CN111107697A - Constant-current control circuit of flyback converter - Google Patents

Constant-current control circuit of flyback converter Download PDF

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CN111107697A
CN111107697A CN201911345964.9A CN201911345964A CN111107697A CN 111107697 A CN111107697 A CN 111107697A CN 201911345964 A CN201911345964 A CN 201911345964A CN 111107697 A CN111107697 A CN 111107697A
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current
flyback converter
demagnetization
primary side
module
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CN111107697B (en
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姜梅
咸泉伟
潘焕燕
温勤琛
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Shenzhen University
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Shenzhen University
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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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal 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
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal 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
    • 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
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention provides a constant current control circuit of a flyback converter, which comprises: the power tube driving module generates demagnetization ending time according to the grid voltage zero crossing point of the flyback converter power tube in the current sampling period; the primary side current peak value and demagnetization time generation module generates a primary side current peak value and demagnetization starting time according to the acquired primary side sampling current of the current sampling period, and generates demagnetization time according to the demagnetization starting time and the demagnetization finishing time; the control module generates a primary side current turn-off value according to the primary side current peak value and the demagnetization time of the current sampling period, and controls the power tube driving circuit module to turn off the power tube of the flyback converter when the primary side sampling current of the next sampling period is equal to the primary side current turn-off value. According to the invention, the primary side current turn-off value generated by the primary side current peak value and the demagnetization time is compared with the primary side sampling current in the next sampling period, and the turn-off time of the power tube of the flyback converter is controlled according to the comparison result, so that the constant current output control of the flyback converter is realized.

Description

Constant-current control circuit of flyback converter
Technical Field
The invention relates to the field of power supply control, in particular to a constant-current control circuit of a flyback converter.
Background
With the rapid development of electronic technology, the variety and functions of electronic devices are increasing, the charging problem of portable electronic devices represented by mobile phones is becoming more prominent, and the output accuracy of chargers during charging affects the safety problem of charging. In another type of electronic device, such as LED lighting, the current accuracy of the power supply directly affects the brightness of the lighting. At present, the flyback converter adopting the primary current feedback scheme is widely applied to the field of power supply equipment due to the fact that the cost of an optical coupler is saved and the service life of a system is prolonged. Because the precision of the constant current output of the flyback converter is directly influenced by the current sampling precision, the demagnetization time sampling precision and the control scheme, and the miller platform current sampling error caused by the miller capacitance of the power tube causes that the sampling precision of the demagnetization time and the current in the prior art is not high enough, and the precision of the current output of the flyback converter is reduced.
Disclosure of Invention
Therefore, the invention aims to overcome the defects of inaccurate constant current control current sampling and demagnetization time sampling and low output current precision in the prior art, and provides the constant current control circuit of the flyback converter.
In order to achieve the purpose, the invention provides the following technical scheme:
the invention provides a constant current control circuit of a flyback converter, which comprises: the device comprises a primary side current peak value and demagnetization time generation module, a control module and a power tube driving module, wherein the power tube driving module is used for generating demagnetization ending time according to the detected grid voltage zero crossing point of the flyback converter power tube in the current sampling period and sending the demagnetization ending time to the primary side current peak value and demagnetization time generation module; the primary side current peak value and demagnetization time generation module is used for generating a primary side current peak value and demagnetization starting time according to the acquired primary side sampling current of the flyback converter in the current sampling period, generating demagnetization time according to the demagnetization finishing time and the demagnetization starting time, and sending the primary side current peak value and the demagnetization time in the current sampling period to the control module; and the control module is used for generating a primary side current turn-off value according to the primary side current peak value and the demagnetization time of the current sampling period, and generating a power tube turn-off signal to control the power tube driving circuit module to turn off the power tube of the flyback converter when the primary side sampling current of the next sampling period is equal to the primary side current turn-off value.
In an embodiment, the flyback converter constant current control circuit further includes: the linear voltage stabilizing module is used for acquiring power supply input voltage and high-voltage starting input voltage of an auxiliary winding of the flyback converter and providing a stable power supply for other modules in a constant-current control circuit of the flyback converter; and the oscillator module is used for providing a clock signal for the control module.
In an embodiment, the flyback converter constant current control circuit further includes: the device comprises a reference parameter circuit module, an over-temperature protection circuit module, a starting circuit module and an overvoltage protection circuit module, wherein the reference parameter circuit module is used for providing electrical quantity parameters for other modules in a constant current control circuit of the flyback converter; the over-temperature protection circuit module is used for generating a power tube turn-off signal and sending the power tube turn-off signal to the control module when detecting that the positive temperature coefficient voltage in the reference parameter circuit module exceeds the over-temperature voltage reference value; the starting circuit module is used for starting the function of the constant current control circuit to operate when the voltage starting input voltage is detected to reach the starting voltage reference value; and the overvoltage protection circuit module is used for disconnecting the power supply of other modules except the starting circuit module and the overvoltage protection circuit module when the voltage starting input voltage is detected to exceed the overvoltage reference voltage.
In one embodiment, the electrical quantity parameter comprises: the starting voltage reference value, the overvoltage voltage reference value, the over-temperature voltage reference value, the conduction voltage reference value and the constant current value.
In one embodiment, the primary current peak and demagnetization time generation module includes: the primary side current peak value generating circuit is used for generating a primary side current peak value according to the acquired primary side sampling current of the flyback converter in the current sampling period and sending the primary side current peak value to the control module and the demagnetization starting time generating circuit; the demagnetization starting time generation circuit is used for generating demagnetization starting time according to the conduction voltage reference value and the primary side current peak value of the flyback converter in the current sampling period; and the demagnetization time circuit is used for generating demagnetization time according to the demagnetization finishing time and the demagnetization starting time and sending the demagnetization time to the control module.
In one embodiment, the control module includes: the primary side current turn-off value generating circuit is used for generating a primary side current turn-off value according to a primary side current peak value, demagnetization time, a constant current value, a sampling period and a current turn-off resistance value; and the driving signal generating circuit is used for comparing the acquired primary side sampling current of the next sampling period with the primary side current turn-off value, generating a power tube turn-off signal and sending the power tube turn-off signal to the power tube driving circuit module.
In an embodiment, the driving signal generating circuit is further configured to generate a power tube conducting signal according to the received clock signal, and send the power tube conducting signal to the power tube driving circuit module.
In one embodiment, when the flyback converter is in a steady state, the secondary side output current value of the flyback converter controlled by the constant current control circuit of the flyback converter is calculated by the following formula:
Figure BDA0002333361870000041
wherein, IoFor the secondary side of the flyback converter, k equals Np/Ns，NpIs the number of turns of the primary winding of the transformer, NsThe number of turns of the secondary winding of the transformer, R is the resistance value of the current turn-off resistor, RCSTo sample the resistance value of the resistor, IcIs a constant current value.
In one embodiment, a power tube driving module includes: and the source end of the driving circuit field effect tube is connected with the sampling resistor of the flyback converter and is used for introducing the Miller platform current of the flyback converter power tube into the primary side current sampling circuit.
In one embodiment, a resistor is connected between the gate terminal of the field effect transistor of the driving circuit and the control module for filtering the current spike.
The technical scheme of the invention has the following advantages:
1. according to the constant-current control circuit of the flyback converter, the primary side current turn-off value generated by the primary side current peak value and the demagnetization time is compared with the primary side sampling current in the next sampling period, the turn-off time of the power tube of the flyback converter is controlled according to the comparison result, and the output of the secondary side constant current of the flyback converter is achieved.
2. The constant-current control circuit of the flyback converter provided by the invention considers the influence of a Miller platform on the sampling of the primary side current peak value when a power tube is turned off, which is brought by a Miller capacitor of a power tube of the flyback converter, and improves the sampling precision of the primary side current peak value by collecting the Miller platform current; according to the primary current peak value, acquiring demagnetization starting time, acquiring a grid voltage zero crossing point of a flyback converter power tube by a power tube driving module, acquiring demagnetization ending time, and improving the sampling precision of the demagnetization time; the flyback converter controlled by the constant-current control circuit of the flyback converter can realize constant output of secondary side current by giving different turn ratio and sampling resistance values.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic circuit topology diagram of a specific example of a flyback converter according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a specific example of a constant current control circuit of a flyback converter according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a specific example of a constant current control circuit of a flyback converter according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a specific example of a constant current control circuit of a flyback converter according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a specific example of a constant current control circuit of a flyback converter according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a specific example of a constant current control circuit of a flyback converter according to an embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Examples
The embodiment of the invention provides a constant current control circuit of a flyback converter, which can be integrated in a control chip in practical application and is applied to the fields of consumer electronic power supplies, portable electronic equipment charging, other linear power supplies and the like.
The primary side current and the secondary side current of the flyback converter are proportional, the proportional relation is shown as a formula (1),
Figure BDA0002333361870000071
wherein, IspIs the secondary peak current, IppIs the primary side peak current, NpIs the number of turns of the primary coil of the transformer, NsThe number of turns of the secondary coil of the transformer is.
The relation between the secondary peak current and the primary current peak value and the demagnetization time can be obtained by a proportional relation between the primary current and the secondary current shown in the formula (1) and a periodic average current formula shown in the formula (2), and is shown in the formula (3).
Figure BDA0002333361870000072
Figure BDA0002333361870000073
Wherein, IoFor the flyback converter output current, TdmFor demagnetization time, TsIs the sampling period.
From the equation (3), the flyback converter outputs the current IoAnd primary side current peak value IppTime of demagnetization TdmThe number of turns of the primary coil of the transformer is NpThe number of turns N of the secondary coil of the transformersAnd a sampling period TsIn relation to, however, the number of turns N of the primary winding of the transformerpThe number of turns N of the secondary coil of the transformersAnd a sampling period TsIs a given value, thereby controlling the primary side current peak value IppAnd a demagnetization time TdmThe flyback converter can be controlled to realize constant current output.
The present embodiment provides a constant current control circuit of a flyback converter, as shown in fig. 2, including:
and the power tube driving module is used for generating demagnetization ending time according to the detected grid voltage zero crossing point of the flyback converter power tube in the current sampling period, and sending the demagnetization ending time to the primary side current peak value and demagnetization time generating module.
The demagnetization time of the flyback converter power tube after being turned off is obtained by the demagnetization starting time and the demagnetization ending time. According to the working principle of the flyback converter, when the secondary side voltage of the flyback converter is reduced, demagnetization is finished, energy remained in an equivalent inductor of a transformer forms oscillation between the equivalent inductor of the transformer and a parasitic capacitor of a power tube of the flyback converter, the oscillation wave pattern can be detected at the drain end of the power tube of the flyback converter, the oscillation voltage wave pattern is conducted to a grid end through the parasitic capacitor of the power tube of the flyback converter, and the grid end is in a high impedance state when the power tube of the flyback converter is in a turn-off state, and the phase difference between a grid end voltage signal and a drain end voltage signal is 90 degrees, so that when the grid end voltage detected by a power tube driving module is zero, namely demagnetization finishing time is obtained.
And the primary side current peak value and demagnetization time generation module is used for generating a primary side current peak value and demagnetization starting time according to the acquired primary side sampling current of the flyback converter in the current sampling period, generating demagnetization time according to the demagnetization finishing time and the demagnetization starting time, and sending the primary side current peak value and the demagnetization time in the current sampling period to the control module.
And the control module is used for generating a primary side current turn-off value according to the primary side current peak value and the demagnetization time of the current sampling period, and generating a power tube turn-off signal to control the power tube driving circuit module to turn off the power tube of the flyback converter when the primary side sampling current of the next sampling period is equal to the primary side current turn-off value.
After the flyback converter power tube is turned off, the primary side sampling current does not drop rapidly due to the demagnetization time of the equivalent inductance of the transformer, but drops to zero suddenly after the flyback converter power tube is completely turned off, and meanwhile, due to the influence of the miller capacitance of the flyback converter, the primary side current peak value is generated in the miller platform time. According to the embodiment of the invention, the constant current control of the flyback converter is realized by continuously adjusting the primary side current turn-off value of each sampling period.
According to the constant-current control circuit of the flyback converter, the primary side current turn-off value generated by the primary side current peak value and the demagnetization time is compared with the primary side sampling current of the next sampling period, the turn-off time of the power tube of the flyback converter is controlled according to the comparison result, and the output of the secondary side constant current of the flyback converter is achieved.
In an embodiment, the flyback converter constant current control circuit further includes:
and the oscillator module is used for providing a clock signal for the control module. In the embodiment of the invention, when the rising of the primary side sampling current of the next period reaches the primary side current turn-off value, the control module generates the power tube turn-off signal to control the power tube driving circuit module to turn off the power tube of the flyback converter, and when the power tube of the flyback converter needs to be controlled to be switched on by the driving signal after the power tube of the flyback converter is completely turned off, meanwhile, the power tube of the flyback converter in the embodiment of the invention is controlled to be switched on by the PWM modulation mode, so the oscillator module provides a clock signal for the control module, and then the control module converts the clock signal into the power tube turn-on signal to control the power tube driving circuit module to switch on the power tube of the flyback.
And the linear voltage stabilizing module is used for acquiring the power supply input voltage and the high-voltage starting input voltage of the auxiliary winding of the flyback converter and providing a stable power supply for other modules in the constant-current control circuit of the flyback converter. In the embodiment of the invention, when the flyback converter circuit is not started, no current flows in the auxiliary winding, the high-voltage starting input voltage supplies power at the time, and when the flyback converter circuit normally operates, the input voltage is supplied by the auxiliary winding of the converter, as shown in fig. 1, a Vs end of the constant current control circuit of the flyback converter is connected to one end of a voltage dividing resistor, and a Vsup end at the other end of the voltage dividing resistor is connected to the auxiliary winding side. And the output end VDD of the linear voltage stabilization module outputs a power supply voltage for providing a stable power supply for other modules in the constant current control circuit of the flyback converter.
In an embodiment, the flyback converter constant current control circuit further includes:
and the reference parameter circuit module is used for providing electrical quantity parameters for other modules in the constant current control circuit of the flyback converter. In the embodiment of the invention, the high-voltage starting input voltage or the auxiliary winding power supply input voltage is utilized, and the state quantity parameters such as voltage or current required by the operation of the constant current control circuit are obtained through the combined action of the parameter circuits such as resistance voltage division and an operational amplifier.
And the over-temperature protection circuit module is used for generating a power tube turn-off signal and sending the power tube turn-off signal to the control module when detecting that the positive temperature coefficient voltage in the reference parameter circuit module exceeds the over-temperature voltage reference value.
And the starting circuit module is used for starting the function operation of the constant current control circuit when detecting that the voltage starting input voltage reaches the starting voltage reference value. As shown in fig. 1, the HV terminal of the constant current control circuit of the flyback converter is connected to a high-voltage starting input voltage, and the high-voltage starting input voltage is generated by filtering a direct current voltage output by the ac-dc rectifying diode circuit through a filter.
And the overvoltage protection circuit module is used for disconnecting the power supply of other modules except the starting circuit module and the overvoltage protection circuit module when the high-voltage starting input voltage is detected to exceed the overvoltage reference value.
In one embodiment, the electrical quantity parameter comprises: the starting voltage reference value, the overvoltage voltage reference value, the over-temperature voltage reference value, the conduction voltage reference value and the constant current value. In the embodiment of the present invention, the reference values of various electrical parameters are compared with the actual values to obtain the voltage, the current, and the like of the constant current control circuit, which are normally operated, and this is only by way of example and not limited thereto.
In one embodiment, as shown in fig. 3, the primary current peak and demagnetization time generation module includes:
and the primary side current peak value generating circuit is used for generating a primary side current peak value according to the acquired primary side sampling current of the flyback converter in the current sampling period, and sending the primary side current peak value to the control module and the demagnetization starting time generating circuit.
As shown in fig. 1, in the embodiment of the present invention, a current sampling circuit is connected to one end of a sampling resistor, and voltage V is sampled by sampling the voltage V of the sampling resistorcsAs the related voltage of the primary sampling current of the current sampling period, the peak value of the primary sampling current can be obtained from the peak value of the voltage of the sampling resistor, i.e. Ipp＝Vcsp/RcsIn which IppIs the primary side sampling circuit peak value, RcsTo adopt the resistance value of a resistor, VcspFor sampling the peak value of the resistor voltage, for obtaining the peak value V of the sampled resistor voltagecspIn the embodiment of the invention, a circuit as shown in fig. 3 is built. In FIG. 3, VDD is the supply voltage, V, output by the linear regulator blockcsFor samplingResistance voltage, VrefIs a reference value of the on-voltage, tdm_onFor demagnetization starting time, M1 is a P-type MOS field effect transistor, A1 is an operational amplifier, C1 is a charging capacitor, and R1 is a filter resistor.
As shown in fig. 3(a), after the flyback converter power transistor is turned off, since the power transistor has an off delay time and the P-type MOS transistor can only pull up the drain voltage from VDD, M1 is in an on state, in the embodiment of the present invention, the operational amplifier a1 and the M1 field effect transistor are used to sample the resistor voltage VcsCharging capacitor C1. Because of the one-way conductivity of the MOS, the capacitor can only be charged and can not be discharged in the charging period, so that the current peak value V of the charging capacitor during the period of charging the charging capacitor by sampling the voltage of the resistor can be collected after the power tube is switched offcsp。
And the demagnetization starting time generation circuit is used for generating the demagnetization starting time according to the conduction voltage reference value and the primary side current peak value of the flyback converter in the current sampling period. As shown in fig. 3(b), when the flyback converter power tube is completely turned off, the peak value of the primary current suddenly drops to zero, which causes the voltage V of the sampling resistorcsSuddenly dropping, namely at the moment of demagnetization starting time, pulling the gate end of the M1 to a high level by the A1 so as to turn off the M1 tube, and enabling the conduction voltage to have a reference value VrefThe demagnetization start time information can be obtained by comparison with the a1 output voltage.
And the demagnetization time circuit is used for generating demagnetization time according to the demagnetization finishing time and the demagnetization starting time and sending the demagnetization time to the control module.
In one embodiment, the control module includes:
and the primary side current turn-off value generating circuit is used for generating a primary side current turn-off value according to the primary side current peak value, the demagnetization time, the constant current value, the sampling period and the current turn-off resistance value.
In the embodiment of the present invention, as shown in fig. 4(b), when demagnetization does not start, that is, when the primary current peak and the demagnetization start time are not generated by the demagnetization time generation module, the power tube in fig. 4(a) has no driving signal, and the constant current source charges the capacitor C; when demagnetization starts, the capacitor C startsDischarging, when the flyback converter is in a steady state, the charging current of the capacitor C is equal to the discharging current, so that the demagnetization time charging voltage V can be detected at the resistance value R of the current turn-off resistorCAnd can be calculated by equation (4):
Figure BDA0002333361870000121
wherein, VCFor the charging voltage of demagnetization time, R is the resistance value of the current turn-off resistor, TsFor a sampling period, TdmIs the demagnetization time.
Sampling the peak value V of the resistor voltagecspAnd demagnetization time charging voltage VCBy comparison of error amplifiers, VcspGreater than VCTime-setting down the turn-off value, VcspBelow VCThe turn-off value is increased in time to generate a sampling resistance voltage turn-off value VcsgdAnd obtaining the primary current turn-off value.
And the driving signal generating circuit is used for comparing the acquired primary side sampling current of the next sampling period with the primary side current turn-off value, generating a power tube turn-off signal and sending the power tube turn-off signal to the power tube driving circuit module.
As shown in fig. 5(a), in the embodiment of the present invention, when the driving signal generating circuit detects that the primary side current of the next sampling period rises to reach the primary side current turn-off value, that is, the voltage V of the sampling resistor is detectedcsReach the voltage turn-off value V of the sampling resistorcsgdThe flyback converter power tube is turned off and is completely turned off after a certain time, and the voltage peak value of the sampling resistor in the next sampling period can reach the voltage peak value V of the sampling resistorcspWhen the voltage peak value of the sampling resistor in the next sampling period can not reach the voltage peak value V of the sampling resistorcspIn time, the voltage turn-off value V of the sampling resistor is continuously adjusted by the primary current peak value and demagnetization time generation module and the control modulecsgdSo as to control the voltage peak value of the sampling resistor in the next sampling period to reach the voltage peak value V of the sampling resistorcsp。
In a specific embodiment, the driving signal generating circuit is further configured to generate a power tube conducting signal according to the received clock signal, and send the power tube conducting signal to the power tube driving circuit module.
In one embodiment, when the flyback converter is in a steady state, the secondary side output current value of the flyback converter controlled by the flyback converter constant current control circuit is calculated by the following formula:
Figure BDA0002333361870000131
wherein, IoFor the secondary side of the flyback converter, k equals Np/Ns，NpIs the number of turns of the primary winding of the transformer, NsThe number of turns of the secondary winding of the transformer, R is the resistance value of the current turn-off resistor, RCSTo sample the resistance value of the resistor, IcIs a constant current value.
In the embodiment of the invention, when the flyback converter circuit reaches a steady state, namely when the secondary side output current is a preset constant value, V is measured at the momentcsp＝VcAs shown in fig. 5(b), the formula (5) can be obtained from the formulae (3) and (4). According to the formula (5), when the flyback converter is in a steady state, the secondary side of the flyback converter controlled by the constant-current control circuit of the flyback converter outputs a current value which is only equal to the transformer turn ratio k, the current turn-off resistance value R and the constant current value IcAnd a sampling resistor RcsIn addition, the constant current control circuit is designed to be a given value, so that the flyback converter controlled by the constant current control circuit of the flyback converter provided by the embodiment can realize constant output of secondary side current by giving different turn ratios and sampling resistance values.
In one embodiment, the power tube driving module includes: and the source end of the driving circuit field effect tube is connected with the sampling resistor of the flyback converter and is used for introducing the Miller platform current of the flyback converter power tube into the primary side current sampling circuit. And a resistor is connected between the grid end of the field effect transistor of the driving circuit and the control module and is used for filtering current spikes.
As shown in fig. 6(a) and 6(b), in the embodiment of the present invention, the source terminal of the fet of the driving circuit is not grounded, but is connected to the sampling resistor. By the method, when the flyback converter power tube is turned off, the current overcharge caused by the Miller platform due to the Miller capacitor can be sampled, and the accurate primary current peak value can be sampled. As shown in fig. 6(d), when the fet of the driving circuit is turned off, a current spike is introduced into the primary current, so that a resistor is added to the gate of the driving transistor to filter out the spike, as shown in fig. 6 (c). Comparing fig. 6(d) and fig. 6(e), after the filtering resistor is connected, the current spike will not affect the sampling.
In order to verify the correctness of the constant current control circuit of the flyback converter provided by the embodiment of the invention, the embodiment of the invention completes design and simulation (only by way of example, but not by way of limitation) through the new tang 350nm BCD process ntc1132, and it is measured that the deviation of the secondary output current value is within ± 1.46% when the input voltage of the chip in the flyback system changes between 85Vac and 220Vac and the secondary load changes from 6W to 23W.
According to the constant-current control circuit of the flyback converter, the turn-off time of the power tube of the flyback converter is controlled according to the primary side current turn-off value generated by the primary side current peak value and the demagnetization time and the primary side sampling current of the next sampling period, so that the output of the secondary side constant current of the flyback converter is realized; the influence of a Miller platform on the sampling of the primary side current peak value when the power tube is turned off, which is caused by the Miller capacitor of the flyback converter power tube, is considered, and the sampling precision of the primary side current peak value is improved by collecting the Miller platform current; according to the primary current peak value, acquiring demagnetization starting time, acquiring a grid voltage zero crossing point of a flyback converter power tube by a power tube driving module, acquiring demagnetization ending time, acquiring the conduction voltage of a P-type MOS tube by a primary current peak value and demagnetization time generating module, acquiring the demagnetization starting time, and improving the sampling precision of the demagnetization time; the flyback converter controlled by the constant-current control circuit of the flyback converter can realize constant output of secondary side current by giving different turn ratio and sampling resistance values.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.

Claims (10)

1. A flyback converter constant current control circuit, characterized in that, includes: a primary side current peak value and demagnetization time generation module, a control module and a power tube driving module, wherein,
the power tube driving module is used for generating demagnetization ending time according to the detected grid voltage zero crossing point of the flyback converter power tube in the current sampling period, and sending the demagnetization ending time to the primary side current peak value and demagnetization time generating module;
the primary side current peak value and demagnetization time generation module is used for generating a primary side current peak value and demagnetization starting time according to the acquired primary side sampling current of the flyback converter in the current sampling period, generating demagnetization time according to the demagnetization finishing time and the demagnetization starting time, and sending the primary side current peak value and the demagnetization time in the current sampling period to the control module;
and the control module is used for generating a primary current turn-off value according to the primary current peak value and the demagnetization time of the current sampling period, and generating a power tube turn-off signal to control the power tube driving circuit module to turn off the power tube of the flyback converter when the primary sampling current of the next sampling period is equal to the primary current turn-off value.
2. The flyback converter constant current control circuit of claim 1, further comprising: a linear voltage stabilizing module and an oscillator module, wherein,
the linear voltage stabilizing module is used for acquiring power supply input voltage and high-voltage starting input voltage of an auxiliary winding of the flyback converter and providing a stable power supply for other modules in the constant-current control circuit of the flyback converter;
and the oscillator module is used for providing a clock signal for the control module.
3. The flyback converter constant current control circuit of claim 2, further comprising: a reference parameter circuit module, an over-temperature protection circuit module, a starting circuit module and an overvoltage protection circuit module, wherein,
the reference parameter circuit module is used for providing electrical quantity parameters for other modules in the constant-current control circuit of the flyback converter;
the over-temperature protection circuit module is used for generating a power tube turn-off signal and sending the power tube turn-off signal to the control module when detecting that the positive temperature coefficient voltage in the reference parameter circuit module exceeds an over-temperature voltage reference value;
the starting circuit module is used for starting the function of the constant current control circuit to operate when the voltage starting input voltage is detected to reach the starting voltage reference value;
and the overvoltage protection circuit module is used for disconnecting the power supply of other modules except the starting circuit module and the overvoltage protection circuit module when detecting that the voltage starting input voltage exceeds an overvoltage reference voltage.
4. The flyback converter constant current control circuit of claim 3, wherein the electrical quantity parameter comprises: the starting voltage reference value, the overvoltage voltage reference value, the over-temperature voltage reference value, the conduction voltage reference value and the constant current value.
5. The flyback converter constant current control circuit of claim 4, wherein the primary current peak and demagnetization time generation module comprises: a primary side current peak value generating circuit, a demagnetization starting time generating circuit and a demagnetization time generating circuit, wherein,
the primary side current peak value generating circuit is used for generating a primary side current peak value according to the acquired primary side sampling current of the flyback converter in the current sampling period and sending the primary side current peak value to the control module and the demagnetization starting time generating circuit;
the demagnetization starting time generation circuit is used for generating demagnetization starting time according to the conduction voltage reference value and the primary side current peak value of the flyback converter in the current sampling period;
and the demagnetization time circuit is used for generating demagnetization time according to the demagnetization ending time and the demagnetization starting time and sending the demagnetization time to the control module.
6. The flyback converter constant current control circuit of claim 5, wherein the control module comprises: a primary side current turn-off value generation circuit and a drive signal generation circuit, wherein,
the primary side current turn-off value generating circuit is used for generating a primary side current turn-off value according to the primary side current peak value, the demagnetization time, the constant current value, the sampling period and the current turn-off resistance value;
and the driving signal generating circuit is used for comparing the acquired primary side sampling current of the next sampling period with the primary side current turn-off value, generating a power tube turn-off signal and sending the power tube turn-off signal to the power tube driving circuit module.
7. The flyback converter constant current control circuit of claim 6, wherein the drive signal generation circuit is further configured to generate a power tube on signal according to the received clock signal and send the power tube on signal to the power tube drive circuit module.
8. The flyback converter constant current control circuit of claim 6, wherein when the flyback converter is in a steady state, a flyback converter secondary side output current value controlled by the flyback converter constant current control circuit is calculated by the following formula:
Figure FDA0002333361860000031
wherein, IoFor the secondary side of the flyback converter, k equals Np/Ns，NpTo becomeNumber of turns of primary winding of transformer, NsThe number of turns of the secondary winding of the transformer, R is the resistance value of the current turn-off resistor, RCSTo sample the resistance value of the resistor, IcIs a constant current value.
9. The flyback converter constant current control circuit of claim 8, wherein the power tube driver module comprises: and the source end of the driving circuit field effect tube is connected with the sampling resistor of the flyback converter and is used for introducing the Miller platform current of the flyback converter power tube into the primary side current sampling circuit.
10. The flyback converter constant current control circuit of claim 9, wherein a resistor is connected between the gate terminal of the field effect transistor of the driving circuit and the control module for filtering current spikes.
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