Primary-side feedback constant-voltage switching power supply circuit

Abstract

The present invention provides a primary-side feedback constant-voltage switching power supply circuit, comprising: a transformer; a voltage sampling module for sampling the output voltage to obtain a feedback signal; a delay sampling module for performing delay sampling on the feedback signal; a voltage sampling feedback module for comparing the delay sampling signal of the feedback signal with a reference signal to obtain a constant-voltage control signal; an output voltage limiting module for comparing the voltage signal output by the power supply module with a voltage limiting signal to obtain a voltage limiting control signal; a current sampling feedback module for outputting a current sampling signal; a switch control module for generating a compensation signal based on the constant-voltage control signal and the voltage limiting control signal, and comparing the compensation signal with the current sampling signal to generate a switch control signal; and a driving module for driving a power switch tube to operate based on the switch control signal. The primary-side feedback constant-voltage switching power supply circuit of the present invention has a low system cost, is more miniaturized, can effectively prevent magnetic interference, and will not fail or enter a protection state due to interference.

Description

Technical Field

[0001] The present invention relates to the field of circuit design, and particularly to a primary-side feedback constant-voltage switching power supply circuit. Background Art

[0002] A switching power supply is a power supply that uses modern power electronics technology to control the on-off time ratio of a switching transistor to maintain a stable output voltage. A switching power supply generally consists of a pulse width modulation (PWM) control IC and a MOSFET. With the development and innovation of power electronics technology, the switching power supply technology is also constantly innovating. The switching power supply is widely used in various electronic devices due to its characteristics of small size, light weight, and high efficiency, and is an indispensable power supply method for the rapid development of the current electronic information industry.

[0003] In a constant-voltage switching power supply with a flyback topology, a primary-side feedback mode is often adopted, and the output voltage is detected by a voltage sampling detection module. In order to avoid sampling errors when the switching transistor is turned off, a delay circuit is usually added before sampling. However, due to the existence of this delay circuit, the voltage sampling module will fail when the system encounters external magnetic field interference. Because when the system encounters external magnetic field interference, the inductance of the transformer decreases. According to L×I CS pk =V out ×T demag it can be known that the decrease in the inductance L of the transformer will lead to the decrease of the demagnetization time T demag When the demagnetization time T demag is less than the delay time T delay set inside the chip, the chip will sample incorrectly. As Figure 1 shown (where T SW is a switching cycle, T ON is the switching conduction time, Ip is the current on the primary winding, Ip_pk is the peak value of the current on the primary winding, Is is the current on the secondary winding, and Is_pk is the peak value of the current on the secondary winding), at this time the chip thinks that the output voltage is always lower than expected. Therefore, the system will output at the maximum power, ultimately resulting in too high an output voltage (out of control), system failure, or entering a protection state, where I CS_pk is the peak value of the sampling current, and Vout is the output voltage.

[0004] To prevent magnetic interference, a secondary-side feedback mode can be adopted, that is, directly sample the output voltage, and then feedback the output voltage signal to the primary side through an optocoupler. The chip then controls the on or off of the primary switching transistor through this signal, and controls the output voltage accordingly. When the system encounters external magnetic field interference, the inductance of the transformer decreases. According to It can be seen that the output energy P will decrease, the output voltage will drop, the current passing through the optocoupler will decrease, resulting in an increase in the primary side feedback voltage. The chip then determines that the output voltage has decreased and increases the conduction time of the switching transistor to increase the peak value of the sampling current I CS_pk , or directly increase the operating frequency F of the chip SW , so as to achieve the purpose of increasing the output power. Since the change in the inductance L of the transformer has little impact on the entire sampling and feedback process, this system can effectively prevent magnetic interference. However, using this control method requires optocoupler feedback, which has a high cost and is not conducive to the miniaturization of the power supply.

[0005] Therefore, how to avoid system failure or entering the protection state while reducing costs and contributing to the miniaturization of the system when encountering external magnetic field interference has become one of the problems that need to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a primary side feedback constant voltage switching power supply circuit to solve the problems in the prior art such as system failure, entering the protection state, high cost and not being conducive to miniaturization when encountering external magnetic field interference.

[0007] To achieve the above purpose and other related purposes, the present invention provides a primary side feedback constant voltage switching power supply circuit, which at least includes:

[0008] A transformer, a power switching transistor, a current sampling module, a voltage sampling module, a current sampling feedback module, a voltage sampling feedback module, a delay sampling module, a switching control module, a driving module, an output voltage limiting module and a power supply module;

[0009] One end of the first primary winding of the transformer is connected to the input voltage, and the other end is grounded through the power switching transistor and the current sampling module in sequence; one end of the second primary winding of the transformer is connected to the power supply module, and the other end is grounded; the secondary winding of the transformer is connected to the load;

[0010] The voltage sampling module is connected in parallel at both ends of the second primary winding, and is used to sample the output voltage and obtain a feedback signal;

[0011] The delay sampling module is connected to the output end of the voltage sampling module to perform delay sampling on the feedback signal;

[0012] The voltage sampling feedback module is connected to the output end of the delay sampling module, compares the delay sampling signal of the feedback signal with a reference signal, and obtains a constant voltage control signal;

[0013] The output voltage limiting module is connected to the output end of the power supply module, compares the voltage signal output by the power supply module with the voltage limiting signal, and obtains a voltage limiting control signal;

[0014] The current sampling feedback module is connected to the output end of the current sampling module and outputs a current sampling signal;

[0015] The switch control module is connected to the output ends of the voltage sampling feedback module, the output voltage limiting module and the current sampling feedback module, generates a compensation signal based on the constant voltage control signal and the voltage limiting control signal, and compares the compensation signal with the current sampling signal to generate a switch control signal;

[0016] The driving module is connected between the output end of the switch control module and the gate of the power switch tube, and drives the power switch tube to work based on the switch control signal.

[0017] Optionally, the primary-side feedback constant voltage switching power supply circuit further includes a first diode and a first capacitor. The anode of the first diode is connected to one end of the secondary-side winding, and the cathode is connected to one end of the first capacitor; the other end of the first capacitor is connected to the other end of the secondary-side winding and grounded.

[0018] Optionally, the primary-side feedback constant voltage switching power supply circuit further includes a working voltage generating module. The working voltage generating module is connected to the power supply module and generates a working voltage based on the voltage signal.

[0019] Optionally, the current sampling module includes a first resistor. One end of the first resistor is connected to the power switch tube, and the other end is grounded.

[0020] Optionally, the voltage sampling module includes a second resistor and a third resistor. The second resistor and the third resistor are connected in series and then connected in parallel across both ends of the second primary-side winding. The middle node of the second resistor and the third resistor outputs the feedback signal.

[0021] Optionally, the power supply module includes a second diode, a fourth resistor and a second capacitor; the anode of the second diode is connected to the second primary-side winding; one end of the fourth resistor is connected to the input voltage, and the other end is connected to the cathode of the second diode; one end of the second capacitor is connected to the cathode of the second diode, and the other end is grounded.

[0022] Optionally, the voltage sampling feedback module includes a constant voltage operational amplifier unit and a first integration unit;

[0023] The inverting input terminal of the constant voltage operational amplifier unit is connected to the delayed sampling signal of the feedback signal, the non-inverting input terminal is connected to the reference signal, and outputs the constant voltage control signal;

[0024] One end of the first integration unit is connected to the inverting input terminal of the constant voltage operational amplifier unit, and the other end is connected to the compensation signal.

[0025] Optionally, the output voltage limiting module includes a voltage limiting operational amplifier unit and a second integration unit;

[0026] The inverting input terminal of the voltage limiting operational amplifier unit is connected to the voltage module, the non-inverting input terminal is connected to the voltage limiting signal, and the voltage limiting control signal is output;

[0027] One end of the second integration unit is connected to the inverting input terminal of the voltage limiting operational amplifier unit, and the other end is connected to the compensation signal.

[0028] More optionally, the switch control module includes a compensation signal generating unit and a switch control signal generating unit;

[0029] The compensation signal generating unit adjusts the magnitude of the compensation signal based on the smaller of the constant voltage control signal and the voltage limiting control signal, and the constant voltage control signal and the voltage limiting control signal are inversely proportional to the compensation signal;

[0030] The switch control signal generating unit is connected to the output terminal of the compensation signal generating unit, and generates the switch control signal based on the difference between the compensation signal and the current sampling signal to adjust the output voltage.

[0031] More optionally, the compensation signal generating unit includes an AND logic, a pull-down transistor, a fifth resistor, and a third capacitor;

[0032] The input terminals of the AND logic are respectively connected to the constant voltage control signal and the voltage limiting control signal, and the output terminal is connected to the control terminal of the pull-down transistor; one end of the pull-down transistor is grounded, and the other end is connected to the operating voltage via the fifth resistor; the connection node between the pull-down transistor and the fifth resistor outputs the compensation signal; one end of the third capacitor is connected to the compensation signal, and the other end is grounded.

[0033] More optionally, the switch control signal generating unit includes a comparator, an oscillator, and an RS latch;

[0034] The input terminals of the comparator respectively receive the compensation signal and the current sampling signal, and output a comparison result;

[0035] The oscillator is connected to the comparison result and generates an oscillation signal based on the comparison result;

[0036] The set terminal of the RS latch is connected to the output terminal of the oscillator, the reset terminal is connected to the output terminal of the comparator, and the switch control signal is generated based on the comparison result and the oscillation signal.

[0037] As described above, the primary-side feedback constant-voltage switching power supply circuit of the present invention has the following beneficial effects:

[0038] The primary-side feedback constant-voltage switching power supply circuit of the present invention adopts a primary-side feedback mode, eliminating secondary-side feedback components such as optocouplers, reducing system costs, and making the circuit more miniaturized.

[0039] The primary-side feedback constant-voltage switching power supply circuit of the present invention adopts a circuit structure in which a constant-voltage operational amplifier and a voltage-limiting operational amplifier operate in parallel, ensuring that the system can still maintain power output after magnetic interference occurs, effectively preventing magnetic interference, and not failing or entering a protection state due to interference.

[0040] The primary-side feedback constant-voltage switching power supply circuit of the present invention determines the occurrence of magnetic interference by detecting VCC overvoltage, which can not only effectively detect the output overvoltage caused by real magnetic interference, but also help filter out noise interference to prevent misoperation. Description of the Drawings

[0041] Figure 1 It shows a schematic diagram of the working waveform of a chip adopting a primary-side feedback mode in the prior art under abnormal conditions.

[0042] Figure 2 It shows a schematic diagram of the structure of the primary-side feedback constant-voltage switching power supply circuit of the present invention.

[0043] Figure 3 It shows a schematic diagram of the structure of the current sampling feedback module, voltage sampling feedback module, and switch control module in the primary-side feedback constant-voltage switching power supply circuit of the present invention.

[0044] Figure 4 It shows a schematic diagram of the working timing of the constant-voltage operational amplifier unit, voltage-limiting operational amplifier unit, and initial voltage in the primary-side feedback constant-voltage switching power supply circuit of the present invention.

[0045] Figure 5 It shows a schematic diagram of the working waveform of the primary-side feedback constant-voltage switching power supply circuit of the present invention under abnormal conditions.

[0046] Description of Component Labels

[0047] 1 Primary-side feedback constant-voltage switching power supply circuit

[0048] 11 Transformer

[0049] 12 Delay sampling module

[0050] 13 Voltage sampling feedback module

[0051] 131 First integration unit

[0052] 14 Power supply module

[0053] 15 Output voltage limiting module

[0054] 151 Second integration unit

[0055] 16 Current sampling feedback module

[0056] 17 Switch control module

[0057] 171 Compensation signal generation unit

[0058] 171a AND logic

[0059] 172 Switch control signal generation unit

[0060] 172a Oscillator

[0061] 18 Driver module

[0062] 19 Operating voltage generation module Detailed implementation manners

[0063] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand 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 implementation manners, and 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.

[0064] Please refer to Figures 2 to 5 . 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.

[0065] As Figures 2 to 5 shown, the present invention provides a primary-side feedback constant-voltage switching power supply circuit 1, and the primary-side feedback constant-voltage switching power supply circuit 1 includes:

[0066] Transformer 11, power switch tube Q1, current sampling module, voltage sampling module, delay sampling module 12, voltage sampling feedback module 13, power supply module 14, output voltage limiting module 15, current sampling feedback module 16, switch control module 17, and driver module 18.

[0067] As Figure 2 shown, the transformer 11 is used for electric energy conversion.

[0068] Specifically, as Figure 2As shown, the transformer 11 includes a first primary winding L1, a second primary winding L2, and a secondary winding L3. One end of the first primary winding L1 is connected to the input voltage Vin, and the other end is grounded sequentially via the power switch Q1 and the current sampling module. One end of the second primary winding L2 is connected to the power supply module 14, and the other end is grounded. The output voltage Vout is obtained across the two ends of the secondary winding L3 to provide a constant voltage for the load.

[0069] As an implementation of the present invention, the primary-side feedback constant-voltage switching power supply circuit 1 further includes a first diode D1 and a first capacitor C1. The anode of the first diode D1 is connected to one end of the secondary winding L3, and the cathode is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the other end of the secondary winding L3 and grounded.

[0070] As Figure 2 shown, the power switch Q1 is connected between the first primary winding L1 and the current sampling module, and adjusts the output voltage Vout to reach the expected value by turning on and off.

[0071] Specifically, as Figure 2 shown, in this embodiment, the power switch Q1 is an NMOS transistor. The drain of the power switch Q1 is connected to the first primary winding, the source is connected to the current sampling module, and the gate is connected to the output end of the driving module. In actual use, the device type of the power switch can be selected according to needs, which will not be elaborated here one by one.

[0072] As Figure 2 shown, the current sampling module is connected to the power switch Q1 to sample the current flowing through the power switch Q1.

[0073] Specifically, as Figure 2 shown, in this embodiment, the current sampling module is implemented by a first resistor R1. One end of the first resistor R1 is connected to the source of the power switch Q1, and the other end is grounded. The connection node between the first resistor R1 and the power switch Q1 outputs a current sampling signal CS. In actual use, any circuit structure that can sample the current flowing through the power switch Q1 is applicable to the present invention, which will not be elaborated here one by one.

[0074] As Figure 2 shown, the voltage sampling module is connected in parallel across the two ends of the second primary winding L2, and is used to sample the output voltage Vout and obtain a feedback signal FB.

[0075] Specifically, as Figure 2As shown, in this embodiment, the voltage sampling module includes a second resistor R2 and a third resistor R3. The second resistor R2 and the third resistor R3 are connected in series and then connected in parallel across both ends of the second primary winding L2. A middle node of the second resistor R2 and the third resistor R3 outputs the feedback signal FB. In actual use, any circuit structure that can sample the voltage on the second primary winding L2 to obtain the feedback signal FB is applicable, and is not limited to this embodiment.

[0076] As Figure 2 shown, the delay sampling module 12 is connected to the output end of the voltage sampling module, delays the sampling of the feedback signal FB, and obtains a delayed sampling signal VFB of the feedback signal.

[0077] Specifically, since the voltage on the second primary winding L2 will jitter at the moment when the power switch Q1 is turned off, in order to avoid sampling errors, the delay sampling module 12 samples after a preset delay time T delay after the power switch Q1 is turned off to ensure the accuracy of sampling.

[0078] As Figure 2 shown, the voltage sampling feedback module 13 is connected to the output end of the delay sampling module 12, compares the delayed sampling signal VFB of the feedback signal with the reference signal Vref, and obtains a constant voltage control signal OUT1.

[0079] Specifically, as Figure 3 shown, in this embodiment, the voltage sampling feedback module 13 includes a constant voltage operational amplifier unit OP1 and a first integration unit 131. The inverting input terminal of the constant voltage operational amplifier unit 13 is connected to the delayed sampling signal VFB of the feedback signal, the non-inverting input terminal is connected to the Vref, and the constant voltage control signal OUT1 is output. One end of the first integration unit 131 is connected to the inverting input terminal of the constant voltage operational amplifier unit OP1, and the other end is connected to the compensation signal Vcomp; as an example, the first integration unit 131 includes a fourth capacitor C4 and a seventh resistor R7. One end of the fourth capacitor C4 is connected to the inverting input terminal of the constant voltage operational amplifier unit OP1, and the other end is connected to the compensation signal Vcomp via the seventh resistor R7.

[0080] As Figure 2 shown, the power supply module 14 is connected to one end of the second primary winding L2 and is used to generate a voltage signal VCC.

[0081] Specifically, as Figure 2As shown, the power supply module 14 includes a second diode D2, a fourth resistor R4, and a second capacitor C2. The anode of the second diode D2 is connected to the second primary winding L2; one end of the fourth resistor R4 is connected to the input voltage Vin, and the other end is connected to the cathode of the second diode D2; one end of the second capacitor C2 is connected to the cathode of the second diode D2, and the other end is grounded; the cathode of the second diode D2 outputs the voltage signal VCC. Any circuit structure that can obtain a voltage signal based on the signal feedback from the output voltage Vout is applicable to the present invention, and is not limited to this embodiment.

[0082] As Figure 2 shown, the output voltage limiting module 15 is connected to the output end of the power supply module 14, compares the voltage signal VCC output by the power supply module 14 with the voltage limiting signal Vlimit, and obtains a voltage limiting control signal OUT2.

[0083] Specifically, as Figure 3 shown, in this embodiment, the output voltage limiting module 15 includes a voltage limiting operational amplifier unit OP2 and a second integration unit 151. The inverting input terminal of the voltage limiting operational amplifier unit OP2 is connected to the voltage signal VCC, the non-inverting input terminal is connected to the voltage limiting signal Vlimit, and the voltage limiting control signal OUT2 is output. One end of the second integration unit 151 is connected to the inverting input terminal of the voltage limiting operational amplifier unit OP2, and the other end is connected to the compensation signal Vcomp; as an example, the second integration unit 151 includes a fifth capacitor C5 and an eighth resistor R8. One end of the fifth capacitor C5 is connected to the inverting input terminal of the voltage limiting operational amplifier unit OP2, and the other end is connected to the compensation signal Vcomp via the eighth resistor R8.

[0084] As Figure 2 shown, the current sampling feedback module 16 is connected to the output end of the current sampling module and outputs a current sampling signal CS.

[0085] As Figure 2 shown, the switch control module 17 is connected to the output ends of the voltage sampling feedback module 13, the output voltage limiting module 15, and the current sampling feedback module 16, generates a compensation signal Vcomp based on the constant voltage control signal OUT1 and the voltage limiting control signal OUT2, and compares the compensation signal Vcomp with the current sampling signal CS to generate a switch control signal.

[0086] Specifically, as Figure 3As shown, the switch control module 17 includes a compensation signal generation unit 171 and a switch control signal generation unit 172. The compensation signal generation unit 171 adjusts the magnitude of the compensation signal Vcomp based on the smaller value of the constant voltage control signal OUT1 and the voltage limit control signal OUT2, and the constant voltage control signal OUT1 and the voltage limit control signal OUT2 are inversely proportional to the compensation signal Vcomp. The switch control signal generation unit 172 is connected to the output terminal of the compensation signal generation unit 171, and generates the switch control signal based on the difference between the compensation signal Vcomp and the current sampling signal CS to adjust the output voltage Vout.

[0087] More specifically, as Figure 3 shown, in this embodiment, the compensation signal generation unit 171 includes an AND logic 171a, a pull-down transistor Q2, a fifth resistor R5, and a third capacitor C3. The input terminals of the AND logic 171a are respectively connected to the constant voltage control signal OUT1 and the voltage limit control signal OUT2, and the output terminal is connected to the control terminal of the pull-down transistor Q2. As an example, the AND logic 171a includes a third diode D3, a fourth diode D4, and a sixth resistor R6. The cathode of the third diode D3 is connected to the constant voltage control signal OUT1, and the anode is connected to the control terminal of the pull-down transistor Q2. The cathode of the fourth diode D4 is connected to the voltage limit control signal OUT2, and the anode is connected to the control terminal of the pull-down transistor Q2. One end of the sixth resistor R6 is connected to the operating voltage Vdd, and the other end is connected to the control terminal of the pull-down transistor Q2. In actual use, any circuit structure that can implement the AND logic is applicable, not limited to this embodiment. One end of the pull-down transistor Q2 is grounded, and the other end is connected to the operating voltage Vdd via the fifth resistor R5. As an example, the pull-down transistor Q2 is a PMOS transistor. In actual use, the corresponding device type can be selected according to needs. The connection node of the pull-down transistor Q2 and the fifth resistor R5 outputs the compensation signal Vcomp. One end of the third capacitor C3 is connected to the compensation signal Vcomp, and the other end is grounded.

[0088] More specifically, as Figure 3 shown, in this embodiment, the switch control signal generation unit 172 includes a comparator CMP, an oscillator 172a, and an RS latch. The input terminals of the comparator CMP respectively receive the compensation signal Vcomp and the current sampling signal CS, and output a comparison result. The oscillator 172a is connected to the comparison result and generates an oscillation signal based on the comparison result. As an example, the larger the comparison result, the higher the frequency of the oscillation signal. The set terminal S of the RS latch is connected to the output terminal of the oscillator 172a, and the reset terminal R is connected to the output terminal of the comparator CMP. The switch control signal is generated based on the comparison result and the oscillation signal.

[0089] It should be noted that the corresponding relationship between the input signals of the constant-voltage operational amplifier unit OP1, the voltage-limiting operational amplifier unit OP2, and the comparator CMP and the polarities of the input ports, and the voltage magnitude corresponding to the conduction of the pull-down transistor Q2 can be set according to actual needs, as long as the logical relationship of the present invention can be achieved (the corresponding relationship can be changed by adding an inverter), and it is not limited to the corresponding relationship of this embodiment.

[0090] As Figure 2 shown, the driving module 18 is connected between the output terminal of the switch control module 17 and the gate of the power switch transistor Q1 to generate the gate control signal CATE of the power switch transistor Q1, and drives the power switch transistor Q1 to operate based on the switch control signal.

[0091] As Figure 2 shown, as an implementation manner of the present invention, the primary-side feedback constant-voltage switching power supply circuit 1 further includes a working voltage generation module 19, and the working voltage generation module 19 is connected to the power supply module 14 to convert the voltage signal VCC to obtain the working voltage Vdd to provide a working voltage for other modules in the primary-side feedback constant-voltage switching power supply circuit 1.

[0092] As Figure 2 shown, as an implementation manner of the present invention, the delay sampling module 12, the voltage sampling feedback module 13, the output voltage limiting module 15, the current sampling feedback module 16, the switch control module 17, the driving module 18, and the voltage generation module 19 are encapsulated in the same chip.

[0093] As Figure 2 shown, as an implementation manner of the present invention, the primary-side feedback constant-voltage switching power supply circuit 1 further includes a sixth capacitor C6 connected across the input voltage Vin.

[0094] As Figure 4 shown, the primary-side feedback constant-voltage switching power supply circuit of the present invention adopts a primary-side feedback mode plus output voltage limitation. The constant-voltage module and the voltage-limiting module operate in parallel. Both operational amplifiers are set with weak pull-up and strong pull-down, and the outputs are combined together. A compensation signal is generated based on the operational amplifier with a lower level, and then the output voltage Vout is adjusted.

[0095] When working normally, the constant-voltage operational amplifier unit OP1 stabilizes the feedback signal at a preset value through closed-loop operation based on the constant-voltage control signal OUT1, and simultaneously obtains a corresponding compensation signal Vcomp. Based on the compensation signal Vcomp, a stable output voltage Vout is obtained; whether magnetic interference occurs is judged by detecting the voltage of the voltage signal VCC port. At this time, since no magnetic interference is detected, the voltage-limiting control signal OUT2 is at a high level (High clamp) and has no effect on the compensation signal Vcomp.

[0096] When the system encounters external magnetic field interference, the output voltage Vout will increase; then the voltage-limiting control signal OUT2 correspondingly becomes low.

[0097] It can be judged that the magnetic interference working mode has been entered. At this time, the voltage-limiting operational amplifier unit OP2 inside the chip starts to take over the closed-loop operation to ensure that the output voltage Vout is stabilized at the set voltage-limiting working point and does not continue to increase, thereby protecting the components on the secondary side from being damaged due to overvoltage, and the system will not power off due to abnormal protection.

[0098] When the system encounters external magnetic field interference, the inductance of the transformer decreases, and the demagnetization time T demag decreases. When the demagnetization time T demag is less than the delay time T set inside the chip delay , as Figure 5 shown, the output voltage limiting module starts to work, and the voltage V AUX on the second primary winding L2 is limited to V AUX_max . The feedback signal FB decreases, and the compensation signal Vcomp gradually increases to the highest value (High clamp). The oscillation frequency of the oscillator 172a and the peak value of the current sampling signal CS also increase correspondingly, resulting in an increase in the output voltage Vout; based on the transformer coupling principle, the voltage VAUX on the second primary winding L2 (auxiliary winding) also increases. After filtering through the second capacitor C2 (electrolytic capacitor) to filter out the switching noise signal, the voltage of the voltage signal VCC port increases. When the voltage signal VCC increases to the voltage-limiting signal Vlimit, the output OUT2 of the voltage-limiting operational amplifier unit OP2 starts to decrease. When it is lower than the output OUT1 of the constant-voltage operational amplifier unit OP1, the voltage-limiting operational amplifier unit OP2 replaces the output of the constant-voltage operational amplifier unit OP1 to work, the compensation signal Vcomp is pulled down, the working frequency of the system starts to decrease, and the peak value of the current sampling signal CS decreases, thereby reducing the output power and finally stabilizing the output voltage at the limiting voltage.

[0099] When the magnetic interference is removed and the feedback signal FB detects an excessive value (higher than the stable output value during normal operation), the output OUT1 of the constant-voltage operational amplifier unit OP1 drops to the lowest value (Low Clamp), and the output OUT2 of the voltage-limiting operational amplifier unit OP2 rises to the highest value (High Clamp). The constant-voltage operational amplifier unit OP1 takes over the closed-loop control again and pulls down the compensation signal Vcomp to further reduce the output energy. At this time, the output voltage drops until it returns to the stable output voltage during normal operation, and the output OUT1 of the constant-voltage operational amplifier unit OP1 also rises back to the original normal value. Therefore, the system will not fail and will not enter the protection state, and it can ensure safe operation without power interruption even under magnetic interference.

[0100] In summary, the present invention provides a primary-side feedback constant-voltage switching power supply circuit, including: a transformer, a power switch transistor, a current sampling module, a voltage sampling module, a current sampling feedback module, a voltage sampling feedback module, a delay sampling module, a switching control module, a driving module, an output voltage limiting module, and a power supply module; one end of the first primary winding of the transformer is connected to the input voltage, and the other end is grounded via the power switch transistor and the current sampling module in sequence; one end of the second primary winding of the transformer is connected to the power supply module, and the other end is grounded; the secondary winding of the transformer is connected to a load; the voltage sampling module is connected in parallel across both ends of the second primary winding, and is used for sampling the output voltage and obtaining a feedback signal; the delay sampling module is connected to the output end of the voltage sampling module to perform delay sampling on the feedback signal; the voltage sampling feedback module is connected to the output end of the delay sampling module, compares the delay sampling signal of the feedback signal with a reference signal, and obtains a constant-voltage control signal; the output voltage limiting module is connected to the output end of the power supply module, compares the voltage signal output by the power supply module with a voltage-limiting signal, and obtains a voltage-limiting control signal; the current sampling feedback module is connected to the output end of the current sampling module and outputs a current sampling signal; the switching control module is connected to the output ends of the voltage sampling feedback module, the output voltage limiting module, and the current sampling feedback module, generates a compensation signal based on the constant-voltage control signal and the voltage-limiting control signal, and compares the compensation signal with the current sampling signal to generate a switching control signal; the driving module is connected between the output end of the switching control module and the gate of the power switch transistor, and drives the power switch transistor to operate based on the switching control signal. The primary-side feedback constant-voltage switching power supply circuit of the present invention adopts a primary-side feedback mode, omits secondary-side feedback components such as optocouplers, reduces the system cost, and makes the circuit more miniaturized; adopts a circuit structure in which a constant-voltage operational amplifier and a voltage-limiting operational amplifier operate in parallel, ensuring that the system can still ensure continuous power output after magnetic interference occurs, can effectively prevent magnetic interference, and will not fail or enter a protection state due to interference; judges the generation of magnetic interference by detecting VCC overvoltage, can not only effectively detect the output overvoltage caused by real magnetic interference, but also helps to filter out noise interference to prevent misoperation. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0101] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit 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 idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A primary-side feedback constant-voltage switching power supply circuit, characterized in that, the primary-side feedback constant-voltage switching power supply circuit at least includes: a transformer, a power switch tube, a current sampling module, a voltage sampling module, a current sampling feedback module, a voltage sampling feedback module, a delay sampling module, a switching control module, a driving module, an output voltage limiting module and a power supply module; one end of the first primary winding of the transformer is connected to the input voltage, and the other end is grounded through the power switch tube and the current sampling module in sequence; one end of the second primary winding of the transformer is connected to the power supply module, and the other end is grounded; the secondary winding of the transformer is connected to the load; the voltage sampling module is connected in parallel across both ends of the second primary winding, and is used for sampling the output voltage and obtaining a feedback signal; the delay sampling module is connected to the output end of the voltage sampling module and performs delay sampling on the feedback signal; the voltage sampling feedback module is connected to the output end of the delay sampling module, compares the delay sampling signal of the feedback signal with a reference signal, and obtains a constant-voltage control signal; the output voltage limiting module is connected to the output end of the power supply module, compares the voltage signal output by the power supply module with a voltage limiting signal, and obtains a voltage limiting control signal; the current sampling feedback module is connected to the output end of the current sampling module and outputs a current sampling signal; the switching control module is connected to the output ends of the voltage sampling feedback module, the output voltage limiting module and the current sampling feedback module, generates a compensation signal based on the constant-voltage control signal and the voltage limiting control signal, and compares the compensation signal with the current sampling signal to generate a switching control signal; wherein, the magnitude of the compensation signal is adjusted based on the smaller of the constant-voltage control signal and the voltage limiting control signal, and the constant-voltage control signal and the voltage limiting control signal are inversely proportional to the compensation signal; the driving module is connected between the output end of the switching control module and the gate of the power switch tube, and drives the power switch tube to work based on the switching control signal.

2. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, characterized in that: the primary-side feedback constant-voltage switching power supply circuit further includes a first diode and a first capacitor, the anode of the first diode is connected to one end of the secondary winding, and the cathode is connected to one end of the first capacitor; the other end of the first capacitor is connected to the other end of the secondary winding and grounded.

3. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, characterized in that: the primary-side feedback constant-voltage switching power supply circuit further includes a working voltage generating module, the working voltage generating module is connected to the power supply module and generates a working voltage based on the voltage signal.

4. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, characterized in that: the current sampling module includes a first resistor, one end of the first resistor is connected to the power switch tube, and the other end is grounded.

5. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, characterized in that: The voltage sampling module includes a second resistor and a third resistor. The second resistor and the third resistor are connected in series and then connected in parallel across both ends of the second primary winding. A middle node of the second resistor and the third resistor outputs the feedback signal.

6. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, wherein: The power supply module includes a second diode, a fourth resistor, and a second capacitor; an anode of the second diode is connected to the second primary winding; one end of the fourth resistor is connected to the input voltage, and the other end is connected to a cathode of the second diode; one end of the second capacitor is connected to the cathode of the second diode, and the other end is grounded.

7. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, wherein: The voltage sampling and feedback module includes a constant-voltage operational amplifier unit and a first integration unit; The inverting input terminal of the constant-voltage operational amplifier unit is connected to a delayed sampling signal of the feedback signal, the non-inverting input terminal is connected to the reference signal, and outputs the constant-voltage control signal; One end of the first integration unit is connected to the inverting input terminal of the constant-voltage operational amplifier unit, and the other end is connected to the compensation signal.

8. The primary-side feedback constant-voltage switching power supply circuit according to claim 1, wherein: The output voltage limiting module includes a voltage-limiting operational amplifier unit and a second integration unit; The inverting input terminal of the voltage-limiting operational amplifier unit is connected to the voltage module, the non-inverting input terminal is connected to the voltage-limiting signal, and outputs the voltage-limiting control signal; One end of the second integration unit is connected to the inverting input terminal of the voltage-limiting operational amplifier unit, and the other end is connected to the compensation signal.

9. The primary-side feedback constant-voltage switching power supply circuit according to any one of claims 1-8, wherein: The switch control module includes a compensation signal generation unit and a switch control signal generation unit; The compensation signal generation unit adjusts the magnitude of the compensation signal based on the smaller of the constant-voltage control signal and the voltage-limiting control signal, and the constant-voltage control signal and the voltage-limiting control signal are inversely proportional to the compensation signal; The switch control signal generation unit is connected to an output terminal of the compensation signal generation unit, and generates the switch control signal based on a difference between the compensation signal and the current sampling signal to adjust the output voltage.

10. The primary-side feedback constant-voltage switching power supply circuit according to claim 9, wherein: The compensation signal generation unit includes an AND logic, a pull-down transistor, a fifth resistor, and a third capacitor; Input terminals of the AND logic are respectively connected to the constant-voltage control signal and the voltage-limiting control signal, and an output terminal is connected to a control terminal of the pull-down transistor; one end of the pull-down transistor is grounded, and the other end is connected to the operating voltage via the fifth resistor; a connection node of the pull-down transistor and the fifth resistor outputs the compensation signal; one end of the third capacitor is connected to the compensation signal, and the other end is grounded.

11. The primary-side feedback constant-voltage switching power supply circuit according to claim 9, wherein: The switch control signal generation unit includes a comparator, an oscillator, and an RS latch; The input terminals of the comparator respectively receive the compensation signal and the current sampling signal, and output a comparison result; The oscillator is connected to the comparison result and generates an oscillation signal based on the comparison result; The set terminal of the RS latch is connected to the output terminal of the oscillator, and the reset terminal is connected to the output terminal of the comparator, and the switch control signal is generated based on the comparison result and the oscillation signal.

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