JP5625650B2 - Vehicle load control device - Google Patents

Description

  The present invention relates to a vehicle load control device that controls a load by turning on and off a switching element.

  The vehicle load control device performs energization control on the vehicle load or drive control of the vehicle load by switching a semiconductor switching element such as a power MOSFET using a PWM signal having a predetermined frequency as a control signal. Since the power supply current and the load current include a harmonic component of the switching frequency, there is a problem that this harmonic noise is mixed into an AM radio for vehicles. In order to solve such problems, many products use noise filter parts such as coils and capacitors (see, for example, Patent Documents 1 and 2).

  For example, according to the technical idea described in Patent Document 1, driving is performed by switching a semiconductor element with a PWM signal at a single switching frequency. In general, when a semiconductor element is driven at a single switching frequency, a harmonic component that is an integral multiple of the driving frequency is generated. The intensity of the harmonic component attenuates as the order increases, but does not decrease monotonously, but the intensity increases or decreases in a certain period, and the frequency period depends on the output duty ratio. Therefore, the peak frequency of the harmonic component changes in accordance with the output duty ratio within a predetermined frequency band (for example, AM band).

Japanese Patent Laid-Open No. 09-42096 Japanese Patent Application Laid-Open No. 2005-269936

  However, for example, even if the filter constant is optimized so that the attenuation value increases at the peak frequency of the harmonic component, the optimum filter constant changes when the duty ratio changes, and the noise level cannot be reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the generation of vehicle noise generated in a frequency band that other vehicle equipment receives as an interference signal even if the duty ratio changes. An object of the present invention is to provide a vehicle load control device that can control a load and suppress the influence on other vehicle equipment as much as possible.

According to the first aspect of the present invention, since the control means controls the vehicle load using the vehicle noise suppression frequency set corresponding to the duty ratio as the control frequency, even if the duty ratio changes, the control means The vehicle load can be controlled while suppressing the generation of vehicle noise that occurs in a frequency band in which the device can receive as an interference signal, and the influence on other vehicle devices can be suppressed as much as possible. At this time, the control means may set the vehicle noise suppression frequency to the control frequency in accordance with the approximate expression (1).

  According to the second aspect of the present invention, the frequency control means is configured so that the attenuation value of the filter circuit has an attenuation value greater than or equal to a predetermined value at a vehicle noise generation frequency predetermined corresponding to the duty ratio and the predetermined frequency. Since the frequency characteristics of the filter circuit are controlled by controlling the terminal voltage of the capacitor, even if the duty ratio changes, while suppressing the occurrence of vehicle noise that occurs in the frequency band where other vehicle equipment receives interference signals The vehicle load can be controlled, and the influence on other vehicle equipment can be suppressed as much as possible. Therefore, the vehicle load can be controlled using the vehicle noise suppression frequency as a control frequency, and the generation of vehicle noise can be suppressed by the action of the filter circuit at the vehicle noise generation frequency.

According to the invention described in claim 3 , the storage means stores the noise table associated with the duty ratio and frequency including the relationship between the duty ratio and the vehicle noise suppression frequency, and the control means stores the noise table of the storage means. In order to search for a frequency at which vehicle noise is minimized according to the duty ratio and to use the search frequency as the vehicle noise suppression frequency, the manufacturer associates the duty ratio with which the control means controls the vehicle load with the frequency. By simply storing the noise level in the noise table, the frequency control means refers to the noise table of the storage means and searches for the frequency at which the vehicle noise is minimized according to the duty ratio, and uses the search frequency as the vehicle noise suppression frequency. Therefore, the vehicle load can be controlled using the vehicle noise suppression frequency as a control frequency.

1 is an electrical configuration diagram schematically showing a first embodiment of the present invention. Diagram showing voltage waveform of main part at switching (A) is a simulation circuit configuration diagram, (b) is a table showing the worst noise level of the AM band harmonic component in the relationship between the duty ratio and the control frequency. Flow chart schematically showing control frequency setting procedure FIG. 1 equivalent view showing a second embodiment of the present invention Diagram showing waveform examples of harmonic components in the frequency domain Characteristic diagram showing an example of filter attenuation characteristics Capacitor equivalent circuit diagram Capacitor impedance vs. frequency characteristics FIG. 1 equivalent view showing a third embodiment of the present invention FIG. 5 equivalent view showing the fourth embodiment of the present invention

(First embodiment)
Hereinafter, a first embodiment in which a vehicle load control device according to the present invention is applied to an in-vehicle motor control device for a fuel pump will be described with reference to FIGS. 1 to 4. FIG. 1 shows an example of an electric circuit configuration diagram of an in-vehicle motor control device.

  As shown in FIG. 1, the in-vehicle motor control device 1 is supplied with power from a battery 2. This motor control device 1 is configured by connecting power MOSFETs 3 and 4 as switching elements, capacitors C1 to C3, coils L1 and L2, and a control circuit (control IC: equivalent to control means) 7, and is mounted on a vehicle as a load. The drive of the motor 8 is controlled. The on-vehicle motor 8 is a rotational drive motor of a fuel pump. The control circuit 7 drives and controls the in-vehicle motor 8 in response to a command from a command control circuit (for example, a vehicle ECU) E. The command control circuit E outputs a target output voltage control signal to the control circuit 7 in accordance with the target rotational speed of the in-vehicle motor 8.

  Between the power supply nodes N1 and N2 of the battery 2, a P-channel power MOSFET 3 and an N-channel power MOSFET 4 are connected in series. A capacitor C1 is connected between power supply terminal nodes N1 and N2. The power supply nodes N1 and N2 of the battery 2 are each formed with a coil L2 for removing high frequency, and are interposed between the battery 2, the power MOSFETs 3 and 4, and the control circuit 7. The power MOSFET 4 functions as a freewheeling diode.

  A capacitor C2 is connected to the power MOSFETs 3 and 4 in parallel. In the present embodiment, these capacitors C2 are connected in series between the node N4 and the node N1 through the coil L2 from the power supply node N2. The capacitors C1 and C2 and the coil L2 constitute a saddle type filter circuit 9 for removing power source noise of the vehicle. The filter circuit 9 smoothes ripples in the power supply line connected to the battery 2 and performs noise removal processing.

  A coil L1 and a motor 8 are connected between the common connection node N3 of the power MOSFETs 3 and 4 and the power supply terminal node N2. A capacitor C3 is connected between the common connection node N5 of the coil L1 and the motor 8 and the node N1. The filter circuit 10 mainly includes a capacitor C3 and a coil L1. The filter circuit 10 performs ripple smoothing and noise removal processing in an in-vehicle motor drive signal supply line connected to the motor 8. Capacitors C1 to C3 are each composed of a ceramic capacitor having a large capacity of about several tens of μF (for example, 10 μF). The control circuit 7 is mainly composed of a logic circuit and an analog circuit, for example, and includes a memory 7a (corresponding to storage means).

  FIG. 2 shows an input-output waveform during the switching operation of the power MOSFET. FIG. 3 shows harmonic components that appear when driving the power MOSFET. As shown in FIG. 2, when the control circuit 7 applies a drive voltage Va to the control terminal (gate) of the power MOSFET 3 at a predetermined duty ratio and turns it on and off so that the power MOSFET 4 is circulated, the action of the coil L1 and the capacitor C3 The drive voltage Vb from which the high frequency component is removed is applied to the on-vehicle motor 8.

  The present embodiment is characterized in that the vehicle-mounted motor 8 that is a vehicle load is drive-controlled using a vehicle noise suppression frequency predetermined corresponding to the duty ratio as a control frequency, and this operation will be described below. .

  FIG. 3A shows an LC series filter circuit, and FIG. 3B shows a noise table associated with a duty ratio and a drive frequency when the LC series filter circuit is applied.

  Hereinafter, simulation results performed by the inventors will be shown. For example, the inductance value of the coil L3 is 7.5 [μH], and the capacitance value of the capacitor C4 is 10 [μF]. Although the coil L3 ideally has an internal resistance of 0Ω but actually has a parasitic resistance component (ESR), the value of the series internal resistance is assumed to be 6.5 [mΩ]. Similarly, the capacitor C4 has a series internal resistance value of 2 [mΩ], which is a parasitic resistance component (ESR). The capacitor C4 also has a parasitic inductance component due to its chip length and the like. For this reason, the parasitic inductance component (ESL) of the capacitor C4 is set to 5 [nH]. Since these parasitic resistance component (ESR) and inductance component (ESL) cannot be controlled, they have constant values.

  FIG. 3B shows an output when a rectangular wave pulse voltage Vin having an amplitude of 12 [V] (for example, Vp−p = 12 V (minimum voltage 0 V, maximum voltage 12 V)) is input to the circuit shown in FIG. The intensity peak level (worst noise level) of the harmonic component in the AM radio band of the voltage Vout is shown in Fig. 3B, where the switching frequency is changed in the range of 100 [kHz] to 200 [kHz]. The simulation result when the duty ratio is changed in the range of 10 [%] to 90 [%] is shown in dB unit with 1 [V] = 0 [dB].

  In FIG. 3 (b), the intensity level of the switching frequency at which the intensity level of the harmonic component becomes the minimum value (minimum value) at each duty ratio is shown in a bold frame, and this frequency is shown for each duty ratio. The optimum switching frequency is such that the vehicle noise intensity level is the minimum value. In this simulation example, since the frequency is selected discretely, it is estimated that the substantially optimum switching frequency is a minimum value and a frequency between the minimum value and the second value at each duty ratio. The

  Considering a duty ratio of 50 [%], driving at an optimum switching frequency of 200 [kHz] reduces the noise level by about 5 [dB] compared to driving at a switching frequency of 100 [kHz]. I understand that I can do it. It can be seen that even under other duty ratio conditions, the noise level can be reduced by several [dB] in a practical driving frequency range between 100 [kHz] and 200 [kHz].

  Therefore, in the circuit configuration shown in FIG. 1, the AM band noise peak level corresponding to the relationship between the duty ratio (for example, 0% to 100%) and the drive control frequency (for example, 100 kHz to 200 kHz) assumed to be actually used is measured. The optimum drive control frequency that minimizes the measured noise peak level is stored in advance in the memory 7a in the control circuit 7 in association with the duty ratio.

  That is, as shown in FIG. 3B, when an optimum frequency corresponding to the duty ratio of the PWM signal is measured, the drive control frequencies 100 [kHz] to 111 [corresponding to the duty ratio 10 [%]. kHz] corresponding to a frequency (for example, 105 [kHz]) and a duty ratio of 20 [%] to 30 [%] and 80 [%], a drive control frequency of 167 [kHz] and a duty ratio of 40 [%] to 70 The drive control frequency is 200 [kHz] corresponding to [%], and the drive control frequency is 100 [kHz] corresponding to the duty ratio of 90 [%].

Then, the control circuit 7 can select a frequency (vehicle noise suppression frequency) that can suppress vehicle noise in accordance with the duty ratio, and the selected vehicle noise suppression frequency is set as a drive control frequency (corresponding to a control frequency). The on-vehicle motor 8 can be driven and controlled by applying an on / off control signal corresponding to the drive control frequency to the gates (control terminals) of the power MOSFETs 3 and 4. In this case, since a predetermined vehicle noise suppression frequency can be set as the drive control frequency, generation of vehicle noise can be suppressed. Further, the peak level of the noise may be stored and held in the memory 7a in the control circuit 7 as a noise table T.

Further, the control circuit 7 may set the vehicle noise suppression frequency by the following approximate expression (relational expression) (1) or (2a) (2b). For example, when the drive frequency (corresponding to the control frequency) is 100 [kHz] to 200 [kHz], when the vehicle noise suppression frequency f [kHz] and the output duty ratio are D [%],
f = - (D-50) 2/25 + 200 ... (1)
It is possible to apply the relationship of the quadratic approximation formula.

f = 2 × D + 100 (0 <D <50) (2a)
f = 2 × D + 300 (50 <D <100) (2b)
The relationship of the first-order approximation equation can be applied. The vehicle noise suppression frequency may be set by applying an approximate expression that associates these relationships. Note that the approximate expression is not limited to the first-order approximation and the second-order approximation.

  FIG. 4 shows a drive control frequency setting flowchart. The control circuit 7 receives the target output voltage control signal from the command control circuit E at the previous stage (S1). When the control circuit 7 reads the voltage of the battery 2 (S2), the control circuit 7 calculates the duty ratio by dividing the target output voltage by the battery voltage and multiplying by 100 (S3). And the control circuit 7 selects the vehicle noise suppression frequency used as the minimum noise level (S4). In this case, as described above, the vehicle noise suppression frequency corresponding to the duty ratio may be selected with reference to the noise table T, or the vehicle noise suppression frequency may be selected from the approximate expression (1) or (2a) (2b). May be set.

  Then, the control circuit 7 sets the vehicle noise suppression frequency as the drive control frequency (S5), and drives and controls the vehicle-mounted motor 8 (S6). Then, the vehicle noise suppression frequency can be set to the drive control frequency, and the generation of vehicle noise can be suppressed.

  As described above, according to the present embodiment, the control circuit 7 sets the vehicle noise suppression frequency corresponding to the duty ratio to the drive control frequency and controls the drive of the in-vehicle motor 8, so even if the duty ratio changes. Since the vehicle noise suppression frequency corresponding to the duty ratio can be set as the drive control frequency, the generation of vehicle noise can be suppressed.

  The control circuit 7 refers to the noise table T, retrieves the frequency (vehicle noise suppression frequency) at which the vehicle noise becomes the minimum noise level from the set duty ratio column, and sets the vehicle noise suppression frequency as the drive control frequency. Since the vehicle motor 8 is driven and controlled, the vehicle noise suppression frequency can be set to the drive control frequency, and the generation of vehicle noise can be suppressed.

  In this case, the manufacturer simply stores the noise level in the noise table T by associating the duty ratio and frequency with which the control circuit 7 controls the in-vehicle motor 8, and the control circuit 7 stores the noise table T in the memory 7 a. Since the frequency at which vehicle noise is minimized is searched according to the duty ratio and the search frequency is set as the vehicle noise suppression frequency, the vehicle-mounted motor 8 can be controlled using the vehicle noise suppression frequency as a control frequency.

  Further, since the control circuit 7 applies the relationship of the approximate expression (1) or (2a) (2b) and sets the frequency at which the vehicle noise is minimized according to the duty ratio, the vehicle noise suppression frequency is set. The in-vehicle motor 8 can be controlled using the frequency as a control frequency. Thereby, the influence given to other equipment for vehicles can be controlled as much as possible.

(Second Embodiment)
FIGS. 5 to 9 show a second embodiment of the present invention. The difference from the above-described embodiment is that a filter is applied at a vehicle noise generation frequency predetermined corresponding to a duty ratio of the PWM signal and a predetermined frequency. The frequency characteristic of the attenuation value of the filter circuit is controlled by controlling the terminal voltage of the capacitor so that the attenuation value of the circuit has an attenuation value not less than a predetermined value. The same parts as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts are described below.

  FIG. 5 shows a circuit configuration in place of FIG. As shown in FIG. 5, a series circuit of capacitors C1 and C5 is configured in FIG. 5 instead of the capacitor C1 in FIG. Further, instead of the capacitor C2 in FIG. 1, a series circuit of capacitors C2 and C6 is configured in FIG. Further, in FIG. 5, a series circuit of capacitors C3 and C7 is configured instead of the capacitor C3 of FIG. Capacitors C1 to C3 and C5 to C7 are configured by ceramic capacitors having a direct current (DC) bias dependency whose capacitance value changes according to the terminal voltage (several tens of volts: for example, 10 to 30 V). The capacitance values of these capacitors C1 to C3 and C5 to C7 decrease when the terminal voltage is increased. The filter circuit 9 includes a saddle type low-pass filter including capacitors C1, C2, C5, and C6 and a coil L2. The filter circuit 10 includes an LC low-pass filter including capacitors C3 and C7 and a coil L1.

  Control signal lines 11, 12, and 13 are connected between the filter circuits 9 and 10 and the control circuit 7, and the filter circuit 9 is adjusted by adjusting the terminal voltages of the capacitors C1 to C3 and C5 to C7. The frequency characteristics of 10 attenuation values can be adjusted.

  The control signal line 11 is connected between the common connection node N6 of the capacitors C1 and C5 and the control circuit 7, and the control signal line 12 is connected between the common connection node N7 of the capacitors C2 and C6 and the control circuit 7. The control signal line 13 is connected between the common connection node N8 of the capacitors C3 and C7 and the control circuit 7, and the control circuit 7 applies a predetermined DC voltage V1 to the control signal lines 11 to 13. The characteristics are changed according to the application of V3.

  When given a command, the control circuit 7 applies a PWM signal having a duty ratio and frequency corresponding to the command to the gates (control terminals) of the MOS transistors 3 and 4 to control the rotational drive of the vehicle-mounted motor 8. In the embodiment, the control circuit 7 adjusts the capacitance values of the capacitors C1 to C6 by applying predetermined DC voltages V1 to V3 to the nodes N6 to N8 through the control signal lines 11 to 13, respectively. In this way, the in-vehicle motor control device 14 that replaces the in-vehicle motor control device 1 is configured.

  FIG. 6 shows an example of higher-order harmonic component signals with respect to the fundamental period when a rectangular wave drive control signal of a predetermined frequency (100 [kHz]) is applied to the gates (control terminals) of the power MOSFETs 3 and 4. ing. FIG. 6A shows harmonic components in the AM band (510 [kHz] to 1710 [kHz]) in the case of a duty ratio of 50% in the frequency domain, and FIG. 6B shows a case of a duty ratio of 10 [%]. The harmonic component in the AM band is shown in the frequency domain. As shown in FIGS. 6 (a) and 6 (b), the harmonic component has an integer-order harmonic component of the rectangular wave signal, and monotonically decreases or monotonically increases with respect to these orders. However, the harmonic intensity peak increases or decreases every period of a predetermined frequency.

The period of this peak frequency is
Tf = (drive control frequency [kHz] × 100) / (duty ratio [%]) (3)
It has been confirmed that there is a relationship. The drive control frequency indicates the switching frequency of the power MOSFETs 3 and 4. That is, for example, as shown in FIG. 6A and FIG. 6B, when the drive control frequency (switching frequency) is 100 [kHz] and the duty ratio is 50 [%], the noise peak component has a cycle of 200 [kHz]. When the drive control frequency is 100 [kHz] and the duty ratio is 10 [%], a noise peak component appears at a cycle of 1 [MHz]. Therefore, it has been confirmed that the peak frequency of the AM band harmonic component changes according to the duty ratio. In this case, it has been confirmed that when the duty ratio is 50 [%], the noise level of the harmonic component peaks when it is about 700 [kHz] and when it is 10 [%] and about 600 [kHz].

  In order to suppress radio noise in the AM band, the circuit configuration and the capacitors C1 to C3 and C5 that configure the circuit are set so that the frequency at which the harmonic noise is large and the frequency at which the attenuation value is maximum are as close as possible or match. It is preferable to adjust the attenuation frequency characteristics of the filter circuits 9 and 10 by adjusting the capacitance value of .about.C7 and the inductance values of the coils L1 and L2.

  Further, for example, a vehicle noise generation frequency at which noise with the highest harmonic noise occurs in the AM band (in the above example, for example, when the duty ratio is 50 [%], about 700 [kHz], and when the duty ratio is 10 [%]. At about 600 [kHz]), the control circuit (frequency control means) 7 sets the attenuation frequency characteristics of the filter circuits 9 and 10 so that the attenuation values of the filter circuits 9 and 10 have a predetermined attenuation value or more. Control. Then, the generation of vehicle noise can be suppressed at the vehicle noise generation frequency. Thereby, even if other vehicle equipment is mounted in the vehicle, the influence given to the other vehicle equipment can be suppressed as much as possible.

  In the following, a method for controlling the frequency at which the attenuation value of the filter circuits 9 and 10 is maximized so as to efficiently suppress the harmonic component in each duty ratio with the drive control frequency (switching frequency) fixed is implemented. This will be described as feature points of the form.

  In order to simplify the explanation, the configuration of the basic LC series circuit shown in FIG. As shown in FIG. 3A, a capacitor C4 is connected between the terminals of the output voltage Vout. FIG. 7 shows the attenuation characteristics when the inductance value of the coil L3 and the capacitance value of the capacitor C4 described in the above embodiment are taken into consideration. FIG. 8 shows an equivalent circuit of the capacitor. Capacitor C4 can be represented by an equivalent circuit of an LCR series resonance circuit including an internal resistance r0, a parasitic inductance component L0, and a capacitor C40 having predetermined values, particularly in a frequency band that generates AM band high-frequency noise.

  FIG. 9 shows the impedance characteristics of the capacitor in this AM frequency band. As shown in FIG. 9, when the frequency is lower than the self-resonant frequency f0 = 1 / 2Π√ ((inductance value of L0) × (capacitance value of C40)), the impedance of the capacitor C4 indicates the characteristic of the capacitor C40. When having a main impedance characteristic and the frequency is higher than the self-resonant frequency f0 = 1 / 2Π√ ((inductance value of L0) × (capacitance value of C40)), the impedance of the capacitor C4 is a parasitic inductance component L0. It has impedance characteristics mainly consisting of the following characteristics. When the terminal voltage of the capacitor C4 is changed, the resonance frequency of the impedance characteristic of the capacitor C4 can be shifted, and the attenuation frequency characteristics of the filter circuits 9 and 10 can be controlled. In this case, the frequency at which the attenuation value becomes the maximum value (the filter gain is the minimum value) matches the frequency at which the impedance of the capacitor C4 becomes the minimum value.

  In order to control the impedance characteristics of the capacitor, the voltage applied by the control circuit 7 to each of the nodes N6 to N8 is changed in the circuit configuration shown in FIG. Thereby, the attenuation frequency characteristics of the filter circuits 9 and 10 can be controlled by controlling the capacitance values of the capacitors C1 to C3 and C5 to C7 constituting the filter circuits 9 and 10.

  Such a frequency characteristic control method can be applied when the filter constant of the LC series circuit is changed by changing the capacitance values of the capacitors C5 and C6 connected to the load output node N5. The present invention can also be applied to changing the filter constant of the saddle type filter connected to N1 or N2.

  As described above, according to the present embodiment, the control circuit 7 reduces the attenuation value of the filter circuits 9 and 10 to a predetermined value or more at a predetermined vehicle noise generation frequency corresponding to the duty ratio and the predetermined frequency. In order to control the frequency characteristics of the filter circuits 9 and 10 by controlling the DC voltage applied to the terminals of the capacitors C1 to C3 and C5 to C7 so as to have a value, the generation of vehicle noise occurring in the AM frequency band is prevented. The on-vehicle motor 8 can be controlled while being suppressed. Thereby, the influence given to other equipment for vehicles can be controlled as much as possible.

(Third embodiment)
FIG. 10 shows a third embodiment of the present invention. The difference from the previous embodiment is that the configuration of the first embodiment is changed to a switching power supply circuit such as a DC-DC converter in the vehicle load control device of the present invention. Is applied to the vehicle load power supply control device. Constituent parts that are the same as or similar to those of the above-described embodiment are assigned the same reference numerals, and descriptions thereof are omitted.

  FIG. 10 shows a circuit configuration example of a step-down chopper type DC-DC converter. As shown in FIG. 10, a vehicle noise suppression filter circuit 22 is configured on the DC power supply 21 side, and a vehicle noise suppression filter circuit 23 is also configured on the load 27 side. Each of the vehicle noise filter circuits 22 and 23 employs a circuit formed of a bowl-shaped low-pass filter. The N-channel MOS transistor 24 is connected in series at the subsequent stage of the filter circuit 22, the diode D1 is connected in parallel at the subsequent stage, and the filter circuit 25 is configured at the subsequent stage. A DC converter 26 is configured, and a load 27 is connected to the subsequent stage.

  The control IC 23 (control means, frequency control means) is configured to apply a PWM signal having a duty ratio corresponding to the output DC target voltage to the gate (control terminal) of the MOS transistor 24, and the DC-DC converter 26 is configured to apply the PWM signal. An output voltage Vout corresponding to the duty ratio of the signal is output.

  This type of DC-DC converter 26 generally employs an electrolytic capacitor as a capacitor constituting the filter circuit 22 on the DC power supply 21 side and the filter circuit 25 on the load 26 side. In this embodiment, instead of these, a large capacity is used. The ceramic capacitors C8 to C10 are used.

  In this case, as shown in the first embodiment, the control frequency of the PWM signal applied to the gate of the MOS transistor 24 is set to a vehicle noise suppression frequency that is predetermined according to the duty ratio. Then, the generation of vehicle noise when the MOS transistor 24 performs a switching operation according to the PWM signal can be suppressed.

According to this embodiment, since it is applied to the vehicle load power supply control device using the DC-DC converter 20, the same effects as those of the above-described embodiment can be obtained.
Although the present embodiment is applied to the step-down chopper type DC-DC converter 20, it may be applied to a step-up chopper type DC-DC converter.

(Fourth embodiment)
FIG. 11 shows a fourth embodiment of the present invention. The difference from the previous embodiment is that the configuration of the second embodiment is changed to a switching power supply circuit such as a DC-DC converter for the vehicle load control device of the present invention. Is applied to the vehicle load power supply control device. Constituent parts that are the same as or similar to those of the above-described embodiment are assigned the same reference numerals, and descriptions thereof are omitted.

  In this embodiment, a series circuit of capacitors C8 and C11 shown in FIG. 11 is applied instead of the capacitor C8 of FIG. 10, and a series circuit of capacitors C9 and C12 shown in FIG. 11 is applied instead of the capacitor C9 of FIG. Instead of the capacitor C10 of FIG. 10, a series circuit of capacitors C10 and C13 shown in FIG. 11 is applied.

  As shown in the second embodiment, by applying a DC voltage from the control IC 23 to the terminals of the ceramic capacitors C8 to C13, the impedance frequency characteristics of the ceramic capacitors C8 to C13 are changed, and the attenuation of the filter circuits 22 and 25, respectively. Change the frequency characteristics. Therefore, as shown in FIG. 11, ceramic capacitors (C8, C11), (C9, C12), (C10, C13) are applied in series, and the DC bias dependency is utilized as in the previous embodiment. The occurrence of vehicle noise can be suppressed by adjusting the frequency characteristics of the impedance.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and other modifications or expansions are possible.
In the first and second embodiments, the embodiment applied when the PWM signal is applied to the P-channel power MOSFET 3 and the N-channel power MOSFET 4 has been described. However, the bipolar junction transistor (BJT), the insulated gate bipolar transistor (IGBT) The present invention can also be applied when a control signal is applied to other semiconductor switching elements such as

Although the embodiment in which the inductive load by the in-vehicle motor 8 is applied as the vehicle load has been described, the present invention can be applied to various vehicle loads (for example, a resistance load such as a heater, a lamp, and a speaker).
In the above-described embodiment, an embodiment to which a simplified circuit configuration is applied is shown to explain the main part of the present invention. However, in order to adjust various characteristics of the filter circuits 9, 10, 22, 25, a ceramic capacitor is used. Capacitors whose capacitance values are appropriately adjusted for C1 to C3 and C5 to C13 may be connected in parallel. Further, if necessary, an electrolytic capacitor may be connected in parallel to the ceramic capacitors C1 to C3 and C5 to C13. That is, the circuit combination form of the capacitors is not limited to the configuration described in the above embodiment.

  In the embodiment, the embodiment has been described in which the generation of noise in the AM band (510 [kHz] to 1710 [kHz]) is suppressed and the noise is removed. However, the frequency of the smart key band for vehicles (frequency band less than 180 [kHz]) is shown. The present invention can be applied to a configuration for suppressing noise generation and removing noise.

  For example, the circuit configuration of FIG. 5 described in the second embodiment may be applied, and the power MOSFETs 3 and 4 may be driven using the vehicle noise suppression frequency as a control frequency as shown in the first embodiment. For example, the power MOSFETs 3 and 4 are driven using the vehicle noise suppression frequency shown in the first embodiment as a control frequency, and the filter circuits 9 and 10 shown in the second embodiment perform filtering at the vehicle noise generation frequency. May be.

  The inductance component according to the present embodiment may be configured in consideration of a parasitic component (about 1 [nH]) when the capacitors C1 to C6 are configured by a chip, or a wiring pattern ( For example, 1 [cm] and about 10 [nH]) may be used, or a combination of these may be used.

  In the drawings, 1 and 14 are on-vehicle motor control devices (vehicle load control devices), 2 is a battery, 3 and 4 are power MOSFETs (switching elements), 7 is a control circuit (control means, frequency control means), and 7a is a memory. (Storage means), 8 is an in-vehicle motor (load), 9 and 10 are filter circuits, 23 is a control IC (control means, frequency control means), and 24 is a MOS transistor (switching element).

Claims (3)

A control means for controlling the vehicle load by applying a PWM signal as a control signal to the switching element;
The control means is shall control the vehicle load by applying a control signal to the switching element of the vehicle noise suppression frequency which is set corresponding to the duty ratio of the PWM signal as the control frequency, said vehicle When the noise suppression frequency is f [kHz], the duty ratio is D [%], and the control frequency is in the range of 100 [kHz] to 200 [kHz]
f = - (D-50) 2/25 + 200 ... (1)
The vehicle load control device, wherein the vehicle noise suppression frequency is set to the control frequency in accordance with the approximate expression of the expression (1) . A filter circuit configured by combining an inductance component and a capacitor, the capacitor having a DC bias dependency in which a capacitance value changes in accordance with a terminal voltage of the capacitor, and an attenuation frequency characteristic changing in accordance with the DC bias dependency; ,
The filter is controlled by controlling a terminal voltage of the capacitor so that an attenuation value of the filter circuit has an attenuation value greater than or equal to a predetermined value at a predetermined vehicle noise generation frequency corresponding to the duty ratio and the predetermined frequency. 2. The vehicle load control device according to claim 1, further comprising frequency control means for controlling an attenuation frequency characteristic of the circuit. Storage means for storing a noise table associated with the duty ratio and the frequency including the relationship between the duty ratio and the vehicle noise suppression frequency;
The control means refers to a noise table of the storage means, searches for a frequency at which vehicle noise is minimized according to the duty ratio, and uses the search frequency as the vehicle noise suppression frequency. 3. The vehicle load control device according to 2.

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