CN113595398B - Control device and control method - Google Patents

Control device and control method Download PDF

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Publication number
CN113595398B
CN113595398B CN202110747537.4A CN202110747537A CN113595398B CN 113595398 B CN113595398 B CN 113595398B CN 202110747537 A CN202110747537 A CN 202110747537A CN 113595398 B CN113595398 B CN 113595398B
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Prior art keywords
flyback converter
auxiliary switch
signal
negative current
control
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CN113595398A (en
Inventor
宋海斌
章进法
许道飞
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Delta Electronics Shanghai Co Ltd
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Delta Electronics Shanghai Co Ltd
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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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • 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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • 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

Abstract

The present disclosure relates to a control apparatus and control method for a flyback converter including an auxiliary switch. The control device includes: the on-time setting unit is used for setting an on-time threshold according to the exciting negative current reference value and the output voltage of the flyback converter; and the on-time control unit is used for outputting a control signal to control the on of the auxiliary switch, and turning off the auxiliary switch when the on-time of the auxiliary switch reaches the on-time threshold. The method and the device can realize zero-voltage turn-on of the primary side switching tube of the flyback converter under different output voltages.

Description

Control device and control method
The present application is a divisional application of patent application number 201710524232.0 entitled "control apparatus and control method", which is incorporated herein by reference in its entirety.
Technical Field
The disclosure relates to the technical field of power electronics, in particular to a control device and a control method applied to a flyback converter.
Background
Currently, quasi-resonant flyback converters are the most popular circuit topologies for low-power switching power supplies. Quasi-resonant flyback converter is provided at low voltage input (V bus <nV o Wherein: v (V) bus Is the input voltage; n is the turns ratio of the primary side coil and the secondary side coil of the transformer; v (V) o For output voltage) can be achieved Zero Voltage Switching (ZVS) of the primary side power switching transistor, at high voltage input (V bus >nV o ) The valley opening of the primary side power switch tube can be realized when the primary side power switch tube is in the open state, therebySwitching losses can be significantly reduced. However, with the development of high frequency, although the quasi-resonant flyback converter can realize valley opening at the time of high-voltage input, the opening loss becomes larger and larger, and the efficiency of the converter is seriously affected. In order to solve the problem that the quasi-resonant flyback converter can not completely realize zero voltage turn-on (ZVS) of a primary side power switch tube during high-voltage input, the prior art proposal provides a new control method for delay turn-on of a secondary side synchronous rectifying tube and the like, and a new circuit topological structure for an active clamp flyback converter and the like.
However, the prior art solution is only suitable for the case of constant output voltage, and cannot ensure that zero-voltage turn-on of the primary side power switch tube can be realized under all working conditions under the application condition of variable output voltage.
It should be noted that the information disclosed in the above background section is only for enhancing understanding of the background of the present disclosure and thus may include information that does not constitute prior art known to those of ordinary skill in the art.
Disclosure of Invention
It is an object of the present disclosure to provide a control apparatus and a control method, which overcome, at least in part, one or more of the problems due to the limitations and disadvantages of the related art.
According to one aspect of the present disclosure, there is provided a control device for use in a flyback converter, the flyback converter including an auxiliary switch, the control device comprising:
the on-time setting unit is used for setting an on-time threshold according to an exciting negative current reference value and the output voltage of the flyback converter; and
and the on-time control unit is used for outputting a control signal to control the on of the auxiliary switch, and turning off the auxiliary switch when the on-time of the auxiliary switch reaches the on-time threshold.
In one exemplary embodiment of the present disclosure, the flyback converter is an RCD clamped flyback converter or an active clamped flyback converter.
In an exemplary embodiment of the present disclosure, the auxiliary switch is a synchronous rectifier, a clamp, a switch connected in parallel to a secondary side rectifier unit of the flyback converter, or a switch connected in series to an auxiliary winding of the flyback converter.
In an exemplary embodiment of the present disclosure, the on-time control unit is configured to output the control signal according to a timing start signal.
In an exemplary embodiment of the present disclosure, the flyback converter is operated in a discontinuous mode or a critical continuous mode.
In one exemplary embodiment of the present disclosure, the on-time control unit includes a timer and an auxiliary switch controller,
the timer receives a timing starting signal and starts the timer to count according to the timing starting signal to generate a timing signal;
the auxiliary switch controller receives the timing signal and generates the control signal according to the timing signal.
In one exemplary embodiment of the present disclosure, the auxiliary switch controller turns on the auxiliary switch according to the timing start signal.
In one exemplary embodiment of the present disclosure, the auxiliary switch controller turns off the auxiliary switch when the timing signal is greater than or equal to the on-time threshold.
In an exemplary embodiment of the present disclosure, the timer further resets the timer according to a reset signal.
In an exemplary embodiment of the present disclosure, in an intermittent mode, the timing start signal is obtained by detecting an on signal of the auxiliary switch; in a critical continuous mode, the timing start signal is obtained by detecting zero crossing of the exciting negative current in the flyback converter.
In one exemplary embodiment of the present disclosure, the zero crossing point of the exciting negative current is detected by a current transformer, a sampling resistor, or an internal resistance of the auxiliary switch itself.
In an exemplary embodiment of the present disclosure, the reset signal is obtained by detecting an off signal of the auxiliary switch.
In an exemplary embodiment of the present disclosure, the on-time setting unit includes:
the exciting negative current setting unit is used for generating the exciting negative current reference value;
and the conduction time calculation unit is used for calculating the conduction time threshold value according to the exciting negative current reference value and the output voltage of the flyback converter.
In an exemplary embodiment of the present disclosure, the exciting negative current setting unit is configured to set the exciting negative current reference value based on an input voltage of the flyback converter.
In one exemplary embodiment of the present disclosure, the exciting negative current setting unit is configured to set the exciting negative current reference value based on an input voltage of the flyback converter and an output voltage of the flyback converter.
In one exemplary embodiment of the present disclosure, the flyback converter has a variable output voltage.
In an exemplary embodiment of the present disclosure, the flyback converter has an output voltage of 5V, 9V, 15V, or 20V.
According to an aspect of the present disclosure, there is provided a switching power supply including the control device according to any one of the above.
According to one aspect of the present disclosure, there is provided a control method applied to a flyback converter, the flyback converter including an auxiliary switch, the control method comprising:
(a) Detecting an output voltage of the flyback converter, and setting a conduction time threshold value based on the output voltage and an excitation negative current reference value;
(b) And controlling the conduction of the auxiliary switch according to a control signal, and turning off the auxiliary switch when the conduction time of the auxiliary switch reaches the conduction time threshold.
In one exemplary embodiment of the present disclosure, the flyback converter is an RCD clamped flyback converter or an active clamped flyback converter.
In an exemplary embodiment of the present disclosure, the auxiliary switch is a synchronous rectifier, a clamp, a switch connected in parallel to a secondary side rectifier unit of the flyback converter, or a switch connected in series to an auxiliary winding of the flyback converter.
In an exemplary embodiment of the present disclosure, the step (b) includes: the control signal is output according to a timing start signal.
In an exemplary embodiment of the present disclosure, the flyback converter is operated in a discontinuous mode or a critical continuous mode.
In an exemplary embodiment of the present disclosure, the step (b) includes: starting a timer to count according to a timing starting signal to generate a timing signal; and generating the control signal according to the timing signal.
In one exemplary embodiment of the present disclosure, the auxiliary switch is turned on according to the timing start signal.
In one exemplary embodiment of the present disclosure, the auxiliary switch is turned off when the timing signal is greater than or equal to the on-time threshold.
In an exemplary embodiment of the present disclosure, the step (b) further includes: the timer is reset according to a reset signal.
In an exemplary embodiment of the present disclosure, in an intermittent mode, the timing start signal is obtained by detecting an on signal of the auxiliary switch; and in a critical continuous mode, obtaining the timing start signal by detecting a zero crossing of an exciting negative current in the flyback converter.
In one exemplary embodiment of the present disclosure, the zero crossing point of the exciting negative current is detected by a current transformer, a sampling resistor, or an internal resistance of the auxiliary switch itself.
In an exemplary embodiment of the present disclosure, the reset signal is obtained by detecting an off signal of the auxiliary switch.
In an exemplary embodiment of the present disclosure, the step (a) includes: and calculating to obtain the on-time threshold value based on the output voltage and the exciting negative current reference value through division operation.
In an exemplary embodiment of the present disclosure, the control method further includes: (c) After the auxiliary switch is turned off, zero voltage turn-on of the primary side power switch tube of the flyback converter is realized through resonance of excitation inductance and parasitic capacitance in the flyback converter.
In an exemplary embodiment of the present disclosure, the step (a) further includes: the exciting negative current reference value is set based on an input voltage of the flyback converter.
In an exemplary embodiment of the present disclosure, the step (a) further includes: the exciting negative current reference value is set based on a maximum value of an input voltage of the flyback converter.
In an exemplary embodiment of the present disclosure, the step (a) further includes: the exciting negative current reference value is set based on an input voltage of the flyback converter and an output voltage of the flyback converter.
In one exemplary embodiment of the present disclosure, the flyback converter has a variable output voltage.
In an exemplary embodiment of the present disclosure, the flyback converter has an output voltage of 5V, 9V, 15V, or 20V.
According to the control device and the control method of the example embodiment of the present disclosure, an on-time threshold is set according to an excitation negative current reference value and an output voltage of a flyback converter, a control signal is output to control the on of an auxiliary switch, and the auxiliary switch is turned off when the on-time of the auxiliary switch reaches the on-time threshold. On one hand, the on-time threshold value under different voltage states can be set in real time through the exciting negative current reference value and the real-time monitored output voltage of the flyback converter; on the other hand, the on time of the auxiliary switch is adjusted in real time according to the on time threshold value, so that the on time of the auxiliary switch follows the on time threshold value, and zero-voltage switching on of the primary side power switch tube in the flyback converter under different output voltages can be realized.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
Fig. 1 schematically shows a circuit diagram of an active clamp flyback converter in one solution.
Fig. 2 schematically shows a discontinuous mode control waveform diagram of an active clamp flyback converter according to one embodiment.
Fig. 3 schematically shows a circuit diagram of an RCD clamp flyback converter in one embodiment.
Fig. 4 schematically shows a critical continuous mode control waveform diagram of an RCD clamp flyback converter in one embodiment.
Fig. 5 schematically shows a circuit diagram of an RCD clamp flyback converter in another embodiment.
Fig. 6 schematically illustrates a control schematic block diagram of a control apparatus according to an exemplary embodiment of the present disclosure.
Fig. 7 schematically illustrates a control schematic block diagram of a control apparatus according to another exemplary embodiment of the present disclosure.
Fig. 8 schematically shows a circuit diagram of an on-time control unit according to still another exemplary embodiment of the present disclosure.
Fig. 9 schematically illustrates a discontinuous mode control waveform diagram of an RCD clamp flyback converter according to yet another exemplary embodiment of the present disclosure.
Fig. 10 schematically illustrates a critical continuous mode control waveform diagram of an active clamp flyback converter according to yet another exemplary embodiment of the present disclosure.
Fig. 11 schematically illustrates one particular embodiment of a method of on-time control of an RCD clamp flyback converter according to yet another exemplary embodiment of the present disclosure.
Fig. 12 schematically illustrates one particular embodiment of a method of on-time control of an active clamp flyback converter according to yet another exemplary embodiment of the present disclosure.
Fig. 13 schematically illustrates one specific embodiment of a method of setting an excitation negative current reference value of an RCD clamp flyback converter as a function of input voltage, according to yet another exemplary embodiment of the present disclosure.
Fig. 14 schematically illustrates one specific embodiment of a method of setting an excitation negative current reference value of an active clamp flyback converter as a function of input voltage according to yet another exemplary embodiment of the present disclosure.
Fig. 15 schematically shows a flowchart of a control method according to still another exemplary embodiment of the present disclosure.
Reference numerals illustrate:
S 1 : primary side power switching tube
S 2 : clamping tube
S R : synchronous rectifying tube
I s : secondary side current
t0-t5: time of day
L m : exciting inductor
V o : output voltage
C EQ : parasitic capacitance
I m_n (t): amplitude of exciting negative current
S aux : switch connected in parallel with diode D1
W aux : auxiliary winding
S aux_VCC : switch connected in series with auxiliary winding
600. 1100, 1200, 1400, 1500: control device
610. 1110, 1210, 1410, 1510: flyback converter
620: conduction time setting unit
630. 1130, 1230, 1430, 1530: on-time control unit
640. 1140, 1240, 1440, 1540: exciting negative current setting unit
650. 1150, 1250, 1450, 1550: conduction time calculation unit
1480. 1580: input voltage detection unit
810: time-piece
820: auxiliary switch controller
I m_N : exciting negative current reference value
t set : on time threshold
T: transformer
C o : output capacitor
V bus : input voltage
R 1 : first resistor
R 2 : second resistor
(a), (b), (c): step (a)
Detailed Description
Some exemplary embodiments embodying features and advantages of the present disclosure will be described in detail in the following description. It will be understood that the present disclosure is capable of various modifications in the various embodiments, all without departing from the scope of the present disclosure, and that the description and illustrations herein are intended to be in essence illustrative of such modifications, and not limiting of the present disclosure.
Fig. 1 shows a circuit diagram of an active clamp flyback converter in one embodiment. The active clamp flyback converter can realize a primary side power switch tube S 1 Zero voltage on (ZVS), the existing control method is: control clamp tube S 2 Power switching tube S on primary side only 1 Before conducting, conducting for a set time, the set time is t2-t3 in the control waveform diagram shown in fig. 2.
Fig. 3 shows a circuit diagram of an RCD clamp flyback converter in one embodiment. The RCD clamping flyback converter is used for conducting the secondary side synchronous rectifying tube S of the quasi-resonant flyback converter through delay R To realize the primary side power switch tube S 1 Zero voltage on (ZVS) of the existing secondary side synchronous rectifier tube S R The delayed conduction control method of (1) comprises the following steps: controlling synchronous rectifying tube S R Current I at the secondary side s After falling to zero, the conduction is continued for a set time, such as t1-t2 in the control waveform diagram shown in fig. 4.
The two kinds of implementation primary side power switch tubes S 1 Zero voltage on (ZVS) by controlling synchronous rectifiers S R Or clamping tube S 2 The set time is turned on, which is applicable to the application case of a fixed output voltage.
However, with the development of power adapters, particularly the popularization and popularity of USB-PD Type-C, applications that become output voltages are becoming more popular. For applications with variable output voltages, the control scheme described above will no longer be applicable, because: the basic principle of implementing a primary side power switching transistor zero voltage on (ZVS), whether an RCD clamped flyback converter or an active clamped flyback converter, is as follows: on the primary side power switching tube S 1 Before being switched on, the exciting inductance L of the transformer is made m Generates an exciting negative current I m_n By the exciting negative current I m_n To realize primary side power switch tube S 1 Is turned on (ZVS) and the magnitude of the exciting negative current is determined by the following formula:
wherein: l (L) m Is the excitation inductance value of the transformer, n is the turns ratio of the transformer, V o Is the output voltage value of the converter, I m_n (t) is the magnitude of the exciting negative current, t is the conduction time of the auxiliary switch (for synchronous rectifier of quasi-resonant flyback converter is the secondary side current I s The on-time after dropping to zero refers to the on-time before the primary side power switch tube turns on for the clamp of the active clamp flyback converter).
As can be seen from the above formula, for a fixed design, the excitation inductance value L m And the turns ratio n is fixed. If the output voltage Vo is fixed, as can be seen from equation (1), the fixed on-time t means a fixed excitation negative current magnitude, and therefore, by controlling the synchronous rectifier S R Or clamping tube S 2 A set time t is turned on, which is applicable to the application situation of a fixed output voltage. If the output voltage is availableThe fixed on-time means that the magnitude of the exciting negative current will follow the output voltage V o Is changed by a change in (a). Taking the application of USB-PD Type-C as an example, the minimum output voltage is 5V, and the maximum output voltage is 20V, if a control method with a fixed on time is adopted, one of the following two results will be caused:
a: if the set on-time just can meet the condition of zero voltage on (ZVS) of the primary side power switch tube when the output voltage is 5V, the generated exciting negative current amplitude is 4 times that when the output voltage is 20V. Excessive exciting negative current introduces additional losses that affect the efficiency of the converter.
B: if the set on time just can meet the condition of zero voltage turn-on (ZVS) of the primary side power switch tube when the output voltage is 20V, when the output voltage is 5V, the generated exciting negative current amplitude is only 1/4 of that when the output voltage is 20V, and the primary side power switch tube cannot realize zero voltage turn-on due to the excessively small exciting negative current amplitude.
Based on the above, in the present exemplary embodiment, there is first provided a control apparatus, and referring to fig. 6, the control apparatus 600 is used to control a flyback converter 610, wherein the flyback converter 610 includes an auxiliary switch. As shown in fig. 6, the control device 600 may include: an on-time setting unit 620, and an on-time control unit 630. Wherein:
The on-time setting unit 620 is used for setting the output voltage V according to the exciting negative current reference value o Setting a conduction time threshold t set The method comprises the steps of carrying out a first treatment on the surface of the And
the on-time control unit 630 is configured to output a control signal to control the conduction of the auxiliary switch, and the on-time of the auxiliary switch reaches the on-time threshold t set The auxiliary switch is turned off. For example, the control signal may be based on the timing start signal and the on-time threshold t set And thus obtained.
According to the control device of the present exemplary embodiment, on the one hand, the on-time threshold values in different voltage states can be set in real time by an exciting negative current reference value and the output voltage of the flyback converter circuit monitored in real time; on the other hand, the on time of the auxiliary switch is adjusted in real time according to the on time threshold value, so that the on time of the auxiliary switch follows the on time threshold value, and zero-voltage switching on of the primary side power switch tube in the flyback converter under different output voltages can be realized.
In this example embodiment, the flyback converter further includes a primary side switching unit, a secondary side rectifying unit, a transformer, and an output capacitor, wherein the primary side switching unit includes a primary side power switching tube, the secondary side rectifying unit includes a first end and a second end, and the first end and the second end are electrically connected to the transformer and the output capacitor, respectively. To adapt to the application situation of variable output voltage, the zero voltage turn-on (ZVS) of the primary side power switch tube in the full input voltage range (e.g. 90-264 Vac) and the full load range under different output voltages needs to directly control the turn-on time of the auxiliary switch. According to the following formula (2):
As can be seen from the above formula (2), for a set excitation negative current reference I m_N On-time threshold t set And output voltage V o In inverse relationship. The conduction time threshold of the auxiliary switch is adjusted according to different output voltages, so that the conduction time of the auxiliary switch is adjusted, and the purpose of controlling exciting negative current can be achieved. The basic principle of the present disclosure is therefore: before the primary side power switch tube is turned on, an exciting negative current is generated in the flyback converter by controlling the on and off of the auxiliary switch. First, the conduction of the auxiliary switch is controlled so that the conduction time of the auxiliary switch reaches a conduction time threshold t set . Then, the auxiliary switch is controlled to be turned off, and after the auxiliary switch is turned off, the exciting negative current at the moment is taken as an initial value, and the exciting inductance L is used for exciting m Parasitic capacitance C with primary line EQ To achieve zero voltage turn-on (ZVS) of the primary side power switch-on. Through reasonable arrangement of auxiliary switch in this disclosureThe zero voltage turn-on (ZVS) of the primary side power switch can be realized in a full input voltage range and a full load range of different output voltages. In the present embodiment, parasitic capacitance C EQ The parasitic capacitance of the primary side power switching transistor S1 and the parasitic capacitance of the primary side coil of the transformer T.
In this exemplary embodiment, the output voltage of the flyback converter 610 may be variable, for example, the output voltage of the flyback converter 610 may be 5V, 9V, 15V, 20V, or the like, which is not particularly limited in this disclosure.
Further, in the present example embodiment, the flyback converter 610 may be an active clamp flyback converter as shown in fig. 1 or an RCD clamp flyback converter as shown in fig. 3 and 5, but the flyback converter in the example embodiments of the present disclosure is not limited thereto. Correspondingly, in the present exemplary embodiment, the auxiliary switch of the flyback converter 610 may be a clamp S as shown in fig. 1 2 Or S of synchronous rectifier as shown in FIG. 3 R The auxiliary switch in the example embodiments of the present disclosure is not limited thereto. For example, the secondary side of the RCD clamp flyback converter shown in FIG. 5 is a diode rectified RCD clamp flyback converter, and the auxiliary switch may be a switch S connected in parallel with a diode D1 aux Or the auxiliary switch thereof can be connected in series with the auxiliary winding W aux Switch S of (2) aux_VCC 。
In this exemplary embodiment, the operation mode of the flyback converter may be an intermittent mode or a critical continuous mode, which is not particularly limited in this disclosure.
Further, as shown in fig. 7, in the present exemplary embodiment, in order to reasonably set the excitation negative current reference value and the on-time threshold value, the on-time setting unit 620 may further include: excitation negative current setting unit 640 and on-time calculating unit 650. The exciting negative current setting unit 640 is used for setting an exciting negative current reference value I based on the input voltage or/and the output voltage of the flyback converter m_N . The on-time calculating unit 650 is used for calculating the reference value I according to the exciting negative current m_N And the output voltage V of the flyback converter o To set the on-time threshold t set 。
In one embodiment, the on-time calculating unit may include a multiplication or division circuit, but is not limited thereto. The multiplication or division circuit receives the exciting negative current reference value I m_N And the output voltage V of the flyback converter o And based on parameters of the circuit itself, e.g. the inductance value L of excitation m And the turns ratio n of the transformer, the conduction time threshold t is set through the calculation of the formula (2) set 。
In the present exemplary embodiment, the implementation of the on-time control unit 630 may be in various ways. Fig. 8 illustrates one embodiment of an on-time control unit 630 according to the present disclosure. As shown in fig. 8, the on-time control unit includes a timer 810 and an auxiliary switch controller 820, wherein the timer 810 is used for starting to count according to a count start signal and generating a count signal. The auxiliary switch controller 820 is used for generating a control signal according to the timing signal.
In the present exemplary embodiment, the auxiliary switch controller 820 turns on the auxiliary switch according to the timing start signal; the timing signal is gradually increased after the timer 810 starts to count, and reaches the on-time threshold t set When the auxiliary switch controller 820 turns off the auxiliary switch.
In the present exemplary embodiment, for the intermittent operation mode, the timing start signal of the timer 810 may be obtained by an on signal of the auxiliary switch. As shown in fig. 2, at time t 2S 2 The rising edge jump signal of the driving signal is an opening signal of the auxiliary switch; alternatively, as shown in FIG. 9, S at time t2 R The rising edge jump signal of the driving signal is the on signal of the auxiliary switch, and the timing starting signal can be obtained by detecting the rising edge jump signal. It should be noted that the timing start signal may be synchronized with the rising edge transition signal, or may be obtained by delaying the rising edge transition signal by a certain amount.
Further, in the present exemplary embodiment, for the critical continuous mode, the timing start signal of the timer may be obtained by detecting the zero crossing point of the exciting negative current (e.g., time t1 of fig. 4). Specifically, detection of the zero crossing point of the excited negative electricity can be realized through a current transformer, a sampling resistor or the internal resistance of a power device such as the internal resistance of an auxiliary switch.
In one embodiment, the timer 810 also enables resetting according to a reset signal. Further, in the present exemplary embodiment, the reset signal of the timer may be obtained by the off signal of the auxiliary switch, for example, the reset signal of the timer may be synchronized with the off signal of the auxiliary switch or may be obtained by a delay of the off signal. As shown in fig. 2, at time S of t3 2 The falling edge jump signal of the driving signal is the turn-off signal of the auxiliary switch; as shown in FIG. 9, S at time t3 R The falling edge jump signal of the driving signal is the turn-off signal of the auxiliary switch; or as shown in FIG. 10, at time S of t2 2 The falling edge jump signal of the driving signal is the turn-off signal of the auxiliary switch, and the reset signal can be obtained by detecting the falling edge jump signal. It should be noted that the reset signal may be synchronous with the falling edge transition signal, or may be obtained by delaying the falling edge transition signal by a certain amount.
In this exemplary embodiment, the exciting negative current is controlled by controlling the on time of the auxiliary switch, and there are a plurality of different methods for different flyback converters, and the RCD clamp flyback converter in the discontinuous mode and the active clamp flyback converter in the discontinuous mode are respectively illustrated below.
Fig. 11 shows a specific embodiment of a control device. As shown in fig. 11, the control device 1100 is configured to control the flyback converter 1110, wherein the control device 1100 includes: an on-time control unit 1130, an exciting negative current setting unit 1140, and an on-time calculation unit 1150. Flyback converter 1110 is an RCD clamp flyback converter and comprises a primary side switching unit, a secondary side rectifying unit, a transformer T and an output capacitor C o Wherein the primary side switching unit comprises a primary side power switching tube S 1 The secondary side rectifying unit comprises a synchronous rectifying tube S R And the secondary side rectifying unit is respectively connected with the transformer T and the output capacitor C o And (5) electric connection.
In this embodiment, on-time calculationThe unit 1150 monitors the output voltage signal V in real time o And an exciting negative current reference value I output from the exciting negative current setting unit 1140 m_N Obtaining the on-time threshold t set And will turn on the time threshold t set To the on-time control unit 1130; the control device 1100 controls the rectifier S through the synchronous rectifier S R The second turn-on signal (S at time t2 in fig. 9 R Drive signal) to obtain a timing start signal; the on-time control unit 1130 obtains the on-time threshold t set And a timing start signal for outputting a control signal to turn on the synchronous rectifying tube S R And when the on time of the auxiliary switch reaches the on time threshold t set Time-off synchronous rectifier S R . Meanwhile, the on-time control unit 1130 controls the synchronous rectifier S R A reset signal generated by the off signal of (c) to effect a reset.
Fig. 12 shows another embodiment of a control device. As shown in fig. 12, the control device 1200 is configured to control a flyback converter 1210, and the control device 1200 includes: an on-time control unit 1230, an excitation negative current setting unit 1240, and an on-time calculation unit 1250. Flyback converter 1210 is an active clamp flyback converter and includes a primary side switching unit, a secondary side rectifying unit, a transformer T and an output capacitor C o Wherein the primary side switching unit comprises a primary side power switching tube S 1 And a clamping tube S 2 The secondary side rectifying unit comprises a synchronous rectifying tube S R And the secondary side rectifying unit is respectively connected with the transformer T and the output capacitor C o And (5) electric connection.
In an embodiment, the on-time calculation unit 1250 calculates the output voltage signal V based on real-time monitoring o And an excitation negative current reference value I output from the excitation negative current setting unit 1240 m_N Obtaining the on-time threshold t set And will turn on the time threshold t set To the on-time control unit 1230; the control device 1200 is composed of a clamping tube S 2 To obtain a timing start signal.
The on-time control unit 1230 acquires the timing start signal and the on-time threshold t set For use inOutputting a control signal to turn on the clamp S 2 And when the on time of the auxiliary switch reaches the on time threshold t set The clamp tube S is turned off at the time 2 . Meanwhile, the on-time control unit 1230 controls the clamp S 2 Generates a reset signal to effect a reset.
Further, in each of the exemplary embodiments of the present disclosure, an excitation negative current setting unit for setting an excitation negative current reference value I m_N . As for setting of the exciting negative current reference value, it is known through research that: at low voltage input (V bus <nV o ) When the zero voltage turn-on (ZVS) of the primary side power tube can be realized without the help of exciting negative current; at high voltage input (V bus >nV o ) In order to realize zero voltage turn-on (ZVS) of the primary side power tube, the minimum amplitude of the exciting negative current needs to satisfy:
wherein: i m_N For exciting negative current reference value V bus For input voltage, V O N is the turns ratio of the transformer for the output voltage; l (L) m Is the exciting inductance; c (C) EQ Is the parasitic capacitance.
According to the above formula (3), n, L for a particular circuit design m C EQ Is fixed, and the reference value of exciting negative current and input voltage V are used for realizing Zero Voltage Switching (ZVS) of primary side power tube bus And output voltage V O Related to the following. Thus, the exciting negative current setting unit can adjust the exciting negative current reference value in real time based on the input voltage and the output voltage of the flyback converter.
However, with the above method, in order to adjust the exciting negative current reference value I in real time m_N Two variables need to be monitored in real time: input voltage V bus And output voltage V O Doing so increases the complexity of the control. Further studies showed that: flyback converter at high voltage input (V bus >nVo) are provided, in operation in the case of a machine,the influence of the output voltage on the reference value of the exciting negative current, i.e. the reference value of the exciting negative current is only related to the input voltage, can be neglected, thereby greatly simplifying the setting of the reference value of the exciting negative current. Then, the above formula (3) can be simplified to the following formula (4):
Thus, the excitation negative current setting unit can set the excitation negative current reference value based on the input voltage of the flyback converter.
In this embodiment, for setting the exciting negative current reference value, there are two setting methods:
fixed reference value setting method: to achieve zero voltage turn-on (ZVS) of the primary side power switching transistor in the full input voltage range, the reference value of the exciting negative current is set according to the maximum input voltage, namely:
wherein: v (V) bus_max Is the maximum value of the input voltage.
For the fixed reference value setting method, when the input voltage is the maximum value, the zero voltage turn-on (ZVS) of the primary side power switch tube can be just satisfied; however, when the input voltage is low, the magnitude of the exciting negative current generated by the control method is larger than the magnitude of the exciting negative current required for realizing zero voltage turn-on (ZVS) of the primary side power tube, thereby bringing about additional loss and being unfavorable for efficiency optimization. A fixed reference value setting method may be used in applications where efficiency requirements are not very high.
For the application occasion with higher efficiency requirement, the setting method that the reference value changes along with the input voltage can be adopted to optimize the efficiency of the converter. Therefore, the excitation negative current reference value can be set to:
Wherein: i m_N (V bus ) For exciting a negative current reference value.
For a particular circuit design, the inductance value L is excited m And parasitic capacitance value C EQ Is fixed, as can be seen from the above formula (6), the exciting negative current reference value and the input voltage V bus In proportion, the exciting negative current setting unit can set the input voltage value V detected by the input voltage detecting unit bus Directly calculated as exciting negative current reference value I m_N 。
Fig. 13 shows a further embodiment of a control device. Fig. 13 is similar to fig. 11 in structure, but fig. 13 also includes a specific example of the exciting negative current setting unit. As shown in fig. 13, the control device further includes an input voltage detection unit 1480, wherein in the present embodiment, the input voltage detection unit 1480 includes a first resistor R 1 And a second resistor R 2 And pass through a first resistor R 1 And a second resistor R 2 Voltage dividing means for detecting input voltage V bus . The input voltage detection unit 1480 outputs an input voltage V bus Is input to an excitation negative current setting unit 1440 for setting an excitation negative current reference value I m_N To excite negative current reference value I m_N Is transmitted to a conduction time calculating unit 1450, the conduction time calculating unit 1450 calculates a reference value I of the exciting negative current according to the exciting negative current m_N And output voltage V monitored in real time o To calculate the on-time threshold t set Will turn on the time threshold t set Input to the on-time control unit 1430; by means of a secondary-conduction on signal of a synchronous rectifier (S at time t2 in FIG. 9 R A driving signal) to obtain a timing start signal to enable the on-time control unit 1430; the on-time control unit 1430 obtains the on-time threshold t set And a timing start signal for outputting a control signal to turn on the synchronous rectifying tube S R And when the on time of the auxiliary switch reaches the on time threshold t set Time-off synchronous rectifier S R . Meanwhile, the on-time control unit 1430 controls the synchronous rectifying tube S R Is turned off of (2)The reset signal generated by the signal realizes the reset.
Fig. 14 shows a further embodiment of a control device. Fig. 14 is similar to fig. 12 in structure, the main difference being that the auxiliary switch in fig. 14 is a clamp S on the primary side of the active clamp flyback converter 2 。
In addition, in the present exemplary embodiment, there is also provided a control method that can be applied to a flyback converter as shown in fig. 6 to 14, the flyback converter including an auxiliary switch, and referring to fig. 15, the control method may include the steps of: step (a): detecting an output voltage of the flyback converter, and setting a conduction time threshold value based on the output voltage and an excitation negative current reference value; step (b): and controlling the conduction of the auxiliary switch according to the control signal, and turning off the auxiliary switch when the conduction time of the auxiliary switch reaches the conduction time threshold.
On one hand, the on time threshold value under different voltage states can be set in real time through an exciting negative current reference value and the real-time monitored output voltage of the flyback converter; on the other hand, the on time of the auxiliary switch is adjusted in real time according to the on time threshold value, so that the on time of the auxiliary switch follows the on time threshold value, and zero-voltage switching on of the primary side power switch tube in the flyback converter under different output voltages can be realized.
Further, in the present exemplary embodiment, the auxiliary switch may be a synchronous rectifier, a clamp, a switch connected in parallel to the secondary side rectifying unit of the flyback converter, or a switch connected in series to the auxiliary winding of the flyback converter.
Further, in the present exemplary embodiment, in the intermittent mode, the timing start signal may be obtained by detecting the on signal of the auxiliary switch; and in the critical continuous mode, the timing start signal can be obtained by detecting the zero crossing point of the exciting negative current.
Furthermore, in this example, step (a) may further include: the on-time threshold is calculated based on the output voltage and the exciting negative current reference value by division.
Furthermore, in the present exemplary embodiment, the control method may further include: (c) After the auxiliary switch is turned off, zero-voltage turn-on of the primary side power switching tube of the flyback converter is realized through resonance of the excitation inductor and the parasitic capacitor in the flyback converter.
Since each step in the control method in this exemplary embodiment corresponds to each unit or module of the control device in a one-to-one manner, a detailed description thereof will be omitted.
Further, another preferred embodiment of the present disclosure provides a switching power supply that may include any of the control devices of the previous embodiments. Since the switching power supply of this preferred embodiment employs the control device described above, it has at least all the advantages corresponding to the control device.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any adaptations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
It is to be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, and that various modifications and changes may be effected without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims (35)

1. A control device for a flyback converter having a variable output voltage, the flyback converter comprising an auxiliary switch and a synchronous rectification switch, wherein when the flyback converter is operated in an intermittent mode, the control device turns off the synchronous rectification switch when the secondary current drops to zero and controls the auxiliary switch to turn on or controls the synchronous rectification switch to turn on twice before the next primary switch is turned on, the control device comprising:
the on-time setting unit is used for setting on-time thresholds in different output voltage states in real time according to an exciting negative current reference value and the output voltage of the flyback converter; and
the on-time control unit is used for outputting a control signal to control the conduction of the auxiliary switch or the synchronous rectification switch, and turning off the auxiliary switch or the synchronous rectification switch when the on-time of the auxiliary switch or the secondary on-time of the synchronous rectification switch reaches the on-time threshold.
2. The control apparatus of claim 1, wherein the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter.
3. The control device of claim 1, wherein the auxiliary switch is a clamp, a switch connected in parallel to a secondary side rectifying unit of the flyback converter, or a switch connected in series to an auxiliary winding of the flyback converter.
4. The control device of claim 1, wherein the on-time control unit is configured to output the control signal according to a timing start signal.
5. The control device of claim 1, wherein the on-time control unit comprises a timer and an auxiliary switch controller,
the timer receives a timing starting signal and starts the timer to count according to the timing starting signal to generate a timing signal;
the auxiliary switch controller receives the timing signal and generates the control signal according to the timing signal.
6. The control device of claim 5, wherein the auxiliary switch controller turns on the auxiliary switch in response to the timing initiation signal.
7. The control device of claim 5, wherein the auxiliary switch controller turns off the auxiliary switch when the timing signal is greater than or equal to the on-time threshold.
8. The control device of claim 5, wherein the timer further resets the timer in response to a reset signal.
9. The control apparatus according to claim 5, wherein in the intermittent mode, the timing start signal is obtained by detecting an on signal of the auxiliary switch; in a critical continuous mode, the timing start signal is obtained by detecting zero crossing of the exciting negative current in the flyback converter.
10. The control device according to claim 9, wherein the zero crossing point of the exciting negative current is detected by a current transformer, a sampling resistor, or the internal resistance of the auxiliary switch itself.
11. The control device of claim 8, wherein the reset signal is derived by detecting an off signal of the auxiliary switch.
12. The control apparatus according to claim 1, wherein the on-time setting unit includes:
the exciting negative current setting unit is used for generating the exciting negative current reference value;
and the conduction time calculation unit is used for calculating the conduction time threshold value according to the exciting negative current reference value and the output voltage of the flyback converter.
13. The control apparatus according to claim 12, wherein the excitation negative current setting unit is configured to set the excitation negative current reference value based on an input voltage of the flyback converter.
14. The control apparatus according to claim 12, wherein the excitation negative current setting unit is configured to set the excitation negative current reference value based on an input voltage of the flyback converter and an output voltage of the flyback converter.
15. The control device of claim 1, wherein the minimum magnitude of the excitation negative current is required to satisfy:
wherein: i m_N For exciting negative current reference value V bus For input voltage, V O N is the turns ratio of the transformer for the output voltage; l (L) m Is the exciting inductance; c (C) EQ Is the parasitic capacitance.
16. The control device of claim 1, wherein the flyback converter has an output voltage of 5V, 9V, 15V, or 20V.
17. A switching power supply comprising a control device according to any one of claims 1 to 16.
18. A control method applied to a flyback converter having a variable output voltage, the flyback converter including an auxiliary switch and a synchronous rectification switch, wherein when the flyback converter is operated in an intermittent mode, a control device turns off the synchronous rectification switch when a secondary side current drops to zero and controls the auxiliary switch to be turned on or controls the synchronous rectification switch to be turned on secondarily before a next primary switch is turned on, the control method comprising:
(a) Detecting the output voltage of the flyback converter, and setting on-time thresholds in different output voltage states in real time based on the output voltage and an excitation negative current reference value;
(b) And according to a control signal, controlling the conduction of the auxiliary switch or the synchronous rectification switch, and turning off the auxiliary switch or the synchronous rectification switch when the conduction time of the auxiliary switch or the secondary conduction time of the synchronous rectification switch reaches the conduction time threshold.
19. The control method of claim 18, wherein the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter.
20. The control method of claim 18, wherein the auxiliary switch is a clamp, a switch connected in parallel to a secondary side rectifying unit of the flyback converter, or a switch connected in series to an auxiliary winding of the flyback converter.
21. The control method of claim 18, wherein the step (b) comprises: the control signal is output according to a timing start signal.
22. The control method of claim 18, wherein the step (b) includes: starting a timer to count according to a timing starting signal to generate a timing signal; and generating the control signal according to the timing signal.
23. The control method of claim 22, wherein the auxiliary switch is turned on in response to the timing initiation signal.
24. The control method of claim 22, wherein the auxiliary switch is turned off when the timing signal is greater than or equal to the on-time threshold.
25. The control method of claim 22, wherein step (b) further comprises: the timer is reset according to a reset signal.
26. The control method according to claim 22, wherein the timing start signal is obtained by detecting an on signal of the auxiliary switch in an intermittent mode; and in a critical continuous mode, obtaining the timing start signal by detecting a zero crossing of an exciting negative current in the flyback converter.
27. The control method of claim 26, wherein the zero crossing of the exciting negative current is detected by a current transformer, a sampling resistor, or the internal resistance of the auxiliary switch itself.
28. The control method of claim 25, wherein the reset signal is obtained by detecting an off signal of the auxiliary switch.
29. The control method of claim 18, wherein the step (a) includes: and calculating to obtain the on-time threshold value based on the output voltage and the exciting negative current reference value through division operation.
30. The control method according to claim 18, characterized in that the control method further comprises: (c) After the auxiliary switch is turned off, zero voltage turn-on of the primary side power switch tube of the flyback converter is realized through resonance of excitation inductance and parasitic capacitance in the flyback converter.
31. The control method of claim 18, wherein the step (a) further comprises: the exciting negative current reference value is set based on an input voltage of the flyback converter.
32. The control method of claim 31, wherein the step (a) further comprises: the exciting negative current reference value is set based on a maximum value of an input voltage of the flyback converter.
33. The control method of claim 18, wherein the step (a) further comprises: the exciting negative current reference value is set based on an input voltage of the flyback converter and an output voltage of the flyback converter.
34. The control method of claim 18, wherein the minimum magnitude of the excitation negative current is required to satisfy:
wherein: i m_N For exciting negative current reference value V bus For input voltage, V O N is the turns ratio of the transformer for the output voltage; l (L) m Is the exciting inductance; c (C) EQ Is the parasitic capacitance.
35. The control method of claim 18, wherein the flyback converter has an output voltage of 5V, 9V, 15V, or 20V.
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