JP4910098B2 - Disconnection detection circuit - Google Patents

Description

  The present invention relates to a disconnection detection circuit that detects disconnection of a light emitting element used in, for example, a card reader.

  Conventionally, high-intensity LEDs (Light Emitting Diodes) have been used as light sources for outdoor signal lights such as traffic signals and railroad crossing alarms, or as light sources for electronic devices such as personal computers and card readers. There is a possibility of disconnection failure (open failure) due to an abnormal voltage (surge voltage) generated instantaneously. For this reason, when an LED is used as a light source for an outdoor signal lamp or an electronic device, a circuit for detecting disconnection is generally incorporated on a substrate on which the LED is arranged (see, for example, Patent Document 1).

  The disconnection detection device disclosed in Patent Document 1 detects the continuity of an LED group in which a plurality of LEDs are connected in series for each group by a plurality of photocouplers, and detects each continuity detection signal obtained thereby. Is output. The detection circuit determines that one of the plurality of LEDs has failed when at least one of the continuity detection signals sent from the respective photocouplers stops, and can detect disconnection of the LEDs. It has become.

Japanese Patent Laid-Open No. 7-287043 (paragraph number [0007], FIG. 3)

  However, since the disconnection detection device disclosed in Patent Document 1 described above requires a plurality of photocouplers, there is a problem that the cost of the disconnection detection device as a whole increases. In addition, if a plurality of photocouplers are arranged on the substrate, there is a problem that the mounting area becomes large and the entire apparatus cannot be reduced in size.

  Furthermore, when a photocoupler that involves photoelectric conversion is used for disconnection detection, the photocoupler itself may also experience a disconnection failure due to a surge voltage or the like, and the photocoupler has a longer life than a general electric device. Since it is short, there is a problem that high reliability cannot be maintained.

  The present invention has been made in view of the above points, and an object of the present invention is to detect disconnection of a light emitting element while realizing low cost and downsizing and maintaining high reliability. It is to provide a simple disconnection detection circuit.

  In order to solve the above problems, the present invention provides the following.

(1) a light-emitting element, a current control unit that is connected to the light-emitting element and controls a current flowing through the light-emitting element, a control signal transmission unit that transmits a control signal to the current control unit, comprising a detection means for detecting the presence or absence of potential level change, wherein the detecting means includes a level converting means for lowering the potential level of the light emitting element, and a data processing means connected to said level converting means, the In addition to the current control means, a second current control means for controlling the current flowing through the light emitting element is connected to the light emitting element, and the control signal transmitting means sends a pulse signal to the current control means. A pulse signal transmission unit for transmitting, and a steady signal transmission unit for transmitting a steady signal to the second current control unit, wherein the information processing unit changes a signal level of the steady signal Can, based on the output of said level converting means, by detecting the presence or absence of the potential level change, disconnection detection circuit and detecting the disconnection of the light emitting element.

  According to the present invention, the current control means for controlling the current flowing through the light emitting element, the control signal transmitting means for transmitting a control signal to the current control means, and the detection means for detecting the presence or absence of a potential level change of the light emitting element, When the signal level of the control signal changes, the detection means detects the presence or absence of the potential level change. As a result, the disconnection of the light emitting element is detected. There is no need to use it.

  Accordingly, the cost for realizing the disconnection detection function can be reduced, and the mounting area can be reduced to reduce the size of the entire circuit. In addition, the present invention detects the presence or absence of a change in the potential level of the light emitting element as described above, and does not involve photoelectric conversion unlike the conventional disconnection detection device. Therefore, high reliability can be maintained.

  Here, the “change in the potential level of the light emitting element” is intended to include a change in potential level that can uniquely lead to a change in potential level of the light emitting element. For example, it may be a change in potential level of a load resistor connected in series with the light emitting element. This is because if the potential level change of the load resistance occurs, the potential level change of the light emitting element also occurs, and these potential level changes correspond one-to-one. The “signal level of the control signal” may be, for example, a voltage value composed of two values of 0V and non-0V, or a predetermined value of Hi and Lo, Any other type may be used.

Before SL detecting means includes level converting means for lowering the potential level of the light emitting device, and a data processing means connected to said level converting means, said information processing means based on the output of said level converting means , you and detecting the disconnection of the light emitting element.

  According to the present invention, the detection means described above is provided with a level conversion means for lowering the potential level of the light emitting element and an information processing means connected to the level conversion means. For example, when the disconnection detection circuit is incorporated in the card reader, the disconnection of the light emitting element can be detected using the CPU in the card reader as the information processing means.

(2) The level converting means includes a bipolar transistor, wherein the bipolar transistor has a base terminal that receives the potential level of the light emitting element, and a collector terminal connected to the information processing means. The disconnection detection circuit according to (1) .

  According to the present invention, the level converting means described above is provided with a bipolar transistor. In this bipolar transistor, the potential level of the light emitting element is input to the base terminal, and information processing is performed on the collector terminal. Since the means are connected, it is possible to detect the disconnection of the light emitting element easily and inexpensively by effectively utilizing a bipolar transistor that is inexpensive and widely used.

(3) When the signal level of the control signal is changed, the information processing unit determines that the light emitting element is disconnected if the output of the level conversion unit does not change. The disconnection detection circuit according to (1) or (2) .

  According to the present invention, when the signal level of the control signal is changed by the information processing means described above, if the output of the level conversion means does not change, it is determined that the light emitting element is disconnected. It is possible to detect disconnection of the light emitting element while realizing low cost and downsizing and maintaining high reliability.

(4) The disconnection detection circuit according to any one of (1) to (3) , wherein the light emitting element is an LED, and the current control means is a bipolar transistor.

  According to the present invention, since the light emitting element described above is an LED and the current control means described above is a bipolar transistor, it is possible to detect disconnection of the light emitting element more inexpensively and easily.

The prior SL-emitting element, separately from the current control means, a second current control means is connected to control the current flowing to the light emitting element, the control signal transmitting means, pulses to said current control means A pulse signal transmission unit that transmits a signal, and a steady signal transmission unit that transmits a steady signal to the second current control unit, and the detection unit, when the signal level of the steady signal changes, by detecting the presence or absence of potential level change, you and detecting the disconnection of the light emitting element.

  According to the present invention, the above-described light emitting element is connected to the second current control unit different from the above-described current control unit, and the above-described control signal transmission unit includes a pulse with respect to the current control unit. A pulse signal transmission unit for transmitting a signal and a steady signal transmission unit for transmitting a steady signal to the second current control unit are provided. When the signal level of the steady signal changes, the detection unit changes the potential level. Since the presence / absence is detected and, as a result, the disconnection of the light emitting element is detected, it becomes possible to detect the disconnection more reliably.

  More specifically, for example, when pulse driving is adopted as a method for driving the light emitting element (when the control signal is a pulse signal), the current flowing through the light emitting element becomes a pulse current. It becomes difficult to synchronize the timing “when the signal level of the signal changes” with the timing “detects whether there is a change in potential level”. As a result, the reliability of disconnection detection is lacking as it is. However, according to the disconnection detection circuit according to the present invention, when the disconnection is detected, the second current control unit to which the steady signal is input is used instead of the current control unit to which the pulse signal is input. The current flowing through the light emitting element becomes a steady current. As a result, it is possible to easily synchronize the two timings described above, and thus more reliably detect disconnection.

  According to the disconnection detection circuit according to the present invention, the disconnection of the light emitting element is detected without using an element accompanied by photoelectric conversion such as a photocoupler, so that the cost required for adding the disconnection detection function can be reduced. Can do. Further, the mounting area of the entire circuit can be reduced to reduce the size of the entire circuit. Furthermore, disconnection can be detected more reliably and high reliability can be maintained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Circuit configuration]
FIG. 1 is a block diagram showing an electrical configuration of a disconnection detection circuit 1 according to an embodiment of the present invention. In addition, in this embodiment, the example when the disconnection detection circuit 1 is integrated in a card reader is shown. Therefore, the LED lighting control circuit 12 and the CPU 142, which will be described later, are circuits and CPUs inside the card reader. Of course, the present invention is not limited to this.

In FIG. 1, a disconnection detection circuit 1 mainly includes a light emitting diode (abbreviated as “LED”) as an example of a light emitting element, a transistor TR ₁ as an example of current control means, and an LED as an example of control signal transmission means. A lighting control circuit (for example, a CPU or a ROM) 12 and a detection circuit 14 as an example of a detection unit are included.

As the transistor TR _1, germanium transistors, small signal transistors, but those of various types such as a power transistor is considered, no limitation on the kind of how. In the present embodiment, an NPN bipolar transistor (transistor TR ₁ ) is described as an example of current control means. However, a PNP bipolar transistor, a JFET (Junction Field Effect Transistor), an enhancement MOSFET (Metal Oxide) is also described. Any device such as a semiconductor field effect transistor or a depletion type MOSFET may be used.

  Moreover, as LED, various things, such as visible light LED, infrared LED, ultraviolet LED, can be considered, but what kind of thing does not ask | require. Further, in this embodiment, an LED is described as an example of a light emitting element, but any other element that can emit light according to the operation of the LED (when a drive current flows) may be used. Absent.

The anode of the LED is connected in series to an LED power supply 13 (voltage value is V _CC , here as 12V as an example) via a load resistor R ₁ . Further, the transistor TR ₁ is LED cathode is connected to the collector terminal, LED lighting control circuit 12 is connected to the base terminal, an emitter terminal is grounded.

Transistor TR ₁ is an element for controlling current flowing the LED. When the control signal transmitted from the LED lighting control circuit 12 is received at the base terminal and the signal level of the control signal is higher than the voltage between the base and the emitter, the collector current (ie, LED Current control) is performed so as to flow.

On the other hand, the detection circuit 14 has a function of detecting the presence or absence of a change in the potential level of the LED. Specifically, the reception circuit 141 as an example of a level conversion unit and a CPU 142 as an example of an information processing unit. And a power source 143 (in this case, 5 V is taken as an example) as main components. Further, the receiving circuit 141 has a function of lowering the anodes of the potential level of the LED, specifically, a base resistor _{R 2,} a pull-down resistor _{R 3,} the collector resistor _{R 4,} a transistor TR ₂ As a component.

Base resistance R ₂ of the receiving circuit 141 has one end connected to the anode of the LED, the other end is connected to the base terminal of the transistor TR _2. Further, the base terminal of the transistor TR _2, between the emitter terminal of the transistor TR ₂ is a pull-down resistor R ₃ is connected. Incidentally, the pull-down resistor R _3, the input to the transistor TR ₂ is prevented from becoming an open state.

The collector terminal of the transistor TR _2, while the power supply 143 via a collector resistor R ₄ is connected in series, the emitter terminal of the transistor TR ₂ is connected to the ground. Further, as the output of the receiver circuit 141, the potential level of the collector of the transistor TR ₂ is taken out, which are input to the CPU 142.

[Circuit operation]
FIG. 2 is a table showing an outline of the operation of the disconnection detection circuit 1. 2A indicates the potential level V of the anode of the LED (see FIG. 1).

1 and 2 (a), the LED is not broken "normal", the control signal from the LED lighting control circuit 12 to the transistor TR ₁ is transmitted (ON), the transistor _{R 1} is turned on, A collector current flows through the LED, and the above-described potential level V is represented by V _CE + V _F. At this time, in the receiving circuit 141, a potential difference of (V _CE + V _F ) × R ₃ / (R ₂ + R ₃ ) is generated between the base and emitter of the transistor TR ₂ .

On the other hand, are not transmitted control signal from the LED lighting control circuit 12 to the transistor TR ₁ and (If left off), the transistor R ₁ is not turned on, LED to the collector current does not flow. Therefore, the above-described potential level V is represented by approximately _Vcc . At this time, in the reception circuit 141, a potential difference of V _cc × R ₃ / (R ₂ + R ₃ ) is generated between the base and emitter of the transistor TR ₂ .

Here, in the present embodiment, the resistance values of the base resistor R ₂ and the pull-down resistor R ₃ are represented by (V _CE + V _F ) × R ₃ / (R ₂ + R) with reference to the voltage V _BE that turns on the transistor TR _{2. 3} ) The value is set so as to satisfy <V _BE and V _cc × R ₃ / (R ₂ + R ₃ )> V _BE .

Accordingly, as shown in FIG. 2 (b), when turning on the control signal to the transistor TR ₁ is the LED lighting control circuit 12, when the transistor TR ₂ is remained off, turning off the control signal the, the transistor TR ₂ is turned on. As described above, in the “normal time” when the LED is not disconnected, the ON / OFF of the transistor TR ₂ changes based on the ON / OFF of the control signal from the LED lighting control circuit 12 to the transistor TR ₁ . Become.

Next, in FIG. 1 and FIG. 2 (a), "burnout" LED is broken, also the control signal from the LED lighting control circuit 12 to the transistor TR ₁ is transmitted (ON), the LED disconnected Therefore, the collector current does not flow. Therefore, the above-described potential level V is represented by approximately _Vcc . At this time, in the receiving circuit 141, a potential difference of V _cc × R ₃ / (R ₂ + R ₃ ) is generated between the base and emitter of the transistor TR ₂ .

On the other hand, if the control signal is not transmitted from the LED lighting control circuit 12 to the transistor TR ₁ (if it remains off), the transistor R ₁ is not turned on, as in “normal” when the LED is not disconnected, There is no collector current. Therefore, a potential difference of V _cc × R ₃ / (R ₂ + R ₃ ) is generated between the base and the emitter of the transistor TR ₂ as in “normal” when the LED is not disconnected.

Here, since the resistance values of the base resistor R ₂ and the pull-down resistor R ₃ are set to the above-described values, the control signal from the LED lighting control circuit 12 to the transistor TR ₁ is turned on. also, even when the clear this control signal, the transistor TR ₂ is turned on in any case. As described above, when the LED is disconnected, “on / off”, the ON / OFF of the transistor TR ₂ is completely changed even if the control signal from the LED lighting control circuit 12 to the transistor TR ₁ is ON / OFF. Will not.

As described above, depending on whether LED is broken, when the on-off control signal from the LED lighting control circuit 12 to the transistor TR _1, a difference in on and off the transistor TR ₂ is produced (FIG. 2 (See (b)). Then, as the output of the receiving circuit 141 takes out the potential level of the collector of the transistor TR ₂ as the output of the receiving circuit 141, by inputting it to CPU 142, CPU 142 can detect the disconnection the LED.

  FIG. 3 is a flowchart including a circuit operation flow of the disconnection detection circuit 1 according to the embodiment of the present invention.

  In FIG. 3, first, the terminal is powered on (step S1). For example, when a card reader incorporating the disconnection detection circuit 1 is installed in an ATM (Automated Teller Machine), the ATM is powered on. Thereafter, an initialization command is issued (step S2). Specifically, the ATM transmits an initialization command to the card reader.

Upon receiving the initialization command, the card reader starts LED disconnection detection (step S3). More specifically, first, LED lighting control circuit 12 sends a control signal to the transistor TR _1. Then, for example, if no LED is disconnected, the transistor TR ₁ is turned on, collector current flows, should LED is turned on (step S4). At this time, the CPU 142, the potential level of the collector of the transistor TR ₂ (disconnection detection signal after the level conversion) is determined (step S5).

Then, LED lighting control circuit 12 stops the transmission of the control signal to the transistor TR ₁ (off). Then, if no example LED is disconnected, the transistor TR ₁ is turned off, the collector current is interrupted, LED should be turned off (step S6). At this time, the CPU 142, as in the above-described case, the potential level of the collector of the transistor TR ₂ (disconnection detection signal after the level conversion) is determined (step S7).

  Here, the CPU 142 compares the disconnection detection signal measured in step S5 with the disconnection detection signal measured in step S7, and determines whether there is a change (step S8). Specifically, for example, the disconnection detection signal measured in step S7 is subtracted from the disconnection detection signal measured in step S5, and it is determined whether or not it is substantially zero (below a predetermined value within the allowable error range). .

  When the CPU 142 determines that there is a change (when there is a change as shown in the middle row in FIG. 2B), the CPU 142 returns that fact to the card reader body, and the card reader continues normal operation processing. (Step S9), other initialization operations are also executed (Step S10). On the other hand, when the CPU 142 determines that there is no change (in FIG. 2B, when there is no change as shown in the lower row), an alarm report is sent to the card reader and ATM, which is the host device ( Step S11) and then the abnormality process is started (Step S12).

Thus, the disconnection detection circuit 1, when the signal level of the control signal transmitted from the LED lighting control circuit 12 (here the on-off) is changed, the CPU 142, the potential level of the collector of the transistor TR ₂ is changed Otherwise, it can be determined that the LED is disconnected. Therefore, disconnection detection can be performed at low cost without using a photocoupler as in the conventional disconnection detection device. In addition, the mounting area can be reduced to reduce the size of the entire circuit. Furthermore, since no photoelectric conversion is involved, high reliability can be maintained.

In the present embodiment, as a detection means for detecting the presence or absence of the anode potential level change of the LED, is adopted detection circuit 14 including transistors TR ₂ and CPU 142, for example, it can be substituted by a logic IC . However, in this case, if the LED lighting control circuit 12 is turned off, or if the LED is disconnected, a voltage of approximately V _CC (for example, 12V) is input. There is a risk of failure. Therefore, it is preferable to use a voltage divider or the like in order to input an appropriate voltage to the logic IC.

[Modification]
FIG. 4 is a block diagram showing an electrical configuration of a disconnection detection circuit 1A according to another embodiment of the present invention.

4 differs from the block diagram shown in FIG. 1 in the electrical configuration of the cathode side of the LED. More specifically, the cathode side of the LED, in parallel with the transistor TR _1, the transistor TR ₃ is connected through a load resistor _{R 5.} Further, the LED lighting control circuit 12. Particularly, the pulse signal transmitter for transmitting a pulse signal is connected to the transistor TR _1, the constant signal transmitting unit which transmits a stationary signal is connected to the transistor TR _3.

The disconnection detecting circuit 1A, inputs a pulse signal to the base terminal of the transistor TR _1, is pulse-driven LED. Therefore, since it is in the collector current is also pulse current of the transistor TR _1, in this state, it is impossible to properly detect the presence or absence of a potential level change of the LED of the collector. That is, even if the pulse signal itself from the pulse signal transmission unit 121 is on, the actual collector current is a pulse current that repeats on and off alternately. It is necessary to measure the disconnection detection signal at the timing to perform, and if this timing is incorrect, appropriate disconnection detection cannot be performed.

Therefore, in order to increase the reliability and simplicity of disconnection detection, transistors TR ₃ and constant signal transmission unit 122 is provided above. Unlike the pulse signal transmitted by the pulse signal transmission unit 121, the steady signal transmission unit 122 transmits a steady signal that is always on when it is on and off when it is off. Therefore, LED lighting control circuit 12 (step S3 in FIG. 3) when performing disconnection detection of the LED, switch means for controlling the current flowing through the LED to the transistor TR _3, to the transistor TR _3, steady A control signal (steady signal ON / OFF) is transmitted from the signal transmitter 122. Then, the signal level of the steady signal transmitted by the steady signal transmission unit 122 is changed, and the presence or absence of a change in the potential level of the collector of the LED is detected by the receiving circuit 141 described above, thereby detecting the disconnection of the LED more reliably. can do.

FIG. 5 is a block diagram showing an electrical configuration of a disconnection detection circuit 1B according to another embodiment of the present invention. FIG. 5 is an improvement of the electrical configuration shown in FIG. In the case of a circuit for driving a normal card reader, the power supply 143 is 5V. Therefore, a voltage for appropriately driving the transistor TR ₂ is generated by the pull-down resistor R ₃ with the base resistor R ₂ (the input voltage to the receiving circuit 141 is divided).

Electrical configuration shown in Figure 5, unlike the electrical configuration shown in FIG. 4, a signal input to the receiving circuit 141, and the voltage signal between the collector load resistor R ₅ and the transistor TR _3. Thereby, the sensitivity of disconnection detection can be improved.

To be more specific, first, in the electrical configuration shown in FIG. 4, when the the LED pulse on, to increase the pulse current flowing through the LED, the load resistor R ₁ has a somewhat smaller. Further, when LED disconnection is detected, that is, when TR ₁ is turned off and TR ₃ is turned on, the load resistance R ₅ has a certain large value in order to prevent the LED from being broken even if a current always flows. That is, the current flowing through the LED at LED disconnection detection has a small value due to the presence of the load resistor R _5.

Then, the electrical configuration shown in FIG. 4, also turns on and off the transistors TR _3, when the voltage drop across the load resistance R ₁ is small, the amplitude of the input signal to the reception circuit 141 (voltage signal) is not sufficient while there is, according to the electrical configuration shown in FIG. 5, a voltage signal between the collector load resistor R ₅ and the transistor TR _3, since the input signal to the reception circuit 141, turns on the transistor TR ₃ -The voltage difference of the input signal when it is turned off can be increased. Accordingly, the sensitivity of disconnection detection can be improved (the receiving circuit 141 can be operated more correctly).

  As described above, according to the disconnection detection circuits 1A and 1B shown in FIG. 4 and FIG. 5, high-voltage driven LEDs and pulse-driven LEDs (for example, infrared LEDs are designed to emit high-voltage pulses. This is suitable for detecting disconnection of a

  The disconnection detection circuit according to the present invention is useful as a circuit that can detect disconnection of a light emitting element while realizing low cost and downsizing and maintaining high reliability.

It is a block diagram which shows the electric constitution of the disconnection detection circuit which concerns on embodiment of this invention. It is the figure which showed the operation | movement outline | summary of the disconnection detection circuit. It is a flowchart including the flow of circuit operation | movement of the disconnection detection circuit which concerns on embodiment of this invention. It is a block diagram which shows the electric constitution of the disconnection detection circuit which concerns on other embodiment of this invention. It is a block diagram which shows the electric constitution of the disconnection detection circuit which concerns on other embodiment of this invention.

Explanation of symbols

1 Disconnection detection circuit 12 LED lighting control circuit 13 LED power supply ( _Vcc )
14 detection circuit 141 reception circuit 142 CPU
143 Power LED light emitting diode TR ₁ to Tr ₃ transistor R _{1, R 5} load resistance R ₂ base resistor R ₃ pull-down resistor R ₄ collector resistance

Claims (4)

A light emitting element;
A current control means connected to the light emitting element for controlling a current flowing through the light emitting element;
Control signal transmitting means for transmitting a control signal to the current control means;
Detecting means for detecting the presence or absence of a potential level change of the light emitting element,
The detection means comprises level conversion means for lowering the potential level of the light emitting element, and information processing means connected to the level conversion means,
Separately from the current control means, the light emitting element is connected to second current control means for controlling the current flowing through the light emitting element,
The control signal transmission unit includes a pulse signal transmission unit that transmits a pulse signal to the current control unit, and a steady signal transmission unit that transmits a steady signal to the second current control unit,
The information processing means detects disconnection of the light emitting element by detecting the presence or absence of the potential level change based on the output of the level conversion means when the signal level of the steady signal changes. Disconnection detection circuit. The level conversion means includes a bipolar transistor,
2. The disconnection detection circuit according to claim 1, wherein the bipolar transistor has a base terminal receiving a potential level of the light emitting element and a collector terminal connected to the information processing means.   2. The information processing means determines that a disconnection of the light emitting element has occurred if the output of the level conversion means does not change when the signal level of the control signal changes. Or the disconnection detection circuit of 2.   4. The disconnection detection circuit according to claim 1, wherein the light emitting element is an LED, and the current control means is a bipolar transistor.

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