CN211720474U - Flyback constant-voltage constant-current switching power supply - Google Patents
Flyback constant-voltage constant-current switching power supply Download PDFInfo
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- CN211720474U CN211720474U CN202020856731.7U CN202020856731U CN211720474U CN 211720474 U CN211720474 U CN 211720474U CN 202020856731 U CN202020856731 U CN 202020856731U CN 211720474 U CN211720474 U CN 211720474U
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Abstract
The application relates to a flyback constant-voltage constant-current switching power supply, which comprises a constant-voltage constant-current control circuit; the constant-voltage constant-current control circuit comprises a constant-current control circuit, a sampling circuit, an error amplification circuit and a peak current control circuit, wherein the sampling circuit is used for sampling an induced voltage signal of an auxiliary coil to a secondary coil, sending the induced voltage signal to the error amplification circuit for amplification, and processing the amplified induced voltage signal by the peak current control circuit to obtain a maximum conduction current control signal VCST _ MAX, the constant-current control circuit is connected to and processes the maximum conduction current control signal VCST _ MAX to control the flyback constant-voltage constant-current switching power supply to output a constant current, and the constant-voltage constant-current control circuit can ensure constant current output by the constant-current control circuit in an active control mode and has high flexibility and reliability.
Description
Technical Field
The utility model relates to a flyback constant voltage constant current switch power supply belongs to flyback power control technical field.
Background
At present, flyback AC/DC switching power supplies are diversified, and internal control modules thereof are becoming more and more complex, but all control modules are used for obtaining accurate Constant Voltage (CV) and Constant Current (CC) outputs. As shown in fig. 1, the switching frequency and the peak current of the switching tube Q6 are controlled to maintain a stable output voltage, and for precise constant current output, a method is usually adopted to fix the peak current and adjust the duty ratio of the secondary winding conduction time. In the prior art, the constant current output achieved by controlling the on-time duty ratio of the secondary coil has great limitation, the peak current of the primary coil is required to be a fixed value, and at the moment, if the output feedback voltage of the circuit is continuously reduced, the on-time of the secondary diode D1 is increased, and the dead time is increased; if the input voltage of the circuit is increased, the conduction time of the primary coil is shortened, and the dead time is increased. The increase of the dead time not only causes the switch period of the circuit to be longer, the switch frequency to be reduced and even enter the audio frequency range, but also reduces the conversion efficiency of the circuit.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide a flyback constant voltage constant current switching power supply, its technical problem that can solve the dead time increase that primary coil on-time is short and lead to, switching cycle length of side, and the simultaneous control mode is simple, and flexibility and reliability are high.
In order to achieve the above purpose, the utility model provides a following technical scheme: a flyback constant-voltage constant-current switching power supply comprises a constant-voltage constant-current control circuit; the constant-voltage constant-current control circuit comprises a constant-current control circuit, a sampling circuit, an error amplification circuit and a peak current control circuit, wherein the sampling circuit is used for sampling an induced voltage signal of an auxiliary coil to a secondary coil, sending the induced voltage signal to the error amplification circuit for amplification, and processing the amplified induced voltage signal by the peak current control circuit to obtain a maximum conduction current control signal VCST _ MAX, and the constant-current control circuit is connected to and processes the maximum conduction current control signal VCST _ MAX to control the flyback constant-voltage constant-current switching power supply to output a constant current.
Further, the constant current control circuit is an average voltage control type constant current control circuit.
Further, the average voltage control type constant current control circuit comprises 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 adjusting tube Q1;
a first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a first end of the second resistor R2 and a drain of a first adjusting transistor Q1, and outputs an output signal VCST of the average voltage control type constant current control circuit to control the flyback constant voltage constant current switching power supply to output a constant current, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and a non-inverting input end of a second operational amplifier AMP2, an inverting input end of the second operational amplifier AMP2 is connected to an output end of the second operational amplifier AMP2 and a first end of a first switch K1, a second end of the first switch K1 is connected to a first end of a third resistor R3 and a first end of a second switch K2, a control end of the first switch K1 is connected to an input end of the inverter and is connected to an output of the sampling circuit to determine whether the sub-coil is turned on or not, the control end of the second switch K2 is connected to the output end of the inverter, the second end of the third resistor R3 is connected to the non-inverting input end of the first operational amplifier AMP1 and the first end of the first capacitor C1, the inverting input end of the first operational amplifier AMP1 is connected to the reference voltage VREF _ CC, the output end of the first operational amplifier AMP1 is connected to the gate of the first adjusting tube Q1, and the source of the first adjusting tube 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 to the ground.
Further, the flyback constant-voltage constant-current switching power supply further comprises a secondary side diode D1 connected to the secondary side coil, and when the secondary side coil is conducted, the secondary side diode D1 is conducted;
the secondary side diode D1 has a conducting time Tsec, the switching period of the flyback constant-voltage constant-current switching power supply is Tsw, and the average voltage VC1 — ave of the average voltage control type constant-current control circuit is:
further, the constant current control circuit is an average current control type constant current control circuit.
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 adjusting tube Q1, a second adjusting tube Q2, a third adjusting tube Q3, a fourth adjusting tube Q4, and a fifth adjusting tube Q5;
a first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a non-inverting input terminal of the second operational amplifier, a drain of a fifth adjusting transistor Q5 and a first end of a second resistor R2, a source of the fifth adjusting transistor Q5 is connected to a second end of the second capacitor C2, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and outputs an output signal VCST of the average current control constant current control circuit to control the flyback constant voltage constant current switch to output a constant current, a first end of the third resistor R3 is connected to an inverting input terminal of the second operational amplifier and a source of a fourth adjusting transistor Q4, an output terminal of the second operational amplifier 2 is connected to a gate of the fourth adjusting transistor Q4, a drain of the fourth adjusting transistor Q4 is connected to an AMP of the drain of the second adjusting transistor Q2, A gate of the second adjusting transistor Q2 and a gate of a third adjusting transistor Q3 are connected, a source of the second adjusting transistor Q2 is connected to a source of the third adjusting transistor Q3, a drain of the third adjusting transistor Q3 is connected to a first end of the first switch K1, a second end of the first switch K1 is connected to a first end of the first capacitor C1, a gate of a fifth adjusting transistor Q5 and a drain of a first adjusting transistor Q1, a control end of the first switch is connected to the signal S _ sec output by the sampling circuit to determine whether the secondary winding is on, a gate of the first adjusting transistor Q1 is connected to an output end of the first operational amplifier AMP1, a non-inverting input end of the first operational amplifier AMP1 is connected to a reference voltage VREF _ CC, and an inverting input end of the first operational amplifier 1 is connected to a source of the first adjusting transistor Q1 and a first end of a 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 tuning transistor Q5, and is grounded.
Further, the flyback constant-voltage constant-current switching power supply further comprises a secondary side diode D1 connected to the secondary side coil, and when the secondary side coil is conducted, the secondary side diode D1 is conducted;
the charging current of the first capacitor is I1, the discharging current of the first capacitor is I2, when the charging current is I1 and the discharging current is I2, the output current of the flyback constant-voltage constant-current switching power supply is constant, and then the average current of the average current control type constant-current control circuit is:
wherein Tsec is the conducting time of the secondary side diode D1, and Tsw is the switching period of the flyback constant-voltage constant-current switching power supply.
Further, the charging current I1 is proportional to the signal VCST processed by the average current control type constant current control circuit.
Further, the discharge current I2 is proportional to the reference voltage VREF _ CC.
Further, the second adjusting tube Q2 and the third adjusting tube Q3 are arranged in a current mirror manner.
The beneficial effects of the utility model reside in that: the sampling circuit is used for sampling an induced voltage signal of the auxiliary coil, sending the induced voltage signal to the error amplifying circuit for amplification, and obtaining a maximum conduction current control signal VCST _ MAX through processing of the peak current control circuit, the constant current control circuit processes the accessed 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 constant current, so that the constancy of the output current is ensured, the switching power supply cannot enable the working frequency to enter an audio frequency range along with the change of the output voltage, and the circuit conversion efficiency is improved.
The above description is only an overview of the technical solution of the present invention, and in order to make the technical means of the present invention clearer and can be implemented according to the content of the description, the following detailed description is made with reference to the preferred embodiments of the present invention and accompanying drawings.
Drawings
Fig. 1 is a schematic diagram of a flyback constant-voltage constant-current switching power supply in the prior art.
Fig. 2 is a waveform diagram of a part of signals in fig. 1 with time.
Fig. 3 is a schematic diagram of a flyback constant-voltage constant-current switching power supply in which the constant-current control circuit of the present application is an average voltage control type.
Fig. 4 is a schematic diagram of a flyback constant-voltage constant-current switching power supply in which the constant-current control circuit of the present application is an average current control type.
Detailed Description
The following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings and examples. The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.
Referring to fig. 1, fig. 1 is a schematic diagram of a flyback constant-voltage constant-current switching power supply in the prior art, which includes a constant-current constant-voltage control circuit. The constant-current and constant-voltage control circuit comprises 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 trigger (DRFF), a driving circuit (DRV), a switching tube Q6, a constant-current control circuit, a current detection resistor RCS and a transformer, wherein the transformer comprises a primary coil, a secondary 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 D1, the auxiliary coil is connected to the control circuit, and the primary coil is connected to the current detection resistor RCS and a source electrode of the switching tube Q6. Wherein the sampling control circuit comprises a sampling circuit (SAMP), an error amplification circuit (EA) and an oscillation circuit (OSC).
The non-inverting input end of the second comparator is connected with the voltage signal VCST output after being processed by the peak current control circuit, the oscillating circuit outputs a control signal FMAX, and the sampling circuit also outputs a signal S _ sec for judging whether the secondary coil is opened or not.
The constant current control circuit comprises a first comparator, a first switch K1, a second switch K2, an inverter and a first capacitor C1, wherein, the first end of the first switch K1 is connected with the power circuit, the control end of the first switch K1 is connected with the output end of the phase inverter, the other end of the inverter and the control end of the second switch K2 are connected into a sampling circuit, the second end of the first switch K1 is connected with the second end of the second switch K2 and the first end of the first capacitor C1, a first end of the second switch K2 is connected to a power circuit, a second end of the first capacitor C1 is connected to one end of the current detection resistor RCS and grounded, a first input end of the first comparator is connected with a first end of the first capacitor C1, a second input end of the first operational amplifier is connected with a reference voltage VREF, and an output end of the first comparator is used as an input signal of the and circuit.
The working process is as follows: when the chip works in a constant voltage mode, the chip samples VS signals which are used for obtaining the maximum switching frequency of the chip and the maximum conduction current of the secondary coil so as to obtain stable output voltage, and the constant current control circuit does not work at the moment;
when the constant current control circuit works in a constant current mode, the chip controls the maximum conduction current of the primary coil to be a fixed value, and meanwhile, the constant current control circuit ensures that the ratio of the conduction time of the secondary coil to the switching period of the chip is a fixed value to ensure that the output current is constant.
When the D flip-flop outputs a high level PWM of 1, the switching signal SW is 1 output through the driving circuit, the switching tube Q6 is turned on, the primary winding has current, and the secondary winding has no current, at this time, S _ sec is 0, the first switch K1 is closed, the second switch K2 is opened, the charging current I1 starts to charge the first capacitor C1, and the voltage VC1 of the first capacitor rises.
Along with the rise of the current, the voltage VCS at the two ends of the current detection resistor RCS rises, and after a period of time, the voltage VCS of the current detection resistor reaches a control voltage value VCST, wherein VCST is the voltage of the sampled output voltage and the reference voltage VREF _ EA after being 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 switching signal SW is equal to 0, the switching tube Q6 is turned off, the secondary diode D1 is turned on, no current flows through the primary coil, and current flows through the secondary coil, at this time, S _ sec is equal to 1, the first switch K1 is turned off, the second switch K2 is turned on, the first capacitor C1 discharges through the discharging current I2, and VC1 drops.
Referring to fig. 2, the current flowing through the secondary winding gradually decreases, and after time Tsec, the secondary diode D1 turns off, and at this time, there is no current in both the primary winding and the secondary winding, S _ sec is 0, the first switch K1 is closed, the second switch K2 is opened, and the current I1 starts to charge the first capacitor C1. Since the on-time Tsec of the secondary diode D1 is longer, at this time, VC1< reference voltage VREF, after t3 time elapses, 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 to output a high level, the switching signal SW is equal to 1, the switching tube Q1 is turned on again, and the control chip enters a second switching period.
Due to the average output current formula:
wherein n is the turn ratio of the primary coil and 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 constant-current switching power supply.
Then the equation can be found in the above switching cycle:
from the above equation:
that is, when the charging current I1 and the discharging current I2 satisfy
Is constant, i.e.
When the output current is constant, the output current is constant.
The constant current output achieved by controlling the switching period in the prior art has great limitation and requirements
Under this condition, if the circuit output feedback voltage is continuously decreased, as shown in fig. 2, the on time Tsec of the secondary diode D1 increases, and the switching cycle of the circuit increases, resulting in a decrease in the switching frequency. Tsec2 > Tsec1 in the figure for guarantee
For a fixed value, the switching period is also increased in equal proportion, namely Tsw2 is greater than Tsw1, if the output feedback voltage of the circuit is too low, the switching period of the power supply is too large, and the switching frequency of the circuit may enter an audio frequency range; because Ipk is a fixed value, the conduction time of the primary coil is completely influenced by the input voltage, when the input voltage of the power supply is increased, the conduction time of the primary coil is correspondingly reduced, and the condition that the conduction time of the primary coil is ensured is the same
For a fixed value, the dead time is also increased, and the increase of the dead time affects the conversion efficiency of the power supply.
Referring to fig. 3, a flyback constant voltage and constant current switching power supply in a preferred embodiment of the present application is different from the prior art in that a peak current control circuit in a flyback constant voltage and constant current switching circuit in the present application outputs a maximum on current control signal VCST _ MAX to the constant current control circuit, and the maximum on current control signal VCST _ MAX is obtained by sampling an induced voltage signal of an auxiliary coil to a secondary coil by the sampling circuit, amplifying the signal by an error amplification circuit, and processing the signal 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, the secondary coil and the secondary coil are mutually inducted to induct the voltage of the secondary load, and then the sampling circuit samples the induction voltage signals mutually sensed by the secondary coil.
The constant current control circuit is an average voltage control type constant current control circuit, and the average voltage control type constant current control circuit comprises 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 adjusting tube Q1.
A first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a first end of the second resistor R2 and a drain of a first adjusting transistor Q1, and outputs an output signal VCST of the average voltage control type constant current control circuit to control the flyback constant voltage constant current switching power supply to output a constant current, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and a non-inverting input end of a second operational amplifier AMP2, an inverting input end of the second operational amplifier AMP2 is connected to an output end of the second operational amplifier AMP2 and a first end of a first switch K1, a second end of the first switch K1 is connected to a first end of a third resistor R3 and a first end of a second switch K2, a control end of the first switch K1 is connected to an input end of the inverter and is connected to an output of the sampling circuit to determine whether the sub-coil is turned on or not, the control end of the second switch K2 is connected to the output end of the inverter, the second end of the third resistor R3 is connected to the non-inverting input end of the first operational amplifier AMP1 and the first end of the first capacitor C1, the inverting input end of the first operational amplifier AMP1 is connected to the reference voltage VREF _ CC, the output end of the first operational amplifier AMP1 is connected to the gate of the first adjusting tube Q1, and the source of the first adjusting tube 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 to the ground. The second resistor R2, the second capacitor C2, the third resistor R3 and the first capacitor C1 form a low-pass filter circuit.
When the switching power supply works in a constant voltage mode, the working principle is consistent with that of the switching power supply in the prior art;
when the constant current source works in a constant current mode, the output current is ensured to be constant by adjusting the maximum conduction current of the primary coil instead of the switching period, and the flexibility is better. The method specifically comprises the following steps: when the constant current mode is operated, the oscillation circuit outputs an FMAX signal to control the on-off of the switching tube Q6, when the Q6 is turned on, the primary coil is conducted, the secondary detection signal S _ sec is 0, the second switch K2 is closed, and the first switch K1 is opened; along with the rise of the current of the primary coil, the voltage VCS on the current detection resistor RCS reaches the voltage VCST, the comparator outputs low level, the D trigger is reset, the switching tube Q6 is turned off, the secondary coil is turned on, S _ sec is 1, the first switch K1 is closed, and the second switch K2 is opened; when both the primary and secondary windings are not conducting, S _ sec is 0, the second switch K2 is closed, and the first switch K1 is open. In the above process, the voltage of the first capacitor C1 has a high level only when the secondary winding is turned on, and the level voltage is the voltage value of the maximum on-current control signal VCST _ MAX output by the peak current control circuit; therefore, when the average voltage VC1_ ave across the first capacitor C1 is greater than the reference voltage VREF _ CC during the entire switching period, the first operational amplifier controls the transistor Q1 to pull down, actively controlling the average voltage VC1_ ave across the first capacitor C1 to be constant, i.e., VREF _ CC, during the entire switching period. The principle of approximating the average output current by the average voltage of the first capacitor C1 over the entire switching period is based on the average output current equation:
while the average voltage over the first capacitor C1
Thereby ensuring constant output currentStator
Referring to fig. 4, in another embodiment, 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 adjusting tube Q1, a second adjusting tube Q2, a third adjusting tube Q3, a fourth adjusting tube Q4, and a fifth adjusting tube Q5.
A first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a non-inverting input terminal of the second operational amplifier, a drain of a fifth adjusting transistor Q5 and a first end of a second resistor R2, a source of the fifth adjusting transistor Q5 is connected to a second end of the second capacitor C2, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and outputs an output signal VCST of the average current control type constant current control circuit to control the flyback constant voltage constant current switch to output a constant current, a first end of the third resistor R3 is connected to an inverting input terminal of the second operational amplifier and a source of a fourth adjusting transistor Q4, an output terminal of the second operational amplifier 2 is connected to a gate of the fourth adjusting transistor Q4, a drain of the fourth adjusting transistor Q4 is connected to an AMP of the drain of the second adjusting transistor Q2, A gate of the second adjusting transistor Q2 and a gate of a third adjusting transistor Q3 are connected, a source of the second adjusting transistor Q2 is connected to a source of the third adjusting transistor Q3, a drain of the third adjusting transistor Q3 is connected to a first end of the first switch K1, a second end of the first switch K1 is connected to a first end of the first capacitor C1, a gate of a fifth adjusting transistor Q5 and a drain of a first adjusting transistor Q1, a control end of the first switch is connected to the signal S _ sec output by the sampling circuit to determine whether the secondary winding is on, a gate of the first adjusting transistor Q1 is connected to an output end of the first operational amplifier AMP1, a non-inverting input end of the first operational amplifier AMP1 is connected to a reference voltage VREF _ CC, and an inverting input end of the first operational amplifier 1 is connected to a source of the first adjusting transistor Q1 and a first end of a 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 tuning transistor Q5, and is grounded.
The first capacitor is provided with a charging current I1 and a discharging current I2, wherein the second resistor R2 and the second capacitor C2 form a low-pass filter circuit, the second adjusting tube Q2 and the third adjusting tube Q3 are arranged in a current mirror mode, the charging current I1 is also in direct proportion to a signal VCST processed by the average current control type constant current control circuit, and the discharging current I2 is in direct proportion to the reference voltage VREF _ CC.
The principle of the constant current mode working is as follows: the oscillation circuit outputs an FMAX signal to control the switching tube Q6 to be switched on, when the switching tube Q6 is switched on, the primary coil is switched on, the detection signal S _ sec is equal to 0, and the first switch K1 is switched off; along with the rise of the current of the primary coil, the voltage VCS on the current detection resistor RCS reaches the voltage value VCST, the comparator outputs low level, the D trigger is reset, the switching tube Q6 is turned off, the secondary coil is turned on, S _ sec is 1, the first switch K1 is closed, and the first capacitor C1 is charged by the charging current I1; when neither the primary coil nor the secondary coil is turned on, S _ sec becomes 0, and the first switch K1 is turned off. 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 to be constant; when the charging current of the first capacitor C1 is I1 greater than the discharging current of I2, the voltage of the first capacitor C1 continuously increases until the regulating transistor Q5 is turned on, the switching transistor Q5 is pulled down, the voltage at the non-inverting input terminal of the second operational amplifier AMP2 decreases, i.e., VCST decreases, the charging current I1 decreases, and the average current I1_ ave of the first capacitor C1 is actively controlled to be a constant value, i.e., VREF _ CC/R4, during the whole switching period. The principle of approximating the average output current with the average current of the first capacitor C1 over the entire switching period is based on the average output current formula:
while the average current over the first capacitor C1
Thereby ensuring a constant output current.
In summary, the following steps: the sampling circuit is used for sampling an induced voltage signal of the auxiliary coil, sending the induced voltage signal to the error amplifying circuit for amplification, and obtaining a maximum conduction current control signal VCST _ MAX through processing of the peak current control circuit, the constant current control circuit processes the accessed 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 constant current, so that the constancy of the output current is ensured, the switching power supply cannot enable the working frequency to enter an audio frequency range along with the change of the output voltage, and the circuit conversion efficiency is improved.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.
Claims (10)
1. A flyback constant-voltage constant-current switching power supply is characterized by comprising a constant-voltage constant-current control circuit; the constant-voltage constant-current control circuit comprises a constant-current control circuit, a sampling circuit, an error amplification circuit and a peak current control circuit, wherein the sampling circuit is used for sampling an induced voltage signal of an auxiliary coil to a secondary coil, sending the induced voltage signal to the error amplification circuit for amplification, and processing the amplified induced voltage signal by the peak current control circuit to obtain a maximum conduction current control signal VCST _ MAX, and the constant-current control circuit is connected to and processes the maximum conduction current control signal VCST _ MAX to control the flyback constant-voltage constant-current switching power supply to output a constant current.
2. The flyback constant voltage and constant current switching power supply as claimed in claim 1, wherein the constant current control circuit is an average voltage control type constant current control circuit.
3. The flyback constant voltage and constant current switching power supply as claimed in claim 2, wherein the average voltage control type constant current control circuit comprises 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, a first regulating transistor Q1;
a first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a first end of the second resistor R2 and a drain of a first adjusting transistor Q1, and outputs an output signal VCST of the average voltage control type constant current control circuit to control the flyback constant voltage constant current switching power supply to output a constant current, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and a non-inverting input end of a second operational amplifier AMP2, an inverting input end of the second operational amplifier AMP2 is connected to an output end of the second operational amplifier AMP2 and a first end of a first switch K1, a second end of the first switch K1 is connected to a first end of a third resistor R3 and a first end of a second switch K2, a control end of the first switch K1 is connected to an input end of the inverter and is connected to an output of the sampling circuit to determine whether the sub-coil is turned on or not, the control end of the second switch K2 is connected to the output end of the inverter, the second end of the third resistor R3 is connected to the non-inverting input end of the first operational amplifier AMP1 and the first end of the first capacitor C1, the inverting input end of the first operational amplifier AMP1 is connected to the reference voltage VREF _ CC, the output end of the first operational amplifier AMP1 is connected to the gate of the first adjusting tube Q1, and the source of the first adjusting tube 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 to the ground.
4. The flyback constant voltage and constant current switching power supply as claimed in claim 3, further comprising a secondary diode D1 connected to the secondary winding, wherein when the secondary winding is turned on, the secondary diode D1 is turned on;
the secondary side diode D1 has a conducting time Tsec, the switching period of the flyback constant-voltage constant-current switching power supply is Tsw, and the average voltage VC1 — ave of the average voltage control type constant-current control circuit is:
5. the flyback constant voltage and constant current switching power supply as claimed in claim 1, wherein the constant current control circuit is an average current control type constant current control circuit.
6. The flyback constant voltage and constant current switching power supply as claimed in claim 5, wherein the average current control type constant current control circuit comprises 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 tube Q1, a second regulating tube Q2, a third regulating tube Q3, a fourth regulating tube Q4 and a fifth regulating tube Q5;
a first end of the first resistor R1 is connected to a maximum on-current control signal VCST _ MAX, a second end of the first resistor R1 is connected to a non-inverting input terminal of the second operational amplifier, a drain of a fifth adjusting transistor Q5 and a first end of a second resistor R2, a source of the fifth adjusting transistor Q5 is connected to a second end of the second capacitor C2, a second end of the second resistor R2 is connected to a first end of the second capacitor C2 and outputs an output signal VCST of the average current control constant current control circuit to control the flyback constant voltage constant current switch to output a constant current, a first end of the third resistor R3 is connected to an inverting input terminal of the second operational amplifier and a source of a fourth adjusting transistor Q4, an output terminal of the second operational amplifier 2 is connected to a gate of the fourth adjusting transistor Q4, a drain of the fourth adjusting transistor Q4 is connected to an AMP of the drain of the second adjusting transistor Q2, A gate of the second adjusting tube Q2 and a gate of a third adjusting tube Q3 are connected, a source of the second adjusting tube Q2 is connected to a source of the third adjusting tube Q3, a drain of the third adjusting tube Q3 is connected to a first end of the first switch K1, a second end of the first switch K1 is connected to a first end of the first capacitor C1, a gate of the fifth adjusting tube Q5 and a drain of the first adjusting tube Q1, a control end of the first switch is connected to the signal S _ sec output by the sampling circuit to determine whether the secondary coil is on, a gate of the first adjusting tube Q1 is connected to an output end of the first operational amplifier AMP1, a non-inverting input end of the first operational amplifier AMP1 is connected to a reference voltage VREF _ CC, an inverting input end of the first operational amplifier AMP 38 is connected to a source of the first adjusting tube Q1 and a first end of the fourth resistor R4, a non-inverting input end of the first capacitor Q3629 is connected to a second end of the fourth resistor C582, The second end of the second capacitor C2 and the source of the fifth adjusting tube Q5 are connected to ground.
7. The flyback constant voltage and constant current switching power supply as claimed in claim 6, further comprising a secondary diode D1 connected to the secondary winding, wherein when the secondary winding is turned on, the secondary diode D1 is turned on;
the charging current of the first capacitor is I1, the discharging current of the first capacitor is I2, when the charging current is I1 and the discharging current is I2, the output current of the flyback constant-voltage constant-current switching power supply is constant, and then the average current of the average current control type constant-current control circuit is:
wherein Tsec is the conducting time of the secondary side diode D1, and Tsw is the switching period of the flyback constant-voltage constant-current switching power supply.
8. The flyback constant voltage and constant current switching power supply as claimed in claim 7, wherein the charging current I1 is proportional to the signal VCST processed by the average current control type constant current control circuit.
9. The flyback constant voltage and constant current switching power supply as claimed in claim 7, wherein the discharge current I2 is proportional to the reference voltage VREF _ CC.
10. The flyback constant voltage and constant current switching power supply as claimed in claim 6, wherein the second Q2 and the third Q3 are current mirror devices.
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| CN202020856731.7U CN211720474U (en) | 2020-05-20 | 2020-05-20 | Flyback constant-voltage constant-current switching power supply |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114189024A (en) * | 2021-12-20 | 2022-03-15 | 浙江特康电子科技有限公司 | Method and device for realizing constant current mode, switching power supply and medium |
| CN114189024B (en) * | 2021-12-20 | 2024-06-11 | 浙江特康电子科技有限公司 | Method and device for realizing constant current mode, switching power supply and medium |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114189024A (en) * | 2021-12-20 | 2022-03-15 | 浙江特康电子科技有限公司 | Method and device for realizing constant current mode, switching power supply and medium |
| CN114189024B (en) * | 2021-12-20 | 2024-06-11 | 浙江特康电子科技有限公司 | Method and device for realizing constant current mode, switching power supply and medium |
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