Driving circuit

Abstract

To provide a driving circuit capable of easily satisfying a minimum application load within a whole use temperature range.SOLUTION: A driving circuit is a driving circuit including a first line to which a power supply voltage is applied, and driving a load on the basis of an ON / OFF of a first switch to be provided to between the first line and the second line, and comprises: a third line that supplies a power to the load from the first line; a second switch that is provided onto a path of the third line; a switch control circuit that controls the ON / OFF of the second switch on the basis of an application of the power supply voltage to the second line; and a current control circuit that is provided to between the second line and a ground, and flows a predetermined current to the first switch when the first switch is ON. The current control circuit contains: an integrated circuit that generates a predetermined voltage by receiving the power supply voltage; and a first resistance to which the predetermined voltage is applied. The current flowing through the first resistance is the largest amount of the predetermined current.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a drive circuit.

Background Art

[0002] In a general vehicle, a drive circuit is provided that turns on or off an accessory lamp based on the on / off operation of a switch by a driver. Further, this switch may be a mechanical switch (for example, a relay). For a mechanical switch, a minimum application load, which is the lower limit current value at which the mechanical switch can be opened and closed, is defined as a reference value (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, depending on the type of mechanical switch, the minimum application load within the operating temperature range is strictly defined, and when operating a generally used constant current circuit as a load, the minimum application load may not be satisfied within the entire operating temperature range (for example, -40 to 80°C).

[0005] An object of the present invention is to provide a drive circuit that can easily satisfy the minimum application load within the entire operating temperature range.

Means for Solving the Problems

[0006] The main aspect of the present invention for achieving the above object is

Effects of the Invention

[0007] According to the present invention, a drive circuit that can easily satisfy the minimum application load within the entire operating temperature range can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] From the description in this specification and the accompanying drawings, at least the following matters become clear.

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and repeated explanations are omitted as appropriate.

[0011] =====This Embodiment===== <<<Vehicle Lamp 1>>> FIG. 1 is a diagram showing an example of the configuration of the vehicle lamp 1. The vehicle lamp 1 includes a switch SW, a drive circuit 10, a battery 11, and a light source 12. The current flowing through the switch SW is defined as the current Isw, and the switch SW corresponds to the "first switch".

[0012] Based on the on / off state of the switch SW, the drive circuit 10 applies the voltage Vbat (e.g., 9 - 16V) from the battery 11 to the light source 12 to turn the light source 12 on and off. Also, the light source 12 is a light source for an accessory lamp and is an illumination lamp used as an auxiliary to the headlamp when visibility is poor due to rain or fog. Further, the drive circuit 10 includes terminals Ta - Te, a PMOS transistor 20, a switch control circuit 21a, a constant current circuit 22a, a Zener diode 23, and a diode 24. Note that the PMOS transistor 20 corresponds to the "second switch", and the voltage Vbat corresponds to the "power supply voltage".

[0013] A line L1 connected to the positive electrode side of the battery 11 (i.e., the line L1 to which the voltage Vbat is applied) is connected to the terminal Ta. The terminal Tb is connected to the terminal Ta via the internal wiring of the drive circuit 10, and the switch SW outside the drive circuit 10 is also connected. Note that the line L1 corresponds to the "first line". The terminal Tc is connected to the switch SW, which is a mechanical switch connected to the line L2. Therefore, the switch SW is provided between the line L1 and the line L2. And when the switch SW is on, the drive circuit 10 passes a current through the switch SW via the terminal Tc to satisfy the minimum applicable load defined for the switch SW.

[0014] Note that the minimum applicable load of the switch SW is, for example, ±10% of 2mA. Also, the "minimum applicable load" is defined as a reference value for the current value flowing through the contacts of the mechanical switch in order to electrically break the poor conductor layer generated due to the oxidation of the contacts of the mechanical switch. Also, the line L2 corresponds to the "second line".

[0015] The terminal Td is connected to the ground, and the terminal Te is connected to the light source 12.

[0016] The PMOS transistor 20 is a switch on the path of line L3 connected to line L1. When the switch SW is turned on and the PMOS transistor 20 is turned on by a switch control circuit 21a (described later), power is supplied to the light source 12 via line L3 and terminal Te based on the voltage Vbat from line L1. Then, the light source 12 is lit. On the other hand, when the switch SW is turned off and the PMOS transistor 20 is turned off by the switch control circuit 21a, the supply of power to the light source 12 is stopped. Then, the light source 12 is turned off. Note that line L3 corresponds to the "third line".

[0017] The switch control circuit 21a is a circuit that controls the on / off of the PMOS transistor 20. Specifically, the switch control circuit 21a controls the on / off of the PMOS transistor 20 based on whether the voltage Vbat is applied to line L2 or not. The switch control circuit 21a includes resistors 30, 31, and an NMOS transistor 32.

[0018] The resistor 30 is an element connected between the gate and source of the PMOS transistor 20, and pulls up the gate of the PMOS transistor 20. Also, when the NMOS transistor 32 is turned on, a current flows through the resistor 30, and a gate-source voltage for turning on the PMOS transistor 20 is generated.

[0019] The resistor 31 is provided between the gate of the PMOS transistor 20 and the drain of the NMOS transistor 32, and is an element that forms a voltage dividing circuit together with the resistor 30. Note that when the NMOS transistor 32 is turned on, the resistors 30 and 31 divide the voltage Vbat of line L3 to turn on the PMOS transistor 20.

[0020] The NMOS transistor 32 is an element that controls the on / off of the PMOS transistor 20. Specifically, the voltage of line L2 is applied to the gate of the NMOS transistor 32 via a diode 24 (described later). Also, a resistor 31 is connected to the drain of the NMOS transistor 32, and the source is grounded.

[0021] Therefore, when the switch SW is on and the voltage Vbat is applied to line L2, the switch control circuit 21a turns on the PMOS transistor 20. And when the switch SW is off and the voltage Vbat is not applied to line L2, the switch control circuit 21a turns off the PMOS transistor 20. Thereby, the drive circuit 10 can turn on the light source 12 when the switch SW is on and turn off the light source 12 when the switch SW is off.

[0022] The constant current circuit 22a is provided between line L2 and ground. When the voltage Vbat is applied to line L2 when the switch SW is on, it operates and passes a predetermined current through the switch SW. Also, at this time, the NMOS transistor 32 is on, but since the current flowing through the gate of the NMOS transistor 32 is minute, the current I0 flowing through the constant current circuit 22a mostly flows through the switch SW. Note that the constant current circuit 22a will be described after a general constant current circuit 22b is described. Also, the constant current circuit 22a corresponds to a "current control circuit".

[0023] When the voltage value of the voltage Vbat applied to the constant current circuit 22a is higher than a predetermined level, the Zener diode 23 clamps the voltage Vbat to protect the constant current circuit 22a. Also, the cathode of the Zener diode 23 is connected to line L2 via a diode 24 (described later), and the anode is connected to ground.

[0024] When a voltage Vbat is applied to the terminal Td and the terminal Tc is grounded (i.e., reverse-connected), for example, the diode 24 prevents current from flowing in the direction opposite to the original direction through the Zener diode 23. Also, the anode of the diode 24 is connected to the line L2, and the cathode is connected to the cathode of the Zener diode 23.

[0025] <<<General constant current circuit 22b>>> FIG. 2 is a diagram showing an example of the configuration of a general constant current circuit 22b. The constant current circuit 22b can be used instead of the constant current circuit 22a, and based on the reference voltage Vref, a constant current I0 flows through the line L2. The constant current circuit 22b includes resistors 40, 43, 45, a Zener diode 41, an operational amplifier 42, and an NMOS transistor 44.

[0026] The resistor 40 and the Zener diode 41 are provided in series between the line L3 and the ground to generate the reference voltage Vref. Note that the reference voltage Vref is the Zener voltage of the Zener diode 41.

[0027] The reference voltage Vref is applied to the non-inverting input terminal of the operational amplifier 42. One end of the resistor 45 for detecting the current I0 flowing through the NMOS transistor 44 and the source electrode of the NMOS transistor 44 are connected to the inverting input terminal of the operational amplifier 42. Also, the output electrode of the operational amplifier 42 is connected to the gate of the NMOS transistor 44 via the resistor 43.

[0028] The current I0 is supplied to the NMOS transistor 44 from the line L2. Then, the operational amplifier 42 controls the NMOS transistor 44 so that the voltage at the inverting input terminal becomes the reference voltage Vref applied to the non-inverting input terminal.

[0029] As a result, a current I0 determined by the reference voltage Vref and the resistance value of the resistor 45 flows through the line L2.

[0030] Also, when using the constant current circuit 22b as the constant current circuit, due to the temperature characteristics of the Zener voltage of the Zener diode 41 (i.e., the reference voltage Vref) and the resistance value of the resistor 45, it is difficult to flow a constant current I0 throughout the entire operating temperature range. Further, since the temperature coefficient of the Zener voltage of the Zener diode 41 is, for example, -0.08% / °C, when the Zener voltage is set to 5V, the Zener voltage becomes 5.24V at -40°C and 4.76V at 80°C. Therefore, the Zener voltage of the Zener diode 41 varies significantly with temperature. That is, it is difficult to satisfy 2mA ± 10%, which is the minimum applicable load of the switch SW, throughout the entire operating temperature range.

[0031] <<<Constant current circuit 22a of the present embodiment>>> Therefore, in the present embodiment, the constant current circuit 22a is used as the constant current circuit. FIG. 3 is a diagram showing an example of the configuration of the constant current circuit 22a.

[0032] The constant current circuit 22a includes a constant voltage circuit 50, capacitors 51 and 53, and a resistor 52. The constant voltage circuit 50 receives the voltage Vbat and generates a predetermined voltage Vout based on a temperature-compensated reference voltage (not shown), and is a series regulator formed by an integrated circuit. The constant voltage circuit 50 has the voltage from line L2 applied to its power supply terminal VCC and outputs the voltage Vout from its output terminal OUT. Also, the ground terminal GND of the constant voltage circuit 50 is grounded.

[0033] The capacitor 51 is provided between the power supply terminal VCC and the ground to stabilize the voltage Vbat applied to the power supply terminal VCC from line L2.

[0034] The resistor 52 is provided between the terminal OUT and the ground and functions as a load of the constant voltage circuit 50. A predetermined voltage Vout is applied to the resistor 52. Also, the current Ir flowing through the resistor 52 is the maximum current amount among the current I0. Note that the resistor 52 corresponds to the "first resistor".

[0035] The capacitor 53 is an element for phase compensation to prevent oscillation of the voltage Vout.

[0036] Also, since the constant voltage circuit 50 outputs the voltage Vout based on a temperature-compensated reference voltage, it is unlikely that the voltage Vout will vary due to the temperature characteristics of the resistance value of the resistor 52. Therefore, the output voltage Vout is substantially constant (for example, 5V), and the power consumed inside the constant voltage circuit 50 is also considered to be substantially constant over the entire operating temperature range.

[0037] Therefore, the current consumption (i.e., the current I0) of the constant voltage circuit 50 also becomes substantially constant over the entire operating temperature range. Thus, if the resistance value of the resistor 52 is appropriately set, the requirement for the minimum applied load of the switch SW (for example, 2 mA ± 10%) can be satisfied over the entire operating temperature range. Therefore, a drive circuit that can easily satisfy the minimum applied load within the entire operating temperature range can be provided.

[0038] Also, among the current Isw flowing through the switch SW in FIG. 1, the sum of the current flowing through the inside of the constant voltage circuit 50 and the capacitors 51 and 53 in FIG. 3 and the current flowing through the NMOS transistor 32 via the line L2 is much smaller than the current value of the current Ir flowing through the resistor 52. For example, in this embodiment, when the current Isw is 2 mA, the current value of the total current is about 0.1% of the current value of the current Isw. That is, the ratio of the current Ir to the current Isw is about 99.9%. Also, in terms of design, the ratio of the current Ir to the current Isw is preferably 90% or more.

[0039] Note that in this embodiment, the drive circuit 10 has been described as turning on and off the light source 12, but the drive circuit 10 can also be used as a drive circuit for driving a load (for example, a motor). Also, in this embodiment, the constant current circuit 22a is a series regulator or an LDO (Low Drop Out), but it may also be a switching regulator IC.

[0040] ===Modification Example=== FIG. 4 is a diagram showing an example of the configuration of the switch control circuit 21b. Different from the switch control circuit 21a, when the switch SW is turned on and the voltage Vbat is applied to the line L2, the switch control circuit 21b turns off the PMOS transistor 20.

[0041] The switch control circuit 21b includes resistors 30, 31, 33 and NMOS transistors 32, 34. The NMOS transistor 34 has the line L2 connected to its gate via the diode 24, and a resistor 33 whose one end is connected to the line L3 is connected to its drain. Then, the source of the NMOS transistor 34 is grounded.

[0042] Therefore, when the switch SW is turned off and the voltage Vbat is not applied to the line L2, the NMOS transistor 34 is turned off, and the voltage at the drain of the NMOS transistor 34 is pulled up to the voltage Vbat of the line L3. On the other hand, when the switch SW is turned on and the voltage Vbat is applied to the line L2, the NMOS transistor 34 is turned on, and the voltage at the drain of the NMOS transistor 34 is set to the ground voltage.

[0043] When the voltage at the drain of the NMOS transistor 34 becomes the voltage Vbat, the NMOS transistor 32 is turned on and the PMOS transistor 20 is turned on. On the other hand, when the voltage at the drain of the NMOS transistor 34 becomes the ground voltage, the NMOS transistor 32 is turned off and the PMOS transistor 20 is turned off.

[0044] Therefore, when the switch SW is turned on and the voltage Vbat is applied to the line L2, the switch control circuit 21b turns off the PMOS transistor 20. And when the switch SW is turned off and the voltage Vbat is not applied to the line L2, the switch control circuit 21b turns on the PMOS transistor 20. Thereby, the drive circuit 10 can turn off the light source 12 when the switch SW is on and turn on the light source 12 when the switch SW is off.

[0045] ===Summary=== The drive circuit 10 of the present embodiment has been described above. The drive circuit 10 includes a line L3, a PMOS transistor 20, a switch control circuit 21a, and a constant current circuit 22a. The constant current circuit 22a includes a constant voltage circuit 50 and a resistor 52. Thereby, a drive circuit that can easily satisfy the minimum applicable load within the entire operating temperature range can be provided.

[0046] Further, when a voltage Vbat is applied to the line L2, the switch control circuit 21a turns on the PMOS transistor 20, and when the voltage Vbat is not applied to the line L2, the switch control circuit 21a turns off the PMOS transistor 20. Thereby, when the switch SW is turned on, the light source 12 can be lit.

[0047] Further, when a voltage Vbat is applied to the line L2, the switch control circuit 21b turns off the PMOS transistor 20, and when the voltage Vbat is not applied to the line L2, the switch control circuit 21b turns on the PMOS transistor 20. Thereby, when the switch SW is turned off, the light source 12 can be lit.

[0048] Further, the constant voltage circuit 50 is a series regulator. Thereby, when the voltage Vbat is applied and the constant voltage circuit 50 operates, a current I0 that satisfies the minimum applicable load of the switch SW within the entire operating temperature range can be passed.

[0049] Further, the drive circuit 10 includes a Zener diode 23. Thereby, even when the voltage Vbat applied to the constant voltage circuit 50 is a high voltage, the constant voltage circuit 50 can be protected.

[0050] Further, the drive circuit 10 includes a diode 24. Thereby, even when the voltage Vbat is applied to the terminal Td and the terminal Tc is grounded, it is possible to suppress a current flowing in a direction opposite to the original current direction in the drive circuit 10.

[0051] The above embodiments are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. Also, the present invention can be changed and improved without departing from its gist, and it goes without saying that equivalents of the present invention are included therein.

Explanation of Signs

[0052] 1 Vehicle lamp 10 Drive circuit 11 Battery 12 Light source 20 PMOS transistor 21a, 21b Switch control circuit 22a, 22b Constant current circuit 23 Zener diode 24 Diode 30, 31, 33, 40, 43, 45, 52 Resistor 32, 34, 44 NMOS transistor 41 Zener diode 42 Operational amplifier 50 Constant voltage circuit 51, 53 Capacitor

Claims

1. A drive circuit having a first line to which a power supply voltage is applied, and driving a load based on on / off of a first switch provided between the first line and a second line, a third line for supplying power from the first line to the load, a second switch provided on a path of the third line, a switch control circuit for controlling on / off of the second switch based on whether the power supply voltage is applied to the second line, a current control circuit provided between the second line and ground and flowing a predetermined current through the first switch when the first switch is on, comprising: the current control circuit a constant voltage circuit that receives the power supply voltage and generates a predetermined voltage, a first resistor to which the predetermined voltage is applied, including: characterized in that a current flowing through the first resistor is the maximum current amount among the predetermined currents, a drive circuit.

2. The drive circuit according to claim 1, wherein the switch control circuit turns on the second switch when the power supply voltage is applied to the second line, and turns off the second switch when the power supply voltage is not applied to the second line. a drive circuit.

3. The drive circuit according to claim 1, wherein the switch control circuit turns off the second switch when the power supply voltage is applied to the second line, and turns on the second switch when the power supply voltage is not applied to the second line. a drive circuit.

4. The drive circuit according to any one of claims 1 to 3, wherein the constant voltage circuit is a series regulator formed by an integrated circuit. a drive circuit.

5. The drive circuit according to claim 4, comprising a Zener diode having a cathode connected to the second line and an anode connected to ground. a drive circuit.

6. The drive circuit according to claim 5, comprising a diode having an anode connected to the second line and a cathode connected to the cathode of the Zener diode. a drive circuit.

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