JP2008172513A - Photo coupler circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To considerably extend the life of a photo coupler circuit. <P>SOLUTION: A current-carrying current to a light emission portion 4 at a photo coupler circuit 1 is suppressed to a low level until a predetermined time is past. Then, the current-carrying current to the light emission portion 4 is increased. Thereby, longer life extension can be realized for the photo coupler circuit 1 by a simple circuit structure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photocoupler circuit, and more particularly to a technique for extending the life of an LED light emitting unit.

A photocoupler circuit using a pair of a light emitting unit made of an LED and a light receiving unit made of a photodiode or a phototransistor is widely used for electrical insulation signal transmission. The light emitting unit is intermittently driven by the driver transistor 20 through a current limiting resistor as shown in FIG. The following Patent Document 1 proposes that the light emitting unit is driven with a constant current as shown in FIG. FIG. 9 shows the reduction characteristic (lifetime characteristic) of the light emission amount of the LED.
Japanese Patent Laid-Open No. 5-21850

  The constant current driving method of the light emitting portion of the photocoupler shown in FIG. 8 can suppress the variation of the driving current due to temperature and extend the design life as compared with the constant voltage driving method using the current limiting resistor shown in FIG. However, as shown in FIG. 9, even if energization is performed at a low current value ia that enables reliable signal transmission, the amount of emitted light deteriorates over time according to the current characteristic a and reaches the end of its life at time t0.

  The relationship between the current value and the lifetime in the constant current drive will be further described with reference to FIG. When the drive current is increased, the margin to the transmitted light emission amount threshold value is increased, but the deterioration of the light emitting element is accelerated and the lifetime is not prolonged. Conversely, when the drive current is reduced, the lifetime of the light emitting element itself is extended, but it is understood that the lifetime does not increase because the margin to the transmitted light emission amount threshold is small.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a photocoupler circuit capable of significantly extending the life while suppressing the complexity of the circuit configuration.

  This invention which solves the above-mentioned problem is a photocoupler circuit comprising a photocoupler having a light emitting part and a light receiving part, and a drive circuit for intermittently controlling the input current of the photocoupler. The present invention is characterized by having a current compensation circuit that obtains an aged signal having a correlation and increases the on-current of the light emitting unit when the aged deterioration increases according to the state of the aged signal.

  That is, according to the present invention, in the initial stage of operation, the light emitting unit is driven with a current as low as possible within a range where signal transmission is possible to prevent the deterioration. To deal with the increase. In this way, the lifetime of the photocoupler circuit can be extended with a simple circuit configuration.

  In a preferred aspect, the current compensation circuit detects a cumulative power-on time of the photocoupler as the aging deterioration signal, and controls the drive circuit when the cumulative power-on time exceeds a predetermined threshold value. The on-current of the photocoupler is increased. In this way, the lifetime of the light emitting unit can be greatly extended with a simple circuit configuration.

  In a preferred aspect, the drive circuit comprises a constant current circuit that stabilizes an on-current of the light emitting unit to a predetermined constant current value, and the current compensation circuit substantially includes the constant current when the aging deterioration increases. Increase the value. In this way, it is possible to extend the life of the light emitting section by simply changing a part of the constant current circuit, the circuit configuration is simplified, and in addition, the effect of extending the life by constant current driving can be expected.

  In a preferred aspect, the current compensation circuit includes a driver transistor that intermittently controls an energization current of the light emitting unit, a resistor circuit connected in series with the driver transistor, a voltage drop of the resistor circuit, and a predetermined threshold voltage And an ON / OFF control circuit for intermittently controlling the driver transistor by the output of the comparator and an input pulse signal. In this way, the circuit configuration can be simplified and the life of the light emitting part can be extended.

  In a preferred aspect, the drive circuit includes a failure-time energization prohibition circuit that discriminates whether the output of the photocoupler is good or bad, and inhibits the energization of the light emitting unit when it is defective. Thereby, it is possible to realize the prohibition of energization at the time of failure while sharing the circuit configuration.

  In a preferred aspect, the current compensation circuit detects an amount of electricity having a correlation with the temperature of the light emitting unit, and based on the amount of electricity, the current flowing to the light emitting unit is lower than when the temperature is high. Reduce. This makes it possible to extend the life while further sharing the circuit.

  A preferred embodiment of the photocoupler circuit of the present invention will be described with reference to the drawings. The present invention should not be construed as being limited to the following embodiments, and the technical idea of the present invention can be realized by a combination of other known techniques.

(overall structure)
FIG. 1 is a circuit diagram showing a photocoupler circuit of this embodiment. 1 is a photocoupler, 2 is a drive circuit for intermittently controlling the input current of the photocoupler 1, 3 is a controller with built-in microcomputer that adjusts the input current amount when the drive circuit is on (current adjustment circuit in the present invention), and 4 is a photo The light emitting unit 5 of the coupler 1 is a light receiving unit of the photocoupler 1. The internal circuit itself of the photocoupler 1 is conventional and is well known and irrelevant to the present invention.

(Configuration of drive circuit)
The drive circuit 2 includes a driver transistor 20 that is a source follower transistor that intermittently controls the energization current of the light emitting unit 4 of the photocoupler 1, an ON / OFF control circuit 21 that intermittently controls the driver transistor 20, and a current adjustment comparator. 22 and a resistance circuit 23 which forms a load on the driver transistor 20.

  The resistance circuit 23 includes resistance elements 24 and 25 that form a load resistance of the driver transistor 20 and a transistor 26. The resistance element 25 and the load resistance value switching transistor 26 connected in series with each other are connected in parallel with the resistance element 24.

  A connection point between the driver transistor 20 and the resistance circuit 23 is connected to a negative input terminal of the comparator 22, and a predetermined threshold voltage is applied to a positive input terminal of the comparator 22. The output voltage of the comparator 22 is input to the ON / OFF control circuit 21, and a constant power supply voltage is applied to the drain of the driver transistor 20 through the light emitting unit 4 of the photocoupler 1. In this embodiment, the ON / OFF control circuit 21 includes an AND gate that makes the driver transistor 20 conductive by a logical product voltage of the input pulse signal voltage and the output voltage of the comparator 22, and an output impedance for reducing the output impedance of the AND gate. And a current amplification buffer.

(Explanation of drive circuit operation)
First, an operation in a state where the transistor 26 is turned off and no current flows through the resistance element 25 will be described. The ON / OFF control circuit 21 switches the driver transistor 20 in response to an input pulse signal input from the outside. When the driver transistor 20 is turned on, a current flows through the light emitting section (LED) 4 and the resistor circuit 23 (here, the resistor element 24). When the voltage drop generated in the resistor circuit 23 exceeds the threshold voltage, the output voltage of the comparator 22 is The driver transistor 20 is turned off at a low level, and when the voltage drop of the resistance circuit 23 becomes less than the threshold voltage due to this turn-off, the output voltage of the comparator 22 becomes a high level and the driver transistor 20 is turned on. Thereby, the current flowing through the light emitting unit 4 during the period when the input pulse voltage is at the high level is adjusted to a value obtained by dividing the threshold voltage by the resistance value of the resistance circuit 23.

  Next, an operation in a state where the transistor 26 is turned on and a current flows through the resistance element 25 will be described. When the transistor 26 is turned on, the resistance value of the resistance circuit 23 becomes a parallel combined resistance (r24 · r25 / (r24 + r25) of the resistance elements 24 and 25 if the on-resistance value of the transistor 26 is ignored. When the value decreases, the comparator 22 does not invert until the current flowing into the resistance circuit 23 becomes ((r24 + r25) / r25) = (r24 / r25 + 1)) times before that, and as a result, the input pulse signal When the voltage is at a high level, the current flowing through the light emitting unit 4 through the driver transistor 20 increases (r24 / r25 + 1) times as much as before.

(Explanation of operation of controller 3)
Next, the operation of the controller 3 having a microcomputer configuration will be described with reference to the flowchart shown in FIG. The following routine shall be repeated at a constant interval during power-on.

  First, a power supply voltage is detected (S100), and it waits until it exceeds a predetermined threshold value, and when it exceeds, a low level as a drive current switching signal is output to the transistor 26 (S102). Thereby, the energization current to the light emitting part 4 of the photocoupler 1 becomes the low level. Thereafter, it is determined whether or not the accumulated power-on time has exceeded a predetermined fixed time (S104). If not, the interval time is added to a counter that counts the accumulated power-on time so far (S106). Return to S104. If the accumulated power-on time exceeds a predetermined fixed time, a high level as a drive current switching signal is output to the transistor 26 (S108), and the routine is terminated. Thereby, the energization current to the light emitting part 4 of the photocoupler 1 becomes the high level.

(Example effect)
According to this embodiment described above, the following effects can be obtained.

  First, when the cumulative power-on time of the LED forming the light emitting unit 4 of the photocoupler 1 exceeds a predetermined value, the energization current increases, so the light emission amount of the LED forming the light emitting unit 4 of the photocoupler 1 decreases due to its aging degradation. Even in this case, the light emission amount can be compensated. As a result, it is possible to suppress a change in the duty ratio of a pulse signal that is electrically insulated and transmitted by the photocoupler 1 due to aged deterioration of the LED light emission amount, thereby suppressing a transmission failure.

  In addition, in a state where the cumulative power-on time of the photocoupler 1 has not yet reached a level at which the aging deterioration of the light emission amount does not become a problem, the current flowing to the light emitting unit 4 can be reduced, thereby extending the life of the light emitting unit 4. And power consumption can be reduced.

  FIG. 3 is a characteristic diagram showing the change in the amount of emitted light over time. a is the light emission amount at the current value ia, b is the light emission amount at the current value ib, and c is the light emission amount at the current value ic. ic> ib> ic. The time until the light emission quantity decreases below the required transmission light quantity threshold value at which the signal transmission failure of the photocoupler occurs is substantially faster when the energization current is large.

  Therefore, in this embodiment, the current value ic is energized to the light emitting unit 4 until the time t1 when the accumulated power-on time reaches the predetermined time T, and when it exceeds, the light emission amount at the current value ic is performed. Since the light emission amount at the current value ic, which is a low current value, has been performed so far, the subsequent temporal change in the light emission amount becomes the characteristic line d, so that the lifetime can be extended to time t2.

  Furthermore, in this embodiment, the circuit can be configured simply by adding the resistance element 25 and the transistor 26 to the constant current circuit, and the circuit load for obtaining the above function. Can be reduced. Note that the routine shown in FIG. 2 only adds a few program steps of a microcomputer that controls the operation of other circuits, and the circuit configuration is hardly complicated.

(Modification)
In the above embodiment, the accumulated power-on time is counted as shown in step S106 of FIG. 2, but there may be a case where there is no input pulse signal or a small on-duty ratio even when the power is on. In this case, since the light emitting part 4 of the photocoupler 1 is not turned on, there is a possibility that the light emission amount will not deteriorate over time.

  Therefore, in this aspect, a pulse signal having a good positive correlation in the high level period of the input pulse signal is read into the controller 3, and the accumulated light emission time is obtained by counting the high level period of the pulse signal. When the predetermined value is reached, the resistance value is switched. In this way, it is possible to provide the light emitting unit 4 with current compensation that is more suitable for actual aging degradation.

  For example, as a pulse signal having a good positive correlation during the high level period of the input pulse signal, the input pulse signal is integrated by the capacitor integrating circuit 6 as shown in FIG. One pulse voltage is output to the counter 8 to the counter 8, and the capacitor of the integrating circuit 6 is reset. The controller 3 periodically reads the numerical value of the counter 8, and when the counter 8 reaches a predetermined value, adds 1 to the stored value of its own nonvolatile memory and clears the counter 8. The controller 3 uses the stored value of the nonvolatile memory as the accumulated light emission time.

  In this way, it is possible to switch the energization current of the light emitting unit 4 more appropriately than in the above embodiment.

(Modification)
In the above embodiment, the resistance value of the resistance circuit 23 that is the load resistance of the driver transistor 20 is switched in order to compensate for the aging deterioration of the light emitting unit 4, but instead, the resistance value is applied to the + input terminal of the comparator 22. The threshold voltage to be switched may be switched. For this switching, for example, an analog threshold voltage is generated by D / A conversion of a digital signal corresponding to the energization current value output from the controller 3, and this is held in the hold circuit and applied to the + input terminal of the comparator 22. What is necessary is just to apply.

(Modification)
In the above embodiment, the resistance value of the resistance circuit 23 of the driver transistor 20 is switched to compensate for the aging deterioration of the light emission amount of the light emitting unit 4. The voltage may be adjusted.

(Modification)
In the above embodiment, in order to compensate for the aging deterioration of the light emission amount of the light emitting unit 4, when the predetermined cumulative time is reached, the transistor 26 is turned on to switch the on-state current amount of the light emitting unit 4. At the same time, the on-state current amount of the light emitting unit 4 may be gradually increased.

  For example, those skilled in the art will understand that the ON current amount can be gradually increased by adjusting the resistance value of the resistance circuit 23 by analog control of the gate voltage of the transistor 26 shown in FIG. .

(Modification)
In the above embodiment, the power supply voltage of the controller 3 is the same as that of the light emitting unit 4. However, the power supply voltage of the controller 3 is the same as that of the light receiving unit 5 of the photocoupler 1, and the photocoupler is different from the controller 3 to the drive circuit 2 side. A pulse signal may be transmitted through.

(Modification)
Other modifications will be described with reference to FIG.

  In this embodiment, the ON / OFF control circuit 21 is changed to a three-input AND gate 21A and a current amplification buffer 10, and a failure energization prohibiting routine shown in FIG.

  A failure energization prohibition signal is input from the controller 3 to the 3-input AND gate 21A together with the same input pulse signal and the output signal of the comparator 22 as in FIG. The failure energization prohibition signal is at a high level when no abnormality of the photocoupler 1 is detected, and at a low level when an abnormality is detected, the three-input AND gate 21A is cut off and the driver transistor 20 is stopped.

  The failure energization prohibiting routine will be described. First, it is determined whether or not the accumulated on-time from the power-on has exceeded a predetermined threshold time, and if not exceeded, the accumulated on-time is incremented. It is determined whether the light receiving unit outputs at least one pulse signal during this threshold time, and if it outputs a pulse signal, the photocoupler 1 determines that it is normal and outputs a pulse signal. If it is determined as defective, a failure energization prohibition signal (low level) is output to the 3-input AND gate 21A.

  In this way, the operation can be stopped when the photocoupler 1 is abnormal with almost no complicated circuit configuration. The controller 3 may be configured to transmit a test pulse signal through the photocoupler 1 within a predetermined time after the power is turned on. Alternatively, the photocoupler 1 may be constantly transmitted with a pulse at a predetermined cycle when the power is turned on. The signal transmission may be performed by changing the duty ratio. As a failure detection method for detecting a transmission failure of the photocoupler 1, another known method may be adopted.

(Modification)
Other modifications will be described with reference to FIG.

  In this embodiment, the ON / OFF control circuit 21 is changed to a three-input AND gate 21A, and a failure energization prohibiting routine described below is added to the controller 3.

  A failure energization prohibition signal is input from the controller 3 to the 3-input AND gate 21A together with the same input pulse signal and the output signal of the comparator 22 as in FIG. The failure energization prohibition signal is at a high level when no abnormality of the photocoupler 1 is detected, and at a low level when an abnormality is detected, the three-input AND gate 21A is cut off and the driver transistor 20 is stopped.

  The failure energization prohibition routine performed by the controller 3 will be described. First, it is determined whether or not the accumulated on-time from the power-on has exceeded a predetermined threshold time, and if not, the accumulated on-time is incremented. If exceeded, it is determined whether or not the light receiving unit 5 of the photocoupler 1 has output at least one pulse signal during this threshold time. If the pulse signal is output, it is determined that the photocoupler 1 is normal and the pulse is output. If no signal is output, it is determined as defective and a power failure prohibition signal (low level) is output to the 3-input AND gate 21A.

  In this way, the operation can be stopped when the photocoupler 1 is abnormal with almost no complicated circuit configuration. Since the presence or absence of the pulse signal output of the light receiving unit 5 of the photocoupler 1 is measured on the light receiving unit 5 side of the photocoupler 1, when the controller 3 is on the light emitting unit 4 side of the photocoupler 1, a measurement signal is sent. The data is transmitted to the controller 3 through the photocoupler 1. Conversely, when the controller 3 is on the light receiving unit 5 side of the photocoupler 1, the controller 3 outputs a failure energization prohibition signal to the 3-input AND gate 21A through the photocoupler.

(Modification)
Other modifications will be described with reference to FIG.

  This aspect is characterized in that a temperature compensation routine is added to the controller 3 and the threshold voltage applied to the + input terminal of the comparator 22 is continuously adjusted by a signal output from the temperature compensation routine.

  First, the temperature compensation routine shown in FIG. 8 will be described. First, a temperature signal having a positive correlation with the temperature of the photocoupler 1 is read. This temperature signal may detect the temperature of the thermistor mounted on the same circuit board as the photocoupler 1. Alternatively, the temperature of the light emitting unit 4 may be obtained by adding the temperature rise of the light emitting unit 4 due to the amount of heat generated by the light emitting unit 4 according to the duty ratio of the input pulse signal to the thermistor temperature.

  The controller 3 reduces the gate voltage of the transistor 26 or adjusts the reference voltage Vref of the comparator 22 according to the calculated temperature of the light emitting unit 4 when the temperature is high, thereby increasing the temperature of the light emitting unit 4. In this case, the on-current of the driver transistor 20 is reduced, and when the temperature of the light emitting unit 4 is low, the on-current of the driver transistor 20 is increased. Since the amount of light emitted from the LED has a positive correlation with the temperature, the life of the light emitting unit 4 can be extended by reducing the current at high temperatures.

  FIG. 6 shows a circuit example. The controller 3 calculates a digital signal S corresponding to the reference voltage Vref, periodically samples and holds it through the D / A converter 11 in the sample-and-hold circuit 12, and uses the sample-and-hold voltage as the reference voltage Vref. What is necessary is just to apply to an input terminal.

It is a circuit diagram which shows the photocoupler circuit of embodiment. It is a flowchart which shows the electric current switching operation | movement of the controller of FIG. It is a time change figure of the emitted light quantity in the photocoupler circuit of FIG. It is a circuit diagram which shows the photocoupler circuit of a deformation | transformation aspect. It is a circuit diagram which shows the ON / OFF control circuit of a deformation | transformation aspect. It is a circuit diagram which shows the photocoupler circuit of a deformation | transformation aspect. It is a circuit diagram which shows the conventional photocoupler circuit. It is a circuit diagram which shows the conventional photocoupler circuit. It is a time change figure of the emitted light quantity in the conventional photocoupler circuit.

Explanation of symbols

1 Photocoupler 2 Drive circuit (current compensation circuit, circuit for prohibiting energization when defective)
3 Controller (current compensation circuit, circuit for prohibiting energization when defective)
DESCRIPTION OF SYMBOLS 4 Light emission part 5 Light reception part 6 Integration circuit 7 Mono multi 8 Counter 10 Current amplification buffer 11 Converter 12 Sample hold circuit 20 Driver transistor 21 Control circuit 21A 3 input AND gate 22 Comparator 23 Resistance circuit 24 Resistance element 25 Resistance element 26 Transistor

Claims (6)

In a photocoupler circuit comprising a photocoupler having a light emitting part and a light receiving part, and a drive circuit for intermittently controlling the input current of the photocoupler,
It has a current compensation circuit for obtaining an aging deterioration signal having a correlation with the aging deterioration of the light emission amount of the light emitting section and increasing the on-current of the light emitting section when the aging deterioration increases according to the state of the aging deterioration signal. A characteristic photocoupler circuit. The photocoupler circuit according to claim 1.
The current compensation circuit is:
A photocoupler that detects the accumulated power-on time of the photocoupler as the aging degradation signal and controls the drive circuit to increase the on-current of the photocoupler when the accumulated power-on time exceeds a predetermined threshold value circuit. The photocoupler circuit according to claim 1 or 2,
The drive circuit is
A constant current circuit that stabilizes the on-current of the light emitting unit to a predetermined constant current value,
The current compensation circuit is a photocoupler circuit that substantially increases the constant current value when the aging deterioration increases. The photocoupler circuit according to claim 3,
The current compensation circuit is:
A driver transistor for intermittently controlling the energization current of the light emitting unit;
A resistor circuit connected in series with the driver transistor;
A comparator for comparing a voltage drop of the resistance circuit with a predetermined threshold voltage;
An ON / OFF control circuit for intermittently controlling the driver transistor by an output of the comparator and an input pulse signal;
A photocoupler circuit. The photocoupler circuit according to claim 1.
The drive circuit is
A photocoupler circuit having a failure energization prohibition circuit that discriminates whether the output of the photocoupler is good or bad and prohibits the energization of the light emitting unit when it is defective. The photocoupler circuit according to claim 1.
The current compensation circuit is:
A photocoupler circuit that detects an amount of electricity having a correlation with the temperature of the light emitting unit, and reduces a current supplied to the light emitting unit based on the amount of electricity when the temperature is high and lower than when the temperature is low.

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