CN116232029A - Overcurrent protection circuit, switch power supply overcurrent protection system and method - Google Patents

Overcurrent protection circuit, switch power supply overcurrent protection system and method Download PDF

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CN116232029A
CN116232029A CN202111466063.2A CN202111466063A CN116232029A CN 116232029 A CN116232029 A CN 116232029A CN 202111466063 A CN202111466063 A CN 202111466063A CN 116232029 A CN116232029 A CN 116232029A
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module
sampling
voltage
overcurrent protection
switch
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盛欢
李亮
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CRM ICBG Wuxi Co Ltd
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CRM ICBG Wuxi 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—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
    • 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

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  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The invention provides an overcurrent protection circuit, a switching power supply overcurrent protection system and a method, wherein the overcurrent protection circuit comprises the following steps: the first sampling and holding module is used for sampling and holding the minimum value of the inductance peak current to obtain a first sampling voltage; the second sampling and holding module is used for sampling and holding the maximum value of the inductance peak current to obtain a second sampling voltage; the operation module sums the first sampling voltage and the second sampling voltage and then multiplies the sum by a preset coefficient to obtain a first voltage; the demagnetization detection module is used for obtaining a demagnetization time detection signal; the multiplication module is used for carrying out multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage; the first comparison module compares the second voltage with the reference voltage to output a comparison result; and the driving control module is used for generating a driving control signal based on the comparison result. The invention can realize unchanged output overcurrent point no matter the system works in the intermittent mode or the continuous mode, and has wide application range and high system stability.

Description

Overcurrent protection circuit, switch power supply overcurrent protection system and method
Technical Field
The present invention relates to the field of integrated circuit design, and in particular, to an overcurrent protection circuit, and a switching power supply overcurrent protection system and method.
Background
An overcurrent protection is usually arranged in the power supply system, namely when the output current exceeds an overcurrent point, the system starts the protection to prevent the overcurrent of the system, so that the normal and stable operation of the system is ensured.
Generally, the overcurrent protection strategies corresponding to different working modes are different, and how to meet the overcurrent protection requirements of the system under various different application conditions becomes one of the problems to be solved urgently by those skilled in the art.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an objective of the present invention is to provide an overcurrent protection circuit, a switching power supply overcurrent protection system and a method for solving the problem that the overcurrent protection in the prior art is not suitable for various application conditions.
To achieve the above and other related objects, the present invention provides an overcurrent protection circuit for implementing overcurrent protection of a switching power supply circuit, the overcurrent protection circuit at least comprising:
the device comprises a first sample-and-hold module, a second sample-and-hold module, an operation module, a demagnetization detection module, a multiplication module, a first comparison module and a drive control module;
the first sampling and holding module receives a sampling signal of the inductance peak current in the switching power supply circuit, and samples and holds the minimum value of the inductance peak current to obtain a first sampling voltage;
the second sampling and holding module receives the sampling signal and samples and holds the maximum value of the inductance peak current to obtain a second sampling voltage;
the operation module is connected with the output ends of the first sampling and holding module and the second sampling and holding module, and multiplies the first sampling voltage and the second sampling voltage by a preset coefficient after summing to obtain a first voltage;
the demagnetization detection module detects the demagnetization time of the inductor to obtain a demagnetization time detection signal;
the multiplication module is connected with the output ends of the operation module and the demagnetization detection module, and performs multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage;
the first comparison module is connected to the output end of the multiplication module, receives a reference voltage, compares the second voltage with the reference voltage, and outputs a comparison result;
the driving control module is connected to the output end of the first comparison module and generates a driving control signal based on the comparison result;
the system comprises a first sampling and holding module, a second sampling and holding module, an operation module, a demagnetization detection module, a multiplication module, a first comparison module and a drive control module, wherein the preset coefficient is a non-zero real number;
the first sampling and holding module receives a sampling signal of the inductance peak current in the switching power supply circuit, and samples and holds the minimum value of the inductance peak current to obtain a first sampling voltage;
the second sampling and holding module receives the sampling signal and samples and holds the maximum value of the inductance peak current to obtain a second sampling voltage;
the operation module is connected with the output ends of the first sampling and holding module and the second sampling and holding module, and multiplies the first sampling voltage and the second sampling voltage by a preset coefficient after summing to obtain a first voltage;
the demagnetization detection module detects the demagnetization time of the inductor to obtain a demagnetization time detection signal;
the multiplication module is connected with the output ends of the operation module and the demagnetization detection module, and performs multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage;
the first comparison module is connected to the output end of the multiplication module, receives a reference voltage, compares the second voltage with the reference voltage, and outputs a comparison result;
the driving control module is connected to the output end of the first comparison module and generates a driving control signal based on the comparison result;
wherein the preset coefficient is a non-zero real number.
Optionally, the first sample-and-hold module includes a first switch, a second switch, and a first capacitor; one end of the first switch receives the sampling signal, and the other end of the first switch is connected with an upper polar plate of the first capacitor and outputs the first sampling voltage; the lower polar plate of the first capacitor is grounded; the second switch is connected in parallel with two ends of the first capacitor.
Optionally, the second sample-and-hold module includes a third switch, a fourth switch, and a second capacitor; one end of the third switch receives the sampling signal, and the other end of the third switch is connected with the upper polar plate of the second capacitor and outputs the second sampling voltage; the lower polar plate of the second capacitor is grounded; the fourth switch is connected in parallel with two ends of the second capacitor.
More optionally, the operation module includes a fifth switch, and the fifth switch is connected to the output ends of the first sample-and-hold module and the second sample-and-hold module.
Optionally, the demagnetization detection module comprises a comparison unit, an RS trigger and an AND logic unit; the first input end of the comparison unit is connected with the driving control signal, the second end of the comparison unit is connected with a reference signal, and the driving control signal is compared with the reference signal; the setting end of the RS trigger is connected with a control signal of an upper driving tube in the driving control module, and the resetting end of the RS trigger is connected with the output end of the comparison unit; the first input end of the AND logic unit is connected with the output end of the RS trigger, the second input end of the AND logic unit is connected with a control signal of a lower driving tube in the driving control module, and the demagnetization time detection signal is output.
Optionally, the multiplication module includes a sixth switch, a seventh switch, a transconductance amplifier, an eighth switch, and a third capacitor; one end of the sixth switch is connected with the output end of the operation module, and the other end of the sixth switch is connected with the non-inverting input end of the transconductance amplifier; one end of the seventh switch is connected with the non-inverting input end of the transconductance amplifier, and the other end of the seventh switch is grounded; the inverting input end of the transconductance amplifier is grounded, and the output end of the transconductance amplifier is connected with the upper polar plate of the third capacitor and outputs the second voltage; the lower polar plate of the third capacitor is grounded; the eighth switch is connected in parallel with two ends of the third capacitor;
the sixth switch is conducted in the demagnetizing time, and the seventh switch and the eighth switch are synchronous with a power switching tube in the switching power supply circuit.
Optionally, the overcurrent protection circuit further includes a leading edge blanking module, and the leading edge blanking module is connected between the sampling signal and the input ends of the first sample hold module and the second sample hold module.
Optionally, the overcurrent protection circuit further includes a second comparison module and a fourth capacitor; the first input end of the second comparison module is connected with the input ends of the first sampling and holding module and the second sampling and holding module, the second input end of the second comparison module is connected with the upper polar plate of the fourth capacitor, and the output end of the second comparison module is connected with the input end of the driving control module; and the upper polar plate of the fourth capacitor is connected with the output voltage sampling feedback signal of the switching power supply circuit, and the lower polar plate is grounded.
To achieve the above and other related objects, the present invention provides a switching power supply overcurrent protection system, which at least includes:
a switching power supply circuit and the overcurrent protection circuit;
the switch power supply circuit realizes overcurrent protection based on a drive control signal output by the overcurrent protection circuit;
and the overcurrent protection circuit acquires a sampling signal of the inductance peak current from the switching power supply circuit.
Optionally, the switching power supply circuit is a flyback converter.
To achieve the above and other related objects, the present invention provides an overcurrent protection method for a switching power supply circuit, which at least includes:
detecting the demagnetization time of the inductor to obtain a demagnetization time detection signal;
sampling the minimum value of the inductance peak current to obtain a first sampling voltage, and sampling the maximum value of the inductance peak current to obtain a second sampling voltage; summing the first sampling voltage and the second sampling voltage and multiplying the sum by a preset coefficient to obtain a first voltage;
multiplying the first voltage with the demagnetization time detection signal to obtain a second voltage;
comparing the second voltage with a reference voltage, and controlling a power switch tube based on a comparison result to realize overcurrent protection;
wherein the preset coefficient is a non-zero real number.
Optionally, the preset coefficient is 1/2, and the first voltage satisfies the following relation:
Figure BDA0003391517280000031
wherein vp_calc is the first voltage, ip_max is the maximum value of the peak inductance current, ip_min is the minimum value of the peak inductance current, and Rcs is the resistance of the sampling resistor of the peak inductance current in the switching power supply circuit.
More optionally, the second voltage satisfies the following relation:
Figure BDA0003391517280000041
wherein Vcalc is the second voltage, vp_calc is the first voltage, tdemag is the demagnetizing time of the inductor, gm is the transconductance of the multiplier, C 3 The capacitance value of the transconductance output capacitor.
More optionally, the overcurrent protection point of the overcurrent protector of the switching power supply circuit satisfies the following relation:
Figure BDA0003391517280000042
wherein Iocp is the overcurrent protection point, eta is the efficiency, nps is the coil turns ratio of the primary side to the secondary side in the flyback switching power supply circuit, fsw is the system working frequency, vocp is the reference signal, and Rcs is the resistance value of the sampling resistor of the inductance peak current in the switching power supply circuit.
As described above, the overcurrent protection circuit, the overcurrent protection system and the overcurrent protection method for the switching power supply have the following beneficial effects:
the overcurrent protection circuit, the switch power supply overcurrent protection system and the switch power supply overcurrent protection method can achieve the unchanged output overcurrent point no matter the system works in an intermittent mode or a continuous mode, and have wide application range and high system stability.
Drawings
Fig. 1 shows a schematic structure of an AC-DC power supply system in a flyback topology.
Fig. 2 shows a schematic diagram of the structure of an AC-DC power supply system of a duty cycle compensated flyback topology.
Fig. 3 is a schematic diagram of an overcurrent protection circuit according to the present invention.
Fig. 4 is a schematic structural diagram of a first sample-and-hold module, a second sample-and-hold module, an operation module and a multiplication module according to the present invention.
Fig. 5 is a schematic structural diagram of a demagnetization detecting module according to the present invention.
Fig. 6 is a schematic structural diagram of the overcurrent protection system for the switching power supply according to the present invention.
Fig. 7 is a schematic diagram of the present invention for detecting demagnetization time in continuous current mode.
Fig. 8 is a schematic diagram of the present invention for detecting demagnetization time in discontinuous current mode.
Fig. 9 is a schematic diagram of the overcurrent protection method according to the invention in the continuous current mode.
Fig. 10 is a schematic diagram of the overcurrent protection method according to the invention in the intermittent current mode.
Description of element reference numerals
11 AC-DC power supply circuit
12. Driving chip
121. Leading edge blanking
122. First comparator
123. Second comparator
124 PWM controller
125. Oscillator
2. Overcurrent protection circuit
21. First sample-and-hold module
22. Second sample-and-hold module
23. Operation module
24. Demagnetizing detection module
241. Comparison unit
242 RS trigger
243. AND logic cell
25. Multiplication module
251. Transconductance amplifier
26. First comparison module
27. Drive control module
28. Front edge blanking module
29. Second comparison module
3. Switching power supply circuit
31. Output voltage sampling feedback module
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
Please refer to fig. 1-10. It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
As shown in fig. 1, an AC-DC power system with flyback topology is shown, wherein an AC-DC power circuit 11 has a flyback topology, and a driving chip 12 includes a front-edge blanking 121, a first comparator 122, a second comparator 123, a PWM controller 124, and an oscillator 125; the sampling voltage of the AC-DC power supply circuit 11 is compared with a reference voltage Vocp after leading edge blanking, and is also compared with an output voltage sampling feedback signal of the AC-DC power supply circuit 11; the PWM controller 124 generates PWM signals based on the output signals of the two comparators and the output signal of the oscillator 125 to control the power switching transistors in the AC-DC power supply circuit 11; thereby realizing overcurrent protection.
The output power Pout thereof satisfies the following relation:
Figure BDA0003391517280000061
wherein Pout is the output power; lp is the primary inductance of the transformer; ip_max is the maximum value of the peak current of the primary side when the power switch tube is conducted; ip_min is the minimum value of the peak current of the primary side when the power switch tube is turned on; fsw is the system operating frequency; η is efficiency.
For a constant voltage power supply system, the overcurrent point Iocp satisfies the following relation:
Figure BDA0003391517280000062
wherein Iocp is an output overcurrent point; pocp is the output power at the time of overcurrent; vout is the output voltage; ip_ocp is the maximum value of the primary peak current when the power switch tube is conducted in the overcurrent state.
In general, we define the overcurrent point Iocp by fixing the primary peak current ip_ocp of the transformer, so that the overcurrent point Iocp is fixed for a system with a fixed operating frequency and operating in the discontinuous mode. However, in a system operating in the continuous mode, since ip_min is not equal to 0 at this time, the overcurrent point is lower than that in the intermittent mode, and the overcurrent point cannot be made constant.
Generally in continuous mode, the larger the duty cycle, the larger ip_min; in order to reduce the amount of change in the output overcurrent point Iocp, the value of ip_ocp is increased accordingly, so that ip_ocp increases with an increase in the duty ratio. As shown in fig. 2, the reference voltage Vocp related to the duty cycle is obtained by compensating the reference voltage Vref by the duty cycle based on the scheme of introducing compensation in fig. 1. After introducing the compensation, the peak voltage on CS is defined as:
V ocp ＝V ref +k·D on ；
wherein Vref is a reference voltage; k is a duty cycle compensation coefficient; don is the duty cycle of the power switch when it is on.
However, the primary side peak current of the fixed transformer is adopted, and the overcurrent protection can be realized by only compensating a fixed amount by combining the compensation method, so that the system under various application conditions can not be satisfied; this approach does not allow for accurate over-current protection, especially when the system is operating in either intermittent or continuous mode.
Therefore, the invention provides an overcurrent protection scheme, and accurate overcurrent protection can be realized no matter the system works in an intermittent mode or a continuous mode.
Example 1
As shown in fig. 3, the present embodiment provides an overcurrent protection circuit 2 for implementing overcurrent protection of a switching power supply circuit, the overcurrent protection circuit 2 including:
the device comprises a first sample and hold module 21, a second sample and hold module 22, an operation module 23, a demagnetization detection module 24, a multiplication module 25, a first comparison module 26 and a drive control module 27.
As shown in fig. 3, the first sample-and-hold module 21 receives the sampling signal Vcs of the peak inductor current in the switching power supply circuit, and samples and holds the minimum value ip_min of the peak inductor current to obtain a first sampling voltage Vcs1.
Specifically, as shown in fig. 4, the first sample-and-hold module 21 includes a first switch S1, a second switch S2, and a first capacitor C1. One end of the first switch S1 receives the sampling signal VCS, and the other end is connected to the upper plate of the first capacitor C1 and outputs the first sampling voltage VCS1. The lower polar plate of the first capacitor C1 is grounded. The second switch S2 is connected in parallel to two ends of the first capacitor C1.
As shown in fig. 3, the second sample-and-hold module 22 receives the sampling signal Vcs, and samples and holds the maximum value ip_max of the peak inductor current to obtain a second sampling voltage Vcs2.
Specifically, as shown in fig. 4, the second sample-and-hold module 22 includes a third switch S3, a fourth switch S4, and a second capacitor C2. One end of the third switch S3 receives the sampling signal Vcs, and the other end is connected to the upper plate of the second capacitor C2 and outputs the second sampling voltage Vcs2. The lower polar plate of the second capacitor C2 is grounded. The fourth switch S4 is connected in parallel to two ends of the second capacitor C2.
Note that, the structures of the first sample-and-hold module 21 and the second sample-and-hold module 22 are not limited, and any circuit structure capable of sampling and holding the minimum value and the maximum value of the inductance peak current is applicable, and the structures of the first sample-and-hold module 21 and the second sample-and-hold module 22 may be different, which is not limited by the embodiment.
As shown in fig. 3, as another implementation of the present invention, the over-current protection circuit 2 further includes a leading edge blanking module 28. The leading edge blanking module 28 is connected between the sampled signal Vcs and the inputs of the first sample-and-hold module 21 and the second sample-and-hold module 22. The front edge blanking module is used for eliminating hidden danger of false triggering action generated by the peak of the pulse front edge, the structure is not limited, and the details are not repeated here.
As shown in fig. 3, the operation module 23 is connected to the output ends of the first sample-and-hold module 21 and the second sample-and-hold module 22, sums the first sampled voltage Vcs1 and the second sampled voltage Vcs2, and multiplies the sum by a preset coefficient to obtain a first voltage vp_calc. Wherein the preset coefficient is a non-zero real number.
Specifically, in this embodiment, the operation module 23 includes a fifth switch S5, where one end of the fifth switch S5 is connected to the output end of the first sample-and-hold module 21, and the other end of the fifth switch S5 is connected to the output end of the second sample-and-hold module 22. When the fifth switch S5 is turned on, the charge on the upper plate of the first capacitor C1 and the charge on the upper plate of the second capacitor C2 are shared, so as to achieve the effect of averaging after adding the output signal of the first sample-and-hold module 21 and the output signal of the second sample-and-hold module 22, i.e. the preset coefficient is 0.5. In practical use, the preset coefficient is not zero, and the circuit structure is correspondingly adjusted based on the difference of the preset coefficients, which is not described in detail herein.
As shown in fig. 3, the demagnetization detecting module 24 detects the demagnetization time of the inductance, and obtains a demagnetization time detection signal.
Specifically, as shown in fig. 5, in the present embodiment, the demagnetization detecting module 24 includes a comparing unit 241, an RS flip-flop 242, and an and logic unit 243. The first input end of the comparison unit 241 is connected with the driving control signal Vgate, the second end is connected with the reference signal Vref, and the driving control signal Vgate is compared with the reference signal Vref; as an example, the inverting input terminal of the comparing unit 241 is connected to the driving control signal Vgate, the non-inverting input terminal is connected to the reference signal Vref, and in actual use, the correspondence between the polarity of the input terminal and the input signal may be adjusted by an inverter, so that the same logic may be implemented. The set terminal of the RS flip-flop 242 is connected to the control signal Gate1 of the upper driving tube Q1 in the driving control module 27, and the reset terminal is connected to the output terminal (output signal DET) of the comparing unit 241. The first input end of the and logic unit 243 is connected to the output end of the RS trigger 242, the second input end is connected to the control signal Gate2 of the lower driving tube Q2 in the driving control module 27, and the demagnetization time detection signal Demag is output; as an example, the and logic unit is implemented by an and gate, and in practical use, any circuit structure capable of implementing the and logic is applicable.
It should be noted that any structure capable of implementing demagnetization time detection is suitable for the present invention, and is not limited to this embodiment.
As shown in fig. 3, the multiplication module 25 is connected to the output ends of the operation module 23 and the demagnetization detection module 24, and multiplies the first voltage vp_calc by the demagnetization time detection signal Demag to obtain a second voltage Vcalc.
Specifically, as shown in fig. 4, in the present embodiment, the multiplication module 25 includes a sixth switch S6, a seventh switch S7, a transconductance amplifier 251, an eighth switch S8, and a third capacitor C3 (transconductance output capacitor). One end of the sixth switch S6 is connected to the output end of the operation module 23, and the other end is connected to the non-inverting input end of the transconductance amplifier 251. One end of the seventh switch S7 is connected to the non-inverting input end of the transconductance amplifier 251, and the other end is grounded. The inverting input terminal of the transconductance amplifier 251 is grounded, and the output terminal is connected to the upper electrode plate of the third capacitor C3 and outputs the second voltage Vcalc. And the lower polar plate of the third capacitor C3 is grounded. The eighth switch S8 is connected in parallel to two ends of the third capacitor C3. The sixth switch S6 receives the control of the demagnetization time detection signal Demag, and the seventh switch S7 and the eighth switch S8 are controlled by the inverse of the demagnetization time detection signal Demag. Any circuit structure capable of multiplying the first voltage vp_calc and the demagnetization time detection signal Demag is suitable for the present invention, but not limited to this embodiment.
As shown in fig. 3, the first comparing module 26 is connected to the output end of the multiplying module 25, receives the reference voltage Vocp, compares the second voltage Vcalc with the reference voltage Vocp, and outputs a comparison result.
Specifically, in the present embodiment, the non-inverting input terminal of the first comparison module 26 is connected to the second voltage Vcalc, and the inverting input terminal is connected to the reference voltage Vocp. The reference voltage Vocp is a fixed voltage set internally, and when the second voltage Vcalc is greater than the reference voltage Vocp, the switching power supply circuit is considered to be overcurrent, and an overcurrent protection measure needs to be taken. In practical use, the corresponding relation between the polarity of the input end and the input signal can be adjusted, and will not be described in detail herein.
As shown in fig. 3, the driving control module 27 is connected to the output end of the first comparing module 26, and generates a driving control signal Vgate based on the comparing result to implement the over-current protection.
As shown in fig. 3, as another implementation manner of the present invention, the over-current protection circuit 2 further includes a second comparing module 29 and a fourth capacitor C4. The first input end of the second comparing module 29 is connected to the input ends of the first sample-and-hold module 21 and the second sample-and-hold module 22, the second input end is connected to the upper electrode plate of the fourth capacitor C4, and the output end is connected to the input end of the driving control module 27. And the upper polar plate of the fourth capacitor C4 is connected with the output voltage sampling feedback signal Vfb of the switching power supply circuit, and the lower polar plate is grounded. As an example, the non-inverting input end of the second comparing module 29 is connected to the input ends of the first sample-and-hold module 21 and the second sample-and-hold module 22, the inverting input end is connected to the upper plate of the fourth capacitor C4, and the corresponding relationship between the polarity of the input end and the input signal can be adjusted in practical use, which is not described in detail herein. At this time, the drive control module 27 generates the drive control signal Vgate based on the output signal of the first comparison module 26 and the output signal of the second comparison module 29.
It should be noted that, the overcurrent protection circuit 2 may be integrated in a chip, and at this time, the fourth capacitor C4 is disposed outside the chip as a compensation capacitor, and other modules are disposed inside the chip.
Example two
The embodiment provides a switching power supply overcurrent protection system, which includes:
the switching power supply circuit 3 and the overcurrent protection circuit 2 according to the first embodiment.
As shown in fig. 6, the switching power supply circuit 3 realizes overcurrent protection based on the drive control signal Vgate output from the overcurrent protection circuit 2.
Specifically, in this embodiment, the switching power supply circuit 3 is a flyback converter, and includes a transformer, a power switch tube M1, a sampling resistor Rcs, a diode D1, an output capacitor Cout, and a load RL. One end of a primary coil of the transformer is connected with an input voltage Vin, and the other end of the primary coil of the transformer is grounded through the power switch tube M1 and the sampling resistor Rcs. One end of a secondary coil of the transformer is connected with the anode of the diode D1, and the other end of the secondary coil of the transformer is grounded. The cathode of the diode D2 is grounded via the output capacitor Cout. The load RL is connected in parallel to both ends of the output capacitor Cout.
Specifically, the input voltage Vin is a dc voltage, and the switching power supply circuit 3 further includes a rectifier (not shown) that converts an ac voltage into the input voltage Vin, as an example.
Specifically, as an example, the switching power supply circuit 3 further includes an output voltage sampling feedback module 31, and the output voltage sampling feedback module 31 is connected to the cathode of the diode D1 to generate the output voltage sampling feedback signal Vfb.
It should be noted that any switching power supply circuit 3 requiring overcurrent protection is applicable to the present invention, and is not limited to the present embodiment.
As shown in fig. 6, the over-current protection circuit 2 obtains the sampling signal Vcs of the peak inductance current from the switching power supply circuit 3, and the specific structure and principle are described in the first embodiment and are not described in detail herein.
Example III
As shown in fig. 7 to 10, the present embodiment provides an overcurrent protection method for a switching power supply circuit, in this embodiment, the overcurrent protection circuit 2 according to the first embodiment is implemented, and in actual use, any hardware or software capable of implementing the method is suitable for the present invention. The overcurrent protection method of the switching power supply circuit comprises the following steps:
1) Detecting the demagnetization time of the inductor to obtain a demagnetization time detection signal Demag.
Specifically, as shown in fig. 7, in the continuous current mode, when the control signal Gate1 of the upper driving tube Q1 in the driving control module 27 is at a high level, the upper driving tube Q1 is turned on; the control signal Gate2 of the lower driving tube Q2 in the driving control module 27 is in opposite phase with Gate1, the lower driving tube Q2 is turned off, the driving control signal Vgate is at a high level, the power switch tube M1 is turned on (Ton), the DRAIN of the power switch tube M1 is at a low level, and the primary winding of the transformer enters a charging mode. When the control signal Gate1 of the upper driving tube Q1 is at a low level, the upper driving tube Q1 is turned off; the control signal Gate2 of the lower driving tube Q2 is inverted to Gate1, the lower driving tube Q2 is turned on, the driving control signal Vgate is at a low level, the power switch tube M1 is turned off (Toff), the DRAIN of the power switch tube M1 is at a high level, the primary coil of the transformer enters a discharge demagnetization mode, and the demagnetization time detection signal Demag jumps to a high level. As shown in fig. 7, in the continuous current mode, the output signal DET of the comparing unit 241 is always at a low level, and the demagnetization time detection signal Demag substantially coincides with the control signal Gate 2.
As shown in fig. 8, in the discontinuous current mode, the waveform of the control signal Gate1 of the upper driving transistor Q1 at the high level is the same as that of fig. 7. When the control signal Gate1 of the upper driving tube Q1 is at a low level, the upper driving tube Q1 is turned off; the control signal Gate2 of the lower driving tube Q2 is in opposite phase with Gate1, the lower driving tube Q2 is turned on, the driving control signal Vgate is at low level, the power switch tube M1 is turned off (Toff), the DRAIN electrode DRAIN of the power switch tube M1 is at high level, the primary coil of the transformer enters a discharge demagnetization mode, and the demagnetization time detection signal Demag jumps to high level; when the demagnetization is completed, the output signal DET of the comparing unit 241 generates a pulse, and the demagnetization time detection signal Demag transitions to a low level. As shown in fig. 7 and 8, the demagnetizing time Tdemag in the discontinuous current mode is smaller than that in the continuous current mode.
2) Sampling the minimum value of the inductance peak current to obtain a first sampling voltage Vcs1, and sampling the maximum value of the inductance peak current to obtain a second sampling voltage Vcs2; summing the first sampling voltage Vcs1 and the second sampling voltage Vcs2, and multiplying the sum by a preset coefficient to obtain a first voltage Vp_calc; the preset coefficient is a non-zero real number.
Specifically, as shown in fig. 9, when the driving control signal Vgate is at a high level, the power switch tube M1 is turned on, and a current flows through the sampling resistor Rcs, so as to obtain a sampling signal Vcs. The second switch S2 and the fourth switch S4 are turned on in a time period of the leading edge blanking, the charges on the first capacitor C1 and the second capacitor C2 are cleared, and the second switch S2 and the fourth switch S4 are turned off after the leading edge blanking is completed. After the front edge blanking is finished, the first switch S1 is turned on for a preset time (pulse signal, and sampling can be realized). Meanwhile, after the leading edge blanking is finished, the third switch S3 is turned on, and when the driving control signal Vgate is at a low level, the third switch S3 is turned off. When the driving control signal Vgate is at a low level, the power switch tube M1 is turned off, no current flows through the sampling resistor Rcs, and the sampling signal Vcs is at a low level; at this time, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are in an off state. The upper plate of the first capacitor C1 obtains the first sampling voltage Vcs1 corresponding to the minimum value of the peak inductance current, and the upper plate of the second capacitor C2 obtains the second sampling voltage Vcs2 corresponding to the maximum value of the peak inductance current.
Specifically, as shown in fig. 9 and 10, in the present embodiment, the fifth switch S5 and the sixth switch S6 are controlled by the demagnetization time detection signal Demag, the fifth switch S5 and the sixth switch S6 are turned on in the demagnetization time, and the first sampling voltage Vcs1 and the second sampling voltage Vcs2 are summed and averaged to obtain the first voltage vp_calc and transmitted to the input end of the transconductance amplifier 251. In this embodiment, the preset coefficient is 1/2, and the first voltage vp_calc satisfies the following relationship:
Figure BDA0003391517280000111
wherein vp_calc is the first voltage, ip_max is the maximum value of the peak inductance current, ip_min is the minimum value of the peak inductance current, and Rcs is the resistance of the sampling resistor of the peak inductance current in the switching power supply circuit.
In practical use, the first sampling voltage Vcs1 and the second sampling voltage Vcs2 may be summed and then multiplied by a predetermined coefficient, and the step of implementing the operation may be independent of the demagnetization time detection signal Demag. Step 1) and step 2) do not have a clear sequence, and are not limited to this embodiment.
3) And multiplying the first voltage Vp_calc by the demagnetization time detection signal Demag to obtain a second voltage Vcalc.
Specifically, as shown in fig. 9 and 10, the seventh switch S7 and the eighth switch S8 are synchronized with the power switch tube M1, the seventh switch S7 and the eighth switch S8 are turned on when the power switch tube M1 is turned on, and the seventh switch S7 and the eighth switch S8 are turned off when the power switch tube M1 is turned off. The multiplication module 25 performs a multiplication operation, and the second voltage Vcalc satisfies the following relationship:
Figure BDA0003391517280000121
wherein Vcalc is the second voltage, vp_calc is the first voltage, tdemag is the demagnetizing time of the inductor, gm is the transconductance of the multiplier, C 3 The capacitance value of the transconductance output capacitor. As can be seen from fig. 9 and 10, the duty ratio of the second voltage Vcalc in the continuous current mode is greater than the duty ratio of the second voltage Vcalc in the discontinuous current mode.
4) And comparing the second voltage Vcalc with the reference voltage Vocp, and controlling a power switch tube based on a comparison result to realize overcurrent protection.
Specifically, the power switching transistor M1 is turned on and off based on the comparison result of the second voltage Vcalc and the reference voltage Vocp, so that the second voltage Vcalc is finally equal to the reference voltage Vocp, that is:
Figure BDA0003391517280000122
under the flyback topological structure, the overcurrent protection point of the invention meets the following relation:
Figure BDA0003391517280000123
the simplified process is as follows:
Figure BDA0003391517280000124
wherein Iocp is the overcurrent protection point, eta is the efficiency, nps is the coil turns ratio of the primary side to the secondary side in the flyback switching power supply circuit, fsw is the system working frequency, vocp is the reference signal, and Rcs is the resistance value of the sampling resistor of the inductance peak current in the switching power supply circuit.
Therefore, for a system with fixed working frequency, whether the system works in an intermittent mode or a continuous mode, the overcurrent point is unchanged, and the accuracy of overcurrent protection is greatly improved.
In summary, the present invention provides an overcurrent protection circuit, a switching power supply overcurrent protection system and a method, including: the device comprises a first sample-and-hold module, a second sample-and-hold module, an operation module, a demagnetization detection module, a multiplication module, a comparison module and a drive control module; the first sampling and holding module receives a sampling signal of the inductance peak current in the switching power supply circuit, and samples and holds the minimum value of the inductance peak current to obtain a first sampling voltage; the second sampling and holding module receives the current sampling signal and samples and holds the maximum value of the inductance peak current to obtain a second sampling voltage; the operation module is connected with the output ends of the first sampling and holding module and the second sampling and holding module, and multiplies the first sampling voltage and the second sampling voltage by a preset coefficient after summing to obtain a first voltage; the demagnetization detection module detects the demagnetization time of the inductor to obtain a demagnetization time detection signal; the multiplication module is connected with the output ends of the operation module and the demagnetization detection module, and performs multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage; the first comparison module is connected to the output end of the multiplication module, receives a reference voltage, compares the second voltage with the reference voltage, and outputs a comparison result; the driving control module is connected to the output end of the first comparison module and generates a driving control signal based on the comparison result; wherein the preset coefficient is a non-zero real number. The overcurrent protection circuit, the switch power supply overcurrent protection system and the switch power supply overcurrent protection method can achieve the unchanged output overcurrent point no matter the system works in an intermittent mode or a continuous mode, and have wide application range and high system stability. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.

Claims (14)

1. An overcurrent protection circuit for implementing overcurrent protection of a switching power supply circuit, the overcurrent protection circuit comprising at least:
the device comprises a first sample-and-hold module, a second sample-and-hold module, an operation module, a demagnetization detection module, a multiplication module, a first comparison module and a drive control module;
the first sampling and holding module receives a sampling signal of the inductance peak current in the switching power supply circuit, and samples and holds the minimum value of the inductance peak current to obtain a first sampling voltage;
the second sampling and holding module receives the sampling signal and samples and holds the maximum value of the inductance peak current to obtain a second sampling voltage;
the operation module is connected with the output ends of the first sampling and holding module and the second sampling and holding module, and multiplies the first sampling voltage and the second sampling voltage by a preset coefficient after summing to obtain a first voltage;
the demagnetization detection module detects the demagnetization time of the inductor to obtain a demagnetization time detection signal;
the multiplication module is connected with the output ends of the operation module and the demagnetization detection module, and performs multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage;
the first comparison module is connected to the output end of the multiplication module, receives a reference voltage, compares the second voltage with the reference voltage, and outputs a comparison result;
the driving control module is connected to the output end of the first comparison module and generates a driving control signal based on the comparison result;
wherein the preset coefficient is a non-zero real number.
2. The overcurrent protection circuit of claim 1, wherein: the first sample hold module comprises a first switch, a second switch and a first capacitor; one end of the first switch receives the sampling signal, and the other end of the first switch is connected with an upper polar plate of the first capacitor and outputs the first sampling voltage; the lower polar plate of the first capacitor is grounded; the second switch is connected in parallel with two ends of the first capacitor.
3. The overcurrent protection circuit of claim 1, wherein: the second sample hold module comprises a third switch, a fourth switch and a second capacitor; one end of the third switch receives the sampling signal, and the other end of the third switch is connected with the upper polar plate of the second capacitor and outputs the second sampling voltage; the lower polar plate of the second capacitor is grounded; the fourth switch is connected in parallel with two ends of the second capacitor.
4. An overcurrent protection circuit according to any one of claims 1 to 3, wherein: the operation module comprises a fifth switch, and the fifth switch is connected to the output ends of the first sampling and holding module and the second sampling and holding module.
5. The overcurrent protection circuit of claim 1, wherein: the demagnetization detection module comprises a comparison unit, an RS trigger and an AND logic unit; the first input end of the comparison unit is connected with the driving control signal, the second end of the comparison unit is connected with a reference signal, and the driving control signal is compared with the reference signal; the setting end of the RS trigger is connected with a control signal of an upper driving tube in the driving control module, and the resetting end of the RS trigger is connected with the output end of the comparison unit; the first input end of the AND logic unit is connected with the output end of the RS trigger, the second input end of the AND logic unit is connected with a control signal of a lower driving tube in the driving control module, and the demagnetization time detection signal is output.
6. The overcurrent protection circuit of claim 1, wherein: the multiplication module comprises a sixth switch, a seventh switch, a transconductance amplifier, an eighth switch and a third capacitor; one end of the sixth switch is connected with the output end of the operation module, and the other end of the sixth switch is connected with the non-inverting input end of the transconductance amplifier; one end of the seventh switch is connected with the non-inverting input end of the transconductance amplifier, and the other end of the seventh switch is grounded; the inverting input end of the transconductance amplifier is grounded, and the output end of the transconductance amplifier is connected with the upper polar plate of the third capacitor and outputs the second voltage; the lower polar plate of the third capacitor is grounded; the eighth switch is connected in parallel with two ends of the third capacitor;
the sixth switch is conducted in the demagnetizing time, and the seventh switch and the eighth switch are synchronous with a power switching tube in the switching power supply circuit.
7. The overcurrent protection circuit of claim 1, wherein: the overcurrent protection circuit further comprises a front edge blanking module, and the front edge blanking module is connected between the sampling signal and the input ends of the first sampling holding module and the second sampling holding module.
8. The overcurrent protection circuit of claim 1, wherein: the overcurrent protection circuit further comprises a second comparison module and a fourth capacitor; the first input end of the second comparison module is connected with the input ends of the first sampling and holding module and the second sampling and holding module, the second input end of the second comparison module is connected with the upper polar plate of the fourth capacitor, and the output end of the second comparison module is connected with the input end of the driving control module; and the upper polar plate of the fourth capacitor is connected with the output voltage sampling feedback signal of the switching power supply circuit, and the lower polar plate is grounded.
9. The utility model provides a switching power supply overcurrent protection system which characterized in that, switching power supply overcurrent protection system includes at least:
a switching power supply circuit and an overcurrent protection circuit as claimed in any one of claims 1 to 8;
the switch power supply circuit realizes overcurrent protection based on a drive control signal output by the overcurrent protection circuit;
and the overcurrent protection circuit acquires a sampling signal of the inductance peak current from the switching power supply circuit.
10. The switching power supply overcurrent protection system of claim 9, wherein: the switching power supply circuit is a flyback converter.
11. The overcurrent protection method for the switching power supply circuit is characterized by at least comprising the following steps of:
detecting the demagnetization time of the inductor to obtain a demagnetization time detection signal;
sampling the minimum value of the inductance peak current to obtain a first sampling voltage, and sampling the maximum value of the inductance peak current to obtain a second sampling voltage; summing the first sampling voltage and the second sampling voltage and multiplying the sum by a preset coefficient to obtain a first voltage;
multiplying the first voltage with the demagnetization time detection signal to obtain a second voltage;
comparing the second voltage with a reference voltage, and controlling a power switch tube based on a comparison result to realize overcurrent protection;
wherein the preset coefficient is a non-zero real number.
12. The method of overcurrent protection for a switching power supply circuit of claim 11, wherein: the preset coefficient is 1/2, and the first voltage satisfies the following relation:
Figure FDA0003391517270000031
wherein vp_calc is the first voltage, ip_max is the maximum value of the peak inductance current, ip_min is the minimum value of the peak inductance current, and Rcs is the resistance of the sampling resistor of the peak inductance current in the switching power supply circuit.
13. The overcurrent protection method of the switching power supply circuit according to claim 11 or 12, wherein: the second voltage satisfies the following relation:
Figure FDA0003391517270000032
wherein Vcalc is the second voltage, vp_calc is the first voltage, tdemag is the demagnetizing time of the inductor, gm is the transconductance of the multiplier, C 3 The capacitance value of the transconductance output capacitor.
14. The method of overcurrent protection for a switching power supply circuit of claim 13, wherein: the overcurrent protection point of the overcurrent protection party of the switching power supply circuit meets the following relation:
Figure FDA0003391517270000041
wherein Iocp is the overcurrent protection point, eta is the efficiency, nps is the coil turns ratio of the primary side to the secondary side in the flyback switching power supply circuit, fsw is the system working frequency, vocp is the reference signal, and Rcs is the resistance value of the sampling resistor of the inductance peak current in the switching power supply circuit.
CN202111466063.2A 2021-12-03 2021-12-03 Overcurrent protection circuit, switch power supply overcurrent protection system and method Pending CN116232029A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117310262A (en) * 2023-11-28 2023-12-29 成都市易冲半导体有限公司 Primary side information detection circuit and detection chip of transformer

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117310262A (en) * 2023-11-28 2023-12-29 成都市易冲半导体有限公司 Primary side information detection circuit and detection chip of transformer
CN117310262B (en) * 2023-11-28 2024-02-09 成都市易冲半导体有限公司 Primary side information detection circuit and detection chip of transformer

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