WO2024067343A1 - 一种dc-dc转换器 - Google Patents

一种dc-dc转换器 Download PDF

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Publication number
WO2024067343A1
WO2024067343A1 PCT/CN2023/120353 CN2023120353W WO2024067343A1 WO 2024067343 A1 WO2024067343 A1 WO 2024067343A1 CN 2023120353 W CN2023120353 W CN 2023120353W WO 2024067343 A1 WO2024067343 A1 WO 2024067343A1
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Prior art keywords
current
output
unit
converter
control signal
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PCT/CN2023/120353
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English (en)
French (fr)
Inventor
于翔
许晶
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圣邦微电子(苏州)有限责任公司
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Publication of WO2024067343A1 publication Critical patent/WO2024067343A1/zh

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/1566—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators with means for compensating against rapid load changes, e.g. with auxiliary current source, with dual mode control or with inductance variation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0009—Devices or circuits for detecting current in a converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0025—Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/157—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators with digital control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention relates to the field of integrated circuits, and more particularly to a DC-DC converter.
  • DC-DC (Direct Current-Direct Current) converter is widely used in integrated circuits as a voltage converter that can convert input voltage and effectively output a fixed voltage.
  • DC-DC (Direct Current-Direct Current) converter is widely used in integrated circuits as a voltage converter that can convert input voltage and effectively output a fixed voltage.
  • boost converter In the boost converter,
  • the DC-DC converter can provide two different working modes, light load and heavy load, to improve its adaptability and meet the power supply requirements of more different types of downstream loads.
  • the peak value of the inductor current will be clamped at a fixed minimum threshold current Ntrip and will no longer decrease.
  • the on or off state of the power tube in the converter will be controlled by the light load working mode, and the normal output of the inductor current will be realized in one period, and the output of the inductor current will be shielded in the next period, and a relatively stable control of the output voltage is achieved through reciprocating cycles.
  • the period when the inductor current is normally output is called the output interval
  • the period when the inductor current cannot be output is called the non-output interval.
  • the switching point of the DC-DC converter in realizing the light load and heavy load working modes varies with the input and output voltages. Since the output ripple of the DC-DC converter will be larger when working at a light load, which affects the application, some applications require that the switching point of the DC-DC converter between light load and heavy load is constant. However, the prior art cannot meet such special applications.
  • the object of the present invention is to provide a DC-DC converter, which can reasonably adjust the minimum value of the inductor current so that the DC-DC enters a light load working mode at a reasonable fixed load current point.
  • the present invention adopts the following technical solution.
  • the present invention relates to a DC-DC converter, comprising a clock generating circuit, a logic unit, a delay unit, a power tube, an inductor, an output capacitor, a voltage dividing resistor and an error amplifier.
  • the converter also comprises a mode switching unit, a first current detection unit, a second current detection unit, a third current detection unit and a logic module; wherein the mode switching unit is used to compare a reference voltage with an output voltage Vea of the error amplifier to obtain a first control signal OUT1; the first current detection unit is used to generate a second control signal OUT2, and the second current detection unit and the third current detection unit are used to generate a third control signal OUT3; the logic unit realizes the conversion of the converter between a light load and a heavy load working state based on the first control signal OUT1, and realizes the control of the on and off states of the power tube in the converter under the light load working state of the converter based on the second control signal OUT2 and the third control signal OUT3.
  • the logic unit controls the converter to enter a light load working state, and the inductor current is shielded or output at a set interval; when the inductor current is in an output interval, the second control signal OUT2 and the third control signal OUT3 control the high-end power tube to turn on, the low-end power tube to turn off and increase the amplitude of the inductor current, or control the high-end power tube to turn off, the low-end power tube to turn on and decrease the amplitude of the inductor current.
  • the mode switching unit comprises a first comparator COMP1, a positive input terminal of the comparator COMP1 is connected to a reference voltage V1, a negative input terminal of the comparator COMP1 is connected to an output voltage Vea of the error amplifier, and an output terminal of the comparator COMP1 generates a first control signal OUT1.
  • the first current detection unit includes a current amplifier circuit and a second comparator COMP2; wherein the current amplifier circuit is used to collect the inductor current and convert it into a detection voltage OUT4 and output it to the positive input terminal of the second comparator COMP2; the negative input terminal of the second comparator is connected to the output voltage Vea of the error amplifier, and the output terminal generates a second control signal OUT2 and inputs it to the logic module.
  • the second current detection unit is used to collect the inductor current and convert it into a detection voltage OUT4 according to the conversion coefficient. It is converted into an amplified current I2, and the amplified current is input to the third current detection unit.
  • the third current detection unit includes an output voltage acquisition unit, an input voltage acquisition unit, a comparison unit and an output mirror unit; wherein, the input ends of the output voltage acquisition unit and the input voltage acquisition unit are respectively connected to the output voltage of the converter and the input voltage of the converter; the output ends of the output voltage acquisition unit and the input voltage acquisition unit are respectively connected to the two input ends of the comparison unit; the comparison unit generates a comparison current ICQ4 after comparison, and generates a detection current I1 after passing through the output mirror unit.
  • the third current detection unit further includes two inverters connected in series, the input ends of the inverters are respectively connected to the output ends of the second current detection unit and the third current detection unit; and the output ends of the inverters are connected to the logic unit.
  • the output voltage acquisition unit includes an operational amplifier OPA1, a voltage dividing resistor R1 and a mirror MOS transistor, which is used to generate a first comparison current Vout/R1 based on the positive input signal Vout of the operational amplifier OPA1;
  • the input voltage acquisition unit includes an operational amplifier OPA2, a voltage dividing resistor R2 and a mirror MOS transistor, which is used to generate a second comparison current Vin/R2 based on the positive input signal Vin of the operational amplifier OPA2.
  • the comparison unit includes a base control tube, primary symmetrical tubes Q2 and Q3, secondary symmetrical tubes Q1 and Q4, a primary current source Iref and a secondary current source Ix; wherein the gate of the base control tube is connected to the output end of the output voltage acquisition unit, the drain is connected to the power supply voltage, the source is respectively connected to the base of the primary symmetrical tubes Q2 and Q3 and one end of the primary current source Iref, and the other end of the primary current source Iref is grounded; the collectors of the primary symmetrical tubes Q2 and Q3 are connected to the power supply voltage, the emitter of Q2 is grounded after passing through the secondary current source Ix, and the collector of Q3 is connected to the output end of the input voltage acquisition unit; the bases of the secondary symmetrical tubes Q1 and Q4 are respectively connected to the emitters of the primary symmetrical tubes Q2 and Q3, and the emitters are respectively grounded, the collector of Q1 is connected to the output end of the output voltage acquisition unit and the gate of the base control
  • the output current of the comparison unit is ;in, , is the output current of the secondary current source.
  • the maximum amplitude of the inductor current is limited to , and the maximum amplitude of the load current is limited to a constant .
  • the beneficial effect of the present invention is that, compared with the prior art, a DC-DC converter in the present invention can reasonably adjust the minimum value of the inductor current so that the DC-DC enters a light-load operating mode at a reasonable fixed load current point.
  • the present invention only uses multiple current detection modules to realize the control of the on or off state of the power tube, and cooperates with the original working logic of the heavy load and light load working mode switching of the logic module, covering the control signal of the power tube on and off under the light load state, thereby realizing the dynamic control of the output amplitude of the inductor current.
  • the present invention ensures that the inductor current can still adjust its own amplitude according to the size of the output voltage and the input voltage even under the light load state, thereby ensuring the matching of the converter to the load circuit under the light load state.
  • the present invention takes into account the conservation between the input power and the output power of the converter, and thus cleverly designs the parameters of the various components in the third current detection unit, so that the converter can flip when the load current is equal to a preset fixed current value, thereby achieving the purpose of being able to predict at which load point to enter the light load mode.
  • Applications that are sensitive to output ripple can accurately avoid this load point without considering the influence of the input and output voltages.
  • FIG1 is a schematic diagram of an output voltage ripple of a DC-DC converter in the prior art of the present invention
  • FIG2 is a schematic diagram of the principle of a DC-DC converter of the present invention.
  • FIG3 is a circuit diagram of a first current detection unit in a DC-DC converter of the present invention.
  • FIG4 is a circuit diagram of a second current detection unit in a DC-DC converter of the present invention.
  • FIG. 5 is a schematic diagram of a partial circuit of a third current detection unit in a DC-DC converter of the present invention.
  • FIG. 6 is a schematic diagram showing an output principle of a third control signal in a third current detection unit in a DC-DC converter according to the present invention.
  • FIG1 is a schematic diagram of the output voltage ripple of a DC-DC converter in the prior art of the present invention.
  • a DC-DC converter can realize two different operating modes, light load and heavy load, based on the state of the load.
  • the amplitude of the inductor current can be adjusted according to the magnitude of the load current, and in this way the output voltage is kept stable.
  • the DC-DC converter can enter a light load state, in which the amplitude of the inductor current is clamped at the minimum threshold current Ntrip, and in order to maintain the working state of the subsequent load, the inductor current cannot become smaller.
  • the DC-DC converter can ensure that the total output power is low by outputting the inductor current at intervals.
  • the circuit designer hopes to accurately switch the on or off state of the power tube in the converter under the light load working state according to the state of both the input voltage and the output voltage, so as to ensure that the light load mode is entered under a fixed load current. Therefore, the present invention provides a new DC-DC converter.
  • Fig. 2 is a schematic diagram of the principle of a DC-DC converter of the present invention.
  • a DC-DC converter includes a clock generation circuit, a logic unit, a delay unit, a power tube, an inductor, an output capacitor, a voltage-dividing resistor and an error amplifier, and the converter also includes a mode switching unit, a first current detection unit, a second current detection unit, a third current detection unit and a logic module; the mode switching unit is used to compare the reference voltage with the output voltage Vea of the error amplifier to obtain a first control signal OUT1; the first current detection unit is used to generate a second control signal OUT2, and the second current detection unit and the third current detection unit are used to generate a third control signal OUT3; the logic unit realizes the conversion of the light-load or heavy-load working state of the converter based on the first control signal OUT1, and realizes the control of the on and off state of the power tube in the converter under the light-load working state of the converter based on the second
  • the first control signal OUT1 has a similar function to the switching control signal between the light load and heavy load working states in the prior art, and both can control the circuit to switch between the light load and heavy load states.
  • the second and third control signals OUT2 and OUT3 can adjust the duration of the rising process and the duration of the falling process of the inductor current in each clock cycle, so that no matter what state the subsequent load is in, the converter can adaptively achieve reasonable output under the light load state.
  • the logic unit controls the converter to enter a light load working state, and the inductor current is shielded or output at a set interval; when the inductor current is in an output interval, the second control signal OUT2 and the third control signal OUT3 control the high-end power tube to turn on, the low-end power tube to turn off and increase the amplitude of the inductor current, or control the high-end power tube to turn off, the low-end power tube to turn on and decrease the amplitude of the inductor current.
  • the idea of the present invention is to compare the second control signal OUT2 containing the inductor current information with the third control signal OUT3 containing the input voltage and output voltage information, so that when the ratio of the output voltage to the input voltage of the circuit is higher than a certain level, the on or off state of the power tube in the circuit will change, so that the inductor current changes from gradually increasing to gradually decreasing.
  • the second control signal OUT2 and the third control signal OUT3 control the state of the power tube, thereby adjusting the maximum amplitude of the inductor current in each output cycle.
  • the product of the output voltage and load current of the converter is equal to the product of the input voltage and inductor current. Therefore, the change in the ratio of the output voltage to the input voltage described above and the change in the maximum amplitude of the inductor current are offset to a certain extent, so that the circuit can flexibly control the amplitude of the inductor current in each cycle and accurately control the maximum amplitude of the load current in each cycle.
  • the mode switching unit comprises a first comparator COMP1, a positive input terminal of the comparator COMP1 is connected to a reference voltage V1, a negative input terminal of the comparator COMP1 is connected to an output voltage Vea of the error amplifier, and an output terminal of the comparator COMP1 generates a first control signal OUT1.
  • the mode switching unit can collect the feedback voltage Vfb through the error amplifier already in the converter. After Vfb is compared with a reference voltage Vref, the output Vea of the error amplifier is realized. After the output voltage Vea is compared with the reference voltage V1, the output of the first control signal is realized.
  • the first control signal OUT1 when Vfb, that is, the divided voltage of the output voltage Vout, is large, the first control signal OUT1 will be in a high level state, and the circuit will switch from a heavy load state to a light load state. When the output voltage is low, the output of the first control signal OUT1 is also in a low level state, and the low level control logic unit implements the heavy load working mode of the circuit. In other words, when the first control signal OUT1 is in a high level state for part of the time, the first control signal will simultaneously shield the control signals of the high-end power tube and the low-end power tube, so that both are in a cut-off state, at which time the inductor current will not be output, and the circuit is in a non-output interval.
  • the first current detection unit includes a current amplifying circuit and a second comparator COMP2; wherein the current amplifying circuit is used to collect the inductor current and convert it into a detection voltage OUT4 and output it to the positive input terminal of the second comparator COMP2; the negative input terminal of the second comparator is connected to the output voltage Vea of the error amplifier, and the output terminal generates a second control signal OUT2 and inputs it into the logic module.
  • the current amplifying circuit is used to collect the inductor current and convert it into a detection voltage OUT4 and output it to the positive input terminal of the second comparator COMP2; the negative input terminal of the second comparator is connected to the output voltage Vea of the error amplifier, and the output terminal generates a second control signal OUT2 and inputs it into the logic module.
  • FIG3 is a circuit diagram of a first current detection unit in a DC-DC converter of the present invention.
  • the current amplification circuit can be a circuit composed of a current mirror and a voltage divider resistor.
  • the MOS tube Mn2 at one end of the current mirror is connected to the low-end power tube Mn0 of the converter in a mirroring manner, that is, the gates of Mn0 and Mn2 are connected to each other, and the sources are both grounded. Therefore, the current mirror can receive the proportional current of the low-end power tube, that is, the proportional current of the inductor current.
  • the voltage divider resistor can realize the detection voltage OUT4 based on the change of the inductor current.
  • the detection voltage is compared with the output voltage Vea of the error amplifier to generate a second control signal OUT2.
  • the second control signal OUT2 when the inductor current After input, the output voltage of the first current detection unit is Therefore, when When it is greater than Vea, the second control signal OUT2 is at a high level, otherwise it is at a low level.
  • the logic module in the circuit executes the original logic to realize the switching of the power tube.
  • the output of the second control signal OUT2 is at a high level, it is necessary to judge the state of another control signal OUT3.
  • the original logic mentioned here is the converter's own control logic, which includes the light-heavy load switching logic.
  • the first current detection unit may also be implemented by other circuits in the prior art, as long as the current detection function can be achieved.
  • the second current detection unit is used to collect the inductor current and convert it into an amplified current I2, and input the amplified current to the third current detection unit.
  • FIG4 is a circuit diagram of a second current detection unit in a DC-DC converter of the present invention.
  • the second current detection unit can be composed of a mirror unit, which can realize the mirroring of the drain current of the low-end power tube of the converter, that is, the inductor current is mirrored into the amplified current I2.
  • the amplification factor of the second current detection unit is , so the output of this unit becomes .
  • the third current detection unit includes an output voltage acquisition unit, an input voltage acquisition unit, a comparison unit and an output mirror unit; wherein, the input ends of the output voltage acquisition unit and the input voltage acquisition unit are respectively connected to the output voltage of the converter and the input voltage of the converter; the output ends of the output voltage acquisition unit and the input voltage acquisition unit are respectively connected to the two input ends of the comparison unit; the comparison unit generates a comparison current ICQ4 after comparison, and generates a detection current I1 after passing through the output mirror unit.
  • the design idea of the third current detection unit is to realize the output of the detection current I1 through the output voltage, the input voltage and a current source of a fixed size, and the detection current I1 can be compared with the amplified current I2 so that the circuit can output the state reversal control signal OUT3 based on whether the amplified current is greater than the detection current I1.
  • the third current detection unit further includes two inverters connected in series, the input ends of the inverters are respectively connected to the output ends of the second current detection unit and the third current detection unit; and the output ends of the inverters are connected to the logic unit.
  • FIG6 is an output schematic diagram of the third control signal in the third current detection unit in a DC-DC converter of the present invention.
  • the third control signal OUT3 can achieve a low level state, and if the detection current I1 is less than the amplified current I2, the third control signal OUT3 is a high level.
  • the circuit implements the working state according to the original logic of the logic unit.
  • the original logic here is the same as the previous text, and is used to characterize the control logic of the converter.
  • the control of the converter refers to the dynamic process of operating an element or a physical quantity in the production process of the electrical signal of the converter, and finally making a certain variable remain constant or move along a preset trajectory.
  • the control logic here may be implemented by open-loop logic or closed-loop logic.
  • the most commonly used implementation method in various power converters is to contain a logic unit in the converter to implement this control logic.
  • the logic unit can include various semiconductor devices, such as logic gate circuits, etc. to implement this control.
  • the ultimate goal is that the logic unit of the DC-DC converter can be used to directly or indirectly control the current, voltage, and inductance of the main components in the circuit. Through this control, the predetermined output of the DC-DC converter can be achieved.
  • the original logic premise of the present invention only limits OUT1, OUT2, and OUT3 in the present invention and is not included in the control of the converter by the logic unit.
  • the logic unit will control the gate of the power tube to turn off the high-end power tube (i.e., Mp0) and turn on the low-end power tube (i.e., Mn0), and the inductor current of the converter will gradually decrease.
  • the clock signal reaches the next cycle pulse, the high-end power tube will be turned on again, and the low-end power tube will be turned off again, causing the inductor current to rise again.
  • Fig. 5 is a schematic diagram of a part of the circuit in the third current detection unit in a DC-DC converter of the present invention.
  • the output voltage acquisition unit includes an operational amplifier OPA1, a voltage-dividing resistor R4 and a mirror MOS tube, which is used to generate a first comparison current Vout/R4 based on the positive phase input signal Vout of the operational amplifier OPA1;
  • the input voltage acquisition unit includes an operational amplifier OPA2, a voltage-dividing resistor R5 and a mirror MOS tube, which is used to generate a second comparison current Vin/R5 based on the positive phase input signal Vin of the operational amplifier OPA2.
  • the OPA1 negative feedback mode is connected to the gate source of the MOS tube.
  • the MOS tube is turned on, so that the negative input voltage is also equal to Vout.
  • the unit can generate Similarly, the current of the input voltage acquisition unit is .
  • the comparison unit includes a base control tube, primary symmetrical tubes Q2 and Q3, secondary symmetrical tubes Q1 and Q4, a primary current source Iref and a secondary current source Ix; wherein the gate of the base control tube is connected to the output end of the output voltage acquisition unit, the drain is connected to the power supply voltage, the source is respectively connected to the base of the primary symmetrical tubes Q2 and Q3 and one end of the primary current source Iref, and the other end of the primary current source Iref is grounded; the collectors of the primary symmetrical tubes Q2 and Q3 are connected to the power supply voltage, the emitter of Q2 is grounded after passing through the secondary current source Ix, and the collector of Q3 is connected to the output end of the input voltage acquisition unit; the bases of the secondary symmetrical tubes Q1 and Q4 are respectively connected to the emitters of the primary symmetrical tubes Q2 and Q3, and the emitters are respectively grounded, the collector of Q1 is connected to the output end of the output voltage acquisition unit and the gate of the base control
  • the comparison unit can input and compare the first comparison current and the second comparison current generated above.
  • the voltage is equal to the sum of the base emitter Vbe of the symmetrical tubes Q1 and Q2, and on the other hand, it can also be equal to the sum of the Vbe of the symmetrical tubes Q3 and Q4.
  • the emitter current of Q1 is approximately equal to the base current of Q1, which is the output current of the output voltage acquisition unit.
  • the emitter current of Q2 is equal to the current of the current source Ix.
  • the emitter current of Q3 is equal to the output current of the input voltage acquisition unit
  • the source current of Q4 is determined by Q1, Q2 and Q3.
  • the calculation formula is ,in is the threshold voltage of the transistor, is the collector current, It can be assumed that the four transistors Q1 to Q4 are of exactly the same model, so the threshold voltage and saturation current are also the same.
  • the output mirror unit also has a certain magnification ratio, and the magnification ratio is multiplied by the ratio of the current mirror , then the output current of the output mirror unit can be .
  • the maximum amplitude of the inductor current is limited to , so the load point Iload entering light load mode is limited to a constant ;in, is the magnification ratio of the output mirror unit and The product of .
  • the beneficial effect of the present invention is that, compared with the prior art, the DC-DC converter of the present invention can reasonably adjust the minimum value of IL, so that the circuit enters the light load working mode at a fixed load current point. Since this fixed load point does not change with the input and output voltages, it is more convenient for subsequent applications.

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Abstract

一种DC-DC转换器，包括模式切换单元、第一电流检测单元、第二电流检测单元、第三电流检测单元和逻辑模块；其中，模式切换单元用于将参考电压（V1）与误差放大器的输出电压（Vea）进行比较，以获得第一控制信号（OUT1）；第一电流检测单元用于生成第二控制信号（OUT2），第二电流检测单元和第三电流检测单元用于生成第三控制信号（OUT3）；逻辑单元，基于第一控制信号（OUT1）实现转换器轻载或重载工作状态的转换，基于第二控制信号（OUT2）和第三控制信号（OUT3）实现轻载工作状态下转换器中功率管的导通和关断状态的控制。

Description

一种DC-DC转换器
技术领域
本发明涉及集成电路领域，更具体地，涉及一种DC-DC转换器。
背景技术
DC-DC（Direct Current-Direct Current，直流-直流）转换器作为一种能够转变输入电压并有效输出固定电压的电压转换器在集成电路中被广泛应用。在升压转换器中，
DC-DC转换器能够提供轻载和重载两种不同的工作方式，以提高其适应性，满足更多不同类型后级负载的供电需求。现有技术中，当DC-DC转换器工作在轻载状态时，电感电流的峰值将会被钳位在一个固定的最小门限电流Ntrip上不再减小，同时转换器中功率管的开启或关断状态将会受到轻载工作模式的控制，在一个时段上实现电感电流的正常输出，而在下一个时段中则屏蔽电感电流的输出，通过循环往复实现对输出电压较为稳定的控制。在本发明中，将电感电流正常输出的时段称为输出间隔，而将电感电流无法输出的时段称为非输出间隔。
现有技术中，DC-DC转换器在实现轻载和重载工作模式的转换点是随输入输出电压变化的。由于DC-DC工作在轻载时输出纹波会较大，影响应用，因此有些应用会要求DC-DC轻载和重载的转换点是恒定的。而现有技术无法满足这类特殊应用。
因此，亟需一种新的DC-DC转换器。
发明内容
为解决现有技术中存在的不足，本发明的目的在于，提供一种DC-DC转换器，通过合理地调整电感电流的最小值，从而使DC-DC在合理的固定负载电流点进入轻载工作模式。
本发明采用如下的技术方案。
本发明涉及一种DC-DC转换器，包括时钟产生电路、逻辑单元、延迟单元、功率管、电感、输出电容、分压电阻和误差放大器，转换器还包括模式切换单元、第一电流检测单元、第二电流检测单元、第三电流检测单元和逻辑模块；其中，模式切换单元，用于将参考电压与误差放大器的输出电压Vea进行比较，以获得第一控制信号OUT1；第一电流检测单元用于生成第二控制信号OUT2，第二电流检测单元和第三电流检测单元，用于生成第三控制信号OUT3；逻辑单元，基于第一控制信号OUT1实现转换器轻载或重载工作状态的转换，基于第二控制信号OUT2和第三控制信号OUT3实现对转换器轻载工作状态下转换器中功率管的导通和关断状态的控制。
优选的，当第一控制信号OUT1处于高电平状态时，逻辑单元控制转换器进入轻载工作状态，电感电流以设定间隔被屏蔽或被输出；当电感电流处于输出间隔时，第二控制信号OUT2和第三控制信号OUT3控制高端功率管开启、低端功率管关断并使得电感电流幅度上升，或者控制高端功率管关断、低端功率管开启并使得电感电流幅度下降。
优选的，模式切换单元包括第一比较器COMP1，比较器COMP1的正相输入端接入参考电压V1、负相输入端接入误差放大器的输出电压Vea，输出端生成第一控制信号OUT1。
优选的，第一电流检测单元包括电流放大电路和第二比较器COMP2；其中，电流放大电路，用于采集电感电流后将其转化为检测电压OUT4并输出至第二比较器COMP2的正相输入端；第二比较器的负相输入端接入误差放大器的输出电压Vea，输出端生成第二控制信号OUT2，并输入至所述逻辑模块中优选的，第二电流检测单元，用于采集电感电流并依据转换系数 将其转换为放大电流I2，并将放大电流输入至第三电流检测单元。
优选的，第三电流检测单元中包括输出电压采集单元、输入电压采集单元、比较单元和输出镜像单元；其中，输出电压采集单元和输入电压采集单元的输入端分别接入转换器的输出电压和转换器的输入电压；输出电压采集单元和输入电压采集单元的输出端则分别接入至比较单元的两个输入端；比较单元实现比较后生成比较电流ICQ4，并通过输出镜像单元后生成检测电流I1。
优选的，第三电流检测单元中还包括两个串联的反相器，反相器的输入端分别接入第二电流检测单元的输出端和第三电流检测单元的输出端；反相器的输出端与逻辑单元连接。
优选的，输出电压采集单元包括运放OPA1、分压电阻R1和镜像MOS管，用于基于所述运放OPA1的正相输入信号Vout生成第一比较电流Vout/R1；输入电压采集单元包括运放OPA2、分压电阻R2和镜像MOS管，用于基于运放OPA2的正相输入信号Vin生成第二比较电流Vin/R2。
优选的，比较单元包括基极控制管、一级对称管Q2和Q3、二级对称管Q1和Q4、一级电流源Iref和二级电流源Ix；其中，基极控制管栅极与输出电压采集单元的输出端连接，漏极接电源电压，源极分别与一级对称管Q2和Q3的基极、一级电流源Iref的一端连接，一级电流源Iref的另一端接地；一级对称管Q2和Q3的集电极与电源电压连接，Q2的发射极经过二级电流源Ix后接地，Q3的集电极与所述输入电压采集单元的输出端连接；二级对称管Q1和Q4的基极分别与一级对称管Q2和Q3的发射极连接，发射极分别接地，Q1的集电极与输出电压采集单元的输出端、基极控制管的栅极连接，Q4的集电极与输出镜像单元的输入端连接；输出镜像单元中包括镜像MOS管。
优选的，比较单元的输出电流为 ；其中， ， 为二级电流源的输出电流。
优选的，当转换器处于轻载工作模式时，电感电流的最大幅值被限制为 ，且负载电流的最大幅值被限制为常量 。
本发明的有益效果在于，与现有技术相比，本发明中一种DC-DC转换器，能够通过合理地调整电感电流的最小值，从而使DC-DC在合理的固定负载电流点上进入轻载工作模式。
本发明的有益效果还包括：
1、本发明中仅采用了多个电流检测模块来实现对于功率管导通或关断状态的控制，并配合逻辑模块重载和轻载工作模式切换的原有工作逻辑，覆盖了轻载状态下功率管导通关断的控制信号，从而实现了对电感电流输出幅值的动态控制。本发明确保了电感电流即使是在轻载状态下仍然能够根据输出电压和输入电压的大小调节其自身幅度，从而确保了轻载状态下转换器对负载电路的匹配。
2、本发明中考虑到转换器输入功率和输出功率之间的守恒，从而巧妙地设计了第三电流检测单元中各项元件的参数，从而使得转换器能够在负载电流等于一个预先设定的固定电流值时发生翻转，达到了可以预知在哪个负载点进入轻载模式的目的，对输出纹波比较敏感的应用可以精确的避开这个负载点，无需再考虑输入和输出电压的影响。
附图说明
图1为本发明现有技术中DC-DC转换器的输出电压纹波示意图；
图2为本发明一种DC-DC转换器的原理示意图；
图3为本发明一种DC-DC转换器中第一电流检测单元的电路示意图；
图4为本发明一种DC-DC转换器中第二电流检测单元的电路示意图；
图5为本发明一种DC-DC转换器中第三电流检测单元中部分电路的示意图；
图6为本发明一种DC-DC转换器中第三电流检测单元中第三控制信号的输出原理图。
具体实施方式
下面结合附图对本申请作进一步描述。以下实施例仅用于更加清楚地说明本发明的技术方案，而不能以此来限制本申请的保护范围。
图1为本发明现有技术中DC-DC转换器的输出电压纹波示意图。如图1所示，在现有技术中，DC-DC转换器可以基于负载的状态实现轻载和重载两种不同的工作模式。当DC-DC转换器工作在重载状态时，电感电流的幅度可以根据负载电流的大小进行调节，并通过这种方式保持输出电压的稳定。而当后级负载所需电能较小时，DC-DC转换器可以进入轻载状态，在这种状态下，电感电流的幅度被钳位在最小门限电流Ntrip上，为了保持后级负载的工作状态，电感电流不能变得更小。此时，为了防止输出电压升高，DC-DC转换器可以通过电感电流的间隔输出确保总的输出功率较低。
 因此，在图1中，在输出间隔时段下，电感电流振荡输出，而输出电压随之缓慢升高。在非输出间隔时段下，电感电流被屏蔽，此时输出电压随之发生缓慢降低。在多个输出间隔和非输出间隔的循环往复下，输出电压会有一定幅度的波动，即在轻载模式下输出电压的纹波比重载时输出电压的纹波要大。对于一些对输出纹波比较敏感的应用，需要避开轻载模式，但是现有技术进入轻载模式的负载电流点是随输入和输出电压变化的，无法精确的预知进入轻载模式的负载电流点。
在本发明中，电路设计者希望能够精准地根据输入电压和输出电压两者的状态精准的实现轻载工作状态下转换器中功率管的导通或截止状态的切换，从而保证在固定的负载电流下进入轻载模式。因此，本发明提供了一种新的DC-DC转换器。
图2为本发明一种DC-DC转换器的原理示意图。如图2所示，一种DC-DC转换器，包括时钟产生电路、逻辑单元、延迟单元、功率管、电感、输出电容、分压电阻和误差放大器，并且，转换器还包括模式切换单元、第一电流检测单元、第二电流检测单元、第三电流检测单元和逻辑模块；模式切换单元，用于将参考电压与误差放大器的输出电压Vea进行比较，以获得第一控制信号OUT1；第一电流检测单元用于生成第二控制信号OUT2，第二电流检测单元和第三电流检测单元，用于生成第三控制信号OUT3；逻辑单元，基于第一控制信号OUT1实现转换器轻载或重载工作状态的转换，基于第二控制信号OUT2和第三控制信号OUT3实现转换器轻载工作状态下转换器中功率管的导通和关断状态的控制。
可以理解的是，在图2所示的电路中，第一控制信号OUT1与现有技术中轻载和重载工作状态的切换控制信号的作用类似，都能够控制电路在轻载和重载两种状态中进行切换。
在第一控制信号OUT1控制电路进入轻载模式的前提下，第二和第三控制信号OUT2和OUT3则可以对于电感电流在每个时钟周期内的上升过程的时长和下降过程的时长进行调节，从而使得无论后级负载处于任何状态下，转换器均能够自适应的实现轻载状态下的合理输出。
优选的，当第一控制信号OUT1处于高电平状态时，逻辑单元控制转换器进入轻载工作状态，电感电流以设定间隔被屏蔽或被输出；当电感电流处于输出间隔时，第二控制信号OUT2和第三控制信号OUT3控制高端功率管开启、低端功率管关断并使得电感电流幅度上升，或者控制高端功率管关断、低端功率管开启并使得电感电流幅度下降。
可以理解的是，当转换器处于轻载状态下时，本发明的思路中，希望根据包含电感电流大小信息的第二控制信号OUT2和包含输入电压、输出电压信息的第三控制信号OUT3进行比较，从而使得电路在输出电压和输入电压的比例高于一定程度时，电路中功率管的导通或关断状态会发生变化，从而使得电感电流从逐渐升高变为逐渐降低。
通过这种方式，第二控制信号OUT2和第三控制信号OUT3会控制功率管的状态，从而调节电感电流在每一个输出周期内的最大幅值。从根本上来说，根据功率守恒，转换器的输出电压、负载电流的乘积与输入电压、电感电流的乘积是相等的。因此上文中所述的输出电压和输入电压的比例变化与电感电流的最大幅值的变化在一定程度上被抵消，从而使得电路在灵活控制每个周期内电感电流的幅值后，实现了对负载电流每个周期内最大幅值的准确控制。
优选的，模式切换单元包括第一比较器COMP1，比较器COMP1的正相输入端接入参考电压V1、负相输入端接入误差放大器的输出电压Vea，输出端生成第一控制信号OUT1。
在该电路中，模式切换单元能够通过转换器中已有的误差放大器来实现反馈电压Vfb的采集。Vfb与一个参考电压Vref进行比较后，实现误差放大器的输出Vea。该输出电压Vea在通过与参考电压V1进行比较后，实现第一控制信号的输出。
具体来说，当Vfb也就是输出电压Vout的分压较大时，第一控制信号OUT1会处于高电平状态，此时电路会由重载切换至轻载状态。而当输出电压较低时，第一控制信号OUT1的输出也为低电平状态，则该低电平控制逻辑单元实现电路的重载工作模式。换言之，当第一控制信号OUT1在高电平状态的部分时间中，第一控制信号会同时屏蔽高端功率管和低端功率管的控制信号，使得两者均处于截止状态，此时电感电流不会输出，电路处于非输出间隔中。
优选的，第一电流检测单元包括电流放大电路和第二比较器COMP2；其中，电流放大电路，用于采集电感电流后将其转化为检测电压OUT4并输出至第二比较器COMP2的正相输入端；第二比较器的负相输入端接入误差放大器的输出电压Vea，输出端生成第二控制信号OUT2，并输入至逻辑模块中。
图3为本发明一种DC-DC转换器中第一电流检测单元的电路示意图。如图3所示，电流放大电路可以为一个电流镜和分压电阻组成的电路。其中，电流镜的一端MOS管Mn2与转换器的低端功率管Mn0之间通过镜像方式连接，也就是Mn0与Mn2的栅极相互连接，源极均接地。因此，电流镜能够接收到低端功率管的比例电流，也就是电感电流的比例电流。另外，该电流通过分压电阻后，分压电阻就能够实现基于电感电流发生变化的检测电压OUT4了。将该检测电压与误差放大器的输出电压Vea进行比较，可以生成第二控制信号OUT2。
具体来说，假设该第一电流检测单元输出电压对电感电流的放大倍数为 ，则当电感电流 输入后，第一电流检测单元输出电压为 。因此，当 大于Vea时，第二控制信号OUT2为高电平，反之为低电平。当第二控制信号OUT2为低电平时，电路中的逻辑模块执行原有的逻辑实现功率管的开关切换。而当第二控制信号OUT2的输出为高电平时，就需要判断另一个控制信号OUT3的状态了。这里提及的原有的逻辑，为转换器的自身控制逻辑，其中包括轻重载切换逻辑。
对于本发明来说，第一电流检测单元还可以采用现有技术中其他的电路来实现，只要能够实现电流的检测功能即可。
优选的，第二电流检测单元，用于采集电感电流后将其转换为放大电流I2，并将放大电流输入至第三电流检测单元。
图4为本发明一种DC-DC转换器中第二电流检测单元的电路示意图。如图4所示，第二电流检测单元可以由镜像单元构成，该镜像单元可以实现对转换器低端功率管漏极电流的镜像，也就是将电感电流镜像为放大电流I2。在本发明一实施例中，可以假设第二电流检测单元的放大倍数为 ，因此该单元的输出则变为 。
优选的，第三电流检测单元中包括输出电压采集单元、输入电压采集单元、比较单元和输出镜像单元；其中，输出电压采集单元和输入电压采集单元的输入端分别接入转换器的输出电压和转换器的输入电压；输出电压采集单元和输入电压采集单元的输出端则分别接入至比较单元的两个输入端；比较单元实现比较后生成比较电流ICQ4，并通过输出镜像单元后生成检测电流I1。
可以理解的是，第三电流检测单元的设计思路是通过输出电压、输入电压和一个固定大小的电流源实现检测电流I1的输出，而该检测电流I1则可以通过与放大电流I2进行比较从而电路能够基于放大电流是否大于检测电流I1而输出状态翻转的控制信号OUT3。
优选的，第三电流检测单元中还包括两个串联的反相器，反相器的输入端分别接入第二电流检测单元的输出端和第三电流检测单元的输出端；反相器的输出端与逻辑单元连接。
图6为本发明一种DC-DC转换器中第三电流检测单元中第三控制信号的输出原理图。如图6所示，当检测电流I1大于放大电流I2时，经过延时后，第三控制信号OUT3可以实现低电平状态，而如果检测电流I1小于放大电流I2，则第三控制信号OUT3为高电平。当第三控制信号OUT3为低电平时，电路根据逻辑单元的原有逻辑实现工作状态。这里的原有逻辑与前文相同，都是用来表征转换器的控制逻辑的。转换器的控制是指对转换器的电信号的生产过程中的一个元件或一个物理量进行操作，最终使得某一个变量保持恒定或沿预设轨迹运动的动态过程。通常，在半导体领域，我们将微电子学视为一个线性系统。这里的控制逻辑可能是通过开环逻辑或闭环逻辑实现的。而转换器中含有逻辑单元来实现这一控制逻辑是在各类电源转换器中最为常用的实现方式。逻辑单元中可以包括各种半导体器件，例如逻辑门电路等等来实施这种控制。最终的目的，DC-DC转换器的逻辑单元可以用来直接或间接的控制电路中主要元件的电流、电压、电感的取值。通过这种控制，就能够实现DC-DC转换器的预定输出。 而本发明中的原有逻辑的前提只限定本发明中的OUT1、OUT2和OUT3并不包含在逻辑单元对转换器的控制中。
而如果第二和第三控制信号OUT2和OUT3均为高电平时，转换器输入端的能量大于输出端，则逻辑单元会控制功率管的栅极实现高端功率管（也就是Mp0）的关断和低端功率管（也就是Mn0）的导通，此时转换器的电感电流将会逐渐降低。而当时钟信号到达下一个周期脉冲时，高端功率管才会重新开启，而低端功率管会重新关断，使得电感电流再次上升。
需要注意的是，当OUT1为高电平时，功率管NMOS和PMOS在部分时间同时关断。当OUT1为低电平时，OUT2和OUT3的功能如上段所述。
图5为本发明一种DC-DC转换器中第三电流检测单元中部分电路的示意图。如图5所示，优选的，输出电压采集单元包括运放OPA1、分压电阻R4和镜像MOS管，用于基于运放OPA1的正相输入信号Vout生成第一比较电流Vout/R4；输入电压采集单元包括运放OPA2、分压电阻R5和镜像MOS管，用于基于运放OPA2的正相输入信号Vin生成第二比较电流Vin/R5。
可以理解的是，在输出电压采集单元中，OPA1负反馈方式与MOS管的栅源极连接，当OPA1正相输入端电压为Vout时，MOS管导通，从而使得负相输入端电压也等于Vout，在电阻的作用下，该单元能够生成 的恒定电流。类似的，输入电压采集单元的电流为 。
优选的，比较单元包括基极控制管、一级对称管Q2和Q3、二级对称管Q1和Q4、一级电流源Iref和二级电流源Ix；其中，基极控制管栅极与输出电压采集单元的输出端连接，漏极接电源电压，源极分别与一级对称管Q2和Q3的基极、一级电流源Iref的一端连接，一级电流源Iref的另一端接地；一级对称管Q2和Q3的集电极与电源电压连接，Q2的发射极经过二级电流源Ix后接地，Q3的集电极与输入电压采集单元的输出端连接；二级对称管Q1和Q4的基极分别与一级对称管Q2和Q3的发射极连接，发射极分别接地，Q1的集电极与输出电压采集单元的输出端、基极控制管的栅极连接，Q4的集电极与输出镜像单元的输入端连接，输出镜像单元中包括镜像MOS管。
对于该电路来说，比较单元可以将上文中生成的第一比较电流和第二比较电流输入并进行比较。具体来说根据上述电路的连接方式，则可以分别采用两种不同的方法计算基极控制的源极电压。一方面，该电压等于对称管Q1和Q2的基极发射极Vbe之和，另一方面还可以等于对称管Q3和Q4的Vbe之和。
由此，可以列出如下等式：
由于基极控制管在输出电压采集单元输出端的作用下保持开启，因此其源极电压较高，能够充分保证对称管Q1至Q4的开启，因此，Q1的发射极电流约等于Q1的基极电流，也就是输出电压采集单元的输出电流 ，而Q2的发射极电流则等于电流源Ix的电流。类似的，Q3的发射极电流等于输入电压采集单元的输出电流 ，而Q4的源极电流则由Q1和Q2、Q3共同决定。
另外， 的计算公式为 ，其中 是晶体管的阈值电压， 为集电极电流， 为饱和电流。可以假设Q1至Q4四个晶体管型号完全相同，因此阈值电压和饱和电流的大小也相同。
因此，可以将上述公式进行如下转化： 对于上述公式进行化简，可得 由此可得
如果输出镜像单元也存在一定的放大比例，且该放大比例与 相乘等于该电流镜的比例 ，则该输出镜像单元的输出电流可以为 。
将放大电流I2和检测电流I1进行比较可以发现，当两者相等时，则有
由此可知，该电路的轻载模式中输出间隔与非输出间隔转换的时间点上，应当存在 。根据转换器的功率守恒，有 。
因此， 由于 和 都是可控的，是固定的，与输入输出电压无关，因此，进入轻载模式时的 大小是固定的。
优选的，当转换器处于轻载工作模式时，电感电流的最大幅值被限制为 ，因此进入轻载模式的负载点Iload被限制在常量 ；其中， 为输出镜像单元的放大比例与 的乘积。
本发明的有益效果在于，与现有技术相比，本发明中一种DC-DC转换器，能够通过合理的调节IL的最小值，从而在固定的负载电流点上使得电路进入轻载工作模式。由于此固定负载点不随输入输出电压变化，因此更便于后级的应用。
本发明申请人结合说明书附图对本发明的实施示例做了详细的说明与描述，但是本领域技术人员应该理解，以上实施示例仅为本发明的优选实施方案，详尽的说明只是为了帮助读者更好地理解本发明精神，而并非对本发明保护范围的限制，相反，任何基于本发明的发明精神所作的任何改进或修饰都应当落在本发明的保护范围之内。

Claims (10)

  1. 一种DC-DC转换器，包括时钟产生电路、逻辑单元、延迟单元、功率管、电感、输出电容、分压电阻和误差放大器，其特征在于：
    所述转换器还包括模式切换单元、第一电流检测单元、第二电流检测单元、第三电流检测单元和逻辑单元；
    其中，所述模式切换单元，用于将参考电压与误差放大器的输出电压Vea进行比较，以获得第一控制信号OUT1；
    所述第一电流检测单元用于生成第二控制信号OUT2，所述第二电流检测单元和所述第三电流检测单元，用于生成第三控制信号OUT3；
    所述逻辑单元，基于所述第一控制信号OUT1实现所述转换器轻载或重载工作状态的转换，基于所述第二控制信号OUT2和第三控制信号OUT3实现对所述转换器轻载工作状态下所述转换器中功率管的导通和关断状态的控制。
  2. 根据权利要求1中所述的一种DC-DC转换器，其特征在于：
    当所述第一控制信号OUT1处于高电平状态时，所述逻辑单元控制所述转换器进入轻载工作状态，所述电感电流以设定间隔被屏蔽或被输出；
    当所述电感电流处于输出间隔时，所述第二控制信号OUT2和第三控制信号OUT3控制高端功率管开启、低端功率管关断并使得所述电感电流幅度上升，或者控制高端功率管关断、低端功率管开启并使得所述电感电流幅度下降。
  3. 根据权利要求2中所述的一种DC-DC转换器，其特征在于：
    所述模式切换单元包括第一比较器COMP1，所述比较器COMP1的正相输入端接入参考电压V1、负相输入端接入误差放大器的输出电压Vea，输出端生成第一控制信号OUT1。
  4. 根据权利要求3中所述的一种DC-DC转换器，其特征在于：
    所述第一电流检测单元包括电流放大电路和第二比较器COMP2；其中，
    所述电流放大电路，用于采集电感电流后将其转化为检测电压OUT4并输出至第二比较器COMP2的正相输入端；
    所述第二比较器的负相输入端接入所述误差放大器的输出电压Vea，输出端生成第二控制信号OUT2，并输入至所述逻辑模块中；
    所述第二电流检测单元，用于采集电感电流并依据转换系数  将其转换为放大电流I2，并将所述放大电流输入至所述第三电流检测单元。
  5. 根据权利要求4中所述的一种DC-DC转换器，其特征在于：
    所述第三电流检测单元中包括输出电压采集单元、输入电压采集单元、比较单元和输出镜像单元；其中，
    所述输出电压采集单元和所述输入电压采集单元的输入端分别接入所述转换器的输出电压和所述转换器的输入电压；
    所述输出电压采集单元和所述输入电压采集单元的输出端则分别接入至所述比较单元的两个输入端；
    所述比较单元实现比较后生成比较电流ICQ4，并通过所述输出镜像单元后生成所述检测电流I1。
  6. 根据权利要求5中所述的一种DC-DC转换器，其特征在于：
    所述第三电流检测单元中还包括两个串联的反相器，所述反相器的输入端分别接入所述第二电流检测单元的输出端和所述第三电流检测单元的输出端；
    所述反相器的输出端与所述逻辑单元连接。
  7. 根据权利要求5中所述的一种DC-DC转换器，其特征在于：
    所述输出电压采集单元包括运放OPA1、分压电阻R4和镜像MOS管，用于基于所述运放OPA1的正相输入信号Vout生成第一比较电流Vout/R4；
    所述输入电压采集单元包括运放OPA2、分压电阻R5和镜像MOS管，用于基于所述运放OPA2的正相输入信号Vin生成第二比较电流Vin/R5。
  8. 根据权利要求7中所述的一种DC-DC转换器，其特征在于：
    所述比较单元包括基极控制管、一级对称管Q2和Q3、二级对称管Q1和Q4、一级电流源Iref和二级电流源Ix；其中，
    所述基极控制管栅极与所述输出电压采集单元的输出端连接，漏极接电源电压，源极分别与一级对称管Q2和Q3的基极、一级电流源Iref的一端连接，所述一级电流源Iref的另一端接地；
    所述一级对称管Q2和Q3的集电极与电源电压连接，Q2的发射极经过二级电流源Ix后接地，Q3的集电极与所述输入电压采集单元的输出端连接；
    所述二级对称管Q1和Q4的基极分别与一级对称管Q2和Q3的发射极连接，发射极分别接地，Q1的集电极与所述输出电压采集单元的输出端、基极控制管的栅极连接，Q4的集电极与所述输出镜像单元的输入端连接；
    所述输出镜像单元中包括镜像MOS管。
  9. 根据权利要求8中所述的一种DC-DC转换器，其特征在于：
    所述比较单元的输出电流为  ；
    其中，  ，  为所述二级电流源的输出电流。
  10. 根据权利要求9中所述的一种DC-DC转换器，其特征在于：
    当所述转换器处于轻载工作模式时，所述电感电流的最大幅值被限制为  ，且负载电流的最大幅值被限制为常量  。
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