Disclosure of Invention
In view of the above, an object of the present invention is to provide a novel boost PFC controller, which can control the switching frequency of the power switching tube without an internal clock signal, and can implement constant frequency operation or variable frequency operation according to actual needs.
A boost PFC controller according to an embodiment of the present invention is applied to an ac/dc converter, and includes: the switching-off signal generating circuit, the switching-on signal generating circuit and the logic control circuit are connected; wherein,
the conducting signal generating circuit receives a first sampling signal representing inductive current, compares the first sampling signal with a first reference voltage, continuously drops the first sampling signal within the turn-off time of a power switch tube in the alternating current/direct current converter, and generates a conducting signal when the first sampling signal drops to the first reference voltage;
the turn-off signal generating circuit compares the first sampling signal with a second reference voltage, the first sampling signal continuously rises within the on time of the power switch tube, and when the first sampling signal rises to the second reference voltage, a turn-off signal is generated;
the first reference voltage is a difference value of a first control signal and a second control signal, and the second reference signal is a sum value of the first control signal and the second control signal; the first control signal is controlled by the direct current input voltage and the output voltage feedback variable after rectification by the alternating current/direct current converter; the second control signal is in a direct proportional relation with the product of the duty ratio of the power switch tube and the direct current input voltage, and the proportionality coefficient is a first proportionality coefficient;
the logic control circuit is respectively connected with the conducting signal generating circuit and the turn-off signal generating circuit, and controls the power switch tube to be conducted when the conducting signal is effective; and when the turn-off signal is effective, controlling the power switch tube to be turned off.
Preferably, the first scaling factor is constant, so as to ensure that the switching period of the power switching tube is constant.
Preferably, the first scaling factor is adjustable, so that the switching period of the power switch tube is variable.
Further, an output voltage feedback loop is included, which receives the output voltage of the ac/dc converter to obtain the output voltage feedback variable, and the output voltage feedback variable controls the first control signal, so as to ensure that the output voltage is kept constant.
The device further comprises an inductor current sampling circuit which is used for sampling the current flowing through an inductor in the AC/DC converter and generating the first sampling signal.
Further, a power feed-forward circuit is included that receives the rectified dc input voltage and performs peak detection to generate a peak voltage signal; and after the direct current input voltage is multiplied by the output voltage feedback variable, the ratio of the direct current input voltage to the square of the peak voltage signal is used as the first control signal so as to ensure that the output voltage feedback variable and the input power of the alternating current/direct current converter are in a direct proportion relation.
The power switch further comprises a second control signal generating circuit, wherein the second control signal generating circuit comprises an average value circuit which receives the on signal and the off signal of the first voltage source and the power switch tube respectively to generate the second control signal, and the ratio of the first voltage source to the direct current input voltage is the first proportionality coefficient.
Preferably, the logic control circuit comprises an RS trigger, a reset end of the RS trigger is connected to the on signal generating circuit, a set end of the RS trigger is connected to the off signal generating circuit, and a switch control signal output by an output end of the RS trigger is used to control the switching action of the power switching tube.
According to the boost PFC controller, the power switch tube can work at a fixed frequency or at a jittering frequency through the internal control circuit without a built-in clock signal, so that the design difficulty of an EMI filter is reduced. In addition, the invention realizes that the output voltage feedback variable is related to the input power and unrelated to the input voltage through the input voltage feedforward circuit, thereby being beneficial to the voltage input design requirement of the global power grid.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to only these embodiments. The invention is intended to cover alternatives, modifications, equivalents, and alternatives that may be included within the spirit and scope of the invention. In the following description of the preferred embodiments of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The boost PFC controller of the present invention is applied to an ac/dc converter, which further includes a power stage circuit, which is described in the background of the invention, and the components of the power stage circuit in the following embodiments are the same as those in the background of the invention.
Referring to fig. 2, there is shown a schematic block diagram of a first embodiment of a boost PFC controller according to the present invention, the boost PFC controller comprising an on signal generating circuit 201, an off signal generating circuit 202 and a logic control circuit 203; the power switch tube SMComprises a conduction time TONAnd off time TOFF(ii) a Wherein,
the on-signal generating circuit 201 receives a characterization inductor current ILAnd comparing the first sampled signal with a first reference voltage, power switching tube S in the ac/dc converterMThe first sampling signal continuously falls during the turn-off time, and when the first sampling signal falls to the first reference voltage, a turn-ON signal ON is generated;
the turn-off signal generating circuit 202 compares the first sampling signal with a second reference voltage, and the power switch tube S is connected to the first sampling signalMThe first sampling signal continuously rises during the on-time, and when the first sampling signal rises to the second reference voltage, an OFF signal OFF is generated;
wherein the first reference voltageThe difference value of the first control signal and the second control signal is obtained, and the second reference signal is the sum value of the first control signal and the second control signal; the first control signal is a direct current input voltage V rectified by the alternating current/direct current convertergAnd an output voltage feedback variable VcControlling; the second control signal and the power switch tube SMAnd the DC input voltage VgThe product of (A) is in a direct proportional relation, and the proportionality coefficient is a first proportionality coefficient K1;
The logic control circuit 203 is respectively connected to the ON signal generating circuit 201 and the off signal generating circuit 202, and controls the power switch tube S when the ON signal is activeMConducting; when the OFF signal is effective, controlling the power switch tube SMAnd (6) turning off.
As can be seen from the above description, the on signal generating circuit is mainly used for controlling the off duration of the power switching tube, the off signal generating circuit is mainly used for controlling the on duration of the power switching tube, and in this process, if the first scaling factor is constant, the switching period of the power switching tube is kept constant; if the first scaling factor is adjustable, the switching period of the power switch tube is changed.
As can be seen from the embodiment shown in fig. 2, with the boost PFC controller according to the present invention, the power switching tube can perform fixed frequency operation or frequency jittering operation without a built-in clock signal through an internal control circuit, thereby reducing the design difficulty of the EMI filter.
Referring to fig. 3, a schematic block diagram of a second embodiment of a boost PFC controller according to the present invention is shown. On the basis of the embodiment shown in fig. 2, this embodiment specifically describes an implementation method of the on-signal generating circuit 201, the off-signal generating circuit 202, and the logic control circuit 203, and further includes an output voltage feedback loop 301, an inductor current sampling circuit 302, and a second control signal generating circuit 303.
The output voltage feedback loop 301 receives the output voltage V of the ac/dc converteroutTo obtain the output voltage feedback variable VcSaid DC input voltage VgAnd an output voltage feedback variable VcPerforming a multiplication operation, the output signal of which is taken as the first control signal Vctr1I.e. Vctr1=VgVc(ii) a The output voltage feedback variable VcControlling the first control signal Vctr1Thereby ensuring the output voltage VoutAnd is maintained constant.
The inductor current sampling circuit 302 is used for sampling the current I flowing through the inductor in the AC/DC converterLAnd generating said first sampling signal Vsen(ii) a In a specific application, the inductor current sampling circuit 302 may average the sampled current signal through a sampling resistor to form a first sampling signal V representing an average value of the inductor currentsen;
The second control signal generating circuit 303 comprises an averaging circuit which respectively receives the first voltage source Vs1The on signal and the off signal of the power switch tube are used for generating the second control signal Vctr2Wherein the first voltage source Vs1And the DC input voltage VgIs the first proportionality coefficient K1I.e. Vs1=K1*Vg. In this embodiment, the averaging circuit includes a first switch S connected in series1And a second switch S2And by the first resistance R1And a first capacitor C1The RC filter circuit is formed; wherein,
the first switch S1Receives the first voltage source Vs1Said second switch S2The second terminal of (1) is grounded; the first resistor R1Is connected to the first switch S1And a second switch S2And the other end of the common connection point is connected with the first capacitor C1And after being connected in series, the power is grounded. Wherein, theFirst switch S1And the power switch tube SMIs in the same state, the second switch S2And the power switch tube SMThe switch states of (2) are opposite. The first capacitor C1As said second control signal Vctr2. The first voltage source Vs1Via the first switch S1And a second switch S2After chopping, averaging the chopped wave by an RC filter circuit to obtain the second control signal Vctr2Then the second control signal Vctr2Is determined by the following formula:
the on-signal generating circuit comprises a comparator 304 having an inverting input receiving the first sampling signal VsenA non-inverting input terminal thereof receiving a first reference voltage Vref1To output the ON signal ON, wherein the first reference voltage Vref1Is said first control signal Vctr1And a second control signal Vctr2A difference of (i.e. V)ref1=Vctr1-Vctr2。
The shutdown signal generation circuit includes a comparator 305,the non-inverting input end of which receives the first sampling signal VsenWhose inverting input receives a second reference voltage Vref2To output the OFF signal OFF, wherein the second reference voltage Vref2Is said first control signal Vctr1And a second control signal Vctr2A sum of, i.e. Vref2=Vctr1+Vctr2。
The logic control circuit comprises an
RS trigger 306, wherein the R end of the reset end of the RS trigger is connected with the conducting signal generating circuit to receive the conducting signal ON, the S end of the reset end of the RS trigger is connected with the turn-OFF signal generating circuit to receive the turn-OFF signal OFF, and the inverted output end of the RS trigger is the inverted output end of the RS trigger
Terminal and the power switch tube S
MIs connected with the control end, and the output signal of the control end is used for controlling the power switch tube S
MThe opening and closing of (2).
The following describes the operation process and operation principle of the PFC controller in detail by combining the functions of the circuits in this embodiment and the operation waveform diagram shown in fig. 4:
as can be seen from fig. 4, when the power switch tube SMIn the off state, the first sampling signal VsenContinuously falling when the first sampling signal VsenDown to the first reference voltage Vref1When the comparator 304 generates the ON signal, the RS flip-flop 308 receives the ON signal and performs a reset operation, which is a logic operationEnd output high level control controls the power switch tube SMConducting;
when the power switch tube S
MWhen in the conducting state, the first sampling signal V
senContinuously rising when the first sampling signal V
senUp to the second reference voltage V
ref2Then, the
comparator 305 outputs the OFF signal OFF.The RS flip-
flop 306 receives the OFF signal OFF to perform a set operation, which
The end outputs low level to control the power switch tube S
MAnd (6) turning off.
Due to the high switching frequency, the difference between the second reference voltage and the first reference voltage is approximately equal to the power switch tube SMWhen the current is conducted, the rising value of the inductance current sampling signal is as follows:
wherein R issFor the equivalent resistance value of the sampling resistor in the inductive current sampling circuit 302, the power switch tube S is obtained by driving the formula (1) into the formula (2)MOn-off period T ofsThe expression of (a) is:
the conclusion can be drawn from equation (3) that the power switch S isMOn-off period T ofsWhen the equivalent resistance values of the main circuit inductor and the sampling resistor are constant values, the equivalent resistance values are only equal to the first proportionality coefficient K1The correlation can be obtained by adjusting the first scaling factor K1The value of (A) is constant or variable, so as to ensure that the switching period of the power switching tube is constant or variable.
The following discusses the process of implementing power factor correction in an embodiment in accordance with the invention: the first sampling signal VsenMay be expressed as an average of the first and second reference voltages, i.e.:
the first sampling signal VsenCan also be represented as IL*Rs,ILFor inductive current, Vsen=IL*RsAndVctr1=Vg*Vcthe inductive current I is obtained by the belt-in type (4)LAs shown in the following formula:
when the boost PFC circuit is in CCM mode, its input impedance Z
inIs composed of
The substitution of equation (5) can be deduced:
since the output voltage feedback circuit has a slow transient response, the output voltage feedback variable V can be considered as the output voltage feedback variable VcThe input impedance Z is kept constant in a network period, so that the input impedance Z can be obtainedinThe constant is constant, so that the input current and the input voltage have the same waveform and the same phase, and the power factor correction process is completed.
It should be noted that, in the embodiment of the present invention, the implementation forms of the on signal generating circuit, the off signal generating circuit, and the logic control circuit are not limited to the circuit structure diagram shown in fig. 3, and circuit structures capable of implementing corresponding control functions to the power switching tube all fall within the protection scope of the present invention.
The average input power P of the AC/DC converter in the embodiment of FIG. 3 can be obtained from equation (6)inComprises the following steps:
as can be seen from equation (7), at this time, although the entire PFC control circuit implements the power factor correction function, the output voltage feedback variable VcInput power P to the AC/DC converterinAnd the DC input voltage VgAre all correlated. For feeding back the variable V to the output voltagecOnly with input power PinDepending on the variation, and regardless of the circuit input voltage, a power feed forward circuit may be added to the embodiment shown in fig. 3, which is a schematic block diagram shown in fig. 5.
The boost PFC controller further includes a power feed-forward circuit that receives a rectified DC input voltage V
gAnd performing peak detection to generate a peak voltage signal V
gpk(ii) a The DC input voltage V
gAnd said output voltage feedback variable V
cAfter multiplication, it is multiplied by the peak voltage signal V
gpkThe squared ratio is used as the first control signal V
ctr1I.e. by
From this the following relationship can be derived:
the input impedance Z of the boost PFC circuit at this timeinComprises the following steps:
the peak voltage signal V in the formula (9)gpkA constant value under the given power grid voltage condition, and an output voltage feedback variable VcThe input impedance Z is kept constant in a network period, so that the input impedance Z can be obtainedinThe constant is constant, so that the input current and the input voltage have the same waveform and the same phase, and the power factor correction process is completed.
The average input power of the circuit obtained from equation (9) is:
in the formula (10) (V)g)2And (V)pk)2Is constant for a given grid voltage condition, so that the input power of the ac/dc converter and the output voltage feedback variable VcIs in a direct proportional relationship, and, as can also be seen from equation (10), the output voltage feedback variable VcOnly with input power PinChange is related toThe input voltage is independent.
In summary, the PFC controller according to the present invention does not need a built-in oscillator to generate a clock signal, and can control the switching frequency of the power switching tube through an internal control circuit, thereby achieving the purpose of power factor correction. When an electromagnetic interference test needs to be performed on the AC/DC converter, the switching frequency of the power switching tube is expected to drift within a small range, so that harmonic interference energy is relatively dispersed, namely, frequency jitter is realized. Compared with the existing switching frequency jitter control technology, the scheme of the invention can adjust the numerical values of the first voltage source and the first current source according to specific conditions, thereby conveniently realizing the jitter frequency, reducing the design difficulty of the input EMI filter and meeting the requirement of the converter on the electromagnetic interference test. In addition, the invention realizes that the output voltage feedback variable is related to the input power and unrelated to the input voltage through the input voltage feedforward circuit, thereby being beneficial to the voltage input design requirement of the global power grid.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.