Low power consumption SSR switching power supply circuit and control method thereof, switching power supply

Abstract

The present invention relates to the technical field of electronic circuits, and in particular to a low-power SSR switching power supply circuit and a control method thereof, and a switching power supply. The low-power SSR switching power supply circuit includes a feedback circuit, and the feedback circuit includes a conduction unit, a first sampling unit, a second sampling unit, a modulation unit, a power supply unit, and a feedback control unit; an optical coupler generates an optical coupler current and outputs it to the conduction unit, and the conduction unit controls the first sampling unit to conduct and outputs the first sampling current to the power supply unit to supply power to the internal power supply of the switching power supply chip; the conduction unit controls the first sampling unit to conduct and mirror-generates the second sampling current to the feedback control unit, and the feedback control unit provides a feedback voltage for the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit; when the switching power supply system is lightly loaded or unloaded, the feedback control unit controls the modulation unit to conduct and output the modulation current, shunts the optical coupler current, and limits the maximum value of the optical coupler current.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to a low-power SSR switching power supply circuit and a control method thereof, and a switching power supply. Background Art

[0002] As a power converter, isolated switching power supplies play an important role in various fields. Switching power supplies efficiently and stably convert input electrical energy into a specific voltage or current output. In the application process of isolated switching power supplies, in order to ensure the effective conversion of input power and output power, it is necessary to transmit feedback signals between the primary circuit and the secondary circuit. The feedback signal is usually converted from the output voltage information of the secondary side, and transmitting the feedback signal can control the efficiency of power conversion.

[0003] Reference Figure 1 , Figure 1 The working principle diagram of the isolated switching power supply circuit using the TL431 feedback circuit in the prior art is shown. Figure 1 The optical coupler shown in the figure realizes the transmission of the above feedback signal. Specifically, the photosensitive diode in the optical coupler can convert the information of the output voltage Vout into the optical coupler current Iop, which is then converted into the feedback voltage FB through the primary feedback circuit and input to the control end of the primary circuit. Figure 2 , Figure 2 The diagram shows the relationship between the optocoupler current Iop and the output current Iout, as well as the feedback voltage FB and the output current Iout in an isolated switching power supply using a TL431 feedback circuit. In a negative feedback control system, when the output current Iout increases, it means that the load demand increases or the output voltage Vout decreases. At this time, in order to maintain the stability of the output voltage Vout, the control system will reduce the drive current of the photodiode in the optocoupler, thereby reducing the optocoupler current Iop. At the same time, the control system will also increase the feedback voltage FB to indicate that the power needs to be increased or the circuit parameters need to be adjusted to maintain the stability of the output voltage Vout. On the contrary, when the output current Iout decreases, it means that the load demand decreases or the output voltage Vout increases. The control system will increase the drive current of the photodiode, thereby increasing the optocoupler current Iop. At the same time, the control system will also reduce the feedback voltage FB to indicate that the power needs to be reduced or the circuit parameters need to be adjusted to maintain the stability of the output voltage Vout.

[0004] From the above content, it can be seen that there is a problem with the isolated switching power supply using the TL431 feedback circuit in the prior art: when lightly loaded or no-loaded, the value of the optocoupler current Iop is large, which will increase the power consumption of the optocoupler, thereby easily reducing the light-load and no-load efficiency of the isolated switching power supply. Summary of the invention

[0005] The embodiment of the present invention provides a low-power SSR switching power supply circuit and a control method thereof, and a switching power supply. By improving the primary feedback circuit and the connection of the optocoupler in the system, the optocoupler current is used to power the internal voltage of the system, and a sampling branch is set to provide a feedback voltage FB for the switching power supply chip, so that the feedback voltage FB is proportional to the optocoupler feedback current. The maximum value of the feedback voltage FB and the optocoupler current are limited by feedback control, so as to reduce the loss under light load and no-load conditions, thereby improving the efficiency.

[0006] To achieve the above object, the present invention discloses the following technical solution:

[0007] On one hand, the present invention provides a low-power SSR switching power supply circuit, comprising a switching power supply chip and a receiving end of an optical coupler arranged in a primary circuit, wherein the transmitting end of the optical coupler is connected to an output voltage, the power supply end of the optical coupler is connected to a power supply end VCC of the switching power supply chip, and the receiving end of the optical coupler is also connected to a feedback circuit, characterized in that the feedback circuit comprises a conduction unit, a first sampling unit, a second sampling unit, a modulation unit, a power supply unit and a feedback control unit; the receiving end of the optical coupler generates an optical coupling current and outputs it to the conduction unit, the conduction unit controls the first sampling unit to conduct and output the first sampling current to the power supply unit to supply power to the internal power supply VDD of the switching power supply chip, so as to reduce the loss generated by the optical coupling current; the conduction unit controls the first sampling unit to conduct and mirror-generate a second sampling current to the feedback control unit, and the feedback control unit provides a feedback voltage for the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit;

[0008] When the switching power supply system is lightly loaded or unloaded, the optocoupler current increases, and the feedback control unit controls the modulation unit to turn on and output the modulation current based on the control voltage, thereby shunting the optocoupler current, and ultimately maintaining the optocoupler current equal to the sum of the first sampling current, the second sampling current and the modulation current, thereby limiting the maximum value of the optocoupler current, thereby reducing losses particularly significantly when the system is lightly loaded or unloaded.

[0009] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the conduction unit includes a current limiting resistor and a third MOS tube, the first end of the third MOS tube is connected to one end of the current limiting resistor, the second end of the third MOS tube is connected to the power supply unit, the third end of the third MOS tube is connected to the first sampling unit, and the other end of the current limiting resistor is connected to the receiving end of the optocoupler.

[0010] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the first sampling unit includes a first MOS tube, a first end of the first MOS tube is connected to the second sampling unit, a second end of the first MOS tube is connected to the receiving end of the optocoupler, and a third end of the first MOS tube and the first end of the first MOS tube are connected to the power supply unit through the third MOS tube.

[0011] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the power supply unit includes an energy storage capacitor, a diode and a clamping diode, the anode of the diode is connected to the second end of the third MOS tube, the cathode of the diode is connected to one end of the energy storage capacitor, the other end of the energy storage capacitor is grounded, and the common point formed by the connection between the energy storage capacitor and the diode is the internal power supply terminal VDD of the switching power supply chip, and the clamping diode is connected in parallel at both ends of the energy storage capacitor.

[0012] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the second sampling unit includes a second MOS tube, a first end of the second MOS tube is connected to the first end of the first MOS tube, a second end of the second MOS tube is connected to the receiving end of the optocoupler, and a third end of the second MOS tube is connected to the input end of the control feedback unit.

[0013] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the first MOS tube and the second MOS tube are mirror images of each other and are in a certain proportional relationship, and both are PMOS tubes; the gate of the first MOS tube, the drain of the first MOS tube and the gate of the second MOS tube are connected, the source of the first MOS tube and the source of the second MOS tube are both connected to the receiving end of the optical coupler, the drain of the first MOS tube is connected to the third end of the third MOS tube, and the drain of the second MOS tube is connected to the input end of the control feedback unit.

[0014] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the feedback control unit includes a first sampling resistor and a second sampling resistor, one end of the first sampling resistor is connected to the drain of the second MOS tube, the other end of the first sampling resistor is connected to one end of the second sampling resistor, and the other end of the second sampling resistor is grounded.

[0015] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the modulation unit includes a fourth MOS tube, a first end of the fourth MOS tube is connected to a common point formed by connecting the first sampling resistor and the second sampling resistor, a second end of the fourth MOS tube is grounded, and a third end of the fourth MOS tube is connected to a common point formed by connecting the first end of the third MOS tube and the current limiting resistor.

[0016] Preferably, in the above-mentioned low-power SSR switching power supply circuit, the third MOS tube and the fourth MOS tube are both NMOS tubes; the gate of the third MOS tube is connected to one end of the current-limiting resistor, the source of the third MOS tube is connected to the anode of the diode, and the drain of the third MOS tube is connected to the drain of the first MOS tube; the gate of the fourth MOS tube is connected to a common point formed by connecting the first sampling resistor and the second sampling resistor; the source of the fourth MOS tube is grounded; and the drain of the fourth MOS tube is connected to a common point formed by connecting the gate of the third MOS tube and the current-limiting resistor.

[0017] In addition, the present invention also provides a control method for a low-power SSR switching power supply circuit, the method is applied to the low-power SSR switching power supply circuit as described above, the method comprising:

[0018] The transmitting end of the optical coupler is connected to the output voltage to generate an optical signal;

[0019] Receiving the optical signal through the receiving end of the optical coupler to generate an optical coupler current and output it to the conduction unit;

[0020] Using the conduction unit to control the first sampling unit to conduct and output a first sampling current to the power supply unit to supply power to the internal power supply VDD of the switching power supply chip;

[0021] Using the mirror relationship between the first sampling unit and the second sampling unit to generate a second sampling current and output it to the feedback control unit;

[0022] The feedback control unit provides a feedback voltage to the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit;

[0023] When the switching power supply system is lightly loaded or unloaded, the optocoupler current increases, and the feedback control unit controls the modulation unit to turn on and output the modulation current based on the control voltage, shunts the optocoupler current, and limits the maximum value of the optocoupler current.

[0024] Another aspect of the present invention provides a switching power supply, which includes a secondary circuit and the low-power SSR switching power supply circuit as described above.

[0025] The effects provided in the content of the invention are only the effects of the embodiments, not all the effects of the invention. One of the above technical solutions has the following advantages or beneficial effects:

[0026] 1) The first MOS tube and the second MOS tube are designed with a current mirror structure and set with a specific proportional relationship, which can accurately sample the optocoupler current in equal proportion to a certain extent.

[0027] 2) In the embodiment of the present application, the optocoupler current is used to power the internal power supply VDD of the switching power supply chip, which can utilize energy that may have been wasted, thereby improving the efficiency of the overall system.

[0028] 3) When the switching power supply system is in a light load or no-load state, the fourth MOS tube is turned on and generates a modulated current, causing the shunting of the optocoupler current Iop and limiting the current rise speed of the first sampling current and the second sampling current, that is, limiting the maximum value of the feedback voltage FB and the maximum charging current of the first sampling current to the internal power supply VDD of the switching power supply chip, thereby realizing the role of the negative feedback circuit to maintain loop balance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0030] Figure 1 The present invention is a working principle diagram of an isolated switching power supply circuit using a TL431 feedback circuit in the prior art.

[0031] Figure 2 FIG. 4 is a relationship diagram between the optocoupler current I op and the output current I out, and between the feedback voltage FB and the output current I out in an isolated switching power supply using a TL431 feedback circuit.

[0032] Figure 3 This is a circuit schematic diagram of a low-power SSR switching power supply circuit according to an embodiment of the present application.

[0033] Figure 4 This is a structural schematic diagram of the feedback circuit in the low-power SSR switching power supply circuit of an embodiment of the present application.

[0034] Figure 5 This is a schematic diagram of the process of controlling the low-power SSR switching power supply circuit according to an embodiment of the present application.

[0035] Figure 6 This is a schematic diagram of the structure of a switching power supply according to an embodiment of the present application.

[0036] Reference numerals:

[0037] 600-switching power supply, 610-secondary circuit, 620-low power consumption SSR switching power supply circuit. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] It should be noted that references to "one embodiment", "embodiment", "example embodiment", etc. in this specification refer to the embodiment being described which may include specific features, structures or characteristics, but not every embodiment must include these specific features, structures or characteristics. In addition, such expressions do not refer to the same embodiment. Furthermore, when describing specific features, structures or characteristics in conjunction with an embodiment, whether or not there is an explicit description, it is indicated that incorporating such features, structures or characteristics into other embodiments is within the knowledge of those skilled in the art.

[0040] In addition, certain words are used in the specification and subsequent claims to refer to specific components or parts. Those with ordinary knowledge in the relevant field should understand that manufacturers can use different nouns or terms to refer to the same component or part. This specification and subsequent claims do not use differences in names as a way to distinguish components or parts, but use differences in the functions of components or parts as the criteria for distinction. "Including" and "including" mentioned throughout the specification and subsequent claims are open-ended terms and should be interpreted as "including but not limited to". In addition, the word "connected" here includes any direct and indirect electrical connection means. Indirect electrical connection means include connection through other devices.

[0041] As background technology and Figure 1 As shown, in the prior art, an isolated switching power supply circuit using a TL431 feedback circuit is used. The photosensitive diode in the optocoupler can convert the information of the output voltage Vout into the optocoupler current Iop, which is then converted into the feedback voltage FB through the primary feedback circuit and input to the control end of the primary circuit. Figure 2 , Figure 2The relationship diagram of the optocoupler current Iop and the output current Iout, as well as the feedback voltage FB and the output current Iout in an isolated switching power supply using a TL431 feedback circuit is shown, that is, the smaller the output current Iout, the larger the corresponding optocoupler current Iop, and the larger the output current Iout, the smaller the corresponding optocoupler current Iop. Therefore, when lightly loaded and no-loaded, the value of the optocoupler current Iop is large, which will increase the power consumption of the optocoupler, thereby easily reducing the light-load and no-load efficiency of the isolated switching power supply. Based on this problem, the present application provides a low-power SSR switching power supply and a control method thereof, by improving the primary feedback circuit and the connection of the optocoupler in the system, using the optocoupler current to power the internal voltage of the system, and setting a sampling branch to provide a feedback voltage FB for the switching power supply chip, so that the feedback voltage FB is proportional to the optocoupler feedback current, and the maximum value of the feedback voltage FB and the optocoupler current are limited by feedback control, and the loss is reduced when lightly loaded and no-loaded, thereby improving efficiency.

[0042] Reference Figure 3 , Figure 3 A circuit schematic diagram of a power consumption SSR switching power supply circuit of an embodiment of the present application is shown. As shown in the figure, the power consumption SSR switching power supply circuit in the embodiment of the present application includes a switching power supply chip and a receiving end of an optical coupler, the power supply end of the optical coupler is connected to the power supply end VCC of the switching power supply chip, and the receiving end of the optical coupler is arranged in the primary circuit and connected to a feedback circuit. It is worth noting that the secondary circuit in the embodiment of the present application is the same as that in the prior art, so it is not outlined in detail.

[0043] Reference Figure 4 The feedback circuit includes a conduction unit, a first sampling unit, a second sampling unit, a modulation unit, a power supply unit and a feedback control unit, combined with Figure 3 , the transmitting end of the optocoupler is connected to the output voltage and generates an optical signal, and the receiving end of the optocoupler generates an optocoupler current Iop after receiving the optical signal and outputs it to the conduction unit. The conduction unit is used to control the first sampling unit to conduct and output the first sampling current to the power supply unit to power the internal power supply VDD of the switching power supply chip, so as to reduce the loss generated by the optocoupler current. The optocoupler current in the prior art is usually directly to the ground, and the present application fully enables this part of the current. The conduction unit controls the first sampling unit to conduct and mirror-generate the second sampling current to the feedback control unit. The feedback control unit provides a feedback voltage to the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit. When the switching power supply system is lightly loaded or unloaded, the optocoupler current Iop increases, and the feedback control unit controls the modulation unit to conduct and output the modulation current based on the control voltage, shunts the optocoupler current Iop, and at the same time limits the maximum value of the optocoupler current Iop, thereby reducing the loss particularly significantly when lightly loaded or unloaded.

[0044] Reference Figure 3 and Figure 4 The conduction unit includes a current limiting resistor R11 and a third MOS tube M3, a first end of the third MOS tube M3 is connected to one end of the current limiting resistor R11, a second end of the third MOS tube M3 is connected to the power supply unit, a third end of the third MOS tube M3 is connected to the first sampling unit, and the other end of the current limiting resistor R11 is connected to the receiving end of the optical coupler.

[0045] Reference Figure 3 and Figure 4 The first sampling unit includes a first MOS tube M1, a first end of the first MOS tube M1 is connected to the second sampling unit, a second end of the first MOS tube M1 is connected to the receiving end of the optical coupler, and a third end of the first MOS tube M1 and a first end of the first MOS tube M1 are connected to the power supply unit through a third MOS tube M3. The power supply unit includes an energy storage capacitor C, a diode D, and a clamping diode D1, an anode of the diode D is connected to the second end of the third MOS tube M3, a cathode of the diode D is connected to one end of the energy storage capacitor C, the other end of the energy storage capacitor C is grounded, and a common point formed by the connection between the energy storage capacitor C and the diode D is the internal power supply terminal VDD of the switching power supply chip, and the clamping diode D1 is connected in parallel to both ends of the energy storage capacitor C. The second sampling unit includes a second MOS tube M2, a first end of the second MOS tube M2 is connected to the first end of the first MOS tube, a second end of the second MOS tube M2 is connected to the receiving end of the optical coupler, and a third end of the second MOS tube M2 is connected to the input end of the control feedback unit.

[0046] In addition, as a preferred embodiment, the first MOS tube M1 and the second MOS tube M2 are both configured as PMOS tubes, and the third MOS tube M3 is configured as an NMOS tube. The source of the third MOS tube M3 is connected to the anode of the diode D, the drain of the third MOS tube M3 is connected to the drain of the first MOS tube M1, the gate of the third MOS tube M3 is connected to one end of the current limiting resistor R11, and the other end of the current limiting resistor R11 is connected to the receiving end of the optical coupler. The cathode of the diode D is connected to one end of the energy storage capacitor C, and the other end of the energy storage capacitor C is grounded. The common point formed by the connection between the energy storage capacitor C and the diode D is the internal power supply terminal VDD of the switching power supply chip, and the energy storage capacitor C is the capacitor of the internal power supply terminal VDD of the switching power supply chip. In implementation, after the receiving end of the optocoupler located on one side of the primary circuit generates the optocoupler current Iop, the optocoupler current Iop flows through the current limiting resistor R11, and the current limiting resistor R11 provides a bias voltage for the third MOS tube M3 to turn on the third MOS tube M3. After the third MOS tube M3 is turned on, the first MOS tube M1 and the second MOS tube M2 are turned on, so that the optocoupler current Iop flows through the first MOS tube M1, the third MOS tube M3, the diode D and the energy storage capacitor C in sequence, so as to realize power supply for the internal power supply terminal VDD of the switching power supply chip.

[0047] At the same time, the source of the first MOS tube M1 and the source of the second MOS tube M2 are connected to the receiving end of the optical coupler, the gate of the first MOS tube M1, the drain of the first MOS tube M1 and the gate of the second MOS tube M2 are connected, and the drain of the first MOS tube M1 is also connected to the power supply unit through the conduction unit. The drain of the second MOS tube M2 is connected to the input end of the control feedback unit. In the implementation, after the receiving end of the optical coupler located on one side of the primary circuit generates the optical coupler current Iop, the optical coupler current Iop flows through the current limiting resistor R11 so that the third MOS tube M3 controls the first MOS tube M1 and the second MOS tube M2 to be turned on, and then the optical coupler current Iop flows through the first MOS tube M1 and the second MOS tube M2 respectively, and accordingly, the first sampling current i1 and the mirror-generated second sampling current i2 are generated respectively, and at this time the optical coupler current Iop=i1+i2.

[0048] In addition, as a preferred embodiment, the clamping diode D1 is set to stabilize the voltage of the internal power supply terminal VDD of the switching power supply chip. The parameters of the clamping diode D1 can select the target voltage value of the internal power supply terminal VDD of the switching power supply chip. For example, if the maximum design limit of the internal power supply terminal VDD of the switching power supply chip is 4V, then the clamping voltage of the clamping diode D1 is 4V. This can avoid the situation that the energy storage capacitor C is always in a charging state, thereby causing the internal power supply terminal VDD of the switching power supply chip to continue to rise. In implementation, if the power consumption of the internal power supply terminal VDD of the switching power supply chip is small, and the first sampling current i1 will charge it every cycle, then the voltage of VDD will continue to rise. By adding the clamping diode D1, the voltage of VDD can be clamped to be greater than the set voltage maximum value, thereby playing a role in stabilizing the VDD voltage.

[0049] In addition, as a preference, in this embodiment, the first MOS tube M1 and the second MOS tube are both configured as PMOS tubes and are mirror images of each other, and the size of the first MOS tube M1 and the size of the second MOS tube have a certain proportional relationship. By designing the above-mentioned current mirror structure and setting a specific proportional relationship, the optocoupler current can be accurately sampled in equal proportion to a certain extent. Optionally, if M1:M2=N:1, then the relationship between the second sampling current i2 and the optocoupler current Iop is: i2=Iop / N.

[0050] In addition, as a preference, in the present embodiment, the third MOS tube M3 is set as an NMOS tube. Based on the above hardware settings, after the optocoupler current Iop flows through the receiving end of the optocoupler, the voltage generated by the current limiting resistor R11 provides a forward bias for the gate of the third MOS tube M3, so that the third MOS tube M3 meets the conduction condition, and thus the third MOS tube M3 starts to conduct. When the third MOS tube M3 is turned on, its drain voltage will decrease, and the decreased voltage will be transmitted to the gates of the first MOS tube M1 and the second MOS tube M2. Since the first MOS tube M1 and the second MOS tube M2 are PMOS tubes, the decrease in the gate voltage of the two will increase the voltage difference between the gate and the source, so that the first MOS tube M1 and the second MOS tube M2 meet the conduction condition, so after the third MOS tube M3 is turned on, the first MOS tube M1 and the second MOS tube M2 will both be turned on.

[0051] Furthermore, preferably, in the present embodiment, the diode D is configured as a unidirectional conducting diode to prevent the voltage at the internal power supply terminal VDD of the switching power supply chip from flowing backwards.

[0052] Reference Figure 3 and Figure 4 The feedback control unit includes a first sampling resistor R12 and a second sampling resistor R13, one end of the first sampling resistor R12 is connected to the drain of the second MOS tube, the other end of the first sampling resistor R12 is connected to one end of the second sampling resistor R13, and the other end of the second sampling resistor R13 is grounded. The modulation unit includes a fourth MOS tube M4, which is set as an NMOS tube. The NMOS tube has a lower on-resistance when turned on, and the power consumed by the NMOS tube in the on state is lower. The gate of the fourth MOS tube M4 is connected to the common point formed by connecting the first sampling resistor R12 and the second sampling resistor R13, the drain of the fourth MOS tube M4 is connected to the common point formed by connecting the gate of the third MOS tube M3 and the current limiting resistor R11, and the source of the fourth MOS tube M4 is grounded. In implementation, after the second MOS tube M2 is turned on, the second sampling current i2 generated by the optocoupler current Iop flowing through the second MOS tube M2 flows through the first sampling resistor R12 and the second sampling resistor R13 in sequence, and the connection point between the second MOS tube M2 and the first sampling resistor R12 is set to the feedback voltage FB. At this time, it can be obtained that FB=i2*(R12+R13), and the feedback voltage FB is input to the primary circuit to control the operation of the power circuit. At the same time, it can be known from the above calculation formula that, unlike the prior art, in the embodiment of the present application, the above feedback voltage FB is proportional to the optocoupler current Iop and inversely proportional to the output current Iout.

[0053] In addition, the connection point between the first sampling resistor R12 and the second sampling resistor R13 is set to the control voltage VA, where it can be known that VA=i2*R13. As the control voltage VA continues to increase, when the control voltage VA is greater than the turn-on voltage Vth of the fourth MOS tube M4, the fourth MOS tube M4 is turned on and generates a modulation current i3. Due to the generation of the modulation current i3, the modulation current i3 causes the shunting of the optocoupler current Iop and limits the current rise speed of the first sampling current i1 and the second sampling current i2. Specifically, when the system is turned to light load or no load, the optocoupler current increases, and i1 and i2 also increase accordingly. When the VA voltage increases to be greater than the turn-on voltage Vth of the fourth MOS tube M4, the fourth MOS tube M4 is turned on, generates a modulation current i3, pulls down the gate voltage of M3, and the gate-source voltage Vgs of M3 decreases, resulting in a decrease in the rise speed of the first sampling current i1, a decrease in the rise speed of the mirror current i2 synchronously, a decrease in the rise speed of the VA voltage, and a slow decrease in the Vgs of the third MOS tube M3. When the Vgs of the third MOS tube M3 decreases to a level that can withstand i 1 maximum current, i1 no longer rises, i1 reaches the maximum value, and the negative feedback loop finally maintains Iop=i1+i2+i3, that is, the maximum value of Iop is limited, and at the same time, the maximum value of the feedback voltage FB and the maximum charging current of the internal power supply VDD of the switching power supply chip by the first sampling current i1 are limited. The fourth MOS tube M4 and the third MOS tube M3 realize the role of the negative feedback circuit to maintain the balance of the loop.

[0054] Combine the following Figure 3 , the working principle of the low power consumption SSR switching power supply circuit of this embodiment is described in detail.

[0055] When the switching power supply system is working normally or in a heavy load state, the optocoupler current Iop is relatively small. After the optocoupler current is generated at the receiving end of the optocoupler located on one side of the primary circuit, the optocoupler current Iop flows through the current limiting resistor R11. The current limiting resistor R11 provides a bias voltage for the third MOS tube M3 to turn on the third MOS tube M3. After the third MOS tube M3 is turned on, the first MOS tube M1 and the second MOS tube M2 are turned on. The optocoupler current Iop flows through the first MOS tube M1 and the second MOS tube M2 respectively, and the first sampling current i1 and the mirror-generated second sampling current i2 are generated respectively. The first sampling current i1 flows through the first MOS tube M1, the third MOS tube M3, the diode D and the energy storage capacitor C in sequence, so as to realize the power supply for the internal power supply VDD of the switching power supply chip. The second sampling current i2 flows through the first sampling resistor R12 and the second sampling resistor R13 in sequence, and the feedback voltage FB is generated at the connection point between the second MOS tube M2 and the first sampling resistor R12, and the control voltage VA is generated at the connection point between the first sampling resistor R12 and the second sampling resistor R13.

[0056] When the switching power supply system is transferred to a light load or no-load state, the optocoupler current Iop will continue to increase. Since VA=i2*R13 and Iop=i1+i2 are known, it can be known that as the optocoupler current Iop increases, the control voltage VA will also continue to increase. When the control voltage VA is greater than the turn-on voltage Vth of the fourth MOS tube M4, the fourth MOS tube M4 is turned on and generates a modulation current i3, and finally maintains Iop=i1+i2+i3. The i3 current pulls down the gate of the third MOS tube M3. When the VGS of M3 drops to a level that can withstand the maximum current of i1, Iop is the maximum value at this time. When the switching power supply system is in a light load or no-load state, the loss is reduced, thereby improving the efficiency.

[0057] Regarding the circuit structure and working process of the switching power supply in this embodiment that are not described in detail, reference can be made to the relevant parts in the above control circuit embodiment, and no further details will be given here.

[0058] In addition, the embodiment of the present application also provides a low-power SSR switching power supply circuit control method, which is applied to the low-power SSR switching power supply circuit in the above embodiment, such as Figure 5 As shown, the method comprises the following steps:

[0059] S510, generating an optical signal by connecting the transmitting end of the optical coupler to the output voltage;

[0060] S520, receiving an optical signal through a receiving end of the optical coupler to generate an optical coupler current and output the current to the conduction unit;

[0061] S530, using the conduction unit to control the first sampling unit to conduct and output the first sampling current to the power supply unit to supply power to the internal power supply VDD of the switching power supply chip;

[0062] S540, generating a second sampling current by using the mirror relationship between the first sampling unit and the second sampling unit and outputting the second sampling current to the feedback control unit;

[0063] S550, the feedback control unit provides a feedback voltage to the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit;

[0064] S560. When the switching power supply system is lightly loaded or unloaded, the optocoupler current increases, and the feedback control unit controls the modulation unit to conduct and output the modulation current based on the control voltage, thereby shunting the optocoupler current and limiting the maximum value of the optocoupler current.

[0065] Regarding the working process not described in detail in the control method of this embodiment, reference may be made to the relevant parts in the above control circuit embodiment, which will not be repeated here.

[0066] refer to Figure 6 , Figure 6The schematic diagram of the switching power supply structure of the present application is shown in FIG. 1 , wherein the switching power supply includes a secondary circuit and a low-power SSR switching power supply circuit as in the above-mentioned embodiment, and the secondary circuit is connected to the low-power SSR switching power supply circuit. Similarly, the transmitting end of the optical coupler is connected to the output voltage to generate an optical signal, and the receiving end of the optical coupler receives the optical signal to generate an optical coupler current and output it to the conduction unit. The conduction unit is used to control the first sampling unit to conduct and output the first sampling current to the power supply unit to power the switching power supply chip. The second sampling current is generated by the mirror relationship between the first sampling unit and the second sampling unit and output to the feedback control unit. The feedback control unit provides a feedback voltage to the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit. When the switching power supply system is lightly loaded or unloaded, the optical coupler current increases, and the feedback control unit controls the modulation unit to conduct and output the modulation current based on the control voltage, thereby shunting the optical coupler current.

[0067] Regarding the working process not described in detail in the control method of this embodiment, reference may be made to the relevant parts in the above control circuit embodiment, which will not be repeated here.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A low-power SSR switching power supply circuit, comprising a switching power supply chip and a receiving end of an optical coupler arranged in a primary circuit, wherein the transmitting end of the optical coupler is connected to an output voltage, the power supply end of the optical coupler is connected to a power supply end VCC of the switching power supply chip, and the receiving end of the optical coupler is also connected to a feedback circuit, characterized in that: The feedback circuit includes a conduction unit, a first sampling unit, a second sampling unit, a modulation unit, a power supply unit and a feedback control unit; the receiving end of the optical coupler generates an optical coupling current and outputs it to the conduction unit, the conduction unit controls the first sampling unit to conduct and output the first sampling current to the power supply unit to supply power to the internal power supply VDD of the switching power supply chip, so as to reduce the loss generated by the optical coupling current; the conduction unit controls the first sampling unit to conduct and mirror-generate the second sampling current to the feedback control unit, and the feedback control unit provides a feedback voltage for the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit; When the switching power supply system is lightly loaded or unloaded, the optocoupler current increases, and the feedback control unit controls the modulation unit to turn on and output the modulation current based on the control voltage, thereby shunting the optocoupler current, and ultimately maintaining the optocoupler current equal to the sum of the first sampling current, the second sampling current and the modulation current, thereby limiting the maximum value of the optocoupler current, thereby reducing losses particularly significantly when the system is lightly loaded or unloaded.

2. The low-power SSR switching power supply circuit according to claim 1, characterized in that: The conduction unit includes a current limiting resistor and a third MOS tube, a first end of the third MOS tube is connected to one end of the current limiting resistor, a second end of the third MOS tube is connected to the power supply unit, a third end of the third MOS tube is connected to the first sampling unit, and the other end of the current limiting resistor is connected to the receiving end of the optical coupler.

3. The low-power SSR switching power supply circuit according to claim 2, characterized in that: The first sampling unit includes a first MOS transistor, a first end of the first MOS transistor is connected to the second sampling unit, a second end of the first MOS transistor is connected to the receiving end of the optical coupler, and a third end of the first MOS transistor and a first end of the first MOS transistor are connected to the power supply unit through the third MOS transistor.

4. The low-power SSR switching power supply circuit according to claim 3, characterized in that: The power supply unit includes an energy storage capacitor, a diode and a clamping diode, the anode of the diode is connected to the second end of the third MOS tube, the cathode of the diode is connected to one end of the energy storage capacitor, the other end of the energy storage capacitor is grounded, the common point formed by the connection between the energy storage capacitor and the diode is the internal power supply terminal VDD of the switching power supply chip, and the clamping diode is connected in parallel to the two ends of the energy storage capacitor.

5. The low power consumption SSR switching power supply circuit according to claim 4, characterized in that: The second sampling unit includes a second MOS tube, a first end of the second MOS tube is connected to the first end of the first MOS tube, a second end of the second MOS tube is connected to the receiving end of the optical coupler, and a third end of the second MOS tube is connected to the input end of the control feedback unit.

6. The low-power SSR switching power supply circuit according to claim 5, characterized in that: The first MOS tube and the second MOS tube are mirror images of each other and are in a certain proportional relationship, and both are PMOS tubes; the gate of the first MOS tube, the drain of the first MOS tube and the gate of the second MOS tube are connected, the source of the first MOS tube and the source of the second MOS tube are both connected to the receiving end of the optical coupler, the drain of the first MOS tube is connected to the third end of the third MOS tube, and the drain of the second MOS tube is connected to the input end of the control feedback unit.

7. The low power consumption SSR switching power supply circuit according to claim 6, characterized in that: The feedback control unit includes a first sampling resistor and a second sampling resistor, one end of the first sampling resistor is connected to the drain of the second MOS tube, the other end of the first sampling resistor is connected to one end of the second sampling resistor, and the other end of the second sampling resistor is grounded.

8. The low-power SSR switching power supply circuit according to claim 7, characterized in that: The modulation unit includes a fourth MOS tube, a first end of the fourth MOS tube is connected to a common point formed by connecting the first sampling resistor and the second sampling resistor, a second end of the fourth MOS tube is grounded, and a third end of the fourth MOS tube is connected to a common point formed by connecting the first end of the third MOS tube and the current limiting resistor.

9. The low-power SSR switching power supply circuit according to claim 8, characterized in that: The third MOS tube and the fourth MOS tube are both NMOS tubes; the gate of the third MOS tube is connected to one end of the current limiting resistor, the source of the third MOS tube is connected to the anode of the diode, and the drain of the third MOS tube is connected to the drain of the first MOS tube; the gate of the fourth MOS tube is connected to a common point formed by connecting the first sampling resistor and the second sampling resistor; the source of the fourth MOS tube is grounded; and the drain of the fourth MOS tube is connected to a common point formed by connecting the gate of the third MOS tube and the current limiting resistor.

10. A control method for a low power consumption SSR switching power supply circuit, characterized in that: Applied to the low-power SSR switching power supply circuit according to any one of claims 1 to 9, the method comprises: The transmitting end of the optical coupler is connected to the output voltage to generate an optical signal; Receiving the optical signal through the receiving end of the optical coupler to generate an optical coupler current and output it to the conduction unit; Using the conduction unit to control the first sampling unit to conduct and output a first sampling current to the power supply unit to supply power to the internal power supply VDD of the switching power supply chip; Using the mirror relationship between the first sampling unit and the second sampling unit to generate a second sampling current and output it to the feedback control unit; The feedback control unit provides a feedback voltage to the switching power supply chip based on the second sampling current and outputs a control voltage to the modulation unit; When the switching power supply system is lightly loaded or unloaded, the optocoupler current increases, and the feedback control unit controls the modulation unit to turn on and output the modulation current based on the control voltage, shunts the optocoupler current, and limits the maximum value of the optocoupler current.

11. A switching power supply, comprising a secondary circuit, characterized in that: It comprises the low power consumption SSR switching power supply circuit as described in any one of claims 1 to 9 above.

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