JP2005080336A - Switching power supply for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the insufficiency or stop of a power supply to a load due to the unintentional operation of an overload protecting function caused by a drop of an input voltage in a switching power supply for a vehicle having the overload protecting function. <P>SOLUTION: The switching power supply for the vehicle lowers a voltage Vlon from an on time limiting voltage circuit CUR2 when an input voltage Vin drops, and lengthens a pulse width of an on time limiting pulse P2 as a result. Meanwhile, when an output from a comparator CMP3 for detecting out of range due to a drop of an output voltage Vout, an RS-FF16 is normally reset so that an SW transistor T1 is forcibly turned off, but when the drop of the output voltage Vout is caused by the drop of the input voltage Vin, before the output from the comparator CMP3 for detecting the out of range becomes a High level, the drop of the input voltage Vin is detected, and the transistor T2 is turned off. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching power supply device for a vehicle that is mounted on a vehicle and that supplies an input from an external power source to various loads in the vehicle by controlling the input to a constant voltage.

  In recent years, power consumption of various in-vehicle electronic devices such as in-vehicle computers and drive devices controlled by the in-vehicle computers has been increasing. Therefore, as a power supply device for these on-vehicle electronic devices, the use of a switching power supply device with high conversion efficiency has become the mainstream in order to reduce the size and to suppress the heat generation of the device. Many switching power supply devices generally have an overload protection function for preventing an excessive current from flowing to the load side due to an overload.

  As one of such overload protection functions, a duty limiting function is known in which the switching duty ratio of the switching element is limited so as not to exceed a certain value so that an excessive current does not flow through the load.

  There is also known an output cutoff function that detects an output current, performs constant current control so as to decrease the output current when the current exceeds a predetermined current value, and further shuts down the output when an overcurrent occurs (for example, Patent Document 1). reference.).

  This output cutoff function is disclosed in Patent Document 1 as operating based on the output current of the switching power supply device, but there are also those operating based on the output voltage. That is, when the output voltage is lowered and constant voltage control cannot be performed for a certain period of time, a load abnormality such as an overload is considered, and the power supply to the load is cut off.

When a switching power supply device having an overload protection function having the above-described configuration is mounted on an automobile and used, it is common to regulate an input voltage from an in-vehicle battery / alternator. Specifically, the input voltage (for example, 12V to 14V) to the switching power supply device is regulated to a desired voltage such as a power supply voltage for an in-vehicle computer (for example, 5V) or a power supply voltage for an in-vehicle drive device (for example, 8V). doing.
JP 2001-103741 A

  However, since the on-board battery also supplies power to the starter motor of the automobile, the battery voltage is lower than normal at the time of engine start (for example, from normal 12V to 9V or less), and thus the switching power supply device In some cases, the output voltage also decreases, and a desired power supply voltage cannot be supplied to the load side.

  In this case, as an operation of the switching power supply device, in order to maintain the output voltage at a normal value, an attempt is made to compensate for a decrease in the input voltage (battery voltage) by increasing the switching duty ratio. However, in the switching power supply device having the above-described duty limiting function, the duty ratio is limited. Therefore, the duty ratio necessary for obtaining a desired output voltage is the upper limit value of the duty ratio (hereinafter referred to as “duty”). If it is larger than the “upper limit value”, a desired voltage cannot be output and the operation of the load may stop.

  In addition, even in a switching power supply device having the above-described output cutoff function that operates based on the output voltage, if the constant voltage control cannot be performed due to the decrease in the output voltage due to the decrease in the input voltage, Although the current is not a current, the output cutoff function operates to interrupt the power supply to the load, and the load operation may stop.

  That is, the duty ratio is limited and the desired output voltage cannot be obtained due to the operation of various overload protection functions as described above in spite of not being in an overload state, or the power output itself is cut off. In other words, the operation of the load stops.

  The present invention has been made in view of the above problems, and in a vehicle switching power supply device having an overload protection function, an overload protection function operates unintentionally due to a decrease in input voltage. It aims at suppressing that power supply is insufficient or stops.

  The switching power supply device for a vehicle according to claim 1, which has been made to solve the above-described problem, has a power supply path from an in-vehicle power supply to a power supply target by smoothing the switching element and an output voltage from the switching element to generate power. The output smoothing means for supplying to the supply target is provided in series, and the control means outputs a control signal to turn on the switching element so that the voltage from the output smoothing means becomes a predetermined set voltage. -It is configured to duty-control off.

  Further, in the present invention (Claim 1), the duty ratio at the time of duty control by the control means is restricted so as not to exceed a predetermined upper limit value, and the upper limit value is inputted to the vehicle switching power supply device. A duty limiter configured to increase with a decrease in power supply voltage (hereinafter referred to as “input voltage”) from a vehicle-mounted power supply.

  According to the switching power supply device for a vehicle having the above configuration, when the input voltage decreases, the control unit performs control so as to obtain a desired set voltage by increasing the duty ratio. At this time, as the input voltage decreases, The upper limit value of the duty ratio is also increased. Therefore, as long as the input voltage does not drop to such an extent that the desired set voltage cannot be obtained even if the duty ratio is 100%, the desired set voltage is supplied to the power supply without actually being limited by the duty ratio by the duty limiter. It becomes possible to supply to.

Here, the “duty ratio” means a so-called on-duty that indicates a ratio of the on-period of the switching element in one cycle of the duty cycle.
According to a second aspect of the present invention, there is provided a switching power supply for a vehicle, wherein a switching element and output smoothing means are provided in series on a power supply path from an in-vehicle power supply to a power supply target, and switching is performed by a control signal from the control means The duty control of the element is the same as in the vehicle switching power supply device according to claim 1.

  In the vehicular switching power supply device of the present invention (Claim 2), the output cut-off means is for the vehicular when the output voltage from the output smoothing means becomes smaller than a predetermined control lower limit voltage lower than the set voltage. The power supply from the switching power supply to the power supply target is cut off, but is cut off when the input voltage becomes lower than a predetermined input lower limit voltage that can supply an output voltage at least equal to or lower than the control lower limit voltage from the output smoothing means. The stopping means stops the blocking operation by the output blocking means.

  According to the vehicular switching power supply device having the above configuration, when the input voltage decreases, the shutoff operation is stopped by the shutoff stopping unit before the output voltage from the output smoothing unit becomes smaller than the limit lower limit voltage. Therefore, it is possible to prevent the power supply to the power supply target from being unintentionally interrupted due to the decrease in the input voltage.

  Next, a vehicle switching power supply device according to a third aspect of the present invention comprises the above-described means constituting the vehicle switching power supply device according to the first aspect and the respective means constituting the vehicle switching power supply device according to the second aspect. We have both.

  That is, the switching element and the output smoothing means are provided in series on the power supply path from the in-vehicle power source to the power supply target, and further includes a control means for duty-controlling on / off of the switching element. The duty limiting means, the output cutoff means, and the cutoff stop means.

  Therefore, according to the switching power supply for a vehicle according to the third aspect, the duty ratio is limited by the duty limiting means as long as the input voltage does not decrease to such an extent that a desired set voltage cannot be obtained even if the duty ratio is 100%. It is possible to supply a desired set voltage to the power supply target without receiving the power, and to prevent the power supply to the power supply target from being unintentionally interrupted by the cutoff stop means.

  More specifically, the switching power supply for a vehicle according to claim 3 configured as described above may be configured as described in claim 4, for example. That is, the duty limiting means includes a limiting pulse output means for outputting a pulse signal whose duty ratio is the above upper limit value, and the control means is switched from the control means to the switching element only when the pulse signal from the limiting pulse output means is on. Control signal output permitting means for permitting the output of the control signal, and when the output voltage from the output smoothing means becomes smaller than the control lower limit voltage, the output shutoff means controls the output reduction signal indicating that Output to signal output permission means. The control signal output permission means forcibly turns off the switching element by not allowing the control means to output the control signal from the control means to the switching element when the output reduction signal is input. When the power supply voltage from the output signal becomes smaller than the input lower limit voltage, the output reduction signal from the output cutoff means to the control signal output permission means is invalidated.

  According to the vehicle switching power supply device having the above-described configuration, the control signal output permission unit is configured to supply power based on the duty ratio limitation based on the pulse signal from the limiting pulse output unit and the output reduction signal from the output cutoff unit. The power supply to the vehicle is cut off together, and the cut-off stopping means can stop the cut-off operation only by invalidating the output reduction signal. The cost of the entire apparatus can be reduced.

  And the switching power supply device for vehicles of this invention (Claims 1-4) is a vehicle-mounted battery which supplies the power supply to the engine starting device which the said vehicle-mounted power supply starts an engine like Claim 5 for example. In some cases, a sufficient duty ratio can be ensured even when the input voltage is reduced when the engine is started, or the power supply is not cut off even if the output voltage is reduced due to the input voltage drop, which is particularly effective. .

Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram illustrating a schematic configuration of an in-vehicle electronic control device 1 according to the present embodiment. As shown in the figure, in the on-vehicle electronic control device 1, the switching power supply circuit 13 generates a constant voltage based on the input voltage Vin from the on-vehicle battery 11 and supplies the constant voltage to the drive circuit 12 as a load. The drive circuit 12 is operated to drive various actuators (not shown).

  The supply voltage from the in-vehicle battery 11 is normally 12 V, and is supplied to various in-vehicle electronic devices (not shown) including the switching power supply circuit 13. Although not shown, the on-vehicle battery 11 is charged by a generator (alternator) driven by the engine during engine operation. Therefore, the voltage (for example, around 14V) from the alternator is mainly the input voltage Vin to the switching power supply circuit 13 during engine operation, and the voltage (12V) of the vehicle-mounted battery 11 is the input voltage Vin when the engine is stopped.

  The starter motor 15 as an engine starter of the present invention is a known motor for rotating the engine when the engine (not shown) is started. The starter motor 15 is rotationally driven by turning on the ignition switch 14 to start the engine.

  The drive circuit 12 is configured to drive various actuators (not shown) and the like according to a control signal from the computer circuit 17 and operates by receiving the output voltage Vout from the switching power supply circuit 13.

  The computer circuit 17 is a core part of the in-vehicle electronic control device 1 and operates by receiving power supply from a power supply circuit having a configuration similar to that of the switching power supply circuit 13 although not shown in the figure. Is output. Specifically, for example, based on map data or vehicle position information provided from the outside, information on the vehicle traveling position and a traveling route to a predetermined destination is provided, or the operation state (speed) of each part of the vehicle Various control processes performed in the vehicle, such as controlling the fuel injection fee based on the engine speed, temperature, etc., can be considered. Then, the drive circuit 12 actually drives the control target (not shown) of each control process by the computer circuit 17.

  A switching power supply circuit 13 which is a switching power supply device for a vehicle according to the present invention converts an input voltage Vin from an in-vehicle battery 11 or an alternator (not shown) into a stable constant voltage (for example, 8 V) necessary for the drive circuit 12 and outputs an output voltage. It is output as Vout. This constant voltage (8V) corresponds to the set voltage of the present invention. The computer circuit 17 is also supplied with a constant voltage (for example, 5 V) from a switching power supply circuit (not shown) as described above. Hereinafter, the switching power supply circuit 13 will be described in detail.

  The switching power supply circuit 13 of the present embodiment feeds back a divided value (hereinafter referred to as “output feedback value”) Vod obtained by dividing the output voltage Vout by the two voltage dividing resistors R2 and R3, and serves as a switching transistor (switching element). The constant output voltage Vout is supplied by duty-controlling the switching operation of T1 (hereinafter referred to as “SW transistor”). The input voltage Vin switched by the SW transistor T1 is smoothed by an output smoothing circuit including an inductor L1, a smoothing capacitor C1, and a diode D1, and is supplied to the drive circuit 12 as an output voltage Vout of DC 8V.

  More specifically, the switching power supply circuit 13 of the present embodiment that operates as described above includes a triangular wave oscillator OSC and a reference voltage circuit CUR1 that generate various reference signals necessary for holding the output voltage Vout constant. The on-time limiting voltage circuit CUR2 for realizing the on-time limiting function for limiting the on-time of the SW transistor T1 as one of the overload protection functions, and the output voltage Vout as one of the overload protection functions And an out-of-control-range detection voltage circuit CUR3 for realizing an output cutoff function for forcibly turning off the SW transistor T1 to protect the load side when the voltage cannot be controlled to a constant voltage.

  The triangular wave oscillator OSC generates a reference triangular wave Vtri serving as a reference when determining the switching duty ratio of the SW transistor T1 (that is, PWM control of a pulse input to the base of the SW transistor T1).

  The reference voltage circuit CUR1 generates a reference voltage Vref that is a comparison target of the output feedback value Vod for maintaining the output voltage Vout at a constant voltage. The differential amplifier AMP amplifies the difference between the output feedback value Vod and the reference voltage Vref, and outputs an error signal corresponding to the difference between the two.

  The on-time limit voltage circuit CUR2 is a circuit that outputs an on-time limit voltage Vlon serving as a reference for determining the upper limit of the on-time of the SW transistor T1 in the on-time limit function. Here, the on-time limiting function and the above-described duty limiting function are synonymous, and the on-time in the on-time limiting function refers to a time during which the SW transistor T1 is turned on within one cycle of duty control of the SW transistor T1. The ON time is set not to be longer than a predetermined upper limit time (hereinafter referred to as “ON upper limit time”), and the duty ratio when the ON time is the ON upper limit time is the above-described duty upper limit value.

  In the present embodiment, the on-time limit voltage Vlon is not made constant, but is changed according to the input voltage Vin to the switching power supply circuit 13, thereby changing the on-up upper limit time according to the input voltage Vin (in other words, the duty upper limit value). Changes in accordance with the input voltage Vin). Specifically, as shown by a one-dot chain line in FIG. 6 (details will be described later), the on-time limit voltage Vlon is changed so that the duty upper limit value changes following the change of the input voltage Vin. As the Vin decreases, the on-time limit voltage Vlon also decreases.

  The out-of-control-range detection voltage circuit CUR3 is provided to realize an output cutoff function. That is, when the output voltage Vout of the switching power supply circuit 13 falls and falls outside the constant voltage controllable range, the RS flip-flop (hereinafter referred to as “RS-FF”) 16 is reset and the SW transistor T1 is forcibly turned off. The out-of-control-range detection voltage Vdet that serves as a reference for the output is output. In the present embodiment, the output from the out-of-range detection comparator CMP3 when the output voltage Vout falls below a predetermined protection execution output threshold voltage lower than the constant voltage 8V (for example, any value between 7.5V and less than 8V). The out-of-control-range detection voltage Vdet is set so that the output becomes a high level and the SW transistor T1 is turned off. This protection execution output threshold voltage corresponds to the control lower limit voltage of the present invention, and the high level output from the out-of-range detection comparator CMP3 corresponds to the output decrease signal of the present invention.

  The output control comparator CMP1 compares the reference triangular wave Vtri from the triangular wave oscillator OSC with the error signal from the differential amplifier AMP, and outputs an output when the reference triangular wave Vtri is larger than the error signal from the differential amplifier AMP (below). P1) (referred to as “control pulse”) goes high. This control pulse corresponds to the control signal of the present invention.

  The on-limit comparator CMP2 compares the reference triangular wave Vtri from the triangular wave oscillator OSC with the on-time limiting voltage Vlon from the on-time limiting voltage circuit CUR2, and outputs when the reference triangular wave Vtri is larger than the on-time limiting voltage Vlon. P2 (hereinafter referred to as “on-time limit pulse”) becomes the high level.

  The out-of-range detection comparator CMP3 compares the error signal from the differential amplifier AMP with the out-of-control detection voltage Vdet from the out-of-control detection voltage circuit CUR3, and the error signal from the differential amplifier AMP is out of the control range. When the voltage becomes lower than the detection voltage Vdet, the output becomes a high level. As described above, in this embodiment, when the output voltage Vout falls below the protection execution output threshold voltage, the error signal is smaller than the detection voltage Vdet outside the control range, the RS-FF 16 is reset, and the SW transistor T1 is turned off. It will be.

  An output from the out-of-range detection comparator CMP3 is input to a reset input terminal of the RS-FF 16 via a delay circuit including a resistor R4 and a capacitor C2. That is, the output of the out-of-range detection comparator CMP3 is transmitted to the RS-FF 16 after a predetermined time (delay time by the delay circuit). Therefore, when the output of the out-of-range detection comparator CMP3 becomes High level due to the decrease in the output voltage Vout, it is input to the reset input terminal of the RS-FF 16 via the delay circuit.

  The protection operation prohibition voltage circuit CUR4 is a predetermined protection operation prohibition that serves as a reference for prohibiting the operation of the output cutoff function so that the RS-FF 16 is not reset regardless of the output state from the out-of-range detection comparator CMP3. The voltage Vstp is output.

  This protection operation prohibiting voltage Vstp is compared with a divided value (hereinafter referred to as “input divided value”) Vid obtained by dividing the input voltage Vin by the two voltage dividing resistors R6 and R7 by the protection prohibiting comparator CMP4. The When the input divided voltage value Vid falls below the protection operation prohibiting voltage Vstp, the output of the protection prohibiting comparator CMP4 becomes high level. In the present embodiment, the protection operation prohibition voltage Vstp is set so that the protection prohibition comparator CMP4 is at a high level when the input voltage Vin falls below a predetermined protection prohibition input threshold voltage (for example, 10V). This protection prohibiting input threshold voltage corresponds to the input lower limit voltage of the present invention.

  As described above, the protection prohibiting comparator CMP4 compares the input voltage dividing value Vid and the protection operation prohibiting voltage Vstp, and its output terminal is connected to the base of the transistor T2 via the base resistor R5. . When the input voltage Vin is equal to or higher than the protection prohibiting input threshold voltage (10 V), the output of the protection prohibiting comparator CMP4 is at a low level, and the transistor T2 is turned off. Therefore, in this case, the output from the out-of-range detection comparator CMP3 is directly input to the RS-FF 16 via the delay circuit.

  On the other hand, when the input voltage Vin falls below 10V, the output of the protection prohibiting comparator CMP4 becomes high level, the transistor T2 is turned on, and the reset input terminal of the RS-FF 16 becomes the ground potential. Therefore, in this case, regardless of the output state of the out-of-range detection comparator CMP3, the reset input terminal of the RS-FF is held at the low level, and the set state (high level) of the output Q of the RS-FF 16 is held. .

  The RS-FF 16 is a well-known reset / set type flip-flop. In this embodiment, the set input terminal is set to the high level when the switching power supply circuit 13 is activated, and thereafter, the output Q is output unless the reset input terminal is set to the high level. Is held in the set state (High level). Note that input to the reset input terminal is prohibited for a certain period after the switching power supply circuit 13 is activated until the output voltage Vout becomes stable.

  The gate circuit G1 is a circuit that takes the logical product of the outputs of the output control comparator CMP1, the on-limit comparator CMP2, and the RS-FF 16, and this logical product is a duty signal for switching the SW transistor T1. It is output as Pg (hereinafter referred to as “gate output pulse”).

  The driver circuit G2 is a circuit for driving the SW transistor T1 in accordance with the gate output pulse Pg from the gate circuit G1, and amplifies the gate output pulse Pg to a level that can drive the SW transistor T1, A signal (hereinafter referred to as “switching pulse”) Ps is input to the base of the SW transistor T1 via the base resistor R1. The SW transistor T1 is driven (switched) in accordance with the switching pulse Ps.

  Regarding the operation of the on-vehicle electronic control device 1 configured as described above, particularly the operation of the switching power supply circuit 13 will be described. FIG. 2 shows the switching power supply circuit 13 when the input voltage Vin is constant and the output voltage Vout does not fall below the protection execution output threshold voltage (that is, the RS-FF holds the set state). It is a time chart showing voltage control. In the following description, “pulse width” means the width (time) of the high level state.

  As shown in FIG. 2, the gate output pulse Pg from the gate circuit G1 is high when the control pulse P1 from the output control comparator CMP1 and the on-time limit pulse P2 from the on-limit comparator CMP2 are both at the high level. Become a level. Then, the SW transistor T1 is switched corresponding to the gate output pulse Pg. That is, the duty ratio of the gate output pulse Pg basically becomes the duty ratio of the switching pulse Ps from the driver circuit G2, and thus the switching duty ratio of the SW transistor T1.

  First, the output voltage Vout is stable between times t1 and t4, and the pulse width of the control pulse P1 has a sufficient margin with respect to the pulse width of the on-time limit pulse P2. However, after time t4, when the output voltage Vout decreases due to some factor such as overload and the output of the differential amplifier AMP decreases, the pulse width of the control pulse P1 widens, and accordingly the pulse width of the gate output pulse Pg also increases. As a result, the pulse width of the switching pulse Ps from the driver circuit G2 increases. That is, control is performed to increase the output voltage Vout by increasing the switching duty ratio of the SW transistor T1 (time t4 to t6).

  On the other hand, the pulse width of the gate output pulse Pg is limited by the on-time limiting function. That is, the time during which the gate output pulse Pg can be turned on (High level) is limited during the period when the on-time limiting pulse P2 is on. Therefore, when the output voltage Vout further decreases and the output level of the differential amplifier AMP becomes lower than the detection voltage Vdet outside the control range, the pulse width of the control pulse P1 increases according to the decrease in the output voltage Vout. The pulse width of the gate output pulse Pg does not exceed the pulse width of the on-time limit pulse P2.

  That is, the gate output pulse Pg is turned on during the on period of the control pulse P1 and the on period of the on time limit pulse P2 (time t6 to t8). The pulse width of the on-time limit pulse P2 is the above-described on-up upper limit time, and the duty ratio thereof is the above-described duty upper-limit value.

  When the output voltage Vout further decreases and falls below the protection execution output threshold voltage, the SW transistor T1 is forcibly turned off by the operation of the output cutoff function. This output cutoff function will be described with reference to FIG. FIG. 3 shows a time representing constant voltage control of the switching power supply circuit 13 when the input voltage Vin is constant and the output voltage Vout is lower than the protection execution output threshold voltage (that is, the RS-FF 16 is reset). It is a chart.

  When the output voltage Vout is equal to or higher than the protection execution output threshold voltage, the output level of the differential amplifier AMP is equal to or higher than the detection voltage Vdet outside the control range. Therefore, during this period, as shown in FIG. 3, the output of the out-of-range detection comparator CMP3 is at the low level, the reset input terminal of the RS-FF 16 is held at the low level, and the output Q is in the set state (high level). Retained. Therefore, the gate output pulse Pg corresponding to the control pulse P1 is output from the gate circuit G1. However, it is restricted by the on-time restriction function.

  On the other hand, when the output voltage Vout continues to decrease and the output of the differential amplifier AMP falls below the out-of-control detection voltage Vdet (time t11), the output of the out-of-range detection comparator CMP3 goes high. As a result, the capacitor C2 constituting the delay circuit is charged and its charging voltage (that is, the voltage applied to the reset input terminal of the RS-FF 16) gradually rises. When the reset threshold voltage is exceeded, the RS-FF 16 The gate output pulse Pg is turned off (low level) and the power output from the switching power supply circuit 13 is stopped (time t12). The time between t11 and t12 until the RS-FF 16 is reset after the out-of-range detection comparator CMP3 becomes high level is the delay time by the delay circuit.

  As described above, the pulse width of the gate output pulse Pg is limited by the on-time limiting function, and further, the pulse width of the switching pulse Ps is limited. Therefore, even if the output voltage Vout decreases due to overload or the like, Is prevented from flowing. Further, the output cutoff function forcibly turns off the SW transistor T1 when the output voltage Vout falls below the protection execution output threshold voltage.

  However, the cause of the decrease in the output voltage Vout is not necessarily an output-side abnormality such as an overload, and the output voltage Vout also decreases due to a temporary voltage drop in the in-vehicle battery 11 when the starter motor 15 is driven. Therefore, in the present embodiment, when the input voltage Vin decreases, the on-time limiting function is relaxed and the output cutoff function is stopped, thereby increasing the duty ratio of the switching pulse Ps to compensate for the decrease in the input voltage Vin. ing. Hereinafter, this will be described with reference to FIGS.

  First, the relationship between the input voltage Vin and the output voltage Vout in the switching power supply circuit 13 is shown in FIG. As shown in the figure, when the input voltage Vin is switched by the SW transistor T1, the output from the SW transistor T1 (input to the output smoothing circuit) becomes a pulsed voltage waveform. This pulse voltage is smoothed by the output smoothing circuit and output as an almost constant output voltage Vout. This output voltage Vout is generally expressed by the following equation.

Vout = Vin * (Ton-α) / Tsw
Here, Ton is the pulse width of the switching pulse Ps, α is the pulse width corresponding to the switching loss, and Tsw is the switching period. That is, in the case of an ideal switching power supply with a conversion efficiency of 100%, α is 0, and the ratio Vout / Vin between the output voltage and the input voltage becomes the switching duty ratio Ton / Tsw as it is. However, there is actually a loss, and in order to obtain the same output voltage Vout, the switching pulse width Ton is equivalently increased by the pulse width α corresponding to the loss.

  The pulse width Tlon of the on-time limit pulse P2 is set to a time longer than the switching pulse width Ton that allows for the pulse width α corresponding to the loss. In other words, the duty ratio (duty upper limit value) of the on-time limit pulse P2 is set larger than the duty ratio of the switching pulse Ps (hereinafter also referred to as “switching duty ratio”).

  This duty upper limit value is conventionally a constant value (for example, 80%), so that the switching duty ratio exceeds 80% even if the output voltage Vout decreases and the duty ratio of the control pulse P1 increases. There were no restrictions. However, in the present embodiment, the duty upper limit value is changed according to the input voltage Vin, thereby realizing the relaxation of the on-time limiting function when the input voltage Vin decreases.

  Specifically, as indicated by the alternate long and short dash line in FIG. 5, the duty upper limit value is increased as the input voltage Vin decreases. FIG. 5 is an explanatory diagram showing changes in the duty upper limit value and the theoretical switching duty ratio with respect to the input voltage Vin when the conversion efficiency is 90% and the output voltage Vout of 8V is generated.

  As shown in FIG. 5, in order to keep the output voltage Vout constant at 8V, the switching duty ratio is approximately 60% when the input voltage Vin is 15V, for example, and the switching duty ratio is approximately when the input voltage Vin is 13V, for example. When the input voltage Vin is 70 V, for example, 70%, the switching duty ratio needs to be about 90%. In this case, if the upper limit of the duty is fixed at 80%, for example, if the input voltage Vin is about 11V or less, the desired constant voltage of 8V can be obtained even if the SW transistor T1 is switched at the duty ratio of 80% of the upper limit. You will not be able to get.

  For this reason, the duty upper limit value is changed according to the change of the input voltage Vin. Specifically, for example, the input voltage Vin is set to be about 70% when the input voltage Vin is 15V, about 80% when the input voltage Vin is 13V, and about 100% when the input voltage Vin is 11V or less. By doing so, even if the input voltage Vin drops to about 10V, for example, a stable output voltage Vout of 8V can be obtained.

  The change in the duty upper limit value is actually realized by changing the on-time limit voltage Vlon from the on-time limit voltage circuit CUR2. That is, as shown in FIG. 1, the input voltage Vin is input to the on-time limit voltage circuit CUR2, and as a result, the duty upper limit value (that is, from the on-limit comparator CMP2) is changed according to the change of the input voltage Vin. The on-time limit voltage Vlon is changed so that the duty ratio of the on-time limit pulse P2 changes as shown in FIG.

  When the upper limit of the duty becomes 100% due to the decrease of the input voltage Vin and the duty limit is substantially eliminated, and further decreases, and the output voltage Vout falls below the protection execution output threshold voltage, the differential amplifier AMP The output falls below the out-of-control detection voltage Vdet. At this time, if the function for stopping the operation of the output cutoff function is not provided, the output cutoff function operates. That is, the output of the out-of-range detection comparator CMP3 becomes a high level, the RS-FF 16 is reset, and the output of the switching pulse Ps stops. After that, even if the input voltage Vin returns to the normal value (12 V), the reset state of the RS-FF 16 continues, so that the switching power supply circuit 13 needs to be restarted in order to output the constant voltage Vout again. .

  However, this embodiment has a function of stopping the operation of the output cutoff function when the input voltage Vin decreases. Specifically, when the input voltage Vin falls below a voltage just before the desired output voltage Vout cannot be obtained even when the switching duty ratio is 100%, the output of the protection prohibiting comparator CMP4 becomes high level. . As a result, the transistor T2 is turned on, the reset input terminal of the RS-FF 16 is held at a low level, and the operation of the output cutoff function is stopped.

  In this embodiment, as shown in FIG. 6, when the input voltage Vin is equal to or higher than the protection prohibited input threshold voltage (10V), the output cutoff function is activated when the output voltage Vout falls below the protection execution output threshold voltage. The output of the switching pulse Ps is stopped. That is, the output from the out-of-range detection comparator CMP3 is made invalid and is not reflected on the reset terminal of the RS-FF 16.

  On the other hand, since the operation of the output cutoff function is stopped when the input voltage Vin falls below 10V, even if the output voltage Vout falls below the protection execution output threshold voltage at this time, the output cutoff function does not operate. Therefore, if the desired constant voltage 8V cannot be obtained even if the switching duty ratio is set to 100% due to the decrease of the input voltage Vin, the output voltage Vout drops together with the input voltage Vin as shown in the figure, and the input voltage Vin is normal again. When the value returns, the output voltage Vout is also normally 8V constant. This eliminates the need for restarting the switching power supply circuit 13.

  The drive circuit 12 according to the present embodiment is configured to operate with an 8V power supply at a rated value, but to a certain extent even if it is lower than 8V (for example, up to about 5-6V). Therefore, even if the input voltage Vin decreases and the constant voltage 8V cannot be obtained, the drive circuit 12 operates with the maximum output voltage Vout that can be generated by the input voltage Vin at that time without operating the output cutoff function. Can continue.

  According to the switching power supply circuit 13 of the present embodiment described in detail above, when the voltage of the in-vehicle battery 11 decreases and the input voltage Vin decreases when the vehicle engine starts, the duty upper limit value also increases (that is, the on-time limit pulse P2). Therefore, it becomes possible to increase the switching duty ratio to compensate for the decrease in the input voltage Vin and to maintain a predetermined constant voltage of 8V.

  Even if the input voltage Vin further decreases and the constant voltage control cannot be performed, the operation of the load is controlled by the maximum output voltage Vout that can be generated by the input voltage Vin at that time by stopping the operation of the output cutoff function. Can continue.

  This makes it possible to provide the switching power supply circuit 13 that can supply a lower power supply voltage to the load, and the load can be operated even when the output voltage Vout decreases due to a decrease in the input voltage Vin.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. In this embodiment, the output smoothing circuit corresponds to the output smoothing means of the present invention, and includes two voltage dividing resistors R2, R3, a differential amplifier AMP, a reference voltage circuit CUR1, a triangular wave oscillator OSC, and an output control circuit. The comparator CMP1 constitutes the control means of the present invention, and the out-of-range detection voltage circuit CUR3 and the out-of-range detection comparator CMP3 constitute the output cutoff means of the present invention, and the voltage dividing resistors R6, R7. The protection operation prohibiting voltage circuit CUR4, the protection prohibiting comparator CMP4, the base resistor R5, and the transistor T2 constitute a cutoff stop means of the present invention. The triangular wave oscillator OSC, the on-time limiting voltage circuit CUR2, The on-limit comparator CMP2 constitutes the limiting pulse output means of the present invention. The gate circuit G1 corresponds to the control signal output permission means of the present invention.

The embodiment of the present invention is not limited to the above-described embodiment, and it goes without saying that various forms can be adopted as long as it belongs to the technical scope of the present invention.
For example, in the above embodiment, the power supply cutoff by the output cutoff function is performed by forcibly turning off the SW transistor T1. However, the present invention is not limited to this. For example, on the power supply path to the drive circuit 12 You may make it interrupt by providing a switch and turning this off.

  In the above embodiment, the drive circuit 12 in the in-vehicle electronic control device 1 is taken as an example of the power supply target from the switching power supply circuit 13, but this is only an example, and the operation is performed by receiving a predetermined constant voltage power supply. Any vehicle-mounted electronic device that can be used can be a power supply target.

It is a block diagram which shows schematic structure of the vehicle-mounted electronic control apparatus of embodiment. It is a time chart showing the constant voltage control of the switching power supply circuit when the input voltage Vin is constant and the RS-FF holds the set state. It is a time chart showing the constant voltage control of the switching power supply circuit when the input voltage Vin is constant and the RS-FF is reset due to the output voltage drop. It is explanatory drawing which shows the relationship between the input voltage Vin and the output voltage Vout in a switching power supply circuit. It is explanatory drawing which shows the change of the duty upper limit with respect to the input voltage Vin and a theoretical switching duty ratio. It is explanatory drawing showing the presence or absence of the output interruption | blocking function with respect to the input voltage Vin and the output voltage Vout.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vehicle-mounted electronic control apparatus, 11 ... Vehicle-mounted battery, 12 ... Drive circuit, 13 ... Switching power supply circuit, 14 ... Ignition switch, 15 ... Starter motor, 16 ... RS-FF, 17 ... Computer circuit, AMP ... Differential amplifier, C1 ... smoothing capacitor, C2 ... capacitor, CMP1 ... output control comparator, CMP2 ... on limit comparator, CMP3 ... out-of-range detection comparator, CMP4 ... protection prohibition comparator, CUR1 ... reference voltage circuit, CUR2 ... ON-time limiting voltage circuit, CUR3 ... out-of-control detection voltage circuit, CUR4 ... protection operation prohibition voltage circuit, D1 ... diode, G1 ... gate circuit, G2 ... driver circuit, L1 ... inductor, OSC ... triangular wave oscillator, R1, R5 ... Base resistance, R2, R3, R6, R7 ... Voltage dividing resistor, T1 ... SW transistor, T2 ... Transition Data

Claims (5)

A switching element that is provided in series in a power supply path from an in-vehicle power source to a power supply target, and is turned on / off according to a control signal;
Output smoothing means provided between the switching element and the power supply target in the power supply path, and smoothing the output voltage of the switching element and supplying the output voltage to the power supply target;
Control means for outputting the control signal for duty-controlling on / off of the switching element so that the voltage smoothed by the output smoothing means becomes a predetermined set voltage;
Duty limiting means for limiting the duty ratio in the duty control by the control means so as not to exceed a predetermined upper limit;
A vehicle switching power supply device comprising:
The duty switching means is configured to increase the upper limit value as the power supply voltage from the in-vehicle power supply input to the vehicle switching power supply decreases. . A switching element that is provided in series in a power supply path from an in-vehicle power source to a power supply target, and is turned on / off according to a control signal;
Output smoothing means provided between the switching element and the power supply target in the power supply path, and smoothing the output voltage of the switching element and supplying the output voltage to the power supply target;
Control means for outputting the control signal for duty-controlling on / off of the switching element so that the voltage smoothed by the output smoothing means becomes a predetermined set voltage;
An output shut-off means for shutting off the power supply from the vehicular switching power supply device to the power supply target when the output voltage from the output smoothing means becomes smaller than a predetermined control lower limit voltage lower than the set voltage;
A vehicle switching power supply device comprising:
When the power supply voltage from the in-vehicle power supply input to the vehicle switching power supply apparatus becomes smaller than a predetermined input lower limit voltage that can supply at least an output voltage equal to or higher than the control lower limit voltage from the output smoothing means, A vehicle switching power supply device comprising: a shut-off stopping unit that stops the shut-off operation by the output shut-off unit. A switching element that is provided in series in a power supply path from an in-vehicle power source to a power supply target, and is turned on / off according to a control signal;
Output smoothing means provided between the switching element and the power supply target in the power supply path, and smoothing the output voltage of the switching element and supplying the output voltage to the power supply target;
Control means for outputting the control signal for duty-controlling on / off of the switching element so that the voltage smoothed by the output smoothing means becomes a predetermined set voltage;
Duty limiting means for limiting the duty ratio in the duty control by the control means so as not to exceed a predetermined upper limit;
An output shut-off means for shutting off the power supply from the vehicular switching power supply device to the power supply target when the output voltage from the output smoothing means becomes smaller than a predetermined control lower limit voltage lower than the set voltage;
A vehicle switching power supply device comprising:
The duty limiting means is configured to increase the upper limit value as the power supply voltage from the in-vehicle power supply input to the vehicle switching power supply apparatus decreases.
Furthermore,
When the power supply voltage from the in-vehicle power supply input to the vehicle switching power supply apparatus becomes smaller than a predetermined input lower limit voltage that can supply at least an output voltage equal to or higher than the control lower limit voltage from the output smoothing means, A vehicle switching power supply device comprising: a shut-off stopping unit that stops the shut-off operation by the output shut-off unit. The duty limiting means includes a limiting pulse output means for outputting a pulse signal whose duty ratio is the upper limit value, and the control means to the switching element only during a period when the pulse signal from the limiting pulse output means is on. Control signal output permission means for permitting the output of the control signal of,
When the output voltage from the output smoothing means becomes smaller than the control lower limit voltage, the output cutoff means outputs an output reduction signal indicating that to the control signal output permission means,
The control signal output permission means is configured to forcibly turn off the switching element by preventing the control signal from being output from the control means to the switching element when the output reduction signal is input. ,
The cutoff stop means is configured to invalidate the output reduction signal from the output cutoff means to the control signal output permission means when a power supply voltage from the in-vehicle power source becomes smaller than the input lower limit voltage. The switching power supply device for vehicles according to claim 3 characterized by things. The switching power supply for a vehicle according to any one of claims 1 to 4, wherein the on-vehicle power supply is an on-vehicle battery that supplies power to an engine starter that starts an engine.

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