LED driving device

Abstract

To provide an LED driving device that can prevent a situation where an excessive surge current flows in an LED and the LED is damaged.SOLUTION: An LED driving device comprises: a light emitting circuit 11 that includes a UV-LED 14; a driving circuit 13 that supplies current to the light emitting circuit 11; and a protection circuit 17 that is provided in the driving circuit 13. The protection circuit 17 comprises an output smoothing capacitor C4 and a resistor for discharge Rr, which are connected in parallel to each other. The LED driving device monitors the current flowing in the UV-LED 14, and when the monitored current falls below a threshold, stops output of the current from the driving circuit 13 to the UV-LED 14. The stop of output of the current causes the resistor for discharge Rr to discharge residual electric charges stored in the output smoothing capacitor C4, and when the output of the current from the driving circuit 13 is resumed, a surge current exceeding the absolute maximum rating due to the residual electric charges does not flow in the UV-LED 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an LED driving device.

Background Art

[0002] Recently, LEDs (light emitting diodes) have come to be used in various products. For example, Patent Document 1 proposes a dispenser provided with an ultraviolet irradiator including a UV-LED that irradiates ultraviolet rays (UV) for sterilizing ice. The ultraviolet irradiator includes a UV-LED and a constant current driving circuit that supplies current to the UV-LED, and is configured to light the UV-LED by supplying a constant current from the constant current driving circuit to the UV-LED with the constant current driving circuit connected to a DC power supply, and irradiate the ice with ultraviolet rays for sterilization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration where the UV-LED is lit (driven) by the constant current drive circuit, after connecting the UV-LED and the constant current drive circuit, and then connecting the constant current drive circuit and the DC power supply, when the power is turned on, a specified constant current is supplied to the UV-LED and it can be lit properly. However, when the connection between the DC power supply and the constant current drive circuit is disconnected while the UV-LED is lit and then reconnected, or when the connection is disconnected with a mechanical safety switch provided between the constant current drive circuit and the UV-LED in the power-on state and then the constant current drive circuit and the UV-LED are reconnected, although it is for a short time, a high surge current exceeding the absolute maximum rating of the UV-LED flows through the UV-LED due to the residual charge stored in the constant current drive circuit, which damages the UV-LED and leads to problems such as immediate failure or performance degradation and failure induction over time. Also, even when the connection between the UV-LED and the constant current drive circuit is interrupted due to failures of various devices and then restored, there is a problem that a high surge current exceeding the absolute maximum rating similarly flows through the UV-LED and causes damage etc.

[0005] In view of the above problems inherent in the prior art described above, the present invention has been proposed to preferably solve these problems, and an object thereof is to provide an LED drive device capable of preventing an excessive surge current from flowing through the LED and causing damage etc.

Means for Solving the Problems

[0006] In order to overcome the above problems and achieve the intended object, the first means is a light emitting circuit (11) provided with an LED (14), a drive circuit (13) for supplying current to the light emitting circuit (11), a protection circuit (17) provided in the drive circuit (13) for discharging the charge stored in the drive circuit (13) to prevent a surge current exceeding the absolute maximum rating of the LED (14) from flowing through the light emitting circuit (11), and the gist is that it is provided with these. According to this configuration, even when there is a mistake in the connection procedure of the light-emitting circuit, the drive circuit, and the power supply, etc., it is possible to prevent the generation of an excessive surge current and prevent the LED from being damaged, etc.

[0007] The second means is characterized in that the protection circuit (17) is a circuit in which a capacitor (C4) and a resistor (Rr) are connected in parallel. According to this configuration, the discharge time constant can be arbitrarily determined by setting the capacitance of the capacitor and the resistance value of the discharge resistor.

[0008] The third means is characterized in that the current flowing through the LED (14) is monitored, and when the current drops below a threshold value, the current output from the drive circuit (13) to the LED (14) is stopped. According to this configuration, when the current flowing through the LED due to a failure or the like drops below the threshold value, the residual charge of the drive circuit can be discharged by the protection circuit, and when the failure or the like is restored, it is possible to prevent an excessive surge current from flowing through the LED and causing damage, etc.

Advantages of the Invention

[0009] The LED driving device according to the present invention can prevent an excessive surge current from being generated at the time of power-on or the like and the LED from being damaged, etc., even when there is a mistake in the connection procedure of each device.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] Next, the LED driving device according to the present invention will be described below with reference to the accompanying drawings by giving preferred embodiments.

Embodiment

[0012] The LED driving device 10 according to the embodiment is provided, for example, in a sterilization device equipped with a UV-LED used for sterilization in a dispenser. As shown in FIG. 1, the LED driving device 10 includes a light emitting circuit 11 and a driving circuit 13 connected to the light emitting circuit 11 via a joint 12 and supplying current to the light emitting circuit 11. The light emitting circuit 11 includes a UV-LED 14 and an interlock switch SW connected to the anode of the UV-LED 14. The driving circuit 13 includes a power supply IC 16 composed of a switching regulator and a protection circuit 17 that prevents a surge current exceeding the absolute maximum rating of the UV-LED 14 from flowing through the light emitting circuit 11 (UV-LED 14). The driving circuit 13 is configured as a chopper circuit capable of supplying a constant current to the light emitting circuit 11. Note that the power supply IC 16 is a so-called constant voltage output type non-isolated switching regulator that is generally used and can be used as a constant current source by changing the wiring of the feedback input (FB terminal 21 described later) of the output voltage.

[0013] As shown in FIG. 1, a power supply line Lp connected to the VCC terminal 18 of the power supply IC 16 is connected to DC24V, which is the main power supply of the sterilization device, and the GND terminal 19 of the power supply IC 16 is connected to a ground line Lg grounded to the ground G. The LX terminal 20 of the power supply IC 16 is connected to one end of an inductor L via a line L1, and a line L2 connected to the other end of the inductor L is connected to one end of the interlock switch SW via the joint 12, and the other end of the interlock switch SW is connected to the anode of the UV-LED 14. Further, the cathode of the UV-LED 14 is connected to one end of a first resistor R1 via a line L3 through the joint 12, and the other end of the first resistor R1 is connected to the ground line Lg. Also, the FB terminal (feedback terminal) 21 of the power supply IC 16 is connected to a line L4 connected to the line L3, and the FB terminal is connected to the cathode of the UV-LED 14 via the line 3, the line 4, and the joint 12.

[0014] A control microcomputer (monitoring means) 22 is connected to the line L4 via a second resistor R2, and an EN terminal 23 of a power supply IC 16 is connected to the control microcomputer 22 via a line L5. The power supply IC 16 is configured such that its operation / stop can be selected by an external logic circuit (not shown) connected to the control microcomputer 22, and the normal lighting / extinguishing operation of the UV-LED 14 is performed by the external logic circuit. In the control microcomputer 22, the line L4 is connected to a voltage input port, and the FB terminal voltage of the power supply IC 16 (the drive current of the UV-LED 14) sent on the line L4 is monitored. Also, the control microcomputer 22 can control the operation of the power supply IC 16 by setting the EN terminal 23 to a high level or a low level. When the EN terminal 23 is at a high level, the power supply IC 16 supplies a constant current to the UV-LED 14 to turn it on, and when the EN terminal 23 is at a low level, the output of the constant current is stopped to turn off the UV-LED 14.

[0015] As shown in FIG. 1, a first capacitor C1 is connected between the line L2 and the line L3, and a second capacitor C2 is connected between the BST terminal 25 of the power supply IC 16 and the line L1. Also, a third capacitor C3 is connected between the power supply line Lp and the ground line Lg, and a third resistor R3 is connected between the line L5 and the ground line Lg. The third resistor R3 is used to ensure the stop of the power supply IC 16 when the control microcomputer 22 is initialized. Also, the cathode of a Schottky barrier diode D is connected between the connection point a of the second capacitor C2 on the line L1 and the inductance L, and the anode of the Schottky barrier diode D is connected to the ground line Lg. The Schottky barrier diode D, the inductance L, and an output smoothing capacitor C4 (described later) constitute a buck chopper circuit. When the power supply IC 16 supplies power to the line L1 in a pulsed manner, power supply to the inductance L from the ground line Lg via the Schottky barrier diode D is maintained during the period when there is no power supply.

[0016] Between the connection point b of the first capacitor C1 and the inductance L on the line L2 and between the connection point c of the Schottky barrier diode D and the first resistor R1 on the ground line Lg, the protection circuit 17 is connected. The protection circuit 17 is configured by connecting an output smoothing capacitor (capacitor) C4 and a discharge resistor (resistor) Rr in parallel, and discharges the charge (residual charge) accumulated in the output smoothing capacitor C4 with the discharge resistor Rr, thereby preventing a surge current exceeding the absolute maximum rating from flowing through the UV-LED 14. Note that the first capacitor C1 is arranged in a substantially parallel relationship with the output smoothing capacitor C4, but the first capacitor C1 is provided for the purpose of not applying an impulse overvoltage to the UV-LED 14, and the capacitance of the first capacitor C1 is set to a value sufficiently smaller than the capacitance of the output smoothing capacitor C4, and the influence on the discharge time constant described later of the protection circuit 17 can be practically ignored. Also, by connecting the current path of the protection circuit 17 (discharge resistor Rr) to the ground line Lg, which is a different path from the current path (line L4) to the control microcomputer 22, it is configured not to be a factor of error in the constant current operation. Further, the output smoothing capacitor C4 has a function of suppressing output fluctuations when power is supplied to the inductance L via the Schottky barrier diode D.

[0017] In the drive circuit 13, the inductance value of the inductance L, the capacitances of the capacitors C1, C2, C3, C4, and the resistance values of the resistors R1, R2, R3 are set so that a constant current of a rated current (for example, 170 mA) capable of lighting the UV-LED 14 flows from a 24V DC power supply. Also, the resistance value of the discharge resistor Rr discharges the residual charge accumulated in the output smoothing capacitor C4 as quickly as possible when the UV-LED 14 is controllably turned off by operating the line L5 path, and considering the current consumption and heat generation during lighting, it is set to an appropriate value that can be discharged within the discharge time (discharge time constant) defined by the capacitance of the output smoothing capacitor C4 and the resistance value of the discharge resistor Rr. For example, when the capacitance of the output smoothing capacitor C4 is 1 μF, by setting the resistance value of the discharge resistor Rr to 20 KΩ, the discharge time constant becomes 30 ms.

[0018] Here, when the reference voltage of the power supply IC 16: VR (the voltage of the FB terminal 21 when the UV-LED 14 is lit, which is a unique value set for each specification of the power supply IC 16) and the resistance value of the first resistor R1: RS are used, the drive current CC has the following relationship. CC = VR ÷ RS ··· (1) Also, when the FB terminal voltage: VK monitored by the control microcomputer 22 and the monitoring current: E flowing through the UV-LED 14 are used, the monitoring current E has the following relationship. E = VK ÷ RS ··· (2) From the relationships of (1) and (2) above, the value of the monitoring current E flowing through the UV-LED 14 is calculated from the FB terminal voltage VK monitored by the control microcomputer 22.

[0019] Even though the signal (power-on signal) is input to the control microcomputer 22 upon power-on and the LED driving device 10 is in a state where the UV-LED 14 is lit, when the monitoring current E does not become equal to or greater than a preset threshold value, or when the monitoring current E that has risen above the threshold value drops below the threshold value, the control microcomputer 22 determines that an abnormality such as a failure, disconnection, hard interlock operation of the UV-LED 14, or interruption of the flowing monitoring current E has occurred, and performs the following abnormal-time control. 1. Control the line L5 path from the control microcomputer 22 to immediately stop the current output of the power supply IC 16. Also, operate the timer built into the control microcomputer 22. Due to the stop of the current output from the power supply IC 16 by the control of 1., the residual charge accumulated in the output smoothing capacitor C4 of the protection circuit 17 is quickly discharged via the discharge resistor Rr. Note that the timer is set with a waiting time based on the discharge time constant in the protection circuit 17. 2. When the waiting time has elapsed and the UV-LED 14 is in a lit state (the power-on signal is input) in terms of control, attempt reconnection. That is, resume the current output from the power supply IC. If the monitoring current E becomes equal to or greater than the threshold value, it is considered a successful reconnection and operation continues. However, if the monitoring current E is less than the threshold value, repeat 1. to 2. 3. Even if the reconnection is attempted for a preset reconnection allowable time or a specified number of reconnection times, if the monitoring current E does not reach the threshold value, an abnormality notification of "sterilization lamp not lit" is performed by notification means such as a lamp, a speaker, a display (not shown) with the EN terminal 23 kept at the L level.

[0020] The abnormal control by the control microcomputer 22 will be described more specifically. When, for example, 50 mA is set as the threshold value, the control microcomputer 22 controls the line L5 path by inputting a power-on signal to set the EN terminal 23 of the power supply IC 16 to the H level. After a predetermined time (for example, 5 ms later), the monitoring current E is checked. If it is less than 50 mA, it is determined that a disconnection abnormality or the like has occurred, and the control in 1. above is performed. Also, the control microcomputer 22 sets the EN terminal 23 to the L level and waits. Note that if the monitoring current E is 50 mA or more, the control microcomputer 22 determines that each device is normal and controls to perform steady lighting of the UV-LED 14 with the EN terminal 23 kept at the H level. Also, when the monitoring current E becomes less than 50 mA in the steady lighting state of the UV-LED 14, the control microcomputer 22 determines that a disconnection abnormality or the like has occurred as described above, performs the control in 1. above, and controls the line L5 path to set the EN terminal 23 to the L level and wait.

[0021] In the standby state, if a power-on signal is input after the waiting time has elapsed, the controls in 2. and 3. above are performed accordingly. Note that in the standby state, if a power-on signal is input before the waiting time has elapsed, the control microcomputer 22 does not attempt reconnection until the waiting time has elapsed. That is, reconnection is not attempted until the discharge by the discharge resistor Rr of the residual charge accumulated in the output smoothing capacitor C4 is completed. Also, if a power-on signal is not input even after the waiting time has elapsed, the control microcomputer 22 keeps the EN terminal 23 at the L level and waits.

[0022] 〔Operation of the embodiment〕 Next, the operation of the LED driving device according to the embodiment will be described.

[0023] With the interlock switch SW closed, after connecting the drive circuit 13 to a 24V DC power supply and then turning on the power (inputting a power-on signal by turning on the power switch), the control microcomputer 22 controls the line L5 path to set the EN terminal 23 of the power supply IC 16 to the H level. As a result, a constant current (170 mA) is supplied from the drive circuit 13 to the UV-LED 14, and the UV-LED 14 lights up properly.

[0024] While the UV-LED 14 is lit, if the connection between the drive circuit 13 and the DC power supply is disconnected and then reconnected, or if the interlock switch SW is opened while the UV-LED 14 is lit to disconnect the connection between the UV-LED 14 and the drive circuit 13, and then the interlock switch SW is closed to reconnect the UV-LED 14 and the drive circuit 13, when the control microcomputer 22 confirms that the monitoring current E flowing through the UV-LED 14 has dropped below the threshold value when the connection between the drive circuit 13 and the DC power supply is disconnected or when the connection between the UV-LED 14 and the drive circuit 13 is disconnected, it controls the line L5 path to set the EN terminal 23 of the power supply IC 16 to the L level and immediately stops the current output from the power supply IC 16. As a result, the residual charge stored in the output smoothing capacitor C4 of the protection circuit 17 is quickly discharged by the discharge resistor Rr. That is, when the drive circuit 13 and the DC power supply are reconnected and when the UV-LED 14 and the drive circuit 13 are reconnected, there is no residual charge left in the output smoothing capacitor C4, and it is possible to prevent a surge current exceeding the absolute maximum rating from flowing through the UV-LED 14 due to the residual charge of the output smoothing capacitor C4, thereby preventing damage to the UV-LED 14.

[0025] Also, when the monitoring current E being monitored by the control microcomputer 22 becomes less than the threshold value while the power-on signal is being input, the control microcomputer 22 determines that an abnormality such as a failure or disconnection of the UV-LED 14 has occurred, controls the line L5 path from the control microcomputer 22 to set the EN terminal 23 of the power supply IC 16 to the L level, and immediately stops the current output of the power supply IC 16. Due to the stop of the current output from the power supply IC 16, the residual charge of the output smoothing capacitor C4 of the protection circuit 17 is quickly discharged via the discharge resistor Rr. After the waiting time of the timer that operates when the current output from the power supply IC 16 stops has elapsed, if the power-on signal is input, the control microcomputer 22 controls the line L5 path to set the EN terminal 23 of the power supply IC 16 to the H level and resumes the current output of the power supply IC. And when the monitoring current E becomes equal to or greater than the threshold value, it is regarded as a successful reconnection and the operation is continued. However, when the monitoring current E is less than the threshold value, the reconnection control is repeated.

[0026] If the monitoring current E does not become equal to or greater than the threshold value even after the control microcomputer 22 attempts reconnection a preset number of reconnection allowable times or a specified number of reconnection times, in addition to controlling the line L5 path to set the EN terminal 23 of the power supply IC 16 to the L level, an abnormality notification of "sterilization lamp not lit" is performed by the notification means.

[0027] According to the LED driving device 10 of the embodiment, since the protection circuit 17 is provided in the driving circuit 13, even when the connection procedures of the light emitting circuit 11, the driving circuit 13, and the DC power supply are mistaken, the residual charge accumulated in the driving circuit 13 can be discharged to prevent the generation of an excessive surge current caused by the residual charge, and damage to the UV-LED 14 can be prevented. When an excessive surge current occurs, an excessive voltage may also be applied to the FB terminal 21 of the power supply IC 16, which may cause the power supply IC 16 to malfunction. However, in the LED driving device 10 of the embodiment, since the generation of an excessive surge current can be prevented, the malfunction of the power supply IC 16 can also be prevented. Further, since the protection circuit 17 is configured by connecting the output smoothing capacitor C4 and the discharge resistor Rr in parallel, the discharge time constant (waiting time) can be arbitrarily determined by setting the capacitance of the output smoothing capacitor C4 and the resistance value of the discharge resistor Rr. Further, the LED driving device 10 monitors the monitoring current E flowing through the UV-LED 14, and when the monitoring current E drops below the threshold value, the current output from the power supply IC of the driving circuit 13 is stopped to discharge the residual charge of the output smoothing capacitor C4. Therefore, even when the connection between the UV-LED 14 and the driving circuit 13 is temporarily interrupted due to a failure or the like and then the failure is restored, the generation of an excessive surge current can be prevented to prevent damage to the UV-LED 14 and the power supply IC 16.

[0028] According to the LED driving device 10 of the embodiment, when the UV-LED 14 does not light up due to a failure of various devices or the like, an abnormality notification of "sterilization lamp not lit" is performed by the notification means, so that it is possible to safely confirm without directly looking that the sterilization UV-LED 14, which is not preferably directly looked at by a person, is not lit.

[0029] Here, since it is not preferable for humans to directly view the UV-LED 14 used for sterilization, in order to ensure safety when accessing the UV-LED 14 for inspection or the like, an external interlock circuit is provided, and the lighting / extinguishing of the UV-LED 14 may be controlled by opening and closing the switch of the external interlock circuit. In this case, if the circuit between the UV-LED 14 and the drive circuit 13 is configured to be opened and closed by the switch of the external interlock circuit, as described in the section of the problem to be solved by the invention, after the circuit between the UV-LED 14 and the drive circuit 13 is opened by the external interlock circuit and then closed again, a problem may occur in that the UV-LED 14 is damaged or the like due to the generation of an excessive surge current caused by the residual charge of the drive circuit 13. However, in the LED drive device 10 of the embodiment, even if the circuit between the UV-LED 14 and the drive circuit 13 is configured to be opened and closed by the external interlock circuit, damage or the like of the UV-LED 14 due to an excessive surge current caused by the residual charge of the drive circuit 13 can be prevented, so that the external interlock circuit can be safely added.

[0030] Also, in a general indicator using a normal LED, in many cases, a quasi-constant current is generated from a constant voltage drive circuit by a current limiting resistor to cause the LED to emit light. However, since the UV-LED has a large emission intensity (operating current) and a larger variation in the forward voltage compared to a normal LED, in the light emission method using a quasi-constant current power supply supplied from a constant voltage drive circuit, heat generation becomes excessive or the emission intensity cannot be set high due to the variation in the forward voltage. However, since the drive circuit 13 of the embodiment of the LED drive device 10 is configured as a constant current drive circuit to supply a constant current to the UV-LED 14, it has a high degree of freedom with respect to the design constraints corresponding to the emission intensity and heat generation of the UV-LED 14. Further, since the drive circuit 13 is a chopper circuit, it can be made highly efficient and compact.

[0031] 〔Modification Example〕 This application is not limited to the configurations of the foregoing embodiments, and other configurations can be adopted as appropriate. Further, not limited to the following modification examples, various embodiments can be adopted for the configurations described in the embodiments within the scope of the gist of the present invention. 1. In the embodiment, the driving device is for a UV-LED for sterilization, but it can also be adopted as a driving device for visible light / infrared LEDs in devices where the opening and closing of a mechanical connection other than control between the driving circuit and the LED may be performed, such as LEDs in lighting devices and indicators.

Description of Reference Numerals

[0032] 11 Light-emitting circuit, 13 Driving circuit, 14 UV-LED, 17 Protection circuit C4 Output smoothing capacitor (capacitor), Rr Discharge resistor (resistor)

Claims

1. A light-emitting circuit including an LED, a drive circuit for supplying current to the light-emitting circuit, and a protection circuit provided in the drive circuit for discharging the charge stored in the drive circuit to prevent a surge current exceeding the absolute maximum rating of the LED from flowing into the light-emitting circuit. An LED driving device characterized by the above.

2. The LED driving device according to Claim 1, wherein the protection circuit is a circuit in which a capacitor and a resistor are connected in parallel.

3. The LED driving device according to Claim 1 or 2, configured to monitor the current flowing through the LED and stop the current output from the drive circuit to the LED when the current drops below a threshold value.

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