JP2007306051A - Light control unit and photoirradiation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent malfunction by noise and the damage of a switch element by an overcurrent ideally even if the period of an ON signal in a PWM signal is extremely short. <P>SOLUTION: There are provided: the switch element 31 for controlling the continuity of current to an LED 11; a light control circuit 32 for controlling the brightness of the LED 11; a current detection circuit 33 for detecting whether current flowing in the switch element 31 exceeds the prescribed maximum value; a determination circuit 34 for determining whether an overcurrent state is set, where the phenomenon where the current detection circuit 33 detects that the value of the current flowing in the switch element 31 exceeds the maximum value for a period when the PWM signal is the ON, at least once, is repeated for a plurality of cycles continuously; and a protection circuit 35 for stopping the operation of the switch element 31 when it is determined that the overcurrent state is set in the determination circuit 34. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light control device that adjusts the brightness of a light emitting diode by PWM control and a light irradiation system including the light control device.

  Conventionally, two typical methods are known as dimming methods for light emitting diodes (hereinafter sometimes referred to as LEDs). One is a continuous current control system that controls the continuous current value that flows to the LED, and the other is repeated ON / OFF at a fast cycle, and the ratio of the ON signal period to the OFF signal period is changed to appear. This is a PWM control method for controlling brightness.

  Compared with the current control method that mainly uses the non-saturation region of the switch element, the PWM control method has an advantage that the loss in the switch element can be suppressed because the saturation region is mainly used. However, the PWM control method merely controls the apparent brightness, and since the LED is actually repeatedly turned on / off, the image is taken at a fast shutter speed that can sense the on / off. If the operation is performed, there may be a problem that the captured image is bright or dark depending on the timing of the shooting.

  In particular, when photographing at a very high shutter speed (for example, 1/1000 second) is performed recently, such as when used for product surface inspection, if the PWM control method is used in such a place, A basic period with a length of 1/10 or less is obtained. Since the dimming is performed by further dividing the basic period, for example, if it is attempted to finely control to 256 gradations, the period (pulse width) of the ON signal is on the order of several tens of nsec during the darkest dimming. .

  However, if an overcurrent occurs when the period of the ON signal is extremely short (several tens of nsec), the overcurrent protection circuit provided on the power supply side may not operate and the switch element may be damaged. The overcurrent protection circuit on the power supply side is designed to be somewhat insensitive for the purpose of preventing malfunction due to noise, and does not react to the above-described overcurrent with a very short time width.

  In order to prevent this, the overcurrent protection circuit is simply made sensitive. However, malfunctions due to noise frequently occur.

  For example, Patent Document 1 discloses a protection circuit that stops operation only when the number of times that the current flowing through the switch element exceeds a certain value reaches a predetermined number. .

However, this protection circuit always detects current regardless of the period of the ON signal and the period of the OFF signal. That is, even if the noise is generated during the ON signal period or the noise generated during the OFF signal period, the current is counted if the current exceeds a certain value. Therefore, if noise occurs multiple times, even if the noise is generated during the OFF signal period, it still malfunctions, and there is no drastic countermeasure.
JP-A-5-300731

  Accordingly, the present invention has been made in view of such a problem, and even when the ON signal period of the PWM signal is extremely short, the malfunction of the switch element is prevented while the switch element is prevented from being damaged due to overcurrent. This is the main desired issue.

  In other words, the light control device according to the present invention is connected in series with the light emitting diode, and when the ON signal is input to the control terminal, the main path is conducted and current flows through the light emitting diode, and the OFF signal is supplied to the control terminal. A switching element that interrupts the main path when current is input to prevent current from flowing to the light emitting diode, and a PWM signal having a predetermined frequency that switches between an ON signal period and an OFF signal period in one cycle. A dimming circuit that outputs to the control terminal of the switch element and controls the brightness of the light emitting diode according to the ratio of the ON signal period and the OFF signal period, and the current flowing through the switch element has a predetermined upper limit value. A current detection circuit for detecting whether or not the current exceeds the upper limit value during a period in which the PWM signal is ON, A determination circuit that determines whether or not the detection circuit is in an overcurrent state that is detected even once and the phenomenon is continuously repeated for a plurality of cycles; and when the determination circuit determines that the current is in an overcurrent state And a protection circuit for stopping the operation of the switch element.

  In such a case, since overcurrent detection is performed only in the period of the ON signal in synchronization with the PWM signal, noise generated in the period of the OFF signal can be ignored, and malfunction can be prevented. Further, even if noise occurs during the ON signal period, it is determined that the overcurrent state occurs only when it is detected continuously for a plurality of cycles, so noise generated during the ON signal period can also be eliminated. Therefore, even when the period of the ON signal in the PWM signal is extremely short, it is possible to suitably prevent damage to the switch element due to overcurrent while preventing malfunction due to noise.

  It further comprises a recovery switch, and after the operation of the switch element is stopped by the protection circuit, the operation of the switch element is maintained in a stopped state until the operation of the recovery switch is performed. desirable. In this case, the light control device can be prevented from starting until the operator eliminates the cause of the overcurrent state after the overcurrent state is reached.

  Instead of the protection circuit, when the determination circuit determines that an overcurrent state is present, it may include notification means for notifying that effect. In such a case, it is known that an overcurrent state has occurred, and the operator can prevent the switch element from being damaged by turning off the main power supply.

  In addition, the light irradiation system according to the present invention includes a light emitting diode and the light emitting diode connected in series. When an ON signal is input to the control terminal, the main path is conducted and current flows through the light emitting diode. , A switching element that interrupts the main path when an OFF signal is input to the control terminal and prevents current from flowing through the light emitting diode, and a predetermined period in which the ON signal period and the OFF signal period are switched within one cycle. A PWM signal having a frequency is output to the control terminal of the switch element, and a dimming circuit that controls the brightness of the light emitting diode according to the ratio of the ON signal period to the OFF signal period, and flows through the switch element A current detection circuit for detecting whether or not the current exceeds a predetermined upper limit value, and a current value flowing through the switch element during a period in which the PWM signal is ON. When the current value exceeds the limit value, the current detection circuit detects even once, and the determination circuit determines whether or not the phenomenon is in an overcurrent state in which the phenomenon is continuously repeated for a plurality of cycles, and the determination circuit sets the overcurrent state. And a protection circuit that stops the operation of the switch element when it is determined to be present.

  In such a case, since overcurrent detection is performed only in the period of the ON signal in synchronization with the PWM signal, noise generated in the period of the OFF signal can be ignored, and malfunction can be prevented. Further, even if noise occurs during the ON signal period, it is determined that the overcurrent state occurs only when it is detected continuously for a plurality of cycles, so noise generated during the ON signal period can also be eliminated. Therefore, even when the period of the ON signal in the PWM signal is extremely short, it is possible to prevent the malfunction of the switch element due to overcurrent while preventing malfunction due to noise.

  In addition, instead of the protection circuit, it may be provided with notifying means for notifying that when the determination circuit determines that an overcurrent state exists.

  According to the present invention configured as described above, since overcurrent detection is performed only in the period of the ON signal in synchronization with the PWM signal, noise generated in the period of the OFF signal can be ignored, and malfunction can be prevented. it can. Further, even if noise occurs during the ON signal period, it is determined that the overcurrent state occurs only when it is detected continuously for a plurality of cycles, so noise generated during the ON signal period can also be eliminated. Therefore, even when the period of the ON signal in the PWM signal is extremely short, it is possible to suitably prevent damage to the switch element due to overcurrent while preventing malfunction due to noise.

  An embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating the entire light irradiation system according to the present embodiment, and FIG. 2 is a schematic circuit configuration diagram of the light irradiation system. This light irradiation system is separated from the illuminating device 1 and the illuminating device 1 and is housed in the same casing as the power source 2 and the power source 2 arranged separately from each other and connected by an electric cable 4. And a light control device 3.

  The illuminating device 1 is, for example, a cylindrical one, and includes a light emitting diode (LED) 11 and a light emission port 13 that emits light from the LED 11 forward. The illuminating device 1 can be used as a light source for coaxial illumination, for example, and directly irradiates light from the light irradiation port 13 or attaches an optical fiber F to the light irradiation port 13 through the optical fiber F. It can be irradiated with light.

  Further, the lighting device 1 is provided with an external connection terminal (not shown) including a plus terminal and a minus terminal, and one or several LEDs 11 and a current limiting resistor 12 are provided between the plus terminal and the minus terminal. Connected directly. And the electric cable 4 is connected and electrically connected with a power supply. Here, the LED 11 can flow a current of 200 mA or more (for example, preferably 200 mA to 2 A) continuously for a predetermined time, and emits light with a much larger light amount than a conventional one. To do.

  The power source 2 is, for example, a constant voltage direct current type that supplies a constant voltage to the LED 11, and is electrically connected to the LED 11 by an electric cable 4 via an external connection terminal.

  The light control device 3 is housed in the casing of the power supply 2 and is a dimming circuit that controls the brightness of the LED 11 and an FET (electrolytic effect transistor) 31 as a switch element that controls conduction of current to the LED 11. A certain PWM controller 32, a current detection circuit 33 that detects whether or not the current flowing through the FET 31 exceeds a predetermined upper limit value, and whether or not an overcurrent state is determined based on the detection result of the current detection circuit 33 And a protection circuit 35 that stops the operation of the FET 31 when it is determined by the determination circuit 34 that the overcurrent state is present.

  Hereinafter, in the present embodiment, a path including the current limiting resistor 12, the LED 11, the FET 31, and a current detection resistor 331 described later is connected to the power supply voltage line and the ground line in series.

  Below, each part 31-35 is demonstrated.

  When an ON signal is input to the gate terminal 311, the FET 31 conducts the main path A and causes a current to flow through the LED 11. When an OFF signal is input to the gate terminal 311, the FET 31 interrupts the main path A and a current flows through the LED 11. It will prevent it from flowing.

  As shown in FIG. 3, the PWM controller 32 outputs a PWM signal having a predetermined frequency at which the ON signal period and the OFF signal period are switched within one cycle to the control terminal 311 of the FET 31, and the ON signal period. The brightness of the light emitting diode 11 is controlled by the ratio of the OFF signal period.

As shown in FIG. 2, the current detection circuit 33 detects whether or not the current flowing through the FET 31 exceeds a predetermined upper limit value. The current detection circuit 33 includes a current detection resistor 331 connected in series to the FET 31 and the current A comparator 332 that compares the output voltage V _s generated when passing through the current detection resistor 331 and a predetermined reference voltage V _ref and outputs the comparison signal to the determination circuit 34 is provided. Here, the reference voltage V _ref is a voltage generated when a current having a predetermined upper limit value flows through the current detection resistor 331.

The comparator 332 compares the output voltage V _s with the reference voltage V _ref, and when the output voltage V _s is equal to or lower than the reference voltage V _ref , the comparator 332 has an L (Low) level, and the output voltage V _s is higher than the reference voltage V _ref. If it is larger, an H (High) level comparison signal is output to the decision circuit 34. That is, a comparison signal of L level is output to the determination circuit 34 when the current flowing through the FET 31 is less than or equal to a predetermined upper limit value, and an H level comparison signal is output when the current flowing through the FET 31 exceeds the predetermined upper limit value.

Judging circuit 34, only by focusing period of the ON signal in the PWM signal whether the overcurrent state based on the comparison result between the output voltage V _s and the reference voltage V _ref in that period by the comparator 332 . Then, the determination signal is output to the protection circuit 35.

  As a specific overcurrent state determination method, as shown in FIG. 4, the current value flowing through the FET 31 is predetermined even once during the ON signal period in synchronization with the PWM signal for each cycle of the PWM signal. When the state exceeds the upper limit value and the state is continuously repeated for a plurality of cycles, it is determined that the state is an overcurrent state. More specifically, when the comparison signal from the determination circuit 34 is received and the comparison signal is an H level signal even once during the ON signal period, and the phenomenon is repeated continuously for a plurality of cycles. It is determined that there is an overcurrent condition. In the OFF signal period, it is not determined whether the comparison signal is L level or H level.

As shown in FIG. 2, the protection circuit 35 stops the operation of the FET 31 when it is determined by the determination circuit 34 that the overcurrent state is present. Specifically, when the determination circuit 34 determines that the output voltage V _s exceeds the reference voltage V _ref continuously for a plurality of cycles, the operation of the FET 31 is stopped and the main path A is set in a non-energized state. In the present embodiment, the protection circuit 35 outputs a stop signal for stopping the FET 31 to the PWM controller 32.

  The PWM controller 32 outputs, to the gate terminal 311 of the FET 31, a PWM signal having a predetermined frequency in which the ON signal period and the OFF signal period are switched within one cycle, and the ON signal period and the OFF signal period. The brightness of the LED is controlled based on the ratio of.

  Further, when a stop signal from the protection circuit 35 is input, the PWM controller 32 outputs an OFF signal to the FET 31 to stop the operation of the FET 31.

  Therefore, the light control device 3 of the present embodiment includes the recovery switch 5 for recovering the operation of the FET 31. Then, after the operation of the FET 31 is stopped by the protection circuit 35, the operation of the FET 31 is maintained in a stopped state until the operation of the recovery switch 5 is performed. When the recovery switch 5 is operated, a recovery signal is output from the recovery switch 5 to the PWM controller 32, and the PWM controller 32 outputs a PWM signal to the FET 31 to control the FET 31.

  Next, the operation of the light irradiation system according to this embodiment configured as described above will be described with reference to FIG.

When normal, the output voltage V _s from the current detection resistor 331 is equal to or lower than the reference voltage V _ref . Therefore, the comparison signal from the comparator 332 becomes L level, and the determination circuit 34 determines that it is not in an overcurrent state and outputs the determination signal to the protection circuit 35. The protection circuit 35 keeps the main path A in a normal state and does not output a stop signal to the PWM controller 32.

During an overcurrent condition, the output voltage _{V s} of the current detecting resistor 331 is larger than the reference voltage _{V ref.} Therefore, the comparison signal from the comparator 332 to the determination circuit 34 becomes H level. At this time, the comparison signal is at the H level in the period of the ON signal continuously for a plurality of cycles, and the determination circuit 34 determines that it is in an overcurrent state. Then, the determination signal is output to the protection circuit 35. The protection circuit 35 outputs a stop signal for stopping the FET 31 to the PWM controller 32. Thereby, the operation of the FET 31 is stopped in an overcurrent state, and damage can be prevented. In the conventional method, when the period of the ON signal is short (in the present embodiment, about 63 ns), the overcurrent protection of the power source 2 does not operate and the FET 31 is damaged.

  As described above, according to the light irradiation system according to the present embodiment, the overcurrent detection is performed only in the period of the ON signal in synchronization with the PWM signal, and therefore noise generated in the period of the OFF signal can be ignored. Malfunctions can be prevented. Further, even if noise occurs during the ON signal period, it is determined that the overcurrent state occurs only when it is detected continuously for a plurality of cycles, so noise generated during the ON signal period can also be eliminated. Therefore, even when the period of the ON signal in the PWM signal is extremely short, it is possible to suitably prevent damage to the FET 31 due to overcurrent while preventing malfunction due to noise.

  Since the recovery switch 5 is provided and the operation of the FET 31 is stopped by the protection circuit 35, the operation of the FET 31 is maintained in the stopped state until the operation of the recovery switch 5 is performed. The light irradiation system can be prevented from starting until the operator or the like eliminates the cause of the overcurrent state after entering the state.

  The present invention is not limited to the above embodiment.

  Regarding the illumination device, a plurality of light emitting diodes (LEDs) 11 may be provided.

  Regarding the protection circuit, in the embodiment, the operation of the FET is stopped by outputting the stop signal to the dimming signal, but in addition, the control signal is directly output to the FET to stop the operation. Alternatively, the main switch of the power source or the light irradiation system may be turned off.

  It is also conceivable to provide notifying means for notifying that when the determination circuit determines that an overcurrent state exists instead of or together with the protection circuit. As a specific example of the notification means, for example, a device that emits sound, a device that blinks light, or the like can be considered. In such a case, since it is possible to notify the operator that an overcurrent has occurred, it is possible to prevent the FET from being damaged by the overcurrent.

  Further, when the ON signal period is relatively long, it may be determined whether or not there is an overcurrent a plurality of times within the ON signal period of one cycle. In this case, it may be considered that the number of times of monitoring in one ON signal period is taken into consideration.

  Furthermore, in the embodiment, the protection circuit outputs a stop signal to the PWM controller to stop the operation of the switch element. In addition to this, the protection circuit outputs a stop signal to the power supply to bring down the power supply. You may do it.

  In addition, some or all of the above-described embodiments and modified embodiments may be combined as appropriate, and the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. .

1 is an overall configuration diagram showing an embodiment of the present invention. The schematic circuit block diagram of the light irradiation system in the embodiment. The figure which shows the period of the ON signal and OFF signal in the embodiment. The figure which shows operation | movement of the light control apparatus in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Illumination device 11 ... Light emitting diode (LED)
2 ... Power supply 3 ... Light control device 31 ... Switch element (FET)
32 ... Dimming circuit (PWM controller)
33 ... Current detection circuit 34 ... Determination circuit 35 ... Protection circuit 4 ... Electric cable 5 ... Recovery switch

Claims (5)

Connected in series with the light emitting diode, the main path becomes conductive when an ON signal is input to the control terminal, current flows through the light emitting diode, and the main path is cut off when the OFF signal is input to the control terminal A switching element for preventing current from flowing through the light emitting diode;
A PWM signal having a predetermined frequency that switches between an ON signal period and an OFF signal period within one cycle is output to the control terminal of the switch element, and a light emitting diode is selected depending on the ratio of the ON signal period and the OFF signal period. A dimming circuit that controls the brightness of the
A current detection circuit for detecting whether or not a current flowing through the switch element exceeds a predetermined upper limit;
Whether or not the current value flowing through the switch element exceeds the upper limit value during the period in which the PWM signal is ON is detected by the current detection circuit even once, and the phenomenon is in an overcurrent state in which the phenomenon is continuously repeated for a plurality of cycles. A determination circuit for determining whether or not
And a protection circuit that stops the operation of the switch element when the determination circuit determines that an overcurrent state is present.   A recovery switch is further provided, and after the operation of the switch element is stopped by the protection circuit, the operation of the switch element is maintained in a stopped state until the operation of the recovery switch is performed. The light control apparatus according to 1. Connected in series with the light emitting diode, the main path becomes conductive when an ON signal is input to the control terminal, current flows through the light emitting diode, and the main path is cut off when the OFF signal is input to the control terminal A switching element for preventing current from flowing through the light emitting diode;
A PWM signal having a predetermined frequency that switches between an ON signal period and an OFF signal period within one cycle is output to the control terminal of the switch element, and light is emitted depending on the ratio of the ON signal period and the OFF signal period. A dimming circuit for controlling the brightness of the diode;
A current detection circuit for detecting whether or not a current flowing through the switch element exceeds a predetermined upper limit;
Whether or not the current value flowing through the switch element exceeds the upper limit value during the period in which the PWM signal is ON is detected by the current detection circuit even once, and the phenomenon is in an overcurrent state in which the phenomenon is continuously repeated for a plurality of cycles. A determination circuit for determining whether or not
A light control device comprising notification means for notifying that when the determination circuit determines that an overcurrent state exists. A light emitting diode;
It is connected in series with the light emitting diode, and when the ON signal is input to the control terminal, the main path becomes conductive and current flows through the light emitting diode, and when the OFF signal is input to the control terminal, the main path is A switching element that cuts off and prevents current from flowing through the light emitting diode;
A PWM signal having a predetermined frequency that switches between an ON signal period and an OFF signal period within one cycle is output to the control terminal of the switch element, and light is emitted depending on the ratio of the ON signal period and the OFF signal period. A dimming circuit for controlling the brightness of the diode;
A current detection circuit for detecting whether or not a current flowing through the switch element exceeds a predetermined upper limit;
Whether or not the current value flowing through the switch element exceeds the upper limit value during the period in which the PWM signal is ON is detected by the current detection circuit even once, and the phenomenon is in an overcurrent state in which the phenomenon is continuously repeated for a plurality of cycles. A determination circuit for determining whether or not
A light irradiation system, comprising: a protection circuit that stops the operation of the switch element when the determination circuit determines that an overcurrent state is present. A light emitting diode;
It is connected in series with the light emitting diode, and when the ON signal is input to the control terminal, the main path becomes conductive and current flows through the light emitting diode, and when the OFF signal is input to the control terminal, the main path is A switching element that cuts off and prevents current from flowing through the light emitting diode;
A PWM signal having a predetermined frequency that switches between an ON signal period and an OFF signal period within one cycle is output to the control terminal of the switch element, and light is emitted depending on the ratio of the ON signal period and the OFF signal period. A dimming circuit for controlling the brightness of the diode;
A current detection circuit for detecting whether or not a current flowing through the switch element exceeds a predetermined upper limit;
Whether or not the current value flowing through the switch element exceeds the upper limit value during the period in which the PWM signal is ON is detected by the current detection circuit even once, and the phenomenon is in an overcurrent state in which the phenomenon is continuously repeated for a plurality of cycles. A determination circuit for determining whether or not
A light irradiation system comprising: notifying means for notifying that when the determination circuit determines that an overcurrent state exists.