JP5199019B2 - Buck-boost DC-DC converter - Google Patents

Description

  The present invention relates to a step-up / step-down DC-DC converter that boosts or steps down an input DC voltage and converts the input DC voltage into a predetermined output voltage.

  2. Description of the Related Art Conventionally, as a power supply device for an electronic device or the like, a chopper type power supply device that can hold an output voltage within a certain range even when an input voltage fluctuates is used.

  As this type of power supply device, for example, a step-down chopper transistor and a step-up chopper transistor are connected via a common choke coil, and when the input voltage is higher than the output voltage, the step-up chopper transistor is turned off and the step-down chopper transistor is turned off. The step-down chopper transistor is turned on and off to step down the input voltage. When the input voltage is lower than the output voltage, the step-down chopper transistor is turned on and the step-up chopper transistor is turned on and off to step up the input voltage. Has been proposed (see Patent Document 1).

  According to this power supply device, the step-down chopper power supply device and the step-up chopper power supply device can be realized by the same circuit.

Japanese Patent Application Laid-Open No. 62-18970 (see pages 2 to 3, see FIG. 1)

  In the prior art, the step-down chopper transistor and the step-up chopper transistor are selectively operated according to the input voltage, so that the output voltage can be kept substantially constant even when the input voltage varies.

  However, when switching between step-down and step-up, the operation of the step-down chopper transistor and step-up chopper transistor are not switched smoothly, so the output voltage cannot be kept constant.

  That is, the transistors used for the step-down chopper transistor and the step-up chopper transistor have a delay time (switching time) at the time of turn-on and turn-off, so that the step-down chopper transistor is simply changed according to the input voltage when switching between step-down and step-up. Even if the step-up chopper transistor is selectively operated, the step-down chopper transistor may be kept on and the step-up chopper transistor may be kept off, and the output voltage cannot be kept constant.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a step-up / step-down DC-DC converter capable of maintaining an output voltage at a specified voltage under all input / output conditions. There is to do.

  In order to achieve the above object, a step-up / step-down DC-DC converter according to claim 1 includes a step-down switch for inputting a direct-current voltage from a direct-current power supply, and a choke coil connected to the step-down switch, which is lower than the input voltage. A step-down unit that outputs an output voltage; a step-up switch connected to the step-down switch via the choke coil; and a step-up unit that outputs an output voltage higher than an input voltage; and the step-down switch or the step-up switch is turned on / off A control unit that controls the first step-down comparison voltage and a first step-down comparison voltage that is higher than the first step-down comparison voltage as a comparison voltage whose voltage level changes along the time axis. A second step-down comparison voltage, a first step-up comparison voltage whose average voltage is higher than the second step-down comparison voltage, and a second step whose average voltage is higher than the first step-up comparison voltage. The step-up comparison voltage inputted respectively, was compared to formed by turning on and off the step-down switch or the boost switches constituting a detection voltage corresponding to the comparison voltage and the output voltage the input.

  (Operation) First, assuming that two comparison voltages are used, two comparison voltages having different average voltages are input, each input comparison voltage is compared with the detected voltage, and the voltage is reduced according to the comparison result. The switch or boost switch is controlled to be turned on / off. In this case, in the process in which the detection voltage changes over the voltage range of the two comparison voltages, if the level of the detection voltage becomes an intermediate level between the two comparison voltages, the step-down switch is turned on by the delay time of the step-down switch and the step-up switch. On, the boost switch is kept off, and the specified output voltage cannot be output.

  On the other hand, assuming that four comparison voltages are used, four comparison voltages having different average voltages (first step-down comparison voltage, second step-down comparison voltage, and first step-up comparison voltage). , The second boosting comparison voltage) is input, the inputted comparison voltages are compared with the detection voltage, and the step-down switch or the boosting switch is controlled to be turned on / off according to the comparison result. In this case, in the process in which the detection voltage changes over the voltage range of the four comparison voltages, there are more opportunities for the detection voltage to be compared with one of the comparison voltages than when there are two comparison voltages.

  For example, even if the detection voltage level is intermediate between the first step-down comparison voltage and the second step-up comparison voltage in the process in which the detection voltage changes over the voltage range of four comparison voltages, the detection is performed. The voltage is compared with the second step-down comparison voltage and the first step-up comparison voltage, and a comparison result for ON / OFF control of the step-down switch and step-up switch is obtained.

  As described above, even when the detection voltage changes over the voltage range of the four comparison voltages as the input voltage changes, the output voltage can be continuously output. Therefore, the output voltage can be held at a specified voltage under any input / output conditions, which can contribute to improvement in performance.

  The step-up / step-down DC-DC converter according to claim 2 is the step-up / step-down DC-DC converter according to claim 1, wherein the control unit compares the first step-down comparison voltage with the detection voltage. The step-up switch is turned on / off, the first control mode for keeping the step-up switch off, the second step-up comparison voltage and the detection voltage are compared, and the step-up switch is turned on / off, The second control mode in which the step-down switch is kept on is compared with the second step-down comparison voltage and the detection voltage, and the step-down switch is controlled to be turned on / off. The detection voltage is compared with a third control mode for controlling on / off of the boost switch.

  (Operation) As a first control mode, the control unit compares the first step-down comparison voltage with the detection voltage, performs on / off control of the step-down switch, and maintains the step-up switch off. The step-down is performed to output an output voltage lower than the input voltage.

  On the other hand, the control unit compares the second boost comparison voltage and the detection voltage as the second control mode, controls the boost switch on and off, and keeps the buck switch on. Boosting that outputs an output voltage higher than the input voltage is executed.

  In addition, as a third control mode, the control unit compares the second step-down comparison voltage and the detection voltage, performs on / off control of the step-down switch, and compares the first step-up comparison voltage and the detection voltage. Thus, the step-up / step-down is performed by operating both the step-down unit and the step-up unit by controlling on / off of the step-up switch. Here, the step-up / step-down refers to an operation capable of outputting both an output voltage lower than and higher than an input voltage.

  That is, from the step-down by the first control mode to the step-up by the second control mode, or vice versa, by not directly moving from the step-up to the step-down, via the step-up / step-down by the third control mode, Under all conditions, the output voltage can be held at a specified voltage.

The step-up / step-down DC-DC converter according to claim 3 is the step-up / step-down DC-DC converter according to claim 1 or 2, wherein each voltage level of the second step-down comparison voltage and the first step-up comparison voltage is used. Is set between the minimum value of the first step-down comparison voltage and the maximum value of the second step-up comparison voltage, and the voltage level between the comparison voltages is the first step-down comparison voltage. <Maximum value of the second step-up comparison voltage <maximum value of the first step-down comparison voltage <maximum value of the second step-down comparison voltage <minimum value of the first step-up comparison voltage < The minimum value of the second step-up comparison voltage is configured to satisfy the relationship of the minimum value of the first step-up comparison voltage <the maximum value of the second step-down comparison voltage.

(Operation) When the detection voltage changes between the minimum value of the first step-down comparison voltage and the maximum value of the second step-up comparison voltage, the voltage level between the comparison voltages is
The maximum value of the first step-down comparison voltage <the minimum value of the second step-up comparison voltage The maximum value of the first step-down comparison voltage <the maximum value of the second step-down comparison voltage If the relationship is set so that the minimum value <the minimum value of the second boost comparison voltage <the minimum value of the first boost comparison voltage <the maximum value of the second boost comparison voltage, the following comparison is performed. Is called.

  The detection voltage is compared with the first step-down comparison voltage when the input voltage is higher than the output voltage, and is compared with the second step-up comparison voltage when the input voltage is lower than the output voltage. When the input voltage and the output voltage are substantially the same, the second step-down comparison voltage and the first step-up comparison voltage are compared.

  For this reason, even if the detection voltage changes between the minimum value of the first step-down comparison voltage and the maximum value of the second step-up comparison voltage as the input voltage changes, the output voltage is reduced. Can output continuously. As a result, the output voltage can be maintained at a specified voltage under any input / output conditions, which can contribute to improvement in performance.

  The step-up / step-down DC-DC converter according to claim 4 is the step-up / step-down DC-DC converter according to claim 1, wherein the first step-down comparison voltage and the second step-down / step-down DC-DC converter are The boost comparison voltage is a triangular wave, a ramp wave, or a sawtooth wave having the same frequency, and the second step-down comparison voltage and the first step-up comparison voltage are the first step-down comparison voltage and the first step-down comparison voltage. The configuration is a triangular wave having a frequency half that of the second boost comparison voltage.

  (Function) When a ramp wave or a sawtooth wave is used as the second step-down comparison voltage and the first step-up comparison voltage, a period during which the step-down switch is turned off in the process of applying an on / off signal to the step-down switch and the step-up switch There are times when the periods when the boost switch is turned on overlap.

  When the period when the step-down switch is turned off and the period when the step-up switch is turned on overlap, a path connecting the choke coil and the boost switch is formed, and energy stored in the choke coil is not transmitted to the output side and is wasted. Consumed and the electrical efficiency of the converter is reduced.

  On the other hand, when a triangular wave is used as the second step-down comparison voltage and the first step-up comparison voltage, the step-up switch and the period during which the step-down switch is turned off in the process of applying the on / off signal to the step-down switch and the step-up switch It is possible to prevent the electric efficiency of the converter from being lowered without overlapping the periods during which the transistors are turned on.

  On the other hand, the first step-down comparison voltage is used to turn on and off the step-down switch in the first control mode and is used to turn on the step-down switch in the second control mode. The second step-up comparison voltage is In the first control mode, the booster switch is turned off, and in the second control mode, the booster switch is used for on / off control. For this reason, even if a ramp wave or a sawtooth wave is used as the first step-down comparison voltage and the second step-up comparison voltage for ON / OFF control of only one of the step-down switch or the step-up switch, the electric efficiency of the converter is improved. There is no decline.

  In addition, since the second step-down comparison voltage and the first step-up comparison voltage have half the frequency of the first step-down comparison voltage and the second step-up comparison voltage, switching is possible even if the control mode changes. The frequency (number of times of switching) does not change, and it is possible to prevent the electrical efficiency of the converter from decreasing.

  That is, if the comparison voltages have the same frequency, the switching frequency of the on / off signal applied to the step-down switch and the step-up switch in the third control mode is the same as that in the first control mode or the second control mode. In the mode, the switching frequency of the on / off signal applied to the step-down switch or the step-up switch is twice. When the switching frequency of the on / off signal applied to the step-down switch and the step-up switch is doubled, the switching loss of the step-down switch and the step-up switch is also doubled, and the electrical efficiency of the converter is reduced.

  Therefore, the frequency of the second step-down comparison voltage and the first step-up comparison voltage is set to half the frequency of the first step-down comparison voltage and the second step-up comparison voltage, so that the electric efficiency of the converter is increased. Can be prevented from decreasing.

  The step-up / step-down DC-DC converter according to claim 5 is the step-up / step-down DC-DC converter according to claim 4, wherein the comparison voltage generator for generating each comparison voltage generates a triangular wave, a ramp wave, or a sawtooth wave. A first step-down comparison voltage generator for generating the first step-down comparison voltage, and generating a triangular wave having a frequency half that of the first step-down comparison voltage to generate the second step-down comparison voltage. A second step-down comparison voltage generator to be generated; a first step-up comparison voltage generator for offsetting the second step-down comparison voltage to generate the first step-up comparison voltage; and the first step-up comparison voltage generator. The second step-up comparison voltage generator for generating the second step-up comparison voltage by offsetting the step-down comparison voltage is provided.

  (Operation) The first step-down comparison voltage can be generated by generating a triangular wave, a ramp wave, or a sawtooth wave, and the second step-up comparison voltage is generated by offsetting the first step-down comparison voltage. Can do. A triangular wave having a frequency half that of the first step-down comparison voltage can be generated to generate the second step-down comparison voltage. The second step-down comparison voltage is offset to obtain the first step-up comparison voltage. Can be generated.

  As is apparent from the above description, according to the first aspect, the output voltage can be held at a specified voltage under any input / output conditions, which can contribute to improvement in performance.

  According to the second aspect, the output voltage can be held at a specified voltage under all input / output conditions, which can contribute to improvement in performance.

  According to the third aspect, the output voltage can be held at a specified voltage under any input / output conditions, which can contribute to improvement in performance.

  According to claim 4, it is possible to prevent the electrical efficiency of the converter from decreasing.

  According to the fifth aspect, the second step-up comparison voltage is generated based on the first step-down comparison voltage, and the first step-up comparison voltage is generated based on the second step-down comparison voltage. be able to.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a power supply device for a vehicular lamp showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a comparison voltage, and FIG. 3 is an operation in a step-down mode, a step-down / step-up mode, and a step-up mode. FIG. 4 is a characteristic diagram showing the relationship between the on-duty of the switching signal and the input / output voltage ratio at the time of step-down. FIG. 5 shows the on-duty of the switching signal and the input / output voltage ratio at the time of step-up. FIG. 6 is a circuit configuration diagram when two comparators are used, and FIG. 7 is a step-down mode, a conduction mode and a boost when two comparators are used, that is, two comparison voltages are used. FIG. 8 is a characteristic diagram showing the relationship between the detection voltage and the output voltage when two comparators, ie, two comparison voltages are used, and FIG. 9 is a comparison chart. FIG. 10A is a characteristic diagram showing the relationship between the detected voltage and the output voltage when the output voltage is given hysteresis using four comparators, that is, four comparison voltages. FIG. FIG. 10B is a waveform diagram for explaining the operation when a ramp wave or a sawtooth wave is used as the comparison voltage. FIG. 10B is a diagram for explaining the operation when a triangular wave is used as the comparison voltage in the step-down / boost mode. FIG. 11 is a circuit diagram for explaining an operation when a ramp wave or a sawtooth wave is used as a comparison voltage in the step-down / boost mode.

  In FIG. 1, a power supply device 10 for a vehicle lamp is a step-up / step-down DC-DC converter that includes a step-down unit 12 that outputs an output voltage lower than an input voltage, a step-up unit 14 that outputs an output voltage higher than the input voltage, and a step-down unit. The control part 16 which controls the part 12 and the pressure | voltage rise part 14 is provided.

  The step-down unit 12 includes a step-down switch 18, a capacitor C1, a diode D1, and a choke coil (inductor) L1. The step-down switch 18 is composed of a switching element, for example, an NMOS transistor, the drain of the NMOS transistor is connected to the input terminal 20, the source is grounded via the diode D1, and is connected to one end of the choke coil L1, A gate is connected to the control unit 16. Both ends of the capacitor C1 are connected to the input terminals 20 and 22, respectively. The input terminal 20 is connected to the plus terminal of the in-vehicle battery (DC power supply) 26 through the power switch 24, and the input terminal 22 is connected to the minus terminal of the in-vehicle battery 26.

  The step-up unit 14 includes a choke coil (inductor) L1 common to the step-down unit 12, and includes a step-up switch 28, a capacitor C2, and a diode D2. The step-up switch 28 is composed of a switching element, for example, an NMOS transistor. The drain of the NMOS transistor is connected to the other end of the choke coil L1, and is connected to the output terminal 30 via the diode D2, and the source is grounded. The gate is connected to the control unit 16. One end of the capacitor C2 is connected to the diode D2 and the output terminal 30, and the other end is grounded and connected to the output terminal 32. Loads 34 such as lamps and LEDs are connected to both ends of the output terminals 30 and 32.

  The step-down switch 18 and the step-up switch 28 are turned on and off in response to an on / off signal (switching signal) from the control unit 16, turned off in response to the off signal, and turned on in response to the on signal.

  For example, when the input voltage Vin applied between the input terminals 20 and 22 is higher than the output voltage Vout applied to the load 34 from the output terminals 30 and 32, the step-down switch is in the step-down mode (first control mode). 18 is turned on / off in response to an on / off signal from the control unit 16, and the booster switch 28 is turned off in response to the off signal.

  When the step-down switch 18 is turned on while the step-up switch 28 is kept off, a DC voltage applied between the input terminals 20 and 22 is applied to both ends of the capacitor C1, and a current is supplied to the step-down switch 18. Flowing. This current flows to the load 34 via the choke coil L1 and the diode D2. As a result, electromagnetic energy is accumulated in the choke coil L1.

  Next, when the step-down switch 18 is turned off while the step-up switch 28 is kept off, the electromagnetic energy accumulated in the choke coil L1 through the choke coil L1 and the diode D2 due to the conduction of the diode D1. The input voltage Vin is stepped down and output from the output terminals 30 and 32.

  When the input voltage Vin is lower than the output voltage Vout and in the boost mode (second control mode), the step-down switch 18 is turned on in response to the ON signal from the control unit 16, and the step-up switch 28 is controlled. It turns on and off in response to an on / off signal from the unit 16.

  When the step-up switch 18 is kept on and the step-up switch 28 is turned on, the current from the in-vehicle battery 26 flows to the step-up switch 28 via the step-down switch 28 and the choke coil L1. As a result, electromagnetic energy is accumulated in the choke coil L1.

  Next, when the step-up switch 18 is kept on and the step-up switch 28 is turned off, the electromagnetic energy accumulated in the choke coil L1 through the choke coil L1 and the diode D2 due to the conduction of the diode D2. Is supplied to the capacitor C2 and the load 34, and the input voltage Vin is boosted and output from the output terminals 30 and 32.

  Further, as the step-down / step-up mode (third control mode) between the step-down mode (first control mode) and the step-up mode (second control mode), the step-down switch 18 and the step-up switch 28 are connected from the control unit 16. Turns on / off in response to an on / off signal.

  That is, the control unit 16 includes a step-down mode (first control mode), a step-up mode (second control mode), and a step-down / step-up mode (third control mode), and a control signal (ON / OFF) according to each mode. Signal, a signal including an ON signal and an OFF signal), and the generated control signal is output to the step-down switch 18 and the step-up switch 28.

  Specifically, the control unit 16 includes an error amplification circuit 36, a comparison wave generation circuit 38, a comparison circuit 40, a determination circuit 42, and a control signal switching circuit 44.

  The error amplification circuit 36 includes an error amplifier (error amplifier) 50, a Zener diode ZD1, a capacitor C3, and resistors R2, R3, R5 to R10.

  The resistors R2 and R3 divide the output voltage Vout and input the voltage obtained by dividing the output voltage Vout to the negative input terminal of the error amplifier 50 via the resistor R8. The error amplifier 50 amplifies and amplifies the voltage difference between the set voltage applied to the plus terminal (the voltage obtained by dividing the reference voltage Vr by the resistors R10 and R9) and the voltage applied to the minus terminal. The detected voltage is output as a detection voltage Ve corresponding to the output voltage Vout to the comparison circuit 40 via the resistor R6. In this case, the voltage amplified by the error amplifier 50 can be regarded as the detection voltage Ve corresponding to the ratio between the input voltage Vin and the output voltage Vout.

The comparison wave generation circuit 38 includes comparison wave generators 54, 56, 58 and 60.
As shown in FIG. 2, the comparison wave generator 54 generates a comparison wave A using, for example, a 2 MHz triangular wave signal as a first step-down comparison voltage generator, and compares the generated comparison wave A with the comparison circuit 40. Output to the wave generator 56.

  The comparison wave generator 56 generates a comparison wave D (see FIG. 2) based on a triangular wave signal in which the level of the comparison wave A is offset in response to the comparison wave A as a second boosting comparison voltage generator. The generated comparison wave D is output to the comparison circuit 40.

  The comparison wave generator 58 generates, for example, a comparison wave B (see FIG. 2) using a 1 MHz triangular wave signal as the second step-down comparison voltage generator, and generates the comparison wave B with the comparison circuit 40 to generate a comparison wave. To the device 60.

  The comparison wave generator 60 generates a comparison wave C (see FIG. 2) based on a triangular wave signal in which the level of the comparison wave B is offset in response to the comparison wave B as the first boosting comparison voltage generator. The generated comparison wave C is output to the comparison circuit 40.

  Here, as shown in FIG. 2, the comparison waves A to D have relatively the same amplitude, but the average voltages are set to different values.

  For example, the comparison wave A is set as the first step-down comparison voltage having the lowest average voltage among the comparison waves A to D. The comparison wave B is set as a second step-down comparison voltage whose average voltage is higher than the first step-down comparison voltage (comparison wave A). The comparison wave C is set as a first boost comparison voltage whose average voltage is higher than the second step-down comparison voltage (comparison wave B). The comparison wave D is set as a second boost comparison voltage whose average voltage is higher than the first boost comparison voltage (comparison wave C).

At this time, each voltage level of the comparison wave B (second step-down comparison voltage) and the comparison wave C (first step-up comparison voltage) is set to the minimum value of the comparison wave A (first step-down comparison voltage). The voltage level of each of the comparison waves A to D is set between the maximum value of the comparison wave D (second boosting comparison voltage) and
Maximum value of comparison wave A <minimum value of comparison wave D <maximum value of comparison wave A <maximum value of comparison wave B <minimum value of comparison wave C <minimum value of comparison wave D <minimum value of comparison wave C> The maximum value relationship is satisfied.

  The comparison circuit 40 includes comparators 62, 64, 66, and 68, and the plus terminals of the comparators 62 to 68 are connected to the output terminal of the error amplifier 50 via a resistor R6.

  The comparator 62 compares the detection voltage Ve input to the plus terminal with the comparison wave A input to the minus terminal, and outputs a voltage corresponding to the comparison result to the control signal switching circuit 44 as the step-down signal a.

  The comparator 64 compares the detection voltage Ve input to the plus terminal with the comparison wave B input to the minus terminal, and outputs a voltage corresponding to the comparison result to the control signal switching circuit 44 as the step-down signal b.

  The comparator 66 compares the detection voltage Ve input to the plus terminal with the comparison wave C input to the minus terminal, and outputs a voltage corresponding to the comparison result to the control signal switching circuit 44 as the boost signal c.

  The comparator 68 compares the detection voltage Ve input to the plus terminal with the comparison wave D input to the minus terminal, and outputs a voltage corresponding to the comparison result to the control signal switching circuit 44 as the boost signal d.

  The determination circuit 42 includes inverters 70 and 72, AND gates 74, 76 and 78, and flip-flops 80 and 82.

  Inverter 70 inverts boosted signal d and outputs the inverted boosted signal d to AND gate 74. The AND gate 74 outputs a high-level signal to the clear terminals of the flip-flops 80 and 82 when the logical product condition of the step-down signal a and the inverted step-up signal d is satisfied.

  The flip-flop 80 takes in the clock signal from the clock generator 52 from the AND gate 76, outputs a pulse signal from the Q terminal to the AND gate 78 in response to the clock signal, and from the Q bar terminal to the clock terminal of the flip-flop 82. Output a pulse signal. The flip-flop 82 outputs a pulse signal from the Q terminal to the AND gate 78 in response to the pulse signal input to the clock terminal.

  When the detection voltage Ve is between the maximum value of the comparison wave A and the minimum value of the comparison wave D in response to the output signals of the flip-flops 80 and 82, the AND gate 78 is in the “L” level switching mode. When the switching signal X is output to the control signal switching circuit 44 and the detection voltage Ve is smaller than the maximum value of the comparison wave A, or when the detection voltage Ve is larger than the minimum value of the comparison wave D, “H”. The level switching mode switching signal X is output to the control signal switching circuit 44. The switching mode switching signal X is inverted by the inverter 72 and output to the control signal switching circuit 44 as the switching mode switching signal Y.

  The control signal switching circuit 44 includes OR gates 84 and 86 and AND gates 88, 90, 92 and 94. The OR gate 84 has an output terminal connected to the step-down switch 18 and an input terminal connected to the output terminals of the AND gates 88 and 90. The OR gate 86 has an output terminal connected to the boost switch 28 and an input terminal connected to the output terminals of the AND gates 92 and 94.

  The AND gate 88 has one input terminal connected to the output terminal of the inverter 72 and the other input terminal connected to the output terminal of the comparator 62. The AND gate 90 has one input terminal connected to the output terminal of the AND gate 78 and the other input terminal connected to the output terminal of the comparator 64. The AND gate 92 has one input terminal connected to the output terminal of the AND gate 78 and the other input terminal connected to the output terminal of the comparator 66. The AND gate 94 has one input terminal connected to the output terminal of the inverter 72 and the other input terminal connected to the output terminal of the comparator 68.

  The AND gate 88 outputs the step-down signal a as an on / off signal (step-down switching signal) to the step-down switch 18 via the OR gate 84 when the level of the switching mode switching signal Y is at the “H” level. When the level of the signal Y is at the “L” level, an “L” level off signal is output to the OR gate 84.

  The AND gate 90 outputs the step-down signal b as an on / off signal (step-down switching signal) to the step-down switch 18 via the OR gate 84 when the level of the switching mode switching signal X is at the “H” level. When the level of the signal X is at the “L” level, an “L” level off signal is output to the OR gate 84.

  When the level of the switching mode switching signal X is at the “H” level, the AND gate 92 outputs the boosting signal c as an on / off signal (boosting switching signal) to the boosting switch 28 via the OR gate 86 to switch the switching mode. When the level of the signal X is at the “L” level, an “L” level off signal is output to the OR gate 86.

  When the level of the switching mode switching signal Y is at the “H” level, the AND gate 94 outputs the boosting signal d as an on / off signal (boosting switching signal) to the boosting switch 28 via the OR gate 86 to switch the switching mode. When the level of the signal Y is at the “L” level, an “L” level off signal is output to the OR gate 86.

  The OR gate 84 outputs an on / off signal or an on signal to the step-down switch 18 in response to the step-down signal a output from the AND gate 88 or the step-down signal b output from the AND gate 90.

  The OR gate 86 outputs an on / off signal or an off signal to the boost switch 28 in response to the boost signal c output from the AND gate 92 or the boost signal d output from the AND gate 94.

  That is, as shown in FIG. 3A, when the detection voltage Ve is smaller than the maximum value of the comparison wave A and the on / off step-down signal a is output from the comparator 62, the determination circuit 42 is in the step-down mode (first step). 1, the control signal switching circuit 44 outputs the “H” level switching mode switching signal Y to the AND gates 90 and 92 of the control signal switching circuit 44. , “L” level switching mode switching signal X is output.

  When the “H” level switching mode switching signal Y is input to the AND gates 88 and 94, an ON / OFF signal is output as a control signal from the OR gate 84 to the step-down switch 18, and from the OR gate 86 to the step-up switch 28. An off signal is output as a control signal. Thereby, as the control in the step-down mode (first control mode), the step-down switch 18 is ON / OFF controlled, and the step-up switch 28 is maintained OFF.

  On the other hand, as shown in FIG. 3C, when the detected voltage Ve is larger than the minimum value of the comparison wave D and the on / off boost signal d is output from the comparator 68, the determination circuit 42 is in the boost mode (first step). 2), the control signal switching circuit 44 outputs an “H” level switching mode switching signal Y to the AND gates 90 and 92 of the control signal switching circuit 44. , “L” level switching mode switching signal X is output.

  When the “H” level switching mode switching signal Y is input to the AND gates 88 and 94, an ON signal is output as a control signal from the OR gate 84 to the step-down switch 18, and from the OR gate 86 to the step-up switch 28. An on / off signal is output as a control signal. As a result, as the control in the boost mode (second control mode), the step-down switch 18 is kept on, and the step-up switch 28 is on / off controlled.

  Further, as shown in FIG. 3B, when the detection voltage Ve is between the maximum value of the comparison wave A and the minimum value of the comparison wave D, the comparators 64 and 66 output the on / off step-down signal b and the on / off step-up signal. When “c” is output, the determination circuit 42 determines that the voltage is in the step-down / boost mode (third control mode), and switches the AND gates 88 and 94 of the control signal switching circuit 44 to “L” level switching mode switching. The signal Y is output, and the “H” level switching mode switching signal X is output to the AND gates 90 and 92 of the control signal switching circuit 44.

  When the “H” level switching mode switching signal X is input to the AND gates 90 and 92, an ON / OFF signal is output as a control signal from the OR gate 84 to the step-down switch 18, and from the OR gate 86 to the step-up switch 28. An on / off signal is output as a control signal. As a result, the step-down switch 18 and the step-up switch 28 are on / off controlled as control in the step-down / step-up mode (third control mode).

  Here, the relationship between the ON duty of the ON / OFF signal applied to the step-down switch 18 and the input / output voltage ratio (Vout / Vin) of the power supply device 10 is represented by the characteristic of FIG. The relationship between the on-duty of the signal and the input / output voltage ratio (Vout / Vin) of the power supply device 10 is represented by the characteristic of FIG.

  Therefore, when the input / output voltage ratio (Vout / Vin) = 1, that is, the on-duty of the on / off signal applied to the step-down switch 18 = 100%, the on-duty of the on / off signal applied to the step-up switch 28 = 0. By switching between the step-down mode and the step-up mode with%, the output voltage Vout can be continuously output from the power supply device 10 also in the step-down mode and the step-up mode.

  At this time, as shown in FIG. 6, as a comparator, a step-down comparator 62A to which a comparison wave A1 based on a triangular wave signal is input, and a comparison wave D1 in which the minimum value of the triangular wave signal is equal to the maximum value of the comparison wave A1 are input. The boosting comparator 68A is used, the detection voltage Ve output from the error amplifier 50A is compared with the comparison wave A1 by the step-down comparator 62A, and the detection voltage Ve and the comparison wave D1 are compared by the boosting comparator 68A. can do.

  In this case, as shown in FIG. 7A, at the time of step-down (Vout / Vin <1), the detection voltage Ve output from the error amplifier 50A and the comparison wave A1 are compared by the step-down comparator 62A. Depending on the result, an on / off signal is output to the step-down switch 18, and the detection voltage Ve and the comparison wave D1 are compared by the step-up comparator 68A, and an off signal is output to the step-up switch 28 according to the comparison result. Thus, the input voltage can be stepped down and output.

  Further, as shown in FIG. 7B, when switching between step-down and step-up (Vout / Vin = 1), an ON signal is output from the step-down comparator 62A to the step-down switch 18, and the step-up comparator 68A boosts the voltage. By outputting an OFF signal to the switch 28, the input and output are brought into conduction through the choke coil without performing a switching operation, and an output voltage equal to the input voltage can be output.

  On the other hand, as shown in FIG. 7C, at the time of boosting (Vout / Vin> 1), the detected voltage Ve output from the error amplifier 50A and the comparison wave A1 are compared by the step-down comparator 62A, and the comparison result In response to this, the ON signal is output to the step-down switch 18, the detection voltage Ve and the comparison wave D1 are compared by the step-up comparator 68A, and the ON / OFF signal is output to the step-up switch 28 according to the comparison result. The input voltage can be boosted and output.

  As described above, when the control in the step-down mode and the step-up mode is executed, the step-down and step-up are automatically switched according to the increase / decrease of the detection voltage Ve by the output of the error amplifier 50A, and the output voltage Vout is continuously output. be able to.

  However, when the switching elements constituting the step-down switch 18 and the step-up switch 28 are turned on and off, there is a minimum on-time and off-time (switching time) that can be switched. Therefore, depending on the on-duty value, the output voltage Vout may not be output continuously.

  For example, if the frequency (switching frequency) of the on / off signal applied to the switching elements constituting the step-down switch 18 and the step-up switch 28 is 2 MHz (cycle = 500 ns), the minimum on-time of the on-off signal = the minimum off-time = 50 ns. As shown in FIG. 8, the switching element constituting the step-down switch 18 performs a switching operation when the on-duty of the on / off signal at the time of step-down (in the step-down mode M1) is smaller than 90%. When the on-duty becomes 90% or more, the switching operation cannot be performed.

  The switching element constituting the boost switch 28 performs a switching operation when the on-duty of the on / off signal at the time of boosting (in the boosting mode M2) is larger than 10%, but the on-duty of the on / off signal at the time of boosting is 10%. Switching operation cannot be performed if

  That is, the switching elements constituting the step-down switch 18 and the step-up switch 28 have an ON duty of ON / OFF signal of 90% or more at the time of step-down (step-down mode M1) to ON duty of the ON / OFF signal at the time of step-up (step-up mode M2). In the range W of 10% or less, conduction is made through the choke coil L1 without performing a switching operation. For this reason, since Vin = Vout is constant, even if it is desired to control the output voltage Vout as indicated by a broken line in accordance with the detection voltage Ve, the output voltage Vout cannot be accurately controlled even if the output voltage Vout is indicated as a solid line. Become.

  In particular, the output voltage Vout cannot be accurately controlled as the switching frequency is high and the input / output voltage is large. This is because as the switching frequency becomes higher, the time of one cycle is shortened and the ratio of the minimum on time and off time to one cycle is increased. In addition, when the input / output voltage is large, it is necessary to increase the withstand voltage of the switching element. Generally, a switching element having a higher withstand voltage has a larger minimum on time and off time.

  On the other hand, in this embodiment, comparison waves A, B, C, and D having different average voltages are used as comparison voltages, and detection voltage Ve and comparison waves A, B, C, and D are used as comparators. Four comparators 62, 64, 66, and 68 to be compared are used.

  In the step-down mode (first control mode) in which the input voltage Vin is higher than the output voltage Vout and the detection voltage Ve is smaller than the maximum value of the comparison wave A, an on-on signal is output to the step-down switch 18 and the step-up switch An off signal is output to 28.

  On the other hand, in the step-up mode (second control mode) in which the input voltage Vin is lower than the output voltage Vout and the detection voltage Ve is larger than the minimum value of the comparison wave D, an ON signal is output to the step-down switch 18 and the step-up switch An on / off signal is output to 28.

  Further, in the step-down / boost mode (third control mode) where the input voltage Vin and the output voltage Vout are substantially the same and the detection voltage Ve is between the maximum value of the comparison wave A and the minimum value of the comparison wave D, An on / off signal is output to the step-down switch 18 and an on / off signal is output to the step-up switch 28.

  Thus, in this embodiment, even if the detection voltage Ve changes from the minimum value of the comparison wave A to the maximum value of the comparison wave D as the input voltage Vin changes, the step-down mode (first 1 control mode), step-up mode (second control mode), or step-down / step-up mode (third control mode), so that the output voltage Vout continues even if the input voltage Vin changes. Can be output automatically.

  Therefore, according to the present embodiment, the output voltage Vout can be held at a specified voltage under any input / output conditions, which can contribute to the improvement of the performance of the power supply device 10.

  Further, when setting the voltage levels of the comparison waves A, B, C, and D, as shown in FIG. 9, the comparison waves are set so that hysteresis H1 and H2 are generated in the relationship between the detection voltage Ve and the output voltage Vout. By setting the voltage levels of A, B, C, and D, the switching between the step-down mode (first control mode) M1 and the step-down / step-up mode (third control mode) M3 or the step-down / step-up mode (first step) 3 control mode) M3 and step-up mode (second control mode) M2 can be prevented from switching frequently.

  In this case, the voltage levels of the comparison waves A, B, C, and D can be set in consideration of the following example.

  For example, the minimum ON time of the ON / OFF signal applied to the switching elements constituting the step-down switch 18 and the step-up switch 28 = the minimum OFF time = 50 ns, and the minimum duty of the ON / OFF signal when using the 2 MHz comparison waves A and D = 10 %, Maximum duty = 90%, and when the 1 MHz comparison waves B and C are used, the on / off signal minimum duty = 5% and the maximum duty = 95%, the comparison wave A includes the on / off signal at the time of step-down. When the on-duty is 90% or less and Vin = 10V, Vout is 9.0V or less.

  Similarly, as the comparison waves B and C, when the voltage is stepped down, the on-duty of the on / off signal is 5% to 30%, and when the voltage is boosted, the on-duty of the on / off signal is 70% to 95% and Vin = 10V. As a result, the voltage is 7.37 to 13.57V.

  Similarly, the comparison wave D is 11.11 V or more as Vout when the on-duty of the on / off signal is 10% or more and Vin = 10 V at the time of boosting.

  In the present embodiment, a triangular wave signal is used as the comparison waves A, B, C, and D instead of a signal using a ramp wave or a sawtooth wave, but this is different from the step-down / boost mode (third control mode). This is because the moment when the step-down switch 18 = OFF and the step-up switch 28 = ON is not created.

  That is, as shown in FIG. 10A, when signals using ramp waves or sawtooth waves are used as the comparison waves B and C, both the period during which the step-down switch 18 is turned off and the period during which the step-up switch 28 is turned on. The timings t1, t2, and t3 at which the two instantaneously overlap occur.

  When the timings t1, t2, and t3 in which the step-down switch 18 is turned off and the step-up switch 28 are turned on instantaneously occur, the diode D1, the choke coil L1, and the step-up switch 28 are generated as shown in FIG. Is formed, the energy stored in the choke coil L1 is not transmitted to the output side, but is wasted, and the electrical efficiency of the power supply device 10 is reduced.

  On the other hand, as shown in FIG. 10B, when triangular wave signals are used as the comparison waves B and C, the period in which the step-down switch 18 is turned off overlaps the period in which the step-up switch 28 is turned on. Therefore, it is possible to prevent the electrical efficiency of the power supply device 10 from being lowered.

  The comparison wave A is used to turn on / off the step-down switch 18 in the step-down mode (first control mode) and to turn on the step-down switch 18 in the step-up mode (second control mode). D is used to turn off the boost switch 28 in the step-down mode (first control mode) and to turn on / off the boost switch 28 in the boost mode (second control mode). For this reason, even if a signal using a ramp wave or a sawtooth wave is used as the comparison waves A and D for generating a control signal for controlling on / off of only one of the step-down switch 18 or the step-up switch 28, the electric efficiency of the power supply device 10 Will not drop.

  In this embodiment, a 2 MHz triangular wave signal is used as the comparison waves A and D, and a 1 MHz triangular wave signal, which is a half frequency of the comparison waves A and D, is used as the comparison waves B and C. Even if the control mode changes, the switching frequency (number of times of switching) does not change, and it is possible to prevent the electrical efficiency of the power supply device 10 from being lowered.

  That is, if triangular wave signals having the same frequency are used as the comparison waves A, B, C, and D, the switching frequency of the on / off signal applied to the switching element in the step-down / step-up mode (third control mode) is step-down. In the mode (first control mode) or the boost mode (second control mode), the switching frequency of the on / off signal applied to the switching element is doubled. When the switching frequency of the on / off signal applied to the switching element is doubled, the switching loss of the switching element is also doubled, and the electrical efficiency of the power supply device 10 is reduced.

  In the present embodiment, the comparison waves A, B, C, and D have the same relative voltage level (amplitude) for each comparison wave. Can be set to different values.

  In this embodiment, a method of feeding back the output voltage Vout is adopted, but a method of feeding back the output current or output power can also be adopted.

It is a circuit block diagram of the power supply device of the vehicle lamp which shows one Example of this invention. It is a wave form diagram of a comparison voltage. It is a waveform diagram for explaining the operation in the step-down mode, step-down / step-up mode and step-up mode. It is a characteristic view showing the relationship between the on-duty of the switching signal and the input / output voltage ratio at the time of step-down. FIG. 5 is a characteristic diagram showing a relationship between an on-duty of a switching signal and an input / output voltage ratio at the time of boosting. It is a circuit block diagram when using two comparators. FIG. 5 is a waveform diagram for explaining operations in a step-down mode, a conduction mode, and a step-up mode when two comparators, that is, two comparison voltages are used. It is a characteristic view which shows the relationship between a detection voltage and output voltage when using two comparators, ie, two comparison voltages. It is a characteristic diagram which shows the relationship between a detection voltage and an output voltage when giving a hysteresis to an output voltage using four comparators, ie, four comparison voltages. (A) is a waveform diagram for explaining an operation when a ramp wave or a sawtooth wave is used as a comparison voltage in the step-down / boost mode, and (b) uses a triangular wave as a comparison voltage in the step-down / step-up mode. It is a wave form diagram for demonstrating operation | movement when there exists. It is a circuit diagram for explaining an operation when a ramp wave or a sawtooth wave is used as a comparison voltage in the step-down / step-up mode.

Explanation of symbols

10 Power supply (Buck-boost DC-DC converter)
12 Step-down Unit 14 Step-up Unit 16 Control Unit 18 Step-Down Switch 28 Step-up Switch 36 Error Amplifier Circuit 38 Comparison Wave Generation Circuit 40 Comparison Circuit 42 Discrimination Circuit 44 Control Signal Switching Circuit

Claims (5)

A step-down switch for inputting a DC voltage from a DC power supply, a step-down unit having a choke coil connected to the step-down switch, and outputting an output voltage lower than the input voltage;
A step-up switch having a step-up switch connected to the step-down switch via the choke coil, and outputting an output voltage higher than the input voltage;
A controller for controlling on / off of the step-down switch or the step-up switch,
The control unit, as a comparison voltage whose voltage level changes along the time axis,
A first step-down comparison voltage;
A second step-down comparison voltage having an average voltage higher than the first step-down comparison voltage;
A first boost comparison voltage having an average voltage higher than the second step-down comparison voltage;
Input a second boosting comparison voltage whose average voltage is higher than the first boosting comparison voltage,
Comparing each input comparison voltage with a detection voltage corresponding to an output voltage, the step-down switch or the step-up switch is controlled to be turned on / off.
Buck-boost DC-DC converter. The step-up / step-down DC-DC converter according to claim 1,
The controller is
A first control mode for comparing the first step-down comparison voltage with the detection voltage, controlling the step-down switch on and off, and maintaining the step-up switch off;
A second control mode for comparing the second boost comparison voltage with the detection voltage, controlling the boost switch on and off, and maintaining the buck switch on;
The second step-down comparison voltage and the detection voltage are compared, the step-down switch is turned on / off, the first step-up comparison voltage and the detection voltage are compared, and the step-up switch is turned on / off. A step-up / step-down DC-DC converter comprising: a third control mode. The step-up / step-down DC-DC converter according to claim 1 or 2,
Each voltage level of the second step-down comparison voltage and the first step-up comparison voltage is between a minimum value of the first step-down comparison voltage and a maximum value of the second step-up comparison voltage. And the voltage level between the respective comparison voltages is
The maximum value of the first step-down comparison voltage <the minimum value of the second step-up comparison voltage> The maximum value of the first step-down comparison voltage <the maximum value of the second step-down comparison voltage The minimum value of the boost comparison voltage <the minimum value of the second boost comparison voltage> the minimum value of the first boost comparison voltage <the maximum value of the second step-down comparison voltage A step-up / step-down DC-DC converter characterized. The step-up / step-down DC-DC converter according to any one of claims 1, 2, and 3,
The first step-down comparison voltage and the second step-up comparison voltage are respectively a triangular wave, a ramp wave, or a sawtooth wave having the same frequency, and the second step-down comparison voltage and the first step-up comparison voltage. The step-up / step-down DC-DC converter is characterized in that the voltage is a triangular wave having a frequency half that of the first step-down comparison voltage and the second step-up comparison voltage. The step-up / step-down DC-DC converter according to claim 4,
As a comparison voltage generator for generating each comparison voltage, a first step-down comparison voltage generator for generating a first step-down comparison voltage by generating a triangular wave, a ramp wave, or a sawtooth wave, and the first A second step-down comparison voltage generator for generating a second step-down comparison voltage by generating a triangular wave having a frequency half that of the step-down comparison voltage, and offsetting the second step-down comparison voltage A first boost comparison voltage generator for generating one boost comparison voltage, and a second boost comparison voltage for generating the second boost comparison voltage by offsetting the first step-down comparison voltage. A step-up / step-down DC-DC converter comprising a generator.

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