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); therefore, the mutual influence of the voltages of the plurality of output branches is small, an isolated application scene is easy to meet, the size is small, and the comprehensive cost is reduced.

Description

Technical Field

[0001] This utility model relates to the field of flyback switching power supplies, and in particular to a flyback single-winding multi-level output power supply circuit. Background Technology

[0002] Traditional flyback switching power supplies achieve level output primarily through the following methods:

[0003] (1) Using multiple windings for output, the output voltage of different windings is controlled by the turns ratio. This method can easily achieve the isolation requirements between multiple output power supplies, but it has the following drawbacks: First, with too many windings, the coupling coefficients between them are large, the leakage inductance of the transformer is large, and in flyback applications, it will cause excessive voltage stress on the MOSFET switching transistor. In order to suppress the voltage stress on the switching transistor, the RCD (Resistor-Capacitor-Diode) clamping circuit needs to consume a lot of power, causing heat generation and efficiency loss. Second, the insulation layer between multiple windings will increase the parasitic capacitance of the transformer. Excessive parasitic capacitance will cause excessive peak current when the MOSFET is turned on, increasing the MOSFET's turn-on loss, causing device heat generation and efficiency loss. At the same time, the presence of parasitic capacitance will also affect the EMI (Electromagnetic Interference) of the power supply. The characteristics of electromagnetic interference make rectification and optimization difficult in EMC certification; in three aspects, the output voltage regulation rate of each branch is uncontrollable. When the main power supply output is fully loaded and other secondary windings are lightly loaded or unloaded, the main voltage can be kept stable due to the control loop. However, when other windings are open-loop, the output voltage of the secondary windings will rise abnormally, which may exceed the upper limit of the load input voltage and cause damage to the downstream load.

[0004] (2) Main output paired with DC / DC boost / buck. This method boosts / bucks the main output voltage to obtain different voltage levels. It is simple in terms of functional unit modules, but it has the following drawbacks: each output voltage level requires a DC / DC control chip, supplemented by external resistors, capacitors, inductors, semiconductors and other devices to obtain the corresponding output voltage. The number of devices used is large and the cost is not optimal. The DC / DC section is cascaded after the main output circuit. The increase in the number of DC / DC branches will increase the loss of the main circuit devices. The efficiency of the DC / DC stage cannot reach 100%, so the efficiency bottleneck after cascading cannot be broken. The output voltages of different branches are not isolated and have a common reference ground. It is not suitable for systems that require partial isolated power supply, and the application scenarios are relatively limited.

[0005] (3) Multi-tap common ground output. This method uses taps on the secondary winding, and its working principle is similar to that of an autotransformer. The output is adjusted by controlling the voltage through different turns ratios. The drawbacks are: since the windings are shared and taps are used for output, the current carrying capacity of the windings needs to be designed according to the maximum current carrying capacity, and the use of copper wire is over-designed, so the cost is not optimal; the common ground output cannot meet the needs of isolated power supply for some circuits, which limits the application scenarios; there is a problem of cross-regulation of the output voltage between taps, and the full load output of the main circuit will cause the output voltage of other no-load / light-load taps to rise abnormally.

[0006] The information disclosed in this background section is included only to enhance the understanding of the context of this disclosure, and therefore may contain information that does not constitute prior art known to those skilled in the art. Utility Model Content

[0007] The technical problem to be solved by this utility model is to provide a flyback single-winding multi-level output power supply circuit that addresses the above-mentioned deficiencies of the prior art.

[0008] The technical solution adopted by this utility model to solve its technical problem is as follows: constructing a flyback single-winding multi-level output power supply circuit, including an input power supply, a flyback main transformer whose primary winding is connected in series with a primary switch and then connected to the input power supply, a secondary winding that is one and outputs a primary power supply, a first-level isolated main power supply circuit that is connected to the primary power supply and converted to a first positive voltage output, and a first control signal generation circuit that generates a first PWM signal based on the first positive voltage and the current flowing through the primary switch to feed back and control the primary switch.

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

[0010] The primary isolated 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] The second control signal generation circuit generates a corresponding second PWM signal based on the second positive voltage of the first-level isolated auxiliary power supply circuit and the first PWM signal to feed back and control the corresponding main power switch.

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

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

[0014] Furthermore, in the flyback single-winding multi-level output power supply circuit of this utility model, the auxiliary transformer includes a first secondary winding for outputting the primary power supply and a second secondary winding for outputting the secondary power supply.

[0015] The secondary isolation power supply circuit includes:

[0016] A secondary isolation positive voltage output circuit is connected to the primary power supply and converted into a third positive voltage output.

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

[0018] Furthermore, in the flyback single-winding multi-level output power supply circuit described in this utility model, the second control signal generation circuit includes:

[0019] The voltage divider and comparator circuit receives the second positive voltage, divides and compares it to generate a set signal;

[0020] The PWM generation circuit receives the first PWM signal and a set signal. When the set signal is at a level representing the second positive voltage being lower than the threshold voltage, and the level of the first PWM signal is at a level that turns off the primary-side 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 described in this utility model, the voltage divider comparator circuit includes the following components connected in sequence:

[0022] The first voltage divider circuit receives the second positive voltage, divides it, and outputs the first voltage divider signal.

[0023] An error amplifier circuit receives the first voltage divider signal, amplifies it, and outputs a voltage modulation signal.

[0024] The second voltage divider circuit receives the voltage modulation signal, divides it, and outputs the second voltage divider signal.

[0025] The regulated voltage is connected to the second voltage divider signal and then regulated for output.

[0026] The comparator circuit receives the regulated second voltage divider signal, compares it with the 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 this utility model, the PWM generation circuit includes:

[0028] The inverter receives the first PWM signal, inverts it, and outputs a reset signal.

[0029] An RS flip-flop has a set terminal that receives the set signal, a reset terminal that receives the reset signal, and an output terminal that outputs the second PWM signal.

[0030] Furthermore, in the flyback single-winding multi-level output power supply circuit of this utility model, the first voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor, the error amplifier circuit includes an operational amplifier and a compensation network, the second voltage divider circuit includes a first diode, a third voltage divider resistor and a fourth voltage divider resistor, the regulated voltage includes a first Zener diode, and the comparator circuit includes a comparator.

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

[0032] Furthermore, in the flyback single-winding multi-level output power supply circuit of this utility model, 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 in sequence via the first compensation resistor and the second compensation capacitor. The first compensation capacitor is connected between the negative input terminal and the output terminal of the operational amplifier.

[0033] Furthermore, in the flyback single-winding multi-level output power supply circuit described in this utility model, the same-name terminal of the primary winding of the flyback main transformer is connected to the input power supply, and the opposite-name terminal is grounded through the primary-side switch; the same-name terminal of the secondary winding of the flyback main transformer is grounded, and the opposite-name terminal outputs the primary power supply.

[0034] The primary isolation main power supply circuit includes a first diode and a first rectifier circuit. The positive terminal of the first diode is connected to the opposite terminal of the secondary winding of the flyback main transformer, and the negative terminal is grounded through the first rectifier circuit.

[0035] The primary isolation auxiliary power supply circuit includes a second diode and a second rectifier circuit. The positive terminal of the second diode is connected to the opposite terminal of the secondary winding of the flyback main transformer via the main power switch, and the negative terminal is grounded via the second rectifier circuit.

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

[0037] Furthermore, in the flyback single-winding multi-level output power supply circuit described in this utility model, the same-name terminal of the primary winding of the flyback main transformer is connected to the input power supply, and the opposite-name terminal is grounded through the primary-side switch; the same-name terminal of the secondary winding of the flyback main transformer is grounded, and the opposite-name terminal outputs the primary power supply.

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

[0039] The secondary isolation positive voltage output circuit includes a third diode and a third rectifier circuit. The positive terminal of the third diode is grounded, and the negative terminal is connected to the opposite terminal of the first secondary winding of the auxiliary transformer. The same terminal of the first secondary winding of the auxiliary transformer is grounded through the third rectifier circuit.

[0040] The secondary isolation negative voltage output circuit includes a fourth diode, a fourth rectifier circuit, a first resistor, a second Zener diode, a first capacitor, a first switch, and a second capacitor. The positive terminal of the fourth diode is connected to the same-name terminal of the second secondary winding of the auxiliary transformer, and the negative terminal of the fourth diode is grounded through the first switch. The opposite-name terminal of the second secondary winding of the auxiliary transformer is connected to the negative terminal of the fourth diode through the fourth rectifier circuit. The first resistor is connected between the negative terminal of the fourth diode and the control terminal of the first switch. The first capacitor is connected in parallel with the second Zener diode. The control terminal of the first switch is connected to the cathode of the second Zener diode. The anode of the second Zener diode is connected to the opposite-name terminal of the second secondary winding of the auxiliary transformer and the first terminal of the second capacitor. The second terminal of the second capacitor is grounded.

[0041] The first positive voltage is output from the same-name terminal of the first secondary winding of the auxiliary transformer, and the negative voltage is output from the first terminal of the second capacitor.

[0042] Furthermore, in the flyback single-winding multi-level output power supply circuit described in this utility model, a clamping circuit is also connected between the same-named end and the opposite-named end of the primary winding of the flyback main transformer.

[0043] This utility model's flyback single-winding multi-level output power supply circuit has the following advantages: The flyback main transformer has only one winding on its secondary side, which connects to multiple output branches. The primary isolation main power supply circuit outputs a higher positive voltage based on closed-loop control, while the primary isolation auxiliary power supply circuit outputs a lower positive voltage based on closed-loop control, ensuring stable voltage output. Combined with the auxiliary transformer, a secondary isolation power supply circuit is connected to achieve isolated power supply for low-power loads and expand the power output branches. Furthermore, both the primary and secondary isolation power supply circuits essentially obtain energy from the secondary side of the flyback main transformer, while the power supply on the secondary side of the flyback main transformer is clamped to the primary isolation... Because the output voltage amplitude of the main power supply circuit is relatively small, the voltage of the primary and secondary isolation power supply circuits will not experience abnormal increases or decreases due to changes in the main output load. Thus, the voltages of the branches in this invention have minimal mutual influence, easily meeting the application scenarios of isolation. In summary, this invention is based on a mature flyback power supply topology, fully utilizing the current output capability and dynamic response speed of the flyback main transformer's output winding. The power circuits are decoupled under different output loads, and the dynamic adjustment of the output voltage between each branch has minimal mutual influence. The transformer winding process is simple, the size is small, the overall circuit cost is reduced, and the performance is significantly optimized. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the structure of the flyback single-winding multi-level output power supply circuit of this utility model;

[0046] Figure 2 This is a schematic diagram of the second control signal generation circuit;

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

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

[0049] Figure 5 It is a waveform diagram of the output voltage of each branch under light load conditions of the main output. Detailed Implementation

[0050] To facilitate understanding of this utility model, a more comprehensive description will be given below with reference to the accompanying drawings. The drawings illustrate typical embodiments of this utility model. However, this utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of this utility model more thorough and complete. It should be understood that the embodiments of this utility model and the specific features thereof are detailed descriptions of the technical solutions of this application, and not limitations thereof. Where there is no conflict, the embodiments of this utility model and the technical features thereof can be combined with each other.

[0051] refer to Figure 1 The flyback single-winding multi-level output power supply circuit of this utility model includes: an input power supply Vbus, a primary-side switch Q1, a flyback main transformer T1, multiple output branches connected to the secondary winding of the flyback main transformer T1, a first control signal generation circuit 6, and a second control signal generation circuit 7. The flyback main transformer T1 has only one secondary winding, which connects to multiple output branches. The multiple 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. The secondary isolation power supply circuit is connected to the secondary winding of the flyback main transformer T1 through an auxiliary transformer T2.

[0052] In this configuration, the primary winding of the flyback main transformer T1 is connected to the input power supply Vbus via a primary-side switch Q1 connected in series, and the secondary winding outputs the primary power supply Vso. Specifically, the same-name terminal of the primary winding of the flyback main transformer T1 is connected to the input power supply Vbus, and the opposite-name terminal of the primary winding of the flyback main transformer T1 is grounded via the primary-side switch Q1, which is controlled by the first PWM signal Q1_DRV1. The same-name terminal of the secondary winding of the flyback main transformer T1 is grounded, and the opposite-name terminal of the secondary winding of the flyback main transformer T1 outputs the primary power supply Vso.

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

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

[0055] In this embodiment, a clamping circuit 1 is also connected between the same-named and opposite-named terminals of the primary winding of the flyback main transformer T1. In this embodiment, the clamping circuit 1 is a conventional RCD snubber circuit. Rc, Cc, and Dc are used to clamp the Q1 turn-off voltage stress caused by the leakage inductance of the T1 transformer, ensuring that Q1 is in a safe operating range when turned off, which is no different from the primary side structure of a normal 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 based on the control signal of the primary side switch Q1, i.e., the first PWM signal Q1_DRV1. Similarly, it can also control the voltage value of the secondary side of T1, effectively improving the voltage cross-regulation of the multi-output switching power supply circuit.

[0056] In this invention, the primary isolated auxiliary power supply circuit 5 is connected to the primary power supply Vso via the corresponding main power switch Q2, and converted into a second positive voltage VCC4 output, where 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 generation circuit 7 generates a corresponding second PWM signal Q2_DRV1 based on the second positive voltage VCC4 of the primary isolated auxiliary power supply circuit 5 and the first PWM signal Q1_DRV1 to provide feedback control to the corresponding main power switch Q2.

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

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

[0059] (1) First output branch: Level 1 isolation main power supply circuit 4.

[0060] The primary isolated main power supply circuit 4, acting as a heavily loaded branch, provides the first positive voltage VCC3 based on a closed-loop control method. The first positive voltage VCC3 is mainly used to power the main output load (generally a power load such as a fan).

[0061] In this embodiment, the primary isolation main power supply circuit 4 includes a first diode D2 and a first rectifier circuit. The positive terminal of the first diode D2 is connected to the opposite-named terminal of the secondary winding of the flyback main transformer T1, and the negative terminal is grounded through the first rectifier circuit. The first rectifier circuit specifically includes a capacitor C4. The first diode D2 is unidirectionally conductive, therefore, the first diode D2 and the capacitor C4 together essentially constitute a half-wave rectifier circuit. The negative terminal of the first diode D2 outputs the first positive voltage VCC3, and RL3 represents the load.

[0062] In this embodiment, the first positive voltage VCC3 acts as feedback to influence the on / off state of the primary-side MOSFET switch Q1, achieving closed-loop control of the first positive voltage VCC3. As explained earlier, the first control signal generation circuit 6 performs PI control by comparing the feedback signal of voltage VCC3 with the sampled signal of current IQ1 of the primary-side MOSFET switch Q1. The output of the PI controller is compared with the carrier signal to obtain PWM control signals Q1_DRV with different duty cycles, thereby controlling the on / off state of Q1 to achieve energy transfer from the primary side to the secondary side of transformer T1. For example, when signal Q1_DRV controls Q1 to be on, the input power supply Vbus charges the primary winding of transformer T1; when signal Q1_DRV controls Q1 to be off, the electrical energy stored in the primary winding of transformer T1 is transferred to the secondary winding, thereby providing the primary power supply Vso to the subsequent multiple output branches.

[0063] (2) Second output branch: Level 1 isolation 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, serving as the power input for the system control board of the switching power supply, and also as a positive power input for the sampling circuit of the switching power supply. It works in conjunction with VCC1 to ensure the dual power supply and reliable operation of the Hall effect sensors and operational amplifiers.

[0065] In this embodiment, the primary isolation auxiliary power supply circuit 5 includes a second diode D4 and a second rectifier circuit. The positive terminal of the second diode D4 is connected to the opposite-named terminal of the secondary winding of the flyback main transformer T1 via the main power switch Q2, and the negative terminal is grounded via the second rectifier circuit. The second rectifier circuit specifically includes a capacitor C5. The second diode D4 is unidirectionally conductive, therefore, the second diode D4 and capacitor C5 together essentially form a half-wave rectifier circuit. The negative terminal of the second diode D4 outputs the second positive voltage VCC4. RL4 represents the load.

[0066] The main power switch Q2 can be a controllable electronic switch such as a MOSFET. In this embodiment, the main power switch Q2 is a MOSFET switch, meaning that both the primary-side switch Q1 and the main power switch Q2 are turned on at high level and turned off at low level. The main power switch Q2 acts as the selection switch for the first-stage isolated auxiliary power supply circuit 5, controlling 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 generation circuit 7.

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

[0068] In this embodiment, the voltage divider and comparator circuit includes a first voltage divider circuit 71, an error amplifier circuit 72, a second voltage divider circuit 73, a regulated voltage 74, and a comparator circuit 75 connected in sequence. The PWM generation circuit includes an inverter 76 and an RS flip-flop 77.

[0069] The first voltage divider circuit 71 is connected to the second positive voltage VCC4, and after dividing it, outputs a first voltage divider signal. The error amplifier circuit 72 is connected to the first voltage divider signal, and after amplification, outputs a voltage modulation signal. The second voltage divider circuit 73 is connected to the voltage modulation signal, and after dividing it, outputs a second voltage divider signal. The regulated voltage circuit 74 is connected to the second voltage divider signal and outputs a regulated voltage. The comparator circuit 75 is connected to the regulated second voltage divider signal, compares it with a reference voltage, and uses the comparison result as the set signal. The relationship between the second voltage divider signal and the reference voltage represents the relationship between VCC4 and the threshold voltage. The inverter 76 is connected to the first PWM signal Q1_DRV1, and after inverting it, outputs a reset signal. The RS flip-flop 77 receives the set signal at its set terminal, connects the reset signal at its reset terminal, and outputs the second PWM signal Q2_DRV1 at its output terminal.

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

[0071] 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. The first compensation capacitor C6 is connected between the negative input terminal and the output terminal of the operational amplifier U1.

[0072] The principle of the second control signal generation circuit 7 is as follows: the output voltage VCC4 is divided by R1 and R2 and compared with the voltage setting value of 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 Zener diode D7. It is then compared with the reference voltage of 0.5V and the output is connected to the set signal input terminal of RS flip-flop U4. The Q1_DRV signal is inverted by inverter U3 and connected to the reset signal input terminal of U4. The output signal of U2 is latched by edge triggering, thereby obtaining the drive signal Q2_DRV of transistor Q2.

[0073] (3) Third output branch: Secondary isolation positive voltage output circuit 3.

[0074] The secondary isolation positive voltage output circuit 3 provides VCC2, which is a positive voltage and is typically 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 to the amplitude of VCC3, VCC2 will not experience abnormal voltage increases or decreases due to changes in the main output load.

[0075] In this embodiment, the secondary isolation positive voltage output circuit 3 includes a third diode D3 and a third rectifier circuit. The positive terminal of the third diode D3 is grounded, and the negative terminal is connected to the opposite-named terminal of the first secondary winding of the auxiliary transformer T2. The same-named terminal of the first secondary winding of the auxiliary transformer T2 is grounded through the third rectifier circuit. The third rectifier circuit specifically includes a capacitor C3. The third diode D3 is unidirectionally conductive; therefore, the third diode D3 and the capacitor C3 together essentially constitute a half-wave rectifier circuit. The same-named terminal of the first secondary winding of the auxiliary transformer T2 outputs the first positive voltage VCC3, where RL3 represents the load.

[0076] (4) Fourth output branch: Secondary isolation negative voltage output circuit 2.

[0077] The second-stage isolated negative voltage output circuit 2 provides VCC1, which is a negative voltage and is typically used in the sampling circuit of a switching power supply. VCC1 is an open-loop voltage output, and its accuracy is limited by load variations. Because the positive peak value of Vso is clamped to the amplitude of VCC3, the VCC1 voltage will not abnormally rise or fall due to changes in the main output load.

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

[0079] Figure 3 This is a timing waveform diagram of key nodes in the circuit during steady-state operation. From top to bottom, it shows: Vso voltage waveform; Q1 state (1 indicates on, 0 indicates off); Q2 state (1 indicates on, 0 indicates off); current I(D2) flowing through diode D2 and current I(D4) flowing through diode D4 (I(D4) is bolded in the diagram); current I(D1) flowing through diode D1 and current I(D3) flowing through diode D3 (I(D3) is bolded in the diagram).

[0080] Combination Figure 3 Diode D4 only flows through the circuit when Q2 is on. During the off-state of Q1, D2 and D4 switch between several modes: 1) Q2 is not working and D4 is off when D2 is on; 2) Q2 is on when D2 is on, and D4 is on; 3) D2 flows normally during the off-state of Q1. D1 and D3 supply power to the load through rectification after transformer T2, providing an open-loop voltage output. The voltage accuracy is limited by load variations. Because the positive peak value of Vso is clamped to the amplitude of the main output voltage VCC3, the rectified output voltage of D1 and D3 will not abnormally rise or fall due to changes in the main output load. Figure 3 The current waveforms of D3 and D4 are displayed in bold.

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

[0082] In summary, the flyback single-winding multi-level output power supply circuit of this invention has the following advantages: the secondary side of the flyback main transformer has only one winding, which connects to multiple output branches. The primary isolation main power supply circuit outputs a higher positive voltage based on closed-loop control, while the primary isolation auxiliary power supply circuit outputs a lower positive voltage based on closed-loop control, ensuring stable voltage output. Furthermore, the auxiliary transformer connects to the secondary isolation power supply circuit to achieve isolated power supply for low-power loads and expand the power output branches. Moreover, both the primary and secondary isolation power supply circuits essentially obtain energy from the secondary side of the flyback main transformer, while the power supply on the secondary side of the flyback main transformer is clamped to a single winding. The amplitude of the output voltage of the primary isolation main power supply circuit is controlled, so the voltage of the primary and secondary isolation power supply circuits will not rise or fall abnormally due to changes in the size of the main output load. Thus, the voltage of the branches in this invention has little mutual influence, which is easy to meet the application scenarios of isolation. In summary, this invention is based on a mature flyback power supply topology, makes full use of the current output capability and dynamic response speed of the output winding of the flyback main transformer, decouples the power circuits under different output loads, minimizes the mutual influence of dynamic adjustment of output voltage between branches, simplifies the transformer winding process, reduces the size, lowers the overall cost of the circuit, and significantly optimizes performance.

[0083] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0084] The terms "first," "second," and other ordinal numbers used in this specification are used to describe various constituent elements, but these constituent elements are not limited by these terms. The purpose of using these terms is solely to distinguish one constituent element from others. For example, without departing from the scope of this utility model, a first constituent element may be named a second constituent element, and similarly, a second constituent element may be named a first constituent element. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0085] The term "connected" or "linked" includes not only directly connecting two entities, but also indirectly connecting them through other entities that have a beneficial improvement effect.

[0086] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0087] Similarly, it should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this disclosure should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the following claims, the inventive aspect lies in fewer than all features of a single foregoing disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims.

[0088] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A flyback single-winding multi-level output power supply circuit, comprising: Input power supply (Vbus); a flyback main transformer (T1) whose primary winding is connected in series with the primary switch (Q1) and whose secondary winding is a single primary power supply (Vso); a first-stage isolated main power supply circuit (4) that is connected to the primary power supply (Vso) and converted to output a first positive voltage (VCC3); a first control signal generation circuit (6) that 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 feed back and control the primary switch (Q1); Its characteristic is that it further includes: The primary isolation auxiliary power supply circuit (5) is connected to the primary power supply (Vso) via the main power switch (Q2) and converted to a second positive voltage (VCC4) output, the second positive voltage (VCC4) being less than the first positive voltage (VCC3); The second control signal generation 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 feed back and control the main power switch (Q2); The auxiliary transformer (T2) has its primary winding connected to the primary power supply (Vso) and at least one secondary winding. The secondary isolation power supply circuit is connected to the secondary winding of the auxiliary transformer (T2) and converted to positive and / or 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) includes a first secondary winding that outputs the primary power supply and a second secondary winding that outputs the secondary power supply. The secondary isolation power supply circuit includes: The secondary isolation positive voltage output circuit (3) is connected to the primary power supply and converted into a third positive voltage (VCC2) output; The secondary isolation negative voltage output circuit (2) is connected to the secondary power supply and converted to a negative voltage (VCC1) 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 generation circuit (7) includes: The voltage divider and comparator circuit is connected to the second positive voltage (VCC4), and after voltage division and comparison, a set signal is generated; The PWM generation circuit receives the first PWM signal (Q1_DRV1) and a set signal. When the set signal is at a level representing the second positive voltage (VCC4) being lower than the threshold voltage, and the level of the first PWM signal (Q1_DRV1) is at a level that turns off the primary-side 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 comparator circuit includes the following components connected in sequence: The first voltage divider circuit (71) is connected to the second positive voltage (VCC4), and outputs the first voltage divider signal after voltage division. The error amplifier circuit (72) is connected to the first voltage divider signal, and after amplification, outputs a voltage modulation signal; The second voltage divider circuit (73) receives 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 output as a regulated voltage; The comparator circuit (75) receives the second voltage divider signal after it has been regulated, compares it with the reference voltage, and uses the comparison result as the set signal.

5. The flyback single-winding multi-level output power supply circuit according to claim 3, characterized in that, The PWM generation circuit includes: Inverter (76) is connected to the first PWM signal (Q1_DRV1), and after inverting it, it outputs a reset signal; The RS flip-flop (77) receives the set signal at its set terminal, receives the reset signal at its reset terminal, and outputs the second PWM signal (Q2_DRV1) at its output terminal.

6. The flyback single-winding multi-level output power supply circuit according to claim 4, characterized in that, The first voltage divider circuit (71) includes a first voltage divider resistor (R1) and a second voltage divider resistor (R2); the error amplifier circuit (72) includes an operational amplifier (U1) and a compensation network; the second voltage divider circuit (73) includes a first diode (D6), a third voltage divider resistor (R4), and a fourth voltage divider resistor (R5); the regulated voltage (74) includes a first Zener diode (D7); and the comparator circuit (75) includes a comparator (U2). The first end of the first voltage divider resistor (R1) is connected to the second positive voltage (VCC4), and the second end is grounded via the second voltage divider resistor (R2). The second end of the first voltage divider resistor (R1) is also connected to the negative input terminal of the operational amplifier (U1). The positive input terminal of the operational amplifier (U1) is connected to the voltage setting value. The negative input terminal of the operational amplifier (U1) is connected to the output terminal of the operational amplifier (U1) via the compensation network. The output terminal of the operational amplifier (U1) is connected to the positive terminal of the first diode (D6). The negative terminal of the first diode (D6) is connected to the first end of the third voltage divider resistor (R4). The second end of the third voltage divider resistor (R4) is grounded via the fourth voltage divider resistor (R5). The second end of the third voltage divider resistor (R4) is also connected to the cathode of the first Zener diode (D7). The anode of the first Zener diode (D7) is grounded. The cathode of the first Zener diode (D7) is connected to the positive input terminal of the comparator (U2). The negative input terminal of the comparator (U2) is connected to the reference voltage. The output terminal 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 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 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 primary winding of the flyback main transformer (T1) is connected to the input power supply (Vbus) at the same-name terminal and grounded at the opposite-name terminal via the primary-side switch (Q1); the secondary winding of the flyback main transformer (T1) is grounded at the same-name terminal and outputs the primary power supply (Vso) at the opposite-name terminal. The primary isolation main power supply circuit (4) includes a first diode (D2) and a first rectifier circuit. The positive terminal of the first diode (D2) is connected to the opposite terminal of the secondary winding of the flyback main transformer (T1), and the negative terminal is grounded through the first rectifier circuit. The primary isolation auxiliary power supply circuit (5) includes a second diode (D4) and a second rectifier circuit. The positive terminal of the second diode (D4) is connected to the opposite terminal of the secondary winding of the flyback main transformer (T1) via the main power switch (Q2), and the negative terminal is grounded via the second rectifier circuit. The cathode of the first diode (D2) outputs the first positive voltage (VCC3), and the cathode of the second diode (D4) outputs the second positive voltage (VCC4).

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

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-named and different-named terminals of the primary winding of the flyback main transformer (T1).

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