is supplied to the first current drive circuit 21, specifically to the input of the operational amplifier 25. As a result, in an abnormal state, the output of the comparator 29A turns off the driving MOS transistor 28 so that no current flows through the second current driving circuit 27A. The MOS transistor 24 is turned off so that no current flows through the first current drive circuit 21. That is, in the first embodiment, by stopping the driving of the second current driving circuit 27, the current flowing to the current setting resistor 23 is temporarily reduced, the potential Vps of the node Ps is lowered, and the driving MOS is again performed. It serves to prevent the transistor 24 from flowing out.

The occurrence condition of the abnormal state is from the equations (4) and (6)
Ibp = (Vpc−Vps) / (Ronb + Rd) <Vs / Rs (7)
It becomes. Therefore, the parameter setting of the resistance value Ronb of the on-resistance of the driving MOS transistor 28 and the resistance value Rd of the shunt current setting resistor 43 needs to be performed so as to satisfy this condition.

In the first and second embodiments, the effect of reducing heat generation will be described using an example of parameters. The parameters exemplified here are examples of the present embodiment and do not limit the configuration of the present invention.
(Parameter)
Current flowing in the light emitting element group 10: ILED = 0.1A
-Resistance value of current setting resistor 23: Rs = 5Ω
・ Setting voltage of operational amplifier 25: Vs = ILED × Rs = 0.1A × 5Ω = 0.5V
On resistance of the driving MOS transistor 24: Ron1 = 5Ω
The necessary minimum voltage to be applied across the driving MOS transistor 24:
Vmin = ILED × Ron1 = 0.1A × 5Ω = 0.5V
-Number of LEDs connected in series in the light emitting element group 10: 10 (N = 10),
・ Individual variation in each LED element 3 and variation range of forward voltage VF value depending on usage environment such as temperature:
3.0V ± 0.2V (Indicated as VF0 ± ΔVF)
The fluctuation value of VLED that is the sum of the forward voltage VF of the light emitting element group 10 is
VLED (maximum value) = 3.2V × 10 = 32V
VLED (minimum value) = 2.8V × 10 = 28V
The fluctuation value is ΔVLED = 32V−28V = 4V
In addition, the drive voltage Vout applied to the anode side end Pa of the light emitting element group 10 is an optimal fixed value that takes into account fluctuations, and needs to be set when the VLED has the maximum value due to VF fluctuations.
Vout = VLED (maximum value) + Vmin + Vs = 32V + 0.5V + 0.5V = 33V
-Resistance value of shunt current setting resistor 43: Rd = 45Ω
On resistance of driving MOS transistor 28: Ronb = 5Ω
In the present embodiment, the first current driving circuit 21 and the second current driving circuit 27 are formed on the same semiconductor substrate, and driving elements, that is, driving MOS transistors arranged in parallel, respectively. 24, the driving MOS transistor 28 is an element related to the power loss and the heat generation problem, and the maximum value of the power loss in this embodiment is set as W′max.

  Further, the power loss becomes the maximum value W′max when (Vpc−Vps) is the maximum, and when this is expressed as Vxmax, it can be obtained from the following equation (8).

Vxmax = (VLED [maximum value] + Vmin + Vs) −Vs−VLED [minimum value])
= (VLED [maximum value] -VLED [minimum value]) + Vmin
= ΔVLED + Vmin
= (N × ΔVF × 2) + Vmin = 4V + 0.5V = 4.5V (8)
Further, the maximum power loss value W′max at this time, that is, the power loss in the driving MOS transistor 24 and the driving MOS transistor 28 is a shunt current setting resistor that is a heat generation dispersion resistance from the conventional maximum power loss value. This is a value obtained by subtracting the power loss (denoted as Wd) generated at 43 and is obtained from the following equation.

Ibp = (Vpc−Vps) / (Ronb + Rd)
= Vxmax / (Ronb + Rd)
= 4.5V / (45Ω + 5Ω) = 0.09A
Wd = Ibp ^ 2 × Rd
= 0.09A ^ 2 x 45Ω = 0.3645W
The conventional maximum power loss is
W = ILED × Vxmax
= 0.1A × 4.5V = 0.45W W′max = 0.45W−0.3645W = 0.0855W
Thus, the power loss in the constant current driving device 26 can be reduced to about 20% of the conventional one.

  Here, as an environment in which the constant current driving device 26 is mounted on an IC, for example, assuming a printed board of paper phenol, its thermal resistance is about 60 ° C./W.

Therefore, the heat generation amount of the driving MOS transistor is ΔT = 0.45 W × 60 ° C./W=+27° C. as a temperature rise, whereas in the present application, ΔT = 0.0855 W × 60 ° C./W. = + 5.13 ° C., which can be significantly reduced.

  Here, assuming a generally allowable temperature increase value, the restriction is generally that the junction temperature of the semiconductor does not exceed 125 ° C. Assuming that the ambient environment of use is 70 ° C., the allowable temperature increase value is 125 ° C.−70 ° C. = 55 ° C.

In this case, the number M (M: integer) of series of constant current drive devices that can be mounted is
M = 55 ° C./5.13° C. ≦ 10 (in the case of the conventional configuration, M ≦ 2)
Thus, the number of series that can be installed can be greatly increased compared to the conventional system.

In addition, when the number of series M = 1, the allowable number N1 of LED elements in series is
N1 = 10 × 55 ° C./5.13° C. ≦ 107 (N1 ≦ 20 in the case of the conventional configuration)
Thus, the number of LED elements that can be mounted can be significantly increased.

  That is, according to the embodiment of the present invention, fluctuations in the voltage drop of the drive load (for example, the individual LED elements 3 constituting the light emitting element group generated due to the forward voltage VF variation of the LED elements 3 and the like) The power loss caused by the constant current drive device due to the fluctuation of the sum of the forward voltage VF) and the heat generation in the constant current drive device caused thereby can be greatly reduced. As a result, (1) the restriction due to heat generation of the number of constant current drive devices configured on the same semiconductor substrate is relaxed, and a larger number of constant current drive devices can be mounted on the same IC, thus simplifying the system. (2) Tolerance of voltage drop difference between multiple drive loads that caused the problem of heat generation restriction and voltage drop fluctuation caused by usage environment or individual variation is eased. Thus, the number of LED elements in series can be increased, and the system can be simplified.

  In addition, the number demonstrated here is illustrated in order to demonstrate this invention concretely, and this invention is not limited to the illustrated number.

(Embodiment 3)
FIG. 3 is a circuit diagram showing a configuration example of a constant current drive device for driving a load according to Embodiment 3 of the present invention. As a change from the first embodiment, the constant current driving device 26 is changed to a constant current driving device 26B, and the diversion control means for operating the second current driving circuit 27B is different. Components having the same configurations as those of the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different configurations are described.

  Since the configuration and operation of the first current drive circuit 21 are the same as those of the first embodiment, description thereof is omitted.

  The second current drive circuit 27B includes a drive MOS transistor 28 and a comparator 29B. The drain of the drive MOS transistor 28 is connected to the cathode side end Pc via the shunt current setting resistor 43, and the source is connected to the node Ps. The output of the comparator 29B is connected to the gate. A non-inverting input of the comparator 29B is connected to a shunt current control power source 37, and a potential higher by the set voltage Vα than the set voltage Vs of the current setting power source 34 is applied, and the inverting input of the driving MOS transistor 24 is applied. A source (node Ps) is connected.

  In normal operation, the inverting inputs of the operational amplifier 25 and the comparator 29B are both connected to the node Ps, and the operational amplifier 25 is controlled so that the node Vps is equal to the set voltage Vs of the current setting power supply 34 as in the first embodiment. However, since the driving MOS transistor 24 is turned on and a potential (Vs + Vα) higher than the set voltage Vs is applied to the non-inverting input of the comparator 29B, the driving MOS transistor 28 is also controlled by the comparator 29B. It is turned on. That is, the current flowing through the light emitting element group 10 is divided and flows into the first current driving circuit 21 and the second current driving circuit 27B. By diverting the current to the shunt current setting resistor 43 provided outside the integrated circuit, heat generation can be released to the outside, and power loss and heat generation in the first current drive circuit 21 and the second current drive circuit 27B can be prevented. It becomes possible to suppress.

  Here, as described in the first embodiment, when the total VLED of the forward voltage VF becomes lower than expected, such as when the LED element 3 is short-circuited, the potential of the cathode side end Pc is increased, which is the second current path. The current to the second current driving circuit 27B increases, and the current Ictrl = 0 flowing in the driving MOS transistor 24 of the first current driving circuit 21 is obtained. In this state, since the current flowing through the current setting resistor 23 exceeds a predetermined value: Irs = Vs / Rs, the potential Vps of the node Ps rises, and when Vps> Vs and Vps> Vs + Vα, the comparator 29B As a result, the driving MOS transistor 28 is turned off, so that no current flows through the second current driving circuit 27B. That is, it is possible to prevent an abnormal current more than necessary due to a rise in the potential of the cathode side end Pc from being generated in the second current path and the driving load.

  In the third embodiment, since the power source Vα is a relatively minute voltage, it can be generated inside the IC, and the shunt current control power source 35 required in the first embodiment is not required. Compared to the first embodiment, the same effect can be obtained with a simpler configuration.

  In addition, since the heat generation reduction effect in this configuration is the same as that in the first embodiment, description thereof is omitted.

  In the abnormal state as described above, control for stopping the current drive to the first current drive circuit 21 may be provided. The embodiment will be described next.

(Embodiment 4)
FIG. 4 is a circuit diagram showing a configuration example of a constant current driving device 26C for driving a load according to the fourth embodiment of the present invention. The constant current driving device 26B according to the third embodiment has a first state in an abnormal state. The configuration for stopping the current drive of the current drive circuit 21 is added. Since the basic configuration is the same as that of the third embodiment, only the configuration of the difference will be described.

  4, the output of the comparator 29C in the second current drive circuit 27C is supplied to the first current drive circuit 21, specifically to the input of the operational amplifier 25. Thus, in an abnormal state, the output of the comparator 29C turns off the driving MOS transistor 28 so that no current flows through the second current driving circuit 27C. The MOS transistor 24 is turned off so that no current flows through the first current drive circuit 21.

  Since the difference between the fourth embodiment and the third embodiment is the same as the difference between the second embodiment and the first embodiment, description of the operation is omitted.

(Embodiment 5)
FIG. 5 is a circuit diagram showing a configuration example of a constant current drive device for driving a load according to Embodiment 5 of the present invention. As a change from the third embodiment, the constant current driving device 26B is a constant current driving device 26D, and the diversion control means for operating the second current driving circuit 27D is different. Components having the same configurations as those of the third embodiment are denoted by the same reference numerals, description thereof is omitted, and only the configuration of differences is described.

  Since the configuration and operation of the first current drive circuit 21 are the same as those of the third embodiment, description thereof is omitted.

  The second current drive circuit 27D includes a drive MOS transistor 28 and an operational amplifier 36. The drain of the drive MOS transistor 28 is connected to the cathode side terminal Pc via the shunt current setting resistor 43, and the source is connected to the node Ps. The output of the operational amplifier 36 is connected to the gate. A non-inverting input of the operational amplifier 36 is connected with a shunt current control power source 37, and a potential higher than the setting voltage Vs of the current setting power source 34 by the set voltage Vα is applied. A source (node Ps) is connected.

  In normal operation, the inverting inputs of the operational amplifier 25 and the operational amplifier 36 are both connected to the node Ps, and the operational amplifier 25 is controlled so that the node Vps is equal to the set voltage Vs of the current setting power supply 34 as in the third embodiment. However, since the driving MOS transistor 24 is turned on and a potential (Vs + Vα) higher than the set voltage Vs is applied to the non-inverting input of the operational amplifier 36, the driving MOS transistor 28 is also driven by the operational amplifier 36. It is turned on. That is, the current flowing through the light emitting element group 10 is divided and flows into the first current driving circuit 21 and the second current driving circuit 27D. By diverting the current to the shunt current setting resistor 43 provided outside the integrated circuit, heat can be released to the outside, and power loss and heat generation in the first current drive circuit 21 and the second current drive circuit 27D can be reduced. It becomes possible to suppress.

Here, as described in the first embodiment, when the total VLED of the forward voltage VF becomes lower than expected, such as when the LED element 3 is short-circuited, the potential of the cathode side end Pc is increased, which is the second current path. The current to the second current driving circuit 27D increases, and the current Ictrl = 0 flowing in the driving MOS transistor 24 of the first current driving circuit 21 is obtained. In this state, since the current flowing through the current setting resistor 23 exceeds a predetermined value: Irs = Vs / Rs, the potential Vps of the node Ps rises and Vps> Vs, but is given to the non-inverting input of the operational amplifier 36. Depending on the potential, Vps does not rise above Vs + Vα. That is,
ILED = (Vs + Vα) / Rs
The driving is continued at a constant current value slightly larger than the initial predetermined current value Vs / Rs. Thereby, it is possible to prevent an abnormal current more than necessary due to a rise in the potential of the cathode side end Pc from being generated in the second current path and the driving load.

  In addition, since the heat generation reduction effect in this configuration is the same as that in the first embodiment, description thereof is omitted.

  If the potential Vpc of the cathode side end Pc is separately detected and the potential rise of the cathode side end Pc is large, both the first current drive circuit 21 and the second current drive circuit 27D are added to this configuration. You may provide control which stops. The embodiment will be described next.

(Embodiment 6)
FIG. 6 is a circuit diagram showing a configuration example of a constant current drive device 26E for driving a load according to the sixth embodiment of the present invention. The constant current drive device 26D according to the fifth embodiment has a first state in an abnormal state. The configuration for stopping the current drive of the current drive circuit 21 and the second current drive circuit 27D is added. Since the basic configuration is the same as that of the fifth embodiment, only the configuration of the difference will be described.

  For the constant current drive device 26D according to the fifth embodiment, in order to detect the potential Vpc of the cathode side end Pc, the cathode side end Pc is connected to the inverting input, the potential Vpc is applied, and a predetermined value is applied to the non-inverting input. A power supply 39 is connected, and a comparator 38 to which the potential Vce is applied is added. The output of the comparator 38 is input to both the operational amplifier 25 and the operational amplifier 36, and the output of the operational amplifier 25 and the operational amplifier 36 is output when the potential Vpc of the cathode side end Pc is higher than the potential Vce of the predetermined power supply 39 in an abnormal state. Thus, the driving MOS transistor 24 and the driving MOS transistor 28 are turned off, and the current driving of the load is stopped.

  In addition, since the heat generation reduction effect in this configuration is the same as that in the first embodiment, description thereof is omitted.

(Embodiment 7)
In Embodiments 1 to 6 of the present invention, description has been made using a configuration for driving one light emitting element group.

  As described in the prior art, when driving a plurality of groups of light emitting element groups of two or more systems, the influence of the forward voltage VF variation of the LED elements is larger due to individual differences between the series. Therefore, the embodiment of the present invention is more effective when driving a plurality of light emitting element groups of two or more systems.

  FIG. 7 shows a configuration diagram in the case of driving a light emitting element group consisting of four systems using the embodiment of the present invention. Here, the description will be made using the first embodiment, but the same applies to the second to sixth embodiments, and the description thereof will be omitted.

  In FIG. 7, as drive loads, for example, the anode side ends Pa1 to Pa4 of the light emitting element groups 11 to 14 in which N (N is an integer of 2 or more) LED elements 3 are connected in series are commonly connected to the drive power supply 1. A voltage VOUT is supplied, and constant current driving devices 261 to 264 and current setting resistors 231 to 234 for driving the light emitting element groups 11 to 14 and the current setting resistors 231 to 234 are connected in series to the cathode side ends Pc1 to Pc4, respectively. One ends of 231 to 234 are connected to the ground terminal 2. The constant current driving devices 261 to 264 connected between the cathode side ends Pc1 to Pc4 and the nodes Ps1 to Ps4 which are the other ends of the current setting resistors 231 to 234 are the first currents flowing through the light emitting element groups 11 to 14, respectively. The first current driving circuit 21 serving as a current path and the second current driving circuit 27 disposed in parallel with the first current driving circuit 21 and shunted to form a second current path. Each second current drive circuit 27 is connected in series with the shunt current setting resistors 431 to 434, and is connected between the cathode side ends Pc1 to Pc4 and the nodes Ps1 to Ps4.

  A current setting power source 34 is connected to the non-inverting input of the operational amplifier of each first current driving circuit 21, and the setting voltage Vs is applied. The non-inverting input of the comparator of each second current driving circuit 27 is A shunt current control power source 35 is connected and a set voltage Vc is applied. Here, the current setting power source 34 and the shunt current control power source 35 are commonly connected to the constant current driving devices 261 to 264, but individual power sources may be connected.

  Since the operation is the same as in the first embodiment, a description thereof will be omitted. However, by dividing the current to the second current driving circuit 27 and flowing the current, the power loss is dispersed by the shunt current setting resistors 431 to 434. In addition, power loss in the constant current driving devices 261 to 264 and heat generation resulting therefrom can be suppressed, and the following effects as in the respective embodiments can be obtained.

  (1) The restriction due to heat generation of the number of current drive devices configured on the same semiconductor substrate can be alleviated, and more current drive devices can be mounted on the same IC, thereby simplifying the system.

  (2) The number of LED elements in series will be reduced because the voltage drop difference between multiple drive loads that has caused the problem of heat generation restriction and the allowable amount of voltage drop fluctuation due to usage environment or individual variation will be alleviated. Can be realized more and the system can be simplified.

  (3) Since the voltage drop difference between multiple drive loads and the allowable amount of voltage fluctuations caused by the usage environment or individual variations are alleviated, the VF variation of each LED element can be alleviated, thus eliminating the need for LED selection. And can contribute to cost reduction of the system.

  The present invention can be used for a light emitting element driving device, a light emitting device, and a display panel driving device using them.

10 to 14 Light emitting element group 21 First current driving circuit 23 Current setting resistor 24, 28 Driving MOS transistor 25, 36 Operational amplifier 26, 26A to 26E Constant current driving device 27, 27A to 27E Second current driving circuit 29 , 29A to 29E, 38 Comparator 34 Current setting power source 35 Shunt current control power source 43 Shunt current setting resistor

Claims (19)

A constant current driving device for driving a load with current,
A first terminal connected to the other end of the load, one end of which is connected to a first power source;
A second terminal connected to the other end of the current setting element for setting a current value of a current flowing through the load, one end of which is connected to a second power source;
A third terminal connected to the other end of the shunt current setting element having one end connected to the load or the other end of the current setting element;
A first current drive circuit connected between the first terminal and the second terminal;
When one end of the shunt setting element is connected to the other end of the load, it is connected between the third terminal and the second terminal, and one end of the shunt setting element is the current setting A second current drive circuit connected between the third terminal and the first terminal, when connected to the other end of the device for use ,
A constant current driving apparatus characterized in that a current flowing through the load is divided and supplied to the first current driving circuit and the second current driving circuit. The first current driving circuit includes a first operational amplifier and a first transistor,
The first transistor is connected so that a current flows between the first terminal and the second terminal, and a control terminal of the first transistor is connected to an output of the first operational amplifier, One input of the first operational amplifier is connected to the second terminal, and the other input of the first operational amplifier is connected to a current setting power source for setting a current value to flow current to the load. The constant current drive device according to claim 1, further comprising a fourth terminal. The second current driving circuit includes a switching element that controls whether or not the current flows between the first terminal or the second terminal and the third terminal, and turns on / off the switching element. 3. The constant current drive device according to claim 2, further comprising a shunt control circuit for controlling. The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a first comparator that is the shunt control circuit, and one input of the first comparator has the input 4. The constant current drive according to claim 3, wherein a first terminal is connected, and the other input of the first comparator includes a fifth terminal to which a shunt current setting power source is connected. apparatus. The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a first comparator that is the shunt control circuit, and one input of the first comparator has the input A second terminal is connected, and the other input of the first comparator includes a fifth terminal to which a third power source having a potential higher than the potential of the current setting power source is connected. 4. The constant current drive device according to claim 3, wherein 6. The constant current drive according to claim 4, wherein an output of the first comparator is input to the first operational amplifier so that on / off of the first transistor can be controlled. apparatus. The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a second operational amplifier serving as the shunt control circuit, and one input of the second operational amplifier includes the input A second terminal is connected, and the other input of the second operational amplifier is provided with a fifth terminal to which a third power supply having a potential higher than the potential of the current setting power supply is connected. 4. The constant current drive device according to claim 3, wherein A second comparator having one input connected to the first terminal and the other input connected to a sixth terminal to which a potential detection power source to be compared for potential detection of the first terminal is connected With
The output of the second comparator is input to the first operational amplifier and the second operational amplifier so that on / off of the first transistor and the second transistor can be controlled. 8. The constant current drive device according to 7. A load connected at one end to a first power source and driven by current;
A current setting element that has one end connected to a second power source and sets a current value of a current flowing through the load;
A first current drive circuit connected between the other end of the load and the other end of the current setting element;
A second current drive circuit connected in series with the shunt current setting element and connected in parallel with the first current drive circuit between the other end of the load and the other end of the current setting element; ,
A load driving apparatus characterized in that a current flowing through the load is divided and supplied to the first current driving circuit and the second current driving circuit. The load driving apparatus according to claim 9, wherein the load is a plurality of light emitting elements connected in series. 10. The load driving device according to claim 9, wherein the current setting element and the shunt current setting element are resistors. The first current driving circuit includes a first operational amplifier and a first transistor,
The first transistor is connected so that a current flows between the other end of the load and the other end of the current setting element, and a control terminal of the first transistor is connected to an output of the first operational amplifier. The other end of the current setting element is connected to one input of the first operational amplifier, and the other input of the first operational amplifier sets a current value for setting a current value to flow through the load. 10. The load driving device according to claim 9, wherein a power supply for setting is connected. The second current driving circuit includes: a switching element that controls whether or not a shunt current flows between the other end of the load or the other end of the current setting element and one end of the shunt current setting element; and the switching 13. The load driving device according to claim 12, further comprising a shunt control circuit for controlling on / off of the element. The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a first comparator that is the shunt control circuit, and one input of the first comparator has the input 14. The load driving device according to claim 13, wherein the other end of the load is connected, and a shunt current setting power source is connected to the other input of the first comparator. The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a first comparator that is the shunt control circuit, and one input of the first comparator has the input The other end of the current setting element is connected, and the other input of the first comparator is connected to a third power source having a potential higher than that of the current setting power source. 13. The load driving device according to 13. The load driving device according to claim 14, wherein an output of the first comparator is input to the first operational amplifier so that on / off of the first transistor can be controlled. . The switching element is a second transistor, and a control terminal of the second transistor is connected to an output of a second operational amplifier serving as the shunt control circuit, and one input of the second operational amplifier includes the input The other end of the current setting element is connected, and the other input of the second operational amplifier is connected to a third power source having a potential higher than that of the current setting power source. 13. The load driving device according to 13. A second comparator to which one input is connected to the other end of the load and the other input is connected to a potential detection power source to be compared for potential detection at the other end of the load;
The output of the second comparator is input to the first operational amplifier and the second operational amplifier so that on / off of the first transistor and the second transistor can be controlled. 17. The load driving device according to 17. A light emitting device including a plurality of light emitting element groups including a plurality of light emitting elements connected in series;
A plurality of constant current driving devices connected to one end of each of the light emitting element groups;
A plurality of current setting elements that are connected to one end of each of the constant current drive devices and set a current value of a current that flows to each of the light emitting element groups;
Each of the constant current driving devices includes a first current driving circuit connected between one end of the light emitting element group and one end of the current setting element, and the constant current driving device includes one end of the light emitting element group. And a second current drive circuit connected in series with the shunt current setting element and in parallel with the first current drive circuit, between one end of the current setting element and
A load driving device characterized in that a current flowing through each of the light emitting element groups is divided and supplied to the first current driving circuit and the second current driving circuit of each of the constant current driving devices.

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