A switching power supply power supply circuit, a power supply method and a switching power supply system

Abstract

The present disclosure discloses a switching power supply power supply circuit, including a starting resistor, a switching circuit, a control unit, a V<subgt;cc< / subgt> charging capacitor, and a V<subgt;cc< / subgt> charging management unit; the present disclosure also discloses a power supply method for a switching power supply; the present disclosure also discloses a switching power supply system, including a power supply circuit, an overvoltage protection unit, an undervoltage protection unit, a voltage signal acquisition unit, and a feedback unit. By controlling the turn-on time of the bootstrap power supply and by connecting the two ends of the starting resistor to the drain and gate of the voltage driving element respectively, the present disclosure can effectively reduce the power consumption generated during the startup process and the standby process.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of electronic circuits, and particularly relates to a switching power supply circuit, a power supply method, and a switching power supply system. Background Art

[0002] Switching power supplies are devices that convert power to power electronic devices and appliances, and their applications are becoming increasingly widespread. With the increasing importance of energy efficiency and environmental protection, as well as the growing emphasis on safety, people are placing higher demands on the standby power consumption of switching power supplies.

[0003] The power consumption of the switching power supply in standby mode mainly comes from the starting resistance loss and the circuit loss when no load. Figure 1 As shown, the startup circuit of the switching power supply consists of a startup resistor R star and Vcc charging capacitor C2, when starting, the current flows through R star When the charging voltage reaches the internal preset value, the control unit starts and maintains the voltage of the charging capacitor C2 by controlling the switching state of the switch tube. star Always connected to the rectified high voltage input voltage V in Between Vcc and Vcc, it will cause continuous power consumption even in standby mode. In order to ensure that a large charging current can be provided for the switching power supply to achieve fast startup, the selected startup resistor R star The resistance value is generally small, R star The smaller the resistance, the greater the standby power consumption.

[0004] In addition, in this traditional circuit structure, since the flyback voltage is much higher than V cc , it is necessary to add resistor R7 to limit it. The introduction of this resistor will further increase the power consumption, resulting in higher power consumption of the traditional circuit, which cannot meet the needs of high-efficiency products.

[0005] In summary, in order to solve the problem of high power consumption of circuits in the prior art, it is urgent to design a switching power supply circuit, a power supply method and a switching power supply system. Summary of the Invention

[0006] To address the above shortcomings, the present invention aims to provide a switching power supply circuit, power supply method, and switching power supply system. By controlling the bootstrap power supply start-up period, the present invention effectively reduces power consumption during startup and standby. By connecting the two ends of a startup resistor to the drain and gate of a voltage-driven element, respectively, the power consumption generated by the startup resistor during startup, normal operation, and standby is significantly reduced.

[0007] The present disclosure achieves the above objectives through the following technical solutions:

[0008] A switching power supply power supply circuit, comprising: a starting resistor, a switching circuit, a control unit, a V cc charging capacitor and a V cc charging management unit; wherein,

[0009] The switching circuit includes a first switching tube and a second switching tube, the drain of the first switching tube is connected to the power supply V in and the source is connected to the drain of the second switching tube;

[0010] Moreover, the common end of the first switching tube and the second switching tube is connected to the V cc charging management unit and connected to the V cc charging capacitor;

[0011] Both ends of the starting resistor are respectively connected to the drain and gate of the first switching tube;

[0012] The control unit is respectively connected to the gates of the first switching tube and the second switching tube;

[0013] V cc The charging management unit is connected to the source of the first switching tube, used to ensure the unidirectional conduction of the charging loop and limit the current of the charging loop to protect the first switching tube.

[0014] Preferably, the control unit includes a PWM module and a driving module; wherein, the output end of the PWM module is connected to the input end of the driving module, the output end of the driving module is respectively connected to the gates of the first switching tube and the second switching tube, and the PWM module controls the switching states of the first switching tube and the second switching tube through the driving module to achieve boost power supply and / or high-voltage power supply.

[0015] Preferably, the first switching tube and the second switching tube are voltage-driven types.

[0016] The present disclosure also provides a power supply method for a switching power supply, including the following steps:

[0017] S100: When the main circuit current of the switching power supply is rising, the control unit controls the states of the first switching tube and the second switching tube in the switching circuit to perform boost power supply to supply power to the V cc charging capacitor;

[0018] S200: When the voltage of the switching power supply drops to a preset value, the control unit controls the states of the first switching tube and the second switching tube in the switching circuit to perform high-voltage power supply.

[0019] Preferably, before step S100, the switching power supply drives the first switching tube in the switching circuit to conduct through the starting resistor, charges the V cc charging capacitor to a preset value, and starts the control unit.

[0020] Preferably, the start and end times of the bootstrap power supply and the high-voltage power supply are determined by timing control and / or voltage detection; wherein,

[0021] The timing control starts or ends according to a preset time or time interval;

[0022] The voltage detection starts or ends by detecting the Vcc voltage, comparing it with a set corresponding threshold, and based on the comparison result.

[0023] Preferably, the step S100 includes:

[0024] S101: The control unit first drives the first switch tube and the second switch tube in the switch circuit to conduct simultaneously;

[0025] S102: After a delay, the second switch tube is turned off, forming a charging path from the power supply, the first switch tube to the charging capacitor C2 to charge Vcc, realizing bootstrap power supply;

[0026] S103: After a delay and before the main circuit current rises to the peak value, the second switch tube is turned on again, and the bootstrap power supply ends.

[0027] Preferably, in step S200, the control unit controlling the states of the first switch tube and the second switch tube in the switch circuit means that the control unit raises the gate voltage of the first switch tube to Vcc, making the first switch tube conduct and the second switch tube turn off.

[0028] The present disclosure also provides a switching power supply system, including: an overvoltage protection unit, an undervoltage protection unit, a voltage signal acquisition unit, and a feedback unit

[0029] The input end of the overvoltage protection unit is connected to the voltage signal acquisition unit, and the output end is connected to the PWM module, and is used for generating an OVP signal and outputting it to the PWM module when detecting that the output voltage exceeds a preset threshold, so that the power supply enters the overvoltage protection state;

[0030] The input end of the undervoltage protection unit is connected to the voltage signal acquisition unit, and the output end is connected to the PWM module. When detecting that the power supply V in is lower than the preset threshold, it is used for generating an undervoltage signal and outputting it to the PWM module, so that the power supply enters the undervoltage protection state;

[0031] The voltage signal acquisition unit is respectively connected to the overvoltage protection unit and the undervoltage protection unit, and is used for detecting the output voltage and / or Vin, and feeding it back to the overvoltage protection unit and the undervoltage protection unit;

[0032] The feedback unit is used for detecting the change of the output voltage and feeding it back to the control unit, and adjusting the output voltage by controlling the duty cycle through the PWM module of the control unit.

[0033] Preferably, the feedback unit includes a three-terminal voltage regulator device, an optocoupler, and a feedback auxiliary device;

[0034] The optocoupler includes a diode D3 and a phototransistor Q1;

[0035] The feedback auxiliary device includes voltage dividing resistors R3, R4, R5, R6, R7, and a capacitor C3;

[0036] One end of the phototransistor Q1 in parallel with the capacitor C3 is connected to the positive or negative plate of the charging capacitor, and the other end is connected to the PWM module. cc One end of the phototransistor Q1 in parallel with the capacitor C3 is connected to the positive or negative plate of the charging capacitor, and the other end is connected to the PWM module.

[0037] Compared with the prior art, the beneficial effects brought by the present disclosure are as follows:

[0038] 1. By utilizing the characteristics of voltage-driven components, the connection method of starting resistors, and the control of the boost power supply on-time period, the power consumption generated during the startup process and standby process can be effectively reduced;

[0039] 2. By adopting the method of connecting both ends of the starting resistor to the drain and gate of the voltage-driven component respectively, the power consumption generated by the starting resistor during the startup, normal operation, and standby processes is greatly reduced;

[0040] 3. By designing the boost power supply of the switching power supply, during the boost power supply process, since the switching transistor is in the saturation conduction state, the dissipated power is extremely small, further reducing the standby power consumption, so that the product meets the requirements of level 6 energy efficiency; at the same time, by controlling the boost power supply on-time period, the monitoring of the current peak value in the main circuit in the conduction state is ensured, which is beneficial to cycle-by-cycle overcurrent protection;

[0041] 4. A power supply method combining boost power supply and high-voltage power supply is proposed, expanding the applicable range, and being applicable to applications such as heavy load, light load, or no load. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic circuit diagram of a traditional switching power supply;

[0043] Figure 2 is a schematic circuit diagram of a switching power supply power supply circuit proposed by the present disclosure;

[0044] Figure 3 is a schematic system diagram of a switching power supply proposed by the present disclosure;

[0045] Figure 4 is another schematic system diagram of a switching power supply proposed by the present disclosure;

[0046] Figure 5 is a schematic timing diagram of a switching power supply proposed by the present disclosure.

[0047] The markings in the figure are shown as follows:

[0048] 1. Power supply circuit; 2. Overvoltage protection unit; 3. Undervoltage protection unit; 4. Voltage signal acquisition unit; 5. Feedback unit (51. Optocoupler; 52. Feedback auxiliary device); 6. Absorption unit; 7. Output rectification and filtering unit; 11. Starting resistor; 12. Switching circuit; 13. Control unit (13-1. PWM module; 13-2. Driving module); 14. V cc Charging capacitor; 15. V cc Charging management unit. Specific implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Figure 1 Appendix Figure 5 , and the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0050] The technical solutions provided in the embodiments of the present invention are applicable to various circuit topologies such as Buck, Boost, and Buck-Boost, which are not limited herein; the switching transistors involved in the technical solutions provided in the embodiments of the present invention can be transistors such as MOS, MOSFET, and JFET, and can be enhancement type or depletion type. In the embodiments of the present invention, MOS transistors are taken as examples for illustration; the connections involved in the technical solutions can be direct connections of components or electrical connections.

[0051] Next, each embodiment of the present invention will be described in detail with reference to the accompanying drawings of the specification. It should be noted that the display order of the embodiments of the present invention only represents the sequence of the embodiments, and does not represent the superiority or inferiority of the technical solutions provided by the embodiments.

[0052] As Figure 2 shown, the present disclosure provides a switching power supply circuit, including: a starting resistor 11, a switching circuit 12, a control unit 13, V cc charging capacitor 14 and V cc charging management unit 15; wherein,

[0053] The switching circuit 12 includes a first switching transistor M1 and a second switching transistor M2. The drain of the first switching transistor M1 is connected to the power supply V in and the source is connected to the drain of the second switching transistor M2;

[0054] Moreover, the common terminal of the first switching transistor M1 and the second switching transistor M2 is connected to V through the cc charging management unit 15 and Vcc is connected to the charging capacitor C214;

[0055] Both ends of the starting resistor R111 are respectively connected to the drain and gate of the first switching transistor M1;

[0056] The control unit 13 is respectively connected to the gates of the first switching transistor M1 and the second switching transistor M2;

[0057] V cc The charging management unit 15 is connected to the source of the first switching transistor M1, which is used to ensure the unidirectional conduction of the charging circuit and limit the current of the charging circuit to protect the first switching transistor M1.

[0058] In the above embodiment, different from the prior art in which the starting resistor R star is always connected between the rectified high-voltage input voltage V in and Vcc, resulting in continuous power consumption: in the above embodiment, by connecting both ends of the starting resistor to the drain and gate of the first switching transistor M1 respectively, the power supply charges the gate-source parasitic capacitance of the first switching transistor M1 through the starting resistor, thereby raising the gate-source voltage of the first switching transistor M1 to be greater than the threshold voltage of the first switching transistor M1 to turn on the first switching transistor M1, and then forming a charging path from the power supply, the first switching transistor M1 to the charging capacitor, for V cc When the charging reaches the preset value, the control unit starts. During the starting process, since the internal resistance of the first switching transistor M1 is very large and the current is very small when voltage control is applied, approximately zero, the starting resistor R1 hardly generates power consumption during starting.

[0059] In another embodiment, the control unit includes a PWM module and a driving module; wherein, the output end of the PWM module is connected to the input end of the driving module, the output end of the driving module is respectively connected to the gates of the first switching transistor and the second switching transistor, and the PWM module controls the switching states of the first switching transistor and the second switching transistor through the driving module to achieve bootstrap power supply and / or high-voltage power supply.

[0060] In this embodiment, when the switching power supply works normally, the first switching transistor M1 and the second switching transistor M2 are turned on simultaneously. After a delay, the second switching transistor M2 is turned off. At this time, the gate-source parasitic capacitance C of the first switching transistor M1 gs generates bootstrap, and the first switching transistor M1 maintains the on state, forming a charging path with the power supply and the charging capacitor C2 for V cc charging, thereby achieving bootstrap power supply; since the first switching transistor M1 is in the bootstrap state at this time, the gate voltage is large and it is in the saturated conduction state with a very small voltage drop, so compared with the prior art, the power consumption generated by the circuit is extremely small.

[0061] Furthermore, when the first switching transistor M1 and the second switching transistor M2 are in the off state for a long time, resulting in Vcc When the power supply is insufficient, the control unit 13 raises the gate voltage of the first switching transistor M1 to V cc At the same time, the power supply charges the gate-source parasitic capacitance C of the first switching transistor M1 through the starting resistor R111 gs to raise the gate-source voltage V of the first switching transistor M1 gs to be greater than the threshold voltage V of the first switching transistor M1 th to turn it on, forming a charging path from the power supply, the first switching transistor M1 to the charging capacitor C214 for high-voltage power supply. cc It can be understood that by combining the bootstrap power supply and the high-voltage power supply in the above embodiments, the applicable range is expanded compared with the prior art, and it can be applied to heavy load, light load or no load conditions.

[0062] In another embodiment, the first switching transistor M1 and the second switching transistor M2 are voltage-driven types.

[0063] In this embodiment, the first switching transistor M1 and the second switching transistor M2 can be selected from at least one of transistors such as MOS, MOSFET, JEFT, etc. In this embodiment, NMOS is preferably used as the switching transistor.

[0064] In another embodiment, the present disclosure also provides a power supply method for a switching power supply, including the following steps:

[0065] S100: When the switching power supply is in the period of rising main circuit current, the control unit controls the states of the first switching transistor and the second switching transistor in the switching circuit to perform bootstrap power supply for the charging capacitor;

[0066] S200: When the voltage of the switching power supply drops to a preset value, the control unit controls the states of the first switching transistor and the second switching transistor in the switching circuit to perform high-voltage power supply. cc For charging the capacitor.

[0067] In a specific embodiment of step 100, when the switching power supply is operating normally, the control unit 13 first drives the first switching transistor M1 and the second switching transistor M2 in the switching circuit 12 to conduct simultaneously, and turns off the second switching transistor M2 after a delay. At this time, the gate-source parasitic capacitance C of the first switching transistor M1 generates bootstrap, and the first switching transistor M1 maintains the conducting state, forming a charging path from the power supply, the first switching transistor M1 to the charging capacitor C2 for charging V

[0068] to achieve bootstrap power supply; before the main circuit current rises to the peak value, the second switching transistor M2 is turned on again, and the bootstrap power supply ends. gs to charge and realize bootstrap power supply; before the main circuit current rises to the peak value, turn on the second switching transistor M2 again, and the bootstrap power supply ends. cc to charge and realize bootstrap power supply; before the main circuit current rises to the peak value, turn on the second switching transistor M2 again, and the bootstrap power supply ends.

[0069] It should be noted that, to ensure the monitoring of the peak value of the main circuit current and achieve cycle-by-cycle overcurrent protection, the bootstrap power supply process is carried out during the rising process of the main circuit current, that is, the bootstrap power supply starts after a delay after the main circuit is turned on and ends before the main circuit current rises to the peak value.

[0070] In a specific embodiment of step S200, when the operating frequency of the switching power supply is low, relying solely on the bootstrap power supply cannot ensure sufficient power supply for V cc Especially for products such as adapters or chargers, there is a no-load operating mode. In this case, since the first switching transistor M1 and the second switching transistor M2 are in the off state for a long time, it leads to insufficient power supply for V cc Therefore, in this embodiment, when the voltage of V cc drops to the preset threshold V cc_min , the control unit raises the gate voltage of the first switching transistor M1 to V cc , and at the same time, the power supply charges the gate of the first switching transistor M1 through the starting resistor R111 to make it conduct, and high-voltage power supply is carried out.

[0071] In another embodiment, before step S100, the switching power supply drives the first switching transistor in the switching circuit to conduct through the starting resistor to charge the charging capacitor for V cc to a preset value to start the control unit.

[0072] In this embodiment, during startup, the power supply charges the gate-source parasitic capacitor C gs of the first switching transistor M1 through the starting resistor R111, raises the gate-source voltage V gs of the first switching transistor M1 to be greater than the threshold voltage V th of the first switching transistor M1 to make the first switching transistor M1 conduct, forming a charging path from the power supply, the first switching transistor M1 to the charging capacitor C214 for V cc to charge the charging capacitor C214 for V cc to a preset value, and the control unit starts.

[0073] In another embodiment, the startup and end times of the bootstrap power supply and the high-voltage power supply are determined by timing control and / or voltage detection; wherein,

[0074] The timing control starts or ends according to a preset time or time interval;

[0075] The voltage detection is to detect the Vcc voltage and compare it with the set corresponding threshold, and start or end according to the comparison result.

[0076] The startup and end of the bootstrap power supply and the high-voltage power supply are described separately as follows:

[0077] 1. Bootstrap power supply: When the switching power supply system is working properly, the control unit first drives M1 and M2 in the switching circuit to conduct simultaneously. After a delay, M2 is turned off. At this time, the gate-source parasitic capacitance C of M1 gs generates bootstrap, and M1 maintains the conducting state, forming a charging path from the power supply, M1 to the charging capacitor C2 to charge V cc , realizing bootstrap power supply; before the main circuit current rises to the peak value, M2 is turned on again, and the bootstrap power supply ends.

[0078] It should be noted that the time for delaying the turn-off of M2 and the time for M2 to be turned on again can be monitored through the V cc voltage. When the V cc voltage drops to the preset threshold V cc_th2 , the control unit drives M2 to turn off; when the V cc voltage rises to the preset threshold V cc_th1 , M2 is turned on again.

[0079] In addition, the time for delaying the turn-off of M2 and the time for M2 to be turned on again can also be controlled by timing, that is, at a fixed time point, the control circuit drives M2 to turn off and on.

[0080] 2. High-voltage power supply: When the operating frequency of the switching power supply is low, relying solely on bootstrap power supply cannot ensure sufficient V cc power supply. Especially for products such as adapters or chargers, there is an idle operating mode. In this case, due to M1 and M2 being in the off state for a long time, the V cc power supply is insufficient. Therefore, in this embodiment, when the V cc voltage drops to the preset threshold V cc_min , the control circuit raises the gate voltage of M1 to V cc , and at the same time, the power supply charges the gate of M1 through the starting resistor R1 to turn on M1 for high-voltage power supply.

[0081] It should be noted that the start and end times of high-voltage power supply can also be executed according to the preset time and realized through timing control.

[0082] In another embodiment, the step S100 includes:

[0083] S101: The control unit first drives the first switch tube and the second switch tube in the switching circuit to conduct simultaneously;

[0084] S102: After a delay, the second switch tube is turned off, forming a charging path from the power supply, the first switch tube to the charging capacitor C2 to charge Vcc, realizing bootstrap power supply;

[0085] S103: After a delay and before the main circuit current rises to the peak value, the second switch tube is turned on again, and the bootstrap power supply ends.

[0086] In another embodiment, in step S200, the control unit controls the states of the first switch tube and the second switch tube in the switching circuit, which means that the control unit raises the gate voltage of the first switch tube to Vcc to turn on the first switch tube and turn off the second switch tube.

[0087] In another embodiment, the present disclosure also provides a switching power supply system, including a power supply circuit 1, an overvoltage protection unit 2, an undervoltage protection unit 3, and a voltage signal acquisition unit 4;

[0088] The input end of the overvoltage protection unit (OVP) 2 is connected to the voltage signal acquisition unit 4, and the output end is connected to the PWM module 13-1, and is used for generating a signal and outputting it to the PWM module 13-1 when detecting that the output voltage V out exceeds a preset threshold, so that the power supply enters the overvoltage protection state;

[0089] The input end of the undervoltage protection unit (Brown out) 3 is connected to the voltage signal acquisition unit 4, and the output end is connected to the PWM module 13-1. When detecting that the power supply V in is lower than a preset threshold, it is used for generating an undervoltage signal and outputting it to the PWM module 13-1, so that the power supply enters the undervoltage protection state;

[0090] The voltage signal acquisition unit 4 is respectively connected to the overvoltage protection unit and the undervoltage protection unit, and is used for detecting the output voltage and / or Vin, and feeding it back to the overvoltage protection unit and the undervoltage protection unit;

[0091] The feedback unit 5 is used for detecting the change of the output voltage and feeding it back to the control unit, and adjusting the output voltage by controlling the duty cycle through the PWM module of the control unit.

[0092] Figure 3 It is a specific application of the above embodiment in the dual-winding secondary feedback topology structure. It should be noted that the switching power supply system of the present invention is not limited to being applied in the dual-winding secondary feedback topology structure, and can also be applied in other topology structures.

[0093] In the above embodiment, the source electrode of the second switch tube M2 is connected to one end of the primary inductor L of the transformer through the sampling resistor R2, p and the other end of the primary inductor L of the transformer is grounded. When the first switch tube M1 and the second switch tube M2 are turned on, the primary side is conducting, and the voltage across the capacitor C1 is applied to the primary side of the transformer, and the current flows through M1, M2, R2 and L p and then flows into the ground, and the transformer stores energy; when M1 and M2 are turned off, the primary side is cut off, and the transformer continues to flow through the secondary side to release energy. p

[0094] ​The output terminal set at the common terminal of resistors R8 and R9 is connected to the overvoltage protection unit (OVP) 2 and the undervoltage protection unit (Brown out) 3 through the prt pin of the chip. When the primary side turns off and enters the flyback stage, the turns ratio relationship between the voltage across L p and the output voltage V out is used, as shown in Equation (1). By monitoring the voltage across L p , the output voltage V out is monitored to achieve an accurate OPV function.

[0095]

[0096] N p : The number of turns of the primary inductor L p ;

[0097] N s : The number of turns of the secondary inductor L s ;

[0098] Vf(d2): The forward conduction voltage drop of the output diode D2.

[0099] When the primary side conducts, the undervoltage protection unit (Brown out) 3 generates a current path to make the prt voltage equal to the gnd voltage. Since the resistance value of R2 is very small, when the primary side conducts, V in is approximately equal to gnd, and the voltage across R8 is approximately equal to V in , then I prt = Vin / R8. Inside the chip, I prt is compared with the reference current I bias . When I prt < I bias is maintained for a period of time, the undervoltage protection unit (Brown out) 3 is triggered for protection, that is, input undervoltage protection.

[0100] The following combines Figures 2 - 5 to describe the working process of this embodiment:

[0101] When the switching power supply starts, the initial voltage of V cc is zero. The power supply V in applies voltage to the gate of the switching transistor M1 through the startup resistor R1, charging the gate-source parasitic capacitor C gs and raising the gate-source voltage V gs of the first switching transistor M1 to be greater than its threshold voltage V th to make it conduct, forming a charging path from the power supply, M1 to the charging capacitor C2 to charge V cc to the preset value V cc_th0When the control unit starts. During the startup process, due to the very large internal resistance of the first switching transistor M1, the current is very small and approximately zero when a voltage is applied for control. Therefore, almost no power consumption is generated in the startup resistor R1 during startup.

[0102] After the switching power supply starts and enters the normal working stage, within one control cycle, first, the PWM module 13-1 controls the first switching transistor M1 and the second switching transistor M2 to conduct simultaneously through the drive module 13-2, and the inductor L p current I Lp starts to increase. As I Lp increases, the voltage V cs across the sampling resistor R2 also gradually increases. At this time, since the charging capacitor is in the discharging state, the voltage of V cc decreases; the first switching transistor M1 is in the saturated conduction state, and the source-drain voltage V cc is extremely small. ds is extremely small.

[0103] After a delay period or when V cc drops to the lower threshold V cc_th2 , the second switching transistor M2 is turned off. At this time, the gate-source parasitic capacitance C gs of the first switching transistor M1 generates bootstrap, and the first switching transistor M1 maintains the conduction state, forming a charging path from the power supply, the first switching transistor M1 to the charging capacitor C2 to charge V cc , realizing bootstrap power supply. Since M1 is in the saturated conduction state at this time and the voltage drop is extremely small, the dissipated power is small and the efficiency is also higher. After the second switching transistor M2 is turned off, the current flowing through the sampling resistor R2 is cut off, and V cs is zero; however, since the primary side is still in the conduction state, the current I p flowing through L Lp continues to increase.

[0104] After a delay period or when V cc rises to the upper threshold V cc_th1 , the PWM module 13-1 drives the second switching transistor M2 to conduct, and the charging of V cc ends, and C2 enters the discharging stage, and the voltage of V cc gradually decreases. The primary side enters the energy storage stage, and the main circuit current I Lp continues to increase, and R2 is in the conduction state, so V cs increases as I Lp increases.

[0105] At the same time, the first switching transistor M1 and the second switching transistor M2 are turned off, the primary side is cut off, and the transformer discharges energy through the secondary side freewheeling to drive the load to work. The primary side enters the flyback stage, and V prt jumps to a high level, and the voltage signal acquisition circuit samples during the high-level period to obtain V outOutput status.

[0106] When under light load or no load, since the frequency is too low, the power supplied by the primary bootstrap cannot sustain the consumption of the control unit throughout the cycle. After multiple cycles, the V cc capacitor will continuously discharge to the undervoltage state. By combining the bootstrap power supply and the high-voltage power supply, when the switching power supply is operating normally, the charging capacitor C2 is still charged by the bootstrap power supply. When in the standby state for a long time, resulting in the V cc voltage being too low, entering the undervoltage protection state or below the preset threshold V cc_min , the control unit raises the gate voltage of the first switching transistor M1 to V cc , and at the same time, the power supply charges the gate of the first switching transistor M1 through the starting resistor R1, making the first switching transistor M1 conduct to perform high-voltage power supply. The above control process can also be controlled by timing. The first switching transistor turns on the high-voltage power supply after a preset delay after M1 and the second switching transistor M2 are turned off.

[0107] In another embodiment, the feedback unit 5 includes a three-terminal voltage regulator device TL431, an optocoupler 51, and a feedback auxiliary device 52; among them,

[0108] The optocoupler 51 includes a diode D3 and a photosensitive triode Q1;

[0109] The feedback auxiliary device 52 includes voltage-dividing resistors R3, R4, R5, R6, R7, and a capacitor C3;

[0110] One end of the photosensitive triode Q1 is connected to the positive or negative plate of the charging capacitor C3 in parallel after being connected to V cc , and the other end is connected to the PWM module 13-1.

[0111] In this embodiment, the output voltage V out is input to TL431 through voltage division for comparison with the reference voltage. The error voltage signal output by the operational amplifier controls the current flowing through the optocoupler. When the output voltage V out is too high, the current flowing through the optocoupler becomes larger, the voltage at the FB port of the controller becomes smaller, and the PWM module 13-1 controls the output duty cycle to become smaller to reduce the energy transferred to the secondary side of the transformer, and the output voltage V out starts to decrease; conversely, if the output voltage is V out low, according to the feedback of the optocoupler current, the PWM module 13-1 controls the duty cycle to increase to increase the energy transferred to the secondary side of the transformer, thereby increasing the output voltage V out . By this method, the output voltage is continuously adjusted and controlled to be stabilized at the set value.

[0112] In another embodiment, the switching power supply system further includes an absorption unit 6 for preventing the appearance of excessive spike pulses at the moment when the switching transistor is turned off from damaging the switching transistor.

[0113] In this embodiment, both ends of the absorption unit 6 are respectively connected to both ends of the primary inductor L of the transformer p The absorption unit includes a voltage-dividing resistor R1, a capacitor C4, and a diode D1. One end of the parallel connection of the resistor R1 and the capacitor C4 is connected to the positive electrode of L through the diode D1 p and the other end is connected to the negative electrode of L p .

[0114] In another embodiment, the switching power supply system further includes an output rectifying and filtering unit 7, and the rectifying and filtering unit 5 includes a diode D2 and a capacitor C5

[0115] In this embodiment, when the primary side is cut off, the mutual inductance electromotive force on the secondary side causes the rectifying diode D2 to conduct. On the one hand, the current flows into the load, and on the other hand, it charges and stores energy in the capacitor C5 so as to release energy to the load when the primary side conducts again

[0116] The above are only some embodiments of the present disclosure and are not used to limit the inventive concept of the present disclosure. Those skilled in the art can make certain substitutions and deformations without departing from the principle of the inventive concept of the present disclosure, but all should fall within the protection scope of the present disclosure

Claims

1. A switching power supply power supply circuit, comprising: Starting resistor, switching circuit, control unit, V cc Charging capacitor and V cc Charging management unit; wherein, The switching circuit includes a first switching transistor and a second switching transistor. The drain of the first switching transistor is connected to the power supply V in and the source is connected to the drain of the second switching transistor; Moreover, the common terminal of the first switching transistor and the second switching transistor is connected to V cc The charge management unit is connected to V cc and the charge capacitor; Both ends of the starting resistor are respectively connected to the drain and gate of the first switching tube; The control unit is respectively connected to the gates of the first switching tube and the second switching tube; V cc The charging management unit is connected to the source electrode of the first switching transistor, and is used to ensure the unidirectional conduction of the charging circuit and limit the current of the charging circuit to protect the first switching transistor; The control unit includes a PWM module and a driving module; wherein, the output end of the PWM module is connected to the input end of the driving module, the output end of the driving module is respectively connected to the gates of the first switching tube and the second switching tube, and the PWM module controls the switching states of the first switching tube and the second switching tube through the driving module to achieve bootstrap power supply and / or high-voltage power supply; When the switching power supply is working normally, the first switching transistor M1 and the second switching transistor M2 are turned on simultaneously. After a delay, the second switching transistor M2 is turned off. At this time, the gate-source parasitic capacitance C of the first switching transistor M1 gs generates bootstrap, and the first switching transistor M1 maintains the on state, forming a charging path with the power supply and the charging capacitor C2 to charge V cc thereby realizing bootstrap power supply; since the first switching transistor M1 is in the bootstrap state at this time, the gate voltage is large and it is in the saturation conduction state with a very small voltage drop, so the power consumption generated by the circuit is extremely small; Furthermore, when the first switch tube M1 and the second switch tube M2 are in the off state for a long time, V cc When the power supply is insufficient, the control unit raises the gate voltage of the first switch tube M1 to V cc At the same time, the power supply is connected to the gate-source parasitic capacitance C of the first switch tube M1 through the starting resistor R1. gs Charging, raising the gate-source voltage V of the first switch tube M1 gs to a voltage greater than the threshold voltage V of the first switch tube M1 th Make it conduct, form power supply, first switch tube M1 to V cc The charging path of the charging capacitor C2 is used for high voltage power supply.

2. The switch power supply circuit according to claim 1, wherein The first switching tube and the second switching tube are voltage-driven types.

3. A power supply method for the switching power supply circuit according to claim 1, comprising the following steps: S100: When the switching power supply is during the rise of the main circuit current, the control unit controls the states of the first switching tube and the second switching tube in the switching circuit to perform bootstrap power supply for the charging capacitor of V cc to supply power to the charging capacitor; S200: When the switching power supply voltage drops to a preset value, the control unit controls the states of the first switching tube and the second switching tube in the switching circuit for high-voltage power supply.

4. The method according to claim 3, characterized in that, Before step S100, the switching power supply drives the first switching tube in the switching circuit to conduct through a startup resistor to charge the cc charging capacitor to a preset value to start the control unit.

5. The power supply method according to claim 3, characterized in that, The start and end times of the bootstrap power supply and the high-voltage power supply are determined by timing control and / or voltage detection; wherein, The timing control starts or ends according to a preset time or time interval; The voltage detection starts or ends by detecting the Vcc voltage and comparing it with a set corresponding threshold value.

6. The power supply method according to claim 3, wherein The step S100 includes: S101: The control unit first drives the first switching tube and the second switching tube in the switching circuit to conduct simultaneously; S102: After a delay, the second switching tube is turned off to form a charging path from the power supply, the first switching tube to the charging capacitor C2 to charge Vcc and achieve bootstrap power supply; S103: After a delay and before the main circuit current rises to the peak value, the second switching tube is turned on again and the bootstrap power supply ends.

7. The power supply method according to claim 3, wherein In step S200, the control unit controlling the states of the first switching tube and the second switching tube in the switching circuit means that the control unit raises the gate voltage of the first switching tube to Vcc to turn on the first switching tube and turn off the second switching tube.

8. A switching power supply system comprising the switching power supply power circuit according to any one of claims 1 to 2, comprising: Overvoltage protection unit, undervoltage protection unit, voltage signal acquisition unit and feedback unit; The input end of the overvoltage protection unit is connected to the voltage signal acquisition unit, and the output end is connected to the PWM module, and is used to generate a signal and output it to the PWM module when it detects that the output voltage exceeds a preset threshold value, so that the power supply enters the overvoltage protection state; The input end of the undervoltage protection unit is connected to the voltage signal acquisition unit, and the output end is connected to the PWM module. When it detects that the power supply V in is lower than the preset threshold value, it is used to generate an undervoltage signal and output it to the PWM module, so that the power supply enters the undervoltage protection state; The voltage signal acquisition unit is respectively connected to the overvoltage protection unit and the undervoltage protection unit, and is used to detect the output voltage and / or Vin and feedback it to the overvoltage protection unit and the undervoltage protection unit; The feedback unit is used to detect the change of the output voltage and feedback it to the control unit, and adjust the output voltage by controlling the duty cycle of the PWM module of the control unit.

9. The switching power supply system according to claim 8, characterized in that, The feedback unit includes a three-terminal voltage regulator device, an optocoupler and a feedback auxiliary device; wherein, The optocoupler includes a diode D3 and a photosensitive triode Q1; The feedback auxiliary device includes voltage-dividing resistors R3, R4, R5, R6, R7 and a capacitor C3; The photosensitive triode Q1 is connected in parallel with the capacitor C3, and one end is connected to the positive or negative plate of the charging capacitor, and the other end is connected to the PWM module. cc The positive or negative plate of the charging capacitor is connected, and the other end is connected to the PWM module.

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