JP2007335930A - Load controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance safety when short circuit failure occurs in a capacitor for setting the frequency of a triangle wave signal when a load is controlled based on a generated triangle wave signal. <P>SOLUTION: The load controller controls a load based on a generated triangle wave signal. The load controller comprises a circuit for generating a triangle wave signal having the same frequency in a first insertion state where a capacitor C1 for setting the frequency of a triangle wave signal is inserted between a constant voltage Vc and the noninput terminal of a comparator CP1 and a second insertion state where the capacitor C1 is inserted between the ground and the noninput terminal of a comparator CP1. Furthermore, patterns P1-P3 are formed such that the capacitor C1 can be inserted in any one of the first insertion state and the second insertion state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a load control device for controlling a load such as a lamp of an automobile, for example.

  Some conventional load control devices include triangular wave generation means, set voltage generation means, comparison means, and drive control means. When a drive command signal for instructing driving of the load is supplied at a constant level corresponding to the fixed input, the triangular wave generating means generates a triangular wave. The set voltage generation means holds and generates the second set voltage set between the maximum voltage and the minimum voltage of the triangular wave. The comparison means compares the triangular wave with the second set voltage. Thus, the drive control means generates a drive control signal whose level changes at a constant frequency and duty based on the comparison result of the comparison means.

  On the other hand, when a drive command signal for instructing to stop driving the load is supplied at a constant level corresponding to the fixed input, the triangular wave generating means generates a triangular wave. The set voltage generation means holds and generates a third set voltage lower than the second set voltage. The comparison means compares the triangular wave with the third set voltage. Thus, the drive control means generates a drive control signal whose level changes at a constant frequency and duty based on the comparison result of the comparison means.

  In addition, when a drive command signal whose level changes with a predetermined frequency and duty corresponding to the pulse input is supplied, the triangular wave generating means has a first setting set between the second set voltage and the third set voltage. Generate voltage. The set voltage generation means generates the switch by switching between the second set voltage and the third set voltage in accordance with the frequency and duty of the drive command signal. The comparison means compares the first set voltage with the second set voltage or the third set voltage. Thus, the drive control means generates a drive control signal whose level changes with the same frequency and duty as the drive command signal (see, for example, Patent Document 1).

JP 2001-148294 A (Claim 1, [0019] to [0053], FIGS. 1 to 3)

  The conventional load control apparatus described above uses, for example, a headlamp of a vehicle such as a two-wheeled vehicle or a four-wheeled vehicle as a load. Examples of the vehicle headlamp include a low-beam lamp and a high-beam lamp attached to one reflector, and a single headlamp having a low-beam filament and a high-beam filament. The low beam is preferably set so that glare does not occur for the other pilot when there is a preceding vehicle or an oncoming vehicle during night driving. On the other hand, the high beam is preferably set when there is no preceding vehicle or oncoming vehicle during night driving.

  In addition, in order to make pedestrians and oncoming vehicles recognize the presence of the vehicle and to prevent traffic accidents, the above-mentioned vehicle is lit in the daytime (DRL: daytime Running Light). ). Vehicles having the DRL function include those using the low beam for DRL and those using the high beam for DRL.

  By the way, the conventional load control device described above is composed of an IC, and a capacitor is inserted as an external component between the connection terminal and the ground in order to set the frequency of the triangular wave generated by the triangular wave generating means. Yes. When this capacitor causes a short circuit failure for some reason, the FET that is the load driving element maintains the on state. As a result, when the load is the headlamp, it remains lit at a duty ratio of 100%.

  In this case, in the vehicle using the low beam for DRL, there is no particular problem even if the headlamp is lit, and the lit state of the headlamp is maintained. Since the safety of the oncoming vehicle and the like is ensured, it can be said that it is preferable from the viewpoint of fail safe. On the other hand, in a vehicle using the above high beam for DRL, glare occurs to the driver of the preceding vehicle or the oncoming vehicle because the lighting state of the headlamp is maintained at a duty ratio of 100%, resulting in a traffic accident. It may lead to

The inconveniences described above can also occur in general devices that control the load based on the generated triangular wave signal.
This invention is made | formed in view of the situation mentioned above, and aims at providing the load control apparatus which can solve the above subjects.

  In order to solve the above problem, a load control device according to a first aspect of the present invention relates to a load control device that controls a load based on a generated triangular wave signal, and includes a capacitor for setting the frequency of the triangular wave signal. In the first insertion state inserted between the power source and the input end of the comparison means, and in the second insertion state inserted between the ground and the input end of the comparison means, the same frequency is obtained. And a triangular wave generation circuit for generating the triangular wave signal, wherein the capacitor is configured to be inserted in either the first insertion state or the second insertion state.

  The invention according to claim 2 relates to the load control device according to claim 1, further comprising a pulse width modulation wave generation circuit that generates a pulse width modulation wave signal based on the triangular wave signal, and the pulse width modulation wave. It is characterized by controlling the load based on the signal.

  According to the present invention, it is possible to improve the safety of the load control device when a short circuit failure occurs in the capacitor. Further, when this load control device is mounted on an automobile, the automobile headlamp is used as a load, and the low beam is used for DRL, fail safe can be ensured. On the other hand, when a high beam is used for DRL, safety can be improved. Moreover, since it is not necessary to produce two types of printed circuit boards according to the type of vehicle using this load control device, the cost is reduced accordingly.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a load control device according to Embodiment 1 of the present invention. The load control device according to the first embodiment is schematically configured from a triangular wave generation circuit 1, a pulse width modulation (PWM) generation circuit 2, an OR gate 3, a drive circuit 4, and a load drive element 5. Has been. The triangular wave generation circuit 1 generates a triangular wave signal having a predetermined frequency and a predetermined shape by switching charging / discharging of an external frequency setting capacitor C1.

  The PWM generation circuit 2 generates a PWM signal (“H” level or “L” level) based on the triangular wave signal supplied from the triangular wave generation circuit 1. The OR gate 3 performs a logical sum of a control signal (“H” level or “L” level) supplied from the outside and a PWM signal (“H” level or “L” level) supplied from the PWM generation circuit 2. The taken logical value (“H” level or “L” level) is supplied to the drive circuit 4. The drive circuit 4 amplifies the logical value supplied from the OR gate 3 and inverts it to apply a drive voltage to the load drive element 5. The load drive element 5 supplies a load current to the load 6 when a drive voltage is applied from the drive circuit 4.

  FIG. 2 is a circuit diagram specifically realizing the block diagram of the load control device shown in FIG. In FIG. 2, a portion surrounded by a one-dot chain line constitutes a load control device. In the load control device, the transistors Q1 to Q9, the resistors R1 to R11, the comparators CP1 and CP2, the OR gate 3, the drive circuit 4, and the constant voltage power supply 21 are configured by an IC. That is, the capacitor C1 and the N-channel type MOSFET 22 that is the load driving element 5 are external components of the IC.

The load control device of this example is a device (low-side switching device) in which an N-channel type MOSFET 22 that is the load driving element 5 is provided on the downstream side of the lamp 11 that is the load 6. Moreover, the load control apparatus of this example is mounted in, for example, an automobile, and FIG. 2 shows, for example, a lamp 11 used for a headlamp as the load 6 shown in FIG. The lamp 11 is connected between the power supply terminal Tb and the output terminal To of the load control device. In FIG. 2, a battery 12 mounted on an automobile is used as a power source, and a battery voltage V _bat is connected between a power supply terminal Tb and a ground terminal Tg of the load control device.

  Further, in FIG. 2, a control signal (“H” level or “L” level) (fixed input) output from an on-vehicle electronic control unit (ECU: Electronic Control Unit) 13 mounted on the vehicle is supplied to the load control device. Is done. The ECU controls the engine by determining the fuel injection amount and ignition timing of the automobile engine, and controls the automatic transmission, the traction control, and the like.

  In FIG. 2, PNP transistors Q1 to Q3, PNP transistors Q4 to Q9, resistors R1 to R8, a comparator CP1, and a capacitor C1 constitute the triangular wave generating circuit 1 shown in FIG. Transistors Q1-Q3 constitute a current mirror circuit. The emitter areas of the transistors Q1 to Q3 are all equal. Accordingly, the collector currents I1 to I3 flowing through the collectors of the transistors Q1 to Q3 are all equal. That is, the expression (1) is satisfied.

I1 = I2 = I3 (1)
Here, the collector current I1, a constant voltage Vc, with the base-emitter voltage _{V BE1} and the resistor R1 of transistor Q1, represented by the formula (2).
I1 = (Vc−V _BE1 ) / R1 (2)
The collector currents I1 to I3 are constant currents that serve as a reference for charging and discharging the capacitor C1. The collector current I3 is a current for discharging the charge accumulated in the capacitor C1 or a current for charging the capacitor C1.

  Transistors Q4 to Q6 form a current mirror circuit. The resistor R2 is provided to compensate for the base current of the transistor Q4. The ratio of the emitter area of transistor Q4 to the combined emitter area of transistors Q5 and Q6 is 1: 2. Further, the collector current flowing through the collector of the transistor Q4 is equal to the collector current I2 of the transistor Q2. Furthermore, from the equation (1), the collector current I2 of the transistor Q2 is equal to the collector current I1 of the transistor Q1.

Therefore, the collector current I5 flowing through the collector of the transistor Q5 is twice the collector currents I1 to I3 of the transistors Q1 to Q3. That is, the expression (3) is satisfied.
I5 = 2 × I1 = 2 × I2 = 2 × I3 (3)
The collector current I5 becomes a current for charging the capacitor C1 with a charge or a current for discharging the charge accumulated in the capacitor C1.

  The transistor Q7 is provided to stop the supply of the collector current I5 when turned on. The transistor Q8 and the resistors R3 to R5 generate a reference voltage Vt1 for generating the triangular wave signal. The resistor R6 is a base resistor connected to the base of the transistor Q8 and the output terminal of the comparator CP1.

  The transistor Q9 and the resistors R7 and R8 are circuits for turning on / off the transistor Q7 by the output signal of the comparator CP1. The triangular wave generation circuit 1 is configured such that the comparator CP1 includes a capacitor C1 based on a constant current obtained by a current mirror circuit composed of transistors Q1 to Q3, a current mirror circuit composed of transistors Q4 to Q6, and a resistor R1 connected to a constant voltage Vc. By comparing the voltage VC1 and the reference voltage Vt1, the charging / discharging of the capacitor C1 is switched to generate a triangular wave signal.

The comparator CP2 and the resistors R9 and R10 constitute the PWM generation circuit 2 shown in FIG. The resistors R9 and R10 generate a reference voltage Vk for generating the PWM signal. The reference voltage Vk is expressed by Expression (4).
Vk = Vc × R10 / (R9 + R10) (4)
The PWM generation circuit 2 generates a PWM signal by the comparator CP2 comparing the triangular wave signal supplied from the triangular wave generation circuit 1 with the reference voltage Vk.

The resistor R11 is inserted between the power supply Vc and the input terminal Ti, and has a function as a pull-up resistor that stably holds the potential of the control signal supplied from the ECU 13. The constant voltage power source 21 generates a constant voltage Vc from the battery voltage V _bat supplied from the battery 12 and supplies it to each part of the load control device. The MOSFET 22 has a gate connected to the output terminal of the drive circuit 4, a drain connected to the output terminal To of the load control device, and a source grounded.

  Next, the operation of the load control device configured as described above will be described. First, as a premise, the load control device having the above configuration includes an IC in which transistors Q1 to Q9, resistors R1 to R11, comparators CP1, CP2, OR gate 3, a drive circuit 4 and a constant voltage power supply 21 are formed on an internal chip. The capacitor C1 and the MOSFET 22 are mounted on one printed board.

  On this printed circuit board, for example, as shown in FIG. 3, patterns P1 to P3 for mounting a capacitor C1, which is an external component of the IC, are formed, and at the ends of the patterns P1 to P3, respectively. Lands L1 to L3 are respectively formed. The pattern P1 is connected to a power supply line connected to the output terminal of the constant voltage power supply 21 shown in FIG. The pattern P2 is connected to the non-inverting input terminal of the comparator CP1 shown in FIG. The pattern P3 is connected to the ground line shown in FIG.

(1) When the vehicle on which this load control device is mounted uses the low beam for DRL In this case, as shown in FIG. 3, one terminal of the capacitor C1 is formed at the end of the pattern P1. The other terminal of the capacitor C1 is inserted into a through hole drilled in the approximate center of the land L2 formed at the end of the pattern P2. Next, for example, by melting cream solder applied in advance on the lands L1 and L2, one terminal of the capacitor C1 and the land L1 are electrically connected, and the other terminal of the capacitor C1 is connected to the land L2. And electrically connect.

Next, the operation of the load control device configured as described above will be described with reference to the timing chart shown in FIG. First, as shown in FIG. 4D, when the control signal supplied from the ECU 13 is at “H” level, the output signal of the OR gate 3 is always at “H” level. Therefore, the drive circuit 4 amplifies the logic value of “H” level supplied from the OR gate 3 and inverts it to apply a drive voltage of “L” level to the MOSFET 22. While the “L” level drive voltage is applied from the drive circuit 4, the MOSFET 22 is off because the gate voltage is “L” level. In this case, since the source voltage of the MOSFET 22 is substantially equal to the battery voltage V _bat , no load current flows through the load 6 and, in this case, the lamp 11 as shown in FIG.

On the other hand, as shown in FIG. 4 (d), when the control signal supplied from the ECU 13 is at "L" level, the output signal of the comparator CP2 constituting the PWM generation circuit 2 becomes the output signal of the OR gate 3 as it is. .
When the voltage VC1 of the capacitor C1 is lower than the reference voltage Vt1 at a certain time, the output signal of the comparator CP1 becomes “L” level, and both the transistors Q8 and Q9 are turned off. In the state where the transistor Q8 is turned off, the reference voltage Vt1 becomes the upper limit voltage Vb of the triangular wave signal as shown in FIG. The upper limit voltage Vb is expressed by Expression (5).
Vb = Vc × R4 / (R3 + R4) (5)

  On the other hand, when the transistor Q9 is turned off, a current flows from the resistor R8 to the base of the transistor Q7, so that the transistor Q7 is turned on. When transistor Q7 is turned on, supply of collector current I5 is stopped. As a result, when the collector current I3 flows, the electric charge accumulated in the capacitor C1 is discharged, and the voltage across the terminals of the capacitor C1 decreases. Accordingly, the voltage VC1 of the capacitor C1 increases.

When the voltage VC1 of the capacitor C1 slightly exceeds the upper limit voltage Vb, the output signal of the comparator CP1 becomes “H” level, and both the transistors Q8 and Q9 are turned on. In a state where the transistor Q8 is turned on, the reference voltage Vt1 is divided by the resistance value of the combined resistance value of the resistors R4 and R5 and the resistance value of the resistor R3, ignoring the saturation voltage of the transistor Q8, as shown in FIG. Furthermore, the lower limit voltage Va of the triangular wave signal is obtained. The lower limit voltage Va is expressed by Equation (6).
Va = Vc × (R4 × R5) / (R3 × R4 + R3 × R5 + R4 × R5) (6)

  On the other hand, when the transistor Q9 is turned on, no current flows from the resistor R8 to the base of the transistor Q7, so that the transistor Q7 is turned off. When transistor Q7 is turned off, supply of collector current I5 is started. As described above, since the collector current I5 is twice the collector current I3, when the collector current I3 is subtracted from the collector current I5, the collector current I3 flows, and the capacitor C1 is charged. . When the capacitor C1 is charged, the voltage between the terminals of the capacitor C1 increases. Accordingly, the voltage VC1 of the capacitor C1 decreases. When the voltage VC1 of the capacitor C1 is slightly below the lower limit voltage Va, the output signal of the comparator CP1 is inverted to “L” level. By repeating the operation described above, a triangular wave signal shown in FIG. 4B is generated.

The period T of the triangular wave signal is expressed by Expression (7).
T = 2 × (Vb−Va) × C1 / I1
= [2 * Vc * {(R4 / (R3 + R4)-(R4 * R5) / (R3 * R4 + R3 * R5 + R4 * R5)} * C1] / {(Vc- _VBE1 ) / R1} (7)

  When the triangular wave signal supplied from the triangular wave generating circuit 1, that is, the voltage VC1 of the capacitor C1 exceeds the reference voltage Vk, the output signal of the comparator CP2 constituting the PWM generating circuit 2 becomes “L” level. On the other hand, when the voltage VC1 of the capacitor C1 falls below the reference voltage Vk, the output signal of the comparator CP2 becomes “H” level. By repeating the operation described above, the PWM signal shown in FIG. 4C is generated.

  The output signal of the comparator CP2, that is, the PWM signal is supplied to the drive circuit 4 through the OR gate 3. The drive circuit 4 amplifies the logical value of the PWM signal supplied from the OR gate 3 and inverts it to apply the drive voltage to the MOSFET 22. When the drive voltage from the drive circuit 4 is at “H” level, the MOSFET 22 is turned on because the gate voltage is at “H” level. Thereby, since the source voltage of the MOSFET 22 is substantially equal to the ground voltage, a load current flows through the load 6, in this case, the lamp 11, as shown in FIG.

On the other hand, when the drive voltage from the drive circuit 4 is “L” level, the MOSFET 22 is turned off. As a result, the source voltage of the MOSFET 22 increases until it becomes substantially equal to the battery voltage V _bat , so that no load current flows through the load 6 and, in this case, the lamp 11 as shown in FIG.
By repeating the operation described above, the lamp 11 is driven to blink in accordance with the supplied drive voltage.

  In such a normal operation state, for example, when the capacitor C1 causes a short circuit failure for some reason, the voltage VC1 of the capacitor C1 becomes the constant voltage Vc. As can be seen from the equation (4), the constant voltage Vc is larger than the reference voltage Vk, so the voltage VC1 of the capacitor C1 is larger than the reference voltage Vk. Therefore, the output signal of the comparator CP3, that is, the PWM signal is fixed to the “L” level.

  The PWM signal fixed to the “L” level is supplied to the drive circuit 4 via the OR gate 3. The drive circuit 4 amplifies the logical value of the PWM signal supplied from the OR gate 3 and inverts and continues to apply the “H” level drive voltage to the MOSFET 22. Since the drive voltage from the drive circuit 4 remains at the “H” level, the MOSFET 22 remains on and continues to pass a load current through the lamp 11. That is, the lamp 11 remains lit at a duty ratio of 100%.

  In this case, since the low beam is used for DRL, there is no particular problem even if the lamp 11 is lit, and the lit state of the lamp 11 is maintained, so that the passengers and pedestrians of the vehicle Since the safety of the oncoming vehicle and the like is ensured, it is preferable from the viewpoint of fail-safe.

(2) When the vehicle on which this load control device is mounted uses the above-mentioned high beam for DRL In this case, one terminal of the capacitor C1 is placed at the approximate center of the land L2 formed at the end of the pattern P2. In addition to being inserted into the drilled through hole, the other terminal of the capacitor C1 is inserted into a through hole drilled at substantially the center of the land L3 formed at the end of the pattern P3. Next, for example, by melting cream solder previously applied on the lands L2 and L3, one terminal of the capacitor C1 and the land L2 are electrically connected, and the other terminal of the capacitor C1 is connected to the land L3. And electrically connect.

Next, the operation of the load control device configured as described above will be described. First, when the control signal supplied from the ECU 13 is at “H” level, the output signal of the OR gate 3 is always at “H” level. Therefore, the drive circuit 4 amplifies the logic value of “H” level supplied from the OR gate 3 and inverts it to apply a drive voltage of “L” level to the MOSFET 22. While the “L” level driving voltage is applied from the driving circuit 4, the MOSFET 22 is off. In this case, since the source voltage of the MOSFET 22 is substantially equal to the battery voltage V _bat , no load current flows through the load 6, in this case, the lamp 11.

On the other hand, when the control signal supplied from the ECU 13 is at the “L” level, the output signal of the comparator CP2 constituting the PWM generation circuit 2 becomes the output signal of the OR gate 3 as it is.
When the voltage VC1 of the capacitor C1 is lower than the reference voltage Vt1 at a certain time, the output signal of the comparator CP1 becomes “L” level, and both the transistors Q8 and Q9 are turned off. In the state where the transistor Q8 is turned off, the reference voltage Vt1 becomes the upper limit voltage Vb of the triangular wave signal.

  On the other hand, when the transistor Q9 is turned off, a current flows from the resistor R8 to the base of the transistor Q7, so that the transistor Q7 is turned on. When transistor Q7 is turned on, supply of collector current I5 is stopped. As a result, when the collector current I3 flows, the capacitor C1 is charged, and the voltage between the terminals of the capacitor C1 increases. Accordingly, the voltage VC1 of the capacitor C1 increases.

  When the voltage VC1 of the capacitor C1 slightly exceeds the upper limit voltage Vb, the output signal of the comparator CP1 becomes “H” level, and both the transistors Q8 and Q9 are turned on. In a state where the transistor Q8 is turned on, the reference voltage Vt1 becomes the lower limit voltage Va of the triangular wave signal.

  On the other hand, when the transistor Q9 is turned on, no current flows from the resistor R8 to the base of the transistor Q7, so that the transistor Q7 is turned off. When transistor Q7 is turned off, supply of collector current I5 is started. As described above, the collector current I5 is twice the collector current I3. Therefore, when the collector current I3 is subtracted from the collector current I5, the collector current I3 flows, and the charge accumulated in the capacitor C1 is discharged. The

  When the electric charge accumulated in the capacitor C1 is discharged, the voltage between the terminals of the capacitor C1 decreases. Accordingly, the voltage VC1 of the capacitor C1 decreases. When the voltage VC1 of the capacitor C1 is slightly below the lower limit voltage Va, the output signal of the comparator CP1 is inverted to “L” level. By repeating the operations described above, a triangular wave signal is generated. The period T of the triangular wave signal is expressed by the above equation (7).

  When the triangular wave signal supplied from the triangular wave generating circuit 1, that is, the voltage VC1 of the capacitor C1 exceeds the reference voltage Vk, the output signal of the comparator CP2 constituting the PWM generating circuit 2 becomes “L” level. On the other hand, when the voltage VC1 of the capacitor C1 falls below the reference voltage Vk, the output signal of the comparator CP2 becomes “H” level. By repeating the operation described above, a PWM signal is generated.

  The output signal of the comparator CP2, that is, the PWM signal is supplied to the drive circuit 4 through the OR gate 3. The drive circuit 4 amplifies the logical value of the PWM signal supplied from the OR gate 3 and inverts it to apply the drive voltage to the MOSFET 22. When the drive voltage from the drive circuit 4 is at “H” level, the MOSFET 22 is turned on. As a result, the source voltage of the MOSFET 22 is substantially equal to the ground voltage, so that a load current flows through the lamp 11.

On the other hand, when the drive voltage from the drive circuit 4 is “L” level, the MOSFET 22 is turned off. As a result, the source voltage of the MOSFET 22 increases until it becomes substantially equal to the battery voltage V _bat , so that no load current flows through the lamp 11.
By repeating the operation described above, the lamp 11 is driven to blink in accordance with the supplied drive voltage.

  In such a normal operation state, for example, when the capacitor C1 causes a short circuit failure for some reason, the voltage VC1 of the capacitor C1 becomes 0V. Since the voltage VC1 of the capacitor C1 is 0V, it is smaller than the reference voltage Vk shown in the above equation (4). Therefore, the output signal of the comparator CP3, that is, the PWM signal is fixed to the “H” level.

  The PWM signal fixed to the “H” level is supplied to the drive circuit 4 via the OR gate 3. The drive circuit 4 amplifies the logical value of the PWM signal supplied from the OR gate 3 and inverts and continues to apply the “L” level drive voltage to the MOSFET 22. Since the drive voltage from the drive circuit 4 remains at the “L” level, the MOSFET 22 remains off and maintains a state in which no load current flows through the lamp 11. That is, the lamp 11 remains off.

  In this case, since the high beam is used for DRL, the lamp 11 remains off. Therefore, glare does not occur for the driver of the preceding vehicle or the oncoming vehicle, and a traffic accident can be prevented in advance.

  As described above, according to the first embodiment of the present invention, in the triangular wave generation circuit 1, the first insertion for inserting the frequency setting capacitor C1 between the constant voltage Vc and the non-inverting input terminal of the comparator CP1. In this state, a triangular wave signal having the same frequency and the same shape is generated in the second insertion state interposed between the ground and the non-inverting input terminal of the comparator CP1.

  Further, according to the first embodiment of the present invention, on the printed circuit board on which the load control device is mounted, for example, as shown in FIG. 3 according to the capacitor C1 and the first or second insertion mode. The patterns P1 to P3 for mounting the capacitor C1 are formed. When the vehicle on which this load control device is mounted uses the low beam for DRL, the two terminals of the capacitor C1 are electrically connected to the land L1 of the pattern P1 and the land L2 of the pattern P2. When the vehicle on which this load control device is mounted uses the high beam for DRL, the two terminals of the capacitor C1 are electrically connected to the land L2 of the pattern P2 and the land L3 of the pattern P3. Yes.

  Therefore, it is possible to improve the safety of the load control device when the capacitor C1 has a short fault. A vehicle using a low beam for DRL can ensure fail-safety, and a vehicle using a high beam for DRL can improve safety. Moreover, since it is not necessary to produce two types of printed circuit boards according to the type of vehicle using this load control device, the cost is reduced accordingly.

Embodiment 2. FIG.
In the first embodiment described above, the example in which the comparator CP2 has no hysteresis is shown. However, the present invention is not limited to this, and the comparator CP2 may have hysteresis. FIG. 5 is a circuit diagram showing an example of the configuration of the comparator CP2 and its peripheral circuits when the hysteresis circuit 31 is added to the comparator CP2.

  The hysteresis circuit 31 includes an inverter INV, a PNP transistor Q21, and resistors R21 and R22. The inverter INV inverts the output signal of the comparator CP2, that is, the PWM signal. The resistor R22 is a base resistor connected between the base of the transistor Q21 and the output terminal of the inverter INV. The PNP transistor Q21 is turned on by an “H” level output signal of the inverter INV supplied via the resistor R22, thereby changing the reference voltage Vk. Note that, in the configuration of the load control device, the configuration of the portion other than the comparator CP2 and its peripheral circuits can be applied with the configuration of FIG.

Next, operations of the comparator CP2 and its peripheral circuits in the load control device having the above configuration will be described with reference to a timing chart shown in FIG.
When the triangular wave signal supplied from the triangular wave generating circuit 1 is higher than the reference voltage Vk at a certain time, the output signal of the comparator CP2 constituting the PWM generating circuit 2 is at the “L” level. Thereby, the output signal of the inverter INV becomes “H” level, and the transistor Q21 is turned on.

In the state where the transistor Q21 is turned on, the reference voltage Vk becomes resistance division of the combined resistance value of the resistors R11 and R21 and the resistance value of the resistor R10 when the saturation voltage of the transistor Q21 is ignored, as shown in FIG. 6B. The second reference voltage Vk2 is obtained. The second reference voltage Vk2 is expressed by Expression (8).
Vk2 = Vc × {(R11 × R21) / (R11 + R21)} / {R10 + (R11 × R21) / (R11 + R21)} (8)

  Next, when the triangular wave signal falls below the second reference voltage Vk2, the output signal of the comparator CP2 becomes “H” level. As a result, the output signal of the inverter INV becomes “L” level, and the transistor Q21 is turned off. In the state where the transistor Q21 is turned off, the reference voltage Vk changes to the value represented by the above-described equation (4) as shown in FIG. That is, the comparator CP2 has hysteresis. By repeating the operation described above, as shown in FIG. 6C, a PWM signal having a wider width than that of each of the above-described embodiments is generated. As described above, according to the second embodiment of the present invention, since the comparator CP2 has hysteresis, it is possible to increase resistance to noise as compared with the above-described embodiments.

Embodiment 3 FIG.
In each of the above-described embodiments, an example is shown in which the present invention is applied to a device (low-side switching device) in which the N-channel MOSFET 22 that is the load driving element 5 is provided on the downstream side of the lamp 11 that is the load 6. However, it is not limited to this. For example, the present invention may be applied to a device (high-side switching device) in which the N-channel type MOSFET 22 that is the load driving element 5 is provided on the upstream side of the lamp 11 that is the load 6. In this case, a P-channel MOSFET may be used as the load driving element 5 instead of the N-channel MOSFET 22.

Embodiment 4 FIG.
In each of the above-described embodiments, the example in which the N-channel type MOSFET 22 or the P-channel type MOSFET is used as the load driving element 5 has been described. However, the present invention is not limited to this. As the load drive element 5, any switching element such as a bipolar transistor, a thyristor, an IGBT (Insulated Gate Bipolar Transistor), or an SIT (Static Induction Transistor) may be used.

As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and the design can be changed without departing from the scope of the present invention. Is included in the present invention.
Moreover, in each embodiment mentioned above, although the example which provides the constant voltage power supply 21 was shown, it is not limited to this, The constant voltage source 21 does not need to be provided. In this case, each emitter of the transistors Q1 to Q3 and one end of each of the resistors R3, R8, R9, and R11 are directly connected to the power supply terminal Tb. Further, the pattern P1 to which one terminal of the capacitor C1 is connected is also directly connected to the power supply terminal Tb.

  Moreover, although each embodiment mentioned above showed the example which forms the patterns P1-P3 shown in FIG. 3 on a printed circuit board, it is not limited to this. For example, you may comprise as shown below. That is, one terminal of the capacitor C1 is electrically connected to the land of the pattern connected to the non-inverting input terminal of the comparator CP1, and the pattern P2 shown in FIG. The other terminal of the capacitor C1 is electrically connected to one land that is not. And when the vehicle in which this load control apparatus is mounted uses the low beam for DRL, a jumper pin is electrically connected between the lands L1 and L2 shown in FIG. On the other hand, when an automobile equipped with this load control device uses a high beam for DRL, a jumper pin is electrically connected between lands L2 and L3 shown in FIG.

Moreover, although each embodiment mentioned above showed the example which mounts the load control apparatus which concerns on this invention in a vehicle, and the load 6 is the lamp | ramp 11 utilized for a headlamp, it is not limited to this. The present invention can be applied to a general apparatus for controlling a load based on a generated triangular wave signal, for example.
In addition, each of the above-described embodiments can divert each other's technology as long as there is no particular contradiction or problem in its purpose and configuration.

It is a block diagram which shows the structure of the load control apparatus which concerns on Embodiment 1 of this invention. FIG. 2 is a circuit diagram specifically realizing the configuration of the load control device shown in FIG. 1. It is a figure which shows an example of the structure of the patterns P1-P3 and lands L1-L3 formed on the printed circuit board in which the load control apparatus shown in FIG. 1 is mounted, and an example of the mounting state of the capacitor C1. 3 is a timing chart for explaining an example of the operation of the load control device shown in FIG. 1. It is a circuit diagram which shows an example of a structure of comparator CP2 of the load control apparatus which concerns on Embodiment 2 of this invention, and its peripheral circuit. 6 is a timing chart for explaining an example of operations of the comparator CP2 and its peripheral circuits shown in FIG.

Explanation of symbols

1 Triangular wave generation circuit 2 PWM generation circuit (pulse width modulation wave generation circuit)
3 OR gate 4 drive circuit 5 load drive element 6 load 11 lamp 12 battery 13 ECU
21 Constant voltage power supply 22 MOSFET
31 Hysteresis circuit C1 Capacitor CP1 Comparator (comparison means)
CP2 Comparator I1-I3, I5 Current INV Inverter Q1-Q9, Q21 Transistors R1-R11, R21, R22 Resistor Tb Power supply terminal Tg Ground terminal Ti Input terminal To Output terminal Va Lower limit voltage Vb Upper limit voltage _Vbat Battery voltage Vc Constant voltage VC1 Capacitor C1 voltage Vt1, Vk reference voltage Vk2 second reference voltage

Claims (2)

In the load control device that controls the load based on the generated triangular wave signal,
A first insertion state in which a capacitor for setting the frequency of the triangular wave signal is inserted between a power supply and an input end of the comparison means, and an insertion between the ground and the input end of the comparison means. A triangular wave generation circuit for generating the triangular wave signal having the same frequency in the second insertion state;
The load control device according to claim 1, wherein the capacitor is configured to be inserted in either the first insertion state or the second insertion state.   The load control device according to claim 1, further comprising a pulse width modulation wave generation circuit that generates a pulse width modulation wave signal based on the triangular wave signal, wherein the load is controlled based on the pulse width modulation wave signal. .

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