CN102780392B - A kind of PFM Switching Power Supply and tremble frequency circuit and tremble frequency method - Google Patents

Abstract

The invention discloses a kind of PFM Switching Power Supply and tremble frequency circuit and tremble frequency method, the described frequency circuit of trembling comprises: frequency jitter module, described frequency jitter module is connected with the former limit peak current detection comparator of described Switching Power Supply, for changing the reference voltage of described former limit peak current detection comparator, to change the former limit peak point current of described former limit peak current detection comparator, the switching frequency of described Switching Power Supply is shaken. By changing the reference voltage of described former limit peak current detection comparator, to change former limit peak point current, the switching frequency of described Switching Power Supply is shaken. Control the excursion of described former limit peak point current by setting the excursion of described reference voltage, and then can control the frequency jitter scope of described Switching Power Supply, make the switching frequency of trembling the Switching Power Supply of frequency circuit described in adopting that controllable periodic jitter occur, thereby make described Switching Power Supply there is good Electro Magnetic Compatibility.

Description

A kind of PFM Switching Power Supply and tremble frequency circuit and tremble frequency method

Technical field

The present invention relates to ic manufacturing process technical field, more particularly, relate to a kind of PFM and openClose power supply and tremble frequency circuit and tremble frequency method.

Background technology

Switching Power Supply is to utilize modern power electronics technology, the time ratio of the conducting of gauge tap pipe and cut-off,Maintain a kind of circuit arrangement of stable output. Wherein, common a kind of Switching Power Supply is for having constant current constant voltageThe pulse frequency of mode of operation regulates (PFM) Switching Power Supply, and described Switching Power Supply is controlled by PFMThe conducting of switching tube processed and cut-off, maintain stable output, thereby make whole switch power supply system be operated in perseverancePress or constant current mode. PFM Switching Power Supply has higher voltage change ratio and current changing rate, andThere is parasitic capacitance and stray inductance in its transformer, device is around formed to electromagnetic interference (EMI), instituteAdopt the method for shake switching frequency to optimize its Electromagnetic Compatibility with needs.

The switch periods (Tsw) of Switching Power Supply equals former limit ON time (Tonp), secondary ON time(Tons) and interrupting time (Tdis) sum, and former limit ON time and secondary ON time all with former limitThe proportional relation of peak point current. Prior art adopts fixing former limit peak point current conventionally, thereby fixingFormer limit ON time and secondary ON time, the change of the switch periods of Switching Power Supply only relies on interrupting timeVariation realize.

With reference to figure 1, Fig. 1 is that in prior art, a kind of common PFM with constant current constant voltage mode of operation opensClose the circuit diagram of power supply. Described Switching Power Supply will exchange defeated by rectifying device 200 and input capacitance CinEnter signal Vac and change direct-flow input signal Vin into, described direct-flow input signal Vin is PFM controller 201Operating voltage is provided. Described Switching Power Supply characterizes secondary coil 205 by the voltage at ancillary coil 206 two endsThe voltage at two ends, described PFM controller 201 obtains by resistor network (comprising resistance 209 and resistance 210)Get the voltage at ancillary coil 206 two ends, according to leading of described Voltage-output control signal gauge tap pipe 202Logical state, thereby the curtage of control primary coil 204, and then guarantee is connected with secondary coil 205Load circuit two ends output voltage V out or output current Iout's is stable.

With reference to figure 2, Fig. 2 is the functional block diagram of the PFM controller of Switching Power Supply shown in Fig. 1. Described PFMController 201 comprises former limit peak current detection comparator 301, Tons detector 302, Tons time delay module303, the first current sources 304 and the second current source 305, the first transmission gates 306 and the second transmission gate 307, electricityHold 308, constant current control comparator 309, error amplifier 310, interrupting time generation module 311, the firstR-S trigger 312 and the 2nd R-S trigger 313, protection module 314, three input nor gates 315, driveModule 316.

With reference to figure 1 and Fig. 2, when signal PFM is logic high, the OUT end of PFM controller 201 becomesHigh level, switching tube 202 conductings, the electric current that current flowing detects resistance 203 becomes large, resistance 203 two endsVoltage rises thereupon. When exceeding reference voltage, the voltage signal Vcs on current sense resistor 203 (is generally0.9V) time, former limit peak current detection comparator 301 is output as logic high; Otherwise be logic lowLevel. The output signal SHUTD of former limit peak current detection comparator 301, described signal SHUTD willThe output signal CVCTRL of R-S trigger 313 puts 1. CVCTRL is input to or three input not gates 315,The output signal PFM of three input nor gates 315. Now signal PFM becomes logic low, and PFM controlsThe OUT end step-down of device 201, power transistor 202 ends.

With reference to figure 3, Fig. 3 is the output characteristic curve figure of the interrupting time of Switching Power Supply shown in Fig. 1, horizontal lineThe sampled value that represents the output voltage of Switching Power Supply, stepped dotted line represents the charging curve of charge pump, twoThe abscissa of person's intersection point represents the interrupting time under certain loads. Wherein, abscissa represents the time, vertical seatMark represents magnitude of voltage. As can be seen from Figure 3, the stepped rising of charge pump, corresponding at step transition pointPOL on, the only corresponding interrupting time of output voltage, a POL correspondence oneThe switch periods of system, system does not have occurrence frequency shake. On POL corresponding to step platform, oneThe corresponding multiple interrupting times of individual output voltage, a POL correspondence switch periods of multiple systems,The shake of system occurrence frequency. Visible, existing Switching Power Supply can only be on some POL when interruptedThereby between the variation variation that realizes switch periods realize the shake of its frequency. But, described charge pumpCharging voltage wayward, the step width of stepped dotted line shown in Fig. 3 can not be controlled, fromAnd cause the scope of the frequency jitter based on above-mentioned mechanism wayward, cause the electromagnetic compatibility of Switching Power SupplyProperty is poor.

Known by above-mentioned analysis, prior art can only realize PFM Switching Power Supply on some POLWhen switching frequency shake, and its frequency jitter is wayward, and the Electro Magnetic Compatibility of Switching Power Supply is poor.

Summary of the invention

For solving the problems of the technologies described above, the invention provides a kind of PFM Switching Power Supply and tremble frequency circuit with tremble, on all POLs, there is controllable week with the switching frequency of realizing described Switching Power Supply in frequency methodThe shake of phase property, thus make described Switching Power Supply there is good Electro Magnetic Compatibility.

For achieving the above object, the invention provides following technical scheme:

PFM Switching Power Supply tremble a frequency circuit, comprising:

Frequency jitter module, the former limit peak current detection of described frequency jitter module and described Switching Power SupplyComparator connects, for changing the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Preferably, in foregoing circuit, described frequency jitter module comprises:

Reference voltage provides unit, and described reference voltage provides unit and described former limit peak current detection ratioConnect compared with device;

Reference voltage controller, described reference voltage controller is used for changing described reference voltage provides unitOutput voltage, thereby change the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Preferably, in foregoing circuit, it is the voltage source of multiple parallel connections that described reference voltage provides unit,Each voltage source by one with it corresponding switch be connected with described former limit peak current detection comparator;

By the on off state of switch described in the control of described reference voltage controller, thereby change described former limitThe reference voltage of peak current detection comparator, to change the former of described former limit peak current detection comparatorLimit peak point current, shakes the switching frequency of described Switching Power Supply.

Preferably, in foregoing circuit, described reference voltage provides unit to comprise: the first voltage source, instituteStating the first voltage source is connected with described former limit peak current detection comparator by the first switch; Second voltageSource; Described second voltage source is connected with described former limit peak current detection comparator by second switch;

Described reference voltage controller is pseudo-noise code generator, the control changing for generation of one-periodSignal, controls the on off state of described the first switch and second switch, thereby changes described former limit peak valueThe reference voltage of current sense comparator.

Preferably, in foregoing circuit, described pseudo-noise code generator is by the d type flip flop structure of 6 series connectionBecome.

Preferably, in foregoing circuit, also comprise:

Dutycycle adjusting module, the constant current control ratio of described dutycycle adjusting module and described Switching Power SupplyDevice connects; In the time that described Switching Power Supply is operated in constant current mode, described dutycycle adjusting module is for adjustingThe secondary ON time of described Switching Power Supply and the ratio of switch periods, make the on average defeated of described Switching Power SupplyGoing out electric current remains unchanged.

Preferably, in foregoing circuit, described dutycycle adjusting module comprises:

Permanent current-controlled current source, described continuous current source is by constant current control transmission gate and described constant current controlComparator connects; Adjust the secondary of described Switching Power Supply leads by controlling the on off state of described transmission gateThe ratio of logical time and switch periods.

The present invention also provides a kind of frequency method of trembling of PFM Switching Power Supply, comprising:

By changing the reference voltage of former limit peak current detection comparator of described Switching Power Supply, change formerLimit ON time and secondary ON time, shake the switching frequency of described Switching Power Supply.

Preferably, in said method, described method also comprises:

Adjust the secondary ON time of described Switching Power Supply and the ratio of switch periods, make described Switching Power SupplyAverage output current while being operated in constant current mode remains unchanged.

The present invention also provides a kind of PFM Switching Power Supply, it is characterized in that, comprising:

Transformer, has for the former limit winding in the input power source that is coupled, for Switching Power Supply is providedThe secondary winding of output voltage and an auxiliary winding;

Switching tube, with described former limit winding coupled;

PFM controller, is connected and controls the Kai Heguan of described switching tube with described switching tube;

Wherein, described PFM controller comprises the frequency circuit of trembling described in claim 1-7 any one.

Preferably, in above-mentioned Switching Power Supply, described switching tube is power transistor.

Can find out from technique scheme, PFM Switching Power Supply provided by the present invention tremble frequency circuit bagDraw together: frequency jitter module, the former limit peak current detection of described frequency jitter module and described Switching Power SupplyComparator connects, for changing the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Former limit ON time, secondary ON time and the proportional relation of former limit peak point current of Switching Power Supply,The two changes with the variation of former limit peak point current, and the switch periods of Switching Power Supply mainly depends on former limitON time and secondary ON time, so, in the time that former limit peak point current changes, described switch electricityThe excursion of the switch periods in source is during mainly by the excursion of described former limit ON time and secondary conductingBetween excursion determine, when now the frequency jitter scope of described Switching Power Supply is by the conducting of described former limitBetween excursion and the excursion of secondary ON time determine, described interrupting time is to Switching Power SupplyThe impact of switching frequency can be ignored. Described technical scheme is by changing described former limit peak current detectionThe reference voltage of comparator, to change the former limit peak point current of described former limit peak current detection comparator,The switching frequency of described Switching Power Supply is shaken. Come by the excursion of setting described reference voltageControl the excursion of described former limit peak point current, and then can control the frequency jitter of described Switching Power SupplyScope, there is controllable periodicity and trembles in the switching frequency that makes to tremble the Switching Power Supply of frequency circuit described in adoptingMoving, thus make described Switching Power Supply there is good Electro Magnetic Compatibility.

Brief description of the drawings

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, below will be to realityThe accompanying drawing of executing required use in example or description of the Prior Art is briefly described, apparently, belowAccompanying drawing in description is only some embodiments of the present invention, for those of ordinary skill in the art,Do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is common a kind of PFM Switching Power Supply with constant current constant voltage mode of operation in prior artCircuit diagram;

Fig. 2 is the circuit of the PFM controller of Switching Power Supply shown in Fig. 1;

Fig. 3 is the output characteristic curve figure of the interrupting time of Switching Power Supply shown in Fig. 1;

A kind of PFM Switching Power Supply that Fig. 4 provides for the embodiment of the present invention tremble frequency circuit;

Fig. 5 is the circuit diagram of trembling the reference voltage controller of frequency circuit described in Fig. 4;

Fig. 6 is the circuit diagram of trembling the PFM controller of frequency circuit shown in a kind of Fig. 4 of having;

Fig. 7 is that PFM shown in Fig. 4 controls the voltage characteristic curve under constant current mode of operation;

The circuit diagram of the another kind of PFM controller that Fig. 8 provides for the embodiment of the present invention.

Detailed description of the invention

Just as described in the background section, existing Switching Power Supply realizes out by the variation of interrupting timeThereby the variation in pass cycle realizes the shake of its frequency. But interrupting time is the output by Switching Power SupplyThe charging voltage of the sampled value of voltage and the charge pump of described Switching Power Supply determines. And the filling of described charge pumpPiezoelectric voltage is wayward, thereby causes the variation of switch periods of described Switching Power Supply wayward, i.e. instituteThe frequency jitter scope of stating Switching Power Supply is wayward, causes its Electro Magnetic Compatibility poor. Meanwhile, ifIn Fig. 3, the intersection point of horizontal line and staircase curve is at the transition point of two steps, and now an output voltage is only rightAnswer an interrupting time, the cycle of Switching Power Supply does not change, and the switching frequency of described Switching Power Supply can notShake, can not reach the effect of optimizing Switching Power Supply electromagnetism compatibility.

Inventor studies discovery, and on most of POL, what draw by charge pump charging curve is interruptedTime is all single, and the switch periods of Switching Power Supply can not be shaken. And on remaining POL,Even if can shine upon multiple interrupting times, the shake that realizes the switch periods of Switching Power Supply is also random,Uncontrollable. In the time that former limit peak point current changes, on whole POLs, former limit ON timeThe excursion of excursion and secondary ON time is all ratio with the excursion of former limit peak point current and closesSystem, all controlled, and now the variation of interrupting time can be ignored, and the excursion of switch periods is mainDepend on the excursion of former limit ON time and the excursion of secondary ON time, i.e. switching frequencyShake is decided by the excursion of former limit ON time and the excursion of secondary ON time.

So the excursion of controlling former limit peak point current by controlling the excursion of reference voltage isCan control the excursion of former limit ON time and the excursion of secondary ON time, thereby make switchThere is controlled periodic jitter in the frequency of power supply, makes it have good Electro Magnetic Compatibility.

Based on above-mentioned research, the invention provides a kind of PFM Switching Power Supply and tremble frequency circuit, comprising:

Frequency jitter module, the former limit peak current detection of described frequency jitter module and described Switching Power SupplyComparator connects, for changing the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Described variation of trembling frequency circuit and control by controlling the excursion of reference voltage former limit peak point currentScope can be controlled the excursion of former limit ON time and the excursion of secondary ON time, thereby makesThere is controlled periodic jitter in the frequency that obtains Switching Power Supply, makes it have good Electro Magnetic Compatibility.

More than the application's core concept, below in conjunction with the accompanying drawing in the embodiment of the present invention, to thisTechnical scheme in bright embodiment is clearly and completely described, and obviously, described embodiment onlyThe present invention's part embodiment, instead of whole embodiment. Based on the embodiment in the present invention, thisField those of ordinary skill is not being made the every other embodiment obtaining under creative work prerequisite,All belong to the scope of protection of the invention.

Set forth in the following description a lot of details so that fully understand the present invention, but thisBrightly can also adopt other to be different from alternate manner described here to implement, those skilled in the art canWithout prejudice to intension of the present invention in the situation that, do similar popularization, therefore the present invention is not subject to following public concreteThe restriction of embodiment.

Secondly, the present invention is described in detail in conjunction with schematic diagram, in the time that the embodiment of the present invention is described in detail in detail, for justIn explanation, the profile of indication device part structure can be disobeyed general ratio and be done local amplification, and described in showIntention is example just, and it should not limit the scope of protection of the invention at this.

Embodiment mono-

Based on above-mentioned thought, the embodiment of the present invention provides a kind of frequency circuit of trembling of PFM Switching Power Supply, instituteState and tremble frequency circuit and comprise:

Frequency jitter module, the former limit peak current detection of described frequency jitter module and described Switching Power SupplyComparator connects, for changing the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Wherein, described frequency jitter module comprises:

Reference voltage provides unit, and described reference voltage provides unit and described former limit peak current detection ratioConnect compared with device;

Reference voltage controller, described reference voltage controller is used for changing described reference voltage provides unitOutput voltage, thereby change the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.

Concrete, it is the voltage source of multiple parallel connections that described reference voltage provides unit, each voltage source passes throughOne with it corresponding switch be connected with described former limit peak current detection comparator;

By the on off state of switch described in the control of described reference voltage controller, thereby change described former limitThe reference voltage of peak current detection comparator, to change the former of described former limit peak current detection comparatorLimit peak point current, shakes the switching frequency of described Switching Power Supply.

With reference to figure 4, the frequency jitter module of a kind of PFM Switching Power Supply that Fig. 4 provides for inventive embodimentsThe circuit diagram of specific implementation, for the annexation of parts between clearer explanation circuit, Fig. 4In the former limit peak current detection comparator 301 of Switching Power Supply has been shown.

Described frequency jitter module comprises: reference voltage provides unit, and described reference voltage provides unit bagDraw together: the first voltage source U1 and second voltage source U2, wherein, described the first voltage source U1 is by theOne switch 502 is connected with the negative input end of described former limit peak current detection comparator; Described second voltageSource U2 is connected with the negative input end of described former limit peak current detection comparator by second switch 503.

Described frequency jitter module is controlled described the first switch and second by reference to voltage controller 501The on off state of switch changes the reference voltage of described former limit peak current detection comparator, described in changing, there is the switching frequency of described Switching Power Supply in the former limit peak point current of former limit peak current detection comparatorShake. Described reference voltage controller 501 control by control signal jitter control described the first switch withAnd the on off state of second switch. Concrete, described reference voltage controller 501 is according to input signal clkGenerate described control signal jitter. Described control signal jitter controls and directly controls described the first voltage sourceU1, described control signal jitter controls described the second electricity after phase inverter 504 carries out low and high level conversionPotential source U2, ensures that described the first switch 502 only has a conducting with second switch 503 at any time.

When described reference voltage controller 501 is controlled described the first switch 502 conductings, and control describedWhen two switches 503 end, described the first voltage source U1 is described former limit peak current detection comparator 301Negative input end the first reference voltage V1 is provided; Otherwise, when described reference voltage controller 501 is controlled instituteState the first switch 502 and end, and control described second switch 503 conductings, described second voltage source U2 isThe negative input end of described former limit peak current detection comparator 301 provides the second reference voltage V2. By upper+ the mode of stating changes the reference voltage of the negative input end of the former limit peak current detection comparator of Switching Power Supply. ItsIn, the first reference voltage V1 and the second reference voltage V2 are two and have the magnitude of voltage of setting difference. FigureNot shown described the first voltage source U1 and second voltage source U2 in 4, only show the two output voltageV1, V2. With reference to figure 5, described voltage controller 501 is pseudo-noise code generator, by 6 series connectionD type flip flop forms, and controls described voltage controller 501 by an input signal clk, makes it produce oneIndividual control signal jitter. Concrete, described input signal clk is to be the square-wave signal of 256us in the cycle, thisTime by rear one cycle of generation of described voltage controller 501 be (2^6-1) * 256us control signal jitter(being the square-wave signal of 160128ms).

Control the switch of described the first switch 502 and second switch 503 by described control signal jitterState, in the time that described control signal jitter is logic high, described the first switch 502 conductings, described inSecond switch 503 ends, the reference electricity of the negative input end of described former limit peak current detection comparator 301The the first reference voltage U1 providing for the first voltage source V 1 is provided; When described control signal jitter is logic lowWhen level, described the first switch 502 ends, described second switch 503 conductings, described former limit peak electricityThe second reference electricity that the reference voltage of the negative input end of stream detection comparator 301 provides for second voltage source V2Press U2, change the negative of described former limit peak current detection comparator 301 by described control signal jitterThe reference voltage of input, thus the size of former limit peak point current changed.

It should be noted that, the logic high of described control signal jitter and the appearance of logic low are severalRate is almost identical, shown in the embodiment of the present invention in circuit structure, because d type flip flop is 010101 this feelingsCondition there will not be, there is ' 1 ' number of times than occur ' 0 ' often 1.

With reference to figure 6, Fig. 6 has the electricity of trembling the PFM controller of frequency circuit described in technical solution of the present inventionLu Tu. Known with existing PFM controller contrast, the controller of PFM shown in Fig. 6 has increased and switchFrequency jitter described in the frequency jitter module 317(that the former limit peak current detection comparator 301 of power supply connectsModule circuit diagram is as shown in Figure 4), described frequency jitter module 317 is described former limit peak current detectionThe negative input end of comparator 301 provides the reference voltage of cycle variation, described former limit peak current detection ratioElectric according to the voltage signal Vcs of current sense resistor 203 and current reference compared with the positive input terminal of device 301Press output control signal SHUTD to control R-S trigger 313.

When for the negative input end of described former limit peak current detection comparator 301 provides reference voltage U, thisTime, former limit ON time is:

$\mathrm{Tonp}=\frac{U\·\mathrm{Lm}}{\sqrt{2}\·\mathrm{Vin}\·\mathrm{Rcs}}$

Secondary ON time is:

$\mathrm{Tons}=\frac{U\·\mathrm{Lm}}{\mathrm{Nps}\·\mathrm{Vout}\·\mathrm{Rcs}}$

Wherein, Lm is the inductance value of primary coil 204, and Rcs is the resistance value of current sense resistor 203,Ipk=U/Rcs is former limit peak point current, the turn ratio of Nps primary coil 204 and secondary coil 205. InstituteState and be directly proportional.

In the time changing reference voltage U, the switch periods of Switching Power Supply changes, and excursion is mainDetermined by the excursion of former limit ON time Tonp and the excursion of secondary ON time Tons. ThisDescribed in embodiment, trembling frequency circuit has two reference voltages and provides unit for the reference electricity of two settings is providedPress: the first reference voltage U1, the second reference voltage U2. By control described the first reference voltage U1 withThe second reference voltage U2 difference is the excursion in controllable switch cycle, thus the frequency of gauge tap power supplyRate jitter range.

Concrete, make the first reference voltage U1=U-△ U, the second reference voltage U2=U+ △ U,U2-U1=2 △ U, the control signal jitter exporting when described reference voltage controller 501 is the high electricity of logicAt ordinary times, described the first switch 502 conductings, second switch 503 ends, described former limit peak point current comparisonWhen the negative input end of device 301 is inputted reference power source U1, now, former limit peak point current is:

$\mathrm{Ipk}=\frac{U-\mathrm{\ΔU}}{\mathrm{rCS}}$

Former limit ON time is:

$\mathrm{Tonp}1=\frac{(U-\mathrm{\ΔU})\·\mathrm{Lm}}{\sqrt{2}\·\mathrm{Vin}\·\mathrm{Rcs}}$

Secondary ON time is:

$\mathrm{Tons}1=\frac{(U-\mathrm{\ΔU})\·\mathrm{Lm}}{\mathrm{Nps}\·\mathrm{Vout}\·\mathrm{Rcs}}$

The frequency of Switching Power Supply is:

$f_H=\frac{1}{\frac{(U-\mathrm{\ΔU})\·\mathrm{Lm}}{\sqrt{2}\·\mathrm{Vin}\·\mathrm{Rcs}}+\frac{(U-\mathrm{\ΔU})\·\mathrm{Lm}}{\mathrm{Nps}\·\mathrm{Vout}\·\mathrm{Rcs}}+\mathrm{Tdis}}$

Otherwise, when the control signal jitter exporting when described reference voltage controller 501 is logic low,Described the first switch 502 ends, second switch 503 conductings, described former limit peak point current comparator 301The reference power source of negative input end input while being U2, now, former limit peak point current is:

$\mathrm{Ipk}=\frac{U+\mathrm{\ΔU}}{\mathrm{rCS}}$

Former limit ON time is:

$\mathrm{Tonp}2=\frac{(U+\mathrm{\ΔU})\·\mathrm{Lm}}{\sqrt{2}\·\mathrm{Vin}\·\mathrm{Rcs}}$

Secondary ON time is:

$\mathrm{Tons}2=\frac{(U+\mathrm{\ΔU})\·\mathrm{Lm}}{\mathrm{Nps}\·\mathrm{Vout}\·\mathrm{Rcs}}$

The frequency of Switching Power Supply is:

$f_L=\frac{1}{\frac{(U+\mathrm{\ΔU})\·\mathrm{Lm}}{\sqrt{2}\·\mathrm{Vin}\·\mathrm{Rcs}}+\frac{(U+\mathrm{\ΔU})\·\mathrm{Lm}}{\mathrm{Nps}\·\mathrm{Vout}\·\mathrm{Rcs}}+\mathrm{Tdis}}$

As above-mentioned, ignore interrupting time, because

$\frac{1}{2}\mathrm{Lm}\·{\mathrm{Ipk}}^2\·f\·\mathrm{eff}=\mathrm{Vo}\·\mathrm{Io}$

Wherein, f is the switching frequency of Switching Power Supply under reference voltage, and eff is switch power efficiency, and Vo isThe output voltage of Switching Power Supply, the output current that Io is Switching Power Supply. Tremble and do not change the defeated of Switching Power Supply frequentlyGo out power, so have:

$\frac{\mathrm{\Δf}}{f}=2*\frac{\mathrm{\ΔVcs}}{\mathrm{Vcs}}=2*\frac{\mathrm{\ΔIpk}}{\mathrm{Ipk}}$

Wherein, Δ f=|f_H-f_L|, as original reference voltage U=0.9V, when △ U=0.0225V, bring intoState formula,

$\frac{\mathrm{\Δf}}{f}=0.05$

As the above analysis, pass through told frequency jitter module, but the switching frequency of Switching Power Supply is sent outRaw ± 5% shake, thereby the Electro Magnetic Compatibility of optimization Switching Power Supply. By setting described first with reference to electricityThe difference of pressure and the second reference voltage, the jitter range of the switching frequency of controllable switch power supply.

Frequency circuit is trembled in above-mentioned adjusting described in showing in the time of constant voltage mode of operation can make Switching Power Supply setOccurrence frequency shake in scope, and stable output; And under constant current mode of operation, fixing for oneLoad, due to above-mentioned corresponding two the former limit peak point currents of mode frequently of trembling, has:

$\mathrm{Ipk}=\frac{U\±\mathrm{\ΔU}}{\mathrm{rCS}}$

The first current source 304 of Switching Power Supply and the current ratio of the second current source 305 are fixed as 1:1,Have:

$\frac{\mathrm{Tons}}{\mathrm{Tsw}}=\frac{1}{2}$

In the time that described PFM controller is operated in constant current mode, the average output current of Switching Power Supply is:

$\mathrm{Iout}=\frac{1}{2}\·\mathrm{Nps}\·\frac{\mathrm{Tons}}{\mathrm{Tsw}}\·\mathrm{Ipk}$

So under constant current mode of operation, the average current of Switching Power Supply is with the variation of former limit peak point currentAnd change, its period of change is with to tremble frequently the cycle identical.

With reference to figure 7, in the time that the former limit peak electricity rheology of Switching Power Supply is large, its average output current will become greatly,May there is the phenomenon that load is overweight in Switching Power Supply, thereby cause the output voltage of Switching Power Supply to decline;In the time that the former limit of Switching Power Supply peak point current diminishes, the load of Switching Power Supply is crossed reconstructed image and is disappeared, its outputVoltage recovery, back and forth changes in this way. So now the output voltage of Switching Power Supply will present sawtooth waveforms.

So in order to make Switching Power Supply under constant current mode of operation, average output current remains unchanged,The described frequency circuit of trembling also comprises: dutycycle adjusting module, and in the time that Switching Power Supply is operated in constant current mode, instituteState dutycycle adjusting module by adjusting Tons/Tsw size, Tons/Tsw remains unchanged and can ensure in perseveranceUnder stream mode of operation, the average output current of Switching Power Supply remains unchanged.

With reference to figure 8, Fig. 8 is for including frequency jitter module and dutycycle adjusting module described in the present embodimentThe circuit diagram of PFM controller. Described dutycycle adjusting module comprises: permanent current-controlled current source 318 withAnd constant current control transmission gate 319, described constant current control transmission gate 319 is by the first transmission gate 306 and constant currentControlling comparator 309 connects; Adjust by the on off state of controlling described constant current control transmission gate 319The secondary ON time of described Switching Power Supply and the ratio of switch periods, and then ensure described Switching Power Supply workMaking average output current under constant current mode remains unchanged.

When U1 value is 0.8775V, U2 value is 0.9225V, and the current value of current source 318 is 0.11I,The control signal of transmission gate 319 is output signal jitter of pseudo-noise code generator 501. When jitter is for patrollingWhile collecting high level, transmission gate 319 closures; Otherwise disconnect. In the time of Ipk=0.8775/Rcs, jitter is for patrollingCollect high level, the electric current I that electric capacity 308 charges_chargeBe that (I+0.11I) is 1.11I, electric capacity 308 dischargesElectric current I_dischargeI, therefore have

$\frac{\mathrm{Tons}}{\mathrm{Tsw}}=\frac{I_{\mathrm{ch}\arg e}}{I_{\mathrm{ch}\arg e}+I_{\mathrm{disch}\arg e}}=0.526$

Switching Power Supply its average output current in the time of constant current mode of operation is:

$\mathrm{Iout}=\frac{1}{2}\·\mathrm{Nps}\·\frac{\mathrm{Tons}}{\mathrm{Tsw}}\·\mathrm{Ipk}=\frac{0.23}{\mathrm{Rcs}}\·\mathrm{Nps}$

In the time of Ipk=0.9225/Rcs, jitter is logic high, and capacitor charge and discharge electric current is I, therefore have:

$\frac{\mathrm{Tons}}{\mathrm{Tsw}}=0.5$

The average output current of Switching Power Supply in the time of constant current mode of operation is:

$\mathrm{Iout}=\frac{1}{2}\·\mathrm{Nps}\·\frac{\mathrm{Tons}}{\mathrm{Tsw}}\·\mathrm{Ipk}=\frac{0.23}{\mathrm{Rcs}}\·\mathrm{Nps}$

As the above analysis, in the time that Ipk changes, Tons/Tsw has made corresponding adjustment, realExisting Switching Power Supply average output current remains unchanged. Ensured that Switching Power Supply is real under constant current mode of operationWhen existing frequency jitter, can ensure the constant of output current.

Known by above-mentioned discussion, tremble frequency circuit described in technical solution of the present invention and can make Switching Power SupplyThere is controlled shake in switching frequency, has ensured its Electro Magnetic Compatibility.

Embodiment bis-

On the basis of above-described embodiment, the present embodiment provides a kind of frequency method of trembling of PFM Switching Power Supply,On all POLs, there is controllable periodicity and tremble to realize the switching frequency of described Switching Power SupplyMoving, thus make described Switching Power Supply there is good Electro Magnetic Compatibility.

The described frequency method of trembling is by changing the reference voltage of Switching Power Supply, thereby changes described Switching Power SupplyFormer limit ON time and secondary ON time, and then the switching frequency of described Switching Power Supply is shaken.

Can adopt multiple controlled voltage sources to become for described former limit peak current detection comparator provides periodicallyThe reference voltage of changing.

Identical with method in embodiment mono-, can adopt two power supplys, the first voltage source and second source are instituteState former limit peak current detection comparator reference voltage be provided, described the first voltage source by the first switch withDescribed former limit peak current detection comparator connects, and described second source is by second switch and described former limitPeak current detection comparator connects, by the first switch and second switch described in a control signal controlConducting and cut-off, thereby make the reference voltage generating period of described former limit peak current detection comparatorSexually revise, thereby can make the switching frequency of Switching Power Supply that controllable shake occurs, thereby open described in makingClose power supply and there is good Electro Magnetic Compatibility.

Described method also comprises: adjust the secondary ON time of described Switching Power Supply and the ratio of switch periods,Average output current while making described Switching Power Supply be operated in constant current mode remains unchanged.

It should be noted that, with identical in embodiment mono-, described in the present embodiment the quantity of power supply andFor described former limit peak current detection comparator connected mode is not unique, for example, can directly adopt oneThe voltage source that periodic square wave signal can be provided provides reference for described former limit peak current detection comparatorVoltage or adopt quantity to be greater than 2 voltage source to provide periodically variable reference voltage. The technology of the present invention sideThe core concept of case is to realize the controllable jitter of the switching frequency of Switching Power Supply by changing reference voltage.

Embodiment tri-

On the basis of above-described embodiment, the present embodiment provides a kind of PFM Switching Power Supply, described PFMSwitching Power Supply comprises: transformer, has for the former limit winding in the input power source that is coupled, for carryingFor secondary winding and an auxiliary winding of switch power source output voltage; Switching tube, described switching tube isPower transistor, with described former limit winding coupled; PFM controller described in embodiment mono-, with describedSwitching tube connects and controls the Kai Heguan of described switching tube.

Except described PFM controller, connected mode and Fig. 1 between miscellaneous part and described miscellaneous partShown in Switching Power Supply all identical. The circuit structure of described Switching Power Supply and operation principle can reference implementationsThe corresponding description of example one, does not repeat them here.

Described in the present embodiment, Switching Power Supply has PFM controller described in embodiment mono-, so described switchCan there is controllable periodic jitter in the switching frequency of power supply, have good Electro Magnetic Compatibility.

It should be noted that the difference embodiment side that three embodiment of the present invention are technical solution of the present inventionFormula, can remark additionally between three mutually. To the above-mentioned explanation of the disclosed embodiments, make this area specialIndustry technical staff can realize or use the present invention. To the multiple amendment of these embodiment to this area speciallyIndustry technical staff will be apparent, and General Principle as defined herein can not depart from thisIn the situation of the spirit or scope of invention, realize in other embodiments. Therefore, the present invention will be not can be byBe limited to these embodiment shown in this article, but will meet and principle disclosed herein and features of noveltyThe widest consistent scope.

Claims (11)

1. PFM Switching Power Supply tremble a frequency circuit, it is characterized in that, comprising:

   Frequency jitter module, the former limit peak current detection of described frequency jitter module and described Switching Power SupplyComparator connects, for changing the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake;

   Wherein, described in, tremble frequency circuit and control former limit peak point current by the excursion of controlling reference voltageExcursion, can control the excursion of former limit ON time and the excursion of secondary ON time,Thereby there is controlled periodic jitter in the frequency that makes Switching Power Supply.
2. 2. circuit according to claim 1, is characterized in that, described frequency jitter module comprises:

   Reference voltage provides unit, and described reference voltage provides unit and described former limit peak current detection ratioConnect compared with device;

   Reference voltage controller, described reference voltage controller is used for changing described reference voltage provides unitOutput voltage, thereby change the reference voltage of described former limit peak current detection comparator, to changeThe former limit peak point current of stating former limit peak current detection comparator, sends out the switching frequency of described Switching Power SupplyRaw shake.
3. 3. circuit according to claim 2, is characterized in that, described reference voltage provides unit to beThe voltage source of multiple parallel connections, each voltage source passes through switch and the described former limit peak electricity of correspondence with itStream detection comparator connects;

   By the on off state of switch described in the control of described reference voltage controller, thereby change described former limitThe reference voltage of peak current detection comparator, to change the former of described former limit peak current detection comparatorLimit peak point current, shakes the switching frequency of described Switching Power Supply.
4. 4. circuit according to claim 2, is characterized in that, described reference voltage provides unit bagDraw together: the first voltage source, described the first voltage source is by the first switch and described former limit peak current detection ratioConnect compared with device; Second voltage source; Described second voltage source is by second switch and described former limit peak point currentDetection comparator connects;

   Described reference voltage controller is pseudo-noise code generator, the control changing for generation of one-periodSignal, controls the on off state of described the first switch and second switch, thereby changes described former limit peak valueThe reference voltage of current sense comparator.
5. 5. circuit according to claim 4, is characterized in that, described pseudo-noise code generator is by 6The d type flip flop of individual series connection forms.
6. 6. circuit according to claim 1, is characterized in that, also comprises:

   Dutycycle adjusting module, the constant current control ratio of described dutycycle adjusting module and described Switching Power SupplyDevice connects; In the time that described Switching Power Supply is operated in constant current mode, described dutycycle adjusting module is for adjustingThe secondary ON time of described Switching Power Supply and the ratio of switch periods, make the on average defeated of described Switching Power SupplyGoing out electric current remains unchanged.
7. 7. circuit according to claim 6, is characterized in that, described dutycycle adjusting module comprises:

   Permanent current-controlled current source, described permanent current-controlled current source is by constant current control transmission gate and described constant currentControl comparator connects; Adjust the pair of described Switching Power Supply by controlling the on off state of described transmission gateThe ratio of limit ON time and switch periods.
8. 8. one kind comprises trembling of the PFM Switching Power Supply of trembling frequency circuit as described in claim 1-7 any oneFrequency method, is characterized in that, comprising:

   By changing the reference voltage of former limit peak current detection comparator of described Switching Power Supply, change formerLimit ON time and secondary ON time, shake the switching frequency of described Switching Power Supply.
9. 9. method according to claim 8, is characterized in that, described method also comprises:

   Adjust the secondary ON time of described Switching Power Supply and the ratio of switch periods, make described Switching Power SupplyAverage output current while being operated in constant current mode remains unchanged.
10. 10. a PFM Switching Power Supply, is characterized in that, comprising:

    Transformer, has for the former limit winding in the input power source that is coupled, for Switching Power Supply is providedThe secondary winding of output voltage and an auxiliary winding;

    Switching tube, with described former limit winding coupled;

    PFM controller, is connected and controls the Kai Heguan of described switching tube with described switching tube;

    Wherein, described PFM controller comprises the frequency circuit of trembling described in claim 1-7 any one.
11. 11. Switching Power Supplies according to claim 10, is characterized in that, described switching tube is powerTransistor.