Flyback switching power supply circuit and control method based on continuous conduction mode

Abstract

The present application relates to a flyback switching power supply circuit and control method based on a continuous conduction mode, including a constant current control circuit, a sampling circuit and a peak current control circuit. The sampling circuit is used to sample the conduction time of the secondary coil to obtain a conduction time duty cycle signal D_SEC, and send the conduction time duty cycle signal D_SEC to the constant current control circuit. The constant current control circuit receives the conduction time duty cycle signal D_SEC, so that the conduction time duty cycle signal D_SEC and a preset reference voltage signal VREF generate a CAC voltage signal. The constant current control circuit converts the CAC voltage signal and the peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT. The adjustment signal CCOUT is used to actively adjust the value of the peak current control signal VCST, so that the flyback switching power supply circuit outputs a constant current. It does not need to stipulate that the starting current of the secondary coil conduction is a fixed value, so that the output current can be constant, which is convenient and quick.

Description

Technical Field

[0001] The invention relates to a flyback switching power supply circuit and a control method based on a continuous conduction mode, belonging to the technical field of flyback switching power supply control. Background Art

[0002] At present, there are two working modes for flyback switching power supplies, discontinuous conduction mode (DCM) and continuous conduction mode (CCM). When the flyback switching power supply works in DCM mode, the constant current output design is simple and easy to implement, because the current on the coil will drop to 0 at the end of each cycle, so its average current output formula is: Where n is the turns ratio of the primary coil to the secondary coil of the transformer, Ipk is the peak current of the primary coil, Tsec is the conduction time of the secondary diode, and Tsw is the power switching cycle. From the formula, it can be seen that constant current output can be achieved by simply determining the peak current and the duty cycle of the secondary coil conduction time; however, when the flyback switching power supply operates in CCM mode, because the current on the coil is not 0 at the end of each cycle, the average current output formula is: Where I1 is the starting current when the secondary coil is turned on. Since the value of I1 is different in different cycles, it is difficult to control the constant current output in CCM mode. Summary of the invention

[0003] The object of the present invention is to provide a flyback switching power supply circuit and control method based on a continuous conduction mode, which can make the output current constant without requiring the starting current of the secondary coil to be set to a fixed value, and is convenient and quick.

[0004] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a flyback switching power supply circuit based on a continuous conduction mode, comprising a constant current control circuit, a sampling circuit and a peak current control circuit, wherein the sampling circuit is used to sample the conduction time of the secondary coil to obtain a conduction time duty cycle signal D_SEC, and send the conduction time duty cycle signal D_SEC to the constant current control circuit, wherein the constant current control circuit receives the conduction time duty cycle signal D_SEC, so that the conduction time duty cycle signal D_SEC and a preset reference voltage signal VREF generate a CAC voltage signal, wherein the constant current control circuit converts the CAC voltage signal and a peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT, wherein the adjustment signal CCOUT is used to actively adjust the value of the peak current control signal VCST, so that the flyback switching power supply circuit outputs a constant current.

[0005] Furthermore, when the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes:

[0006] A signal generating module, the signal generating module is used to generate a CAC voltage signal by using the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF;

[0007] A first timing module, when the VCS signal is equal to the CAC voltage signal, the first timing module is used to start outputting or stop outputting a first time signal t1;

[0008] A second timing module, the second timing module is used to output a second time signal t2;

[0009] The timing comparison module is used to compare the first time signal t1 with the second time signal t2, and determine whether to output the adjustment signal CCOUT to actively adjust the value of the peak current control signal VCST according to the comparison result, so that the flyback switching power supply circuit outputs a constant current.

[0010] Furthermore, the constant current control circuit also includes a delay module, which is used to receive the adjustment signal CCOUT sent by the timing comparison module, determine whether the adjustment signal CCOUT is continuously at a high level, and determine whether to output an overload protection signal PRO based on the judgment result. The overload protection signal PRO is used to control the flyback switching power supply circuit drive signal to shut down.

[0011] The present invention further provides a flyback switching power supply control method based on a continuous conduction mode, using the flyback switching power supply circuit based on a continuous conduction mode as described above, the method comprising:

[0012] The sampling circuit is used for sampling the conduction time of the secondary coil to obtain a conduction time duty cycle signal D_SEC, and sending the conduction time duty cycle signal D_SEC to the constant current control circuit;

[0013] The constant current control circuit receives the on-time duty cycle signal D_SEC, and enables the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF to generate a CAC voltage signal;

[0014] The constant current control circuit then converts the CAC voltage signal and the peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT. The adjustment signal CCOUT is used to actively adjust the value of the peak current control signal VCST so that the flyback switching power supply circuit outputs a constant current.

[0015] Further, when the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes a signal generating module, a first timing module, a second timing module, and a timing comparison module;

[0016] The signal generating module is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF;

[0017] When the primary coil is turned on, the first timing module and the second timing module start timing at the same time, and output the first timing signal t1 and the second timing signal t2, and the VCS signal rises;

[0018] When the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module stops timing;

[0019] When the primary coil is turned off, the second timing module stops timing, and the timing comparison module compares the first time signal t1 with the second time signal t2;

[0020] The second time signal t2 is greater than twice the first time signal t1, and the timing comparison module outputs an adjustment signal CCOUT. The adjustment signal CCOUT is at a high level to control the peak current control circuit to reduce the value of the peak current control signal VCST, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current.

[0021] Further, when the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes a signal generating module, a first timing module, a second timing module, and a timing comparison module;

[0022] The signal generating module is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF;

[0023] When the primary coil is turned on, the second timing module starts timing to output a second timing signal t2, and the VCS signal rises;

[0024] When the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module starts timing to output a first timing signal t1;

[0025] When the primary coil is turned off, the first timing module and the second timing module stop timing, and the timing comparison module compares the first time signal t1 with the second time signal t2;

[0026] The second time signal t2 is less than twice the first time signal t1, and the timing comparison module outputs an adjustment signal CCOUT. The adjustment signal CCOUT is at a high level to control the peak current control circuit to reduce the value of the peak current control signal VCST, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current.

[0027] Furthermore, when the second time signal t2 is equal to twice the first time signal t1, the average current output by the flyback switching power supply circuit based on the continuous conduction mode is:

[0028]

[0029] Among them, RCS is the resistance of the current detection resistor, and n is the turns ratio of the primary coil to the secondary coil.

[0030] Furthermore, the constant current control circuit also includes a delay module.

[0031] The delay module receives the adjustment signal CCOUT sent by the timing comparison module, determines whether the adjustment signal CCOUT is continuously at a high level, and determines whether to output an overload protection signal PRO based on the judgment result. The overload protection signal PRO is used to control the flyback switching power supply circuit drive signal to shut down.

[0032] The beneficial effect of the present invention lies in that a constant current control circuit is provided, which receives the on-time duty cycle signal D_SEC sent by the sampling circuit when sampling the secondary coil, and generates a CAC voltage signal by combining the on-time duty cycle signal D_SEC with a preset reference voltage signal VREF, so that the constant current control circuit adjusts the voltage value of the VCS signal, thereby enabling the flyback switching power supply circuit to output a constant current, which is convenient and quick.

[0033] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The invention is a circuit diagram of a flyback switching power supply circuit based on a continuous conduction mode.

[0035] Figure 2 for Figure 1 Schematic diagram of some modules in the middle.

[0036] Figure 3 It is a signal waveform diagram of the flyback switching power supply circuit based on the continuous conduction mode of the present invention.

[0037] Figure 4It is another signal waveform diagram of the flyback switching power supply circuit based on the continuous conduction mode of the present invention. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0039] See also Figure 1 In a preferred embodiment of the present invention, a flyback switching power supply circuit based on a continuous conduction mode includes a power supply circuit (POWER), a transformer connected to the power supply circuit, a sampling circuit (SAMP) for sampling the secondary coil of the transformer, a constant current control circuit (CC) and a drive circuit connected to the sampling circuit, and a power tube Q1 for controlling the conduction or shutdown of the secondary coil, wherein the transformer also includes a primary coil and an auxiliary coil, the primary coil, the auxiliary coil and the secondary coil are mutually inducted, the secondary coil is connected to a secondary diode D2, the auxiliary coil is connected to a control circuit, and the primary coil is connected to a current detection resistor RCS and the source of the power tube Q1.

[0040] The driving circuit includes an error amplifier (EA), an oscillation module (OSC), a peak current control module (CS), a comparator (CMP), a logic AND gate module, a D flip-flop (DRFF) and a driving module. When PWM=1, the power tube Q1 is turned on, the primary coil is turned on, and the current starts to flow through the RCS resistor. The current increases with time, thereby causing the VCS voltage to rise with time. When the VCS voltage rises to the VCST voltage, the peak current of the primary coil is reached, and the comparator CMP generates a low-level signal to the logic AND gate circuit. The logic AND gate circuit outputs a low-level signal to the D flip-flop to reset it, and outputs PWM=0, the power tube Q1 is turned off, and the secondary coil is turned on. The sampling circuit is used to sample the conduction time of the secondary coil to obtain The on-time duty cycle signal D_SEC is generated, and the on-time duty cycle signal D_SEC is sent to the constant current control circuit. The constant current control circuit receives the on-time duty cycle signal D_SEC, so that the on-time duty cycle signal D_SEC and the preset reference voltage signal VREF generate a CAC voltage signal. The constant current control circuit converts the CAC voltage signal and the peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT. The adjustment signal CCOUT is used to actively adjust the value of the peak current control signal VCST, thereby providing a stable voltage or current for the load until the next cycle PWM=1, and the power tube Q1 is turned on again. In this embodiment, VCST is the primary coil peak current control voltage, wherein D_SEC=TSEC / TSW, CAC=VREF / D_SEC.

[0041] Specifically, the constant current control circuit includes a signal generating module 3, a first timing module 1, a second timing module 2 and a timing comparison module 4, wherein the signal generating module 3 is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC with a preset reference voltage signal VREF; the first timing module 1 is used to receive the CAC voltage signal and the VCS signal, and when the voltage value of the CAC voltage signal is equal to the voltage value of the VCS signal, the first timing module 1 works to start outputting or stop outputting the first time signal t1; the second timing module 2 is used to output the second time signal t2, and the timing comparison module is used to compare the first time signal t1 with the second time signal t2, and determine whether to output the adjustment signal CCOUT to control the peak current control circuit to output a constant current according to the comparison result.

[0042] The constant current control circuit also includes a delay module 5, which is used to receive the adjustment signal CCOUT sent by the timing comparison module to output an overload protection signal PRO, and the overload protection signal PRO is used to control the switching power supply drive signal to turn off. Among them, the logic AND gate module is used to receive the PRO signal and output a low level, and the D flip-flop is triggered by the low level of the logic AND gate module and drives the power tube to turn off.

[0043] The present invention further provides a flyback switching power supply control method based on a continuous conduction mode, using the flyback switching power supply circuit based on a continuous conduction mode as described above, the method comprising:

[0044] The sampling circuit is used to sample the on-time duty cycle signal D_SEC of the secondary coil, and send the on-time duty cycle signal D_SEC to the constant current control circuit;

[0045] The constant current control circuit receives the on-time duty cycle signal D_SEC, and enables the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF to generate a CAC voltage signal;

[0046] The CAC voltage signal controls the constant current control circuit to output a regulating signal CCOUT, and the regulating signal CCOUT is used to actively adjust the value of the peak current control signal VCST so that the flyback switching power supply circuit outputs a constant current.

[0047] For details, please combine Figure 2 and Figure 4 When the primary coil is turned on, the signal generating module 3 is used to generate a CAC voltage signal from the on-time duty cycle signal D_SEC and the preset reference voltage signal VREF; when the primary coil is turned on, the first timing module 1 and the second timing module 2 start timing at the same time, and output the first timing signal t1 and the second timing signal t2, at which time the VCS signal rises; when the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module 1 stops timing; when the secondary coil is turned on, the second timing module 2 stops timing, and the timing comparison module compares the first time signal t1 and the second time signal t2; when the second time signal t2 is greater than twice the first time signal t1, the timing comparison module outputs an adjustment signal CCOUT to control the peak current control circuit output VCST to decrease, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current. That is, t2>2×t1, then its output adjustment signal CCOUT controls the VCST signal to decrease; if the second time signal t2 is less than twice the first time signal t1, that is, t2<2×t1, then its output adjustment signal CCOUT will not act, that is, the VCST signal remains unchanged.

[0048] Please combine Figure 2 and Figure 3 In other embodiments, the signal generating module 3 is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC with a preset reference voltage signal VREF; when the primary coil is turned on, the second timing module 2 starts timing to output a second timing signal t2, and the VCS signal rises; when the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module 1 starts timing to output a first timing signal t1; when the secondary coil is turned on, the first timing module 1 and the second timing module 2 stop timing, and the timing comparison module compares the first time signal t1 with the second time signal t2; when the second time signal t2 is less than twice the first time signal t1, the timing comparison module outputs an adjustment signal CCOUT to control the peak current control circuit output VCST to decrease, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current. That is, t2<2×t1, then its output adjustment signal CCOUT controls the VCST signal to decrease; if the second time signal t2 is greater than twice the first time signal t1, that is, t2>2×t1, then its output adjustment signal CCOUT will not act, that is, the VCST signal remains unchanged.

[0049] When the second time signal t2 is equal to twice the first time signal t1, the average current output by the flyback switching power supply circuit based on the continuous conduction mode is:

[0050]

[0051] Among them, RCS is the resistance of the current detection resistor, and n is the turns ratio of the primary coil to the secondary coil.

[0052] It can be seen from the above formula that since the preset voltage VREF and the RCS resistance are both constant values, a constant current is output.

[0053] The constant current control circuit also includes a delay module 5, which receives the adjustment signal CCOUT sent by the timing comparison module, determines whether the adjustment signal CCOUT is continuously at a high level, and determines whether to output a PRO signal based on the judgment result. The PRO signal is used to control the flyback switching power supply circuit drive signal to turn off.

[0054] Specifically, Figure 2As shown, when the primary coil is turned on, that is, SW=1, the second timing module 2 starts timing, and the voltage value of the VCS signal continues to rise. When the voltage value of the VCS signal rises to the voltage value of the preset CAC voltage signal, the first timing module 1 also starts timing, until the SW signal=0, the first timing module 1 and the second timing module 2 stop timing at the same time, and the timing comparison module 4 compares the first time signal t1 with the second time signal t2. If the second time signal t2 is less than twice the first time signal t1, that is, t2<2×t1;

[0055] Alternatively, when the primary coil is turned on, that is, SW=1, the second timing module 2 starts timing, and the first timing module 1 also starts timing. At this time, the voltage value of the VCS signal continues to rise. When the voltage value of the VCS signal rises to the voltage value of the preset CAC voltage signal, the first timing module 1 stops timing. When SW=0, the second timing module 2 also stops timing, and the timing comparison module 4 compares the first time signal t1 with the second time signal t2. If the second time signal t2 is greater than twice the first time signal t1, that is, t2>2×t1;

[0056] In the above two cases, the timing comparison module 4 outputs the adjustment signal CCOUT to the delay module 5. When the adjustment signal CCOUT is continuously output high for multiple cycles, the delay module 5 outputs the PRO signal to the logic AND gate module. PRO=0, the D flip-flop outputs PWM=0, the power tube Q1 is turned off, and the switching power supply is in the protection state.

[0057] To sum up: by providing a constant current control circuit, it receives the on-time duty cycle signal D_SEC sent by the sampling circuit when sampling the secondary coil, and generates a CAC voltage signal by combining the on-time duty cycle signal D_SEC with a preset reference voltage signal VREF, so that the constant current control circuit adjusts the voltage value of the VCST signal, thereby enabling the flyback switching power supply circuit to output a constant current in the CCM mode, which is convenient and quick.

[0058] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A flyback switching power supply circuit based on continuous conduction mode, characterized in that: The invention comprises a constant current control circuit, a sampling circuit and a peak current control circuit, wherein the sampling circuit is used for sampling the conduction time of the secondary coil to obtain a conduction time duty cycle signal D_SEC, and sends the conduction time duty cycle signal D_SEC to the constant current control circuit, the constant current control circuit receives the conduction time duty cycle signal D_SEC, so that the conduction time duty cycle signal D_SEC and a preset reference voltage signal VREF generate a CAC voltage signal, the constant current control circuit converts the CAC voltage signal and the peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT, the adjustment signal CCOUT is used for actively adjusting the value of the peak current control signal VCST, so that the flyback switching power supply circuit outputs a constant current; When the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes: A signal generating module, the signal generating module is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF; A first timing module, when the VCS signal is equal to the CAC voltage signal, the first timing module is used to start outputting or stop outputting a first timing signal t1; A second timing module, the second timing module is used to output a second timing signal t2; The timing comparison module is used to compare the first timing signal t1 with the second timing signal t2, and determine whether to output the adjustment signal CCOUT to actively adjust the value of the peak current control signal VCST according to the comparison result, so that the flyback switching power supply circuit outputs a constant current.

2. The flyback switching power supply circuit based on continuous conduction mode according to claim 1, characterized in that: The constant current control circuit also includes a delay module, which is used to receive the adjustment signal CCOUT sent by the timing comparison module, determine whether the adjustment signal CCOUT is continuously at a high level, and determine whether to output an overload protection signal PRO based on the judgment result. The overload protection signal PRO is used to control the flyback switching power supply circuit drive signal to shut down.

3. A flyback switching power supply control method based on continuous conduction mode, characterized in that: Using the flyback switching power supply circuit based on the continuous conduction mode as claimed in claim 1, the method comprises: The sampling circuit is used for sampling the conduction time of the secondary coil to obtain a conduction time duty cycle signal D_SEC, and sending the conduction time duty cycle signal D_SEC to the constant current control circuit; The constant current control circuit receives the on-time duty cycle signal D_SEC, and makes the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF generate a CAC voltage signal; The constant current control circuit then converts the CAC voltage signal and the peak current control signal VCST of the peak current control circuit into a time signal, and compares the time signal to output an adjustment signal CCOUT. The adjustment signal CCOUT is used to actively adjust the value of the peak current control signal VCST so that the flyback switching power supply circuit outputs a constant current.

4. The flyback switching power supply control method based on continuous conduction mode according to claim 3, characterized in that: When the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes a signal generation module, a first timing module, a second timing module, and a timing comparison module; The signal generating module is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF; When the primary coil is turned on, the first timing module and the second timing module start timing at the same time, and output the first timing signal t1 and the second timing signal t2, and the VCS signal rises; When the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module stops timing; When the primary coil is turned off, the second timing module stops timing, and the timing comparison module compares the first timing signal t1 with the second timing signal t2; The second timing signal t2 is greater than twice the first timing signal t1, and the timing comparison module outputs an adjustment signal CCOUT. The adjustment signal CCOUT is at a high level to control the peak current control circuit to reduce the value of the peak current control signal VCST, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current.

5. The flyback switching power supply control method based on continuous conduction mode according to claim 3, characterized in that: When the primary coil is turned on, the current detection resistor connected to the primary coil outputs a VCS signal, and the constant current control circuit includes a signal generation module, a first timing module, a second timing module, and a timing comparison module; The signal generating module is used to generate a CAC voltage signal by combining the on-time duty cycle signal D_SEC and a preset reference voltage signal VREF; When the primary coil is turned on, the second timing module starts timing to output a second timing signal t2, and the VCS signal rises; When the voltage of the VCS signal is equal to the voltage of the CAC voltage signal, the first timing module starts timing to output a first timing signal t1; When the primary coil is turned off, the first timing module and the second timing module stop timing, and the timing comparison module compares the first timing signal t1 with the second timing signal t2; The second timing signal t2 is less than twice the first timing signal t1, and the timing comparison module outputs an adjustment signal CCOUT. The adjustment signal CCOUT is at a high level to control the peak current control circuit to reduce the value of the peak current control signal VCST, thereby causing the flyback switching power supply circuit based on the continuous conduction mode to output a constant current.

6. The flyback switching power supply control method based on continuous conduction mode according to claim 4 or 5, characterized in that: When the second timing signal t2 is equal to twice the first timing signal t1, the average current output by the flyback switching power supply circuit based on the continuous conduction mode is: Among them, RCS is the resistance of the current detection resistor, and n is the turns ratio of the primary coil to the secondary coil.

7. The flyback switching power supply control method based on continuous conduction mode according to claim 6, characterized in that: The constant current control circuit also includes a delay module. The delay module receives the adjustment signal CCOUT sent by the timing comparison module, determines whether the adjustment signal CCOUT is continuously at a high level, and determines whether to output an overload protection signal PRO based on the judgment result. The overload protection signal PRO is used to control the flyback switching power supply circuit drive signal to shut down.

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