Novel flyback power supply switching frequency regulation and control method

Abstract

The invention discloses a novel flyback power supply switching frequency regulation and control method. A flyback power supply circuit comprises a power supply, a rectification filter circuit, an RCD clamping circuit, a transformer module, a PWM circuit, a frequency regulation and control module and an output rectification circuit. Elements used in the circuit comprise a Mosfet, an output diode, a transformer, an output capacitor and a load resistor. The frequency regulation and control method comprises the steps of monitoring voltage and current of a load through a voltage sensor and a current sensor, adjusting switching frequency according to dynamic change of output voltage, enabling the frequency regulation and control module to be combined with a voltage feedback loop, and controlling a switch through a PWM (Pulse-Width Modulation) signal. The real-time adjustment requirement of the switching frequency can be met, the PWM signal can be output through the combination of the control signal and the duty ratio signal, and therefore the overall performance of the power supply system is improved, better adaptability and higher efficiency can be shown especially in the scene with severe load change, and the power supply system is suitable for various actual engineering application scenes.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a novel flyback power supply switching frequency control method. Background Art

[0002] The traditional flyback power supply circuit has a simple topology, requires fewer components, and mostly uses a fixed frequency control method. Regardless of how the load changes, the switching frequency remains unchanged. Although this method is simple in design, it will lead to low efficiency when light load or no load, and is only suitable for small and medium power scenarios. In high power applications, the voltage and current stress of the switching device is large, which will lead to increased switching losses and reduced efficiency. It is not suitable as a high power application solution. In the case of large load changes, the dynamic response performance of the flyback power supply is not as good as other topologies. Therefore, a flyback power supply switching frequency control method is needed to optimize the efficiency and performance of the switch. Summary of the invention

[0003] Purpose of the invention: The purpose of the invention is to provide a novel method for controlling the switching frequency of a flyback power supply.

[0004] Technical solution: The flyback power supply circuit of the present invention includes a power supply, a rectifier filter circuit, an RCD clamp circuit, a transformer module, a PWM circuit, a frequency control module and an output rectifier circuit; the components used in the circuit include Mosfet, an output diode, a transformer, an output capacitor and a load resistor;

[0005] The frequency control method includes monitoring the load voltage and current through voltage and current sensors, adjusting the switching frequency according to the dynamic change of the output voltage, combining the frequency control module with the voltage feedback loop, and controlling the switch through the PWM signal. At the same time, the effectiveness of the frequency control method is verified through theoretical calculation and Matlab / Simlink circuit simulation.

[0006] Furthermore, the field effect transistor includes two kinds of losses, namely conduction loss and switching loss, which are expressed as:

[0007]

[0008] Among them, P cond is the conduction loss, P sw is the switching loss, I d is the drain current of the MOSFET, R ds_on is the drain resistance of the Mosfet when it is turned on, D is the duty cycle, V ds is the voltage between the drain and source of the switch tube, t on and t off are the Mosfet on-time and off-time, respectively, sw is the switching frequency, Ploss is the total loss.

[0009] Furthermore, the switching frequency f sw With the output voltage V o The relationship is:

[0010]

[0011] Among them, V o is the output voltage, I o is the output current, and L is the critical inductance.

[0012] The output voltage is proportional to the switching frequency, and the following relationship can be obtained:

[0013] f sw = kV o

[0014] Among them, the latter is the proportional coefficient.

[0015] The relationship between the total Mosfet loss and the output voltage is:

[0016]

[0017] Among them, t on and t off are the Mosfet on-time and off-time, respectively, sw is the switching frequency, P loss is the total loss.

[0018] Furthermore, the total loss of the Mosfet is at low frequency, and the switching loss P sw Lower, the total loss is dominated by the conduction loss P cond Dominant, at this time the MOS tube efficiency is higher; in high frequency, the switching loss P sw As the frequency increases, the conduction loss P cond Not affected by the switching frequency, the switching loss P at high frequency sw dominates, resulting in an increase in total losses.

[0019] Furthermore, in the construction of the Matlab / Simlink circuit simulation platform, a variable resistor is selected as the load.

[0020] Furthermore, the PWM circuit and frequency control include the following steps:

[0021] S1: Compare the load voltage with the reference voltage, get the partial duty cycle through the PID controller, then compare the load voltage with the input voltage, and finally add the two to get the ideal duty cycle;

[0022] S2: Set the upper and lower limits of the switching frequency and the frequency variable range to achieve real-time control of the switching frequency according to voltage changes;

[0023] S3: The monitored output voltage and output current are used as input signals to the control module of the Mosfet, and the appropriate switching frequency is calculated. The switching frequency signal and the duty cycle signal are then combined through the PWM generator to obtain the final PWM signal for controlling the Mosfet.

[0024] Furthermore, the step S2 comprises:

[0025] Connect a voltage sensor at both ends of the load resistor R1 to monitor the output voltage, and connect a current sensor between the output capacitor and the load resistor to monitor the output current. Sample the output voltage and current in real time, establish a data storage area to store the current sampled voltage value, and then calculate the average value of the sampled voltage within the specified range and use it as the current voltage.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention can not only meet the real-time adjustment requirements of the switching frequency, but also output a PWM signal by combining the control signal with the duty cycle signal, thereby improving the overall performance of the power supply system, especially in scenarios with drastic load changes. It can show better adaptability and higher efficiency, and is suitable for various practical engineering application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural diagram of the overall circuit;

[0028] Figure 2 This is the circuit framework diagram of the Simkink simulation platform;

[0029] Figure 3 This is the output voltage comparison chart;

[0030] Figure 4 It is the PWM circuit and frequency control flow chart;

[0031] Figure 5 This is the PWM output frequency diagram;

[0032] Figure 6 Schematic diagram of the monitored current output. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0034] like Figure 1As shown, the entire circuit module can be divided into a power supply, a rectifier and filter circuit, an RCD clamping circuit, a transformer module, a PWM circuit, a frequency control module and an output rectifier circuit; the components used in the circuit include a field effect transistor (Mosfet), an output diode, a transformer, an output capacitor (C1) and a load resistor (R1); the transformer (T) includes a primary winding (L1) and a secondary winding (L2); the RCD clamping circuit includes a resistor (R2), a capacitor (C2) and a fast recovery diode (D1).

[0035] Mosfet has two main losses, conduction loss and switching loss. The conduction loss is related to the drain current, and the switching loss depends on the switching frequency of the switch. The higher the switching frequency, the faster the switching loss increases. The power loss calculation formula is as follows:

[0036]

[0037] Among them, P cond is the conduction loss, P sw is the switching loss, I d is the drain current of the MOSFET, R ds_on is the drain resistance of the Mosfet when it is turned on, D is the duty cycle, V ds is the voltage between the drain and source of the switch tube, t on and t off are the Mosfet on-time and off-time, respectively, sw is the switching frequency.

[0038] From this, we can get the total loss P loss Calculation formula:

[0039]

[0040] At low frequency, the switching loss P sw is lower, so the total loss is dominated by the conduction loss P cond Dominant, at this time the MOS tube efficiency is higher; in high frequency, the switching loss P sw As the frequency increases, it rises rapidly, while the conduction loss P cond Not affected by the switching frequency, so the switching loss P at high frequency sw It dominates, resulting in increased total losses and decreased efficiency.

[0041] In critical conduction (CRM) mode, the switching frequency f is derived from the following formula: sw , switching loss P loss and output voltage V o The relationship between.

[0042] The primary current increases from zero to the peak value and then returns to zero in each switching cycle. The energy stored in the primary inductor is fully released in each cycle. The primary current peak value is calculated as follows:

[0043]

[0044] Among them, I peak is the peak current of the primary side, V in is the input voltage, t on is the switch on time, L p is the inductance of the primary winding.

[0045] According to the definition of duty cycle:

[0046]

[0047] Where D is the duty cycle, t on is the switch on time, and T is the switch cycle time.

[0048] The calculation formula of the primary side current peak value is further rewritten as:

[0049]

[0050] Among them, I peak is the peak current of the primary side, V in is the input voltage, D is the duty cycle, f sw is the switching cycle, L p is the inductance of the primary winding.

[0051] The output power calculation formula of the flyback power supply is as follows:

[0052]

[0053] Among them, P o is the output power, V o is the output voltage, and R is the load resistance.

[0054] During the operation of the flyback power supply, the inductor stores and releases energy in each switching cycle. When the Mosfet is turned on, the input power charges the primary inductor; when the Mosfet is turned off, the energy stored in the primary inductor is transferred to the secondary winding through transformer coupling, and is provided to the load after rectification and filtering. At this time, the energy stored in the inductor begins to be released. Therefore, from the perspective of energy balance, in each switching cycle, almost all of the energy stored in the inductor is transferred to the load.

[0055] In critical conduction mode, the relationship between the energy storage of the primary inductor and the output power is as follows:

[0056] EL =P o *T sw (8)

[0057] Among them, E L is the energy storage of the primary side inductor, P o is the output power, T sw is the switching cycle time.

[0058] According to the above energy balance perspective, the energy transferred from the primary side to the secondary side is equal to the energy stored in the inductor, which is calculated as follows:

[0059]

[0060] Among them, E L is the energy storage of the primary side inductor, L is the critical inductance, I peak is the peak current of the primary side.

[0061] According to the definition of duty cycle (Formula 5), ​​the above formula can be further sorted out to obtain:

[0062]

[0063] According to the relationship between the primary and secondary voltages of the flyback power supply and the turns ratio n, the critical inductance L, load resistance R, duty cycle D and switching period T can be further simplified. sw The relationship is:

[0064]

[0065] Rewriting formula 12, we can get the relationship between switching frequency and output voltage:

[0066]

[0067] Among them, I o is the output current.

[0068] It can be clearly seen from formula 13 that the output voltage is proportional to the switching frequency, and the following relationship can be obtained:

[0069] f sw = kV o (14)

[0070] Where k is the proportionality coefficient.

[0071] Substituting Equation 14 into Equation 2, the switching loss P can be derived. sw Relationship with output voltage:

[0072]

[0073] From this we can deduce the total loss P loss The relationship between the output voltage and

[0074]

[0075] like Figure 2 The circuit framework is constructed on the Simlink simulation platform. The load R1 is a variable resistor to test the feasibility of the present invention when the load changes drastically.

[0076] The present invention performs simulation under the condition of sudden load change, such as Figure 3 As shown, the stable output voltage is 12V. Compared with the traditional fixed frequency, the output voltage of the present invention is more ideal. (The blue line is the output voltage waveform of the present invention, and the red line is the output voltage waveform of the traditional fixed frequency)

[0077] like Figure 4 As shown, the PWM circuit and frequency control module include the following steps:

[0078] S1. Compare the load voltage with the reference voltage, obtain the partial duty cycle through the PID controller, then compare the load voltage with the input voltage, and finally add the two together to obtain the ideal duty cycle.

[0079] S2, circuit as Figure 2 As shown, a voltage sensor is connected across the load resistor R1 to monitor the output voltage V o , connect a current sensor between the output capacitor C1 and the load resistor to monitor the output current I o , sample the output voltage and current in real time, establish a data storage area to store the current sampled voltage value, then calculate the average value of the sampled voltage within the specified range and use it as the current voltage, and finally set the upper and lower limits of the switching frequency and the variable frequency range to ensure that the switching power supply works in discontinuous conduction mode, so as to achieve real-time regulation of the switching frequency according to voltage changes.

[0080] S3, the monitored output voltage and output current are used as input signals and input to the control module of the Mosfet. After the above formula 13 is used to calculate the appropriate switching frequency, the switching frequency signal and the duty cycle signal are combined through the PWM generator to obtain the final PWM signal for controlling the Mosfet. Its frequency is as follows Figure 5 shown.

[0081] according to Figure 5 and Figure 6 As shown, it can be found that when the load increases, the switching frequency of the Mosfet shows an obvious downward trend. According to formula 16, the reduction in switching frequency will inevitably lead to a reduction in switching losses. It can be concluded that the optimized switching loss is lower than the traditional fixed frequency. The MOS loss comparison is shown in Table 1.

[0082] Table 1 MOS loss comparison

[0083]

[0084]

[0085] The present invention relates to a novel flyback power supply switching frequency control method, which monitors the load voltage and current through voltage and current sensors and adjusts the switching frequency according to the dynamic change of the output voltage. The present invention combines the frequency control module with the voltage feedback loop and controls the switch through the PWM signal. At the same time, the effectiveness of the system is verified through theoretical calculation and Matlab / Simlink circuit simulation.

Claims

1. A novel flyback power supply switching frequency control method, characterized in that: The flyback power supply circuit includes a power supply, a rectifier filter circuit, an RCD clamp circuit, a transformer module, a PWM circuit, a frequency control module and an output rectifier circuit; the components used in the circuit include Mosfet, an output diode, a transformer, an output capacitor and a load resistor; The frequency control method includes monitoring the load voltage and current through voltage and current sensors, adjusting the switching frequency according to the dynamic change of the output voltage, combining the frequency control module with the voltage feedback loop, and controlling the switch through the PWM signal. At the same time, the effectiveness of the frequency control method is verified through theoretical calculation and Matlab / Simlink circuit simulation.

2. The novel flyback power supply switching frequency control method according to claim 1 is characterized in that: The field effect transistor includes two kinds of losses, namely conduction loss and switching loss, which are expressed as: Among them, P cond is the conduction loss, P sw is the switching loss, I d is the drain current of the MOSFET, R ds_on is the drain resistance of the Mosfet when it is turned on, D is the duty cycle, V ds is the voltage between the drain and source of the switch tube, t on and t off are the Mosfet on-time and off-time, respectively, sw is the switching frequency, P loss is the total loss.

3. The novel flyback power supply switching frequency control method according to claim 1 is characterized in that: The switching frequency f sw With output voltage V o The relationship is: Among them, V o is the output voltage, I o is the output current, and L is the critical inductance. The output voltage is proportional to the switching frequency, and the following relationship can be obtained: f sw =kV o Among them, the latter is the proportional coefficient.

4. The novel flyback power supply switching frequency control method according to claim 1 is characterized in that: The relationship between the total Mosfct loss and the output voltage is: Among them, t on and t off are the Mosfet on-time and off-time, respectively, sw is the switching frequency, P loss is the total loss.

5. The novel flyback power supply switching frequency control method according to claim 4 is characterized in that: The total loss of the Mosfct is at low frequency, the switching loss P sw Lower, the total loss is dominated by the conduction loss P cond Dominant, at this time the MOS tube efficiency is higher; in high frequency, the switching loss P sw As the frequency increases, the conduction loss P cond Not affected by the switching frequency, the switching loss P at high frequency sw dominates, resulting in an increase in total losses.

6. The novel flyback power supply switching frequency control method according to claim 1 is characterized in that: In the construction of the Matlab / Simlink circuit simulation platform, a variable resistor is selected as the load.

7. The novel flyback power supply switching frequency control method according to claim 1 is characterized in that: The PWM circuit and frequency control include the following steps: S1: Compare the load voltage with the reference voltage, get the partial duty cycle through the PID controller, then compare the load voltage with the input voltage, and finally add the two together to get the ideal duty cycle; S2: Set the upper and lower limits of the switching frequency and the frequency variable range to ensure that the flyback power supply operates in discontinuous conduction mode; S3: The monitored output voltage and output current are used as input signals to the control module of the Mosfet, and the appropriate switching frequency is calculated. The switching frequency signal and the duty cycle signal are then combined through the PWM generator to obtain the final PWM signal for controlling the Mosfet.

8. The novel flyback power supply switching frequency control method according to claim 6 is characterized in that: The step S2 comprises: Connect a voltage sensor at both ends of the load resistor R1 to monitor the output voltage, and connect a current sensor between the output capacitor and the load resistor to monitor the output current. Sample the output voltage and current in real time, establish a data storage area to store the current sampled voltage value, and then calculate the average value of the sampled voltage within the specified range and use it as the current voltage.

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