JP2024063307A - Light emitting element driving device - Google Patents

Abstract

The present invention provides a light-emitting element driving device capable of suppressing the effects of NBTI. In the light-emitting element driving device (5), an input transistor (141), a first output transistor (142), a MOS transistor (12), and a first switch (13) provided in a light-emitting element driver section (1) are all composed of NMOS transistors. [Selected Figure]

Description

This disclosure relates to a light-emitting element driving device.

Conventionally, light-emitting element driving devices for driving light-emitting elements such as LEDs (light-emitting diodes) are known. For example, Patent Document 1 discloses a proximity sensor that uses an LED as a light-emitting element.

JP 2020-187847 A

When the light-emitting element is an LED, the light-emitting element driving device has an LED driver unit. When the power supply voltage of the LED driver unit is the power supply voltage of the LED, the power supply voltage of the LED is relatively high, so if a PMOS transistor (P-channel MOSFET (metal-oxide-semiconductor field-effect transistor)) is provided in the LED driver unit, there is a risk of NBTI occurring in the PMOS transistor. NBTI (Negative Bias Temperature Instability) is a time-dependent deterioration characteristic that occurs when a negative bias is applied to the gate of a PMOS transistor in a high-temperature state, and the threshold voltage of the PMOS transistor shifts over time.

In view of the above situation, the present disclosure aims to provide a light-emitting element driving device that can suppress the effects of NBTI.

For example, a light emitting element driving device according to the present disclosure may include:
A light emitting element driving device configured to drive a first light emitting element having a positive terminal connected to an application terminal of a first power supply voltage,
a light emitting element driver configured to drive the first light emitting element;
An internal circuit;
Equipped with
The internal circuitry includes a current pre-driver configured to generate a drive current;
The light emitting element driver unit
a first current mirror including an input transistor configured to receive the driving current and a first output transistor configured to be connected to a negative terminal of the first light emitting element;
a first MOS transistor including a gate configured to receive a first switching signal;
a first pull-up resistor including a first terminal configured to be connected to an application terminal of the first power supply voltage and a second terminal connected to a drain of the first MOS transistor;
a first switch including a gate connected to a first node to which the second end of the first pull-up resistor and a drain of the first MOS transistor are connected, the first switch being configured to switch on and off the driving of the first output transistor;
having
The input transistor, the first output transistor, the first MOS transistor, and the first switch are all configured with NMOS transistors.

The light-emitting element driving device disclosed herein can suppress the effects of NBTI.

FIG. 1 is a diagram showing a configuration of an LED driving device according to an exemplary embodiment of the present disclosure. FIG. 2 is a diagram showing a case where the switching signal S1 is at a low level in the configuration of FIG. FIG. 3 is a diagram showing a case where the switching signal S1 is at a high level in the configuration of FIG. FIG. 4 is a diagram showing a configuration of an LED driving device according to a first modified example of the present disclosure. FIG. 5 is a diagram showing a configuration of an LED driving device according to a second modified example of the present disclosure. FIG. 6 is a diagram showing a configuration of an LED driving device according to a comparative example.

1. Configuration of LED driving device
1 is a diagram showing a configuration of an LED driving device 5 according to an exemplary embodiment of the present disclosure. The LED driving device 5 is a device for driving an LED 3. In other words, the LED driving device 5 is an example of a light-emitting element driving device.

The LED driving device 5 is an IC (integrated circuit) that integrates an LED driver section 1 and an internal circuit 2. The LED driving device 5 has an anode terminal 51, a cathode terminal 52, and a ground terminal 53 as external terminals for establishing an electrical connection with the outside.

The LED driver unit 1 has a pull-up resistor 11, a MOS transistor 12, a switch 13, a current mirror 14, voltage-dividing resistors R1 and R2, voltage-dividing resistors R3 and R4, and a resistor R5.

The anode terminal 51 is connected to the anode (positive terminal) of the LED 3 externally and is applied with the first power supply voltage Vcc1. The cathode terminal 52 is connected to the cathode (negative terminal) of the LED 3 externally. In other words, the LED 3 is attached externally to the LED driving device 5. The ground terminal 53 is connected to the application terminal of the ground potential.

The first end of the pull-up resistor 11 is connected to the anode terminal 51. The MOS transistor 12 is composed of an NMOS transistor (N-channel MOSFET). The second end of the pull-up resistor 11 is connected to the drain of the MOS transistor 12 at the node Nd1. The source of the MOS transistor 12 is connected to the ground terminal 53.

The internal circuit 2 includes an ADC (Analog-to-digital converter) 21, a current pre-driver 22, an inverter 23, and PMOS switches PM1 and PM2. The internal circuit 2 operates using the second power supply voltage Vcc2 as a power supply. The first power supply voltage Vcc1 is higher than the second power supply voltage Vcc2. For example, Vcc1=5V, and Vcc2=3.3V.

The gate of the MOS transistor 12 is supplied with a switching signal S1, which is the output of the inverter 23. The on/off state of the MOS transistor 12 is switched according to the level of the switching signal S1.

The current mirror 14 has an input transistor 141 and an output transistor 142. Both the input transistor 141 and the output transistor 142 are configured with NMOS transistors. The drain of the input transistor 141 is connected to the output terminal of the current pre-driver 22. The gate and drain of the input transistor 141 are shorted. The source of the input transistor 141 and the source of the output transistor 142 are connected to the ground terminal 53. The gate of the output transistor 142 is connected to the gate of the input transistor 141.

The switch 13 is composed of an NMOS transistor. The source of the switch 13 is connected to the drain of the output transistor 142. The drain of the switch 13 is connected to the cathode terminal 52.

The current pre-driver 22 is configured to generate a drive current Id. The drive current Id is supplied to the drain of the input transistor 141.

As described above, in this embodiment, the MOS transistor 12, switch 13, input side transistor 141, and output side transistor 142 used in the LED driver unit 1 are all configured as NMOS transistors, so there is no need to consider NBTI, which would be necessary if PMOS transistors were used.

Here, for example, when an inverter is configured with MOS transistor 12 and PMOS transistor 15, as in the comparative example configuration shown in Figure 6, it is necessary to take into account NBTI caused by PMOS transistor 15.

2. LED current on/off control
The on/off control of the LED current I _LED flowing through the LED 3 will be described with reference to FIG. 2 and FIG.

2 is a diagram showing a case where the switching signal S1 is at a low level (i.e., the input to the inverter 23 is at a high level) in the configuration of FIG. 1. In this case, the MOS transistor 12 is turned off, the gate of the switch 13 is set to a high level (Vcc1) by the pull-up resistor 11, and the switch 13 is turned on. The drive current Id generated by the current pre-driver 22 is mirrored by the current mirror 14. Therefore, an LED current _ILED flows through the path of the LED 3, the switch 13, and the output-side transistor 142, and the LED 3 emits light.

3 is a diagram showing a case where the switching signal S1 is at a high level (i.e., the input to the inverter 23 is at a low level) in the configuration of FIG. 1. In this case, the MOS transistor 12 is turned on, the gate of the switch 13 is set to a low level, and the switch 13 is turned off. Therefore, the LED current I _LED does not flow through the path via the switch 13.

<3. Vf monitoring function>
The LED driving device 5 according to this embodiment has a function of monitoring Vf (forward voltage) of the LED 3. A function of monitoring Vf for monitoring the environmental temperature or for detecting an abnormality is provided.

Voltage-dividing resistors R1 and R2 are connected in series between the anode terminal 51 and the ground terminal 53. A connection node Nr1 to which the voltage-dividing resistors R1 and R2 are connected is input to the input terminal of the ADC 21 via the PMOS switch PM1. Voltage-dividing resistors R3 and R4 are connected in series between the cathode terminal 52 and the ground terminal 53. A connection node Nr2 to which the voltage-dividing resistors R3 and R4 are connected is input to the input terminal of the ADC 21 via the PMOS switch PM2. Both PMOS switches PM1 and PM2 are composed of PMOS transistors, and are switched between on and off states depending on the level of the voltage applied to the gates.

When the PMOS switch PM1 is on, the anode potential of LED3 is divided by the voltage dividing resistors R1 and R2, and the resulting potential is input to the ADC 21. On the other hand, when the PMOS switch PM2 is on, the cathode potential of LED3 is divided by the voltage dividing resistors R3 and R4, and the resulting potential is input to the ADC 21. The potential difference input to the ADC 21 is AD converted, and the Vf of LED3 is monitored.

It is desirable to avoid applying the first power supply voltage Vcc1 to the PMOS switch PM1 in consideration of NBTI, so the first power supply voltage Vcc1 is divided by voltage dividing resistors R1 and R2. The voltage division ratio here is, for example, 1/2.

<4. LED light suppression function>
Since the voltage-dividing resistors R3 and R4 are connected to the cathode terminal 52 as described above, even when the switch 13 is in the off state, a current flows to the LED 3 via the voltage-dividing resistors R3 and R4, causing the LED 3 to emit unnecessary light. As a countermeasure, a resistor R5 having a resistance value sufficiently smaller than that of the voltage-dividing resistors R3 and R4 is connected between the anode terminal 51 and the cathode terminal 52. As a result, when the switch 13 is in the off state, a current flows to the voltage-dividing resistors R3 and R4 via the resistor R5, suppressing the current from flowing to the LED 3 and suppressing unnecessary light emission by the LED 3 (the current path indicated by the dashed arrow in FIG. 3).

5. First Modified Example
Fig. 4 is a diagram showing a configuration of an LED driving device 5 according to a first modified example of the present disclosure. The LED driving device 5 shown in Fig. 4 is configured to be capable of driving an LED 31 in addition to an LED 3. As a result, the LED driving device 5 shown in Fig. 4 further includes a cathode terminal 521 as an external terminal in addition to the configuration shown in Fig. 1 described above. The LED driver unit 1 shown in Fig. 4 further includes a pull-up resistor 111, a MOS transistor 121, and a switch 131 in addition to the configuration shown in Fig. 1 described above. The internal circuit 2 shown in Fig. 4 further includes an inverter 231 in addition to the configuration shown in Fig. 1 described above.

The switch 131 and the MOS transistor 121 are composed of NMOS transistors. The drain of the switch 131 is connected to the cathode terminal 521. The source of the switch 131 is connected to the drain of the output transistor 142. The first end of the pull-up resistor 111 is connected to the anode terminal 51. The second end of the pull-up resistor 111 is connected to the drain of the MOS transistor 121 at the node Nd11. The source of the MOS transistor 121 is connected to the ground terminal 53. The node Nd11 is connected to the gate of the switch 131.

A switching signal S11, which is the output of the inverter 231, is applied to the gate of the MOS transistor 121. The on/off state of the MOS transistor 121 is switched according to the level of the switching signal S11. This switches the on/off state of the switch 131, and switches the light emission/extinguishing of the LED 31. Therefore, in this modified example, the light emission/extinguishing of the LEDs 3 and 31 can be individually selected by the switching signals S1 and S11. Here, since the switch 131 and the MOS transistor 121 are composed of NMOS transistors, there is no need to consider NBTI in the LED driver unit 1.

It is also possible to add one or more LEDs similar to LED 31 and modify the configuration of LED driver 5 accordingly.

6. Second Modification
Fig. 5 is a diagram showing a configuration of an LED driving device 5 according to a second modified example of the present disclosure. The configuration shown in Fig. 5 differs from the configuration shown in Fig. 1 in the location where the switch 13 is provided. Specifically, in the configuration shown in Fig. 5, the switch 13 is disposed so as to connect between the gate of the input side transistor 141 and the gate of the output side transistor 142 that configure the current mirror 14. The drain of the switch 13 is connected to the gate of the input side transistor 141. The source of the switch 13 is connected to the gate of the output side transistor 142.

In addition, in the LED driving device 5 configured as shown in FIG. 5, a pair of pull-up resistor 11A and MOS transistor 12A, and a pair of pull-up resistor 11B and MOS transistor 12B are provided instead of the pull-up resistor 11 and MOS transistor 12 shown in FIG. 1. The MOS transistors 12A and 12B are configured with NMOS transistors. A node Nd11 to which the pull-up resistor 11A and MOS transistor 12A are connected is connected to the gate of the MOS transistor 12B. A node Nd12 to which the pull-up resistor 11B and MOS transistor 12B are connected is connected to the gate of the switch 13.

Also, in the LED driving device 5 configured as shown in FIG. 5, analog switches AS1 and AS2 are provided. Analog switch AS1 is configured by a parallel connection of PMOS switch PM1 and NMOS switch NM1. Analog switch AS2 is configured by a parallel connection of PMOS switch PM2 and NMOS switch NM2. Node Nd11 is connected to the gate of NMOS switch NM1 as well as the gate of PMOS switch PM2. Node Nd12 is connected to the gate of PMOS switch PM1 as well as the gate of NMOS switch NM2. Switching signal S1 is applied to the gate of MOS transistor 12A.

With this configuration, when the switching signal S1 is at a low level, the voltage of node Nd11 is at a high level, the voltage of node N12 is at a low level, and the switch 13 is in an off state. This causes the output transistor 142 to be driven in an off state. At this time, the analog switch AS1 is in an on state, the analog switch AS2 is in an off state, and the voltage obtained by dividing the first power supply voltage Vcc1 (the anode potential of LED3) by the voltage dividing resistors R1 and R2 is input to the AD converter 21.

When the switching signal S1 is at a high level, the voltage of node Nd11 is at a low level, the voltage of node N12 is at a high level, and the switch 13 is in an on state. This causes the output transistor 142 to be driven in an on state. At this time, the analog switch AS1 is in an off state, the analog switch AS2 is in an on state, and the voltage obtained by dividing the cathode potential of LED3 by the voltage-dividing resistors R3 and R4 is input to the AD converter 21. This allows the Vf of LED3 to be monitored.

7. Application Examples
The LED driving device 5 according to the present disclosure can be applied to various applications, and is preferably used for in-vehicle applications. For example, the LED driving device 5 is provided in a vehicle to drive an LED provided in a light-emitting portion of a proximity sensor. In addition, for example, the LED driving device 5 may be provided in a vehicle to drive an LED provided in a head lamp, a rear lamp, or the like of the vehicle.

<8. Other>
In addition, various technical features according to the present disclosure can be modified in various ways without departing from the spirit of the technical creation, in addition to the above-mentioned embodiment. In other words, the above-mentioned embodiment should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention should be understood to include all modifications that are within the meaning and scope of the claims, and are not limited to the above-mentioned embodiment. In addition, the above-mentioned embodiments may be implemented in appropriate combinations as long as there is no contradiction.

<8. Notes>
As described above, for example, the light-emitting element driving device (5) according to the present disclosure has:
A light emitting element driving device configured to drive a first light emitting element (3) having a positive terminal connected to an application terminal of a first power supply voltage (Vcc1),
a light emitting element driver section (1) configured to drive the first light emitting element;
An internal circuit (2);
Equipped with
The internal circuitry includes a current pre-driver (22) configured to generate a drive current (Id);
The light emitting element driver unit
a first current mirror (14) including an input transistor (141) configured to receive the driving current and a first output transistor (142) configured to be connected to a negative terminal of the first light-emitting element;
a first MOS transistor (12) including a gate configured to receive a first switching signal (S1);
a first pull-up resistor (11) including a first terminal configured to be connected to an application terminal of the first power supply voltage and a second terminal connected to a drain of the first MOS transistor;
a first switch (13) including a gate connected to a first node (Nd1) to which the second end of the first pull-up resistor and the drain of the first MOS transistor are connected, the first switch (13) being configured to switch on and off the driving of the first output transistor;
having
The input transistor, the first output transistor, the first MOS transistor, and the first switch are all configured with NMOS transistors (first configuration).

In the first configuration, the light-emitting element driver section (1)
A first voltage dividing resistor (R1, R2) configured to be connected to the positive terminal;
A second voltage dividing resistor (R3, R4) configured to be connected to the negative terminal;
having
The internal circuit (2)
An AD converter (21);
a first PMOS switch (PM1) connected between a connection node (Nr1) of the first voltage dividing resistor and the AD converter;
A second PMOS switch (PM2) may be connected between the connection node (Nr2) of the second voltage dividing resistor and the AD converter (second configuration).

In the second configuration, the light-emitting element driver unit (1) has a resistor (R5) configured to be connected between the positive terminal and the negative terminal,
The resistance value of the resistor may be smaller than the resistance value of the second voltage dividing resistor (R3, R4) (third configuration).

In any one of the first to third configurations, the light-emitting element driving device (5) is configured to drive a second light-emitting element (31) having a positive terminal connected to an application terminal of the first power supply voltage (Vcc1),
The light emitting element driver unit (1)
a second current mirror (14) including the input transistor (141) and a second output transistor (142) configured to be connected to a negative terminal of the second light-emitting element;
a second MOS transistor (121) including a gate configured to receive a second switching signal (S11);
a second pull-up resistor (111) including a first terminal configured to be connected to an application terminal of the first power supply voltage and a second terminal connected to a drain of the second MOS transistor;
a second switch (131) including a gate connected to a second node (Nd11) to which the second end of the second pull-up resistor and the drain of the second MOS transistor are connected, and configured to switch on and off the driving of the second output side transistor;
having
The second MOS transistor and the second switch may each be configured with an NMOS transistor (fourth configuration).

In addition, in any of the first to fourth configurations, the internal circuit may be configured to operate using a second power supply voltage, and the first power supply voltage may be higher than the second power supply voltage (fifth configuration).

It is also preferable that the light-emitting element driving device of any of the first to fifth configurations be mounted on a vehicle (sixth configuration).

This disclosure can be used to drive light-emitting elements for a variety of applications.

1 LED driver section 2 Internal circuit 3, 31 LED
5 LED driver 11 Pull-up resistor 11A, 11B Pull-up resistor 12 MOS transistor 12A, 12B MOS transistor 13 Switch 14 Current mirror 15 PMOS transistor 21 AD converter 22 Current pre-driver 23 Inverter 51 Anode terminal 52 Cathode terminal 53 Ground terminal 111 Pull-up resistor 121 MOS transistor 131 Switch 141 Input transistor 142 Output transistor 231 Inverter 521 Cathode terminal AS1, AS2 Analog switch NM1, NM2 NMOS switch PM1, PM2 PMOS switch R1, R2 Voltage dividing resistor R3, R4 Voltage dividing resistor R5 Resistor

Claims (6)

A light emitting element driving device configured to drive a first light emitting element having a positive terminal connected to an application terminal of a first power supply voltage,
a light emitting element driver configured to drive the first light emitting element;
An internal circuit;
Equipped with
The internal circuitry includes a current pre-driver configured to generate a drive current;
The light emitting element driver unit
a first current mirror including an input transistor configured to receive the driving current and a first output transistor configured to be connected to a negative terminal of the first light emitting element;
a first MOS transistor including a gate configured to receive a first switching signal;
a first pull-up resistor including a first terminal configured to be connected to an application terminal of the first power supply voltage and a second terminal connected to a drain of the first MOS transistor;
a first switch including a gate connected to a first node to which the second end of the first pull-up resistor and a drain of the first MOS transistor are connected, the first switch being configured to switch on and off the driving of the first output transistor;
having
the input transistor, the first output transistor, the first MOS transistor, and the first switch are all configured with NMOS transistors. The light emitting element driver unit
A first voltage dividing resistor configured to be connected to the positive terminal;
A second voltage dividing resistor configured to be connected to the negative terminal;
having
The internal circuit includes:
An AD converter;
a first PMOS switch connected between a connection node of the first voltage dividing resistor and the AD converter;
a second PMOS switch connected between the connection node of the second voltage dividing resistor and the AD converter;
The light emitting element driving device according to claim 1 , The light-emitting element driver unit has a resistor configured to be connected between the positive terminal and the negative terminal,
3. The light-emitting element driving device according to claim 2, wherein a resistance value of the resistor is smaller than a resistance value of the second voltage dividing resistor. The light emitting element driving device is configured to drive a second light emitting element having a positive terminal connected to an application terminal of the first power supply voltage,
The light emitting element driver unit
a second current mirror including the input transistor and a second output transistor configured to be connected to a negative terminal of the second light emitting element;
a second MOS transistor including a gate configured to receive a second switching signal;
a second pull-up resistor including a first terminal configured to be connected to an application terminal of the first power supply voltage and a second terminal connected to a drain of the second MOS transistor;
a second switch including a gate connected to a second node to which the second end of the second pull-up resistor and the drain of the second MOS transistor are connected, the second switch being configured to switch on and off the driving of the second output transistor;
having
2. The light-emitting element driving device according to claim 1, wherein the second MOS transistor and the second switch are both constituted by an NMOS transistor. the internal circuit is configured to operate using a second power supply voltage;
2. The light emitting element driving device according to claim 1, wherein the first power supply voltage is higher than the second power supply voltage. A light-emitting element driving device according to any one of claims 1 to 5, which is mounted on a vehicle.

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