Flyback constant voltage and constant current switching power supply

Abstract

The present application relates to a flyback constant-voltage and constant-current switching power supply, including a constant-voltage and constant-current control circuit; the constant-voltage and constant-current control circuit includes a constant-current control circuit, a sampling circuit, an error amplification circuit and a peak current control circuit. The sampling circuit is used to sample the induced voltage signal of the auxiliary coil to the secondary coil, and send the induced voltage signal to the error amplification circuit for amplification, and process it through the peak current control circuit to obtain a maximum conduction current control signal VCST_MAX. The constant-current control circuit accesses and processes the maximum conduction current control signal VCST_MAX to control the flyback constant-voltage and constant-current switching power supply to output a constant current. It ensures that the current output by the constant-current control circuit is constant through an active control method, with high flexibility and reliability.

Description

Technical Field

[0001] The present invention relates to a flyback constant voltage and constant current switching power supply, belonging to the technical field of flyback power control. Background Art

[0002] Currently, there are various types of flyback AC / DC switching power supplies, and their internal control modules have become increasingly complex. However, all control modules aim to obtain accurate constant voltage (CV) and constant current (CC) outputs. As Figure 1 shown, the switching frequency and peak current of the switching transistor Q6 are controlled to maintain a stable output voltage. For accurate constant current output, the commonly used method is to adjust the duty cycle of the conduction time of the secondary coil while fixing the peak current. There are significant limitations in achieving constant current output by controlling the duty cycle of the conduction time of the secondary coil in the prior art. It requires the peak current of the primary coil to be a fixed value. At this time, if the output feedback voltage of the circuit continuously decreases, the conduction time of the secondary diode D1 will increase, and the dead time will also increase accordingly; if the input voltage of the circuit increases, the conduction time of the primary coil will become shorter, and the dead time will also increase. The increase in dead time will not only cause the switching period of the circuit to become longer and the switching frequency to decrease, even entering the audio range, but also reduce the conversion efficiency of the circuit. Summary of the Invention

[0003] The purpose of the present invention is to provide a flyback constant voltage and constant current switching power supply, which can solve the technical problems of increased dead time and longer switching period caused by short conduction time of the primary coil, and at the same time has a simple control method, high flexibility and reliability.

[0004] To achieve the above object, the present invention provides the following technical solution: A flyback constant voltage and constant current switching power supply includes a constant voltage and constant current control circuit; the constant voltage and constant current control circuit includes a constant current control circuit, a sampling circuit, an error amplification circuit, and a peak current control circuit. The sampling circuit is used to sample the induced voltage signal of the auxiliary coil to the secondary coil, and send the induced voltage signal to the error amplification circuit for amplification, and process it through the peak current control circuit to obtain the maximum conduction current control signal VCST_MAX. The constant current control circuit accesses and processes the maximum conduction current control signal VCST_MAX to control the flyback constant voltage and constant current switching power supply to output a constant current.

[0005] Further, the constant current control circuit is an average voltage control type constant current control circuit.

[0006] Further, the average voltage controlled constant current control circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a first switch K1, a second switch K2, an inverter, a first operational amplifier AMP1, a second operational amplifier AMP2, and a first regulating transistor Q1;

[0007] The first terminal of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX. The second terminal of the first resistor R1 is connected to the first terminal of the second resistor R2, the drain of the first regulating transistor Q1, and outputs the output signal VCST of the average voltage controlled constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The second terminal of the second resistor R2 is connected to the first terminal of the second capacitor C2 and the non-inverting input terminal of the second operational amplifier AMP2. The inverting input terminal of the second operational amplifier AMP2 is connected to the output terminal of the second operational amplifier AMP2 and the first terminal of the first switch K1. The second terminal of the first switch K1 is connected to the first terminal of the third resistor R3 and the first terminal of the second switch K2. The control terminal of the first switch K1 is connected to the input terminal of the inverter and receives the signal S_sec output by the sampling circuit to determine whether the secondary coil is turned on. The control terminal of the second switch K2 is connected to the output terminal of the inverter. The second terminal of the third resistor R3 is connected to the non-inverting input terminal of the first operational amplifier AMP1 and the first terminal of the first capacitor C1. The inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The output terminal of the first operational amplifier AMP1 is connected to the gate of the first regulating transistor Q1. The source of the first regulating transistor Q1, the second terminal of the second capacitor C2, the second terminal of the first capacitor C1, and the second terminal of the second switch K2 are connected and grounded.

[0008] Further, the flyback constant voltage and constant current switching power supply further includes a secondary diode D1 connected to the secondary coil. When the secondary coil is conducting, the secondary diode D1 is conducting;

[0009] The secondary diode D1 has a conduction time Tsec, and the switching period of the flyback constant voltage and constant current switching power supply is Tsw. Then, the average voltage VC1_ave of the average voltage controlled constant current control circuit is:

[0010]

[0011] Further, the constant current control circuit is an average current controlled constant current control circuit.

[0012] Further, the average current control type constant current control circuit includes a first switch K1, a first operational amplifier AMP1, a second operational amplifier AMP2, a first capacitor C1, a second capacitor C2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first regulating transistor Q1, a second regulating transistor Q2, a third regulating transistor Q3, a fourth regulating transistor Q4, and a fifth regulating transistor Q5;

[0013] The first end of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX. The second end of the first resistor R1 is connected to the non-inverting input terminal of the second operational amplifier, the drain of the fifth regulating transistor Q5, and the first end of the second resistor R2. The source of the fifth regulating transistor Q5 is connected to the second end of the second capacitor C2. The second end of the second resistor R2 is connected to the first end of the second capacitor C2 and outputs the output signal VCST of the average current control type constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The first end of the third resistor R3 is connected to the inverting input terminal of the second operational amplifier and the source of the fourth regulating transistor Q4. The output terminal of the second operational amplifier AMP2 is connected to the gate of the fourth regulating transistor Q4. The drain of the fourth regulating transistor Q4 is connected to the drain of the second regulating transistor Q2, the gate of the second regulating transistor Q2, and the gate of the third regulating transistor Q3. The source of the second regulating transistor Q2 is connected to the source of the third regulating transistor Q3. The drain of the third regulating transistor Q3 is connected to the first end of the first switch K1. The second end of the first switch K1 is connected to the first end of the first capacitor C1, the gate of the fifth regulating transistor Q5, and the drain of the first regulating transistor Q1. The control terminal of the first switch is connected to the signal S_sec output by the sampling circuit to determine whether the secondary coil is turned on. The gate of the first regulating transistor Q1 is connected to the output terminal of the first operational amplifier AMP1. The non-inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The inverting input terminal of the first operational amplifier AMP1 is connected to the source of the first regulating transistor Q1 and the first end of the fourth resistor R4. The second end of the first capacitor C1 is connected to the second end of the fourth resistor R4, the second end of the second capacitor C2, and the source of the fifth regulating transistor Q5 and is grounded.

[0014] Further, the flyback constant voltage and constant current switching power supply further includes a secondary diode D1 connected to the secondary coil. When the secondary coil is conducting, the secondary diode D1 is conducting;

[0015] The charging current of the first capacitor is I1, and the discharging current of the first capacitor is I2. When the charging current I1 is equal to the discharging current I2, the output current of the flyback constant voltage and constant current switching power supply is constant. Then the average current of the average current control type constant current control circuit is:

[0016]

[0017] Among them, Tsec is the conduction time of the secondary-side diode D1, and Tsw is the switching period of the flyback constant-voltage and constant-current switching power supply.

[0018] Furthermore, the charging current I1 is proportional to the signal VCST processed by the average-current-controlled constant-current control circuit.

[0019] Furthermore, the discharge current I2 is proportional to the reference voltage VREF_CC.

[0020] Furthermore, the second regulating transistor Q2 and the third regulating transistor Q3 are arranged as a current mirror.

[0021] The beneficial effects of the present invention are as follows: By providing a sampling circuit, an error amplification circuit, a peak control circuit, and a constant-current control circuit, the sampling circuit is used to sample the induced voltage signal of the auxiliary coil, and send the induced voltage signal to the error amplification circuit for amplification, and process it through the peak current control circuit to obtain the maximum conduction current control signal VCST_MAX. The constant-current control circuit processes the input maximum conduction current control signal VCST_MAX and outputs the signal VCST to control the flyback constant-voltage and constant-current switching power supply to output a constant current, thereby ensuring the constancy of the output current, so that the switching power supply will not make the operating frequency enter the audio range as the output voltage changes, and improving the circuit conversion efficiency.

[0022] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it in accordance with the content of the specification, the following takes the preferred embodiments of the present invention and combines with the accompanying drawings to describe in detail as follows. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of a flyback constant-voltage and constant-current switching power supply in the prior art.

[0024] Figure 2 For Figure 1 The waveform diagram of some signals changing with time in

[0025] Figure 3 It is a schematic diagram of a flyback constant-voltage and constant-current switching power supply with an average-voltage-controlled constant-current control circuit in this application.

[0026] Figure 4 It is a schematic diagram of a flyback constant-voltage and constant-current switching power supply with an average-current-controlled constant-current control circuit in this application. Detailed Embodiments

[0027] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0028] Please refer to Figure 1 , Figure 1 which is the schematic diagram of a flyback constant voltage and constant current switching power supply in the prior art, including a constant current and constant voltage control circuit. The constant current and constant voltage control circuit includes a power supply circuit (POWER), a sampling control circuit, a peak current control circuit (CS), a second comparator (CMP), an AND gate circuit, a D flip-flop (DRFF), a drive circuit (DRV), a switching transistor Q6, a constant current control circuit, a current detection resistor RCS, and a transformer. The transformer includes a primary coil, a secondary coil, and an auxiliary coil. The primary coil and the auxiliary coil are mutually inductive with the secondary coil. The secondary coil is connected to a secondary diode D1, and the auxiliary coil is connected to the control circuit. The primary coil is connected to the current detection resistor RCS and the source electrode of the switching transistor Q6. Among them, the sampling control circuit includes a sampling circuit (SAMP), an error amplification circuit (EA), and an oscillation circuit (OSC).

[0029] The non-inverting input terminal of the second comparator is connected to the voltage signal VCST output after being processed by the peak current control circuit. The oscillation circuit outputs a control signal FMAX. The sampling circuit also outputs a signal S_sec for judging whether the secondary coil is turned on.

[0030] The constant current control circuit includes a first comparator, a first switch K1, a second switch K2, an inverter, and a first capacitor C1. Among them, the first terminal of the first switch K1 is connected to the power supply circuit. The control terminal of the first switch K1 is connected to the output terminal of the inverter. The other end of the inverter and the control terminal of the second switch K2 are connected to the sampling circuit together. The second terminal of the first switch K1 is connected to the second terminal of the second switch K2 and the first terminal of the first capacitor C1. The first terminal of the second switch K2 is connected to the power supply circuit. The second terminal of the first capacitor C1 is connected to one end of the current detection resistor RCS and grounded. The first input terminal of the first comparator is connected to the first terminal of the first capacitor C1. The second input terminal of the first operational amplifier is connected to a reference voltage VREF. The output terminal of the first comparator serves as an input signal to the AND gate circuit.

[0031] The working process is as follows: When operating in the constant voltage mode, the chip will sample the VS signal. This VS signal is used to obtain the maximum switching frequency of the chip and the maximum conduction current of the secondary coil, so as to obtain a stable output voltage. At this time, the constant current control circuit does not work;

[0032] When working in the constant current mode, the chip controls the maximum conduction current of the primary coil to be a fixed value. At the same time, the constant current control circuit is used to ensure that the ratio of the conduction time of the secondary coil to the switching period of the chip is a fixed value, so as to ensure a constant output current. The specific working principle is as follows.

[0033] When the D flip-flop outputs a high level PWM = 1, the switch signal SW = 1 is output through the drive circuit, the switch tube Q6 is turned on, there is current in the primary coil, and there is no current in the secondary coil. At this time, S_sec = 0, the first switch K1 is closed, the second switch K2 is opened, and the charging current I1 starts to charge the first capacitor C1, and the voltage VC1 of the first capacitor rises.

[0034] As the current rises, the voltage VCS across the current detection resistor RCS rises. After a period of time, the voltage VCS of the current detection resistor reaches the control voltage value VCST. Among them, VCST is the voltage after the sampled output voltage and the reference voltage VREF_EA are amplified by the error amplification circuit and processed by the peak current control circuit. The comparator outputs a low level, the D flip-flop is reset, the switch signal SW = 0, the switch tube Q6 is turned off, the secondary diode D1 is turned on, there is no current in the primary coil, and there is current in the secondary coil. At this time, S_sec = 1, the first switch K1 is opened, the second switch K2 is closed, and the first capacitor C1 discharges with the discharge current I2, and VC1 drops.

[0035] Please combine Figure 2 , the current flowing through the secondary coil gradually decreases. After Tsec time, the secondary diode D1 is turned off. At this time, there is no current in both the primary coil and the secondary coil, S_sec = 0, the first switch K1 is closed, the second switch K2 is opened, and the current I1 starts to charge the first capacitor C1 again. Since the conduction time Tsec of the secondary diode D1 is relatively long, at this time VC1 < the reference voltage VREF. After t3 time, the charging current I1 charges the voltage VC1 on the first capacitor to the reference voltage VREF, the comparator outputs a high level, the D flip-flop is triggered, outputs a high level, the switch signal SW = 1, and the switch tube Q1 is turned on again, and the control chip enters the second switching period.

[0036] Since the average output current formula:

[0037] 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 D1, and Tsw is the switching period of the flyback constant voltage and constant current switching power supply.

[0038] Then in the above switching period, the equation can be found:

[0039] From the above equation, it can be seen that: That is, when the charging current I1 and the discharging current I2 satisfy is a constant value, that is is a constant value, the output current is constant.

[0040] There are great limitations in achieving constant current output by controlling the switching period in the prior art, which requires to be a constant value. Under this condition, as Figure 2 shown, if the output feedback voltage of the circuit continuously decreases, it will cause the conduction time Tsec of the secondary diode D1 to increase, resulting in a longer switching period of the circuit and a decrease in the switching frequency. In the figure, Tsec2 > Tsec1. To ensure is a constant value, the switching period will also increase in proportion, that is, Tsw2 > Tsw1. If the output feedback voltage of the circuit is too low, it will cause the power supply switching period to be too large, and the switching frequency of the circuit may enter the audio range; since Ipk is a constant value, the conduction time of the primary coil is completely affected by the input voltage. When the power supply input voltage increases, the conduction time of the primary coil will decrease accordingly. At this time, to ensure is a constant value, the dead time will also increase, and the increase in the dead time will affect the conversion efficiency of the power supply.

[0041] Please refer to Figure 3 , the flyback constant voltage and constant current switching power supply in a preferred embodiment of the present application is different from the above-mentioned prior art in that the peak current control circuit in the flyback constant voltage and constant current switching circuit of the present application outputs a maximum conduction current control signal VCST_MAX to the constant current control circuit. The maximum conduction current control signal VCST_MAX is obtained by the sampling circuit sampling the induced voltage signal of the auxiliary coil to the secondary coil, amplifying it through an error amplification circuit, and processing it by the peak current control circuit, so that the flyback constant voltage and constant current switching power supply outputs a constant current. Specifically, the secondary coil is connected to a load, and the auxiliary coil is mutually inducted with the secondary coil to induce the voltage of the secondary load. Then, the sampling circuit samples the induced voltage signal mutually inducted by the auxiliary coil.

[0042] Among them, the constant current control circuit is an average voltage control type constant current control circuit. The average voltage control type constant current control circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a first switch K1, a second switch K2, an inverter, a first operational amplifier AMP1, a second operational amplifier AMP2, and a first regulating transistor Q1.

[0043] The first end of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX. The second end of the first resistor R1 is connected to the first end of the second resistor R2, the drain of the first adjustment transistor Q1, and outputs the output signal VCST of the average voltage control type constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The second end of the second resistor R2 is connected to the first end of the second capacitor C2 and the non-inverting input terminal of the second operational amplifier AMP2. The inverting input terminal of the second operational amplifier AMP2 is connected to the output terminal of the second operational amplifier AMP2 and the first end of the first switch K1. The second end of the first switch K1 is connected to the first end of the third resistor R3 and the first end of the second switch K2. The control terminal of the first switch K1 is connected to the input terminal of the inverter and receives the signal S_sec output by the sampling circuit to determine whether the secondary coil is turned on. The control terminal of the second switch K2 is connected to the output terminal of the inverter. The second end of the third resistor R3 is connected to the non-inverting input terminal of the first operational amplifier AMP1 and the first end of the first capacitor C1. The inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The output terminal of the first operational amplifier AMP1 is connected to the gate of the first adjustment transistor Q1. The source of the first adjustment transistor Q1, the second end of the second capacitor C2, the second end of the first capacitor C1, and the second end of the second switch K2 are connected and grounded. Among them, the second resistor R2 and the second capacitor C2, the third resistor R3 and the first capacitor C1 form a low-pass filter circuit.

[0044] When it works in the constant voltage mode, its working principle is the same as that of the switching power supply in the prior art;

[0045] When it works in the constant current mode, it ensures a constant output current by adjusting the maximum conduction current of the primary coil instead of the switching period, which has better flexibility. Specifically: when working in the constant current mode, the oscillation circuit outputs an FMAX signal to control the turn-on of the switching transistor Q6. When Q6 is turned on, the primary coil conducts, the secondary detection signal S_sec = 0, the second switch K2 closes, and the first switch K1 opens; as the current in the primary coil rises, the voltage VCS on the current detection resistor RCS reaches the voltage VCST, the comparator outputs a low level, the D flip-flop is reset, the switching transistor Q6 turns off, the secondary coil conducts, S_sec = 1, the first switch K1 closes, and the second switch K2 opens; when neither the primary nor the secondary coil conducts, S_sec = 0, the second switch K2 closes, and the first switch K1 opens. In the above process, the voltage on the first capacitor C1 has a high level only when the secondary coil conducts, and its voltage level is the voltage value of the maximum conduction current control signal VCST_MAX output by the peak current control circuit; therefore, when the average voltage VC1_ave on the first capacitor C1 in the entire switching period is greater than the reference voltage VREF_CC, the first operational amplifier will control the pull-down of the regulating transistor Q1, actively controlling the average voltage VC1_ave on the first capacitor C1 in the entire switching period to be a fixed value, that is, VREF_CC. Using the principle that the average voltage of the first capacitor C1 in the entire switching period approximates the average output current, according to the average output current formula: And the average voltage on the first capacitor C1 Thus ensuring a constant output current

[0046] Please refer to Figure 4 , in other embodiments, the constant current control circuit is an average current control type constant current control circuit, and the average current control type constant current control circuit includes a first switch K1, a first operational amplifier AMP1, a second operational amplifier AMP2, a first capacitor C1, a second capacitor C2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first regulating transistor Q1, a second regulating transistor Q2, a third regulating transistor Q3, a fourth regulating transistor Q4, and a fifth regulating transistor Q5.

[0047] The first end of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX. The second end of the first resistor R1 is connected to the non-inverting input terminal of the second operational amplifier, the drain of the fifth adjustment transistor Q5, and the first end of the second resistor R2. The source of the fifth adjustment transistor Q5 is connected to the second end of the second capacitor C2. The second end of the second resistor R2 is connected to the first end of the second capacitor C2 and outputs the output signal VCST of the average current control type constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The first end of the third resistor R3 is connected to the inverting input terminal of the second operational amplifier and the source of the fourth adjustment transistor Q4. The output terminal of the second operational amplifier AMP2 is connected to the gate of the fourth adjustment transistor Q4. The drain of the fourth adjustment transistor Q4 is connected to the drain of the second adjustment transistor Q2, the gate of the second adjustment transistor Q2, and the gate of the third adjustment transistor Q3. The source of the second adjustment transistor Q2 is connected to the source of the third adjustment transistor Q3. The drain of the third adjustment transistor Q3 is connected to the first end of the first switch K1. The second end of the first switch K1 is connected to the first end of the first capacitor C1, the gate of the fifth adjustment transistor Q5, and the drain of the first adjustment transistor Q1. The control terminal of the first switch is connected to the output of the sampling circuit to receive the signal S_sec for judging whether the secondary coil is turned on. The gate of the first adjustment transistor Q1 is connected to the output terminal of the first operational amplifier AMP1. The non-inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The inverting input terminal of the first operational amplifier AMP1 is connected to the source of the first adjustment transistor Q1 and the first end of the fourth resistor R4. The second end of the first capacitor C1 is connected to the second end of the fourth resistor R4, the second end of the second capacitor C2, and the source of the fifth adjustment transistor Q5 and is grounded.

[0048] The first capacitor has a charging current I1 and a discharging current I2. Among them, the second resistor R2 and the second capacitor C2 form a low-pass filter circuit. The second adjustment transistor Q2 and the third adjustment transistor Q3 are arranged as a current mirror. The charging current I1 is also proportional to the signal VCST processed by the average current control type constant current control circuit. The discharging current I2 is proportional to the reference voltage VREF_CC.

[0049] The principle of its operation in the constant current mode is as follows: The oscillation circuit outputs an FMAX signal to control the turning on of the switching transistor Q6. When the switching transistor Q6 is turned on, the primary coil conducts, the detection signal S_sec = 0, and the first switch K1 opens; as the current in the primary coil rises, the voltage VCS on the current detection resistor RCS reaches the VCST voltage value, the comparator outputs a low level, the D flip-flop is reset, the switching transistor Q6 turns off, the secondary coil conducts, S_sec = 1, the first switch K1 closes, and the first capacitor C1 has a charging current I1 to charge it; when neither the primary coil nor the secondary coil conducts, S_sec = 0, and the first switch K1 opens. In the above process, when the charging current I1 flowing into the first capacitor C1 is equal to the discharging current I2 flowing out of the first capacitor C1, the output current is considered constant; when the charging current I1 of the first capacitor C1 is greater than the discharging current I2, the voltage on the first capacitor C1 continuously rises until the regulating transistor Q5 is turned on, the switching transistor Q5 pulls down, and the voltage at the non-inverting input terminal of the second operational amplifier AMP2 decreases, that is, VCST decreases, the charging current I1 decreases, and the average current I1_ave on the first capacitor C1 in the entire switching cycle is actively controlled to be a constant value, that is, VREF_CC / R4. Using the principle of approximating the average output current with the average current of the first capacitor C1 in the entire switching cycle, according to the average output current formula: And the average current on the first capacitor C1 Thus, the constancy of the output current is ensured.

[0050] In summary: By providing a sampling circuit, an error amplification circuit, a peak control circuit, and a constant current control circuit, the sampling circuit samples the induced voltage signal of the auxiliary coil, sends the induced voltage signal to the error amplification circuit for amplification, and processes it through the peak current control circuit to obtain the maximum conduction current control signal VCST_MAX. The constant current control circuit processes the input maximum conduction current control signal VCST_MAX and outputs a signal VCST to control the flyback constant voltage and constant current switching power supply to output a constant current, thus ensuring the constancy of the output current, so that the switching power supply does not enter the audio range with the change of the output voltage, and improving the circuit conversion efficiency.

[0051] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0052] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A flyback constant voltage and constant current switching power supply, characterized in that, it includes a constant voltage and constant current control circuit; the constant voltage and constant current control circuit includes a constant current control circuit, a sampling circuit, an error amplification circuit and a peak current control circuit; the constant current control circuit is an average voltage control type constant current control circuit; the average voltage control type constant current control circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a first switch K1, a second switch K2, an inverter, a first operational amplifier AMP1, a second operational amplifier AMP2, and a first regulating transistor Q1; the first end of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX, the second end of the first resistor R1 is connected to the first end of the second resistor R2, the drain of the first regulating transistor Q1, and outputs the output signal VCST of the average voltage control type constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The second end of the second resistor R2 is connected to the first end of the second capacitor C2 and the non-inverting input terminal of the second operational amplifier AMP2. The inverting input terminal of the second operational amplifier AMP2 is connected to the output terminal of the second operational amplifier AMP2 and the first end of the first switch K1. The second end of the first switch K1 is connected to the first end of the third resistor R3 and the first end of the second switch K2. The control terminal of the first switch K1 is connected to the input terminal of the inverter and receives the output signal S_sec of the sampling circuit. The signal S_sec is used to determine whether the secondary coil is turned on. The control terminal of the second switch K2 is connected to the output terminal of the inverter. The second end of the third resistor R3 is connected to the non-inverting input terminal of the first operational amplifier AMP1 and the first end of the first capacitor C1. The inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The output terminal of the first operational amplifier AMP1 is connected to the gate of the first regulating transistor Q1. The source of the first regulating transistor Q1, the second end of the second capacitor C2, the second end of the first capacitor C1, and the second end of the second switch K2 are connected and grounded.

2. The flyback constant voltage and constant current switching power supply according to claim 1, characterized in that, the sampling circuit is used to sample the induced voltage signal of the auxiliary coil to the secondary coil, send the induced voltage signal to the error amplification circuit for amplification, and process it through the peak current control circuit to obtain the maximum conduction current control signal VCST_MAX. The constant current control circuit accesses and processes the maximum conduction current control signal VCST_MAX to control the flyback constant voltage and constant current switching power supply to output a constant current.

3. The flyback constant voltage and constant current switching power supply according to claim 1, characterized in that, the flyback constant voltage and constant current switching power supply further includes a secondary diode D1 connected to the secondary coil. When the secondary coil conducts, the secondary diode D1 conducts; The secondary diode D1 has a conduction time Tsec, and the switching period of the flyback constant voltage and constant current switching power supply is Tsw. Then, the average voltage VC1_ave of the average voltage control type constant current control circuit is as follows:

4. The flyback constant voltage and constant current switching power supply according to claim 1, characterized in that the constant current control circuit is an average current control type constant current control circuit, and includes a first switch K1, a first operational amplifier AMP1, a second operational amplifier AMP2, a first capacitor C1, a second capacitor C2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first regulating transistor Q1, a second regulating transistor Q2, a third regulating transistor Q3, a fourth regulating transistor Q4, and a fifth regulating transistor Q5; The first end of the first resistor R1 is connected to the maximum conduction current control signal VCST_MAX. The second end of the first resistor R1 is connected to the non-inverting input terminal of the second operational amplifier, the drain of the fifth regulating transistor Q5, and the first end of the second resistor R2. The source of the fifth regulating transistor Q5 is connected to the second end of the second capacitor C2. The second end of the second resistor R2 is connected to the first end of the second capacitor C2 and outputs the output signal VCST of the average current control type constant current control circuit to control the flyback constant voltage and constant current switching power supply to output a constant current. The first end of the third resistor R3 is connected to the inverting input terminal of the second operational amplifier and the source of the fourth regulating transistor Q4. The output terminal of the second operational amplifier AMP2 is connected to the gate of the fourth regulating transistor Q4. The drain of the fourth regulating transistor Q4 is connected to the drain of the second regulating transistor Q2, the gate of the second regulating transistor Q2, and the gate of the third regulating transistor Q3. The source of the second regulating transistor Q2 is connected to the source of the third regulating transistor Q3. The drain of the third regulating transistor Q3 is connected to the first end of the first switch K1. The second end of the first switch K1 is connected to the first end of the first capacitor C1, the gate of the fifth regulating transistor Q5, and the drain of the first regulating transistor Q1. The control terminal of the first switch is connected to the output signal S_sec of the sampling circuit, and the signal S_sec is used to determine whether the secondary coil is turned on. The gate of the first regulating transistor Q1 is connected to the output terminal of the first operational amplifier AMP1. The non-inverting input terminal of the first operational amplifier AMP1 is connected to the reference voltage VREF_CC. The inverting input terminal of the first operational amplifier AMP1 is connected to the source of the first regulating transistor Q1 and the first end of the fourth resistor R4. The second end of the first capacitor C1 is connected to the second end of the fourth resistor R4, the second end of the second capacitor C2, and the source of the fifth regulating transistor Q5 and is grounded.

5. The flyback constant voltage and constant current switching power supply according to claim 4, characterized in that the flyback constant voltage and constant current switching power supply further includes a secondary diode D1 connected to the secondary coil. When the secondary coil is turned on, the secondary diode D1 is turned on; The charging current of the first capacitor is I1, and the discharging current of the first capacitor is I2. When the charging current I1 is equal to the discharging current I2, the output current of the flyback constant voltage and constant current switching power supply is constant. Then the average current of the average current control type constant current control circuit is: Where, Tsec is the conduction time of the secondary side diode D1, and Tsw is the switching period of the flyback constant voltage and constant current switching power supply.

6. The flyback constant voltage and constant current switching power supply according to claim 5, characterized in that the charging current I1 is proportional to the signal VCST processed by the average current control type constant current control circuit.

7. The flyback constant voltage and constant current switching power supply according to claim 5, characterized in that the discharging current I2 is proportional to the reference voltage VREF_CC.

8. The flyback constant voltage and constant current switching power supply according to claim 4, characterized in that the second regulating transistor Q2 and the third regulating transistor Q3 are arranged as a current mirror.

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