PSR flyback conversion circuit, constant current control method and power system

Abstract

The invention provides a PSR flyback conversion circuit, a constant current control method and a power system.The circuit comprises a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, and the auxiliary winding circuit is a voltage sensing loop used for PSR; the switch tube control unit of the primary winding circuit is configured as follows: when the voltage of the second end of the power switch tube of the primary winding circuit is greater than or equal to a constant current reference voltage, the circuit enters a constant current output mode; and when the circuit enters the constant current output mode, at least setting an excitation reset time ratio based on a first voltage value sensed by the auxiliary winding circuit, the set excitation reset time ratio being greater than or equal to 0.5. Therefore, when the input voltage is far larger than the output reflection voltage N * Vo, it is guaranteed that the secondary winding circuit can output the correspondingly set constant current, the primary and secondary RMS current of the PSR flyback conversion circuit is reduced by increasing the excitation reset time ratio, and then the conduction loss is reduced, and the efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic power technology, and in particular to a PSR flyback conversion circuit, a constant current control method and a power system. Background Art

[0002] In the flyback conversion circuit, the PSR (primary side regulation) scheme is widely used in isolated fixed low voltage (3V~24V) output situations within 75W because of its simple control and small number of peripheral devices.

[0003] The flyback conversion circuit of the PSR scheme generally adopts a CV (constant voltage) + CC (constant current) control strategy. Specifically, before the current output by its secondary circuit reaches the maximum value, the flyback conversion circuit is in a constant voltage control mode, and after the current output by its secondary circuit reaches the maximum value, the flyback conversion circuit is in a constant current control mode.

[0004] However, after the flyback converter circuit of the traditional PSR solution enters the constant current control mode and works in the DCM mode, its excitation reset time ratio Kcc=Trst / Tp usually reaches a maximum fixed value of 0.5. This will result in that when the input voltage is much larger than the output reflected voltage N*Vo, such as 1.5 times N*Vo, the RMS (Root Mean Square Current) current value of the primary and secondary sides will be relatively large, and the corresponding conduction loss will also increase.

[0005] Therefore, how to reduce the primary-secondary RMS current of the PSR flyback conversion circuit under high input voltage conditions, thereby reducing conduction losses and improving efficiency, has become a technical problem that the industry urgently needs to solve. Summary of the invention

[0006] The present invention provides a PSR flyback conversion circuit, a constant current control method and a power system, which solve the technical problem of reducing the primary and secondary RMS currents of the PSR flyback conversion circuit when the input voltage is much larger than the output reflected voltage N*Vo, thereby reducing the conduction loss and improving the efficiency.

[0007] According to a first aspect of the present invention, an embodiment of the present invention provides a PSR flyback conversion circuit, comprising: a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, wherein the auxiliary winding circuit is a voltage sensing circuit for PSR, and the primary winding circuit comprises a primary winding, a switch tube control unit, a power switch tube and an absorption module;

[0008] The first end of the power switch tube is respectively coupled to the first end of the primary winding and the first end of the absorption module, the second end of the power switch tube is grounded through a detection resistor, the second end of the absorption module is coupled to the second end of the primary winding, and the second end of the primary winding also receives an input voltage;

[0009] The output end of the switch tube control unit is coupled to the control end of the power switch tube, the first input end of the switch tube control unit is coupled to the second end of the power switch tube, and is used to detect the voltage of the second end of the power switch tube, and the second input end of the switch tube control unit is coupled to the output end of the auxiliary winding circuit, and is used to receive the first voltage value sensed by the auxiliary winding circuit;

[0010] The switch tube control unit is configured to: when the voltage at the second end of the power switch tube is greater than or equal to the constant current reference voltage, the circuit enters a constant current output mode; and

[0011] When the circuit enters the constant current output mode, at least the excitation reset time ratio is set based on the first voltage value, so that under different input voltages, the secondary winding circuit can output the set constant current, wherein the excitation reset time ratio is the ratio of the excitation current reset time to the total switching period of the power switch tube, and the excitation reset time ratio is greater than or equal to 0.5.

[0012] Optionally, at least setting an excitation reset time ratio based on the first voltage value so that the secondary winding circuit can output a corresponding set constant current includes:

[0013] The first voltage value is compared with the first threshold voltage, and the current value of the constant current output by the secondary winding circuit is determined according to the comparison result, wherein:

[0014] If the comparison result indicates that the first voltage value is less than a first threshold voltage, setting the excitation reset time ratio to a first ratio so that the secondary winding circuit outputs a first set constant current;

[0015] If the comparison result indicates that the first voltage value is greater than or equal to a first threshold voltage, setting the excitation reset time ratio to a second ratio so that the secondary winding circuit outputs a second set constant current;

[0016] Wherein, the first ratio is smaller than the second ratio.

[0017] Optionally, the first threshold voltage has a value range of 180 Vdc to 255 Vdc.

[0018] Optionally, the switch tube control unit is further configured to: when the circuit enters the constant current output mode, at least set the excitation reset time ratio and the constant current reference voltage based on the first voltage value;

[0019] The method for enabling the secondary winding circuit to output a corresponding set constant current includes:

[0020] Based on the first voltage value, a constant current control parameter is set, wherein the constant current control parameter is the product of the excitation reset time ratio and the constant current reference voltage;

[0021] When the circuit enters the constant current output mode, the constant current control parameter is set so that the secondary winding circuit can output a set constant current under different input voltages.

[0022] Optionally, the secondary winding circuit includes a secondary winding, and before setting the excitation reset time ratio, the method further includes:

[0023] Determining the maximum value of the excitation reset time ratio that can be set includes:

[0024] Obtaining a turns ratio of the secondary winding to the primary winding, a voltage value of the input voltage, and a voltage value output by the secondary winding circuit;

[0025] Obtaining a minimum duty cycle of the power switch tube based on a turns ratio of the secondary winding to the primary winding, a voltage value of the input voltage, and a voltage value output by the secondary winding circuit;

[0026] Based on the minimum duty cycle, a maximum value of the excitation reset time ratio that can be set is obtained.

[0027] Optionally, the auxiliary winding circuit includes an auxiliary winding, a first diode, a first voltage-dividing resistor, a second voltage-dividing resistor, a first capacitor and a first resistor;

[0028] The first end of the auxiliary winding is coupled to the first end of the first voltage-dividing resistor and the positive electrode of the first diode, the second end of the first voltage-dividing resistor is coupled to the first end of the second voltage-dividing resistor, and the second end of the first voltage-dividing resistor is also coupled to the second input end of the switch tube control unit to output a first signal, the cathode of the first diode is coupled to the first end of the first capacitor, the second end of the second voltage-dividing resistor is respectively coupled to the second end of the auxiliary winding and the second end of the first capacitor, and the first resistor is connected in parallel with the first capacitor; wherein, the first signal includes the first voltage value information sensed by the auxiliary winding circuit.

[0029] Optionally, after setting the excitation reset time ratio, the method further includes:

[0030] Based on the waveform of the first voltage value, obtaining the excitation current reset time;

[0031] Based on the excitation reset time ratio and the excitation current reset time, a total switching period of the power switch tube is determined.

[0032] Optionally, the first signal is a current signal, and the switch tube control unit is configured as follows:

[0033] When the power switch tube is turned on, the first voltage value information sensed by the auxiliary winding circuit is obtained according to the current flowing through the first voltage-dividing resistor.

[0034] Optionally, after the circuit enters the constant current output mode and before the excitation reset time ratio is set, the switch tube control unit is further configured to:

[0035] The constant current reference voltage is set to be a default constant current reference voltage, and the excitation reset time ratio is set to be a default excitation reset time ratio.

[0036] According to a second aspect of the present invention, an embodiment of the present invention provides a constant current control method for controlling the output current of the secondary winding circuit of the PSR flyback conversion circuit according to any one of the first aspects of the present invention, the method comprising:

[0037] Obtaining a voltage at the second end of the power switch tube;

[0038] When the voltage at the second end of the power switch tube is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode and performs the following steps:

[0039] Based on the first voltage value, at least the excitation reset time ratio is set so that under different input voltages, the secondary winding circuit can output a set constant current, wherein the excitation reset time ratio is the ratio of the excitation current reset time to the total switching period of the power switch tube, and the excitation reset time ratio is greater than or equal to 0.5.

[0040] Optionally, at least setting an excitation reset time ratio based on the first voltage value so that the secondary winding circuit can output a corresponding set constant current includes:

[0041] The first voltage value is compared with the first threshold voltage, and the current value of the constant current output by the secondary winding circuit is determined according to the comparison result, wherein:

[0042] If the comparison result indicates that the first voltage value is less than a first threshold voltage, setting the excitation reset time ratio to a first ratio so that the secondary winding circuit outputs a first set constant current;

[0043] If the comparison result indicates that the first voltage value is greater than or equal to a first threshold voltage, setting the excitation reset time ratio to a second ratio so that the secondary winding circuit outputs a second set constant current;

[0044] Wherein, the first ratio is smaller than the second ratio.

[0045] Optionally, when the circuit enters the constant current output mode, at least the excitation reset time ratio and the constant current reference voltage are set based on the first voltage value;

[0046] The method for enabling the secondary winding circuit to output a corresponding set constant current includes:

[0047] Based on the first voltage value, a constant current control parameter is set, wherein the constant current control parameter is the product of the excitation reset time ratio and the constant current reference voltage;

[0048] When the circuit enters the constant current output mode, the constant current control parameter is set so that the secondary winding circuit can output a set constant current under different input voltages.

[0049] According to a second aspect of the present invention, an embodiment of the present invention provides a power system, comprising the PSR flyback conversion circuit as described in any one of the first aspect of the present invention.

[0050] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0051] In the PSR flyback conversion circuit, constant current control method and power system of the technical solution of the present invention, the circuit includes: a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, the auxiliary winding circuit is a voltage sensing circuit for PSR, and the switch tube control unit of the primary winding circuit is configured as follows: when the voltage at the second end of the power switch tube of the primary winding circuit is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode; and when the circuit enters the constant current output mode, based on the first voltage value sensed by the auxiliary winding circuit, at least the excitation reset time ratio is set, and the set excitation reset time ratio is greater than or equal to 0.5. When the input voltage of the present invention is much greater than the output reflected voltage N*Vo, it not only ensures that the secondary winding circuit can output the corresponding set constant current, but also reduces the primary and secondary RMS currents of the PSR flyback conversion circuit by increasing the excitation reset time ratio, thereby reducing the conduction loss and improving the efficiency.

[0052] Further, the method for enabling the secondary winding circuit to output a corresponding set constant current includes: comparing the first voltage value with the first threshold voltage, and determining the current value of the constant current output by the secondary winding circuit according to the comparison result, wherein: if the comparison result is characterized as the first voltage value being less than the first threshold voltage, then setting the excitation reset time ratio to a first ratio, so that the secondary winding circuit outputs a first set constant current; if the comparison result is characterized as the first voltage value being greater than or equal to the first threshold voltage, then setting the excitation reset time ratio to a second ratio, so that the secondary winding circuit outputs a second set constant current; wherein the first ratio is less than the second ratio. The present invention can set different excitation reset time ratios according to different input voltages, so that the secondary winding circuit outputs different set constant currents. At the same time, when the input voltage is much greater than the output reflected voltage N*Vo, by increasing the excitation reset time ratio, the peak current can be reduced, thereby reducing the primary and secondary RMS currents of the PSR flyback conversion circuit, thereby reducing the conduction loss and improving the efficiency.

[0053] Further, the switch control unit is also configured to: when the circuit enters the constant current output mode, at least set the excitation reset time ratio and the constant current reference voltage based on the first voltage value; then the method for enabling the secondary winding circuit to output the corresponding set constant current includes: based on the first voltage value, setting the constant current control parameter, the constant current control parameter being the product of the excitation reset time ratio and the constant current reference voltage; when the circuit enters the constant current output mode, setting the constant current control parameter so that under different input voltages, the secondary winding circuit can output the set constant current. Thus, the present invention can enable the circuit to output different constant currents under the same input voltage by setting the constant current control parameter, and can also enable the circuit to output the same constant current under different input voltages. When adjusting the excitation reset time ratio, the constant current reference voltage also changes accordingly. Without changing the constant current control parameter, reducing the constant current reference voltage can significantly reduce the primary and secondary RMS currents of the PSR flyback conversion circuit, thereby reducing the conduction loss and improving the efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0055] Figure 1 It is the key waveform diagram of PSR flyback in the prior art;

[0056] Figure 2 It is an output voltage and current curve waveform diagram of a PSR flyback circuit in a constant voltage control mode and a constant current control mode in the prior art;

[0057] Figure 3 is a structural diagram of a PSR flyback conversion circuit provided by an embodiment of the present invention;

[0058] Figure 4 It is a key waveform diagram of a PSR flyback conversion circuit in a constant current control mode provided by an embodiment of the present invention;

[0059] Figure 5 The following is a flow chart of a constant current control method provided by an embodiment of the present invention. Figure 1 ;

[0060] Figure 6 The following is a flow chart of a constant current control method provided by an embodiment of the present invention. Figure 2 ;

[0061] Figure 7 The following is a flow chart of a constant current control method provided by an embodiment of the present invention. Figure 3 ;

[0062] Figure 8 The following is a flow chart of a constant current control method provided by an embodiment of the present invention. Figure 4 .

[0063] Reference numerals:

[0064] Np-primary winding;

[0065] Naux - auxiliary winding;

[0066] Ns-secondary winding;

[0067] 10- switch tube control unit;

[0068] 11- Absorption module;

[0069] Q1-power switch tube;

[0070] D1-first diode;

[0071] Rup - the first voltage dividing resistor;

[0072] Rdw- the second voltage dividing resistor;

[0073] C1-first capacitor;

[0074] R1 - First resistor. DETAILED DESCRIPTION

[0075] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0076] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0077] The technical solution of the present invention is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0078] As described in the background technology, it is difficult in the prior art to reduce the primary-secondary RMS current of the PSR flyback conversion circuit and thus reduce the conduction loss when the input voltage is much larger than the secondary-side reflected voltage N*Vo, which will be described in detail below with reference to the accompanying drawings.

[0079] Please refer to Figure 1 and Figure 2 , Figure 1 shows the key waveforms of PSR flyback, Figure 2 The output voltage and current curves of the PSR flyback circuit in the constant voltage control mode and the constant current control mode are shown, where:

[0080] Vgs can be understood as a gate control signal for controlling the on / off of the power switch tube;

[0081] Vds, which can be understood as the voltage of the first end of the power switch tube;

[0082] Is, which can be understood as the secondary output winding current or the peak current;

[0083] V_vms, can be understood as the voltage waveform sensed by the auxiliary winding circuit;

[0084] I_vms can be understood as a current signal corresponding to the first voltage sensed by the auxiliary winding circuit;

[0085] V TH , can be understood as the first voltage sensed by the auxiliary winding circuit;

[0086] Trst can be understood as the excitation current reset time;

[0087] Td is understood as the oscillation time after the excitation current is reset;

[0088] Tp can be understood as the switching cycle time of the power switch tube;

[0089] Vo can be understood as the output voltage of the PSR flyback variation circuit;

[0090] CV, can be understood as constant voltage control mode;

[0091] CC, can be understood as constant current control mode;

[0092] I o , which can be understood as constant current output;

[0093] Po_max can be understood as the maximum output power point.

[0094] It can be seen that the PSR flyback variation circuit is configured as:

[0095] Before the maximum output current point, constant voltage control is adopted. The switch control unit samples the auxiliary winding voltage through the VMS pin to perform constant voltage control. The output voltage of the secondary winding circuit satisfies the following relationship:

[0096]

[0097] Among them, V ref is the constant voltage reference, N s is the number of turns of the secondary winding, N aux is the number of turns of the auxiliary winding, R up is the resistance of the first voltage divider resistor, R dw is the resistance of the second voltage divider resistor, V d is the conduction voltage drop of the output rectifier diode.

[0098] When the output current of the secondary winding circuit reaches the maximum output current I o_cc When the circuit output is at the maximum output power point, the circuit enters the constant current control mode. At this time, the excitation reset time ratio It usually reaches a maximum fixed value of 0.5. rst is the excitation current reset time, T p is the total switching period of the power switch tube.

[0099] In the constant current control mode, the output current of the secondary winding circuit remains unchanged, and the voltage of the secondary winding circuit changes based on the change of the load, wherein the output voltage decreases as the load increases, and the output current of the secondary winding circuit satisfies the relationship:

[0100] I o =I o_cc =0.5×I pk_max ×N×Kcc

[0101]

[0102] Where N is the turns ratio of the primary winding to the secondary winding, N = Np / Ns, I pk_max is the maximum peak current of the primary side, V cs_cc V for constant current cs Reference voltage, R cs is the resistance of the primary current sensing resistor.

[0103] The flyback current waveform under DCM is triangular, and its RMS current formula is:

[0104]

[0105] The average AVG current formula is:

[0106] I AVG =0.5×I pk ×D

[0107] Relationship between RMS current and AVG current:

[0108]

[0109] For the primary side, D = Ton / Tp; for the secondary side, D = Trst / Tp = Kcc;

[0110] Taking the secondary side as an example, I AVG That is, the output current Io. Under constant current conditions, increasing its D (Kcc) value can reduce I RMS The current can be reduced, and at the same time, its Ipk current can be reduced, the primary Ipk current is also reduced accordingly, and the primary RMS current can also be reduced.

[0111] It can be seen that increasing the Kcc value can reduce the Ipk peak current and reducing I RMS Current, improve efficiency, but Kcc will have a minimum value. When the input voltage is the lowest, it will usually enter CRM mode (critical conduction mode, Critical Conduction Mode), at this time:

[0112]

[0113] When Vin is minimum, 1-Kcc will be maximum, and Kcc reaches the minimum value. In order to take into account the withstand voltage requirements of the primary and secondary switching tubes, it is usually set at 0.5 when the input voltage is lowest.

[0114] The fixed value of Kcc can only take its minimum value of 0.5 to meet the output power requirements under the full voltage range. The circuit can only achieve a low conduction loss and high efficiency when the voltage difference between the input and output reflected voltage N*Vo is low. When the input voltage is much greater than N*Vo, the RMS current will be larger and the conduction loss will be large.

[0115] In view of this, the technical solution of the present invention provides a PSR flyback conversion circuit, the circuit includes: a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, the auxiliary winding circuit is a voltage sensing circuit for PSR, and the switch tube control unit of the primary winding circuit is configured as follows: when the voltage at the second end of the power switch tube of the primary winding circuit is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode; and when the circuit enters the constant current output mode, based on the first voltage value sensed by the auxiliary winding circuit, at least the excitation reset time ratio is set, and the set excitation reset time ratio is greater than or equal to 0.5. When the input voltage of the present invention is much greater than the output reflected voltage N*Vo, it not only ensures that the secondary winding circuit can output the corresponding set constant current, but also reduces the primary and secondary RMS currents of the PSR flyback conversion circuit by increasing the excitation reset time ratio, thereby reducing the conduction loss and improving the efficiency. As an example, the input voltage much greater than the output reflected voltage N*Vo can be understood as the input voltage being greater than 1.5 times the output reflected voltage. Of course, the present invention is not limited to this. Under different input voltages, the secondary winding circuit of the circuit of the present invention can output a corresponding set constant current, while reducing the primary and secondary RMS current of the PSR flyback conversion circuit, thereby reducing conduction losses and improving efficiency.

[0116] Please refer to Figure 3 The present invention provides a PSR flyback conversion circuit, comprising: a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, wherein the auxiliary winding circuit is a voltage sensing circuit for PSR, and the primary winding circuit comprises a primary winding Np, a switch tube control unit 10, a power switch tube Q1 and an absorption module 11;

[0117] The first end of the power switch tube Q1 is respectively coupled to the first end of the primary winding Np and the first end of the absorption module 11, the second end of the power switch tube Q1 is grounded through a detection resistor, the second end of the absorption module 11 is coupled to the second end of the primary winding Np, and the second end of the primary winding Np also receives the input voltage Vin;

[0118] The output end of the switch control unit 10 is coupled to the control end of the power switch Q1, and the first input end of the switch control unit 10 is coupled to the second end of the power switch Q1, for detecting the voltage V at the second end of the power switch Q1. cs The second input terminal of the switch control unit 10 is coupled to the output terminal of the auxiliary winding circuit, and is used to receive the first voltage value V sensed by the auxiliary winding circuit. TH ;

[0119] The switch tube control unit 10 is configured to: at a voltage V at the second end of the power switch tube Q1 cs Greater than or equal to the constant current reference voltage V cs_cc When , the circuit enters the constant current output mode; and

[0120] When the circuit enters the constant current output mode, based on the first voltage value V TH At least the excitation reset time ratio Kcc is set so that under different input voltages Vin, the secondary winding circuit can output a set constant current, wherein the excitation reset time ratio Kcc is the ratio of the excitation current reset time to the total switching period of the power switch tube Q1, and the excitation reset time ratio Kcc is greater than or equal to 0.5.

[0121] The excitation reset time ratio Kcc in the embodiment of the present invention has the following relationship:

[0122]

[0123] Among them, T rst is the excitation current reset time, T p is the total switching period of the power switch tube Q1.

[0124] In actual work, the excitation current reset time T rst The waveform detected by the second input terminal of the switch tube control unit 10 can be measured in real time. The switch tube control unit 10 controls the total switching period T of the power switch tube Q1. p , thereby controlling the excitation reset time ratio Kcc.

[0125] Of course, the present invention also needs to limit the maximum value of the excitation reset time ratio Kcc. If the excitation reset time ratio Kcc is too large, it will limit the duty cycle when the input voltage Vin is at a low voltage, causing the circuit to be unable to output the maximum output power. In addition, in the embodiment of the present invention, the circuit needs to be in at least DCM mode or QR mode to normally enter the CC (constant current) state. Therefore, when setting the maximum value of the excitation reset time ratio Kcc, the minimum value of the input voltage Vin in the circuit can be considered to correspond to the required duty cycle of the power switch tube Q1.

[0126] For details, please continue to refer to Figure 3 In the example of , the secondary winding circuit includes a secondary winding Ns, before setting the excitation reset time ratio Kcc, the method further includes:

[0127] Determining the maximum value of the excitation reset time ratio Kcc that can be set includes:

[0128] Obtain the turns ratio of the primary winding Np to the secondary winding Ns, the voltage value of the input voltage Vin, and the voltage value V output by the secondary winding Ns circuit. o ;

[0129] Based on the turns ratio of the primary winding Np to the secondary winding Ns, the voltage value of the input voltage Vin, and the voltage value V output by the secondary winding Ns circuit o , obtaining the minimum duty cycle of the power switch tube Q1;

[0130] Based on the minimum duty cycle, a maximum value of the excitation reset time ratio Kcc that can be set is obtained.

[0131] Specifically, in DCM and CRM modes, the duty cycle requirement D that meets the output power requirement corresponds to the following relationship:

[0132]

[0133] Wherein, N is the turns ratio of the primary winding Np to the secondary winding Ns, Vo is the voltage value output by the secondary winding Ns circuit, and Vin is the voltage value of the input voltage Vin.

[0134] The duty cycle requirement D of the power switch tube Q1 also corresponds to the relationship:

[0135] D=1-Kcc

[0136] It can be seen that for a fixed output voltage and turns ratio, N×Vo is a certain value. As the input voltage Vin decreases, the duty cycle requirement D will increase. As long as the lowest input voltage Vin is determined, the minimum value that Kcc can be set to in actual use can be determined.

[0137] In a preferred embodiment, after the circuit enters the constant current output mode and before setting the excitation reset time ratio Kcc, the switch tube control unit 10 is further configured as follows:

[0138] Set the constant current reference voltage V cs_cc is the default constant current reference voltage, and the excitation reset time ratio Kcc is the default excitation reset time ratio.

[0139] It can be seen that the present invention can first work with the default constant current reference voltage and the default excitation reset time ratio, and then make corresponding adjustments, so that the control safety of the present invention is higher and can adapt to the PSR flyback conversion circuit of various working conditions.

[0140] The embodiments of the present invention provide two methods for outputting a set constant current while reducing the RMS current, which are now further described.

[0141] In one implementation, based on the first voltage value V TH At least the excitation reset time ratio Kcc is set so that the secondary winding Ns circuit can output a corresponding set constant current, including:

[0142] Compare the first voltage value V TH and the first threshold voltage, and determine the current value of the constant current output by the secondary winding Ns circuit according to the comparison result, wherein:

[0143] If the comparison result is characterized by the first voltage value V TH is less than a first threshold voltage, setting the excitation reset time ratio Kcc to a first ratio, so that the secondary winding Ns circuit outputs a first set constant current;

[0144] If the comparison result is characterized by the first voltage value V TH is greater than or equal to the first threshold voltage, setting the excitation reset time ratio Kcc to a second ratio, so that the secondary winding Ns circuit outputs a second set constant current;

[0145] Wherein, the first ratio is smaller than the second ratio.

[0146] This embodiment is suitable for applications where different output constant current control points are required for high input voltage Vin (greater than 255Vdc) and low input voltage Vin (less than 180Vdc). In this case, the value range of the first threshold voltage is 180Vdc to 255Vdc.

[0147] Of course, the first threshold voltage may be a voltage or a voltage range between 180 Vdc and 255 Vdc, and the present invention is not limited thereto.

[0148] It should be understood that the present invention does not limit the number of input voltage segments. The input voltage can be divided into a high voltage segment and a low voltage segment, or can be divided into more segments for processing. Those skilled in the art can segment the input voltage as needed.

[0149] It can be seen that through this method, the present invention can set different excitation reset time ratios Kcc according to different input voltages Vin, so that the secondary winding Ns circuit outputs constant currents with different settings, and can also allow the system to operate in a state close to the CRM state, thereby reducing the RMS current of the primary and secondary, reducing conduction losses, and improving efficiency, so that higher efficiency can be achieved within the entire voltage input range.

[0150] The effect of this implementation is now described, please refer to Figure 4 , Figure 4 The key waveform diagram of the PSR flyback conversion circuit in the constant current control mode provided by the embodiment of the present invention; Figure 4 In the example of , the first set constant current is equal to the second set constant current, wherein:

[0151] Vin, can be understood as the input voltage Vin;

[0152] Vgs can be understood as a gate control signal for controlling the on / off of the power switch tube Q1;

[0153] Vcs, can be understood as the voltage V at the second end of the power switch tube Q1 cs or peak voltage;

[0154] Vds, which can be understood as the voltage of the first end of the power switch tube Q1;

[0155] Is, which can be understood as the secondary output winding current or the peak current;

[0156] V_vms can be understood as the voltage waveform sensed by the auxiliary winding circuit;

[0157] I_vms can be understood as the first voltage value V sensed by the auxiliary winding circuit TH The corresponding current;

[0158] V TH , can be understood as the first voltage value sensed by the auxiliary winding circuit.

[0159] It can be seen that in Figure 4 In the example, before time t1, the comparison result is characterized by the first voltage value V TH is less than the first threshold voltage ( Figure 4 The excitation reset time ratio Kcc is set to the first ratio (Kcc=Trst1 / Tp1). After time t2, the comparison result is characterized by the first voltage value V TH is greater than or equal to the first threshold voltage, and the excitation reset time ratio Kcc is set to a second ratio (Kcc=Trst2 / Tp2).

[0160] The output current of the secondary winding Ns circuit satisfies the following relationship:

[0161] I o =I o_cc =0.5×I pk_max ×N×Kcc

[0162]

[0163] Where, N is the turns ratio of the primary winding Np to the secondary winding Ns, I pk_max is the maximum peak current, V cs_cc is the constant current reference voltage V cs_cc , R cs is the resistance value of the detection resistor.

[0164] While ensuring that the output constant current remains unchanged, by increasing the excitation reset time ratio Kcc, the peak current and peak voltage can be reduced, thereby reducing the RMS current of the PSR flyback conversion circuit and reducing the conduction loss.

[0165] In another embodiment, the switch control unit 10 is further configured to: when the circuit enters the constant current output mode, based on the first voltage value V TH At least set the excitation reset time ratio Kcc and the constant current reference voltage V cs_cc ;

[0166] The method for enabling the secondary winding Ns circuit to output a corresponding set constant current includes:

[0167] Based on the first voltage value V TH , set the constant current control parameter, the constant current control parameter is the excitation reset time ratio Kcc and the constant current reference voltage V cs_cc The product of

[0168] When the circuit enters the constant current output mode, the constant current control parameters are set so that the secondary winding Ns circuit can output the set constant current under different input voltages Vin.

[0169] Wherein, the constant current control parameter m has the following relational expression:

[0170] n=Kcc×V cs_cc

[0171] Among them, V cs_cc It is the Vcs reference voltage during constant current.

[0172] The output current of the secondary winding Ns circuit satisfies the following relationship:

[0173] Io =I o_cc =0.5×I pk_max ×N×Kcc

[0174]

[0175] Where, N is the turns ratio of the primary winding Np to the secondary winding Ns, I pk_max is the maximum peak current, V cs_cc is the constant current reference voltage V cs_cc , R cs is the resistance value of the detection resistor.

[0176] It can be seen that the present invention can make the circuit output different constant currents under the same input voltage Vin by setting the constant current control parameters to change, and can also make the circuit output the same constant current under different input voltages Vin by setting the constant current control parameters unchanged.

[0177] In this implementation, the RMS current of the PSR flyback conversion circuit can also be reduced, thereby reducing the conduction loss, so that the system can operate in a state close to the CRM working state when fully loaded, with higher conversion efficiency.

[0178] Specifically, the secondary side RMS current I RMS There is also the following relationship:

[0179] I oavg =0.5×I pks ×Kcc

[0180]

[0181] Among them, I pks is the peak current on the secondary side, which is proportional to the peak current on the primary side. oavg is the average current output on the secondary side.

[0182] It can be seen that the present invention can adjust the excitation reset time ratio Kcc and the constant current reference voltage V cs_cc The size of the PSR flyback converter circuit is reduced, thereby reducing the RMS current and conduction loss.

[0183] Now, the excitation current reset time T is obtained by real-time measurement of the waveform detected by the second input terminal of the switch tube control unit 10. rst way of explaining.

[0184] In one implementation, please refer to Figure 3 , the auxiliary winding circuit includes an auxiliary winding Naux, a first diode D1, a first voltage-dividing resistor Rup, a second voltage-dividing resistor Rdw, a first capacitor C1 and a first resistor R1;

[0185] The first end of the auxiliary winding Naux is coupled to the first end of the first voltage-dividing resistor Rup and the anode of the first diode D1, the second end of the first voltage-dividing resistor Rup is coupled to the first end of the second voltage-dividing resistor Rdw, the second end of the first voltage-dividing resistor Rup is also coupled to the second input end of the switch tube control unit 10 to output a first signal, the cathode of the first diode D1 is coupled to the first end of the first capacitor C1, the second end of the second voltage-dividing resistor Rdw is respectively coupled to the second end of the auxiliary winding Naux and the second end of the first capacitor C1, the first resistor R1 is connected in parallel with the first capacitor C1; wherein the first signal includes a first voltage value V sensed by the auxiliary winding Naux circuit TH information.

[0186] In one embodiment, the excitation current reset time T is obtained by measuring the voltage waveform detected by the second input terminal of the switch tube control unit 10 in real time. rst .

[0187] In this case, after setting the excitation reset time ratio Kcc, the method further includes:

[0188] Based on the V_ VMS The excitation current reset time T is obtained rst ;

[0189] Based on the excitation reset time ratio Kcc and the excitation current reset time T rst , determine the total switching period T of the power switch tube Q1 p .

[0190] In another embodiment, the first signal is a current signal, and the switch control unit 10 is configured as follows:

[0191] When the power switch tube Q1 is turned on, a first voltage value V sensed by the auxiliary winding Naux circuit is obtained according to the current flowing through the first voltage divider resistor Rup. TH information.

[0192] In this case, the method also corresponds to obtaining the excitation current reset time T based on the current waveform flowing through the first voltage-dividing resistor Rup. rst .

[0193] For example, when the power switch tube Q1 is turned on, the voltage at the first end of the auxiliary winding Naux is -V in ×N aux ÷N p , the current of I_vms is approximately V aux÷R up , the current value is negative and the direction is Figure 3 The switch control unit 10 obtains the first voltage value V sensed by the auxiliary winding Naux circuit according to the circuit. TH information.

[0194] V TH =I_th×Rup×Np÷Naux

[0195] In addition, the embodiment of the present invention further provides a constant current control method for controlling the output current of the secondary winding circuit of the PSR flyback conversion circuit described in any one of the above items, please refer to Figure 5 , the method comprising:

[0196] S1: Obtaining the voltage of the second end of the power switch tube;

[0197] S2: When the voltage at the second end of the power switch tube is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode and performs the following steps:

[0198] S3: Based on the first voltage value, at least the excitation reset time ratio is set so that under different input voltages, the secondary winding circuit can output a set constant current, wherein the excitation reset time ratio is the ratio of the excitation current reset time to the total switching period of the power switch tube, and the excitation reset time ratio is greater than or equal to 0.5.

[0199] Therefore, under different input voltages, the secondary winding circuit of the present invention can output a corresponding set constant current, while reducing the RMS current of the PSR flyback conversion circuit, thereby reducing the conduction loss.

[0200] In a preferred embodiment, please refer to Figure 6 , step S2 comprises:

[0201] S21: setting the constant current reference voltage to a default constant current reference voltage, and the excitation reset time ratio to a default excitation reset time ratio;

[0202] S22: When the voltage at the second end of the power switch tube is greater than or equal to the default constant current reference voltage, the circuit enters a constant current output mode with a default excitation reset time ratio.

[0203] It can be seen that the present invention can first work with the default constant current reference voltage and the default excitation reset time ratio, and then make corresponding adjustments, so that the control safety of the present invention is higher and can adapt to the PSR flyback conversion circuit of various working conditions.

[0204] Regarding step S3, in one implementation, please refer to Figure 7 , step S3 comprises:

[0205] S311: comparing the first voltage value with a first threshold voltage. If the comparison result indicates that the first voltage value is less than the first threshold voltage, proceed to S312; if the comparison result indicates that the first voltage value is greater than or equal to the first threshold voltage, proceed to S313.

[0206] S312: Setting the excitation reset time ratio to a first ratio so that the secondary winding circuit outputs a first set constant current;

[0207] S313: Setting the excitation reset time ratio to a second ratio so that the secondary winding circuit outputs a second set constant current; wherein the first ratio is smaller than the second ratio.

[0208] The present invention can set different excitation reset time ratios according to different input voltages, so that different constant current settings are output in the secondary winding circuit. At the same time, when the voltage difference between the input voltage and the output voltage is large, the peak current can be reduced by increasing the excitation reset time ratio, thereby reducing the RMS current of the PSR flyback conversion circuit and reducing the conduction loss.

[0209] In another embodiment, when the circuit enters the constant current output mode, at least the excitation reset time ratio and the constant current reference voltage are set based on the first voltage value;

[0210] In this case, please refer to Figure 8 , step S3 comprises:

[0211] S321: Based on the first voltage value, setting a constant current control parameter, the constant current control parameter being the product of the excitation reset time ratio and the constant current reference voltage;

[0212] S322: When the circuit enters the constant current output mode, the constant current control parameter is set so that the secondary winding circuit can output a set constant current under different input voltages.

[0213] Therefore, the present invention can set the constant current control parameters so that the circuit can output different constant currents under the same input voltage, and can also enable the circuit to output the same constant current under different input voltages. When adjusting the excitation reset time ratio, the constant current reference voltage also changes accordingly. Without changing the constant current control parameters, lowering the constant current reference voltage can significantly reduce the RMS current of the PSR flyback conversion circuit, thereby reducing the conduction loss.

[0214] In addition, an embodiment of the present invention further provides a power system, including any of the above-mentioned PSR flyback conversion circuits. As an example, the power system can be a power system with a low voltage and high current output on the secondary side, such as a low voltage power system with a high voltage difference of 90Vac to 264Vac and an output voltage of 3V, 5V, or 12V on the secondary winding circuit.

[0215] Of course, the present invention does not limit the specific power system in which the PSR flyback conversion circuit is applied, and those skilled in the art can select a suitable system as needed.

[0216] In summary, the embodiment of the present invention sets a circuit including: a primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, the auxiliary winding circuit is a voltage sensing circuit for PSR, and the switch tube control unit of the primary winding circuit is configured as follows: when the voltage at the second end of the power switch tube of the primary winding circuit is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode; and when the circuit enters the constant current output mode, based on the first voltage value sensed by the auxiliary winding circuit, at least the excitation reset time ratio is set, and the set excitation reset time ratio is greater than or equal to 0.5. In this way, under different input voltages, the secondary winding circuit of the present invention can output a corresponding set constant current, while reducing the RMS current of the PSR flyback conversion circuit, thereby reducing the conduction loss.

[0217] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A PSR flyback conversion circuit, characterized in that: include: A primary winding circuit, a secondary winding circuit and an auxiliary winding circuit, wherein the auxiliary winding circuit is a voltage sensing circuit for PSR, and the primary winding circuit includes a primary winding, a switch tube control unit, a power switch tube and an absorption module; The first end of the power switch tube is respectively coupled to the first end of the primary winding and the first end of the absorption module, the second end of the power switch tube is grounded through a detection resistor, the second end of the absorption module is coupled to the second end of the primary winding, and the second end of the primary winding also receives an input voltage; The output end of the switch tube control unit is coupled to the control end of the power switch tube, the first input end of the switch tube control unit is coupled to the second end of the power switch tube, and is used to detect the voltage of the second end of the power switch tube, and the second input end of the switch tube control unit is coupled to the output end of the auxiliary winding circuit, and is used to receive the first voltage value sensed by the auxiliary winding circuit; The switch tube control unit is configured to: when the voltage at the second end of the power switch tube is greater than or equal to the constant current reference voltage, the circuit enters a constant current output mode; as well as When the circuit enters the constant current output mode, at least the excitation reset time ratio is set based on the first voltage value, so that under different input voltages, the secondary winding circuit can output the set constant current, wherein the excitation reset time ratio is the ratio of the excitation current reset time to the total switching period of the power switch tube, and the excitation reset time ratio is greater than or equal to 0.

5.

2. The PSR flyback converter circuit according to claim 1, characterized in that: At least setting the excitation reset time ratio based on the first voltage value so that the secondary winding circuit can output a corresponding set constant current includes: The first voltage value is compared with the first threshold voltage, and the current value of the constant current output by the secondary winding circuit is determined according to the comparison result, wherein: If the comparison result indicates that the first voltage value is less than a first threshold voltage, setting the excitation reset time ratio to a first ratio so that the secondary winding circuit outputs a first set constant current; If the comparison result indicates that the first voltage value is greater than or equal to a first threshold voltage, setting the excitation reset time ratio to a second ratio so that the secondary winding circuit outputs a second set constant current; Wherein, the first ratio is smaller than the second ratio.

3. The PSR flyback converter circuit according to claim 2, characterized in that: The first threshold voltage has a value range of 180 Vdc to 255 Vdc.

4. The PSR flyback converter circuit according to claim 1, characterized in that: The switch control unit is further configured to: when the circuit enters a constant current output mode, at least set an excitation reset time ratio and a constant current reference voltage based on the first voltage value; The method for enabling the secondary winding circuit to output a corresponding set constant current includes: Based on the first voltage value, a constant current control parameter is set, wherein the constant current control parameter is the product of the excitation reset time ratio and the constant current reference voltage; When the circuit enters the constant current output mode, the constant current control parameter is set so that the secondary winding circuit can output a set constant current under different input voltages.

5. The PSR flyback converter circuit according to claim 1, characterized in that: The secondary winding circuit includes a secondary winding, and before setting the excitation reset time ratio, the method further includes: Determining the maximum value of the excitation reset time ratio that can be set includes: Obtaining a turns ratio of the secondary winding to the primary winding, a voltage value of the input voltage, and a voltage value output by the secondary winding circuit; Obtaining a minimum duty cycle of the power switch tube based on a turns ratio of the secondary winding to the primary winding, a voltage value of the input voltage, and a voltage value output by the secondary winding circuit; Based on the minimum duty cycle, a maximum value of the excitation reset time ratio that can be set is obtained.

6. The PSR flyback converter circuit according to any one of claims 1 to 5, characterized in that: The auxiliary winding circuit includes an auxiliary winding, a first diode, a first voltage-dividing resistor, a second voltage-dividing resistor, a first capacitor and a first resistor; The first end of the auxiliary winding is coupled to the first end of the first voltage-dividing resistor and the positive electrode of the first diode, the second end of the first voltage-dividing resistor is coupled to the first end of the second voltage-dividing resistor, and the second end of the first voltage-dividing resistor is also coupled to the second input end of the switch tube control unit to output a first signal, the cathode of the first diode is coupled to the first end of the first capacitor, the second end of the second voltage-dividing resistor is respectively coupled to the second end of the auxiliary winding and the second end of the first capacitor, and the first resistor is connected in parallel with the first capacitor; wherein, the first signal includes the first voltage value information sensed by the auxiliary winding circuit.

7. The PSR flyback converter circuit according to claim 6, characterized in that: After setting the excitation reset time ratio, the method further includes: Based on the waveform of the first voltage value, obtaining the excitation current reset time; Based on the excitation reset time ratio and the excitation current reset time, a total switching period of the power switch tube is determined.

8. The PSR flyback converter circuit according to claim 7, characterized in that: If the first signal is a current signal, the switch tube control unit is configured as follows: When the power switch tube is turned on, the first voltage value information sensed by the auxiliary winding circuit is obtained according to the current flowing through the first voltage-dividing resistor.

9. The PSR flyback converter circuit according to claim 1, characterized in that: After the circuit enters the constant current output mode and before setting the excitation reset time ratio, the switch tube control unit is further configured as follows: The constant current reference voltage is set to be a default constant current reference voltage, and the excitation reset time ratio is set to be a default excitation reset time ratio.

10. A constant current control method, characterized in that: The method for controlling the output current of the secondary winding circuit of the PSR flyback conversion circuit according to any one of claims 1 to 9 comprises: Obtaining a voltage at the second end of the power switch tube; When the voltage at the second end of the power switch tube is greater than or equal to the constant current reference voltage, the circuit enters the constant current output mode and performs the following steps: Based on the first voltage value, at least the excitation reset time ratio is set so that under different input voltages, the secondary winding circuit can output a set constant current, wherein the excitation reset time ratio is the ratio of the excitation current reset time to the total switching period of the power switch tube, and the excitation reset time ratio is greater than or equal to 0.

5.

11. The constant current control method according to claim 10, characterized in that: At least setting the excitation reset time ratio based on the first voltage value so that the secondary winding circuit can output a corresponding set constant current includes: The first voltage value is compared with the first threshold voltage, and the current value of the constant current output by the secondary winding circuit is determined according to the comparison result, wherein: If the comparison result indicates that the first voltage value is less than a first threshold voltage, setting the excitation reset time ratio to a first ratio so that the secondary winding circuit outputs a first set constant current; If the comparison result indicates that the first voltage value is greater than or equal to a first threshold voltage, setting the excitation reset time ratio to a second ratio so that the secondary winding circuit outputs a second set constant current; Wherein, the first ratio is smaller than the second ratio.

12. The constant current control method according to claim 10, characterized in that: When the circuit enters the constant current output mode, at least the excitation reset time ratio and the constant current reference voltage are set based on the first voltage value; The method for enabling the secondary winding circuit to output a corresponding set constant current includes: Based on the first voltage value, a constant current control parameter is set, wherein the constant current control parameter is the product of the excitation reset time ratio and the constant current reference voltage; When the circuit enters the constant current output mode, the constant current control parameter is set so that the secondary winding circuit can output a set constant current under different input voltages.

13. A power system, characterized in that: The invention comprises the PSR flyback conversion circuit as described in any one of claims 1 to 9.

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