CN210297540U - Constant current control circuit and switching power supply circuit - Google Patents
Constant current control circuit and switching power supply circuit Download PDFInfo
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- CN210297540U CN210297540U CN201921102709.7U CN201921102709U CN210297540U CN 210297540 U CN210297540 U CN 210297540U CN 201921102709 U CN201921102709 U CN 201921102709U CN 210297540 U CN210297540 U CN 210297540U
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Abstract
The utility model relates to a constant current control technical field specifically discloses a constant current control circuit, wherein, constant current control circuit includes: the demagnetization detection circuit and the sample and hold circuit are connected with the input end of the transconductance operational amplification circuit, the output end of the transconductance operational amplification circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverted input end of the PWM comparator, the output end of the PWM comparator is connected to the input end of the RS trigger, the output end of the RS trigger is connected to the input end of the sample and hold circuit in a feedback mode, and the input end of the sample and hold circuit and the in-phase input end of the PWM comparator are further used for inputting sampling voltage signals. The utility model also discloses a switching power supply circuit. The utility model provides a constant current control circuit can realize the regulation of output current precision, and then realizes exporting the high accuracy electric current.
Description
Technical Field
The utility model relates to a constant current control technical field especially relates to a constant current control circuit and including this constant current control circuit's switching power supply circuit.
Background
The general expression of the output current of the flyback topology applied to primary side control is as follows:
wherein N ispRepresenting the number of turns of the primary side of the transformer, NsIndicating the number of secondary turns of the transformer, Ip,pkRepresenting the peak current, T, of the primary side of the transformerdemDenotes the demagnetization time, TswIndicating the switching tube duty cycle.
In the existing traditional constant current control mode, the turn ratio of the primary side and the secondary side of the transformer
And a sampling resistor RcsAll are kept unchanged, and in a constant current control loop, V can be ensured through loop feedback controlcs,pkAnd
the average value of the output current is a constant value, so that the average value of the output current is ensured to be a constant value. For example, in a control circuit, the primary-secondary side turn ratio of the topological flyback transformer is assumed
Sampling resistor Rcs862.5m omega. If the traditional constant current control mode is adopted, the two variables are respectively controlled to be constant values, and the CS peak voltage V is controlled through a feedback loopcs,pkWith 500mV, the demagnetization time and period being controlled simultaneouslyRatio of
The resulting final load output current may be constant at 2A. However, in the conventional constant current control mode, because variables need to be controlled separately, the variables have their distribution ranges and their affected factors, which results in low precision of final constant current output. For example, in the above example, due to Vcs,pkVariable control of 500mV, and
the final output condition is not ideal when the final output condition is theoretically designed, and the actual obtained control variable V is assumed to have 1% deviationcs,pk＝495mV，
The load output current is 1.96A, and 2% of error exists between the load output current and the preset 2A current output, namely the error of the final output current is amplified.
Therefore, how to improve the accuracy of the output current in the constant current control circuit is a technical problem to be solved at present.
Disclosure of Invention
The utility model discloses aim at solving one of the technical problem that exists among the prior art at least, provide a constant current control circuit and including this constant current control circuit's switching power supply circuit to solve the problem among the prior art.
As a first aspect of the present invention, there is provided a constant current control circuit, wherein the constant current control circuit includes: the demagnetization detection circuit and the sample and hold circuit are connected with the input end of the transconductance operational amplification circuit, the output end of the transconductance operational amplification circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverted input end of the PWM comparator, the output end of the PWM comparator is connected to the input end of the RS trigger, the output end of the RS trigger is connected to the input end of the sample and hold circuit in a feedback manner, and the input end of the sample and hold circuit and the non-inverting input end of the PWM comparator are also used for inputting a sampling voltage signal;
the sampling hold circuit is used for sampling and holding the sampling voltage signal to obtain a sampling hold voltage;
the demagnetization detection circuit is used for outputting a demagnetization time signal;
the transconductance operational amplification circuit is used for controlling the sampling holding voltage through the demagnetization time signal to obtain a sampling current signal;
the proportional buffer is used for carrying out proportional reduction control on the sampling current signal to obtain a proportional reduction signal;
the PWM comparator is used for comparing the proportional reduction signal with the sampling voltage signal to obtain a turn-off signal;
and the RS trigger is used for processing the turn-off signal to obtain a switch tube logic control signal so as to control the on and off of the power switch tube.
Preferably, the constant current control circuit further comprises a power tube on signal generator, and the power tube on signal generator is used for generating an on signal.
Preferably, an S input end of the RS flip-flop is connected to the power tube on-signal generator, an R input end of the RS flip-flop is connected to an output end of the PWM comparator, and the RS flip-flop is configured to process the off signal under the effect of the on signal to obtain the switching tube logic control signal.
Preferably, the constant current control circuit further comprises a gate driving circuit, an input end of the gate driving circuit is connected to an output end of the RS flip-flop, and the gate driving circuit is configured to process the switching tube logic control signal to obtain a switching tube driving signal and output the switching tube driving signal.
Preferably, the constant current control circuit further comprises a reference circuit, and the reference circuit is respectively connected with the demagnetization detection circuit, the transconductance operational amplification circuit, the sample-and-hold circuit, the proportional buffer and the PWM comparator, and is configured to provide a reference voltage signal and a reference current signal.
Preferably, the sample-and-hold circuit includes a first switch tube and a sample-and-hold capacitor, a driving end of the first switch tube is connected to an output end of the RS flip-flop, a first end of the first switch tube is connected to one end of the sample-and-hold capacitor, a second end of the first switch tube is used for inputting the sampled voltage signal, and the other end of the sample-and-hold capacitor is connected to a signal ground.
Preferably, the transconductance operational amplifier circuit includes: second switch tube, third switch tube and transconductance operational amplifier, the drive end of second switch tube with demagnetization detection circuitry's output is connected, the first end of third switch tube is connected to the first end of second switch tube, the second end of second switch tube is connected the one end of sample hold capacitor, the drive end of third switch tube is connected demagnetization detection circuitry's output, the second end of third switch tube is connected signal ground, transconductance operational amplifier's normal phase input is used for the input reference voltage signal, transconductance operational amplifier's inverting input end is connected the first end of second switch tube, transconductance operational amplifier's output is used for exporting the sampling current signal.
Preferably, the proportional buffer includes: the sampling circuit comprises an operational amplifier, a fourth switch tube, a first voltage-dividing resistor and a second voltage-dividing resistor, wherein a positive phase input end of the operational amplifier is used for inputting a sampling current signal, an inverting input end of the operational amplifier is connected to a second end of the fourth switch tube, an output end of the operational amplifier is connected with a driving end of the fourth switch tube, a first end of the fourth switch tube is connected with an input voltage signal, a second end of the fourth switch tube is connected with one end of the first voltage-dividing resistor, and the other end of the first voltage-dividing resistor is connected with a signal ground through the second voltage-dividing resistor.
Preferably, the first switching tube, the second switching tube, the third switching tube and the fourth switching tube each include an N-type switching tube.
As a second aspect of the present invention, there is provided a switching power supply circuit, wherein the switching power supply circuit includes: the rectifier filter circuit is connected with the RCD energy absorption circuit and the constant current control circuit, the output end of the constant current control circuit is connected with the drive end of the power switch tube, the power switch tube and the RCD energy absorption circuit are both connected with the source side of the transformer, the secondary side of the transformer is connected with the output control circuit, and the constant current control circuit can process the sampling voltage signal to obtain a switch tube logic control signal so as to control the on and off of the power switch tube.
The utility model provides a constant current control circuit, realize sampling and keeping sampling voltage signal through the sample hold circuit, control proper sampling current signal under demagnetization time signal's effect to the sample hold voltage through transconductance operational amplifier circuit, obtain switch tube logic control signal through handling sampling current signal at last, can realize the control of switching on and turn-off to power switch tube through switch tube logic control signal, thereby can realize the regulation of output current precision when this constant current control circuit uses in switching power supply circuit, and then realize exporting the high accuracy electric current.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a block diagram of the constant current control circuit provided by the present invention.
Fig. 2 is a circuit structure diagram of the switching power supply circuit provided by the present invention.
Fig. 3 is a structural diagram of the sample-and-hold circuit and the transconductance operational amplifier circuit provided by the present invention.
Fig. 4 is a circuit diagram of the proportional buffer and the PWM comparator provided in the present invention.
Fig. 5a is a structural diagram of an embodiment of the power tube conducting signal generator according to the present invention.
Fig. 5b is a structural diagram of another embodiment of the power tube conducting signal generator according to the present invention.
Fig. 6 is a waveform diagram of respective signals in fig. 1.
Fig. 7 is a waveform diagram of the respective signals in fig. 5 a.
Detailed Description
The following detailed description of the embodiments of the present invention will be made with reference to the accompanying drawings. It is to be understood that the description of the embodiments herein is for purposes of illustration and explanation only and is not intended to limit the invention.
In order to realize can improving the output current precision among the constant current control circuit, the utility model discloses use the primary side control isolation formula flyback converter who is applied to work in critical conduction mode (BCM) as an example. Energy is transferred between the primary coil and the secondary coil; the secondary coil transmits output information to the auxiliary winding, and the input and the output are isolated by using a transformer. A general switching power supply control system has two processes of starting and stopping of a power tube. When the power tube is started, the primary side inductor forms a path to the ground, the input end supplies energy to the transformer, the primary side inductor stores energy, the secondary side diode is cut off, and the load output energy is supplied by the energy stored in the output capacitor; when the power tube is turned off, the transformer releases energy, and the secondary inductor releases energy. The on and off of the power tube are controlled through an internal feedback circuit, and the final output current is constant.
The formula of the output current obtained by the control principle of the system power level is as follows:
wherein N ispRepresenting the number of turns of the primary side of the transformer, NsTo representNumber of secondary turns of transformer, Ip,pkRepresenting the peak current, T, of the primary side of the transformerdemDenotes the demagnetization time, TswIndicating the switching tube duty cycle.
Through the analysis of the traditional constant current control mode principle, the output of high-precision constant current can be realized by adopting a 'unique' variable control mode. Therefore, the utility model provides a constant current control circuit to control among the above-mentioned output current formula
The product of the three variables is a constant quantity, and the product of the three variables can be called as a sampling mean value and is a unique variable in the constant-current control system.
Specifically, as a first aspect of the present invention, there is provided a constant current control circuit 112, wherein, as shown in fig. 1, the constant current control circuit 112 includes: the demagnetization detection circuit 206, the sample-and-hold circuit 207, the transconductance operational amplifier circuit 203, the proportional buffer 204, the PWM comparator 205, and the RS flip-flop 208, wherein both the demagnetization detection circuit 206 and the sample-and-hold circuit 207 are connected to an input terminal of the transconductance operational amplifier circuit 203, an output terminal of the transconductance operational amplifier circuit 203 is connected to an input terminal of the proportional buffer 204, an output terminal of the proportional buffer 204 is connected to an inverted input terminal of the PWM comparator 205, an output terminal of the PWM comparator 205 is connected to an input terminal of the RS flip-flop 208, an output terminal of the RS flip-flop 208 is connected to an input terminal of the sample-and-hold circuit 207 in a feedback manner, and an input terminal of the sample-and-hold circuit 207 and a non-inverting input terminal of the PWM comparator 205 are further used for inputting a sampling voltage signal;
the sample-and-hold circuit 207 is configured to sample and hold the sampled voltage signal to obtain a sample-and-hold voltage;
the demagnetization detection circuit 206 is used for outputting a demagnetization time signal;
the transconductance operational amplifier circuit 203 is configured to control the sample-hold voltage according to the demagnetization time signal to obtain a sample current signal;
the proportional buffer 204 is configured to perform proportional reduction control on the sampling current signal to obtain a proportional reduction signal;
the PWM comparator 205 is configured to compare the scaling-down signal and the sampling voltage signal to obtain a turn-off signal;
the RS flip-flop 208 is configured to process the turn-off signal to obtain a switching tube logic control signal to control the power switching tube to be turned on and off.
The utility model provides a constant current control circuit, realize sampling and keeping sampling voltage signal through the sample hold circuit, control proper sampling current signal under demagnetization time signal's effect to the sample hold voltage through transconductance operational amplifier circuit, obtain switch tube logic control signal through handling sampling current signal at last, can realize the control of switching on and turn-off to power switch tube through switch tube logic control signal, thereby can realize the regulation of output current precision when this constant current control circuit uses in switching power supply circuit, and then realize exporting the high accuracy electric current.
Specifically, as shown in fig. 1, the constant current control circuit 112 further includes a power tube on signal generator 202, and the power tube on signal generator 202 is configured to generate an on signal.
Specifically, an S input end of the RS flip-flop 208 is connected to the power tube on signal generator 112, an R input end of the RS flip-flop 208 is connected to an output end of the PWM comparator 205, and the RS flip-flop 208 is configured to process the off signal under the effect of the on signal to obtain the switching tube logic control signal.
Specifically, the constant current control circuit 112 further includes a gate driving circuit 219, an input end of the gate driving circuit 219 is connected to an output end of the RS flip-flop 208, and the gate driving circuit 219 is configured to process the switching tube logic control signal to obtain a switching tube driving signal, and output the switching tube driving signal.
Specifically, as shown in fig. 1, the constant current control circuit 112 further includes a reference circuit 201, and the reference circuit 201 is connected to the demagnetization detection circuit 206, the transconductance operational amplifier circuit 203, the sample-and-hold circuit 207, the proportional buffer 204, and the PWM comparator 205, respectively, and is configured to provide a reference voltage signal and a reference current signal.
Note that the connection relationship between the reference circuit 201 and other circuits is not shown in fig. 1.
Specifically, as shown in fig. 1 and fig. 2, a reference circuit 201 is used to generate various reference voltages and reference currents required by the constant current control circuit 112, such as a reference voltage Vref required by a transconductance operational amplifier circuit 203, and the voltage determines the value of a "sampling average value"; a demagnetization detection circuit 206 for extracting a demagnetization time signal from the FB signal; a sample-and-hold circuit 207 that samples and holds the input voltage Vcs of the CS pin of the constant current control circuit 112; a transconductance operational amplifier circuit 203 for converting the voltage held by the sample-and-hold circuit 207 into a current by controlling a demagnetization time signal; a built-in compensation capacitor 217, which in this embodiment is 50 pF; a proportional buffer circuit 204 which performs a proportional reduction on the sampling current signal 213 and performs a buffer function; a PWM comparator 205 that compares the scaled-down signal 218 with the sampled voltage signal 216 and outputs a shutdown signal 214; an RS flip-flop 208 receiving the on control signal 215 and the off signal 214 to finally generate the switch tube logic control signal 210; the power transistor gate driver 219 converts the switching transistor logic control signal 210 into a high voltage power transistor driving signal 220, and outputs the high voltage power transistor driving signal through the BD pin of the constant current control circuit 112 to control the power transistor 113 to be turned on or off.
Specifically, as shown in fig. 3, the sample-and-hold circuit 207 includes a first switch tube 301 and a sample-and-hold capacitor 302, a driving end of the first switch tube 301 is connected to the output end of the RS flip-flop 208, a first end of the first switch tube 301 is connected to one end of the sample-and-hold capacitor 302, and a second end of the first switch tube 301 is used for inputting the sampled voltage signal 216VCSThe other end of the sample-and-hold capacitor 302 is connected to signal ground.
Specifically, as shown in fig. 3, the transconductance operational amplifier circuit 203 includes: second switch tube 303, third switch tube 306 and transconductance operational amplifier 307, the drive end of second switch tube 303 with demagnetization detection circuitry 206's output is connected, the first end of third switch tube 306 is connected to the first end of second switch tube 303, the second end of second switch tube 303 is connected the one end of sample hold capacitor 302, the drive end of third switch tube 306 is connected the output of demagnetization detection circuitry 206, the second end of third switch tube 306 is connected signal ground, transconductance operational amplifier 307's normal phase input end is used for inputing reference voltage signal 209, transconductance operational amplifier 307's inverting input end is connected the first end of second switch tube 303, transconductance operational amplifier 307's output is used for exporting sampling current signal 213.
Preferably, the first switching tube 301, the second switching tube 303 and the third switching tube 306 may be N-type switching tubes.
In fig. 3, taking an N-type switch tube as an example, the first switch tube 301, the second switch tube 303 and the third switch tube 306 are controlled by a switch tube logic control signal 210, a demagnetization signal 212 and a demagnetization non-signal 305, respectively.
A primary peak current sampling signal is obtained through a pin CS of the constant current control circuit 112, a sampling voltage signal 216 is obtained through a sampling resistor, and the sampling voltage signal 216 is sampled through a first switching tube 301 controlled by the power tube logic control signal 210. Next, an average value operation is performed in a switching period based on the excitation inductance demagnetization time signal 212, thereby obtaining an average current. During the on-time of the power tube logic control signal 210, the sample-and-hold capacitor 302 samples the primary sampling voltage signal 216, i.e., the sample-and-hold capacitor 302 charges; during the off time of the power tube logic control signal 210, the first switch tube 301 is turned off, and the sample-hold capacitor 302 passes through the sample-hold signal 211VsampleAnd (4) discharging. In the non-demagnetization process, the demagnetization non-signal 305 is at high level, the demagnetization signal 212 is at low level, the third switching tube 306 is correspondingly controlled to be turned on, the second switching tube 303 is correspondingly controlled to be turned off, and at this time, the sampling mean value signal 304V isCS,sampleGrounding, charging the on-chip compensation capacitor 217; in thatIn the demagnetization time, the demagnetization signal 212 is at a high level, the demagnetization non-signal 305 is at a low level, the second switching tube 303 is correspondingly controlled to be switched on, the third switching tube 306 is correspondingly controlled to be switched off, and the on-chip compensation capacitor 217 discharges. From the principle of charge-discharge balance on the on-chip compensation capacitor 217 in a single cycle, the following equation can be obtained:
gm·(Vref-0)·(T-Tdem)+gm·(Vref-Vcs1)·Tdem＝0，
wherein, VrefThe reference voltage 209, T required by the transconductance operational amplifier 203 is showndemRepresenting demagnetization time, T representing the switching tube duty cycle, VCS1Represents the mean voltage of the samples at the demagnetization time, gmThe equivalent transconductance values of the transconductance operational amplifier 307 shown in fig. 3 are shown.
Transconductance g of OTA during charging time and discharging timemWhen held constant, the following equation is obtained:
control "sample mean" as described previously "
It can be found that,
this equation is the "unique" variable that needs to be controlled in a constant current loop. By
Equality under the constant current topology of the present invention, the transconductance operational amplifier 307 is required to be changed within the full range (0-1V), and the transconductance is constant. Transconductance 307 generates a sampling current signal 213 required by PWM comparator 205, and after scaling with a certain proportion by proportional buffer 204, PWM comparator 205 compares the output of the previous stage circuit with a corresponding sampling voltage signal 216 to generate a corresponding off signal of the constant current loop.
As shown in fig. 4, the proportional buffer 204 includes: the sampling circuit comprises an operational amplifier 400, a fourth switching tube 401, a first voltage-dividing resistor 402 and a second voltage-dividing resistor 403, wherein a positive phase input end of the operational amplifier 400 is used for inputting the sampling current signal 213, an inverted phase input end of the operational amplifier 400 is connected to a second end of the fourth switching tube 401, an output end of the operational amplifier 400 is connected to a driving end of the fourth switching tube 401, a first end of the fourth switching tube 401 is connected to an input voltage signal VDD, a second end of the fourth switching tube 401 is connected to one end of the first voltage-dividing resistor 402, and the other end of the first voltage-dividing resistor 402 is connected to a signal ground through the second voltage-dividing resistor 403.
It should be noted that, when the first switching tube 301, the second switching tube 303, the third switching tube 306, and the fourth switching tube 401 are all N-type switching tubes, the driving end of each switching tube is a gate, the first end is a drain, and the second end is a source.
As shown in fig. 4, the proportional buffer 204 is only an embodiment and is composed of an operational amplifier 400, a fourth switch 401, a first voltage dividing resistor 402 and a second voltage dividing resistor 403, and the output voltage at the node Y of the node 405 and the input voltage at the node X of the non-inverting input of the operational amplifier 400 have the following corresponding relationship:
wherein, VYThe voltage at Y of node 405, i.e., the proportional buffer output voltage, X represents the transconductance operational amplifier output voltage, RaRepresents a first divider resistor 402, RbA second voltage dividing resistor 403 is shown.
Note that the signal ground is connected at node 405 through a filter capacitor 404.
The waveforms corresponding to the respective nodes are shown in fig. 6. A negative feedback closed loop control loop formed by the above method, namely a general formula
Is maintained at the reference voltage signal 209 and,resulting in a constant output current.
FIG. 5a is a specific embodiment of the power tube on signal generator 202, with 508 representing the bias voltage from the reference circuit 201; the fifth switching tube 501, the sixth switching tube 502, the seventh switching tube 504 and the eighth switching tube 505 form a current comparator together, and when the output voltage feedback signal FB is a negative voltage, the quasi-resonant valley conduction signal (QR)509 is at a low level; when FB is zero level or positive voltage, the quasi-resonant valley conduction signal 509 is high level; the ninth switching tube 503 and the tenth switching tube 506 together form an inverter, the quasi-resonant valley bottom conduction signal 509 is inverted and then output to obtain a non-signal 510 of the quasi-resonant valley bottom conduction signal, and the non-signal 510 of the quasi-resonant valley bottom conduction signal outputs the final conduction control signal 215 through the first flip-flop 507. The waveforms corresponding to the respective signals are shown in fig. 7.
Fig. 5b is another embodiment of the power tube on signal generator 202. The output voltage feedback pin FB voltage is compared with the reference voltage 514 from the reference circuit 201 by the comparator 511, and when the FB voltage is higher than the reference voltage 514, the output signal 513 of the comparator 511 is at a high level; when the FB voltage is lower than the reference voltage 514, the output 513 is low, and the final on control signal 215 is output through the second flip-flop 512.
The fifth switching tube 501, the sixth switching tube 502, and the ninth switching tube 503 may be P-type switching tubes, and the seventh switching tube 504, the eighth switching tube 505, and the tenth switching tube 506 may be N-type switching tubes.
The RS flip-flop 208 receives the on control signal 215 and the off signal 214 to generate the switch tube logic control signal 210; the power transistor gate driver 219 converts the switching transistor logic control signal 210 into a high voltage power transistor driving signal 220, and outputs the high voltage power transistor driving signal through the BD pin of the constant current control circuit 112 to control the power transistor 113 to be turned on or off.
As a second aspect of the present invention, there is provided a switching power supply circuit, wherein, as shown in fig. 2, the switching power supply circuit includes: the rectifier filter circuit is connected with the RCD energy absorption circuit 111 and the constant current control circuit 112, the output end of the constant current control circuit 112 is connected with the drive end of the power switch tube 113, the power switch tube 113 and the RCD energy absorption circuit 111 are both connected with the source side of the transformer 115, the secondary side of the transformer 115 is connected with the output control circuit, and the constant current control circuit 112 can process the sampling voltage signal to obtain a switch tube logic control signal to control the on and off of the power switch tube.
The utility model provides a switching power supply circuit, because adopt the constant current control circuit in the front as the controller, realize sampling and keeping sampling voltage signal through the sample hold circuit, control proper sampling current signal under demagnetization time signal's effect to the sample hold voltage through transconductance operational amplifier circuit, at last through handling sampling current signal and obtain switch tube logic control signal, can realize the control of switching on and turn-off to power switch tube through switch tube logic control signal, thereby can realize the regulation of output current precision, and then realize exporting the high accuracy electric current.
Specifically, as shown in fig. 2, in order to implement the primary side controlled switching power supply circuit of the present invention, the first rectifier diode 101, the second rectifier diode 102, the third rectifier diode 103, the fourth rectifier diode 104 and the filter capacitor 105 form a rectifier and filter circuit, Vdc represents the rectified and filtered dc high voltage; 106 denotes a high voltage starting resistance; 107 denotes an energy storage capacitor for supplying electric power to the constant current control circuit 112; 108 denotes a transformer auxiliary winding rectifier diode; 109 and 110 are two voltage dividing resistors for output voltage feedback; 111 denotes an RCD energy absorbing network; 113 denotes an external high-voltage power switch tube; 114 represents a primary side inductance current sampling resistor of the transformer; 115 is a transformer; 116 is a rectifier diode of the secondary output winding of the transformer; 117 is an output filter capacitor; 118 is the output load. Vout is the output voltage.
After the switching power supply circuit is powered on, VIN charges the filter capacitor 107 through the high-voltage starting resistor 106, and the voltage of the filter capacitor 107 gradually increases; when the voltage of the filter capacitor rises to a certain preset value, the constant current control circuit 12 starts to work. The BD pin outputs high level to control the conduction of the power tube 113; after the power tube 113 is conducted, the current flows through the primary inductor Np of the transformer 115 to store energy; when the power transistor 113 is turned on, the secondary rectifier diode 116 is turned off, and the output load current is supplied by the energy stored in the output capacitor 117. With the increase of the inductive current, the voltage on the sampling resistor 114 gradually increases, and when the current reaches a current limiting point designed in advance in the constant current control circuit 112, the BD output low level of the constant current control circuit 112 controls the power tube 113 to be cut off; the secondary rectifier diode 116 is turned on; the transformer 115 discharges the stored energy in the form of current through the output winding Ns; the output current powers the load and the output capacitor 117. Therefore, by sampling the sampling voltage signal CS on the primary inductor current sampling resistor 114 and the output voltage FB on the output voltage feedback pin FB, the constant current control circuit 112 can adjust the on-time of the output waveform of the BD pin, thereby controlling the output power of the switching power supply circuit.
It is to be understood that the above embodiments are merely exemplary embodiments that have been employed to illustrate the principles of the present invention, and that the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (10)
1. A constant current control circuit, comprising: the demagnetization detection circuit and the sample and hold circuit are connected with the input end of the transconductance operational amplification circuit, the output end of the transconductance operational amplification circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverted input end of the PWM comparator, the output end of the PWM comparator is connected to the input end of the RS trigger, the output end of the RS trigger is connected to the input end of the sample and hold circuit in a feedback manner, and the input end of the sample and hold circuit and the non-inverting input end of the PWM comparator are also used for inputting a sampling voltage signal;
the sampling hold circuit is used for sampling and holding the sampling voltage signal to obtain a sampling hold voltage;
the demagnetization detection circuit is used for outputting a demagnetization time signal;
the transconductance operational amplification circuit is used for controlling the sampling holding voltage through the demagnetization time signal to obtain a sampling current signal;
the proportional buffer is used for carrying out proportional reduction control on the sampling current signal to obtain a proportional reduction signal;
the PWM comparator is used for comparing the proportional reduction signal with the sampling voltage signal to obtain a turn-off signal;
and the RS trigger is used for processing the turn-off signal to obtain a switch tube logic control signal so as to control the on and off of the power switch tube.
2. The constant current control circuit according to claim 1, further comprising a power tube on signal generator for generating an on signal.
3. The constant current control circuit according to claim 2, wherein an S input terminal of the RS flip-flop is connected to the power tube on signal generator, an R input terminal of the RS flip-flop is connected to an output terminal of the PWM comparator, and the RS flip-flop is configured to process the off signal under the effect of the on signal to obtain the switching tube logic control signal.
4. The constant current control circuit according to claim 1, further comprising a gate driving circuit, wherein an input terminal of the gate driving circuit is connected to an output terminal of the RS flip-flop, and the gate driving circuit is configured to process the switching tube logic control signal to obtain a switching tube driving signal and output the switching tube driving signal.
5. The constant current control circuit according to claim 1, further comprising a reference circuit, connected to the demagnetization detection circuit, the transconductance operational amplification circuit, the sample-and-hold circuit, the proportional buffer, and the PWM comparator, respectively, for providing a reference voltage signal and a reference current signal.
6. The constant current control circuit according to claim 1, wherein the sample-and-hold circuit includes a first switch tube and a sample-and-hold capacitor, a driving end of the first switch tube is connected to an output end of the RS flip-flop, a first end of the first switch tube is connected to one end of the sample-and-hold capacitor, a second end of the first switch tube is used for inputting the sampled voltage signal, and the other end of the sample-and-hold capacitor is connected to a signal ground.
7. The constant current control circuit according to claim 6, wherein the transconductance operational amplification circuit comprises: second switch tube, third switch tube and transconductance operational amplifier, the drive end of second switch tube with demagnetization detection circuitry's output is connected, the first end of third switch tube is connected to the first end of second switch tube, the second end of second switch tube is connected the one end of sample hold capacitor, the drive end of third switch tube is connected demagnetization detection circuitry's output, the second end of third switch tube is connected signal ground, transconductance operational amplifier's normal phase input is used for the input reference voltage signal, transconductance operational amplifier's inverting input end is connected the first end of second switch tube, transconductance operational amplifier's output is used for exporting the sampling current signal.
8. The constant current control circuit according to claim 7, wherein the proportional buffer includes: the sampling circuit comprises an operational amplifier, a fourth switch tube, a first voltage-dividing resistor and a second voltage-dividing resistor, wherein a positive phase input end of the operational amplifier is used for inputting a sampling current signal, an inverting input end of the operational amplifier is connected to a second end of the fourth switch tube, an output end of the operational amplifier is connected with a driving end of the fourth switch tube, a first end of the fourth switch tube is connected with an input voltage signal, a second end of the fourth switch tube is connected with one end of the first voltage-dividing resistor, and the other end of the first voltage-dividing resistor is connected with a signal ground through the second voltage-dividing resistor.
9. The constant current control circuit according to claim 8, wherein the first switching tube, the second switching tube, the third switching tube and the fourth switching tube each comprise an N-type switching tube.
10. A switching power supply circuit characterized by comprising: the constant current control circuit comprises a rectification filter circuit, an RCD energy absorption circuit, a transformer, an output control circuit, a power switch tube and the constant current control circuit of any one of claims 1 to 9, wherein the rectification filter circuit is connected with the RCD energy absorption circuit and the constant current control circuit, the output end of the constant current control circuit is connected with the drive end of the power switch tube, the power switch tube and the RCD energy absorption circuit are both connected with the source side of the transformer, the secondary side of the transformer is connected with the output control circuit, and the constant current control circuit can process the sampling voltage signal to obtain a switch tube logic control signal so as to control the on and off of the power switch tube.
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| CN201921102709.7U CN210297540U (en) | 2019-07-15 | 2019-07-15 | Constant current control circuit and switching power supply circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110277897A (en) * | 2019-07-15 | 2019-09-24 | 无锡硅动力微电子股份有限公司 | A kind of constant-current control circuit and switching power circuit |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110277897A (en) * | 2019-07-15 | 2019-09-24 | 无锡硅动力微电子股份有限公司 | A kind of constant-current control circuit and switching power circuit |
| CN110277897B (en) * | 2019-07-15 | 2023-12-29 | 无锡硅动力微电子股份有限公司 | Constant current control circuit and switching power supply circuit |
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Inventor after: Zhu Qinwei Inventor after: Liye Inventor after: Huang Feiming Inventor before: Yu Nannan Inventor before: Zhu Qinwei Inventor before: Liye Inventor before: Huang Feiming |