Variable frequency starting method and system of flyback power supply

Abstract

The invention relates to the technical field of flyback switching power supplies, in particular to a variable frequency starting method and system of a flyback power supply. Comprising a frequency control module, a voltage detection module, a power conversion module and a feedback module, the frequency control module sets the lowest frequency and limits the peak current during starting, the lowest frequency prolongs the demagnetization time, the limiting current reduces the storage energy, and the two cooperate to ensure that the energy of a transformer is completely released before next switching. A deep continuous state is avoided, the voltage detection module monitors the output voltage in real time and ensures that the frequency switching time is accurate (supporting dynamic adjustment), the power conversion module transmits energy under low frequency and small current, primary and secondary common energy is reduced, and therefore the peak of an output diode is restrained. The system reliability is improved, and the system design is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of flyback switching power supplies, and particularly to a frequency conversion starting method and system for a flyback power supply. Background Art

[0002] Traditional secondary feedback flyback power supplies usually operate in a fixed frequency mode. During the startup phase, the system starts with the maximum fixed frequency while limiting the primary peak current. At this time, since the output voltage is close to 0 and the demagnetization time is relatively long, the system operates in a deep continuous state. This operating state can cause a very large spike voltage to be generated across the output diode, which easily leads to diode failure.

[0003] In the prior art, this problem is usually alleviated only by limiting the primary peak current, but the effect is limited. The main reasons are as follows:

[0004] Under the fixed frequency operating mode, the demagnetization time is insufficient;

[0005] The excessive common energy causes the diode to withstand too high a voltage stress.

[0006] Therefore, a technical solution that can effectively reduce the spike of the output diode during the startup phase is needed. Summary of the Invention

[0007] The purpose of the present invention is to provide a frequency conversion starting method and system for a flyback power supply, so as to solve the problem that when only limiting the primary peak current to alleviate the problem that the diode is prone to failure when the secondary feedback flyback power supply operates in a deep continuous state, the effect is limited.

[0008] To achieve the above purpose, the present invention provides a frequency conversion starting system for a flyback power supply. The frequency conversion starting system for the flyback power supply includes a frequency control module, a voltage detection module, a power conversion module, and a feedback module. The frequency control module is used to set the operating frequency to a preset minimum frequency and limit the primary peak current during the startup phase, and at the same time control the rising slope of the MOS tube turn-on. The voltage detection module is used to detect the output voltage state in real time. The power conversion module is used to achieve the energy transfer from the primary side to the secondary side. The feedback module feeds back the secondary side voltage error to the primary side through opto-isolation;

[0009] The frequency control module dynamically adjusts the operating frequency according to the output signal of the voltage detection module, so that the startup system of the flyback power supply gradually transitions from the lowest frequency at startup to the rated operating frequency.

[0010] Among them, the physical implementation carrier of the frequency control module is the CR6900H chip. The frequency control module includes a frequency control unit, a peak current limiting unit, and a soft drive unit. The frequency control unit is configured to maintain the lowest frequency when the output voltage does not reach the threshold, and linearly increase the frequency to the rated value after the output voltage reaches the threshold. The peak current limiting unit is configured to limit the primary peak current to 30%-50% of the rated value during the startup phase. The soft drive unit is configured to reduce the common energy by reducing the rising slope of the MOS transistor gate drive signal.

[0011] Among them, the specific implementation content of the voltage detection module is as follows:

[0012] Using an auxiliary winding voltage sampling circuit, whose output voltage satisfies the relationship:

[0013]

[0014] Among them, V AUX is the auxiliary winding voltage, is the ratio of the auxiliary winding to the secondary winding, V O is the output voltage, and ΔV is the output diode voltage drop;

[0015] The PRT pin of the CR6900H chip, which is the physical implementation carrier of the frequency control module, is connected to V PRT through a resistor R AUX . By detecting the current I PRT flowing into the PRT pin, the state of the output voltage V O can be reflected.

[0016] Among them, the voltage detection module further includes a voltage dividing unit, which consists of high-precision resistors R*, and is used to divide the auxiliary winding voltage V AUX to an amplitude suitable for detection.

[0017] Among them, in the voltage detection module, the relationship for using the current I PRT of the PRT pin to feedback the output voltage V O is:

[0018]

[0019] Using the CR6900H chip, which is the physical implementation carrier of the frequency control module, the state of the output voltage V PRT can be deduced by measuring I O .

[0020] Among them, the power conversion module includes a transformer and an output diode. The output diode uses a fast recovery diode, and its reverse recovery time is less than 100 ns.

[0021] Among them, the feedback module includes a TL431 reference error amplifier and an optocoupler isolation circuit. The TL431 reference error amplifier is used to generate an error signal proportional to the output voltage deviation, and the optocoupler isolation circuit is used to transmit the error signal to the feedback pin of the frequency control module.

[0022] The present invention also provides a frequency conversion startup method for a flyback power supply, which is applied to the frequency conversion startup system of the flyback power supply as described above, and includes the following steps:

[0023] When powered on, the frequency control module sets the operating frequency to the lowest frequency;

[0024] Limit the primary peak current to 30%-50% of the rated value;

[0025] Sample and monitor the output voltage in real time through the voltage detection module;

[0026] When the output voltage reaches 10% of the rated value, cooperate with the power conversion module through the frequency control module to linearly increase the operating frequency;

[0027] When the output voltage reaches 90% of the rated value, switch to the rated operating frequency, the feedback module takes over the closed-loop control, and the frequency control module switches to the conventional PWM mode.

[0028] A frequency conversion startup method and system for a flyback power supply according to the present invention includes a frequency control module, a voltage detection module, a power conversion module, and a feedback module. The frequency control module sets the lowest frequency and limits the peak current during startup. The lowest frequency extends the demagnetization time, and the limited current reduces the stored energy. The two work together to ensure that the energy of the transformer is completely released before the next switch, avoiding the deep continuous state. The voltage detection module monitors the output voltage in real time to ensure accurate frequency switching timing (supporting dynamic adjustment). The power conversion module transmits energy at low frequency and small current, reducing the common energy between the primary and secondary, thereby suppressing the output diode spike. This technical solution effectively reduces the output diode spike during startup, improves the system reliability, and simplifies the system design. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is an application diagram of the frequency conversion startup system of the flyback power supply provided by the present invention.

[0031] Figure 2 It is the flowchart of the steps of the frequency conversion startup method of the flyback power supply provided by the present invention.

[0032] 101 is a transformer, 102 is an output diode, 103 is an opto-isolation circuit, 104 is a CR6900H chip, and 105 is a TL431 reference error amplifier. Detailed implementation manners

[0033] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0034] The present invention provides a frequency conversion startup system for a flyback power supply. The frequency conversion startup system for the flyback power supply includes a frequency control module, a voltage detection module, a power conversion module, and a feedback module. The frequency control module is used to set the operating frequency to a preset minimum frequency and limit the primary peak current during the startup phase, and at the same time control the rising slope of the MOS tube turn-on. The voltage detection module is used to detect the output voltage state in real time. The power conversion module is used to achieve energy transfer from the primary side to the secondary side. The feedback module feeds back the secondary side voltage error to the primary side through opto-isolation;

[0035] The frequency control module dynamically adjusts the operating frequency according to the output signal of the voltage detection module, so that the startup system of the flyback power supply gradually transitions from the minimum frequency at startup to the rated operating frequency.

[0036] In this embodiment, the frequency control module sets the minimum frequency and limits the peak current at startup. The minimum frequency prolongs the demagnetization time, and the limited current reduces the stored energy. The two work together to ensure that the energy of the transformer 101 is completely released before the next switch, avoiding the deep continuous state. The voltage detection module monitors the output voltage in real time to ensure the accuracy of the frequency switching timing (supporting dynamic adjustment). The power conversion module transfers energy at low frequency and small current, reducing the common energy between the primary and secondary sides, thereby suppressing the spike of the output diode 102. This technical solution effectively reduces the spike of the output diode 102 at startup, improves the system reliability, and simplifies the system design.

[0037] Further, the physical implementation carrier of the frequency control module is the CR6900H chip 104. The frequency control module includes a frequency control unit, a peak current limiting unit, and a soft drive unit. The frequency control unit is configured to maintain the lowest frequency when the output voltage does not reach the threshold, and linearly increase the frequency to the rated value after the output voltage reaches the threshold. The peak current limiting unit is configured to limit the primary peak current to 30%-50% of the rated value during the startup phase. The soft drive unit is configured to reduce the common energy by decreasing the rising slope of the MOS transistor gate drive signal.

[0038] Further, the specific implementation content of the voltage detection module is as follows:

[0039] Using an auxiliary winding voltage sampling circuit, whose output voltage satisfies the relationship:

[0040]

[0041] where, V AUX is the auxiliary winding voltage, is the ratio of the auxiliary winding to the secondary winding, V O is the output voltage, and ΔV is the output diode voltage drop;

[0042] The PRT pin of the CR6900H chip 104, which is the physical implementation carrier of the frequency control module, is connected to V PRT through a resistor R AUX . By detecting the current I PRT flowing into the PRT pin, the state of the output voltage V O can be reflected.

[0043] Further, the voltage detection module further includes a voltage division unit, which consists of high-precision resistors R* and is used to divide the auxiliary winding voltage V AUX to an amplitude suitable for detection.

[0044] Further, in the voltage detection module, the relationship for using the current I PRT of the PRT pin to feedback the output voltage V O is:

[0045]

[0046] Using the CR6900H chip 104, which is the physical implementation carrier of the frequency control module, the state of the output voltage V PRT can be deduced by measuring I O .

[0047] Further, the power conversion module includes a transformer 101 and an output diode 102. The output diode 102 is a fast recovery diode with a reverse recovery time less than 100 ns.

[0048] Further, the feedback module includes a TL431 reference error amplifier 105 and an opto-isolation circuit 103. The TL431 reference error amplifier 105 is used to generate an error signal proportional to the output voltage deviation, and the opto-isolation circuit 103 is used to transmit the error signal to the feedback pin of the frequency control module.

[0049] In summary, please refer to Figure 1 , where Figure 1 is the application diagram of the frequency conversion startup system of the flyback power supply provided by the present invention.

[0050] Please refer to Figure 2 , the present invention also provides a frequency conversion startup method for a flyback power supply, which is applied to the frequency conversion startup system of the flyback power supply as described above, and includes the following steps:

[0051] S1: When power is applied, the frequency control module sets the operating frequency to the lowest frequency;

[0052] S2: Limit the primary peak current to 30%-50% of the rated value;

[0053] S3: Sampling and real-time monitoring of the output voltage through the voltage detection module;

[0054] S4: When the output voltage reaches 10% of the rated value, linearly increase the operating frequency through the cooperation of the frequency control module and the power conversion module;

[0055] S5: When the output voltage reaches 90% of the rated value, switch to the rated operating frequency, the feedback module takes over the closed-loop control, and the frequency control module switches to the conventional PWM mode.

[0056] In this embodiment, when power is applied, the frequency control module sets the operating frequency to the lowest frequency and limits the primary peak current to 30%-50% of the rated value. The output voltage is sampled and real-time monitored through the voltage detection module. When it is detected that the output voltage reaches 10% of the rated value, the operating frequency is linearly increased through the cooperation of the frequency control module and the power conversion module. When it is detected that the output voltage reaches 90% of the rated value, switch to the rated operating frequency, the feedback module takes over the closed-loop control, and the frequency control module switches to the conventional PWM mode.

[0057] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A variable frequency starting system for a flyback power supply, characterized in that: It includes a frequency control module, a voltage detection module, a power conversion module and a feedback module. The frequency control module is used to set the operating frequency to a preset minimum frequency and limit the primary peak current during the startup phase, and at the same time control the rising slope of the MOS tube. The voltage detection module is used to detect the output voltage state in real time. The power conversion module is used to realize energy transmission from the primary side to the secondary side. The feedback module feeds back the secondary side voltage error to the primary side through optocoupler isolation. The frequency control module dynamically adjusts the operating frequency according to the output signal of the voltage detection module, so that the start-up system of the flyback power supply gradually transitions from the lowest frequency at startup to the rated operating frequency.

2. The variable frequency starting system of the flyback power supply according to claim 1, characterized in that: The physical implementation carrier of the frequency control module is a CR6900H chip. The frequency control module includes a frequency control unit, a peak current limiting unit and a soft drive unit. The frequency control unit is configured to maintain the minimum frequency when the output voltage does not reach the threshold, and linearly increase the frequency to the rated value after the output voltage reaches the threshold. The peak current limiting unit is configured to limit the primary peak current to 30%-50% of the rated value during the startup phase, and the soft drive unit is configured to reduce the common energy by reducing the rising slope of the MOS tube gate drive signal.

3. The variable frequency starting system of the flyback power supply according to claim 2, characterized in that: The specific implementation content of the voltage detection module is: Using the auxiliary winding voltage sampling circuit, the output voltage satisfies the relationship: Among them, V AUX is the auxiliary winding voltage, is the ratio of the auxiliary winding to the secondary winding, V O is the output voltage, ΔV is the output diode voltage drop; The frequency control module is physically implemented on the carrier CR6900H chip. The PRT pin is connected to the CR6900H chip through a resistor R PRT Connect to V AUX , by detecting the current I flowing into the PRT pin PRT , then the output voltage V O status.

4. The variable frequency starting system of the flyback power supply according to claim 3, characterized in that: The voltage detection module also includes a voltage dividing unit, which is composed of a high-precision resistor R* and is used to divide the auxiliary winding voltage V AUX Divide the voltage to an amplitude suitable for detection.

5. The variable frequency starting method and system of the flyback power supply according to claim 4, characterized in that: In the voltage detection module, the current I of the PRT pin is used. PRT Feedback output voltage V O The relationship is: The physical implementation carrier CR6900H chip of the frequency control module can be measured by I PRT Reverse output voltage V O status.

6. The variable frequency starting system of the flyback power supply according to claim 5, characterized in that: The power conversion module comprises a transformer and an output diode. The output diode adopts a fast recovery diode, and its reverse recovery time is less than 100ns.

7. The variable frequency starting system of the flyback power supply according to claim 6, characterized in that: The feedback module includes a TL431 reference error amplifier and an optocoupler isolation circuit. The TL431 reference error amplifier is used to generate an error signal proportional to the output voltage deviation, and the optocoupler isolation circuit is used to transmit the error signal to the feedback pin of the frequency control module.

8. A variable frequency starting method for a flyback power supply, applied to the variable frequency starting system for a flyback power supply as claimed in claim 1, characterized in that: The steps include: When powered on, the frequency control module sets the operating frequency to the lowest frequency; Limit the primary peak current to 30%-50% of the rated value; The output voltage is sampled and monitored in real time by the voltage detection module; When the output voltage reaches 10% of the rated value, the frequency control module cooperates with the power conversion module to linearly increase the operating frequency; When the output voltage reaches 90% of the rated value, it switches to the rated operating frequency, the feedback module takes over the closed-loop control, and the frequency control module switches to the conventional PWM mode.

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