Power Converter

Abstract

The present invention discloses a power converter, which connects a secondary switch tube in series to a second output circuit, and makes the voltage reflected by the output voltage of the second secondary winding to the first secondary winding smaller than the output voltage of the first secondary winding, so that when the primary switch tube is turned off and the secondary switch tube is turned on, the freewheeling current flows through the secondary winding of the second output circuit, and when the secondary switch tube is turned off, the freewheeling current flows through the secondary windings of other output circuits, thereby realizing time-sharing freewheeling for the constant current output circuit and the constant voltage output circuit in each switching cycle, and then realizing multi-channel constant current / constant voltage output under the premise of only one power conversion, improving the working efficiency, and only requiring one set of magnetic components, reducing the system volume. In addition, in one switching cycle, the second control circuit controls the secondary switch tube to start conducting before the primary switch tube is turned off, so as to reduce switching interference.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and more particularly to a power converter. Background Art

[0002] In the prior art, a power supply used in an LED backlight display screen usually has multiple outputs, at least one constant current output to provide driving current to an LED load, and at least one constant voltage output to supply power to a system or other loads.

[0003] Figure 1 FIG. 1 is a circuit diagram of a power converter having constant voltage and constant current multi-channel output in the prior art. Figure 1 As shown, the multi-output power converter 1 realizes multi-output through multiple secondary windings of the transformer. Each secondary winding corresponds to an output circuit, and in the constant current output circuit, the secondary winding Ns2 is coupled with the primary winding Np. Since the primary switch tube Q1 connected in series with the primary winding is controlled to be turned on and off, a square wave voltage is generated at both ends of the secondary winding Ns2, and then a relatively stable output voltage Vo1 is generated after rectification and filtering by a rectifier circuit composed of a diode D2 and a capacitor C2. A boost switching converter composed of an inductor L, a switch tube Q2, a diode D3 and a capacitor C3 is connected between the rectifier circuit and the LED load. The voltage Vo1 is converted into a constant output current I by the boost switching converter under the control of a constant current control circuit 13. LED Output to the LED load. The constant current control circuit 13 generates a control signal based on the current sampling signal Vs2 and the current reference signal Iref. At the same time, in the constant voltage output circuit, the secondary winding Ns1 is coupled with the primary winding Np, and after being rectified and filtered by the rectifier circuit composed of the diode D1 and the capacitor C1, a stable output voltage Vo2 is generated. The voltage sampling signal Vs1 representing the output voltage Vo2 is transmitted to the primary side through the optocoupler circuit 11, and the constant voltage control circuit 12 controls the switching state of the switch tube Q1 according to the voltage sampling signal Vs1 and the reference voltage Vref so that the output voltage Vo2 remains stable. Thus, Figure 1 The power converter shown achieves constant current output and constant voltage output simultaneously through a two-stage power stage circuit.

[0004] However, in the constant current output circuit, the two-stage power conversion increases the conversion loss and reduces the working efficiency. At the same time, the two-stage power stage circuit requires two magnetic components, which increases the system volume and is not conducive to miniaturization. Summary of the invention

[0005] In view of this, the present invention proposes a power converter to reduce the number of power conversions when performing multi-channel constant voltage / constant current outputs, improve work efficiency, and reduce the number of magnetic components and the size of the system.

[0006] The present invention provides a power converter, comprising:

[0007] An input circuit includes a primary winding and a primary switch tube connected in series between an input terminal and a ground terminal;

[0008] at least one first output circuit including a first secondary winding coupled to the primary winding;

[0009] at least one second output circuit, comprising a second secondary winding coupled to the primary winding and at least one secondary switch tube;

[0010] A first control circuit controls the on and off of the primary switch tube to adjust the output parameter of the first output circuit;

[0011] a second control circuit, controlling the on and off of the secondary switch tube to adjust an output parameter of the second output circuit;

[0012] Wherein, in the first state, within a switching cycle, the secondary switch tube starts to conduct before the primary switch tube is turned off.

[0013] Preferably, a voltage reflected from the output voltage of the second secondary winding to the first secondary winding is smaller than the output voltage of the first secondary winding, so that the first output circuit is turned off during the conduction period of the secondary switch tube.

[0014] Preferably, the second output circuit is a constant current output circuit, further comprising:

[0015] Current output port;

[0016] a second rectifier circuit connected between the current output port and the second secondary winding; and

[0017] a current sampling circuit, connected in series with the second secondary winding;

[0018] The secondary switch tube is connected in series with the second secondary winding, and the secondary switch tube is turned on and off in a controlled manner so that the output current remains constant.

[0019] Preferably, the second output circuit is a constant voltage output circuit, further comprising:

[0020] Voltage output port;

[0021] A rectifier tube and the secondary switch tube are connected in series between the voltage output port and the second secondary winding; and

[0022] A filter capacitor connected in parallel to the voltage output port;

[0023] The secondary switch tube is turned on and off in a controlled manner so that the output voltage of the output port remains constant.

[0024] Preferably, in the first state, when the primary switch tube is turned on, the secondary switch tube also starts to be turned on.

[0025] Preferably, in the first state, the second control circuit controls the secondary switch tube to be turned on during a period in which the primary switch tube is turned on.

[0026] Preferably, in the first state, the primary switch tube and the secondary switch tube have the same switching cycle, and the second control circuit controls the secondary switch tube to be turned on for at least part of the time during the period when the primary switch tube is turned off so that the output parameter of the second output circuit remains constant.

[0027] Preferably, in the first state, the second control circuit controls the turn-on timing of the secondary switch tube according to a first sampling signal representing the first secondary winding voltage or representing the second secondary winding voltage.

[0028] Preferably, in the second state, the second control circuit controls the turn-on timing of the secondary-side switch tube according to an internal clock signal generated by an internal clock generating circuit.

[0029] Preferably, after the primary switch tube is turned on, when the first sampling signal is greater than a first threshold, the secondary switch tube is turned on.

[0030] Preferably, the internal clock generating circuit comprises a first capacitor, and generates an internal clock signal by charging and discharging the first capacitor.

[0031] Preferably, the first capacitor is charged, and when the voltage on the first capacitor is greater than a second threshold, the internal clock signal is at a high level, and the first capacitor is discharged; when the voltage on the first capacitor is less than the second threshold, the internal clock signal is at a low level, and the discharge of the first capacitor is stopped.

[0032] Preferably, the second control circuit adjusts the duty cycle of the secondary switch tube according to the current sampling signal, the current reference signal and the first sampling signal representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal, so that the output current of the second output circuit remains constant;

[0033] The current sampling signal is acquired by the current sampling circuit, and the current reference signal is used to characterize the expected value of the output current.

[0034] Preferably, the second control circuit controls the turn-off moment of the secondary-side switch tube according to the current sampling signal and the current reference signal.

[0035] Preferably, the second control circuit adjusts the duty cycle of the secondary switch tube according to the voltage sampling signal, the voltage reference signal and the first sampling signal representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal, so that the output voltage of the second output circuit remains constant;

[0036] The voltage sampling signal represents the output voltage, and the voltage reference signal is used to represent the expected value of the output voltage.

[0037] Preferably, the second control circuit controls the turn-off moment of the secondary-side switch tube according to the voltage sampling signal and the voltage reference signal.

[0038] Preferably, the second control circuit is further configured to adjust the current reference signal according to a current intensity adjustment signal.

[0039] Preferably, the second output branch also includes a fifth switch tube, the fifth switch tube and the load are connected in series at the current output port, the control end of the fifth switch tube receives a current strength adjustment signal, and the fifth switch tube adjusts the current strength of the current output port according to the current strength adjustment signal.

[0040] Preferably, the first output circuit is a constant voltage output circuit, further comprising:

[0041] a voltage output port; and

[0042] a first rectifier circuit connected between the voltage output port and the first secondary winding;

[0043] The primary switch tube is turned on and off in a controlled manner so that the output voltage of the first output circuit remains constant.

[0044] Preferably, the first output circuit is a constant current output circuit, and the first output circuit further includes:

[0045] Current output port;

[0046] A first rectifier circuit is connected between the first secondary winding and the current output port; and

[0047] a current sampling circuit, connected in series with the first secondary winding;

[0048] The primary switch tube is turned on and off in a controlled manner so that the output current remains constant.

[0049] Compared with the prior art, the technical solution of the present invention has the following advantages: the present invention connects the secondary switch tube in series on the second output circuit, and at the same time makes the voltage reflected by the output voltage of the second secondary winding to the first secondary winding smaller than the output voltage of the first secondary winding, so that when the primary switch tube is turned off and the secondary switch tube is turned on, the freewheeling current flows through the secondary winding of the second output circuit, and when the secondary switch tube is turned off, the freewheeling current flows through the secondary windings of other output circuits, thereby realizing time-sharing freewheeling for the constant current output circuit and the constant voltage output circuit in each switching cycle, and then realizing multi-channel constant current / constant voltage output under the premise of only one power conversion, improving the working efficiency, and only requiring one set of magnetic components, reducing the system volume. In addition, in the first state, within a switching cycle, the second control circuit controls the secondary switch tube to start turning on before the primary switch tube is turned off, so as to reduce switching interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0051] Figure 1 A circuit diagram of a power converter with constant voltage and constant current multi-channel output in the prior art;

[0052] Figure 2a is a circuit diagram of a power converter according to a first embodiment of the present invention;

[0053] Figure 2b is a circuit diagram of a power converter according to a second embodiment of the present invention;

[0054] Figure 2c is a circuit diagram of a power converter according to a third embodiment of the present invention;

[0055] Figure 3 is a circuit diagram of a second control signal generating circuit according to a first embodiment of the present invention;

[0056] Figure 4 is a circuit diagram of a conduction signal generating circuit according to a first embodiment of the present invention;

[0057] Figure 5 is an exemplary operating waveform diagram of the power converter according to the first embodiment of the present invention;

[0058] Figure 6 is a circuit diagram of a power converter according to a fourth embodiment of the present invention;

[0059] Figure 7a is a circuit diagram of a power converter according to a fifth embodiment of the present invention;

[0060] Figure 7b is a circuit diagram of a power converter according to a sixth embodiment of the present invention;

[0061] Figure 8 FIG. 4 is a circuit diagram of a power converter according to a seventh embodiment of the present invention. DETAILED DESCRIPTION

[0062] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. It is possible for a person skilled in the art to fully understand the present invention without the description of these details. In order to avoid confusing the essence of the present invention, known methods, processes, flows, components and circuits are not described in detail.

[0063] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes and are not necessarily drawn to scale.

[0064] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected between" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0065] The present invention provides a power converter, comprising:

[0066] An input circuit includes a primary winding and a primary switch tube connected in series between an input terminal and a ground terminal;

[0067] at least one first output circuit including a first secondary winding coupled to the primary winding;

[0068] at least one second output circuit, comprising a second secondary winding coupled to the primary winding and at least one secondary switch tube;

[0069] A first control circuit controls the on and off of the primary switch tube to adjust the output parameter of the first output circuit;

[0070] a second control circuit, controlling the on and off of the secondary switch tube to adjust an output parameter of the second output circuit;

[0071] Wherein, in the first state, within a switching cycle, the secondary side switch tube starts to conduct before the primary side switch tube is turned off, so as to reduce switching interference.

[0072] Preferably, in the first state, when the primary switch tube is turned on, the secondary switch tube also starts to turn on. Further, in the first state, the second control circuit controls the secondary switch tube to turn on during the period when the primary switch tube is turned on.

[0073] In the first state, the primary switch tube and the secondary switch tube have the same switching cycle, and the second control circuit controls the secondary switch tube to be turned on for at least part of the time during the period when the primary switch tube is turned off so that the output parameter of the second output circuit remains constant.

[0074] The first state is that the power converter operates in CCM or DCM.

[0075] Figure 2a FIG. 1 is a circuit diagram of a power converter according to a first embodiment of the present invention. Figure 2a As shown, the power converter 2 includes an input circuit 21 , at least one first output circuit 22 , at least one second output circuit 23 , a first control circuit 24 and a second control circuit 25 .

[0076] The input circuit 21 includes a primary winding Np and a primary switch tube Q1. The primary winding Np and the primary switch tube Q1 are connected in series between the input terminal and the ground terminal. The voltage Vin at the input terminal is obtained by rectifying the AC voltage through a rectifier bridge and filtering it through an input capacitor.

[0077] In this embodiment, the first output circuit 22 is a constant voltage output circuit, and the second output circuit 23 is a constant current output circuit.

[0078] The first output circuit 22 is similar to the existing constant voltage output circuit, and includes a first secondary winding Ns1 coupled to the primary winding Np. The second output circuit 23 includes a second secondary winding Ns2 coupled to the primary winding Np. The primary winding Np, the first secondary winding Ns1 and the second secondary winding Ns2 form a transformer.

[0079] At the same time, in this embodiment, the second output circuit 23 includes a secondary switch tube Q2 connected in series in the output circuit loop. In the first state, within a switching cycle, the secondary switch tube Q2 starts to turn on before the primary switch tube Q1 is turned off to reduce switching interference. Preferably, in the first state, when the primary switch tube is turned on, the secondary switch tube also starts to turn on. Further, in the first state, the second control circuit controls the secondary switch tube to turn on during the conduction period of the primary switch tube.

[0080] When the primary switch tube Q1 is turned off and the secondary switch tube Q2 is turned on, the circuit loop of the second output circuit 23 is at least partially turned on (in this embodiment, the entire loop is turned on); when the secondary switch tube Q2 is turned off, the circuit loop of the second output circuit 23 is at least partially turned off (in this embodiment, the entire loop is turned off).

[0081] In this embodiment, the first output circuit 22 and the second output circuit 23 are configured so that when the secondary switch tube Q2 is turned on, the voltage reflected by the output voltage of the second secondary winding Ns2 to the first secondary winding Ns1 is less than the output voltage of the first secondary winding Ns1, so that the first output circuit 22 is cut off by the rectifier device (that is, the diode D1 in the rectifier circuit) when the primary switch tube Q1 is turned off and the secondary switch tube Q2 is turned on (that is, the freewheeling current flowing through the first output circuit is zero or tends to zero). This can be achieved by adjusting the turns ratio or other parameters of the first secondary winding Ns1 and the second secondary winding Ns2. Due to the effect of electromagnetic induction, the voltage at both ends of the first secondary winding Ns1 and the second secondary winding Ns2 rises after the primary switch tube Q1 is turned off. When the circuit loop of the second output circuit 23 is turned on (that is, when the primary switch tube Q1 is turned off and the secondary switch tube Q2 is turned on), since the reflected voltage of the output voltage of the second secondary winding Ns2 on the first secondary winding Ns1 is less than the output voltage of the first winding Ns1 itself, when the voltage of the second secondary winding Ns2 reaches the output voltage, the diode D2 is turned on and the second output circuit 23 starts to freewheel. At this time, the voltage reflected to the first winding Ns1 does not reach its corresponding output voltage, thereby keeping the diode D1 in the off state and the first output circuit 22 is turned off. Since the energy accumulated by the magnetic element is released through the second secondary winding Ns2, the first secondary winding Ns1 has no freewheeling current. Therefore, the energy accumulated in the primary winding Np is preferentially released through the secondary loop where the second secondary winding Ns2 is located, that is, the energy is released through the second output circuit 23. At this time, the freewheeling current flowing through the first output circuit 22 tends to zero or is equal to zero. When the circuit loop of the second output circuit 23 is turned off (that is, when the secondary switch tube Q2 is turned off), the primary winding Np releases energy through the first output circuit 22, and the freewheeling current flows through the first output circuit 22. Thus, time-sharing freewheeling between the constant current output circuit and the constant voltage output circuit can be achieved by controlling the on and off of the secondary switch tube Q2. Moreover, in the present invention, in the first state, within a switching cycle, the secondary switch tube starts to turn on before the primary switch tube is turned off to reduce switching interference.

[0082] The first output circuit 22 is a constant voltage output circuit, which includes a first secondary winding Ns1, a voltage output port and a first rectifier circuit. The first rectifier circuit is connected between the voltage output port and the first secondary winding Ns1, and includes a diode D1 and a capacitor C1.

[0083] At the same time, the first control circuit 24 controls the primary switch tube Q1 to turn on and off to adjust the output parameter of the first output circuit 22 (ie, the output voltage Vo).

[0084] Specifically, the first control circuit 24 samples the output voltage Vo to obtain a voltage sampling signal Vs1, obtains an error compensation signal Verr1 based on a voltage reference signal Vref1 representing a desired output voltage and the voltage sampling signal Vs1, and generates a switch control signal Vg1 based on the error compensation signal Verr1 to control the primary switch tube Q1 to keep the voltage Vo stable.

[0085] The first control circuit 24 may include a first error amplifier circuit EA1, an optocoupler circuit 24a, and a first control signal generating circuit 24b. The first error amplifier circuit EA1 generates an error compensation signal Verr1 according to the voltage sampling signal Vs1 and the voltage reference signal Vref1. The optocoupler circuit 24a transmits the error compensation signal Verr1 from the secondary side to the first control signal generating circuit 24b on the primary side by optical coupling. The first control signal generating circuit 24b generates a switch control signal Vg1 according to the error compensation signal Verr1 to control the primary switch tube Q1.

[0086] It should be understood that the structure of the first control circuit 24 is only an example, and any control circuit that can control the primary switch tube according to the output voltage to achieve constant voltage output can be applied to this embodiment.

[0087] The second output circuit 23 is a constant current output circuit, which includes a second secondary winding Ns2, a current output port, a second rectifier circuit, a current sampling circuit Rs and a secondary switch tube Q2. The second rectifier circuit is connected between the current output port and the second secondary winding Ns2. The second rectifier circuit includes a diode D2 and a capacitor C2.

[0088] The current sampling circuit Rs and the secondary switch tube Q2 are connected in series in the loop of the constant current output circuit (that is, connected in series with the second secondary winding Ns2). Figure 2a As shown, the current sampling circuit Rs is preferably a sampling resistor, which is connected between the ground terminal and the first end of the secondary switch tube Q2, and the second end of the secondary switch tube Q2 is connected to one end of the current output port. In this embodiment, the load of the constant current output circuit is an LED load, which is connected to the current output port, and the LED load can be integrated with the entire power converter. It should be understood that the current sampling circuit can also be connected to other positions in the constant current output circuit loop, and the current sampling signal V representing the current intensity can be obtained by detecting the voltage drop across the sampling resistor. ISEN .

[0089] Further, in a preferred embodiment, Figure 2bIn the circuit diagram of the power converter of the second embodiment shown, the sampling resistor is connected between the ground terminal and the first end of the secondary switch tube Q2, the second end of the secondary switch tube Q2 is connected to one end of the second secondary winding, the load of the constant current output circuit is an LED load, which is connected to the current output port, and the positive end of the LED is grounded to facilitate sampling of the voltage on the LED to determine whether the LED is short-circuited or open-circuited. In other embodiments, the position of the secondary switch tube Q2 and the sampling resistor can be changed so that the negative end of the LED is grounded, which can also achieve the effect of facilitating sampling of the voltage on the LED.

[0090] The second control circuit 25 samples the current sampling circuit Rs to obtain a current sampling signal V ISEN Averaging is performed to obtain an average sampling signal Vs2 representing the average current flowing through the load, and then a switch control signal Vg2 is generated according to the average sampling signal Vs2, a current reference signal Vref2 representing the desired output current, and a first sampling signal V11 representing the first secondary winding voltage or representing the second secondary winding voltage, or an internal clock signal Clock1 to control the secondary switch tube Q2 to keep the average value of the output current stable.

[0091] Specifically, the second control circuit is based on the current sampling signal V ISEN The turn-off moment of the secondary switch tube is controlled by the current reference signal Vref2, and the turn-on moment of the secondary switch tube is controlled according to the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal Clock1.

[0092] As described above, the embodiment of the present invention controls the on and off of the secondary switch tube Q2 through the second control circuit 25, so that the first output circuit 22 and the second output circuit 23 are time-sharing continuous current during the shutdown period of the primary switch tube Q1, thereby realizing multi-channel constant current / constant voltage output. At the same time, the intensity of its output current is adjusted by adjusting the continuous current output time of the second output circuit 23.

[0093] The second control circuit 25 may include an averaging circuit, a second error amplifier circuit EA2, and a second control signal generating circuit 25a. The averaging circuit includes a resistor R and a capacitor C, that is, the averaging circuit is formed in the form of an RC circuit to sense the current sampling signal V ISENThe average sampling signal Vs2 obtained after the average processing is input to the second error amplifier circuit EA2. The second error amplifier circuit EA2 generates an error compensation signal Verr2 according to the average sampling signal Vs2 and the current reference signal Vref2. The second control signal generating circuit 25a generates a switch control signal Vg2 to control the secondary switch tube Q2 according to the error compensation signal Verr2 and the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal Clock1.

[0094] It should be understood that the structure of the second control circuit 25 is only an example, and any control circuit that can control the secondary switch tube according to the output voltage to achieve constant current output can be applied to this embodiment.

[0095] Furthermore, when LED load dimming (ie, adjusting the output current intensity) is required, the current reference signal Vref2 can be adjusted according to the current intensity adjustment signal (dimming signal) to change the output current expected value, thereby achieving the adjustment of the output current intensity.

[0096] In other embodiments, LED load dimming may be performed in other ways, such as Figure 2c In the circuit diagram of the power converter of the third embodiment shown, a fifth switch tube Q5 is connected between the positive electrode of the LED and the ground, and the control end of the fifth switch tube Q5 receives a current intensity adjustment signal Vg5, and the fifth switch tube Q5 adjusts the intensity of the current flowing through the LED according to the current intensity adjustment signal Vg5. The fifth switch tube can also be connected to the negative electrode of the LED, and the present invention is not limited to this.

[0097] Figure 3 FIG. 4 is a circuit diagram of a second control signal generating circuit according to a first embodiment of the present invention; Figure 3 As shown, the second control signal generating circuit 25a may include an RS trigger RS1, a conduction signal generating circuit 25a1 and a comparator CMP. The conduction signal generating circuit 25a1 receives the first sampling signal V11 or the internal clock signal Clock1 representing the first secondary winding voltage or the second secondary winding voltage, generates a conduction signal Clock and outputs it to the set end of the RS trigger RS1. At the same time, the input end of the comparator CMP respectively inputs the error compensation signal Verr2 and the periodic ramp signal Vramp, and the output end is connected to the reset end of the RS trigger RS1. The output end of the RS trigger outputs the switch control signal Vg2.

[0098] The power converter of the present invention works in a first state, and the first state is a normal working state such as CCM and DCM. At this time, within a switching cycle, the secondary switch tube starts to conduct before the primary switch tube is turned off. Preferably, after the primary switch tube is turned on during the conduction period, the secondary switch tube also starts to conduct. After the primary switch tube is turned on, the voltage of the first secondary winding rises rapidly, so the conduction time of the secondary switch tube is controlled according to the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage. When the first sampling signal V11 reaches the first threshold Vr1, it is considered that the primary switch tube is not turned off (or the primary switch tube is turned on) at this time, and the secondary switch tube is turned on at this time; when the first sampling signal V11 does not reach the first threshold Vr1, the conduction time of the secondary switch tube can be controlled according to the internal clock signal Clock1, or the secondary switch tube can be controlled not to be turned on at this time, and the present invention does not limit this.

[0099] When the power converter operates in the second state, which is the burst state, the circuit is extremely lightly loaded, and the first sampling signal V11 cannot reach the first threshold Vr1, so the conduction time of the secondary switch is controlled according to the internal clock signal Clock1.

[0100] Figure 4 A circuit schematic diagram of a conduction signal generating circuit of a first embodiment of the present invention is given; the conduction signal generating circuit 25a1 includes a comparator CMP1 and an internal clock generating circuit 25a11, the internal clock generating circuit generates an internal clock signal Clock1, a first input terminal of the comparator CMP1 receives a first sampling signal V11 representing the voltage of the first secondary winding Ns1, and a second input terminal receives a first threshold value Vr1, an output terminal of the comparator CMP1 and an output terminal of the internal clock generating circuit are connected to an input terminal of an OR gate, and an output terminal of the OR gate outputs a conduction signal Clock.

[0101] exist Figure 4 The resistors R3 and R4 are connected in series between one end of the first secondary winding Ns1 and the ground, and the first sampling signal V11 is the common terminal voltage of the resistors R3 and R4. The present invention is not limited by comparison, and the first sampling signal V11 representing the voltage of the first secondary winding Ns1 can be obtained in any way.

[0102] The internal clock generating circuit 25a11 includes a first capacitor C11, and generates an internal clock signal Clock1 by charging and discharging the first capacitor C11.

[0103] The first capacitor C11 is charged, and when the voltage on the first capacitor C11 is greater than the second threshold value Vr2, the internal clock signal is at a high level, and the first capacitor C11 is discharged, and when the voltage on the first capacitor C11 is less than the second threshold value Vr2, the internal clock signal is at a low level, and the discharge of the first capacitor C11 is stopped. The second threshold value Vr2 is greater than the first threshold value Vr1.

[0104] Specifically, the internal clock generation circuit 25a11 further includes a comparator CMP2, a current source I11, a switch S11 and a first capacitor C11. The first capacitor C11, the current source I11 and the switch S11 are connected in parallel to form a parallel structure. The high potential end of the parallel structure is connected to the first input end of the comparator CMP2. The second input end of the comparator receives the second threshold Vr2. The output end of the comparator is connected to the input end of the OR gate. The output end of the OR gate is connected to the control end of the switch S11 through a buffer. The ground potential end of the parallel structure can be a ground potential or a voltage VTN (the second threshold Vr2 is greater than VTN), and the present invention is not limited to this. The buffer is used to enhance the driving capability.

[0105] The internal clock generating circuit 25a11 further includes a diode D11, which is connected in parallel with the parallel structure, and a cathode of the diode is connected to a high potential end of the parallel structure.

[0106] The internal clock generating circuit 25a11 is not limited to the above-mentioned structure, and other methods of generating the internal clock Clock1 are all within the protection scope of the present invention.

[0107] also, Figure 3 The periodic ramp signal Vramp can be generated by other circuits or by the internal clock generating circuit 25a11. The voltage signal at the high potential end of the parallel structure in the internal clock generating circuit 25a11 can be used as Figure 3 The periodic ramp signal Vramp described in .

[0108] It should be noted that Figure 4 The first sampling signal V11 in the present invention is characterized by sampling the voltage of the first secondary winding Ns1. The first sampling signal V11 can also be characterized by sampling the voltage of the second secondary winding Ns2. Figure 1The voltage of the non-same-name end of the second secondary winding in the first embodiment shown is divided as the first sampling signal V11. Therefore, the present invention does not limit the first sampling signal V11, as long as it can represent the voltage of the first secondary winding or the second secondary winding, it is within the protection scope of the present invention. Secondly, it should be noted that when the first sampling signal V11 is selected differently, the first threshold value Vr1 is different, so the first threshold value Vr1 in the present invention refers to different values ​​when the first sampling signal V11 is different.

[0109] Figure 5 is an exemplary working waveform diagram of the power converter of the first embodiment of the present invention. Wherein, the power converter works in the first working state, such as Figure 5 As shown, from time t0 to time t1, the switch control signal Vg1 is at a high level, at which time the primary switch tube Q1 is turned on, and the current Ip flowing through the primary winding Np starts to rise from zero. It is detected that the first sampling signal V11 reaches the first threshold Vr1 (since the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage quickly reaches the first threshold Vr1 after the primary is turned on, it can be considered that the primary and secondary switch tubes are turned on at the same time), then Figure 3 The RS trigger in is set, and the switch control signal Vg2 is also at a high level. At this time, the secondary switch tube Q2 is also turned on, but the diodes D1 and D2 in the rectifier circuits of the first output circuit 22 and the second output circuit 23 on the secondary side are in a blocked state due to reverse bias, and there is no current in the two output circuits.

[0110] The explanation needed is, Figure 5 The secondary switch tube Q2 is also turned on during the conduction period of the primary switch tube Q1 is only an embodiment. In the first state, within a switching cycle, the secondary switch tube Q2 starts to turn on before the primary switch tube Q1 is turned off, which is within the protection scope of the present invention.

[0111] At time t1 , the switch control signal Vg1 switches to a low level, and the primary switch tube Q1 is turned off.

[0112] From time t1 to time t2, the secondary switch tube Q2 remains turned on. As mentioned above, during the conduction period of the secondary switch tube Q2, the energy stored in the primary winding is only released through the second output circuit 23, and the current Is2 flowing through the second secondary winding Ns2 continues to decrease from the peak value, while the current Is1 flowing through the first secondary winding Ns1 approaches or is equal to zero.

[0113] At time t2 , the ramp signal Vramp rises to be greater than the error compensation signal Verr2 , the RS flip-flop RS1 is reset, and the switch control signal Vg2 is switched to a low level.

[0114] From time t2 to time t3, the switch control signal Vg1 remains at a low level, the primary switch tube remains off, and at the same time, the switch control signal Vg2 remains at a low level, and the secondary switch tube Q2 also remains off. At this time, since the loop of the second output circuit 23 is disconnected, the current can only be continued through the first output circuit 22. The current Is2 flowing through the second secondary winding Ns2 is zero, and the current Is1 flowing through the first secondary winding Ns1 continues to decrease from the peak value, thereby providing energy for the voltage output port.

[0115] At time t3, according to the control of the first control circuit 24, the switch control signal Vg1 is switched to a high level, the primary switch tube Q1 is turned on, and a new switching cycle begins.

[0116] In this way, the output parameters of the first output circuit 22 (constant voltage output circuit) can be stabilized near the expected output voltage through the control of the first control circuit 24, and the output parameters of the second output circuit 23 (constant current output circuit) can be stabilized near the expected output current through the control of the second control circuit 25.

[0117] It should be noted that Figure 3 The second control signal generating circuit shown, Figure 4 The conduction signal generating circuit shown and Figure 5 The working waveforms shown are only examples, and the freewheeling sequence of the first output circuit 22 and the second output circuit 23 in this embodiment is not limited to the above method. In other implementations, the second control circuit 25 can also control the secondary switch tube Q2 to be turned off first, so that the first output circuit 22 freewheels first, and then control the secondary switch tube Q2 to be turned on, so that the second output circuit 23 freewheels next.

[0118] By connecting the secondary switch tube in series to the second output circuit, and making the output voltage of the second secondary winding reflected to the voltage on the first secondary winding smaller than the output voltage of the first secondary winding, the freewheeling current flows through the secondary winding of the second output circuit when the primary switch tube is turned off and the secondary switch tube is turned on, and the freewheeling current flows through the secondary windings of other output circuits when the secondary switch tube is turned off, thereby realizing time-sharing freewheeling for the constant current output circuit and the constant voltage output circuit in each switching cycle, thereby realizing multi-channel constant current / constant voltage output under the premise of only one power conversion, improving the working efficiency, and only requiring one set of magnetic components, reducing the system volume. At the same time, in the first state, within a switching cycle, the second control circuit controls the secondary switch tube to start turning on before the primary switch tube is turned off, so as to reduce switching interference. And the present invention can be applied to multiple working states such as CCM, BCM, DCM, burst, etc.

[0119] It should be understood that although the present embodiment is described using a first output circuit (constant voltage output circuit) as an example, the number of first output circuits (constant voltage output circuits) can also be set to multiple, and the first control circuit 24 can control the primary switch tube based on the output voltage of one of them, or can control the primary switch tube based on the total output voltage.

[0120] Meanwhile, although the present embodiment is described by taking one second output circuit (constant current output circuit) as an example, in the power converter according to the present embodiment, the second output circuit may also be provided as a plurality, each of which has the same structure. Meanwhile, the second control circuit includes a plurality of control subcircuits to respectively control the secondary switch tube of each second output circuit, so that the plurality of second output circuits simultaneously or in a time-sharing manner continue to output a constant current while the primary switch tube remains off.

[0121] Figure 6 FIG. 4 is a circuit diagram of a power converter according to a fourth embodiment of the present invention; Figure 6 As shown, the power converter 5 includes an input circuit 51 , at least one first output circuit 52 , at least one second output circuit 53 , a first control circuit 54 and a second control circuit 55 .

[0122] The circuit structures of the input circuit 51 , the first output circuit 52 and the first control circuit 54 are the same as those of the first embodiment, and are not described again herein.

[0123] The second output circuit 53 includes a second secondary winding Ns2 and at least two output branches. The second output circuit 53 is configured so that the voltage reflected by the output voltage of the second secondary winding Ns2 to the first secondary winding Ns1 is less than the output voltage corresponding to the first secondary winding Ns1. Each output branch includes a current output port, a second rectifier circuit connected between the current output port and the branch input terminal m, and a current sampling circuit Rsi and a secondary switch tube Q2i (i=1~N, N is an integer greater than or equal to 2) connected in series in the output branch. All output branches are connected in parallel at both ends of the second secondary winding Ns2, that is, all output branches share the second secondary winding Ns2. When any number of secondary switch tubes Q2i are turned on, the freewheeling current generated by the second secondary winding Ns2 flows through the corresponding output branch to drive the corresponding LED load. By controlling the on-time of the secondary switch tube Q2i, different output branches can be used to drive LED loads with different brightness.

[0124] Specifically, in Figure 6In the second output circuit 53 shown, the current sampling circuit Rsi is a sampling resistor, which is connected between the ground terminal (i.e., the same-name terminal of the second secondary winding Ns2) and the first end of the secondary switch tube Q2i. The secondary switch tube Q2i is connected to the second end of the current output port of the corresponding output branch. The LED load is connected to the corresponding current output port. The second rectifier circuit includes a diode D2i and a capacitor C2i. It should be understood that the above connection method is not unique, as long as the secondary switch tube Q2i and the current sampling circuit Rsi are connected in series in the output branch.

[0125] According to a preferred embodiment of the present invention, the second control circuit 55 may include a plurality of control subcircuits. Each control subcircuit samples the current sampling signal V obtained by the current sampling circuit Rsi of the corresponding output branch. ISENi Averaging is performed to obtain an average sampling signal Vs2i representing the average current flowing through the output branch to drive the LED load, and then a switch control signal Vg2i is generated according to the average sampling signal Vs2i and the current reference signal Vref2i representing the expected output current of the branch and the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal Clock1. The switch control signal Vg2i is used to control the corresponding secondary switch tube Q2i so that the average value of the output current of the corresponding output branch remains stable. Different control subcircuits can perform freewheeling simultaneously or in a time-sharing manner.

[0126] Each control subcircuit may include a corresponding averaging circuit, a second error amplifier circuit EA2i, and a second control signal generating circuit 55ai. In this embodiment, the averaging circuit is formed as an RC circuit. The second control signal generating circuit 55ai may preferably be formed as follows: Figure 3 and Figure 4 It should be understood that the structure of the second control signal generating circuit 55ai is only an example, and any control circuit that can control the secondary switch tube according to the output voltage to achieve constant current output can be applied to this embodiment.

[0127] When dimming is required, the current reference signal Vref2i in each control subcircuit can be adjusted respectively to change the expected value of the output current, thereby achieving the adjustment of the output current intensity.

[0128] Thus, the output current of each output branch can be controlled independently to realize complex dimming logic.

[0129] According to another preferred embodiment of the present invention, when all LED loads are the same, all secondary switch tubes Q2i can be controlled based on the current of one output branch, thereby reducing the complexity of the control circuit.

[0130] In this embodiment, multiple output branches are set in the second output circuit (constant current output circuit) so that the multiple output branches share a second secondary winding. While achieving multi-channel constant current output, the number of magnetic components does not increase, thereby reducing the volume of the multi-channel constant current output circuit.

[0131] It should be understood that although the present embodiment is described using a first output circuit as an example, the number of first output circuits (constant voltage output circuits) may also be set to multiple, and the first control circuit 54 may be controlled based on one of the output voltage primary switching tubes, or may be controlled based on the total output voltage primary switching tube.

[0132] Meanwhile, although this embodiment is described by taking one second output circuit as an example, the second output circuit (constant current output circuit) may also be set to be multiple, and each second output circuit has the same structure. The second control circuit includes multiple control subcircuits to respectively control the secondary switch tube of each second output circuit, so that the multiple second output circuits simultaneously or in a time-sharing manner continue to output a constant current while the primary switch tube remains off.

[0133] Figure 7a FIG. 1 is a circuit diagram of a power converter according to a fifth embodiment of the present invention. Figure 7a As shown, the power converter 6 includes an input circuit 61 , a first output circuit 62 , at least one second output circuit 63 , a first control circuit 64 and a second control circuit 65 .

[0134] The input circuit 61 has the same structure as that of the input circuit of the first embodiment, and will not be described in detail herein.

[0135] Different from the first embodiment, in this embodiment, the first output circuit 62 is a constant current output circuit, and the second output circuit 63 is a constant voltage output circuit.

[0136] In this embodiment, the first output circuit 62 includes a first secondary winding Ns1, a current output port, a first rectifier circuit and a current sampling circuit Rs. The first rectifier circuit is connected between the first secondary winding Ns1 and the current output port, and includes a diode D3 connected between the first secondary winding Ns1 and one end of the current output port and a capacitor C3 connected in parallel to the current output port. The current output port is connected to the load of the constant current output circuit. In this embodiment, the load is an LED load. The current sampling circuit Rs is preferably a sampling resistor connected between the ground terminal and the other end of the current output port. Therefore, there is no need to add other circuit components. The voltage at one end of the sampling circuit can be directly obtained to obtain the current sampling signal V representing the output current. ISEN The current sampling circuit may also have other connection modes, such as being connected in series with the current output port or being connected in series with the first secondary winding Ns1.

[0137] The first control circuit 64 is a constant current control circuit, which samples the current sampling circuit Rs to obtain a current sampling signal V ISEN Averaging is performed to obtain an average sampling signal Vs3 representing the average current flowing through the LED load, and then a switch control signal Vg3 is generated based on the average sampling signal Vs3 and a current reference signal Vref3 representing the desired output current to control the original switch tube Q3 so that the output current of the first output circuit 62 remains stable.

[0138] Furthermore, when it is necessary to dim the LED load (ie, adjust the output current intensity), the current reference signal Vref3 may be adjusted according to the dimming signal to change the output current expected value, thereby achieving the adjustment of the output current intensity.

[0139] Further, in other embodiments, LED load dimming can also be performed in other ways, where a fifth switch tube Q5 is connected between the LED positive electrode and the ground, a control end of the fifth switch tube Q5 receives a current intensity adjustment signal Vg5, and the fifth switch tube Q5 adjusts the intensity of the LED current according to the current intensity adjustment signal Vg5. The fifth switch tube can also be connected to the LED negative electrode, and the present invention is not limited to this.

[0140] The first control circuit 64 may include an averaging circuit, a first error amplifier circuit EA3, an optocoupler circuit 64a, and a first control signal generating circuit 64b. The averaging circuit includes a resistor R and a capacitor C, that is, the averaging circuit is formed in the form of an RC circuit to sense the current sampling signal V ISEN The average processing is performed. The average sampling signal Vs3 obtained after the average processing is input to the first error amplifier circuit EA3. The first error amplifier circuit EA3 generates an error compensation signal Verr3 according to the average sampling signal Vs3 and the current reference signal Vref3. The optocoupler circuit 64a transmits the error compensation signal Verr3 from the secondary side to the first control signal generating circuit 64b on the primary side by optical coupling. The first control signal generating circuit 64b generates a switch control signal Vg3 according to the error compensation signal Verr3 to control the primary switch tube Q3.

[0141] It should be understood that the structure of the first control circuit 64 is only an example, and any control circuit that can control the primary switch tube according to the current sampling signal to achieve constant current output can be applied to this embodiment.

[0142] The second output circuit 63 includes a second secondary winding Ns2, a voltage output port, a secondary switch tube Q4, and a diode D4 and a capacitor C4 for rectification and filtering. The diode D4 and the secondary switch tube Q4 are connected in series between the voltage output port and the second secondary winding Ns2. The capacitor C4 is connected in parallel to the voltage output port; the secondary switch tube Q4 is controlled to be turned on and off so that the voltage of the output port remains constant. Figure 7a In the embodiment, the secondary switch tube Q4 can also be connected between the high potential end of the voltage output port and the second secondary winding Ns2. In other embodiments, such as Figure 7b As shown in the circuit diagram of the power converter according to the fifth embodiment of the present invention, the secondary switch tube Q4 can also be connected between the low potential end of the voltage output port and the second secondary winding Ns2.

[0143] The second control circuit 65 samples the output voltage Vo to obtain a voltage sampling signal Vs4, obtains an error compensation signal Verr4 based on a voltage reference signal Vref4 representing the desired output voltage and the voltage sampling signal Vs4, and generates a switch control signal Vg4 to control the secondary switch tube Q4 based on the error compensation signal Verr4 and the first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal Clock1.

[0144] Specifically, the second control circuit controls the turn-off moment of the secondary switch tube according to the error compensation signal Verr4 generated by the voltage sampling signal Vs4 and the voltage reference signal Vref4, and controls the turn-on moment of the secondary switch tube according to the first sampling signal V11 of the first secondary winding voltage or the internal clock signal Clock1.

[0145] The second control circuit 65 may include a second error amplifier circuit EA4 and a second control signal generating circuit 65a. The second error amplifier circuit EA4 is used to obtain an error compensation signal Verr4 according to a voltage reference signal Vref4 representing a desired output voltage and a voltage sampling signal Vs4. The second control signal generating circuit 65a is used to generate a switch control signal Vg4 to control the secondary switch tube Q4 according to the error compensation signal Verr4 and a first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or an internal clock signal Clock1.

[0146] In this embodiment, the second control signal generating circuit 65a can preferably adopt the following Figure 3 and Figure 4 The circuit structure shown is implemented.

[0147] Therefore, by controlling the on and off of the secondary switch tube Q2, the freewheeling time of the second output circuit in each switching cycle can be controlled, thereby controlling the energy flowing into the second output circuit, so that the output voltage remains stable.

[0148] By setting the second output circuit as a constant voltage output circuit, this embodiment can realize the output of multiple constant voltages and a single constant current under the condition of using only one magnetic element (transformer), thereby improving the system working efficiency and reducing the system volume.

[0149] At the same time, although the present embodiment is described by taking a second output circuit as an example, the second output circuit (constant voltage output circuit) can also be set to multiple, and each second output circuit has the same structure. Specifically, multiple output branches are set in the second output circuit (constant voltage output circuit), so that multiple output branches share a second secondary winding, and the number of magnetic components can be increased while realizing multi-channel constant current output, thereby reducing the volume of the multi-channel constant current output circuit. The second control circuit includes multiple control subcircuits that respectively control the secondary switch tube of each second output circuit, so that the multiple second output circuits are simultaneously or time-sharingly continuous during the period when the primary switch tube remains turned off to maintain a constant output voltage.

[0150] Figure 8 is a circuit diagram of a power converter according to a seventh embodiment of the present invention. Figure 8 As shown, the power converter 7 includes an input circuit 71 , a first output circuit 72 , at least one second output circuit 73 , a first control circuit 74 and a second control circuit 75 .

[0151] The input circuit 71 , the first output circuit 72 , and the first control circuit 74 are the same as those in the fifth embodiment, and are not described in detail herein.

[0152] In this embodiment, the second output circuit 73 is also a constant voltage output circuit. However, unlike the fifth embodiment, the second output circuit 73 includes a plurality of output branches in addition to the second secondary winding Ns2. Each output branch includes a voltage output port, a diode D4i and a secondary switch tube Q4i (i=1-N, N is an integer greater than or equal to 2) connected in series between the voltage output port and the input end of the output branch, and a capacitor C4i connected in parallel to the voltage output port, and all output branches are connected in parallel to the two ends of the second secondary winding Ns2.

[0153] The secondary switch tube Q4i can control the on / off of the corresponding output branch. It is turned on and off in a controlled manner so that the output voltage of the corresponding output branch remains constant.

[0154] When any number of secondary switch tubes Q4i are turned on, the freewheeling current generated by the second secondary winding Ns2 flows through the corresponding output branch to drive the corresponding load. By controlling the on-time of the secondary switch tubes Q4i of the corresponding output branch, different output branches can output different stable voltages.

[0155] According to a preferred embodiment of the present invention, the second control circuit 75 may include a plurality of control subcircuits. Each control subcircuit generates a switch control signal Vg4i according to the voltage sampling signal Vs4i, a voltage reference signal Vref4i representing the desired output voltage of the branch, and a first sampling signal V11 representing the first secondary winding voltage or the second secondary winding voltage or an internal clock signal Clock1. The switch control signal Vg4i is used to control the corresponding secondary switch tube Q4i so that the output voltage of the corresponding output branch remains stable.

[0156] Each control subcircuit may include a corresponding second error amplifier circuit EA4i and a second control signal generating circuit 75ai. The second control signal generating circuit 75ai may preferably be implemented as follows: Figure 3 and Figure 4 It should be understood that the structure of the second control circuit 75 is only an example, and any control circuit that can control the secondary switch tube according to the output voltage to achieve constant current output can be applied to this embodiment.

[0157] It should be understood that the structure of the above second control circuit is only an example, and any control circuit that can control the secondary side switch tube according to the output voltage to achieve constant current output can be applied to this embodiment.

[0158] Thus, the output voltage of each output branch can be controlled independently.

[0159] According to another preferred embodiment of the present invention, when all loads of the second output circuit 73 are the same, all secondary switch tubes Q4i can be controlled based on the output voltage of one output branch, thereby reducing the complexity of the control circuit.

[0160] In this embodiment, multiple output branches are set in the second output circuit (constant voltage output circuit) so that the multiple output branches share a second secondary winding. While achieving multi-channel constant current output, the number of magnetic components does not increase, thereby reducing the volume of the multi-channel constant current output circuit.

[0161] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0162] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A power converter, characterized in that: include: An input circuit includes a primary winding and a primary switch tube connected in series between an input terminal and a ground terminal; at least one first output circuit including a first secondary winding coupled to the primary winding; at least one second output circuit, comprising a second secondary winding coupled to the primary winding and at least one secondary switch tube; A first control circuit controls the on and off of the primary switch tube to adjust the output parameter of the first output circuit; a second control circuit, controlling the on and off of the secondary switch tube to adjust an output parameter of the second output circuit; Wherein, in the first state, within a switching cycle, the secondary switch tube starts to conduct before the primary switch tube is turned off; The voltage reflected from the output voltage of the second secondary winding to the first secondary winding is smaller than the output voltage of the first secondary winding, so that the first output circuit is turned off during the conduction period of the secondary switch tube.

2. The power converter according to claim 1, characterized in that: The second output circuit is a constant current output circuit, and further includes: Current output port; a second rectifier circuit connected between the current output port and the second secondary winding; and a current sampling circuit connected in series with the second secondary winding; The secondary switch tube is connected in series with the second secondary winding, and the secondary switch tube is turned on and off in a controlled manner so that the output current remains constant.

3. The power converter according to claim 1, characterized in that: The second output circuit is a constant voltage output circuit, and further includes: Voltage output port; A rectifier tube and the secondary switch tube are connected in series between the voltage output port and the second secondary winding; and A filter capacitor connected in parallel to the voltage output port; The secondary switch tube is turned on and off in a controlled manner so that the output voltage of the output port remains constant.

4. The power converter according to any one of claims 1 to 3, characterized in that: In the first state, when the primary switch tube is turned on, the secondary switch tube also starts to be turned on.

5. The power converter according to any one of claims 1 to 3, characterized in that: In the first state, the second control circuit controls the secondary switch tube to be turned on during the conduction period of the primary switch tube.

6. The power converter according to any one of claims 1 to 3, characterized in that: In the first state, the primary switch tube and the secondary switch tube have the same switching cycle, and the second control circuit controls the secondary switch tube to be turned on for at least part of the time during the shutdown period of the primary switch tube so that the output parameter of the second output circuit remains constant.

7. The power converter according to any one of claims 1 to 3, characterized in that: In the first state, the second control circuit controls the turn-on time of the secondary switch tube according to a first sampling signal representing the first secondary winding voltage or representing the second secondary winding voltage.

8. The power converter according to any one of claims 1 to 3, characterized in that: In the second state, the second control circuit controls the turn-on time of the secondary-side switch tube according to the internal clock signal generated by the internal clock generating circuit.

9. The power converter according to claim 7, characterized in that: After the primary switch tube is turned on, when the first sampling signal is greater than a first threshold, the secondary switch tube is turned on.

10. The power converter according to claim 8, characterized in that: The internal clock generating circuit includes a first capacitor, and generates an internal clock signal by charging and discharging the first capacitor.

11. The power converter according to claim 10, characterized in that: The first capacitor is charged. When the voltage on the first capacitor is greater than a second threshold, the internal clock signal is at a high level and the first capacitor is discharged. When the voltage on the first capacitor is less than the second threshold, the internal clock signal is at a low level and the discharge of the first capacitor is stopped.

12. The power converter according to claim 2, characterized in that: The second control circuit adjusts the duty cycle of the secondary switch tube according to the current sampling signal, the current reference signal and the first sampling signal representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal, so that the output current of the second output circuit remains constant; The current sampling signal is acquired by the current sampling circuit, and the current reference signal is used to characterize the expected value of the output current.

13. The power converter according to claim 12, characterized in that: The second control circuit controls the turn-off moment of the secondary side switch tube according to the current sampling signal and the current reference signal.

14. The power converter according to claim 3, characterized in that: The second control circuit adjusts the duty cycle of the secondary switch tube according to the voltage sampling signal, the voltage reference signal and the first sampling signal representing the first secondary winding voltage or the second secondary winding voltage or the internal clock signal, so that the output voltage of the second output circuit remains constant; The voltage sampling signal represents the output voltage, and the voltage reference signal is used to represent the expected value of the output voltage.

15. The power converter according to claim 14, characterized in that: The second control circuit controls the turn-off moment of the secondary side switch tube according to the voltage sampling signal and the voltage reference signal.

16. The power converter according to claim 14, characterized in that: The second control circuit is further configured to adjust the current reference signal according to the current intensity adjustment signal.

17. The power converter according to claim 2, characterized in that: The second output circuit also includes a fifth switch tube, which is connected in series with the load at the current output port, and the control end of the fifth switch tube receives a current strength adjustment signal, and the fifth switch tube adjusts the current strength of the current output port according to the current strength adjustment signal.

18. The power converter according to claim 2, characterized in that: The first output circuit is a constant voltage output circuit, and further includes: a voltage output port; and a first rectifier circuit connected between the voltage output port and the first secondary winding; The primary switch tube is turned on and off in a controlled manner so that the output voltage of the first output circuit remains constant.

19. The power converter according to claim 3, characterized in that: The first output circuit is a constant current output circuit, and the first output circuit further includes: Current output port; A first rectifier circuit is connected between the first secondary winding and the current output port; and a current sampling circuit, connected in series with the first secondary winding; The primary switch tube is turned on and off in a controlled manner so that the output current remains constant.

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