Flyback single-winding multi-level output power supply circuit

Abstract

A flyback single-winding multi-level output power supply circuit comprises a flyback main transformer (T1) which has one secondary winding and outputs a primary power supply (Vso), a primary isolation main power supply circuit (4) which outputs a first positive voltage (VCC3), a first control signal generation circuit (6) which generates a first PWM signal based on the first positive voltage (VCC3) to feed back and control a primary switch (Q1), and a second control signal generation circuit (7) which generates a second PWM signal based on the first positive voltage (VCC3). The primary isolation auxiliary power supply circuit (5) is connected to the primary power supply (Vso) through a main power supply switch (Q2) and outputs a second positive voltage (VCC4); the second control signal generation circuit (7) generates a second PWM (Pulse Width Modulation) signal based on the second positive voltage (VCC4) and the first PWM signal (Q1DRV1) to perform feedback control on the main power supply switch (Q2); a primary winding of the auxiliary transformer (T2) is connected to the primary power supply (Vso); the secondary isolation power supply circuit is connected to a secondary winding of the auxiliary transformer (T2); the mutual influence of the voltages of the multiple output branches is small, the isolated application scene is easy to meet, the size is small, and the comprehensive cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of flyback switching power supplies, and in particular to a flyback single-winding multi-level output power supply circuit. Background Art

[0002] The traditional flyback switching power supply can achieve level output in the following ways:

[0003] (1) Use multiple winding outputs and use the turns ratio to control the output voltage of different windings. This method can easily achieve the isolation requirements between multiple output power supplies, but there are defects: on the one hand, there are too many windings, the coupling coefficients between them are quite different, the leakage inductance of the transformer is large, and the voltage stress of the MOSFET switch tube is too high in the flyback application. In order to suppress the voltage stress of the switch tube, the RCD (Resistor-Capacitor-Diode) clamping circuit needs to consume a large amount of power, causing heat and efficiency loss; on the other hand, the insulation layer between the multiple windings will increase the parasitic capacitance of the transformer. Excessive parasitic capacitance will cause excessive peak current when the MOSFET is turned on, increase the turn-on loss of the MOSFET, cause device heat and efficiency loss; at the same time, the presence of parasitic capacitance will also affect the EMI (Electromagnetic Interference, electromagnetic interference) characteristics, it is difficult to rectify and optimize in EMC certification; thirdly, the output voltage adjustment rate of each branch is uncontrollable. When the main power supply output is fully loaded and other secondary windings are lightly loaded or no-loaded, the main voltage has a control loop to ensure stable voltage output, but other windings are open-loop output, the output voltage of the secondary winding will increase abnormally, which may exceed the upper limit of the load input voltage and cause damage to the subsequent load.

[0004] (2) Main output with DC / DC boost / buck. This method is to boost / buck the main output voltage to obtain outputs of different voltage levels. The functional unit module is simple, but there are defects: each level of output voltage requires a DC / DC control chip, supplemented by peripheral resistors, capacitors, inductors, semiconductors and other devices to obtain the corresponding output voltage. The device usage is large and the cost is not optimal; the DC / DC part is cascaded after the main output circuit, and the increase in DC / DC branches will cause the main device loss to increase. The DC / DC level efficiency cannot reach 100%, so the efficiency bottleneck after cascading cannot be broken through; the output voltages of different branches are not isolated and have a common reference ground. It is not suitable for systems that require partial isolation power supply, and the usage scenarios are relatively limited.

[0005] (3) Multi-tap common ground output. This method uses taps on the secondary winding. The working principle is similar to that of an autotransformer. The output is adjusted by controlling the voltage with different turns ratios. However, the following defects exist: due to the shared winding and tap output, the current carrying capacity of the winding needs to be designed according to the maximum current carrying capacity. The use of copper wire is over-designed and the cost is not optimal. The common ground of the output cannot meet the needs of isolated power supply for some circuits, and the usage scenarios are limited. There is a problem of cross-regulation rate between the output voltages of the taps. The full-load output of the main line will cause the output voltage of other no-load / light-load taps to increase abnormally.

[0006] The above information disclosed in this Background section is included only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is currently known to a person of ordinary skill in the art. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a flyback single-winding multi-level output power supply circuit in view of the above-mentioned defects of the prior art.

[0008] The technical solution adopted by the present invention to solve the technical problem is: construct a flyback single-winding multi-level output power supply circuit, including an input power supply, a primary winding connected in series with a primary switch and connected to the input power supply, a flyback main transformer with one secondary winding and outputting a primary power supply, a primary isolation main power supply circuit connected to the primary power supply and converted into a first positive voltage output, and a first control signal generating circuit that generates a first PWM signal based on the first positive voltage and the current flowing through the primary switch to feedback control the primary switch;

[0009] The flyback single-winding multi-level output power supply circuit also includes:

[0010] A primary isolation auxiliary power supply circuit is connected to the primary power supply via a corresponding main power switch and converted into a second positive voltage output, wherein the second positive voltage is less than the first positive voltage;

[0011] A second control signal generating circuit, based on the second positive voltage of the primary isolated auxiliary power supply circuit and the first PWM signal, generates a corresponding second PWM signal to feedback control the corresponding main power switch;

[0012] an auxiliary transformer, wherein the primary winding is connected to the primary power supply and the secondary winding is at least one;

[0013] The secondary isolation power supply circuit is connected to the secondary winding of the auxiliary transformer and converted into positive voltage and / or negative voltage output.

[0014] Further, in the flyback single-winding multi-level output power supply circuit of the present invention, the auxiliary transformer includes a first secondary winding for outputting a first secondary power supply and a second secondary winding for outputting a second secondary power supply;

[0015] The secondary isolation power supply circuit comprises:

[0016] A secondary isolated positive voltage output circuit is connected to the first secondary power supply and converted into a third positive voltage output;

[0017] The secondary isolated negative voltage output circuit is connected to the second secondary power supply and converted into a negative voltage output.

[0018] Furthermore, in the flyback single-winding multi-level output power supply circuit of the present invention, the second control signal generating circuit includes:

[0019] A voltage division comparison circuit is connected to the second positive voltage, and generates a set signal after voltage division and comparison.

[0020] The PWM generating circuit is connected to the first PWM signal and the set signal. When the set signal represents that the second positive voltage is lower than the threshold voltage and the level of the first PWM signal is the level that turns off the primary switch, the level of the output second PWM signal is set to turn on the main power switch.

[0021] Furthermore, in the flyback single-winding multi-level output power supply circuit of the present invention, the voltage division comparison circuit includes:

[0022] a first voltage-dividing circuit, connected to the second positive voltage, dividing the second positive voltage and outputting a first voltage-dividing signal;

[0023] an error amplifier circuit, connected to the first voltage-divided signal, amplifying the signal and outputting a voltage modulation signal;

[0024] A second voltage divider circuit is connected to the voltage modulation signal, divides the voltage modulation signal and outputs a second voltage divider signal;

[0025] A regulated voltage is connected to the second divided voltage signal and outputted in a regulated voltage;

[0026] The comparison circuit receives the second voltage-divided signal after voltage stabilization, compares it with a reference voltage, and uses the comparison result as the set signal.

[0027] Furthermore, in the flyback single-winding multi-level output power supply circuit of the present invention, the PWM generation circuit includes:

[0028] An inverter is connected to the first PWM signal, inverts the first PWM signal, and then outputs a reset signal;

[0029] The RS trigger has a set end receiving the set signal, a reset end receiving the reset signal, and an output end outputting the second PWM signal.

[0030] Further, in the flyback single-winding multi-level output power supply circuit described in the present invention, the first voltage-dividing circuit includes a first voltage-dividing resistor and a second voltage-dividing resistor, the error amplification circuit includes an operational amplifier and a compensation network, the second voltage-dividing circuit includes a first diode, a third voltage-dividing resistor, and a fourth voltage-dividing resistor, the regulated voltage includes a first regulated diode, and the comparison circuit includes a comparator;

[0031] The first end of the first voltage-dividing resistor is connected to the second positive voltage, and the second end is grounded via the second voltage-dividing resistor. The second end of the first voltage-dividing resistor is also connected to the negative input end of the operational amplifier. The positive input end of the operational amplifier is connected to the voltage setting value. The negative input end of the operational amplifier is connected to the output end of the operational amplifier via the compensation network. The output end of the operational amplifier is connected to the positive electrode of the first diode. The negative electrode of the first diode is connected to the first end of the third voltage-dividing resistor. The second end of the third voltage-dividing resistor is grounded via the fourth voltage-dividing resistor. The second end of the third voltage-dividing resistor is also connected to the cathode of the first voltage-dividing diode. The anode of the first voltage-dividing diode is grounded. The cathode of the first voltage-dividing diode is connected to the positive input end of the comparator. The negative input end of the comparator is connected to the reference voltage. The output end of the comparator outputs the set signal.

[0032] Furthermore, in the flyback single-winding multi-level output power supply circuit described in the present invention, the compensation network includes a first compensation resistor, a first compensation capacitor, and a second compensation capacitor. The negative input terminal of the operational amplifier is connected to the output terminal of the operational amplifier via the first compensation resistor and the second compensation capacitor in sequence, and the first compensation capacitor is connected between the negative input terminal of the operational amplifier and the output terminal of the operational amplifier.

[0033] Furthermore, in the flyback single-winding multi-level output power supply circuit described in the present invention, the same-name end of the primary winding of the flyback main transformer is connected to the input power supply, and the opposite-name end is grounded via the primary switch; the same-name end of the secondary winding of the flyback main transformer is grounded, and the opposite-name end outputs the primary power supply;

[0034] The primary isolation main power supply circuit comprises a first diode and a first rectifier circuit, wherein the positive electrode of the first diode is connected to the opposite pole end of the secondary winding of the flyback main transformer, and the negative electrode of the first diode is grounded via the first rectifier circuit;

[0035] The primary isolated auxiliary power supply circuit includes a second diode and a second rectifier circuit, the anode of the second diode is connected to the opposite pole end of the secondary winding of the flyback main transformer via the main power switch, and the cathode is grounded via the second rectifier circuit;

[0036] The cathode of the first diode outputs the first positive voltage to the outside, and the cathode of the second diode outputs the second positive voltage to the outside.

[0037] Furthermore, in the flyback single-winding multi-level output power supply circuit described in the present invention, the same-name end of the primary winding of the flyback main transformer is connected to the input power supply, and the opposite-name end is grounded via the primary switch; the same-name end of the secondary winding of the flyback main transformer is grounded, and the opposite-name end outputs the primary power supply;

[0038] The opposite-name end of the primary winding of the auxiliary transformer is grounded, and the same-name end is connected to the opposite-name end of the secondary winding of the flyback main transformer;

[0039] The secondary isolated positive voltage output circuit comprises a third diode and a third rectifier circuit, wherein the anode of the third diode is grounded, and the cathode is connected to the opposite-name end of the first secondary winding of the auxiliary transformer, and the same-name end of the first secondary winding of the auxiliary transformer is grounded via the third rectifier circuit;

[0040] The secondary isolated negative voltage output circuit includes a fourth diode, a fourth rectifier circuit, a first resistor, a second voltage zener diode, a first capacitor, a first switch, and a second capacitor, wherein the positive electrode of the fourth diode is connected to the same-name end of the second secondary winding of the auxiliary transformer, the negative electrode of the fourth diode is grounded via the first switch, the opposite-name end of the second secondary winding of the auxiliary transformer is connected to the negative electrode of the fourth diode via the fourth rectifier circuit, the first resistor is connected between the negative electrode of the fourth diode and the control end of the first switch, the first capacitor is connected in parallel with the second voltage zener diode, the control end of the first switch is connected to the cathode of the second voltage zener diode, the anode of the second voltage zener diode is connected to the opposite-name end of the second secondary winding of the auxiliary transformer and the first end of the second capacitor, and the second end of the second capacitor is grounded;

[0041] The same-name end of the first secondary winding of the auxiliary transformer outputs the first positive voltage to the outside, and the first end of the second capacitor outputs the negative voltage to the outside.

[0042] Furthermore, in the flyback single-winding multi-level output power supply circuit described in the present invention, a clamping circuit is further connected between the same-name end and the opposite-name end of the primary winding of the flyback main transformer.

[0043] The flyback single-winding multi-level output power supply circuit of the present invention has the following beneficial effects: the secondary side of the flyback main transformer has only one winding, and the winding is connected to multiple output branches, wherein the primary isolation main power supply circuit outputs a higher positive voltage based on closed-loop control, and the primary isolation auxiliary power supply circuit outputs a lower positive voltage based on closed-loop control to ensure stable voltage output, and then cooperates with the auxiliary transformer to connect the secondary isolation power supply circuit to realize the isolated power supply of low-power loads and the expansion of power supply output branches, and the primary and secondary isolation power supply circuits essentially obtain energy from the secondary side of the flyback main transformer, and the power supply of the secondary side of the flyback main transformer is clamped in the primary isolation power supply circuit. The amplitude of the output voltage of the isolated main power supply circuit is controlled, so the voltage of the primary and secondary isolated power supply circuits will not increase or decrease abnormally due to changes in the size of the main output load; in this way, the branch voltages of the present invention have little influence on each other, and it is easy to meet the application scenarios of isolation. In short, the present invention is based on a mature flyback power supply topology structure, fully utilizes the current output capacity and dynamic response speed of the output winding of the flyback main transformer, decouples the power circuits from each other under different output loads, and the dynamic adjustment of the output voltages between the branches has little influence on each other. The winding process of the transformer is simple, the volume is small, the overall cost of the circuit is reduced, and the performance is significantly optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the provided drawings without creative work:

[0045] Figure 1 It is a structural schematic diagram of a flyback single-winding multi-level output power supply circuit of the present invention;

[0046] Figure 2 is a schematic diagram of a second control signal generating circuit;

[0047] Figure 3 It is the timing waveform diagram of key nodes;

[0048] Figure 4 It is the output voltage waveform of each branch under the full load condition of the main output;

[0049] Figure 5 It is the output voltage waveform of each branch under the light load condition of the main output. DETAILED DESCRIPTION

[0050] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations on the technical solutions of the present application. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0051] refer to Figure 1 The flyback single-winding multi-level output power supply circuit of the present invention includes: an input power supply Vbus, a primary switch Q1, a flyback main transformer T1, a plurality of output branches connected to the secondary winding of the flyback main transformer T1, a first control signal generating circuit 6, and a second control signal generating circuit 7. The flyback main transformer T1 has only one secondary winding, and the secondary winding is connected to a plurality of output branches. The plurality of output branches include a primary isolation main power supply circuit 4, a primary isolation auxiliary power supply circuit 5, and a secondary isolation power supply circuit, and the secondary isolation power supply circuit is connected to the secondary winding of the flyback main transformer T1 through an auxiliary transformer T2.

[0052] Among them, the primary winding of the flyback main transformer T1 is connected in series with the primary switch Q1 and then connected to the input power supply Vbus, and the secondary winding outputs the primary power supply Vso. Specifically: the same-name end of the primary winding of the flyback main transformer T1 is connected to the input power supply Vbus, the opposite-name end of the primary winding of the flyback main transformer T1 is grounded via the primary switch Q1, the primary switch Q1 is controlled by the first PWM signal Q1_DRV1, the same-name end of the secondary winding of the flyback main transformer T1 is grounded, and the opposite-name end of the secondary winding of the flyback main transformer T1 outputs the primary power supply Vso.

[0053] The primary isolation main power circuit 4 is connected to the primary power supply Vso and converted into a first positive voltage VCC3 output. The first control signal generating circuit 6 generates a first PWM signal Q1_DRV1 based on the first positive voltage VCC3 and the current IQ1 flowing through the primary switch Q1 to feedback control the primary switch Q1.

[0054] The first switch can be a field effect transistor. In this embodiment, the primary switch Q1 is an N-type MOSFET. When Q1 is turned on, the input power supply Vbus charges the primary winding of the transformer T1. When Q1 is turned off, the electric energy stored in the primary winding of the transformer T1 is transferred to the secondary winding, thereby providing the primary power supply Vso to the subsequent multiple output branches. The driving input Q1_DRV signal of the primary switch Q1 is derived from the modulation signal output of the first control signal generating circuit 6. The first control signal generating circuit 6 is a PWM control chip, which can be a conventional flyback power supply control chip, such as the common UC3842, UC2845, or a commonly used quasi-resonant flyback power supply control chip, such as the commonly used NCP1380. The first control signal generating circuit 6 performs PI control through the feedback signal of the voltage VCC3 and the sampling signal of the current IQ1 of the primary MOSFET switch tube Q1, and compares the output of the PI controller with the carrier signal to obtain a PWM control signal Q1_DRV with different duty cycles, thereby controlling the opening and closing of Q1 to achieve energy transfer from the primary side to the secondary side of the transformer T1.

[0055] In this embodiment, a clamping circuit 1 is also connected between the same-name end and the opposite-name end of the primary winding of the flyback main transformer T1. In this embodiment, the clamping circuit 1 is a conventional RCD absorption circuit, and Rc, Cc, and Dc are used to clamp the Q1 turn-off voltage stress caused by the leakage inductance of the T1 transformer to ensure that the Q1 turn-off is in a safe working area, which is no different from the primary structure of an ordinary flyback power supply. Of course, it can be understood that the clamping circuit 1 can also be other types of clamping circuits, such as an active clamping control circuit. The control signal of the active clamping control circuit can be a control signal based on the primary switch Q1, that is, the first PWM signal Q1_DRV1, and can also control the voltage value of the secondary side of T1, effectively improving the voltage cross-regulation rate of the multi-channel output of the switching power supply circuit.

[0056] In the present invention, the primary isolation auxiliary power supply circuit 5 is connected to the primary power supply Vso by the corresponding main power switch Q2, and converted into a second positive voltage VCC4 output, and the second positive voltage VCC4 is less than the first positive voltage VCC3. The main power switch Q2 is based on closed-loop control, specifically, the second control signal generating circuit 7 generates a corresponding second PWM signal Q2_DRV1 based on the second positive voltage VCC4 of the primary isolation auxiliary power supply circuit 5 and the first PWM signal Q1_DRV1 to feedback control the corresponding main power switch Q2.

[0057] In addition to the primary isolated auxiliary power supply circuit 5, the present invention is also connected to a secondary isolated power supply circuit through an auxiliary transformer T2. The auxiliary transformer T2 is a three-winding isolation transformer with a turns ratio of 1:1, which is used to meet the isolated power supply of small power loads and the expansion of power supply output branches. The primary winding of the auxiliary transformer T2 is connected to the primary power supply Vso. Specifically, the opposite-name end of the primary winding of the auxiliary transformer T2 is grounded, and the same-name end of the primary winding of the auxiliary transformer T2 is connected to the opposite-name end of the secondary winding of the flyback main transformer T1. The auxiliary transformer T2 has at least one secondary winding, and the secondary isolated power supply circuit is connected to the secondary winding of the auxiliary transformer T2 and converted into positive voltage or / and negative voltage output. Specifically, in this embodiment, the auxiliary transformer T2 includes a first secondary winding that outputs a first secondary power supply, a second secondary winding that outputs a second secondary power supply, and the secondary isolated power supply circuit includes a secondary isolated positive voltage output circuit 3 and a secondary isolated negative voltage output circuit 2. The secondary isolation positive voltage output circuit 3 is connected to the first secondary power supply and converted into a third positive voltage VCC2 output, and the secondary isolation negative voltage output circuit 2 is connected to the second secondary power supply and converted into a negative voltage VCC1 output.

[0058] The four output branches are introduced in detail below.

[0059] (1) The first output branch: primary isolation main power supply circuit 4.

[0060] The primary isolated main power supply circuit 4 is used as a branch circuit with heavy load, and provides a first positive voltage VCC3 based on a closed-loop control method. The first positive voltage VCC3 is mainly used to supply power to the main output load (generally powering power loads such as fans).

[0061] In this embodiment, the primary isolated main power supply circuit 4 includes a first diode D2 and a first rectifier circuit, wherein the positive electrode of the first diode D2 is connected to the opposite pole of the secondary winding of the flyback main transformer T1, and the negative electrode is grounded via the first rectifier circuit. The first rectifier circuit specifically includes a capacitor C4. The first diode D2 is unidirectionally conductive, so the first diode D2 and the capacitor C4 together substantially constitute a half-wave rectifier circuit. The negative electrode of the first diode D2 outputs the first positive voltage VCC3 to the outside, and RL3 represents the load.

[0062] In this embodiment, the first positive voltage VCC3 will act as feedback to affect the on and off of the primary MOSFET switch tube Q1, thereby realizing closed-loop control of the first positive voltage VCC3. As explained above, the first control signal generating circuit 6 performs PI control through the feedback signal of the voltage VCC3 and the sampling signal of the current IQ1 of the primary MOSFET switch tube Q1, and compares the output of the PI controller with the carrier signal to obtain the PWM control signal Q1_DRV with different duty ratio outputs, thereby controlling the on and off of Q1 to realize the energy transfer from the primary side of the transformer T1 to the secondary side. For example, when the signal Q1_DRV controls Q1 to be on, the input power supply Vbus charges the primary winding of the transformer T1, and when the signal Q1_DRV controls Q1 to be off, the electric energy stored in the primary winding of the transformer T1 is transferred to the secondary winding, thereby providing the primary power supply Vso to the subsequent multiple output branches.

[0063] (2) The second output branch: a primary isolated auxiliary power supply circuit 5.

[0064] The primary isolation auxiliary power supply circuit 5 provides a second positive voltage VCC4 based on a closed-loop control method. VCC4 is a positive voltage, which serves as the power input of the system control board of the switching power supply, and also provides a positive voltage power input as the sampling circuit of the switching power supply, and cooperates with VCC1 to provide power, ensuring dual power supply and reliable operation of the Hall and operational amplifiers.

[0065] In this embodiment, the primary isolated auxiliary power supply circuit 5 includes a second diode D4 and a second rectifier circuit, wherein the positive electrode of the second diode D4 is connected to the opposite end of the secondary winding of the flyback main transformer T1 via the main power switch Q2, and the negative electrode is grounded via the second rectifier circuit. The second rectifier circuit specifically includes a capacitor C5. The second diode D4 is unidirectionally conductive, so the second diode D4 and the capacitor C5 together substantially constitute a half-wave rectifier circuit. The negative electrode of the second diode D4 outputs the second positive voltage VCC4 to the outside. RL4 represents a load.

[0066] The main power switch Q2 can be a controllable electronic switch such as a MOS tube. In this embodiment, the main power switch Q2 is a MOSFET switch tube, that is, the primary switch Q1 and the main power switch Q2 are both turned on at a high level and turned off at a low level. The main power switch Q2 serves as a gate switch of the primary isolation auxiliary power circuit 5 to control the rectification time of D4 to ensure the regulated output of VCC4. The main power switch Q2 is controlled by the second PWM signal Q2_DRV1 generated by the second control signal generating circuit 7.

[0067] refer to Figure 2The second control signal generating circuit 7 includes a voltage division comparison circuit and a PWM generating circuit. The voltage division comparison circuit is connected to the second positive voltage VCC4, and generates a set signal after voltage division and comparison. The PWM generating circuit is connected to the first PWM signal Q1_DRV1 and the set signal. When the set signal represents that the second positive voltage VCC4 is lower than the threshold voltage level, and the level of the first PWM signal Q1_DRV1 is the level that turns off the primary switch Q1, the level of the output second PWM signal Q2_DRV1 is set to turn on the main power switch Q2.

[0068] In this embodiment, the voltage division comparison circuit includes a first voltage division circuit 71, an error amplifier circuit 72, a second voltage division circuit 73, a voltage regulator 74 and a comparison circuit 75 connected in sequence. The PWM generation circuit includes an inverter 76 and an RS trigger 77.

[0069] The first voltage divider circuit 71 is connected to the second positive voltage VCC4, divides it and outputs the first voltage divider signal; the error amplifier circuit 72 is connected to the first voltage divider signal, amplifies it and outputs the voltage modulation signal; the second voltage divider circuit 73 is connected to the voltage modulation signal, divides it and outputs the second voltage divider signal; the regulated voltage 74 is connected to the second voltage divider signal, and outputs it after regulated voltage; the comparison circuit 75 is connected to the second voltage divider signal after regulated voltage, compares it with the reference voltage, and uses the comparison result as the set signal. The magnitude relationship between the second voltage divider signal and the reference voltage represents the magnitude relationship between VCC4 and the threshold voltage. The inverter 76 is connected to the first PWM signal Q1_DRV1, inverts it and outputs the reset signal; the RS trigger 77, its set end receives the set signal, its reset end is connected to the reset signal, and its output end outputs the second PWM signal Q2_DRV1.

[0070] More specifically, the first voltage-dividing circuit 71 includes a first voltage-dividing resistor R1 and a second voltage-dividing resistor R2, the error amplifier circuit 72 includes an operational amplifier U1 and a compensation network, the second voltage-dividing circuit 73 includes a first diode D6, a third voltage-dividing resistor R4, and a fourth voltage-dividing resistor R5, the regulated voltage 74 includes a first regulated diode D7, and the comparison circuit 75 includes a comparator U2. The first end of the first voltage-dividing resistor R1 is connected to the second positive voltage VCC4, and the second end is grounded via the second voltage-dividing resistor R2. The second end of the first voltage-dividing resistor R1 is also connected to the negative input end of the operational amplifier U1. The positive input end of the operational amplifier U1 is connected to the voltage setting value 2.5V. The negative input end of the operational amplifier U1 is connected to the output end of the operational amplifier U1 via the compensation network. The output end of the operational amplifier U1 is connected to the positive electrode of the first diode D6. The negative electrode of the first diode D6 is connected to the first end of the third voltage-dividing resistor R4. The second end of the third voltage-dividing resistor R4 is grounded via the fourth voltage-dividing resistor R5. The second end of the third voltage-dividing resistor R4 is also connected to the cathode of the first voltage-dividing diode D7. The anode of the first voltage-dividing diode D7 is grounded. The cathode of the first voltage-dividing diode D7 is connected to the positive input end of the comparator U2. The negative input end of the comparator U2 is connected to the reference voltage 0.5V. The output end of the comparator U2 outputs the set signal.

[0071] Wherein, the compensation network includes a first compensation resistor R3, a first compensation capacitor C6, and a second compensation capacitor C7. The negative input terminal of the operational amplifier U1 is connected to the output terminal of the operational amplifier U1 via the first compensation resistor R3 and the second compensation capacitor C7 in sequence. The first compensation capacitor C6 is connected between the negative input terminal of the operational amplifier U1 and the output terminal of the operational amplifier U1.

[0072] The principle of the second control signal generating circuit 7 is: the output voltage VCC4 is divided by R1 and R2 and compared with the voltage setting value 2.5V to generate a voltage modulation signal Vam, R3, C7, and C6 are control loop compensation parameters, Vam is divided by D6, R4, and R5 and then limited by the voltage zener diode D7, and then compared with the reference voltage 0.5V, and the output is connected to the set signal input terminal of the RS trigger U4; the Q1_DRV signal is inverted by the inverter U3 and connected to the reset signal input terminal of U4, and the output signal of U2 is latched by edge triggering, thereby obtaining the drive signal Q2_DRV of the Q2 tube.

[0073] (3) The third output branch: secondary isolated positive voltage output circuit 3.

[0074] The secondary isolated positive voltage output circuit 3 provides VCC2, which is a positive voltage and is usually used to power the monitoring equipment of the switching power supply. Similarly, VCC2 is an open-loop voltage output, but because the positive peak value of Vso is clamped at the amplitude of VCC3, VCC2 will not have an abnormal voltage increase or decrease due to changes in the size of the main output load.

[0075] In this embodiment, the secondary isolated positive voltage output circuit 3 includes a third diode D3 and a third rectifier circuit. The positive electrode of the third diode D3 is grounded, and the negative electrode is connected to the opposite end of the first secondary winding of the auxiliary transformer T2. The same end of the first secondary winding of the auxiliary transformer T2 is grounded via the third rectifier circuit. The third rectifier circuit specifically includes a capacitor C3. The third diode D3 is unidirectionally conductive, so the third diode D3 and the capacitor C3 together substantially constitute a half-wave rectifier circuit. The same end of the first secondary winding of the auxiliary transformer T2 outputs the first positive voltage VCC3 to the outside, and RL3 represents the load.

[0076] (4) The fourth output branch: secondary isolated negative voltage output circuit 2.

[0077] The secondary isolated negative voltage output circuit 2 provides VCC1, which is a negative voltage and is generally used in the sampling circuit of the switching power supply. VCC1 is an open-loop voltage output, and the accuracy of the voltage is limited by the change of the load. Since the positive peak value of Vso is clamped at the amplitude of VCC3, the voltage of VCC1 will not increase or decrease abnormally due to the change of the size of the main output load.

[0078] In this embodiment, the secondary isolated negative voltage output circuit 2 includes a fourth diode D1, a fourth rectifier circuit, a first resistor Rb, a second voltage stabilizing diode D5, a first capacitor C8, a first switch Q3, and a second capacitor C2. The positive electrode of the fourth diode D1 is connected to the same-name end of the second secondary winding of the auxiliary transformer T2, the negative electrode of the fourth diode D1 is grounded via the first switch Q3, the opposite-name end of the second secondary winding of the auxiliary transformer T2 is connected to the negative electrode of the fourth diode D1 via the fourth rectifier circuit, the first resistor Rb is connected between the negative electrode of the fourth diode D1 and the control end of the first switch Q3, the first capacitor C8 is connected in parallel with the second voltage stabilizing diode D5, the control end of the first switch Q3 is connected to the cathode of the second voltage stabilizing diode D5, the anode of the second voltage stabilizing diode D5 is connected to the opposite-name end of the second secondary winding of the auxiliary transformer T2 and the first end of the second capacitor C2, and the second end of the second capacitor C2 is grounded. The fourth rectifier circuit specifically includes a capacitor C1. The fourth diode D1 is unidirectionally conductive, so the fourth diode D1 and the capacitor C1 together substantially constitute a half-wave rectifier circuit. The first end of the second capacitor C2 outputs the negative voltage VCC1 to the outside, and RL1 represents a load.

[0079] Figure 3 It is a timing waveform diagram of the key nodes of the circuit in steady-state operation, from top to bottom: Vso voltage waveform; state of Q1 (1 means on, 0 means off); state of Q2 (1 means on, 0 means off); current I(D2) flowing through diode D2 and current I(D4) flowing through diode D4, the bold one in the figure is I(D4); current I(D1) flowing through diode D1 and current I(D3) flowing through diode D3, the bold one in the figure is I(D3).

[0080] Combination Figure 3 , only when Q2 is on will the current flow through the D4 diode. During the off period of Q1, D2 and D4 will switch in multiple modes: 1) Q2 does not work during the on period of D2, and D4 is off; 2) Q2 is on during the on period of D2, and D4 is on at this time; 3) During the off period of Q2, D2 normally flows current during the off period of Q1. D1 and D3 are rectified after transformer T2 to supply power to the load, and the open-loop voltage output has an accuracy limited by the change of the load. Since the forward peak of Vso is clamped to the amplitude of the main output voltage VCC3, the voltage output of D1 and D3 after rectification will not increase or decrease abnormally due to the change of the main output load. Figure 3 The current waveforms of D3 and D4 are shown in bold.

[0081] Figure 4 The output voltage waveforms of each branch circuit under full load condition of the main circuit output are shown (VCC3=24V, I3=4A). Figure 5 The waveforms of the output voltages of each branch circuit under the light-load condition of the main circuit output are shown (VCC3=24V, I3=0.2A). The waveforms of VCC1 and VCC4 are shown in bold. Figure 4 and Figure 5 In the comparison, light load and full load of the main circuit do not affect the abnormal increase or decrease of the voltage of other branches.

[0082] In summary, the flyback single-winding multi-level output power supply circuit of the present invention has the following beneficial effects: the secondary side of the flyback main transformer has only one winding, and the winding is connected to multiple output branches, wherein the primary isolation main power supply circuit outputs a higher positive voltage based on closed-loop control, and the primary isolation auxiliary power supply circuit outputs a lower positive voltage based on closed-loop control to ensure stable voltage output, and then cooperates with the auxiliary transformer to connect the secondary isolation power supply circuit to realize isolated power supply of low-power loads and expansion of power supply output branches, and the primary and secondary isolation power supply circuits essentially obtain energy from the secondary side of the flyback main transformer, and the power supply of the secondary side of the flyback main transformer is clamped at The amplitude of the output voltage of the primary isolated main power supply circuit, so the voltage of the primary and secondary isolated power supply circuits will not increase or decrease abnormally due to changes in the size of the main output load; in this way, the branch voltages of the present invention have little influence on each other, and it is easy to meet the application scenarios of isolation. In short, the present invention is based on a mature flyback power supply topology structure, fully utilizes the current output capacity and dynamic response speed of the output winding of the flyback main transformer, decouples the power circuits from each other under different output loads, and the dynamic adjustment of the output voltages between the branches has little influence on each other. The winding process of the transformer is simple, the volume is small, the overall cost of the circuit is reduced, and the performance is significantly optimized.

[0083] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0084] Terms including ordinal numbers such as "first", "second" etc. used in this specification may be used to describe various constituent elements, but these constituent elements are not limited by these terms. The purpose of using these terms is only to distinguish one constituent element from other constituent elements. For example, without departing from the scope of the present invention, the first constituent element may be named as the second constituent element, and similarly, the second constituent element may also be named as the first constituent element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0085] The term “connected” or “connected” not only includes directly connecting two entities, but also includes indirectly connecting two entities through other entities having a beneficial improvement effect.

[0086] In the specification provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this specification.

[0087] Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed scheme should not be interpreted as reflecting the following intention: the claimed invention requires more features than the features explicitly recited in each claim. More specifically, as reflected in the following claims, the inventive aspects lie in less than all the features of the single embodiment disclosed above. Therefore, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, wherein each claim itself serves as a separate embodiment of the present invention. In the claims, any reference symbol located between brackets should not be constructed as a limitation to the claim.

[0088] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A flyback single-winding multi-level output power supply circuit, comprising: An input power supply (Vbus); a primary winding connected in series with a primary switch (Q1) and then connected to the input power supply (Vbus); a flyback main transformer (T1) having one secondary winding and outputting a primary power supply (Vso); a primary isolation main power supply circuit (4) connected to the primary power supply (Vso) and converted into a first positive voltage (VCC3) output; a first control signal generating circuit (6) for generating a first PWM signal (Q1_DRV1) based on the first positive voltage (VCC3) and a current (IQ1) flowing through the primary switch (Q1) to feedback control the primary switch (Q1); It is characterized by further comprising: A primary isolation auxiliary power supply circuit (5) is connected to the primary power supply (Vso) via a main power switch (Q2) and converted into a second positive voltage (VCC4) for output, wherein the second positive voltage (VCC4) is less than the first positive voltage (VCC3); A second control signal generating circuit (7) generates a corresponding second PWM signal (Q2_DRV1) based on the second positive voltage (VCC4) and the first PWM signal (Q1_DRV1) to feedback control the main power switch (Q2); an auxiliary transformer (T2), wherein the primary winding is connected to the primary power supply (Vso) and the secondary winding is at least one; The secondary isolation power supply circuit is connected to the secondary winding of the auxiliary transformer (T2) and converts the voltage into positive voltage or / and negative voltage output.

2. The flyback single-winding multi-level output power supply circuit according to claim 1, characterized in that: The auxiliary transformer (T2) comprises a first secondary winding for outputting a first secondary power supply and a second secondary winding for outputting a second secondary power supply; The secondary isolation power supply circuit comprises: A secondary isolated positive voltage output circuit (3), connected to the first secondary power supply and converted into a third positive voltage (VCC2) output; The secondary isolated negative voltage output circuit (2) is connected to the second secondary power supply and converted into a negative voltage (VCC1) for output.

3. The flyback single-winding multi-level output power supply circuit according to claim 1 or 2, characterized in that: The second control signal generating circuit (7) comprises: A voltage division comparison circuit is connected to the second positive voltage (VCC4), and generates a set signal after voltage division and comparison. The PWM generating circuit is connected to the first PWM signal (Q1_DRV1) and the set signal. When the set signal represents that the second positive voltage (VCC4) is lower than the threshold voltage, and the level of the first PWM signal (Q1_DRV1) is a level that turns off the primary switch (Q1), the level of the output second PWM signal (Q2_DRV1) is set to turn on the main power switch (Q2).

4. The flyback single-winding multi-level output power supply circuit according to claim 3, characterized in that: The voltage divider comparison circuit includes: A first voltage dividing circuit (71) is connected to the second positive voltage (VCC4), divides the voltage thereof and outputs a first voltage dividing signal; an error amplifier circuit (72), connected to the first voltage-divided signal, amplifying it and then outputting a voltage modulation signal; A second voltage dividing circuit (73) receives the voltage modulation signal, divides the voltage modulation signal, and then outputs a second voltage dividing signal; A regulated voltage (74) is connected to the second divided voltage signal and outputs it in a regulated voltage; The comparison circuit (75) receives the second voltage-divided signal after voltage stabilization, compares it with a reference voltage, and uses the comparison result as the setting signal.

5. The flyback single-winding multi-level output power supply circuit according to claim 3, characterized in that: The PWM generating circuit comprises: An inverter (76) receives the first PWM signal (Q1_DRV1), inverts the first PWM signal, and then outputs a reset signal; An RS flip-flop (77), whose set end receives the set signal, whose reset end receives the reset signal, and whose output end outputs the second PWM signal (Q2_DRV1).

6. The flyback single-winding multi-level output power supply circuit according to claim 4, characterized in that: The first voltage divider circuit (71) comprises a first voltage divider resistor (R1) and a second voltage divider resistor (R2); the error amplification circuit (72) comprises an operational amplifier (U1) and a compensation network; the second voltage divider circuit (73) comprises a first diode (D6), a third voltage divider resistor (R4) and a fourth voltage divider resistor (R5); the regulated voltage (74) comprises a first regulated diode (D7); and the comparison circuit (75) comprises a comparator (U2); The first end of the first voltage-dividing resistor (R1) is connected to the second positive voltage (VCC4), and the second end is grounded via the second voltage-dividing resistor (R2). The second end of the first voltage-dividing resistor (R1) is also connected to the negative input end of the operational amplifier (U1), the positive input end of the operational amplifier (U1) is connected to the voltage setting value, the negative input end of the operational amplifier (U1) is connected to the output end of the operational amplifier (U1) via the compensation network, the output end of the operational amplifier (U1) is connected to the positive electrode of the first diode (D6), the negative electrode of the first diode (D6) is connected to the first end of the third voltage-dividing resistor (R4), the second end of the third voltage-dividing resistor (R4) is grounded via the fourth voltage-dividing resistor (R5), the second end of the third voltage-dividing resistor (R4) is also connected to the cathode of the first voltage-dividing diode (D7), the anode of the first voltage-dividing diode (D7) is grounded, the cathode of the first voltage-dividing diode (D7) is connected to the positive input end of the comparator (U2), the negative input end of the comparator (U2) is connected to the reference voltage, and the output end of the comparator (U2) outputs the set signal.

7. The flyback single-winding multi-level output power supply circuit according to claim 6, characterized in that: The compensation network comprises a first compensation resistor (R3), a first compensation capacitor (C6), and a second compensation capacitor (C7); the negative input terminal of the operational amplifier (U1) is connected to the output terminal of the operational amplifier (U1) via the first compensation resistor (R3) and the second compensation capacitor (C7) in sequence; and the first compensation capacitor (C6) is connected between the negative input terminal of the operational amplifier (U1) and the output terminal of the operational amplifier (U1).

8. The flyback single-winding multi-level output power supply circuit according to claim 1, characterized in that: The same-name end of the primary winding of the flyback main transformer (T1) is connected to the input power supply (Vbus), and the opposite-name end is grounded via the primary switch (Q1); the same-name end of the secondary winding of the flyback main transformer (T1) is grounded, and the opposite-name end outputs the primary power supply (Vso); The primary isolation main power supply circuit (4) comprises a first diode (D2) and a first rectifier circuit, wherein the positive electrode of the first diode (D2) is connected to the opposite pole end of the secondary winding of the flyback main transformer (T1), and the negative electrode is grounded via the first rectifier circuit; The primary isolated auxiliary power supply circuit (5) comprises a second diode (D4) and a second rectifier circuit, wherein the positive electrode of the second diode (D4) is connected to the opposite pole end of the secondary winding of the flyback main transformer (T1) via the main power switch (Q2), and the negative electrode is grounded via the second rectifier circuit; The cathode of the first diode (D2) outputs the first positive voltage (VCC3) to the outside, and the cathode of the second diode (D4) outputs the second positive voltage (VCC4) to the outside.

9. The flyback single-winding multi-level output power supply circuit according to claim 2, characterized in that: The same-name end of the primary winding of the flyback main transformer (T1) is connected to the input power supply (Vbus), and the opposite-name end is grounded via the primary switch (Q1); the same-name end of the secondary winding of the flyback main transformer (T1) is grounded, and the opposite-name end outputs the primary power supply (Vso); The opposite-name end of the primary winding of the auxiliary transformer (T2) is grounded, and the same-name end is connected to the opposite-name end of the secondary winding of the flyback main transformer (T1); The secondary isolated positive voltage output circuit (3) comprises a third diode (D3) and a third rectifier circuit, the positive electrode of the third diode (D3) is grounded, the negative electrode is connected to the opposite-name end of the first secondary winding of the auxiliary transformer (T2), and the same-name end of the first secondary winding of the auxiliary transformer (T2) is grounded via the third rectifier circuit; The secondary isolated negative voltage output circuit (2) comprises a fourth diode (D1), a fourth rectifier circuit, a first resistor (Rb), a second voltage stabilizing diode (D5), a first capacitor (C8), a first switch (Q3), and a second capacitor (C2); the positive electrode of the fourth diode (D1) is connected to the same-name end of the second secondary winding of the auxiliary transformer (T2); the negative electrode of the fourth diode (D1) is grounded via the first switch (Q3); the opposite-name end of the second secondary winding of the auxiliary transformer (T2) is connected to the negative electrode of the fourth diode (D1) via the fourth rectifier circuit; the first resistor (Rb) is connected between the negative electrode of the fourth diode (D1) and the control end of the first switch (Q3); the first capacitor (C8) is connected in parallel with the second voltage stabilizing diode (D5); the control end of the first switch (Q3) is connected to the cathode of the second voltage stabilizing diode (D5); the anode of the second voltage stabilizing diode (D5) is connected to the opposite-name end of the second secondary winding of the auxiliary transformer (T2) and the first end of the second capacitor (C2); and the second end of the second capacitor (C2) is grounded; The same-name end of the first secondary winding of the auxiliary transformer (T2) outputs the first positive voltage (VCC3) to the outside, and the first end of the second capacitor (C2) outputs the negative voltage (VCC1) to the outside.

10. The flyback single-winding multi-level output power supply circuit according to claim 1, characterized in that: A clamping circuit (1) is also connected between the same-name end and the opposite-name end of the primary winding of the flyback main transformer (T1).

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