CN111585435B - Control circuit of voltage converter and voltage converter - Google Patents
Control circuit of voltage converter and voltage converter Download PDFInfo
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- CN111585435B CN111585435B CN202010528713.0A CN202010528713A CN111585435B CN 111585435 B CN111585435 B CN 111585435B CN 202010528713 A CN202010528713 A CN 202010528713A CN 111585435 B CN111585435 B CN 111585435B
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- 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
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- 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
- H02M1/092—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 the control signals being transmitted optically
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- 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
- H02M1/36—Means for starting or stopping converters
Abstract
The invention provides a control circuit of a voltage converter and the voltage converter, wherein the control circuit comprises: the device comprises a reference voltage generating unit, a feedback loop and a control unit; the first input end of the reference voltage generating unit is connected with the input voltage of the voltage converter, the second input end of the reference voltage generating unit is connected with the output end of the control unit, and the output end of the reference voltage generating unit is connected with the first input end of the feedback loop so as to output the changed reference voltage to the feedback loop in the starting process of the voltage converter; and the output end of the control unit is used for outputting a driving signal so as to control the working state of the power transistor in the voltage converter. Therefore, the control circuit generates the changed reference voltage by using the driving signal of the voltage converter and adds the changed reference voltage into the whole soft start process, thereby avoiding the phenomena of uncontrolled and overshooting of the output current in the start process of the voltage converter.
Description
Technical Field
The invention relates to the technical field of voltage conversion, in particular to a control circuit of a voltage converter and the voltage converter.
Background
At present, the voltage converter is mainly subjected to soft start by the aid of a soft start function of a control unit, the scheme starts the voltage converter in an open-loop soft start mode, and the open-loop soft start mode is that after the voltage converter is electrified, the duty ratio of a control driving signal is controlled to be increased from small to large by the control unit until the output voltage of the voltage converter is equal to the reference voltage, and the soft start of the voltage converter is completed. When the load of the voltage converter is an inductive load or a resistive load, the soft start scheme can meet the requirement of soft start.
However, when the load of the voltage converter is a capacitive load, when the voltage converter is started according to the starting scheme, the output end of the voltage converter is in a short-circuit state when the voltage converter is started due to the existence of the output end capacitor, so that the phenomena of output current overshoot and uncontrolled are caused.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, a first object of the present invention is to provide a control circuit of a voltage converter, which generates a varying reference voltage by using a driving signal of the voltage converter and adds the varying reference voltage to the whole soft start process, so as to avoid the phenomena of uncontrolled and overshooting output current during the start process of the voltage converter.
A second object of the invention is to propose a voltage converter.
To achieve the above object, an embodiment of a first aspect of the present invention provides a control circuit for a voltage converter, including: the device comprises a reference voltage generating unit, a feedback loop and a control unit; a first input end of the reference voltage generating unit is connected with an input voltage of the voltage converter, a second input end of the reference voltage generating unit is connected with an output end of the control unit, and an output end of the reference voltage generating unit is connected with a first input end of a feedback loop so as to output a changed reference voltage to the feedback loop in the starting process of the voltage converter; the second input end of the feedback loop is connected with the output end of the voltage converter; the input end of the control unit is connected with the output end of the feedback loop, and the output end of the control unit is used for outputting a driving signal so as to control the working state of a power transistor in the voltage converter.
According to the control circuit of the voltage converter, the reference voltage generating unit generates the changed reference voltage by using the driving signal of the voltage converter, and outputs the changed reference voltage to the feedback loop in the starting process of the voltage converter, so that the feedback loop controls the driving signal of the output end of the control unit according to the changed reference voltage, and the working state of the power transistor in the voltage converter is controlled by the driving signal. Therefore, the control circuit generates the changed reference voltage by using the driving signal of the voltage converter and adds the changed reference voltage into the whole soft start process, thereby avoiding the phenomena of uncontrolled and overshooting of the output current in the start process of the voltage converter.
In addition, the control circuit of the voltage converter according to the above embodiment of the present invention may further have the following additional technical features:
according to an embodiment of the present invention, the reference voltage generating unit includes: the circuit comprises a first resistor, a first photoelectric coupler and a transistor; one end of the first resistor is connected with the input voltage of the voltage converter, and the other end of the first resistor is connected with the first input end of the first photoelectric coupler and the first end of the transistor; a second input end of the first photoelectric coupler is connected with a power ground, a first output end of the first photoelectric coupler is connected with a first input end of the feedback loop, and a second output end of the first photoelectric coupler is connected with a signal ground; the second end of the transistor is connected with a power ground, and the control end of the transistor is connected with the output end of the control unit.
According to an embodiment of the present invention, the reference voltage generating unit further includes: a voltage regulator diode and a first capacitor; the anode of the voltage stabilizing diode is connected with the output end of the control unit, and the cathode of the voltage stabilizing diode is connected with the control end of the transistor; one end of the first capacitor is connected with the control end of the transistor, and the other end of the first capacitor is connected with the power ground.
According to an embodiment of the invention, the feedback loop comprises: the operational amplifier, a second capacitor, a second resistor and a third capacitor; a first input end of the operational amplifier is connected with an output end of the reference voltage generating unit, a second input end of the operational amplifier and an output end of the voltage converter are connected with one end of the second capacitor, which is connected with the output end of the operational amplifier, and one end of the third capacitor, and the other end of the second capacitor is connected with one end of the second resistor; the other end of the second resistor is connected with a second input end of the operational amplifier and the other end of the third capacitor; one end of the third capacitor is connected with the output end of the operational amplifier, and the other end of the third capacitor is connected with the second input end of the operational amplifier.
According to an embodiment of the present invention, the control circuit of the voltage converter further includes: a third resistor and a voltage stabilizer; one end of the third resistor is connected with the input voltage of the voltage converter, and the other end of the third resistor is connected with the first input end of the feedback loop and the first end of the voltage stabilizer; the second end of the voltage stabilizer is connected with a signal ground, and the third end of the voltage stabilizer is connected with the first input end of the feedback loop.
According to an embodiment of the present invention, the control circuit of the voltage converter further includes: one end of the fourth capacitor is connected with the third end of the voltage stabilizer, and the other end of the fourth capacitor is connected with a signal ground.
According to an embodiment of the present invention, the control circuit of the voltage converter further includes: a second photoelectric coupler and a diode; a first input end of the second photoelectric coupler is connected with the input voltage of the voltage converter, a second input end of the second photoelectric coupler is connected with the anode of the diode, a first output end of the second photoelectric coupler is connected with the input end of the control unit, and a second output end of the second photoelectric coupler is connected with the power ground; the other pole of the diode is connected with the output end of the feedback loop.
According to an embodiment of the present invention, the control circuit of the voltage converter further includes: a fifth capacitor and a sixth capacitor; one end of the fifth capacitor is connected with the input voltage of the voltage converter, and the other end of the fifth capacitor is connected with a power ground; one end of the sixth capacitor is connected with the soft start control end of the control unit, and the other end of the sixth capacitor is connected with a power ground.
According to an embodiment of the present invention, the control circuit of the voltage converter further includes: a fourth resistor, and a fifth resistor; one end of the fourth resistor is connected with the input voltage of the voltage converter, and the other end of the fourth resistor is connected with the first input end of the second photoelectric coupling unit and one end of the fifth resistor; one end of the fifth resistor is connected with the first input end of the second photoelectric coupling unit, and the other end of the fifth resistor is connected with the second input end of the second photoelectric coupling unit.
To achieve the above object, a second embodiment of the present invention provides a voltage converter, which includes the control circuit of the voltage converter of the first embodiment of the present invention.
According to the voltage converter provided by the embodiment of the invention, the control circuit of the voltage converter provided by the embodiment of the invention utilizes the driving signal of the voltage converter to generate the changed reference voltage, and the changed reference voltage is added into the whole soft start process, so that the phenomena of uncontrolled and overshooting of the output current are avoided in the starting process of the voltage converter.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a block diagram of a control circuit of a voltage converter according to an embodiment of the present invention;
FIG. 2 is a circuit diagram of a reference voltage generating unit according to one embodiment of the present invention;
FIG. 3 is a circuit diagram of a feedback loop according to one embodiment of the present invention;
FIG. 4 is a schematic diagram of the connection of a voltage regulator of the control circuit of the voltage converter according to one example of the invention;
FIG. 5 is a circuit diagram of a control circuit of a voltage converter according to one example of the present invention;
FIG. 6 is a waveform schematic diagram of a prior art voltage converter for soft start;
FIG. 7 is a waveform diagram illustrating a voltage converter performing soft start according to one embodiment of the present invention;
fig. 8 is a block diagram of a voltage converter according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
A control circuit of a voltage converter and a voltage converter of an embodiment of the present invention are described below with reference to the drawings.
Fig. 1 is a block diagram of a control circuit of a voltage converter according to an embodiment of the present invention.
As shown in fig. 1, the control circuit 100 includes: a reference voltage generating unit 10, a feedback loop 20, and a control unit 30.
Wherein, a first input terminal of the reference voltage generating unit 10 is connected with an input voltage of the voltage converter, a second input terminal of the reference voltage generating unit 10 is connected with an output terminal of the control unit 30, and an output terminal of the reference voltage generating unit 10 is connected with a first input terminal of the feedback loop 20, so as to output a changed reference voltage to the feedback loop 20 during the starting process of the voltage converter; a second input of the feedback loop 20 is connected to the output of the voltage converter; an input terminal of the control unit 30 is connected to an output terminal of the feedback loop 20, and an output terminal of the control unit 30 is used for outputting a driving signal to control an operating state of a power transistor in the voltage converter. The driving signal may be a PWM (Pulse Width Modulation) signal, that is, the control unit 30 controls the operating state of the power transistor in the voltage converter according to a duty ratio of the PWM signal.
It should be noted that the voltage converter in the embodiment of the present invention may be an isolated switching power supply or a non-isolated switching power supply, wherein when the voltage converter is an isolated switching power supply, the first input terminal of the reference voltage generating unit 10 is connected to the primary voltage 12VP of the input voltage of the voltage converter. The voltage converter realizes the conversion of voltage through the power transistor, namely, the voltage input into the voltage converter is converted according to the actual requirement and then output, and before that, the control circuit 100 of the voltage converter of the embodiment of the invention controls the voltage converter to carry out soft start.
Specifically, at the time of starting the voltage converter, the reference voltage generating unit 10 generates a varying reference voltage VREF according to an input voltage of the voltage converter and a driving signal output by the control unit 30, and outputs the varying reference voltage VREF to the feedback loop 20, the feedback loop 20 controls a voltage of a second input terminal thereof (i.e., an output terminal of the voltage converter) by controlling (adjusting) a voltage of an output terminal thereof, the control unit 30 outputs the driving signal to the reference voltage generating unit 10 according to the voltage output by the output terminal of the feedback loop 20, so that the reference voltage VREF output by the reference voltage generating unit 10 is raised from 0 to a target value of the reference voltage, when the voltage of the second input terminal of the feedback loop 20 (i.e., the output terminal of the voltage converter) and the reference voltage VREF simultaneously reach the same voltage magnitude, a soft start process of the voltage converter is completed, during the start-up process, since the reference voltage VREF rises from 0 to the target value of the reference voltage, the output current of the voltage converter gradually increases from 0A with the changing reference voltage.
Compared with the scheme of the prior art that the voltage converter is only subjected to soft start by depending on the soft start function of the control unit, the control circuit of the voltage converter of the embodiment of the invention is provided with the reference voltage generating unit 10, so that the reference voltage generating unit 10 outputs the changed reference voltage VREF to the feedback loop 20 according to the driving signal of the voltage converter, and the feedback loop 20 acts earlier, thereby realizing the closed-loop soft start of the voltage converter.
Therefore, the control circuit generates the changed reference voltage by using the driving signal of the voltage converter and adds the changed reference voltage into the whole soft start process, thereby avoiding the phenomena of uncontrolled and overshooting of the output current in the start process of the voltage converter.
It should be noted that, in the prior art, a scheme of performing soft start on a voltage converter by simply depending on a soft start function of a control unit itself has the following disadvantages when a load of the voltage converter is a capacitive load: when the duty ratio of a driving signal of the voltage converter reaches the maximum or the working frequency reaches the minimum, the output signal VO is still smaller than the reference voltage VREF, and then the converter transmits energy to an output end under the maximum duty ratio or the minimum working frequency, so that output current overshoots and is not controlled; when the capacitive load is fully charged, the converter will operate in Burst mode, and the soft start function of the control unit itself is disabled every time a driving signal is present, so that the converter always delivers energy to the output terminal at the maximum duty cycle or the minimum operating frequency, causing the output current to overshoot and be uncontrolled.
Therefore, the present invention solves the problem of output current overshoot and uncontrolled output current in the prior art through the following embodiments.
In one embodiment of the present invention, as shown in fig. 2, the reference voltage generating unit 10 includes: the circuit comprises a first resistor R1, a first photoelectric coupler OC1 and a transistor Q1; one end of the first resistor R1 is connected to the input voltage of the voltage converter, and the other end of the first resistor R1 is connected to the first input end of the first photocoupler OC1 and the first end of the transistor Q1; a second input end of the first photoelectric coupler OC1 is connected to a power ground PWRGND, a first output end of the first photoelectric coupler OC1 is connected to a first input end of the feedback loop 20, and a second output end of the first photoelectric coupler OC1 is connected to a signal ground AGND; a second terminal of the transistor Q1 is connected to the power ground PWRGND, and a control terminal of the transistor Q1 is connected to the output terminal of the control unit 30.
The transistor Q1 may be a MOS (Metal Oxide Semiconductor) transistor, and the first end of the transistor Q1 may be a drain, the second end may be a source, and the control end is a gate.
When the voltage converter is an isolated voltage converter (isolated switching power supply), one end of the first resistor R1 is connected to the primary voltage 12VP of the input voltage of the voltage converter. The first output terminal of the first photo coupler OC1 outputs the varying reference voltage VREF until the reference voltage VREF reaches its target value.
Further, the reference voltage generating unit 10 further includes: a zener diode ZD and a first capacitor C1; wherein, the anode of the zener diode ZD is connected to the output end of the control unit 30, and the cathode of the zener diode ZD is connected to the control end of the transistor Q1; one end of the first capacitor C1 is connected to the control terminal of the transistor Q1, and the other end of the first capacitor C1 is connected to the power ground PWRGND. The output end of the control unit 30 outputs a driving signal OUT, and sends the driving signal OUT to the anode of the zener diode ZD.
Specifically, when the voltage converter is turned on, firstly, the driving signal OUT is not generated (i.e., the driving signal is a low-level signal), that is, the duty ratio of the driving signal OUT is 0, and further, due to the generation of the input voltage of the voltage converter, a current flows through the primary side of the first photocoupler OC1, the value of the current is determined by the input voltage of the voltage converter and the magnitude of the first resistor R1, due to the characteristics of the first photocoupler OC1, when a current flows through the primary side, the secondary side is in saturated conduction and presents a low impedance characteristic, and at this time, the reference voltage VREF is pulled down to 0V by the first photocoupler OC 1.
Then, the driving signal OUT of the voltage converter is generated, and the duty ratio of the driving signal OUT is changed from the minimum to the maximum direction or the operating frequency is changed from the maximum to the minimum direction. After a first driving signal (high-level signal) is generated, the peak value formed by the voltage-stabilizing diode ZD and the first capacitor C1 is used for keeping current, the level of the first capacitor C1 is high level, then the transistor Q1 is turned on, the first photoelectric coupler OC1 is short-circuited, and at this time, the reference voltage VREF starts to be controlled to be increased from 0V to the target value of the reference voltage VREF, so that the closed-loop soft start of the voltage converter is realized, in the process, the feedback loop 20 already starts to adjust the output signal of the voltage converter, and the purpose of limiting the duty ratio or the working frequency change of the driving signal is achieved.
And finally, when the amplitudes of the output signal VO and the reference voltage VREF of the voltage converter reach the same target value at the same time, the duty ratio or the working frequency of the driving signal OUT is fixed, so that the floppy drive starting process is finished.
Therefore, in the soft start process, the output current of the voltage converter is slowly increased along with the change trend of the reference voltage from 0A, so that the phenomenon that the output signal VO is still smaller than the reference voltage VREF when the duty ratio of the driving signal OUT of the voltage converter reaches the maximum or the working frequency reaches the minimum is avoided, and the output current is completely controlled and has no overshoot; when the capacitive load is fully charged, the converter works in a Burst mode, and the phenomena of output current overshoot and uncontrolled are avoided when a driving signal OUT appears every time.
In one embodiment of the present invention, as shown in fig. 3, the feedback loop 20 comprises: an operational amplifier OPA, a second capacitor C2, a second resistor R2 and a third capacitor C3; wherein a first input terminal of the operational amplifier OPA is connected to the output terminal of the reference voltage generating unit 10, and a second input terminal of the operational amplifier OPA is connected to the output terminal of the voltage converter; one end of the second capacitor C2 is connected to the output end of the operational amplifier OPA and one end of the third capacitor C3, and the other end of the second capacitor C2 is connected to one end of the second resistor R2; the other end of the second resistor R2 is connected with the second input end of the operational amplifier OPA and the other end of the third capacitor C3; one end of the third capacitor C3 is connected to the output terminal of the operational amplifier OPA, and the other end of the third capacitor C3 is connected to the second input terminal of the operational amplifier OPA. The first input terminal of the operational amplifier OPA is a non-inverting input terminal, and the second input terminal of the operational amplifier OPA is an inverting input terminal.
Specifically, in the process that the reference voltage VREF rises from 0V to the target value, the feedback loop 20 adjusts parameters of the second capacitor C2, the second resistor R2 and the third capacitor C3 according to the output signal of the operational amplifier OPA to adjust the output signal VO of the voltage converter until the amplitudes of the output signal VO and the reference voltage VREF reach the same target value at the same time. That is, in this embodiment, a feedback loop 20 is provided at the output of the voltage converter to achieve a closed-loop soft start of the voltage converter by adjusting the feedback parameter of the feedback loop 20.
Compared with the prior art in which the target value of the reference voltage VREF is directly input to the first input terminal of the feedback loop, the embodiment enables the feedback loop to function earlier, thereby achieving the purpose of closed-loop soft start.
In an embodiment of the present invention, as shown in fig. 4, the control circuit 100 of the voltage converter may further include: a third resistor R3 and a voltage regulator T; one end of the third resistor R3 is connected to the input voltage of the voltage converter, and the other end of the third resistor R3 is connected to the first input terminal of the feedback loop 20 and the first end of the regulator T; the second terminal of the regulator T is connected to the signal ground AGND, and the third terminal of the regulator T is connected to the first input terminal of the feedback loop 20. Wherein the model of the voltage regulator T may be TL431 AIDBZ.
When the voltage converter is an isolated voltage converter (isolated switching power supply), one end of the third resistor R3 is connected to the secondary side voltage 12VS of the input voltage of the voltage converter.
Further, referring to fig. 2, the control circuit 100 of the voltage converter may further include a fourth capacitor C4, one end of the fourth capacitor C4 is connected to the third terminal of the regulator T, and the other end of the fourth capacitor C4 is connected to the signal ground AGND.
Specifically, when the first photo coupler OC1 of the reference voltage generating unit 10 is shorted out by the transistor Q1, the input voltage of the voltage converter starts to charge the fourth capacitor C4 through the third resistor R3, so that the voltage across the fourth capacitor C4 rises from 0V to its target value.
In an example of the present invention, as shown in fig. 5, the control circuit 100 of the voltage converter may further include: a second photocoupler OC2 and a diode VD; a first input end of the second photoelectric coupler OC2 is connected with the input voltage of the voltage converter, a second input end of the second photoelectric coupler OC2 is connected with the anode of the diode VD, a first output end of the second photoelectric coupler OC2 is connected with the input end of the control unit, and a second output end of the second photoelectric coupler OC2 is connected with a power ground PWRGND; and the cathode of the diode VD is connected with the output end of the feedback loop.
Referring to fig. 5, the control circuit 100 of the voltage converter may further include: a fifth capacitor C5 and a sixth capacitor C6; one end of the fifth capacitor C5 is connected with the input voltage of the voltage converter, and the other end of the fifth capacitor C5 is connected with the power ground PWRGND; one end of the sixth capacitor C6 is connected to the soft-start control terminal SS of the control unit 10, and the other end of the sixth capacitor is connected to the power ground PWRGND.
When the voltage converter is an isolated voltage converter (isolated switching power supply), one end of the fifth capacitor C5 and the first input VCC of the control unit 30 are respectively connected to the primary side voltage 12VP of the input voltage of the voltage converter, and one end of the fourth resistor R4 is connected to the secondary side voltage 12VS of the input voltage of the voltage converter.
The operation principle of the control circuit 100 of the voltage converter of this example is described below with reference to fig. 4 and 5:
when the voltage converter is started, firstly, the primary side voltage 12VP and the secondary side voltage 12VS of the voltage converter are generated simultaneously to charge the sixth capacitor C6 and the fourth capacitor C4 respectively, so that the voltage across the sixth capacitor C6 rises from 0V to its target value (the target value can be determined by the characteristics of the control unit 10 itself), because of the existence of the first photocoupler OC1 and the driving signal OUT of the voltage converter is not generated at this time, and the reference voltage generating unit 10 takes the driving signal OUT of the voltage converter as a control signal, when there is no driving signal OUT, the primary side of the first photocoupler OC1 flows a current whose value is determined by the sizes of the primary side voltage 12VP of the input voltage of the voltage converter and the first resistor R1 together, because of the characteristics of the first photocoupler OC1 itself, when there is a current flowing through the primary side, the secondary side is in saturated conduction, it presents a low impedance characteristic, and at this time, the reference voltage VREF is pulled down to 0V by the first photo coupler OC1, that is, in fig. 4, the voltage across the fourth capacitor C4 is always at a low level of 0V.
Then, the control unit 10 starts to charge the soft-start control terminal SS, when the soft-start control terminal SS is charged to a certain voltage, the driving signal OUT of the voltage converter is generated, and the duty ratio of the driving signal OUT changes from the minimum to the maximum or the operating frequency changes from the maximum to the minimum along with the rise of the voltage of the soft-start control terminal SS. When the first driving signal OUT (high level signal) is generated, the peak holding current formed by the zener diode ZD and the first capacitor C1 is passed, the level of the first capacitor C1 is high level, and the transistor Q1 is turned on, the first photocoupler OC1 is short-circuited, and at this time, the secondary side voltage 12VS of the voltage converter starts to charge the fourth capacitor C4 through the third resistor R3, so that the voltage across the fourth capacitor C4 rises from 0V to its target value. In the process, the feedback loop 20 has already started to regulate the output signal VO of the voltage converter, and the output signal of the operational amplifier OPA regulates the voltage of the COMP end of the control unit (the input end of the control unit 10) through the second photocoupler OC2, so as to achieve the purpose of limiting the duty ratio or the working frequency variation of the driving signal OUT. The charging process in which the reference voltage VREF rises from 0V to the target value is a closed-loop soft start process of the voltage converter.
Finally, when the amplitudes of the output signal VO and the reference voltage VREF of the voltage converter reach the same target value at the same time, the duty ratio or the operating frequency of the driving signal OUT is fixed, and thus, the soft start process is completed. The output current of the voltage converter is slowly increased along with the change trend of the reference voltage VREF from 0A, the output current does not overshoot and is completely controlled.
That is, the control circuit 100 of the voltage converter according to the embodiment of the present invention implements the closed-loop soft start of the voltage converter, and at the start, causes the reference voltage VREF to gradually increase from 0V to its target value at the beginning of the first pulse generated by the driving signal, thereby causing the output current to gradually change from 0A to its target value following the change of the reference voltage VREF.
It should be noted that, as described above, the controlled object for performing the closed-loop soft start in the embodiment of the present invention is the output current of the voltage converter, and the reference object of the controlled object is the reference voltage VREF. Besides, the controlled object of the embodiment of the present invention may also be the output voltage or the output power of the voltage converter.
Fig. 6 is a waveform diagram illustrating a soft start of a voltage converter according to the prior art, and fig. 7 is a waveform diagram illustrating a soft start of a voltage converter according to a specific example of the present invention.
In a specific example, a phase-shift full-bridge circuit with power of 2.5kW is used as a voltage converter, the input voltage Vin of the circuit is 400V, the output voltage Vo of the circuit is 700V, and the load capacitance Co of the circuit is 10mF, and a start waveform (including a charging current waveform, a driving signal waveform and an output voltage waveform of the voltage converter) for starting the phase-shift full-bridge circuit by the control circuit 100 of the voltage converter, that is, a waveform shown in fig. 7 is compared with a start waveform for starting the phase-shift full-bridge circuit by the control circuit 100 without the voltage converter, that is, a waveform shown in fig. 6, so that: referring to fig. 6, without the control circuit 100, the set output current point is 6A, and the actually measured output current peak value has 12A, i.e. the output current overshoots; referring to fig. 7, the output current is gradually increased from 0A after the control circuit 100 is added, and the output current is completely controlled without overshoot.
In summary, the control circuit generates the changed reference voltage by using the driving signal of the voltage converter, and adds the changed reference voltage into the whole soft start process, thereby avoiding the phenomena of uncontrolled and overshooting of the output current in the start process of the voltage converter.
In order to implement the above embodiments, the present invention further provides a voltage converter, and fig. 8 is a block diagram of a voltage converter according to an embodiment of the present invention.
As shown in fig. 8, the voltage converter 1000 includes the control circuit 100 of the voltage converter of the present invention described above.
The voltage converter generates the changed reference voltage by using the driving signal of the voltage converter through the control circuit of the voltage converter of the embodiment of the invention, and adds the changed reference voltage into the whole soft start process, thereby avoiding the phenomena of uncontrolled and overshooting output current in the start process of the voltage converter.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (8)
1. A control circuit for a voltage converter, comprising: the device comprises a reference voltage generating unit, a feedback loop and a control unit;
a first input end of the reference voltage generating unit is connected with an input voltage of the voltage converter, a second input end of the reference voltage generating unit is connected with an output end of the control unit, and an output end of the reference voltage generating unit is connected with a first input end of a feedback loop so as to output a changed reference voltage to the feedback loop in the starting process of the voltage converter;
the reference voltage generating unit includes: the circuit comprises a first resistor, a first photoelectric coupler and a transistor; one end of the first resistor is connected with the input voltage of the voltage converter, and the other end of the first resistor is connected with the first input end of the first photoelectric coupler and the first end of the transistor; a second input end of the first photoelectric coupler is connected with a power ground, a first output end of the first photoelectric coupler is connected with a first input end of the feedback loop, and a second output end of the first photoelectric coupler is connected with a signal ground; the second end of the transistor is connected with a power ground, and the control end of the transistor is connected with the output end of the control unit;
the second input end of the feedback loop is connected with the output end of the voltage converter;
the feedback loop, comprising: the operational amplifier, a second capacitor, a second resistor and a third capacitor; the first input end of the operational amplifier is connected with the output end of the reference voltage generating unit, and the second input end of the operational amplifier is connected with the output end of the voltage converter; one end of the second capacitor is connected with the output end of the operational amplifier and one end of the third capacitor, and the other end of the second capacitor is connected with one end of the second resistor; the other end of the second resistor is connected with a second input end of the operational amplifier and the other end of the third capacitor; one end of the third capacitor is connected with the output end of the operational amplifier, and the other end of the third capacitor is connected with the second input end of the operational amplifier;
the input end of the control unit is connected with the output end of the feedback loop, and the output end of the control unit is used for outputting a driving signal so as to control the working state of a power transistor in the voltage converter.
2. The control circuit of claim 1, wherein the reference voltage generating unit further comprises: a voltage regulator diode and a first capacitor;
the anode of the voltage stabilizing diode is connected with the output end of the control unit, and the cathode of the voltage stabilizing diode is connected with the control end of the transistor;
one end of the first capacitor is connected with the control end of the transistor, and the other end of the first capacitor is connected with the power ground.
3. The control circuit of claim 1, further comprising: a third resistor and a voltage stabilizer;
one end of the third resistor is connected with the input voltage of the voltage converter, and the other end of the third resistor is connected with the first input end of the feedback loop and the first end of the voltage stabilizer;
the second end of the voltage stabilizer is connected with a signal ground, and the third end of the voltage stabilizer is connected with the first input end of the feedback loop.
4. The control circuit of claim 3, further comprising:
one end of the fourth capacitor is connected with the third end of the voltage stabilizer, and the other end of the fourth capacitor is connected with a signal ground.
5. The control circuit of claim 1, further comprising: a second photoelectric coupler and a diode;
a first input end of the second photoelectric coupler is connected with the input voltage of the voltage converter, a second input end of the second photoelectric coupler is connected with the anode of the diode, a first output end of the second photoelectric coupler is connected with the input end of the control unit, and a second output end of the second photoelectric coupler is connected with the power ground;
and the cathode of the diode is connected with the output end of the feedback loop.
6. The control circuit of claim 1, further comprising: a fifth capacitor and a sixth capacitor;
one end of the fifth capacitor is connected with the input voltage of the voltage converter, and the other end of the fifth capacitor is connected with a power ground;
one end of the sixth capacitor is connected with the soft start control end of the control unit, and the other end of the sixth capacitor is connected with a power ground.
7. The control circuit of claim 5, further comprising: a fourth resistor, and a fifth resistor;
one end of the fourth resistor is connected with the input voltage of the voltage converter, and the other end of the fourth resistor is connected with the first input end of the second photoelectric coupler and one end of the fifth resistor;
one end of the fifth resistor is connected with the first input end of the second photoelectric coupler, and the other end of the fifth resistor is connected with the second input end of the second photoelectric coupler.
8. A voltage converter, characterized in that it comprises a control circuit of a voltage converter according to any of claims 1-7.
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| CN207542990U (en) * | 2017-10-31 | 2018-06-26 | 长沙广义变流技术有限公司 | A kind of soft starting circuit based on TL431 closed-loop controls |
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