CN101488702B - PWM control circuit - Google Patents

Abstract

The invention discloses a PWM control circuit which comprises a PWM chip and a chaotic circuit used for generating chaotic signals, wherein, the chaotic circuit is electrically connected with a crystal oscillator control end of the PWM chip. The chaotic circuit comprises a negative impedance circuit and a gyrator which are sequentially connected with each other, wherein, the negative impedance circuit is output into the crystal oscillator control end of the PWM chip after impedance conversion of the gyrator. After being generated, the chaotic signals are superimposed onto a constant flow source inside the chip from the crystal oscillator control end of the PWM chip, thus generating chaotic PWM working frequency, leading the chip to work in a chaotic state and reducing the EMI of the system. A chaotic PWM controller is different from conventional fixed-frequency PWM controller, and the PWM controller of the invention can fundamentally inhibit electromagnetic interference of a switch converter from the source.

Description

A kind of pwm control circuit

Technical field

The present invention relates to the switch converters technical field, especially a kind of pwm control circuit based on chaology.

Background technology

The braking measure of existing switch converters electromagnetic interference from eliminating coupling and the radiation between interference source and the disturbed equipment, is cut off the route of transmission of electromagnetic interference and is set out mostly.As utilize metal or macromolecular material mask switch converter electromagnetic coupling to close radiation; Utilize resistor-type, dielectric type and magnetizing mediums type absorbing material that the electromagnetic radiation energy that switch converters produced is converted into other energy (mainly being heat energy) and dissipate; Utilize various filters or suppress the switch converters Conducted Electromagnetic Interference with high-power factory rectifier, and utilize ground connection, float, photoelectricity coupling, pcb board wiring technique reduce that electromagnetic pollution is propagated and emission.But their distinct disadvantage is to eliminate interference less than directly controlling interference source, has only increased hardware volume and cost, has bigger blindness.

Soft switch technique is attempted by reducing electric current, the voltage stress of power switch pipe, reach and reduce electric current, voltage high-frequency harmonic, to improve Electro Magnetic Compatibility, 1996, the researcher in CPES research center adopts Zero voltage transition and hard switching circuit that the conducted interference of two single-phase 400W PFC booster converter experimental models is compared experiment respectively, test result is unexpected, adopt the soft switch transducer and the EMI difference between hard-switching converter of ZVT technology very little, if the resonant circuit of ZVT is improper even, can make EMI higher.In soft switch circuit topology, the electromagnetic interference of main switch element reduces, but auxiliary switch element is introduced new electromagnetic interference, becomes important interference source, is difficult to realize optimize when main topological sum is assisted topology.Because soft switch technique does not improve EMI yet on mechanism at all, actual effect is limited.

Various voltages, the current mode PWM of exploitations such as the at present main TI of PWM chip manufacturer, IR, SG, onsemi, Intersil, Fairchild, the SPWM control chip mostly is the fixed carrier frequency, and people have recognized gradually that the cycling state of fixed carrier frequency decision is the main source of power electronic system EMI.Therefore each large chip manufacturer has introduced in the PWM chip and has trembled the notion of (frequency jitter) frequently in recent years, and the operating frequency that promptly refers to switch converters is not to immobilize, but linear change periodically.Each big PWM chip manufacturer developed one after another NCP101X series, SM8012, TOP249 etc. a series of have tremble the PWM chip of function frequently; Maxim has developed the DC-DC converter with the oscillator DS1090 cooperation Maxim that trembles the frequency function and has used to reduce EMI.

The expression formula of frequency jitter is as follows

$f_i=f_s+f_m\frac{2\·t}{T}$ $t\∈\left[\begin{array}{cc}-\frac{T}{2}& \frac{T}{2}\end{array}\right]$

F in the formula _s-central task frequency; f _m-modulating frequency

The multiple fourier coefficient of its frequency spectrum is

${\stackrel{\·}{F}}_m=\underset{i=-\frac{N}{2}}{\overset{\frac{N}{2}-1}{\mathrm{\Σ}}}\frac{{\mathrm{\τ}}_i}{T_i}{e}^{\mathrm{j\ωk}{T}_i}\frac{\sin \left(\frac{\mathrm{n\ω}{\mathrm{\τ}}_i}{2}\right)}{\frac{\mathrm{n\ω}{\mathrm{\τ}}_i}{2}}$ n＝0，±1，±2，…

Because the frequency spectrum stack, $\mathrm{\ω}=\frac{2\mathrm{n\π}}{{\mathrm{\τ}}_i}$ Everywhere, having single envelope amplitude is 0, but total envelope amplitude is not 0, $\mathrm{\ω}=\frac{2\mathrm{n\π}}{T}$ With other frequency places, the spectrum amplitude mutual superposition can not reach maximum, may not be 0 yet.Though tremble the peak value that PWM frequently can partly reduce the pwm pulse power spectrum, the still discrete spectrum that obtains, concentration of energy is with nf _s± kf _mFor the specific frequency at center, not expanded completely, the effect that frequency jitter suppresses EMI still is limited, often can not reach people's requirement.

The cycling state of PWM control mode decision in the switch converters, make spectrum energy concentrate on switching frequency and frequency multiplication place thereof, causing the peak value of switch converters electromagnetic interference also mainly to concentrate on the frequency multiplication place of switching frequency, is the source of switching converter EMI from the PWM driving pulse of mechanism explanation period state.

The achievement in research of nonlinear kinetics shows that chaotic signal has continuous frequency spectrum, and system capacity is distributed in the frequency band of broad during chaos state.Studies show that in recent years, switch converters are typical chaos systems, when system parameters when certain limit changes, it will produce period doubling bifurcation, border collision fork, Hough fork and chaotic motion.And can change by Control Parameter, switch converters is switched in chaos state and normal operating condition.The research of bifurcation chaos complex behavior deepens continuously in recent years in the switch converters, system capacity no longer concentrated on switching frequency and frequency multiplication place thereof when result of study showed chaos state, therefore provided a theoretical foundation for the electromagnetic interference that effectively suppresses switch converters.

Summary of the invention

The objective of the invention is to overcome prior art do not have directly to control interference source and eliminate interference, only increased hardware volume and cost, easily introduce new electromagnetic interference, optimize when being difficult to realize the auxiliary topology of main topological sum, the limited technical problem of EMI control effect, a kind of Electro Magnetic Compatibility that can improve switch converters by the chaos spread spectrum characteristic is provided, reaches the electromagnetic pollution of control switch converter and greatly improve the purpose of its EMI from mechanism.

For realizing above purpose, the present invention has taked following technical scheme: a kind of pwm control circuit, comprise the PWM chip, and also include the chaos circuit that is used to produce chaotic signal, this chaos circuit is electrically connected with the crystal oscillator control end of described PWM chip.

Chaotic signal produces on the back is added to the chip internal constant-current source from the crystal oscillator control end of pwm chip, thereby produces the PWM operating frequency of chaos, makes the state of chip operation in chaos, reduces the EMI of system.

Described chaos circuit comprises negative impedance circuit, the gyrator that is electrically connected successively, and this negative impedance circuit outputs to the crystal oscillator control end of described PWM chip after the gyrator impedance conversion.

Described negative impedance circuit comprises the 3rd amplifier, the 4th amplifier, described gyrator comprises first amplifier, second amplifier, be electrically connected with the 5th resistance between the normal phase input end of described the 3rd amplifier and the output, be electrically connected with the 4th resistance between inverting input and the output, be electrically connected with the 9th resistance and the 6th resistance between reverse input end and described second amplifier's inverting input, normal phase input end is electrically connected with the normal phase input end of described the 4th amplifier, second amplifier, first amplifier respectively;

Be electrically connected with the 8th resistance between the normal phase input end of described the 4th amplifier and the output, be electrically connected with the 7th resistance between inverting input and the output, this inverting input is electrically connected between described the 9th resistance and the 6th resistance by the tenth resistance;

Be electrically connected with second resistance between the normal phase input end of described first amplifier and the output, be electrically connected with the 3rd resistance between inverting input and the output, normal phase input end output is electrically connected to the crystal oscillator control end of described PWM chip, its inverting input is electrically connected with the output of described second amplifier by first resistance, is electrically connected with filter capacitor between described second amplifier's inverting input and output.

Also include between the normal phase input end that an end is electrically connected on described the 4th amplifier, first amplifier, the other end is electrically connected on filter circuit between described the 4th amplifier, second amplifier's inverting input.

Compare with trembling frequency, the Chaotic PWM frequency spectrum is:

$S_{F_m}\left(s\right)=\frac{1}{T}\left\{E\right[{\left|F\left(s\right)\right|}^2]-{\left|E\left(F\left(s\right)\right)\right|}^2+\frac{1}{T^2}{\left|E\left(F\left(s\right)\right)\right|}^2\underset{k=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\mathrm{\δ}(f-\frac{k}{T})\}.$

The Chaotic PWM frequency spectrum has continuity, energy is no longer concentrated and is distributed in specific frequency, but comprised the energy of each frequency, energy spread on whole frequency range, so it is far better that Chaotic PWM suppresses effect than the EMI that trembles frequency PWM, also becomes the effective way that solves the switching converter EMI problem.

The present invention compared with prior art has following advantage: this chaotic PWM controller is different from conventional fixed-frequency PWM controller, and PWM controller of the present invention can be from the basic electromagnetic interference that suppresses switch converters on the source.

Description of drawings

Fig. 1 is a pwm control circuit of the present invention.

Embodiment

Below in conjunction with the drawings and specific embodiments content of the present invention is described in further details.

Embodiment:

See also shown in Figure 1ly, a kind of pwm control circuit comprises PWM chip U1, also includes the chaos circuit that is used to produce chaotic signal, and this chaos circuit is electrically connected with the crystal oscillator control end RI of described PWM chip U1.Chaotic signal produces on the back is added to the chip internal constant-current source from the crystal oscillator control end of pwm chip, thereby produces the PWM operating frequency of chaos, makes the state of chip operation in chaos, reduces the EMI of system.

Chaos circuit comprises negative impedance circuit 102, filter circuit 101, the gyrator 103 that is electrically connected successively, and this negative impedance circuit 102 outputs to the crystal oscillator control end RI of PWM chip U1 after gyrator 103 impedance conversions.

According to nonlinear theory, an autonomous circuit can produce chaos and must satisfy three conditions: 1) at least one non-linear element; 2) at least one active impedance; 3) at least three energy-storage travelling wave tubes, according to this condition, the physical circuit syndeton in the present embodiment is as follows:

Negative impedance circuit 102 comprises the 3rd amplifier X3, the 4th amplifier X4, gyrator 103 comprises the first amplifier X1, the second amplifier X2, be electrically connected with the 5th resistance R 5 between the normal phase input end of the 3rd amplifier X3 and the output, be electrically connected with the 4th resistance R 4 between inverting input and the output, be electrically connected with the 9th resistance R 9 and the 6th resistance R 6 between the inverting input of the reverse input end and the second amplifier X2, normal phase input end is electrically connected with the normal phase input end of the 4th amplifier X4, the second amplifier X2, the first amplifier X1 respectively; Be electrically connected with the 8th resistance R 8 between the normal phase input end of the 4th amplifier X4 and the output, be electrically connected with the 7th resistance R 7 between inverting input and the output, this inverting input is electrically connected between the 9th resistance R 9 and the 6th resistance R 6 by the tenth resistance R 10; Be electrically connected with second resistance R 2 between the normal phase input end of the first amplifier X1 and the output, be electrically connected with the 3rd resistance R 3 between inverting input and the output, normal phase input end output is electrically connected to the crystal oscillator control end RI of PWM chip U1, its inverting input is electrically connected with the output of the second amplifier X2 by first resistance R 1, is electrically connected with filter capacitor C5 between the inverting input of the second amplifier X2 and output.

Wherein resistance R 4, R5, and R7, R8, R9, R10 constitutes negative impedance circuit 102, and this circuit is formed in parallel by two identical negative resistance assembly the 3rd amplifier X3 and the 4th amplifier X4, and circuit is simple and low to requirement on devices.For a negative impedance assembly, owing to be subjected to the restriction of amplifier saturation voltage, its characteristic curve is a sectional broken line, and the equiva lent impedance of X3 is: $G_1=\frac{R4}{R9R5}{G}_2=\frac{1}{R5};$ The equiva lent impedance of X4 is: $G_1=\frac{R7}{R10R8}{G}_2=\frac{1}{R8};$ Equiva lent impedance after the parallel connection of two negative resistance assemblies is $G_a=-\frac{R4}{R9R5}-\frac{R7}{R10R8},$ $G_b=\frac{1}{R5}-\frac{R7}{R10R8},$ $G_c=\frac{1}{R5}+\frac{1}{R8}.$

Resistance R 1, R2, R3, R6, capacitor C 5 constitutes gyrator 103 and plays impedance conversion, and the equivalent inductance of gyrator is

The first amplifier X1, the second amplifier X2 in the present embodiment, the two ends of the 3rd amplifier X3, the 4th amplifier X4 are respectively by power supply V1 and V2 ground connection, are in series with capacitor C 4 respectively and capacitor C 3 is power filter on power supply V1 and V2.Pwm chip U1 is SG6846, and main circuit topology is a circuit of reversed excitation, and that switching tube and rectifier diode adopt respectively is coolMOS pipe SPI07N65C3 and SIC diode STP41H100CR.

Above-listed detailed description is at the specifying of possible embodiments of the present invention, and this embodiment is not in order to limiting claim of the present invention, and the equivalence that all the present invention of disengaging do is implemented or change, all should be contained in the claim of this case.

Claims (2)

1. a pwm control circuit comprises PWM chip (U1), it is characterized in that: also include the chaos circuit that is used to produce chaotic signal, this chaos circuit is electrically connected with the crystal oscillator control end of described PWM chip (U1); Described chaos circuit comprises negative impedance circuit (102), the gyrator (103) that is electrically connected successively, and this negative impedance circuit (102) outputs to the crystal oscillator control end of described PWM chip (U1) after gyrator (103) impedance conversion;

Described negative impedance circuit (102) comprises the 3rd amplifier (X3), the 4th amplifier (X4), described gyrator (103) comprises first amplifier (X1), second amplifier (X2), be electrically connected with the 5th resistance (R5) between the normal phase input end of described the 3rd amplifier (X3) and the output, be electrically connected with the 4th resistance (R4) between inverting input and the output, be electrically connected with the 9th resistance (R9) and the 6th resistance (R6) between the inverting input of reverse input end and described second amplifier (X2), normal phase input end respectively with described the 4th amplifier (X4), second amplifier (X2), the normal phase input end of first amplifier (X1) is electrically connected;

Be electrically connected with the 8th resistance (R8) between the normal phase input end of described the 4th amplifier (X4) and the output, be electrically connected with the 7th resistance (R7) between inverting input and the output, this inverting input is electrically connected between described the 9th resistance (R9) and the 6th resistance (R6) by the tenth resistance (R10);

Be electrically connected with second resistance (R2) between the normal phase input end of described first amplifier (X1) and the output, be electrically connected with the 3rd resistance (R3) between inverting input and the output, normal phase input end output is electrically connected to the crystal oscillator control end of described PWM chip (U1), its inverting input is electrically connected with the output of described second amplifier (X2) by first resistance (R1), is electrically connected with filter capacitor (C5) between the inverting input of described second amplifier (X2) and output.

2. pwm control circuit as claimed in claim 1, it is characterized in that: also include between the normal phase input end that an end is electrically connected on described the 4th amplifier (X4), first amplifier (X1), the other end is electrically connected on filter circuit (101) between the inverting input of described the 4th amplifier (X4), second amplifier (X2).

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