CN110277897B - 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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- CN110277897B CN110277897B CN201910636071.3A CN201910636071A CN110277897B CN 110277897 B CN110277897 B CN 110277897B CN 201910636071 A CN201910636071 A CN 201910636071A CN 110277897 B CN110277897 B CN 110277897B
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0009—Devices or circuits for detecting current in a converter
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention relates to the technical field of constant current control, and particularly discloses a constant current control circuit, wherein the constant current control circuit comprises: the device comprises a demagnetization detection circuit, a sample hold circuit, a transconductance operational amplifier circuit, a proportional buffer, a PWM comparator and an RS trigger, wherein the demagnetization detection circuit and the sample hold circuit are connected with the input end of the transconductance operational amplifier circuit, the output end of the transconductance operational amplifier circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverting 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 hold circuit in a feedback manner, and the input end of the sample hold circuit and the non-inverting input end of the PWM comparator are also used for inputting sampling voltage signals. The invention also discloses a switching power supply circuit. The constant current control circuit provided by the invention can realize the adjustment of the precision of the output current, thereby realizing the output of high-precision current.
Description
Technical Field
The invention relates to the technical field of constant current control, in particular to a constant current control circuit and a switching power supply circuit comprising the same.
Background
The general expression of the output current of the flyback topology applied to primary side control is as follows:
wherein N is p Indicating the number of turns of the primary side of the transformer, N s Indicating the number of turns of the secondary side of the transformer, I p,pk Representing the primary side peak current of the transformer, T dem Indicates the demagnetizing time T sw Indicating the switching tube duty cycle.
In the existing traditional constant current control mode, the primary and secondary side turn ratios of the transformerAnd sampling resistor R cs All remain unchanged, in the constant current control loop, V can be ensured through loop feedback control cs,pk And->The output current average value is ensured to be constant. For example, in the control circuit, it is assumed that the topology flyback transformer has a primary-to-secondary side turn ratio +.>Sampling resistor R cs = 862.5mΩ. If the traditional constant current control mode is adopted, two variables are respectively controlled to be constant values, the CS peak voltage V is controlled through a feedback loop cs,pk =500 mV, while controlling the ratio of demagnetizing time to period +.>The resulting final load output current may be constant at 2A. However, in the conventional constant current control mode, because the variables need to be controlled separately, the variables have their distribution ranges and affected factors, respectively, which results in low final constant current output precision. For example, in the above example, due to V cs,pk Variable control of =500 mV +.>The variable control of (2) is independently controlled by feedback in separate loops, the final output condition is often not ideal when theoretically designed, and the actual control variable V is obtained assuming that 1% deviation exists in the respective final output cs,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 output current accuracy in the constant current control circuit is a technical problem to be solved.
Disclosure of Invention
The invention aims to at least solve one of the technical problems in the prior art, and provides a constant current control circuit and a switching power supply circuit comprising the same, so as to solve the problems in 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 device comprises a demagnetization detection circuit, a sample-and-hold circuit, a transconductance operational amplifier circuit, a proportional buffer, a PWM (pulse-width modulation) comparator and an RS trigger, wherein the demagnetization detection circuit and the sample-and-hold circuit are both connected with the input end of the transconductance operational amplifier circuit, the output end of the transconductance operational amplifier circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverting 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 in feedback connection with the input end of the sample-and-hold circuit, 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 sampling voltage signals;
the sampling and holding circuit is used for sampling and holding the sampling voltage signal to obtain sampling and holding voltage;
the demagnetization detection circuit is used for outputting a demagnetization time signal;
the transconductance operational amplification circuit is used for controlling the sampling hold voltage through the demagnetizing 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 switching tube logic control signal so as to control the on and off of the power switching tube.
Preferably, the constant current control circuit further comprises a power tube conduction signal generator, and the power tube conduction signal generator is used for generating a conduction 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 switch tube logic control signal.
Preferably, the constant current control circuit further comprises a gate driving circuit, wherein an input end of the gate driving circuit is connected with an output end of the RS trigger, and the gate driving circuit is used for processing the switching tube logic control signal to obtain a switching tube driving signal and outputting 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 hold circuit, the proportional buffer and the PWM comparator and is used for providing a reference voltage signal and a reference current signal.
Preferably, the sample hold circuit includes a first switching tube and a sample hold capacitor, a driving end of the first switching tube is connected with an output end of the RS trigger, a first end of the first switching tube is connected with one end of the sample hold capacitor, a second end of the first switching tube is used for inputting the sample voltage signal, and the other end of the sample hold capacitor is connected with a signal ground.
Preferably, the transconductance operational amplification circuit includes: the device comprises a first switching tube, a second switching tube, a third switching tube and a transconductance operational amplifier, wherein the driving end of the first switching tube is connected with the output end of a demagnetization detection circuit, the first end of the first switching tube is connected with the first end of the third switching tube, the second end of the first switching tube is connected with one end of a sampling holding capacitor, the driving end of the first switching tube is connected with the output end of the demagnetization detection circuit, the second end of the first switching tube is connected with a signal ground, the non-inverting input end of the transconductance operational amplifier is used for inputting a reference voltage signal, the inverting input end of the transconductance operational amplifier is connected with the first end of the first switching tube, and the output end of the transconductance operational amplifier is used for outputting the sampling current signal.
Preferably, the proportional buffer includes: the sampling circuit comprises an operational amplifier, a fourth switching tube, a first voltage dividing resistor and a second voltage dividing resistor, wherein the normal-phase input end of the operational amplifier is used for inputting a sampling current signal, the reverse-phase input end of the operational amplifier is connected to the second end of the fourth switching tube, the output end of the operational amplifier is connected with the driving end of the fourth switching tube, the first end of the fourth switching tube is connected with an input voltage signal, the second end of the fourth switching 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 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 all comprise N-type switching tubes.
As a second aspect of the present invention, there is provided a switching power supply circuit, wherein the switching power supply circuit includes: the power switch 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, 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 driving 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 obtain a switch tube logic control signal after processing a sampling voltage signal so as to control the on and off of the power switch tube.
According to the constant current control circuit provided by the invention, sampling and holding of a sampling voltage signal are realized through the sampling and holding circuit, the sampling and holding voltage is controlled to be a sampling current signal under the action of a demagnetizing time signal through the transconductance operational amplification circuit, finally a switching tube logic control signal is obtained through processing of the sampling current signal, and the control of on and off of a power switching tube can be realized through the switching tube logic control signal, so that when the constant current control circuit is applied to a switching power supply circuit, the regulation of the precision of output current can be realized, and the output of high-precision current can be realized.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain, without limitation, the invention. In the drawings:
fig. 1 is a block diagram of a constant current control circuit provided by the invention.
Fig. 2 is a circuit configuration diagram of the switching power supply circuit provided by the invention.
Fig. 3 is a block diagram of a sample-and-hold circuit and a transconductance operational amplifier circuit provided by the present invention.
Fig. 4 is a circuit diagram of a proportional buffer and a PWM comparator according to the present invention.
Fig. 5a is a block diagram of an embodiment of a power tube turn-on signal generator according to the present invention.
Fig. 5b is a block diagram of another embodiment of the power tube turn-on signal generator according to the present invention.
Fig. 6 is a waveform diagram of each signal in fig. 1.
Fig. 7 is a waveform diagram of each signal in fig. 5 a.
Detailed Description
The following describes specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.
In order to realize that the output current precision in a constant current control circuit can be improved, the invention is exemplified as being applied to a primary side control isolated flyback converter working in a critical conduction mode (BCM). Energy transfer is carried out between the primary coil and the secondary coil; the secondary coil transmits output information to the auxiliary winding, and the input and output isolation is realized by using a transformer. The general switch power supply control system has two processes of switching on and switching off the power tube. When the power tube is started, the primary side inductor forms a passage, the input end provides energy for the transformer, meanwhile, the primary side inductor stores energy, the secondary side diode is cut off, and load output energy is supplied by the energy stored on the output capacitor; when the power tube is turned off, the transformer releases energy, and the secondary inductor releases energy. The internal feedback circuit is used for controlling the on and off of the power tube, so that the final output current is constant.
The output current formula obtained by the system power stage control principle is as follows:
wherein N is p Indicating the number of turns of the primary side of the transformer, N s Indicating the number of turns of the secondary side of the transformer, I p,pk Representing the primary side peak current of the transformer, T dem Indicates the demagnetizing time T sw Indicating the switching tube duty cycle.
Through analysis of the principle of the traditional constant flow control mode, the output of high-precision constant current can be realized by adopting a mode of 'unique' variable control. Therefore, the present invention provides a constant current control circuit for controlling the output current formulaThe product of the three variables is a constant quantity, and can be called as a sampling mean value, and is the only 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 device comprises a demagnetization detection circuit 206, a sample-and-hold circuit 207, a transconductance operational amplifier circuit 203, a proportional buffer 204, a PWM comparator 205 and an RS trigger 208, wherein the demagnetization detection circuit 206 and the sample-and-hold circuit 207 are both connected with the input end of the transconductance operational amplifier circuit 203, the output end of the transconductance operational amplifier circuit 203 is connected with the input end of the proportional buffer 204, the output end of the proportional buffer 204 is connected with the inverting input end of the PWM comparator 205, the output end of the PWM comparator 205 is connected with the input end of the RS trigger 208, the output end of the RS trigger 208 is in feedback connection with the input end of the sample-and-hold circuit 207, and the input end of the sample-and-hold circuit 207 and the non-inverting input end of the PWM comparator 205 are also used for inputting sampling voltage signals;
the sample-hold circuit 207 is configured to sample and hold the sampled voltage signal to obtain a sample-hold voltage;
the demagnetization detecting circuit 206 is configured to output a demagnetization time signal;
the transconductance operational amplifier circuit 203 is configured to control the sample hold voltage through the demagnetizing time signal to obtain a sampling current signal;
the scaling buffer 204 is configured to scale down the sampled current signal to obtain a scaled down signal;
the PWM comparator 205 is configured to compare the scaled-down signal and the sampled voltage signal to obtain a shutdown signal;
the RS flip-flop 208 is configured to process the off signal to obtain a switching tube logic control signal to control on and off of the power switching tube.
According to the constant current control circuit provided by the invention, sampling and holding of a sampling voltage signal are realized through the sampling and holding circuit, the sampling and holding voltage is controlled to be a sampling current signal under the action of a demagnetizing time signal through the transconductance operational amplification circuit, finally a switching tube logic control signal is obtained through processing of the sampling current signal, and the control of on and off of a power switching tube can be realized through the switching tube logic control signal, so that when the constant current control circuit is applied to a switching power supply circuit, the regulation of the precision of output current can be realized, and the output of high-precision current can be realized.
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 action 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 respectively connected to the demagnetization detection circuit 206, the transconductance operational amplification circuit 203, the sample hold circuit 207, the proportional buffer 204, and the PWM comparator 205, and is configured to provide a reference voltage signal and a reference current signal.
Note that, in fig. 1, the connection relationship between the reference circuit 201 and other circuits is not shown.
Specifically, as shown in fig. 1 and 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, which determines the value of "sampling average value"; a demagnetization detection circuit 206 that extracts a demagnetization time signal from the FB signal; a sample-and-hold circuit 207 that samples and holds an 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 a demagnetization time signal control; a built-in compensation capacitor 217, in this embodiment, the built-in compensation capacitor is 50pF; a proportional buffer circuit 204 for scaling down the sampling current signal 213 and performing a buffer function; PWM comparator 205 compares downscaled signal 218 with sampled voltage signal 216 to output shutdown signal 214; RS flip-flop 208 receives on control signal 215 and off signal 214, ultimately generating switch tube logic control signal 210; the power transistor gate driving circuit 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 on and off of the power transistor 113.
Specifically, as shown in fig. 3, the sample-and-hold circuit 207 includes a first switching tube 301 and a sample-and-hold capacitor 302, wherein a driving end of the first switching tube 301 is connected to an output end of the RS flip-flop 208, a first end of the first switching tube 301 is connected to one end of the sample-and-hold capacitor 302, and a second end of the first switching tube 301 is used for inputting the sampled voltage signal 216V CS The 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: the output end of the demagnetization detection circuit 206 is connected with the driving end of the second switching tube 303, the first end of the second switching tube 303 is connected with the first end of the third switching tube 306, the second end of the second switching tube 303 is connected with one end of the sample holding capacitor 302, the driving end of the third switching tube 306 is connected with the output end of the demagnetization detection circuit 206, the second end of the third switching tube 306 is connected with signal ground, the non-inverting input end of the transconductance operational amplifier 307 is used for inputting a reference voltage signal 209, the inverting input end of the transconductance operational amplifier 307 is connected with the first end of the second switching tube 303, and the output end of the transconductance operational amplifier 307 is used for outputting the 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, an N-type switching tube is taken as an example, and the first switching tube 301, the second switching tube 303 and the third switching tube 306 are controlled by a switching tube logic control signal 210, a demagnetizing signal 212 and a demagnetizing non-signal 305 respectively.
The primary side peak current sampling signal is obtained through the pin CS of the constant current control circuit 112, the sampling voltage signal 216 is obtained through the sampling resistor, and the sampling voltage signal 216 is sampled through the first switching tube 301 controlled by the power tube logic control signal 210. Next, according to excitationThe inductor demagnetizing time signal 212 is averaged over the switching period to obtain an average current. During the on time of the power tube logic control signal 210, the sampling voltage signal 216 of the primary side is sampled by the sampling hold capacitor 302, that is, the sampling hold capacitor 302 is charged; 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 211V sample And (5) discharging. In the non-demagnetizing period, the demagnetized non-signal 305 is at high level, the demagnetized 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 the average signal 304V is sampled CS,sample Grounding, the on-chip compensation capacitor 217 charges; during the demagnetization time, the demagnetization signal 212 is at a high level, the demagnetized non-signal 305 is at a low level, and the second switching tube 303 is correspondingly controlled to be turned on, and the third switching tube 306 is correspondingly controlled to be turned off, so that the on-chip compensation capacitor 217 is discharged. According to the principle of charge-discharge balance on the on-chip compensation capacitor 217 in a single cycle, the following equation can be obtained:
g m ·(V ref -0)·(T-T dem )+g m ·(V ref -V cs1 )·T dem ＝0，
wherein V is ref Represents reference voltages 209, T required by the transconductance operational amplifier circuit 203 dem The demagnetizing time is represented, T represents the working period of the switching tube, and V CS1 Represents the sampled average voltage, g, at demagnetization time m An equivalent transconductance value of the transconductance operational amplifier 307 of fig. 3 is shown.
Transconductance g of OTA during charging and discharging m While remaining unchanged, the following equation is obtained:
control the "sample mean" described above "It can be found that->This equation is the "only" variable that needs to be controlled under a constant current loop. By->Equation under the constant current topology of the present invention, the transconductance operational amplifier 307 is required to be constant under a full range of variation (0-1V). The transconductance 307 generates a sampling current signal 213 required by the PWM comparator 205, and after scaling by the scaling buffer 204, the PWM comparator 205 compares the output of the previous stage circuit with the corresponding sampling voltage signal 216 to generate a corresponding turn-off signal of the constant current loop.
As shown in fig. 4, the proportional buffer 204 includes: the non-inverting input end of the operational amplifier 400 is used for inputting the sampling current signal 213, the inverting input end of the operational amplifier 400 is connected to the second end of the fourth switching tube 401, the output end of the operational amplifier 400 is connected to the driving end of the fourth switching tube 401, the first end of the fourth switching tube 401 is connected to the input voltage signal VDD, the 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 the 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 switching tube 401, a first voltage dividing resistor 402 and a second voltage dividing resistor 403, and the correspondence between the output voltage at the Y of the node 405 and the input voltage of the non-inverting input node X of the operational amplifier 400 is as follows:
wherein V is Y Represents the voltage at node 405 at Y, i.e., the proportional buffer output voltage, X represents the transconductance operational amplifier output voltage, R a Representing the first divider resistor 402, R b A second voltage divider resistor 403 is shown.
Note that the node 405 is connected to signal ground through a filter capacitor 404.
Waveforms corresponding to the nodes are shown in fig. 6. The negative feedback closed-loop control loop formed by the method can realize the following methodIs maintained at the reference voltage signal 209 to obtain a constant output current.
FIG. 5a is a schematic diagram of one embodiment of a power tube turn-on signal generator 202, 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 together form a current comparator, 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 or positive, quasi-resonant valley turn-on signal 509 is high; the ninth switching tube 503 and the tenth switching tube 506 together form an inverter, and after inverting the quasi-resonant valley conduction signal 509, the non-signal 510 of the quasi-resonant valley conduction signal is output, and the non-signal 510 of the quasi-resonant valley conduction signal outputs the final conduction control signal 215 through the first trigger 507. The corresponding waveforms of the signals are shown in fig. 7.
Fig. 5b shows another embodiment of the power tube turn-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 high; 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.
Note that, 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 final RS flip-flop 208 receives the on control signal 215 and the off signal 214, generating the switch tube logic control signal 210; the power transistor gate driving circuit 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 on and off of the power transistor 113.
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 power switch comprises a rectification filter circuit, an RCD energy absorbing circuit 111, a transformer 115, an output control circuit, a power switch tube 113 and the constant current control circuit 112, wherein the rectification filter circuit is connected with the RCD energy absorbing circuit 111 and the constant current control circuit 112, the output end of the constant current control circuit 112 is connected with the driving end of the power switch tube 113, the power switch tube 113 and the RCD energy absorbing 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 signals to obtain switch tube logic control signals so as to control the on and off of the power switch tube.
According to the switching power supply circuit, the constant current control circuit is used as the controller, sampling and holding of the sampling voltage signal are achieved through the sampling and holding circuit, the sampling and holding voltage is controlled to be the proper sampling current signal under the action of the demagnetizing time signal through the transconductance operational amplifying circuit, finally the sampling current signal is processed to obtain the switching tube logic control signal, the switching tube logic control signal can be used for controlling the on and off of the power switching tube, and therefore output current precision can be adjusted, and high-precision current output is achieved.
Specifically, as shown in fig. 2, in a specific embodiment of a primary-side controlled switching power supply circuit of the present invention, a rectifying and filtering circuit is formed by a first rectifying diode 101, a second rectifying diode 102, a third rectifying diode 103, a fourth rectifying diode 104 and a filtering capacitor 105, and Vdc represents a dc high voltage after rectification and filtering; 106 denotes a high voltage start-up resistor; 107 represents an energy storage capacitor for supplying electric energy to the constant current control circuit 112; 108 denotes a transformer auxiliary winding rectifier diode; 109 and 110 are two divider 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 inductor current sampling resistor of the transformer; 115 is a transformer; 116 is a transformer secondary output winding rectifier diode; 117 is the output filter capacitance; 118 is the output load. Vout is the output voltage.
After the switching power supply circuit is electrified, VIN charges the filter capacitor 107 through the high-voltage starting resistor 106, and the voltage of the filter capacitor 107 is gradually increased; when the filter capacitor voltage rises to a certain preset value, the constant current control circuit 12 starts to operate. BD pin outputs high level to control the power tube 113 to be conducted; after the power tube 113 is conducted, current flows through the primary inductor Np of the transformer 115 to store energy; when the power tube 113 is turned on, the secondary rectifying diode 116 is turned off, and the output load current is supplied by the energy stored in the output capacitor 117. As the inductance current increases, the voltage on the sampling resistor 114 gradually increases, and after the current reaches a preset current limiting point 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; 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 and the output voltage feedback pin FB voltage FB on the primary inductor current sampling resistor 114, 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 illustrative of the application of the principles of the present invention, but not in limitation thereof. Various modifications and improvements may be made by those skilled in the art without departing from the spirit and substance of the invention, and are also considered to be within the scope of the invention.
Claims (7)
1. A constant current control circuit, characterized in that the constant current control circuit comprises: the device comprises a demagnetization detection circuit, a sample-and-hold circuit, a transconductance operational amplifier circuit, a proportional buffer, a PWM (pulse-width modulation) comparator and an RS trigger, wherein the demagnetization detection circuit and the sample-and-hold circuit are both connected with the input end of the transconductance operational amplifier circuit, the output end of the transconductance operational amplifier circuit is connected with the input end of the proportional buffer, the output end of the proportional buffer is connected to the inverting 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 in feedback connection with the input end of the sample-and-hold circuit, 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 sampling voltage signals;
the sampling and holding circuit is used for sampling and holding the sampling voltage signal to obtain sampling and holding voltage;
the demagnetization detection circuit is used for outputting a demagnetization time signal;
the transconductance operational amplification circuit is used for controlling the sampling hold voltage through the demagnetizing 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;
the RS trigger is used for processing the turn-off signal to obtain a switching tube logic control signal so as to control the turn-on and turn-off of the power switching tube;
the constant current control circuit further comprises a power tube conduction signal generator, wherein the power tube conduction signal generator is used for generating a conduction signal;
the sampling and holding circuit comprises a first switching tube and a sampling and holding capacitor, wherein the driving end of the first switching tube is connected with the output end of the RS trigger, the first end of the first switching tube is connected with one end of the sampling and holding capacitor, the second end of the first switching tube is used for inputting the sampling voltage signal, and the other end of the sampling and holding capacitor is connected with signal ground;
wherein the transconductance operational amplifier circuit comprises: the device comprises a first switching tube, a second switching tube, a third switching tube and a transconductance operational amplifier, wherein the driving end of the first switching tube is connected with the output end of a demagnetization detection circuit, the first end of the first switching tube is connected with the first end of the third switching tube, the second end of the first switching tube is connected with one end of a sampling holding capacitor, the driving end of the first switching tube is connected with the output end of the demagnetization detection circuit, the second end of the first switching tube is connected with a signal ground, the non-inverting input end of the transconductance operational amplifier is used for inputting a reference voltage signal, the inverting input end of the transconductance operational amplifier is connected with the first end of the first switching tube, and the output end of the transconductance operational amplifier is used for outputting the sampling current signal.
2. The constant current control circuit according to claim 1, wherein 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.
3. The constant current control circuit according to claim 1, further comprising a gate driving circuit, wherein 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.
4. The constant current control circuit of claim 1, further comprising a reference circuit coupled to the demagnetization detection circuit, the transconductance operational amplifier 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.
5. The constant current control circuit according to claim 1, wherein the proportional buffer includes: the sampling circuit comprises an operational amplifier, a fourth switching tube, a first voltage dividing resistor and a second voltage dividing resistor, wherein the normal-phase input end of the operational amplifier is used for inputting a sampling current signal, the reverse-phase input end of the operational amplifier is connected to the second end of the fourth switching tube, the output end of the operational amplifier is connected with the driving end of the fourth switching tube, the first end of the fourth switching tube is connected with an input voltage signal, the second end of the fourth switching 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 signal ground through the second voltage dividing resistor.
6. The constant current control circuit of claim 5, 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.
7. A switching power supply circuit, the switching power supply circuit comprising: the power switch 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 according to any one of claims 1 to 6, 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 driving end of the power switch tube, the power switch tube and the RCD energy absorption circuit are both connected with the primary side of the transformer, the secondary side of the transformer is connected with the output control circuit, and the constant current control circuit can obtain a switch tube logic control signal to control the on and off of the power switch tube after processing the sampling voltage signal.
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| CN111294034B (en) * | 2020-03-23 | 2024-04-02 | 广东美的白色家电技术创新中心有限公司 | Gate drive circuit, power switch circuit and electrical equipment |
| CN113630121B (en) * | 2021-08-19 | 2023-07-04 | 电子科技大学 | Sample-hold and knee point detection circuit |
| CN114499121B (en) * | 2022-04-14 | 2022-07-15 | 深圳市芯茂微电子有限公司 | Controller of switching power supply and switching power supply |
| CN117310262B (en) * | 2023-11-28 | 2024-02-09 | 成都市易冲半导体有限公司 | Primary side information detection circuit and detection chip of transformer |
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