JP5939899B2 - Load drive circuit - Google Patents

Description

  The present invention relates to a load driving circuit including a first control circuit that controls a current flowing in a load such as an LED to have a constant value.

  In recent years, LEDs have been used in various fields as illumination and LCD backlights. Since the luminance of the LED changes depending on the value of the flowing current, it is necessary to perform control so that a constant current always flows in order to keep the luminance constant.

  FIG. 6 shows an example of a conventional load driving circuit for driving an LED (see Patent Document 1). In FIG. 6, 10 is a load in which a plurality of LEDs are connected in series, 11 is a voltage source of voltage V1, and 20C is a first control circuit for allowing a constant current to flow through the load 10. The first control circuit 20C has an NMOS transistor M1 whose drain is connected to the node N1 of the load 10 and whose source is connected to GND via the resistor R1, and the reference voltage Vref1 of the voltage source 23 is input to the non-inverting input terminal. The operational amplifier 22 has an inverting input terminal connected to the source of the transistor M1, and an output terminal connected to the gate of the transistor M1.

  In this load driving circuit, the current flowing through the LED of the load 10 is detected by the resistor R1, and the transistor M1 is controlled via the operational amplifier 22 so that the voltage generated across the resistor R1 is equal to the reference voltage Vref1. Thus, the drain current of the transistor M1 is controlled to have a value corresponding to the reference voltage Vref1.

  The following states are conceivable as possible failures in such a circuit. (1) The load 10 is short-circuited due to a destructive short circuit of the LED (load short circuit), (2) the LED of the load 10 is not lit due to the destructive opening of the LED or the disconnection of the LED wiring (load disconnection), (3) The cathode side (node N1) of the LED of the load 10 is short-circuited to GND, and an excessive current flows to the LED (GND short-circuit). In such a case, the load driving circuit is required to have a function of detecting these failure states and stopping the operation or issuing a signal notifying abnormality.

JP2011-249145A

  When trying to detect the states (1) to (3) above, it is possible to detect (1) by detecting that the voltage Va at the node N1 has become a predetermined value or more. However, in the case of load disconnection or GND short-circuit in (2) and (3), the voltage Va at the node N1 is almost 0V, and simply by monitoring the voltage Va at the node N1, load disconnection or GND short-circuit Cannot be determined. Further, when the voltage V1 supplied from the voltage source 11 decreases due to some problem and the voltage V1 is not sufficient to light the LED, almost no current flows through the LED. Also at this time, the voltage Va at the node N1 is lowered, and it is difficult to distinguish from the load disconnection and the GND short-circuit of the above (2) and (3).

An object of the present invention is to provide a load drive circuit that solves the above-described problems and that can detect failures such as load disconnection, GND short-circuit, and voltage source voltage drop.

In order to achieve the above object, the invention according to claim 1 is connected between a load connected to the first voltage source and GND, and controls so that the current flowing through the load becomes a predetermined value. In a load driving circuit having one control circuit, a potential difference between a first node at a common connection point between the load and the first control circuit and the GND is detected, and the potential difference is controlled to a predetermined value. A second control circuit; a first voltage detection circuit for detecting a voltage of the first voltage source; and / or a second voltage detection circuit for detecting a potential difference between the first node and the GND. And an abnormality determination circuit that performs an abnormality determination based on a combination of the content of the control operation of the second control circuit and the detection result of the first voltage detection circuit and / or the second voltage detection circuit. Features.
According to a second aspect of the present invention, there is provided a load drive having a first control circuit which is connected between a load connected to the GND and the first voltage source and controls the current flowing through the load to a predetermined value. In the circuit, a second control for detecting a potential difference between a first node at a common connection point between the load and the first control circuit and the first voltage source and controlling the potential difference to a predetermined value. A circuit, a first voltage detection circuit that detects a voltage of the first voltage source, and / or a third voltage detection circuit that detects a potential difference between the first node and the first power supply; An abnormality determination circuit that performs abnormality determination based on a combination of the content of the control operation of the second control circuit and the detection result of the first voltage detection circuit and / or the third voltage detection circuit. And

According to the first aspect of the present invention, a load drive having a first control circuit that is connected between a load connected to the first voltage source and GND and controls the current flowing through the load to a predetermined value. In the circuit, the voltage drop of the voltage source can be determined separately from the load disconnection and the GND short circuit, or the GND short circuit can be determined separately from the voltage drop of the voltage source and the load disconnection, or the voltage drop of the voltage source and the load disconnection and the GND short circuit can be determined. Can be distinguished from each other.
According to the second invention, the load drive having the first control circuit that is connected between the load connected to the GND and the first voltage source and controls the current flowing through the load to have a predetermined value. In the circuit, the voltage drop of the voltage source can be determined separately from the load disconnection and the voltage source short circuit, or the voltage source short circuit can be determined separately from the voltage drop of the voltage source and the load disconnection, or The voltage source short circuit can be distinguished from each other.

It is a circuit diagram of the load drive circuit of the first embodiment. It is a circuit diagram of the load drive circuit of the 2nd example. It is a circuit diagram of the load drive circuit of the 3rd example. It is a circuit diagram of the load drive circuit of the 4th example. It is a circuit diagram of the load drive circuit of a 5th Example. It is a circuit diagram of the conventional load drive circuit.

  In the present invention, the voltage Va at the node N1 is detected, and the value of the voltage Va is controlled by the second control circuit. In this control, when the voltage Va approaches a predetermined value, the current of the first control circuit is reduced and a constant current is supplied from the second control circuit. For example, if the load is disconnected, the voltage Va is a predetermined value. Control is performed so as not to be below, and if the GND is short-circuited, the value is controlled to a low value. In addition, it is detected that this control operation is being performed. For example, if this control operation has been performed for a predetermined time or more, it is determined that there is some abnormality in the load, and the voltage source 11 supplies the voltage to the load. Processing such as stopping the operation is performed.

<First embodiment>
FIG. 1 shows the configuration of the load driving circuit of the first embodiment. Reference numeral 10 denotes a load, and 11 denotes a voltage source, which is the same as that described with reference to FIG. Reference numeral 20A denotes a first control circuit, and the current of the current source 21 can be controlled externally. Reference numeral 30A denotes a second control circuit, which includes an operational amplifier 31, a current source 32, and a voltage source 33. The second control circuit 30A compares the voltage Va at the node N1 between the load 10 and the first control circuit 20A with the reference voltage Vref2 of the voltage source 33. When Va <Vref2, the first control circuit 30A The current of the current source 21 of the circuit 20A is controlled so that the voltage Va at the node N1 does not drop below the reference voltage Vref2, and the current of the current source 32 supplied to the node N1 is controlled. Reference numeral 40A denotes an abnormality determination circuit. When the second control circuit 30A operates and the output voltage of the operational amplifier 31 changes greatly, the change is detected and abnormality determination is performed.

  In this embodiment, when the voltage Va at the node N1 is higher than the reference voltage Vref2, the output voltage of the operational amplifier 31 is low, and the current source 21 of the first control circuit 20A is not externally controlled, and the second control circuit. The current source 32 of 30A does not output current. That is, since the second control circuit 30A does not detect a failure, the abnormality determination circuit 40A does not perform abnormality determination.

  However, when the LED of the load 10 is disconnected, when the node N1 is short-circuited to GND, or when the voltage V1 of the voltage source 11 is significantly decreased, the voltage Va of the node N1 is significantly decreased. Therefore, the output voltage of the operational amplifier 31 of the second control circuit 30A becomes a high voltage, the current is output from the current source 32 to the node N1, and the current source 21 of the first control circuit 20A is lower than the reference voltage Vref2. Therefore, the control is performed so that the voltage Va of the node N1 becomes the reference voltage Vref2 or a lower voltage. At this time, since the output voltage of the operational amplifier 31 varies greatly, abnormality determination is performed by the abnormality determination circuit 40A.

  Note that a load short circuit can be determined by detecting with a comparator whether or not the voltage Va at the node N1 exceeds a predetermined value, as in the conventional example (not shown).

<Second embodiment>
FIG. 2 shows the configuration of the load driving circuit of the second embodiment. In the present embodiment, a first control circuit 20B is connected to the voltage source 11, and an LED load 10 is connected between the first control circuit 20B and GND. The second control circuit 30 </ b> B connects the current source 32 between the operational amplifier 31, the inverting input terminal of the operational amplifier 31, and GND, and the voltage source 33 between the non-inverting input terminal and the voltage source 11. Connected and configured. Reference numeral 40B denotes an abnormality determination circuit.

  In the present embodiment, when the potential difference between the voltage V1 of the voltage source 11 and the voltage Va of the node N1 is higher than the reference voltage Vref2, the output voltage of the operational amplifier 31 is low, and the current source 21 of the first control circuit 20B is External control is not performed, and the current source 32 of the second control circuit 30B does not output current. That is, since the second control circuit 30B does not detect a failure, the abnormality determination circuit 40B does not perform abnormality determination.

However, when the load disconnection LED load 10 is disconnected, when the node N1 is a voltage source shorted shorted to a voltage source 11, when the voltage V1 of the voltage source 11 was significantly reduced, the voltage V1 of the voltage source 11 Since the potential difference with the voltage Va at the node N1 becomes smaller than the reference voltage Vref2, the output voltage of the operational amplifier 31 of the second control circuit 30B becomes a high voltage, the current of the current source 32 is sucked from the node N1, and the first Since the current source 21 of the control circuit 20B is controlled, control is performed so that the node N1 becomes the reference voltage Vref2 or a lower voltage. At this time, since the output voltage of the operational amplifier 31 changes greatly, abnormality determination is performed by the abnormality determination circuit 40B.

  Note that a load short circuit can be determined by detecting with a comparator whether or not the voltage Va at the node N1 has fallen below a predetermined value (not shown).

<Third embodiment>
FIG. 3 shows the configuration of the load driving circuit of the third embodiment. Reference numeral 50 denotes a voltage dividing circuit that generates a voltage Vb obtained by dividing the voltage V1 of the voltage source 11. Reference numeral 60 denotes a first voltage detection circuit including a comparator 61 and a voltage source 62 of the reference voltage Vref3. The first voltage detection circuit 60 sets the output of the comparator 61 to a high voltage when the divided voltage Vb drops below the voltage Vref3. The abnormality determination circuit 40C makes an abnormality determination based on the control content of the second control circuit 30A and the detection result of the first voltage detection circuit 60. Others are the same as in FIG.

  In this embodiment, as in the embodiment of FIG. 1, when the load of the LED of the load 10 is broken, when the node N1 is short-circuited to GND, and when the voltage V1 of the voltage source 11 is significantly reduced. In addition, the output voltage of the operational amplifier 31 of the second control circuit 30A changes greatly, and a failure detection signal is output. At this time, particularly when the voltage V1 of the voltage source 11 is greatly reduced, the voltage Vb obtained by the voltage dividing circuit 50 is lower than the reference voltage Vref3, so that the output of the comparator 61 becomes a high voltage. Therefore, in this embodiment, when the voltage V1 of the voltage source 11 is significantly reduced, it can be determined by the abnormality determination circuit 40C in distinction from the load disconnection and the GND short circuit.

  Note that the voltage dividing circuit 50 and the first voltage detecting circuit 60 of the present embodiment are similarly applied to the load driving circuit described in FIG. 2, and the voltage V1 of the voltage source 11 is greatly reduced. Can be detected (not shown).

<Fourth embodiment>
FIG. 4 shows the configuration of the load driving circuit of the fourth embodiment. Reference numeral 70 denotes a second voltage detection circuit, which includes a comparator 71 and a voltage source 72 having a reference voltage Vref4. Vref4 <Vref2. The abnormality determination circuit 40D performs abnormality determination based on the control content of the second control circuit 30A and the detection result of the second voltage detection circuit 70. Others are the same as in FIG.

  In this embodiment, as in the embodiment of FIG. 1, when the load of the LED of the load 10 is broken, when the node N1 is short-circuited to GND, and when the voltage V1 of the voltage source 11 is significantly reduced. In addition, the output voltage of the operational amplifier 31 of the second control circuit 30A changes greatly, and a failure detection signal is output. At this time, particularly when the node N1 is short-circuited to GND, Va <Vref4, and the output of the comparator 71 of the second voltage detection circuit 70 becomes a high voltage. Therefore, in the present embodiment, the GND short-circuit can be determined by the abnormality determination circuit 40D in distinction from the load disconnection and the voltage V1 significant decrease.

  2, whether or not the node N1 is short-circuited to the voltage source 11 by providing a third voltage detection circuit that detects that the voltage of the node N1 is higher than the predetermined value. Can be detected (not shown).

<Fifth embodiment>
FIG. 5 shows a specific configuration in which the load drive circuit of FIG. 3 and the load drive circuit of FIG. 4 are combined. The first control circuit 20A has an NMOS transistor M1 whose drain is connected to the node N1 and whose source is connected to GND via the resistor R1, and the reference voltage Vref1 of the voltage source 23 is input to the non-inverting input terminal, and the inverting input The operational amplifier 22 has a terminal connected to the source of the transistor M1 via the resistor R2, and an output terminal connected to the gate of the transistor M1. The second control circuit 30A includes an operational amplifier 31, a voltage source 33 that applies a reference voltage Vref2 to the non-inverting input terminal of the operational amplifier 31, a voltage source 34 having a voltage V2, and an NMOS transistor M2 as a current source 32. And an NMOS transistor M3 that outputs a current control signal to the first control circuit 20A, a resistor R3, and a PMOS transistor M4 that outputs an operation signal indicating that the second control circuit 30A has been operated. The gates of the transistors N2 and M3 are connected to the output terminal of the operational amplifier 31. The load 10, the voltage dividing circuit 50, and the first voltage detection circuit 60 are the same as those in FIG. 3, and the second voltage detection circuit 70 is the same as that in FIG.

  Now, in the case of a load disconnection in which the LED of the load 10 is disconnected, the current flowing from the node N1 to the drain of the transistor M1 stops. For this reason, the voltage Va at the node N1 decreases. When this voltage Va drops below the reference voltage Vref2 of the second control circuit 30A, the output voltage of the operational amplifier 31 of the second control circuit 30A rises, raising the gate voltages of the transistors M2 and M3. As a result, the transistor M2 supplies a current to the node N1, and the transistor M3 supplies a current to the resistor R2 of the first control circuit 20A to raise the inverting input terminal voltage of the operational amplifier 22 of the first control circuit 20A. As a result, the gate voltage of the transistor M1 decreases, the drain current decreases, and eventually converges to a predetermined value. With the above operation, the voltage Va at the node N1 is controlled to be equal to the reference voltage Vref2 of the voltage source 33 of the second control circuit 30A.

  At this time, if the divided voltage Vb of the voltage V1 of the voltage source 11 is Vb> Vref3 with respect to the reference voltage Vref3 of the first voltage detection circuit 60, it is detected at the output terminal 63 of the first detection circuit 60. No signal is output. Since the voltage Va at the node N1 is equal to the reference voltage Vref2, Va> Vref4 with respect to the reference voltage Vref4 of the second voltage detection circuit 70, and the detection signal is output to the output terminal 73 of the second voltage detection circuit 70. Is not output. Therefore, a detection signal is output from the output terminal 35 of the second control circuit 30A, and a detection signal is output from either the output terminal 63 of the first voltage detection circuit 60 or the output terminal 73 of the second voltage detection circuit 70. It is possible to determine a load disconnection by determining that it is not performed by an abnormality determination circuit (not shown).

  Further, even when the voltage V1 of the voltage source 11 is lowered, a signal indicating abnormality is output to the output terminal 35 of the second control circuit 30A. At this time, since the divided voltage Vb is Vb <Vref3 with respect to the reference voltage Vref3 of the first voltage detection circuit 60, a detection signal is output to the output terminal 63 of the first voltage detection circuit 60. Since the voltage Va of the node N1 is controlled to be equal to the reference voltage Vref2, Va> Vref4 with respect to the reference voltage Vref4 of the second voltage detection circuit 70, and the output terminal 73 of the second voltage detection circuit 70. No detection signal is output. Therefore, the detection signal is output from the output terminal 35 of the second control circuit 30A, the detection signal is output from the output terminal 63 of the first voltage detection circuit 60, and is detected from the output terminal 73 of the second voltage detection circuit 70. By determining that a signal is not output by an abnormality determination circuit (not shown), it is possible to determine a significant decrease in the voltage V1 of the power source 11.

  When the node N1 is short-circuited to GND, the drain current of the transistor M2 has a limit regulated by the voltage of the voltage source 34. Therefore, a current exceeding the limit value of the drain current of the transistor M2 is equal to the GND. In this state, the voltage Va at the node N1 drops to near the GND potential. At this time, the voltage Va at the node N1 is Va <Vref4 with respect to the reference voltage Vref4 of the voltage source 72 of the second voltage detection circuit 70, and a detection signal is output from the output terminal 73 of the second voltage detection circuit 70. To do. If the voltage V1 of the voltage source 11 is normal, no detection signal is output from the output terminal 63 of the first voltage detection circuit 60. Therefore, the detection signal is output from the output terminal 35 of the second control circuit 30A, the detection signal is not output from the output terminal 63 of the first voltage detection circuit 60, and from the output terminal 73 of the second voltage detection circuit 70. By determining that a detection signal is output by an abnormality determination circuit (not shown), it is possible to determine that a GND short circuit has occurred. In this case, by taking measures such as stopping the voltage V1 of the voltage source 30, it is possible to prevent an excessive current from flowing through the LED of the load 10 and causing the LED to break down.

  As described above, when the load 10 is short-circuited, the voltage Va at the node N1 becomes higher than that at the normal time. Therefore, by detecting this, the load short-circuit can be detected.

  As described above, in this embodiment, when the LED of the load 10 is disconnected, the load is short-circuited when the voltage V1 of the voltage source 11 is significantly reduced, or when the node N1 is short-circuited to GND. Thus, it becomes possible to distinguish and determine the occurrence of the four types of abnormal situations.

  When the first voltage detection circuit 60 and the second voltage detection circuit 70 for detecting the voltage V1 drop of the voltage source 11 are combined with the load driving circuit of FIG. 2, the first detection circuit 60 is combined as it is. However, since the second voltage detection circuit 70 detects a short circuit of the node N1 to the voltage source 11, whether or not the voltage Va at the node N1 is higher than a predetermined value (voltage close to the voltage V1). It is necessary to use a third voltage detection circuit for detecting the above. Further, a voltage detection circuit similar to the second voltage detection circuit 70 may be used to detect a load short circuit in the load drive circuit of FIG.

  10: Load such as LED, 11: Voltage source, 20A to 20C: First control circuit, 30A, 30B: Second control circuit, 40A to 40D: Abnormality determination circuit, 50: Voltage dividing circuit, 60: First Voltage detection circuit 70: second voltage detection circuit

Claims (2)

In a load driving circuit having a first control circuit that is connected between a load connected to a first voltage source and GND and that controls a current flowing in the load to a predetermined value,
A second control circuit that detects a potential difference between a first node at a common connection point between the load and the first control circuit and the GND and controls the potential difference to a predetermined value; and A first voltage detection circuit for detecting a voltage of a voltage source and / or a second voltage detection circuit for detecting a potential difference between the first node and the GND, and a control operation of the second control circuit. A load driving circuit comprising: an abnormality determination circuit that performs abnormality determination based on a combination of contents and a detection result of the first voltage detection circuit and / or the second voltage detection circuit. In a load driving circuit having a first control circuit that is connected between a load connected to GND and a first voltage source and controls the current flowing through the load to have a predetermined value.
A second control circuit that detects a potential difference between a first node at a common connection point between the load and the first control circuit and the first voltage source, and controls the potential difference to a predetermined value; A first voltage detection circuit for detecting a voltage of the first voltage source and / or a third voltage detection circuit for detecting a potential difference between the first node and the first power supply; A load comprising: an abnormality determination circuit that performs abnormality determination based on a combination of the content of the control operation of the control circuit and the detection result of the first voltage detection circuit and / or the third voltage detection circuit Driving circuit.

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