Overcurrent protection circuit, switching power supply overcurrent protection system and method

Abstract

The present invention provides an overcurrent protection circuit, a switching power supply overcurrent protection system and method, including: a first sampling and holding module that samples and holds the minimum value of the inductor peak current to obtain a first sampling voltage; a second sampling and holding module that samples and holds the maximum value of the inductor peak current to obtain a second sampling voltage; an operation module that sums the first and second sampling voltages and multiplies by a preset coefficient to obtain a first voltage; a demagnetization detection module that obtains a demagnetization time detection signal; a multiplication module that performs a multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage; a first comparison module that compares the second voltage with a reference voltage and outputs a comparison result; and a drive control module that generates a drive control signal based on the comparison result. The present invention can achieve an unchanged output overcurrent point whether the system operates in a discontinuous mode or a continuous mode, has a wide application range, and high system stability.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit design, and particularly to an overcurrent protection circuit, a switching power supply overcurrent protection system and method. Background Art

[0002] Overcurrent protection is usually set in a power supply system. That is, when the output current exceeds the overcurrent point, the system will start protection to prevent the system from overcurrent, thereby ensuring the normal and stable operation of the system.

[0003] Generally, the overcurrent protection strategies corresponding to different operating modes are also different. How to meet the overcurrent protection requirements of the system under various different application conditions has become one of the problems that need to be solved urgently by those skilled in the art. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an overcurrent protection circuit, a switching power supply overcurrent protection system and method, which are used to solve the problem that the overcurrent protection in the prior art is not applicable to various different application conditions.

[0005] To achieve the above purpose and other related purposes, the present invention provides an overcurrent protection circuit for realizing overcurrent protection of a switching power supply circuit. The overcurrent protection circuit at least includes:

[0006] 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;

[0007] The first sample-and-hold module receives the sampling signal of the inductor peak current in the switching power supply circuit, samples and holds the minimum value of the inductor peak current, and obtains a first sampling voltage;

[0008] The second sample-and-hold module receives the sampling signal, samples and holds the maximum value of the inductor peak current, and obtains a second sampling voltage;

[0009] The operation module is connected to the output ends of the first sample-and-hold module and the second sample-and-hold module, sums the first sampling voltage and the second sampling voltage and multiplies by a preset coefficient to obtain a first voltage;

[0010] The demagnetization detection module detects the demagnetization time of the inductor to obtain a demagnetization time detection signal;

[0011] The multiplication module is connected to the output ends of the operation module and the demagnetization detection module, multiplies the first voltage and the demagnetization time detection signal to perform a multiplication operation, and obtains a second voltage;

[0012] 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;

[0013] The drive control module is connected to the output end of the first comparison module and generates a drive control signal based on the comparison result;

[0014] Wherein, the preset coefficient is a non-zero real number. The first sample and hold module, the second sample and hold module, the operation module, the demagnetization detection module, the multiplication module, the first comparison module and the drive control module;

[0015] The first sample and hold module receives the sampling signal of the peak inductor current in the switching power supply circuit, samples and holds the minimum value of the peak inductor current, and obtains a first sampled voltage;

[0016] The second sample and hold module receives the sampling signal, samples and holds the maximum value of the peak inductor current, and obtains a second sampled voltage;

[0017] The operation module is connected to the output ends of the first sample and hold module and the second sample and hold module, sums the first sampled voltage and the second sampled voltage and multiplies by a preset coefficient to obtain a first voltage;

[0018] The demagnetization detection module detects the demagnetization time of the inductor and obtains a demagnetization time detection signal;

[0019] The multiplication module is connected to the output ends of the operation module and the demagnetization detection module, performs a multiplication operation on the first voltage and the demagnetization time detection signal, and obtains a second voltage;

[0020] 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;

[0021] The drive control module is connected to the output end of the first comparison module and generates a drive control signal based on the comparison result;

[0022] Wherein, the preset coefficient is a non-zero real number.

[0023] 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, the other end is connected to the upper plate of the first capacitor and outputs the first sampled voltage; the lower plate of the first capacitor is grounded; the second switch is connected in parallel across the two ends of the first capacitor.

[0024] 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 is connected to the upper plate of the second capacitor and outputs the second sampling voltage; the lower plate of the second capacitor is grounded; the fourth switch is connected in parallel across the two ends of the second capacitor.

[0025] 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.

[0026] Optionally, the demagnetization detection module includes a comparison unit, an RS flip-flop, and an AND logic unit; the first input end of the comparison unit is connected to the drive control signal, the second end is connected to the reference signal, and the drive control signal and the reference signal are compared; the set end of the RS flip-flop is connected to the control signal of the upper drive transistor in the drive control module, and the reset end is connected to the output end of the comparison unit; the first input end of the AND logic unit is connected to the output end of the RS flip-flop, and the second input end is connected to the control signal of the lower drive transistor in the drive control module, and outputs the demagnetization time detection signal.

[0027] 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 to the output end of the operation module, and the other end is connected to the positive-phase input end of the transconductance amplifier; one end of the seventh switch is connected to the positive-phase input end of the transconductance amplifier, and the other end is grounded; the inverting input end of the transconductance amplifier is grounded, and the output end is connected to the upper plate of the third capacitor and outputs the second voltage; the lower plate of the third capacitor is grounded; the eighth switch is connected in parallel across the two ends of the third capacitor;

[0028] Wherein, the sixth switch is turned on during the demagnetization time, and the seventh switch and the eighth switch are synchronized with the power switch transistor in the switching power supply circuit.

[0029] Optionally, the overcurrent protection circuit further includes a front-edge blanking module, and the front-edge blanking module is connected between the sampling signal and the input ends of the first sample-and-hold module and the second sample-and-hold module.

[0030] 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 to the input ends of the first sample-and-hold module and the second sample-and-hold module, the second input end is connected to the upper plate of the fourth capacitor, and the output end is connected to the input end of the drive control module; the upper plate of the fourth capacitor is connected to the output voltage sampling feedback signal of the switching power supply circuit, and the lower plate is grounded.

[0031] To achieve the above and other related objectives, the present invention provides an overcurrent protection system for a switching power supply. The overcurrent protection system for the switching power supply at least includes:

[0032] A switching power supply circuit and the above overcurrent protection circuit;

[0033] The switching power supply circuit realizes overcurrent protection based on the drive control signal output by the overcurrent protection circuit;

[0034] The overcurrent protection circuit obtains a sampling signal of the inductor peak current from the switching power supply circuit.

[0035] Optionally, the switching power supply circuit is a flyback converter.

[0036] To achieve the above and other related objectives, the present invention provides an overcurrent protection method for a switching power supply circuit. The overcurrent protection method for the switching power supply circuit at least includes:

[0037] Detect the demagnetization time of the inductor to obtain a demagnetization time detection signal;

[0038] Sample the minimum value of the inductor peak current to obtain a first sampling voltage, and sample the maximum value of the inductor peak current to obtain a second sampling voltage; sum the first sampling voltage and the second sampling voltage and multiply by a preset coefficient to obtain a first voltage;

[0039] Perform a multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage;

[0040] Compare the second voltage with a reference voltage, and control a power switch tube based on the comparison result to achieve overcurrent protection;

[0041] Wherein, the preset coefficient is a non-zero real number.

[0042] Optionally, the preset coefficient is 1 / 2, and the first voltage satisfies the following relationship:

[0043]

[0044] Wherein, Vp_calc is the first voltage, Ip_max is the maximum value of the inductor peak current, Ip_min is the minimum value of the inductor peak current, and Rcs is the resistance value of the sampling resistor of the inductor peak current in the switching power supply circuit.

[0045] More optionally, the second voltage satisfies the following relationship:

[0046]

[0047] Among them, Vcalc is the second voltage, Vp_calc is the first voltage, Tdemag is the demagnetization time of the inductor, gm is the transconductance of the multiplier, and C3 is the capacitance value of the transconductance output capacitor.

[0048] More optionally, the overcurrent protection point of the overcurrent protection method of the switching power supply circuit satisfies the following relational expression:

[0049]

[0050] Among them, Iocp is the overcurrent protection point, η is the efficiency, Nps is the turns ratio of the primary side to the secondary side in the flyback switching power supply circuit, Fsw is the system operating frequency, Vocp is the reference signal, and Rcs is the resistance value of the sampling resistor for the peak current of the inductor in the switching power supply circuit.

[0051] As described above, the overcurrent protection circuit, the switching power supply overcurrent protection system and method of the present invention have the following beneficial effects:

[0052] The overcurrent protection circuit, the switching power supply overcurrent protection system and method of the present invention can keep the output overcurrent point unchanged whether the system operates in the discontinuous mode or the continuous mode, have a wide application range, and high system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic structural diagram of an AC-DC power supply system shown as a flyback topology.

[0054] Figure 2 Schematic structural diagram of an AC-DC power supply system shown as a flyback topology with duty cycle compensation.

[0055] Figure 3 Schematic structural diagram of the overcurrent protection circuit of the present invention.

[0056] Figure 4 Schematic structural diagram of the first sample-and-hold module, the second sample-and-hold module, the operation module and the multiplication module of the present invention.

[0057] Figure 5 Schematic structural diagram of the demagnetization detection module of the present invention.

[0058] Figure 6 Schematic structural diagram of the switching power supply overcurrent protection system of the present invention.

[0059] Figure 7 Schematic diagram of the principle of detecting the demagnetization time of the present invention in the continuous current mode.

[0060] Figure 8 Schematic diagram of the principle of detecting the demagnetization time of the present invention in the discontinuous current mode.

[0061] Figure 9 It shows a schematic diagram of the principle of the overcurrent protection method of the present invention in continuous current mode.

[0062] Figure 10 It shows a schematic diagram of the principle of the overcurrent protection method of the present invention in discontinuous current mode.

[0063] Description of component labels

[0064] 11 AC-DC power supply circuit

[0065] 12 Driver chip

[0066] 121 Front edge blanking

[0067] 122 First comparator

[0068] 123 Second comparator

[0069] 124 PWM controller

[0070] 125 Oscillator

[0071] 2 Overcurrent protection circuit

[0072] 21 First sample and hold module

[0073] 22 Second sample and hold module

[0074] 23 Operation module

[0075] 24 Demagnetization detection module

[0076] 241 Comparison unit

[0077] 242 RS flip-flop

[0078] 243 AND logic unit

[0079] 25 Multiplication module

[0080] 251 Transconductance amplifier

[0081] 26 First comparison module

[0082] 27 Drive control module

[0083] 28 Front edge blanking module

[0084] 29 Second comparison module

[0085] 3 Switching power supply circuit

[0086] 31 Output voltage sampling and feedback module Detailed implementation

[0087] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0088] Please refer to Figures 1 to 10 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0089] As Figure 1 shown is an AC-DC power supply system with a flyback topology. Among them, the AC-DC power circuit 11 has a flyback topology structure. The drive chip 12 includes a front edge blanking 121, a first comparator 122, a second comparator 123, a PWM controller 124, and an oscillator 125. After the sampled voltage of the AC-DC power circuit 11 passes through the front edge blanking, it is compared with the reference voltage Vocp, and is also compared with the output voltage sampling feedback signal of the AC-DC power circuit 11. The PWM controller 124 generates a PWM signal based on the output signals of the two comparators and the output signal of the oscillator 125 to control the power switch tube in the AC-DC power circuit 11, thereby realizing overcurrent protection.

[0090] Its output power Pout satisfies the following relationship:

[0091]

[0092] Wherein, Pout is the output power; Lp is the inductance of the primary side of the transformer; Ip_max is the maximum value of the primary side peak current when the power switch tube is conducting; Ip_min is the minimum value of the primary side peak current when the power switch tube is conducting; Fsw is the system operating frequency; η is the efficiency.

[0093] For a constant voltage power supply system, its overcurrent point Iocp satisfies the following relationship:

[0094]

[0095] Wherein, Iocp is the output overcurrent point; Pocp is the output power at overcurrent; Vout is the output voltage; Ip_ocp is the maximum value of the primary side peak current when the power switch tube is conducting in the overcurrent state.

[0096] Generally, we use the method of fixing the peak current Ip_ocp of the primary side of the transformer to limit the overcurrent point Iocp. Therefore, for a system with a fixed operating frequency and operating in the discontinuous mode, its overcurrent point Iocp is fixed. However, for a system operating in the continuous mode, since Ip_min is not equal to 0 at this time, its overcurrent point is lower than that in the discontinuous mode, and it is impossible to keep the overcurrent point constant.

[0097] Generally in the continuous mode, the larger the duty cycle, the larger Ip_min; in order to reduce the variation of the output overcurrent point Iocp, the value of Ip_ocp will be correspondingly increased, so that Ip_ocp also increases with the increase of the duty cycle. As Figure 2 shown in Figure 1 is a scheme of introducing compensation on the basis of

[0098] V ocp = V ref + k·D on ;

[0099] wherein, Vref is the reference voltage; k is the duty cycle compensation coefficient; Don is the duty cycle when the power switch is on.

[0100] However, using the method of fixing the peak current of the primary side of the transformer and combining compensation to implement overcurrent protection can only compensate a fixed amount and cannot meet the systems under various different application conditions; especially when the system may work in the discontinuous mode or the continuous mode, this method cannot achieve accurate overcurrent protection.

[0101] Therefore, the present invention proposes an overcurrent protection scheme that can achieve accurate overcurrent protection regardless of whether the system is operating in the discontinuous mode or the continuous mode.

[0102] Embodiment 1

[0103] As Figure 3 shown, this embodiment provides an overcurrent protection circuit 2 for realizing overcurrent protection of a switching power supply circuit. The overcurrent protection circuit 2 includes:

[0104] A first sample-and-hold module 21, a second sample-and-hold module 22, an arithmetic module 23, a demagnetization detection module 24, a multiplication module 25, a first comparison module 26 and a drive control module 27.

[0105] As Figure 3As shown, the first sample-and-hold module 21 receives the sampling signal Vcs of the peak inductor current in the switching power supply circuit, samples and holds the minimum value Ip_min of the peak inductor current, and obtains the first sampled voltage Vcs1.

[0106] Specifically, as Figure 4 shown, 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 sampled voltage Vcs1. The lower plate of the first capacitor C1 is grounded. The second switch S2 is connected in parallel across the two ends of the first capacitor C1.

[0107] As Figure 3 shown, the second sample-and-hold module 22 receives the sampling signal Vcs, samples and holds the maximum value Ip_max of the peak inductor current, and obtains the second sampled voltage Vcs2.

[0108] Specifically, as Figure 4 shown, 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 sampled voltage Vcs2. The lower plate of the second capacitor C2 is grounded. The fourth switch S4 is connected in parallel across the two ends of the second capacitor C2.

[0109] It should be noted that the structures of the first sample-and-hold module 21 and the second sample-and-hold module 22 are not limited. Any circuit structure that can sample and hold the minimum and maximum values of the peak inductor current is applicable. The structures of the first sample-and-hold module 21 and the second sample-and-hold module 22 may also be different, and are not limited to this embodiment.

[0110] As Figure 3 shown, as another implementation manner of the present invention, the overcurrent protection circuit 2 further includes a front-edge blanking module 28. The front-edge blanking module 28 is connected between the sampling signal Vcs and the input ends of the first sample-and-hold module 21 and the second sample-and-hold module 22. The front-edge blanking module is used to eliminate the hidden danger of mis-triggering actions caused by the spikes at the leading edge of the pulse. The structure is not limited and will not be elaborated here one by one.

[0111] As Figure 3 shown, 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 by a preset coefficient to obtain the first voltage Vp_calc. Wherein, the preset coefficient is a non-zero real number.

[0112] Specifically, in this embodiment, the operation module 23 includes a fifth switch S5. 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 is connected to the output end of the second sample-and-hold module 22. When the fifth switch S5 is turned on, the charges on the upper plates of the first capacitor C1 and the second capacitor C2 are shared, achieving the effect of averaging the output signals of the first sample-and-hold module 21 and the second sample-and-hold module 22 after addition, that is, the preset coefficient is 0.5. In actual use, the preset coefficient can be non-zero. Based on different preset coefficients, the circuit structure is adjusted accordingly, which will not be elaborated here one by one.

[0113] As Figure 3 shown, the demagnetization detection module 24 detects the demagnetization time of the inductor to obtain a demagnetization time detection signal.

[0114] Specifically, as Figure 5 shown, in this embodiment, the demagnetization detection module 24 includes a comparison unit 241, an RS flip-flop 242, and an AND logic unit 243. The first input end of the comparison unit 241 is connected to the drive control signal Vgate, and the second end is connected to the reference signal Vref to compare the drive control signal Vgate with the reference signal Vref. As an example, the inverting input end of the comparison unit 241 is connected to the drive control signal Vgate, and the non-inverting input end is connected to the reference signal Vref. In actual use, the input terminal polarity and the corresponding relationship of the input signal can be adjusted through an inverter, as long as the same logic can be achieved. The set end of the RS flip-flop 242 is connected to the control signal Gate1 of the upper drive transistor Q1 in the drive control module 27, and the reset end is connected to the output end (output signal DET) of the comparison unit 241. The first input end of the AND logic unit 243 is connected to the output end of the RS flip-flop 242, and the second input end is connected to the control signal Gate2 of the lower drive transistor Q2 in the drive control module 27 to output the demagnetization time detection signal Demag. As an example, the AND logic unit is implemented by an AND gate. In actual use, any circuit structure that can implement the AND logic is applicable.

[0115] It should be noted that any structure that can implement the demagnetization time detection is applicable to the present invention, not limited to this embodiment.

[0116] As Figure 3 shown, the multiplication module 25 is connected to the output ends of the operation module 23 and the demagnetization detection module 24 to perform a multiplication operation on the first voltage Vp_calc and the demagnetization time detection signal Demag to obtain a second voltage Vcalc.

[0117] Specifically, as Figure 4 shown, in this 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 positive-phase input end of the transconductance amplifier 251. One end of the seventh switch S7 is connected to the positive-phase input end of the transconductance amplifier 251, and the other end is grounded. The inverting input end of the transconductance amplifier 251 is grounded, and the output end is connected to the upper plate of the third capacitor C3 and outputs the second voltage Vcalc. The lower plate of the third capacitor C3 is grounded. The eighth switch S8 is connected in parallel across the two ends of the third capacitor C3. Among them, 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 signal of the demagnetization time detection signal Demag. Any circuit structure that can multiply the first voltage Vp_calc by the demagnetization time detection signal Demag is applicable to the present invention, and is not limited to this embodiment.

[0118] As Figure 3 shown, the first comparison module 26 is connected to the output end of the multiplication module 25, receives the reference voltage Vocp, compares the second voltage Vcalc with the reference voltage Vocp, and outputs a comparison result.

[0119] Specifically, in this embodiment, the positive-phase input end of the first comparison module 26 is connected to the second voltage Vcalc, and the inverting input end is connected to the reference voltage Vocp. The reference voltage Vocp is a fixed voltage set internally. When the second voltage Vcalc is greater than the reference voltage Vocp, it is considered that the switching power supply circuit is overcurrent, and overcurrent protection measures need to be taken. In actual use, the corresponding relationship between the input terminal polarity and the input signal can be adjusted, which will not be elaborated here one by one.

[0120] As Figure 3 shown, the drive control module 27 is connected to the output end of the first comparison module 26, and generates a drive control signal Vgate based on the comparison result to achieve overcurrent protection.

[0121] As Figure 3As shown, as another implementation of the present invention, the overcurrent protection circuit 2 further includes a second comparison module 29 and a fourth capacitor C4. The first input terminal of the second comparison module 29 is connected to the input terminals of the first sample and hold module 21 and the second sample and hold module 22, the second input terminal is connected to the upper plate of the fourth capacitor C4, and the output terminal is connected to the input terminal of the drive control module 27. The upper plate of the fourth capacitor C4 is connected to the output voltage sampling feedback signal Vfb of the switching power supply circuit, and the lower plate is grounded. As an example, the non-inverting input terminal of the second comparison module 29 is connected to the input terminals of the first sample and hold module 21 and the second sample and hold module 22, and the inverting input terminal is connected to the upper plate of the fourth capacitor C4. Similarly, in actual use, the corresponding relationship between the input terminal polarities and the input signals can be adjusted, which will not be elaborated here one by one. 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.

[0122] It should be noted that the overcurrent protection circuit 2 can be integrated in a chip. At this time, the fourth capacitor C4 is provided outside the chip as a compensation capacitor, and other modules are provided inside the chip.

[0123] Embodiment 2

[0124] This embodiment provides a switching power supply overcurrent protection system, which includes:

[0125] A switching power supply circuit 3 and the overcurrent protection circuit 2 of Embodiment 1.

[0126] As Figure 6 shown, the switching power supply circuit 3 implements overcurrent protection based on the drive control signal Vgate output by the overcurrent protection circuit 2.

[0127] Specifically, in this embodiment, the switching power supply circuit 3 is a flyback converter, which includes a transformer, a power switch M1, a sampling resistor Rcs, a diode D1, an output capacitor Cout, and a load RL. One end of the primary coil of the transformer is connected to the input voltage Vin, and the other end is grounded via the power switch M1 and the sampling resistor Rcs. One end of the secondary coil of the transformer is connected to the anode of the diode D1, and the other end is grounded. The cathode of the diode D2 is grounded via the output capacitor Cout. The load RL is connected in parallel across the two ends of the output capacitor Cout.

[0128] Specifically, the input voltage Vin is a DC voltage. As an example, the switching power supply circuit 3 further includes a rectifier (not shown in the figure), and the rectifier converts the AC voltage into the input voltage Vin.

[0129] Specifically, as an example, the switching power supply circuit 3 further includes an output voltage sampling and feedback module 31, which is connected to the cathode of the diode D1 and generates the output voltage sampling and feedback signal Vfb.

[0130] It should be noted that any switching power supply circuit 3 that requires overcurrent protection is applicable to the present invention, and is not limited to this embodiment.

[0131] As Figure 6 shown, the overcurrent protection circuit 2 obtains the sampling signal Vcs of the inductor peak current from the switching power supply circuit 3. For the specific structure and principle, refer to Embodiment 1, and details will not be repeated here.

[0132] Embodiment 3

[0133] As Figures 7 to 10 shown, this embodiment provides an overcurrent protection method for a switching power supply circuit. In this embodiment, it is implemented based on the overcurrent protection circuit 2 in Embodiment 1. In actual use, any hardware or software that can implement this method is applicable to the present invention. The overcurrent protection method for the switching power supply circuit includes:

[0134] 1) Detect the demagnetization time of the inductor to obtain the demagnetization time detection signal Demag.

[0135] Specifically, as Figure 7 shown, in the continuous current mode, when the control signal Gate1 of the upper drive transistor Q1 in the drive control module 27 is at a high level, the upper drive transistor Q1 is turned on; the control signal Gate2 of the lower drive transistor Q2 in the drive control module 27 is inverted with Gate1, the lower drive transistor Q2 is turned off, the drive control signal Vgate is at a high level, the power switch transistor M1 is turned on (Ton), the drain DRAIN of the power switch transistor M1 is at a low level, and the primary coil of the transformer enters the charging mode. When the control signal Gate1 of the upper drive transistor Q1 is at a low level, the upper drive transistor Q1 is turned off; the control signal Gate2 of the lower drive transistor Q2 is inverted with Gate1, the lower drive transistor Q2 is turned on, the drive control signal Vgate is at a low level, the power switch transistor M1 is turned off (Toff), the drain DRAIN of the power switch transistor M1 is at a high level, the primary coil of the transformer enters the discharge and demagnetization mode, and the demagnetization time detection signal Demag jumps to a high level. As Figure 7 shown, in the continuous current mode, the output signal DET of the comparison unit 241 is always at a low level, and the demagnetization time detection signal Demag is basically the same as the control signal Gate2.

[0136] As Figure 8As shown, in discontinuous current mode, when the control signal Gate1 of the upper drive transistor Q1 is at a high level, the waveform is the same as that of Figure 7 . When the control signal Gate1 of the upper drive transistor Q1 is at a low level, the upper drive transistor Q1 is turned off; the control signal Gate2 of the lower drive transistor Q2 is inverted with Gate1, the lower drive transistor Q2 is turned on, the drive control signal Vgate is at a low level, the power switch transistor M1 is turned off (Toff), the drain DRAIN of the power switch transistor M1 is at a high level, the primary coil of the transformer enters the discharge and demagnetization mode, and the demagnetization time detection signal Demag jumps to a high level; when the demagnetization ends, the output signal DET of the comparison unit 241 generates a pulse, and the demagnetization time detection signal Demag jumps to a low level. As Figure 7 and Figure 8 shown, the demagnetization time Tdemag in discontinuous current mode is less than the demagnetization time Tdemag in continuous current mode.

[0137] 2) The minimum value of the sampled inductor peak current is sampled to obtain the first sampled voltage Vcs1, and the maximum value of the sampled inductor peak current is sampled to obtain the second sampled voltage Vcs2; the first sampled voltage Vcs1 and the second sampled voltage Vcs2 are summed and then multiplied by a preset coefficient to obtain the first voltage Vp_calc; the preset coefficient is a non-zero real number.

[0138] Specifically, as Figure 9 shown, when the drive control signal Vgate is at a high level, the power switch transistor M1 is turned on, and current flows through the sampling resistor Rcs to obtain the sampling signal Vcs. The second switch S2 and the fourth switch S4 are turned on during the blanking period to clear the charges on the first capacitor C1 and the second capacitor C2, and the second switch S2 and the fourth switch S4 are turned off after the blanking ends. After the blanking ends, the first switch S1 is turned on for a preset time (a pulse signal that can achieve sampling). At the same time, after the blanking ends, the third switch S3 is turned on and turned off when the drive control signal Vgate is at a low level. When the drive control signal Vgate is at a low level, the power switch transistor 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 the off state. The upper plate of the first capacitor C1 obtains the first sampled voltage Vcs1 corresponding to the minimum value of the inductor peak current, and the upper plate of the second capacitor C2 obtains the second sampled voltage Vcs2 corresponding to the maximum value of the inductor peak current.

[0139] Specifically, as Figure 9 andFigure 10 As shown, in this embodiment, the fifth switch S5 and the sixth switch S6 are controlled by the demagnetization time detection signal Demag. During the demagnetization time, the fifth switch S5 and the sixth switch S6 are turned on, 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 relational expression:

[0140]

[0141] Wherein, Vp_calc is the first voltage, Ip_max is the maximum value of the inductor peak current, Ip_min is the minimum value of the inductor peak current, and Rcs is the resistance value of the sampling resistor of the inductor peak current in the switching power supply circuit.

[0142] It should be noted that in actual use, the first sampling voltage Vcs1 and the second sampling voltage Vcs2 can be summed and then multiplied by a preset coefficient, and the steps of the operation can also be independent of the demagnetization time detection signal Demag. There is no clear sequence between step 1) and step 2), and this embodiment is not limiting.

[0143] 3) Perform a multiplication operation on the first voltage Vp_calc and the demagnetization time detection signal Demag to obtain a second voltage Vcalc.

[0144] Specifically, as Figure 9 and Figure 10 shown, the seventh switch S7 and the eighth switch S8 are synchronized with the power switch tube M1. When the power switch tube M1 is turned on, the seventh switch S7 and the eighth switch S8 are turned on, and when the power switch tube M1 is turned off, the seventh switch S7 and the eighth switch S8 are turned off. The multiplication operation is implemented by the multiplication module 25, and the second voltage Vcalc satisfies the following relational expression:

[0145] [[ID=2C]]

[0146] Wherein, Vcalc is the second voltage, Vp_calc is the first voltage, Tdemag is the demagnetization time of the inductor, gm is the transconductance of the multiplier, and C3 is the capacitance value of the transconductance output capacitor. From Figure 9 and Figure 10 it can be seen that the duty cycle of the second voltage Vcalc in the continuous current mode is greater than the duty cycle of the second voltage Vcalc in the discontinuous current mode.

[0147] 4) Compare the second voltage Vcalc with the reference voltage Vocp, and control the power switch transistor based on the comparison result to achieve overcurrent protection.

[0148] Specifically, adjust the conduction and turn-off of the power switch transistor M1 based on the comparison result between the second voltage Vcalc and the reference voltage Vocp, and finally make the second voltage Vcalc equal to the reference voltage Vocp, that is:

[0149]

[0150] Under the flyback topology, the overcurrent protection point of the present invention satisfies the following relational expression:

[0151]

[0152] After simplification, it is obtained:

[0153]

[0154] Wherein, Iocp is the overcurrent protection point, η is the efficiency, Nps is the turns ratio of the primary side to the secondary side coils in the flyback switching power supply circuit, Fsw is the system operating frequency, Vocp is the reference signal, and Rcs is the resistance value of the sampling resistor for the peak current of the inductor in the switching power supply circuit.

[0155] It can be seen that for a system with a fixed operating frequency, whether it operates in the discontinuous mode or the continuous mode, the overcurrent point of the present invention remains unchanged, and the accuracy of overcurrent protection is greatly improved.

[0156] In summary, the present invention provides an overcurrent protection circuit, a switching power supply overcurrent protection system and method, including: a first sample-and-hold module, a second sample-and-hold module, an arithmetic module, a demagnetization detection module, a multiplication module, a comparison module and a drive control module; the first sample-and-hold module receives the sampling signal of the inductor peak current in the switching power supply circuit, samples and holds the minimum value of the inductor peak current to obtain a first sampling voltage; the second sample-and-hold module receives the current sampling signal, samples and holds the maximum value of the inductor peak current to obtain a second sampling voltage; the arithmetic module is connected to the output ends of the first sample-and-hold module and the second sample-and-hold module, sums the first sampling voltage and the second sampling voltage and multiplies by a preset coefficient 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 to the output ends of the arithmetic module and the demagnetization detection module, performs a 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 and receives a reference voltage, compares the second voltage with the reference voltage and outputs a comparison result; the drive control module is connected to the output end of the first comparison module and generates a drive control signal based on the comparison result; wherein, the preset coefficient is a non-zero real number. The overcurrent protection circuit, the switching power supply overcurrent protection system and method of the present invention can keep the output overcurrent point unchanged whether the system works in the discontinuous mode or the continuous mode, have a wide application range and high system stability. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0157] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An overcurrent protection circuit for implementing overcurrent protection of a switching power supply circuit, characterized in that, The overcurrent protection circuit at least includes: 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 sample-and-hold module receives the sampling signal of the inductor peak current in the switching power supply circuit, samples and holds the minimum value of the inductor peak current, and obtains a first sampling voltage; The second sample-and-hold module receives the sampling signal, samples and holds the maximum value of the inductor peak current, and obtains a second sampling voltage; The operation module is connected to the output ends of the first sample-and-hold module and the second sample-and-hold module, sums the first sampling voltage and the second sampling voltage and then multiplies by a preset coefficient to obtain a first voltage; The demagnetization detection module detects the demagnetization time of the inductor and obtains a demagnetization time detection signal; The multiplication module is connected to the output ends of the operation module and the demagnetization detection module, performs a multiplication operation on the first voltage and the demagnetization time detection signal, and obtains 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 drive control module is connected to the output end of the first comparison module and generates a drive control signal based on the comparison result; Wherein, the preset coefficient is a non-zero real number.

2. The overcurrent protection circuit according to claim 1, wherein: 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, the other end is connected to the upper plate of the first capacitor and outputs the first sampling voltage; the lower plate of the first capacitor is grounded; the second switch is connected in parallel across the two ends of the first capacitor.

3. The overcurrent protection circuit according to claim 1, wherein: 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, the other end is connected to the upper plate of the second capacitor and outputs the second sampling voltage; the lower plate of the second capacitor is grounded; the fourth switch is connected in parallel across the two ends of the second capacitor.

4. The overcurrent protection circuit according to any one of claims 1-3, characterized in that: 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.

5. The overcurrent protection circuit according to claim 1, wherein: The demagnetization detection module includes a comparison unit, an RS flip-flop, and an AND logic unit; the first input end of the comparison unit is connected to the drive control signal, the second end is connected to a reference signal, and compares the drive control signal with the reference signal; the set end of the RS flip-flop is connected to the control signal of the upper drive transistor in the drive control module, the reset end is connected to the output end of the comparison unit; the first input end of the AND logic unit is connected to the output end of the RS flip-flop, the second input end is connected to the control signal of the lower drive transistor in the drive control module, and outputs the demagnetization time detection signal.

6. The overcurrent protection circuit according to claim 1, characterized in that: 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 to the output end of the operation module, and the other end is connected to the non-inverting input end of the transconductance amplifier; one end of the seventh switch is connected to the non-inverting input end of the transconductance amplifier, and the other end is grounded; the inverting input end of the transconductance amplifier is grounded, and the output end is connected to the upper plate of the third capacitor and outputs the second voltage; the lower plate of the third capacitor is grounded; the eighth switch is connected in parallel across both ends of the third capacitor; Wherein, the sixth switch is turned on during the demagnetization time, and the seventh switch and the eighth switch are synchronized with the power switch tube in the switching power supply circuit.

7. The overcurrent protection circuit according to claim 1, wherein: The overcurrent protection circuit further includes a front-edge blanking module, and the front-edge blanking module is connected between the sampling signal and the input ends of the first sample-and-hold module and the second sample-and-hold module.

8. The overcurrent protection circuit according to claim 1, wherein: 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 to the input ends of the first sample-and-hold module and the second sample-and-hold module, the second input end is connected to the upper plate of the fourth capacitor, and the output end is connected to the input end of the drive control module; the upper plate of the fourth capacitor is connected to the output voltage sampling feedback signal of the switching power supply circuit, and the lower plate is grounded.

9. A switching power supply overcurrent protection system, characterized by The switching power supply overcurrent protection system at least includes: A switching power supply circuit and the overcurrent protection circuit according to any one of claims 1-8; The switching power supply circuit realizes overcurrent protection based on the drive control signal output by the overcurrent protection circuit; The overcurrent protection circuit obtains a sampling signal of the inductor peak current from the switching power supply circuit.

10. The over-current protection system for a switching power supply according to claim 9, characterized in that: The switching power supply circuit is a flyback converter.

11. An overcurrent protection method for a switching power supply circuit, characterized in that, The overcurrent protection method of the switching power supply circuit at least includes: Detecting the demagnetization time of the inductor to obtain a demagnetization time detection signal; Sampling the minimum value of the inductor peak current to obtain a first sampling voltage, and sampling the maximum value of the inductor peak current to obtain a second sampling voltage; adding the first sampling voltage and the second sampling voltage and multiplying by a preset coefficient to obtain a first voltage; Performing a multiplication operation on the first voltage and the demagnetization time detection signal to obtain a second voltage; Comparing the second voltage with a reference voltage, and controlling the power switch tube based on the comparison result to achieve overcurrent protection; Wherein, the preset coefficient is a non-zero real number.

12. The overcurrent protection method for the switching power supply circuit according to claim 11, characterized in that: The preset coefficient is 1 / 2, and the first voltage satisfies the following relationship: Wherein, Vp_calc is the first voltage, Ip_max is the maximum value of the inductor peak current, Ip_min is the minimum value of the inductor peak current, and Rcs is the resistance value of the sampling resistor of the inductor peak current in the switching power supply circuit.

13. The overcurrent protection method for the switching power supply circuit according to claim 11 or 12, characterized in that: The second voltage satisfies the following relationship: Wherein, Vcalc is the second voltage, Vp_calc is the first voltage, Tdemag is the demagnetization time of the inductor, gm is the transconductance of the multiplier, and C3 is the capacitance value of the transconductance output capacitor.

14. The overcurrent protection method for the switching power supply circuit according to claim 13, characterized in that: The overcurrent protection point of the overcurrent protection method of the switching power supply circuit satisfies the following relationship: Among them, Iocp is the overcurrent protection point, η is the efficiency, Nps is the turns ratio of the primary and secondary windings in the flyback switching power supply circuit, Fsw is the system operating frequency, Vocp is the reference signal, and Rcs is the resistance value of the sampling resistor for the peak inductor current in the switching power supply circuit.

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