JP5528240B2 - Constant current generation circuit - Google Patents

Description

  The present invention relates to a constant current generating circuit.

  In a power supply circuit in which the input side is driven by alternating current or direct current and supplies a bias specified for a load connected to the output side, a capacitor is connected to smooth the bias specified for the output side (for example, Patent Document 1). Moreover, in such a power supply circuit, a method is disclosed in which a semiconductor element in which a bidirectional thyristor and a diac are combined is used to protect a load when an abnormal current flows (see, for example, Patent Document 2). .

Japanese Patent Laid-Open No. 2007-336682 Japanese Utility Model Publication No. 5-59869

  However, if the above-described power supply circuit is a power supply circuit (constant current generation circuit) using a constant current power supply and a failure occurs that causes the load to be in an open state, the constant current power supply causes a constant current to flow to the output side. As a result of the control, the output voltage increases. For this reason, the voltage applied to the capacitor may exceed the withstand voltage of the capacitor, and the capacitor may be damaged. In order to prevent damage to the capacitor, there are a method using a capacitor having a high withstand voltage and a method of providing an overvoltage detection circuit as in Patent Document 1 to stop the output of the constant current power source. However, there is a problem that the use of a capacitor with a high breakdown voltage increases the size or cost. Further, when the overvoltage detection circuit is used, there is a problem that the circuit configuration becomes complicated.

  The present invention has been made in view of the above problems, and without using a capacitor (capacitance element) having a high withstand voltage or an overvoltage detection circuit, the capacitor (capacitance element) can be used even when a load is in an open state. An object of the present invention is to provide a constant current generating circuit capable of preventing breakage.

In order to solve the above problems, the present invention provides a constant current power source that supplies a constant current that is a rated output current to a load, a capacitive element that is connected in parallel to the load, and a thyristor that is connected in parallel to the load. The thyristor has a breakover voltage lower than a withstand voltage of the capacitive element, a holding current smaller than a rated output current of the constant current power source, and a rated current larger than a rated output current of the constant current power source. This is a constant current generating circuit.

  In the present invention, the thyristor may have a breakover voltage higher than a rated output voltage of the constant current power source.

  In the present invention, the load may be a light emitting diode, and the thyristor may have a breakover voltage lower than a voltage at which an avalanche phenomenon occurs when a reverse voltage is applied to the light emitting diode. .

  In the present invention, the thyristor may be a bidirectional two-terminal thyristor.

  According to the present invention, since a capacitor element and a thyristor having a breakover voltage lower than the breakdown voltage of the capacitor element are connected to the output side of the constant current power source in parallel with the load, a failure that causes the load to be in an open state occurs. The output voltage rises when the constant current power supply tries to pass a constant current, but the thyristor becomes conductive before exceeding the withstand voltage of the capacitive element. When the thyristor is turned on, a holding current flows through the thyristor, so that the increase in the output voltage of the constant current power supply stops. For this reason, the output voltage of the constant current power supply does not exceed the withstand voltage of the capacitive element, and damage to the capacitive element can be prevented. Therefore, it is possible to prevent the capacitive element from being damaged even in the case of a failure in which the load is in an open state without using a capacitive element with a high breakdown voltage or an overvoltage detection circuit.

1 is a block diagram showing a constant current generating circuit according to a first embodiment of the present invention. 3 is a time chart showing the operation of the constant current generating circuit in the same embodiment. It is a block diagram which shows the constant current generation circuit by the 2nd Embodiment of this invention.

[First Embodiment]
Hereinafter, a constant current generating circuit according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram showing a constant current generating circuit 10 according to the present embodiment.
In this figure, a constant current generating circuit 10 includes a constant current power source 1, an output capacitor 2, and a thyristor 3.

  The constant current power supply 1 is connected to the load 4 via the power supply line L1 and the power supply line L2. The constant current power source 1 generates a constant current and supplies the generated constant current to the load 4. The constant current power source 1 supplies a constant current, which is a desired rated output current, to the load 4, and the rated output voltage is determined by the electric resistance of the load 4. The direction of the constant current flows from the power supply line L1 to the power supply line L2 via the load 4. The rated output voltage indicates a potential difference between the power supply line L1 and the power supply line L2 when a constant current flows through the load 4.

  The output capacitor 2 (capacitance element) has a power supply line L1 connected to one end and a power supply line L2 connected to the other end. That is, the output capacitor 2 (capacitance element) is connected in parallel with the load 4.

  The thyristor 3 (THY) is, for example, a bidirectional two-terminal thyristor. In the thyristor 3, the power supply line L1 is connected to one terminal, and the power supply line L2 is connected to the other terminal. The thyristor 3 is connected in parallel with the load 4. That is, the thyristor 3 is connected in parallel with both the output capacitor 2 and the load 4. The breakover voltage of the thyristor 3 is lower than the withstand voltage of the output capacitor 2 and higher than the rated output voltage of the constant current power supply 1. Further, the holding current of the thyristor 3 is smaller than the rated output current of the constant current power source 1 and the rated current of the thyristor 3 is larger than the rated output current of the constant current power source 1 (relational expressions (1) and (2) reference).

  (Rated output voltage of constant current power supply 1) <(Breakover voltage of thyristor 3) <(Withstand voltage of output capacitor 2) (1)

  (Holding current of thyristor 3) <(Rated output current of constant current power supply 1) <(Rated current of thyristor 3) (2)

  The load 4 is connected to the constant current power supply 1 via the power supply line L1 and the power supply line L2. The load 4 represents a circuit or element to which a constant current is supplied by the constant current power source 1.

  Here, the breakover voltage indicates the maximum voltage until the thyristor 3 shifts to the turn-on state (conduction state). That is, the thyristor 3 shifts to a turn-on state (conducting state) when the breakover voltage is reached. The holding current indicates a conduction current necessary for the thyristor 3 to hold the turn-on state (conduction state). Therefore, the thyristor 3 shifts to the turn-off state (cut-off state) when the conduction current becomes less than the holding current in the turn-on state (conduction state). The rated current of the thyristor 3 is a current value that can be passed through the thyristor 3 when the thyristor 3 is in a turn-on state (conductive state).

  Here, the rated output current supplied to the load 4 by the constant current power source 1 is, for example, 30 mA (milliampere), and the rated output voltage with respect to the load 4 is, for example, 12 V (volt). Further, the withstand voltage of the output capacitor 2 is, for example, 25V. In this case, the holding current of the thyristor 3 is, for example, 20 mA, which is smaller than the rated output current 30 mA of the constant current power source 1. Moreover, the rated current of the thyristor 3 is, for example, 40 mA, which is larger than the rated output current 30 mA of the constant current power source 1. The breakover voltage of the thyristor 3 is, for example, 20V, which is higher than the rated output voltage 12V of the constant current power supply 1 and lower than the withstand voltage 25V of the output capacitor 2.

Next, the operation of this embodiment will be described.
Here, the output current flowing through both ends of the load 4 in FIG. 1 is I _out , the output voltage of the constant current power supply 1 is V _out, and the passing current (conduction current) of the thyristor 3 is I _THY .
FIG. 2 is a time chart showing the operation of the constant current generating circuit 10 in the present embodiment.
FIG. 2A is a graph showing the output voltage V _out of the constant current power source 1. In this graph, the vertical axis represents voltage, and the horizontal axis represents time (t). Here, the output voltage _Vout of the constant current power supply 1 indicates a potential difference between the power supply line L1 and the power supply line L2.

FIG. 2B is a graph showing the output current I _out flowing at both ends of the load 4. In this graph, the vertical axis represents current, and the horizontal axis represents time (t). Here, the output current _Iout indicates a current output from the power supply line L1 to the power supply line L2 via the load 4.
FIG. 2C is a graph showing the passing current (conduction current) I _THY of the thyristor 3. In this graph, the vertical axis represents current, and the horizontal axis represents time (t). Here, the passing current (conduction current) I _THY of the thyristor 3 indicates a current output from the power supply line L1 to the power supply line L2 via the thyristor 3.
In the graphs shown in FIGS. 2A, 2B, and 2C, the time scale of the horizontal axis (t) is a common scale.

FIG. 2 shows a case where a failure occurs in which the load 4 is in an open state at time T1. In the period from time 0 to time T1, the output voltage _Vout of the constant current power source 1 in FIG. 2A indicates a voltage value V1 (for example, 12V), and the output of the constant current power source 1 in FIG. The current I _out indicates a current value I1 (for example, 30 mA). Further, since the voltage value V1 is lower than the breakover voltage of the thyristor 3, the thyristor 3 is in the cut-off state during this period. Accordingly, the passing current I _THY of the thyristor 3 in FIG. 2C shows a current of 0 mA.

Next, when a failure occurs in which the load 4 is in an open state at time T1, first, in FIG. 2B, the output current I _out flowing through the load 4 does not flow and becomes 0 mA. As a result, the constant current power source 1 tries to pass the current of the rated current, and the output voltage V _out of the constant current power source 1 in FIG. 2A increases with time. Here, when the output voltage _Vout of the constant current power supply 1 reaches a breakover voltage (for example, 20 V) of the thyristor 3, the thyristor 3 shifts to a turn-on state (conducting state). Time T2 indicates the time when the thyristor 3 reaches the breakover voltage. In the period after time T2, the output voltage _Vout of the constant current power supply 1 is in a turn-on state and thus has a low impedance, for example, approximately equal to the forward voltage value of a general rectifier diode.

Since the passing current I _THY of the thyristor 3 in FIG. 2C is turned on at the time T2, the current starts to flow. In the period after time T2, the passing current I _THY of the thyristor 3 becomes a current value I2 (for example, 30 mA). Here, the holding current of the thyristor 3 is a current value I3 (for example, 20 mA). This current value I2 is larger than the holding current I3 of the thyristor 3. Therefore, the thyristor 3 maintains a turn-on state (conduction state).
The current value I2 is equal to the current value I1 that is the rated current of the constant current power source 1. Further, since the current value I2 is smaller than the rated current (for example, 40 mA) of the thyristor 3, the thyristor 3 is not damaged by the current value I2.

  In this series of operations, the maximum value of the voltage applied to the output capacitor 2 is the breakover voltage (for example, 20 V) of the thyristor 3. For this reason, if the withstand voltage of the output capacitor 2 is, for example, 25 V, it is possible to prevent the output capacitor 2 from being damaged even when a failure occurs in which the load 4 is in an open state.

  As described above, in the constant current generation circuit 10, the constant current power source 1 supplies a constant current to the load 4. The output capacitor 2 is connected in parallel with the load 4, and the thyristor 3 is connected in parallel with the load 4. Further, the breakover voltage of the thyristor 3 is lower than the breakdown voltage of the output capacitor 2. Further, the holding current of the thyristor 3 is smaller than the rated output current of the constant current power source 1 and the rated current of the thyristor 3 is larger than the rated output current of the constant current power source 1.

That is, in the constant current generation circuit 10, the output capacitor 2 and the thyristor 3 having a breakover voltage lower than the withstand voltage of the output capacitor 2 are connected to the output side of the constant current power supply 1 in parallel with the load 4. Therefore, when a failure that causes the load 4 to be in an open state occurs, the output voltage _Vout increases as the constant current power source 1 tries to pass a constant current, but the thyristor 3 becomes conductive before the breakdown voltage of the output capacitor 2 is exceeded. Become. When the thyristor 3 becomes conductive, a holding current flows through the thyristor 3, and thus the increase of the output voltage _Vout of the constant current power supply 1 is stopped. For this reason, the output voltage _Vout of the constant current power source 1 does not exceed the withstand voltage of the output capacitor 2 and can prevent the output capacitor 2 from being damaged. Therefore, the constant current generating circuit 10 can prevent the output capacitor 2 from being damaged even when a failure occurs when the load 4 is in an open state without using a capacitor with a high withstand voltage or an overvoltage detection circuit.

  Capacitors tend to be more expensive and have a larger element size as the breakdown voltage is higher. In the constant current generation circuit 10, the output capacitor 2 having a low withstand voltage can be used within a range that does not fall below the breakover voltage of the thyristor 3. Therefore, the manufacturing cost of the constant current generation circuit 10 can be reduced.

[Second Embodiment]
Hereinafter, a constant current generating circuit according to another embodiment of the present invention will be described with reference to the drawings.
FIG. 3 is a schematic block diagram showing the constant current generating circuit 10a according to the present embodiment.
In this figure, the same components as those in FIG.
In FIG. 3, the constant current generation circuit 10 a is an embodiment in the case where light emitting diodes 41 to 4 n (or 41 a to 4 na) are used as loads. FIG. 3A shows a case where the light emitting diodes 41 to 4n are correctly connected in the constant current generation circuit 10a.
In this figure, a constant current generating circuit 10a includes a constant current power source 1, an output capacitor 2, and a thyristor 3a.

  The thyristor 3a (THY) is, for example, a bidirectional two-terminal thyristor. The thyristor 3a is connected to the power line L1 at one end and the power line L2 to the other end. The thyristor 3a is connected in parallel with the light emitting diodes 41 to 4n. That is, the thyristor 3a is connected in parallel with both the output capacitor 2 and the light emitting diodes 41 to 4n. Further, as in the relational expression (1) described above, the breakover voltage of the thyristor 3a is lower than the withstand voltage of the output capacitor 2, and the rated output voltage of the constant current power source 1, that is, the combined forward voltage of the light emitting diodes 41 to 4n. taller than. Further, as shown in the relational expression (2), the holding current of the thyristor 3 a is smaller than the rated output current of the constant current power source 1, and the rated current of the thyristor 3 a is larger than the rated output current of the constant current power source 1.

  Further, the thyristor 3a has a breakover voltage lower than a voltage at which an avalanche phenomenon occurs when a reverse voltage is applied to the light emitting diodes 41 to 4n (see relational expression (3)). Here, the reverse voltage indicates a case where a voltage higher than that of the anode terminal is applied to the cathode terminals of the light emitting diodes 41 to 4n. The voltage at which the avalanche phenomenon occurs indicates the combined breakdown voltage of the light emitting diodes 41 to 4n when a voltage higher than the anode terminal is applied to the cathode terminals of the light emitting diodes 41 to 4n.

  (Rated output voltage of constant current power supply 1) <(breakover voltage of thyristor 3a) <(total breakdown voltage when reverse voltage of light emitting diodes 41 to 4n) (3)

  The light emitting diodes 41 to 4n have the anode terminal connected to the power supply line L1 and the cathode terminal connected to the power supply line L2. The light emitting diodes 41 to 4 n emit light when supplied with a constant current from the constant current power source 1. The direction of the constant current that flows when the light is emitted flows in a direction from the power supply line L1 toward the power supply line L2.

  FIG. 3B shows a case where the light emitting diodes 41 to 4n are erroneously connected in the reverse direction in the constant current generating circuit 10a. In this figure, the light emitting diodes 41a to 4na indicate the light emitting diodes 41 to 4n in which the anode terminal and the cathode terminal are erroneously connected in reverse. That is, in the light emitting diodes 41a to 4na, the power supply line L2 is connected to the anode terminal, and the power supply line L1 is connected to the cathode terminal.

Next, the operation of this embodiment will be described.
The operation of the present embodiment is the same as that of the constant current generation circuit 10 shown in FIG. 1 except that the load 4 is replaced with light emitting diodes 41 to 4n (or 41a to 4na). That is, in FIG. 3A, when the light emitting diodes 41 to 4n are correctly connected and when a failure occurs in which one of the light emitting diodes 41 to 4n is in an open state, The operation is the same as that of the constant current generating circuit 10.

3B, the operation of the constant current generating circuit 10a when the light emitting diodes 41 to 4n are erroneously connected in the reverse direction (such as the light emitting diodes 41a to 4na) will be described.
In this figure, the light-emitting diodes 41a to 4na have the anode terminal and the cathode terminal connected in error. For this reason, the output current flowing through the light emitting diodes 41a to 4na stops flowing, and becomes 0 mA. As a result, the output voltage of the constant current power source 1 tends to flow through the rated current, and thus increases with time. Here, when the output voltage of the constant current power supply 1 reaches the breakover voltage of the thyristor 3a, the thyristor 3a shifts to a turn-on state (conducting state). In the period after the thyristor 3a reaches the breakover voltage, the output voltage of the constant current power supply 1 is in a turn-on state, and thus has a low impedance, for example, approximately equal to the forward voltage value of a general rectifier diode. Become.

  Moreover, the thyristor 3a starts to flow a current by shifting to a turn-on state (conductive state). At this time, the passing current flowing into the thyristor 3a is larger than the holding current of the thyristor 3a. For this reason, the thyristor 3a maintains the turn-on state (conduction state).

  In this series of operations, the maximum value of the voltage applied to the light emitting diodes 41 a to 4 na is the breakover voltage of the thyristor 3. The breakover voltage of the thyristor 3a is lower than the combined breakdown voltage (voltage at which an avalanche phenomenon occurs) when a reverse voltage is applied to the light emitting diodes 41a to 4na. For this reason, the constant current generating circuit 10a can prevent damage to the light emitting diodes 41a to 4na that are erroneously connected in the reverse direction.

As described above, in the constant current generation circuit 10a, the constant current power source 1 supplies a constant current to the light emitting diodes 41 to 4n. The output capacitor 2 is connected in parallel with the light emitting diodes 41 to 4n, and the thyristor 3a is connected in parallel with the light emitting diodes 41 to 4n. In addition, the breakover voltage of the thyristor 3 a is lower than the withstand voltage of the output capacitor 2. Further, the holding current of the thyristor 3a is smaller than the rated output current of the constant current power source 1, and the rated current of the thyristor 3a is larger than the rated output current of the constant current power source 1.
Thereby, the constant current generation circuit 10a can be expected to have the same effect as the constant current generation circuit 10 in the first embodiment.

  That is, in the constant current generating circuit 10a, it is possible to prevent the output capacitor 2 from being damaged even when a failure occurs when any one of the light emitting diodes 41 to 4n is in an open state without using a capacitor having a high withstand voltage or an overvoltage detection circuit.

  The thyristor 3a has a breakover voltage lower than a voltage at which an avalanche phenomenon occurs when a reverse voltage is applied to the light emitting diodes 41 to 4n. Even if the light emitting diodes 41 to 4n are erroneously connected (attached) in the reverse direction, the thyristor 3a is turned on (conductive state) at a voltage lower than the voltage at which the avalanche phenomenon occurs due to the reverse voltage of the light emitting diodes 41 to 4n. become. As a result, the increase in the output voltage of the constant current power supply 1 stops, and the output voltage of the constant current power supply 1 does not exceed the combined breakdown voltage at the time of the reverse voltage of the light emitting diodes 41 to 4n. That is, in the constant current generating circuit 10a, it is possible to prevent the light emitting diodes 41a to 4na mounted in the reverse direction from being damaged.

According to the embodiment of the present invention, the constant current generating circuit 10 (or 10a) includes a constant current power source 1 that supplies a constant current to the load 4, and an output capacitor 2 (capacitive element) connected in parallel with the load 4. ) And a thyristor 3 (or 3a) connected in parallel with the load 4. The thyristor 3 (or 3a) has a breakover voltage lower than the withstand voltage of the output capacitor 2 (capacitance element), a holding current smaller than the rated output current of the constant current power source 1, and a rated current of the constant current power source 1. Greater than rated output current.
Thereby, in the constant current generation circuit 10 (or 10a), it is possible to prevent the output capacitor 2 from being damaged even when a failure occurs when the load 4 is in an open state without using a capacitor with a high withstand voltage or an overvoltage detection circuit.

The thyristor 3 (or 3a) has a breakover voltage higher than the rated output voltage of the constant current power supply 1.
As a result, during normal operation, the thyristor 3 (or 3a) is in a cut-off state and does not hinder circuit operation.

The load 4 is the light emitting diodes 41 to 4n, and the thyristor 3a has a breakover voltage lower than a voltage at which an avalanche phenomenon occurs when a reverse voltage is applied to the light emitting diodes 41 to 4n.
Thereby, in the constant current generation circuit 10a, even when the light emitting diodes 41 to 4n are erroneously connected in the reverse direction (in the case of the light emitting diodes 41a to 4na), the element damage of the light emitting diodes 41 to 4n is suppressed. be able to.

The thyristor 3 (or 3a) is a bidirectional two-terminal thyristor.
Thereby, even when an abnormal state in which the potential of the power supply line L2 is higher than that of the power supply line L1 occurs, the output capacitor 2 can be prevented from being damaged (and the light emitting diodes 41 to 4n are damaged).

  The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention. In said 2nd Embodiment, although the light emitting diodes 41-4n were connected as a load, the form was demonstrated, but it is not limited to this. The load 4 connected to the constant current generating circuit 10 (or 10a) of the present invention can be applied to all kinds of circuits and elements as long as they are circuits or elements that require constant current. Moreover, in 2nd Embodiment, although the form which connects the light emitting diodes 41-4n in series was demonstrated, the form used by a light emitting diode single-piece | unit may be sufficient.

  Further, in each of the above-described embodiments, the form using the bidirectional two-terminal thyristor has been described, but the present invention is not limited to this. For example, a unidirectional two-terminal thyristor may be used for the thyristor 3 (or 3a).

DESCRIPTION OF SYMBOLS 1 Constant current power supply 2 Output capacitor 3, 3a Thyristor 4 Load 10, 10a Constant current generation circuit 41-4n, 41a-4na Light emitting diode

Claims (4)

A constant current power source that supplies a constant current that is a rated output current to the load;
A capacitive element connected in parallel with the load;
A thyristor connected in parallel with the load;
With
The thyristor is
A constant current generating circuit characterized in that a breakover voltage is lower than a withstand voltage of the capacitive element, a holding current is smaller than a rated output current of the constant current power source, and a rated current is larger than a rated output current of the constant current power source. . The constant current generating circuit according to claim 1, wherein the thyristor has a breakover voltage higher than a rated output voltage of the constant current power source. The load is a light emitting diode;
The thyristor is
The constant current generation circuit according to claim 1, wherein a breakover voltage is lower than a voltage at which an avalanche phenomenon occurs when a reverse voltage is applied to the light emitting diode. 4. The constant current generating circuit according to claim 1, wherein the thyristor is a bidirectional two-terminal thyristor. 5.

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