CN102780392A - Pulse-width modulation (PWM) switching power supply, frequency jitter circuit thereof and frequency jitter method - Google Patents

Abstract

The invention discloses a pulse-width modulation (PWM) switching power supply, a frequency jitter circuit thereof and a frequency jitter method, wherein the frequency jitter circuit comprises a frequency jitter module, wherein the frequency jitter module is connected with a primary side peak current detection comparator of the switching power supply for improving the reference voltage of the primary side peak current detection comparator, so the primary side peak current of the primary side peak current detection comparator is changed, and the switching frequency of the switching power supply is jittered. Through changing the reference voltage of the primary side peak current detection comparator to change the primary side peak current, the switching frequency of the switching power supply is jittered. The variation range of the primary side peak current is controlled through setting the variation range of the reference voltage, so the frequency jitter range of the switching power supply can be controlled, the switching frequency of the switching power supply which adopts the frequency jitter circuit can be controlled to periodically jitter, and accordingly, the switching power supply has better electromagnetic compatibility.

Description

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

Technical field

The present invention relates to the ic manufacturing process technical field, more particularly, relate to a kind of PFM Switching Power Supply and tremble frequency circuit and tremble frequency method.

Background technology

Switching Power Supply is to utilize modern power electronics technology, and conducting of control switch pipe and the time ratio that ends are kept stable a kind of circuit arrangement of exporting.Wherein, Common a kind of Switching Power Supply is that the pulse frequency with constant current constant voltage mode of operation is regulated (PFM) Switching Power Supply; Be that said Switching Power Supply is come the conducting of control switch pipe through PFM and ended; Keep stable output, thereby make whole switch power supply system be operated in constant voltage or constant current mode.The PFM Switching Power Supply has higher voltage rate of change and current changing rate; And its transformer exists parasitic capacitance and stray inductance; Device is on every side formed electromagnetic interference (EMI), so need to adopt the method for shake switching frequency to optimize its Electromagnetic Compatibility.

The switch periods of Switching Power Supply (Tsw) 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 the proportional relation of former limit peak current.Prior art adopts fixing former limit peak current usually, thereby has fixed former limit ON time and secondary ON time, and the change of the switch periods of Switching Power Supply only relies on the variation of interrupting time to realize.

With reference to figure 1, Fig. 1 is the circuit diagram of a kind of common PFM Switching Power Supply with constant current constant voltage mode of operation in the prior art.Said Switching Power Supply changes ac input signal Vac into direct-flow input signal Vin through rectifying device 200 and input capacitance Cin, and said direct-flow input signal Vin is that PFM controller 201 provides operating voltage.Said Switching Power Supply characterizes the voltage at secondary coil 205 two ends through the voltage at ancillary coil 206 two ends; Said PFM controller 201 obtains the voltage at ancillary coil 206 two ends through resistor network (comprising resistance 209 and resistance 210); Conducting state according to said voltage output control signal control switch pipe 202; Thereby the curtage of control primary coil 204, and then assurance is connected the stable of load circuit two ends output voltage V out or output current Iout with secondary coil 205.

With reference to figure 2, Fig. 2 is the functional block diagram of the PFM controller of Switching Power Supply shown in Fig. 1.Said PFM controller 201 comprises former limit peak current detection comparator 301, Tons detector 302, Tons time delay module 303, the first current sources 304 and second current source 305; First transmission gate 306 and second transmission gate 307, electric capacity 308, constant current control comparator 309; Error amplifier 310, interrupting time generation module 311, the one R-S triggers 312 and the 2nd R-S trigger 313; Protection module 314, three input NOR gates 315, driver module 316.

With reference to figure 1 and Fig. 2, when signal PFM is a logic high, the OUT of PFM controller 201 end becomes high level, switching tube 202 conductings, and the electrorheological that flows through current sense resistor 203 is big, and the voltage at resistance 203 two ends rises thereupon.When the voltage signal Vcs on the current sense resistor 203 surpassed reference voltage (being generally 0.9V), former limit peak current detection comparator 301 was output as logic high; Otherwise be logic low.The output signal SHUTD of former limit peak current detection comparator 301, said signal SHUTD puts 1 with the output signal CV CTRL of R-S trigger 313.CV CTRL is input to or the output signal PFM of three input not gates 315, three input NOR gates 315.This moment, signal PFM became logic low, the OUT end step-down of PFM controller 201, and 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 line is represented the sampled value of the output voltage of Switching Power Supply, and stepped dotted line is represented the charging curve of charge pump, and the abscissa of both intersection points is represented the interrupting time under the certain loads.Wherein, the abscissa express time, ordinate is represented magnitude of voltage.As can be seen from Figure 3, the stepped rising of charge pump, on step transition point corresponding load point, the only corresponding interrupting time of output voltage, the switch periods of a system that promptly POL is corresponding, system does not have the occurrence frequency shake.On step platform corresponding load point, the corresponding a plurality of interrupting times of output voltage, promptly POL the is corresponding switch periods of a plurality of systems, system's occurrence frequency shake.It is thus clear that, thereby existing Switching Power Supply can only the variation through interrupting time realize that the variation of switch periods realizes the shake of its frequency on some POL.Yet the charging voltage of said charge pump is wayward, and promptly the step width of stepped dotted line shown in Fig. 3 can not Be Controlled, thereby causes based on the scope of the frequency jitter of above-mentioned mechanism waywardly, causes the Electro Magnetic Compatibility of Switching Power Supply relatively poor.

Can know that through above-mentioned analysis when prior art can only realize the switching frequency shake of PFM Switching Power Supply on some POL, and its frequency jitter is wayward, the Electro Magnetic Compatibility of Switching Power Supply is relatively poor.

Summary of the invention

For solving the problems of the technologies described above; The present invention provides a kind of PFM Switching Power Supply and trembles frequency circuit and tremble frequency method; Controllable periodic jitter takes place in the switching frequency to realize said Switching Power Supply on all POLs, thereby makes said Switching Power Supply have Electro Magnetic Compatibility preferably.

For realizing above-mentioned purpose, the present invention provides following technical scheme:

A kind of PFM Switching Power Supply tremble frequency circuit, comprising:

The frequency jitter module; Said frequency jitter module is connected with the former limit peak current detection comparator of said Switching Power Supply; Be used to change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

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

Reference voltage provides the unit, and said reference voltage provides the unit to be connected with said former limit peak current detection comparator;

The reference voltage controller; Said reference voltage controller is used to change the output voltage that said reference voltage provides the unit; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

Preferably, in foregoing circuit, it is the voltage source of a plurality of parallel connections that said reference voltage provides the unit, each voltage source through one with it corresponding switch be connected with said former limit peak current detection comparator;

Control the on off state of said switch through said reference voltage controller; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

Preferably, in foregoing circuit, said reference voltage provides the unit to comprise: first voltage source, and said first voltage source is connected with said former limit peak current detection comparator through first switch; Second voltage source; Said second voltage source is connected with said former limit peak current detection comparator through second switch;

Said reference voltage controller is a pseudo-noise code generator, is used to produce the control signal that one-period changes, and controls the on off state of said first switch and second switch, thereby changes the reference voltage of said former limit peak current detection comparator.

Preferably, in foregoing circuit, said pseudo-noise code generator is made up of the d type flip flop of 6 series connection.

Preferably, in foregoing circuit, also comprise:

The duty ratio adjusting module, said duty ratio adjusting module is connected with the constant current control comparator of said Switching Power Supply; When said Switching Power Supply was operated in constant current mode, said duty ratio adjusting module was used to adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods, and the average output current of said Switching Power Supply is remained unchanged.

Preferably, in foregoing circuit, said duty ratio adjusting module comprises:

Constant current Control current source, said continuous current source is connected with said constant current control comparator through constant current control transmission door; Adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods through the on off state of controlling said transmission gate.

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

The reference voltage of the former limit peak current detection comparator through changing said Switching Power Supply changes former limit ON time and secondary ON time, and the switching frequency of said Switching Power Supply is shaken.

Preferably, in said method, said method also comprises:

Adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods, the average output current when making said Switching Power Supply be 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, have the input power source that is used to be coupled former limit winding, be used to provide secondary winding and an auxiliary winding of switch power source output voltage;

Switching tube is with said former limit winding coupled;

The PFM controller is connected and controls the Kai Heguan of said switching tube with said switching tube;

Wherein, said PFM controller comprises each described frequency circuit of trembling of claim 1-7.

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

Can find out from technique scheme; The frequency circuit of trembling of PFM Switching Power Supply provided by the present invention comprises: the frequency jitter module; Said frequency jitter module is connected with the former limit peak current detection comparator of said Switching Power Supply; Be used to change the reference voltage of said former limit peak current detection comparator,, the switching frequency of said Switching Power Supply shaken to change the former limit peak current of said former limit peak current detection comparator.

The former limit ON time of Switching Power Supply, secondary ON time and the proportional relation of former limit peak current; The two variation with former limit peak current changes; And the switch periods of Switching Power Supply mainly depends on former limit ON time and secondary ON time; So; When former limit peak current changes; The excursion of the switch periods of said Switching Power Supply is mainly by the excursion of said former limit ON time and the excursion decision of secondary ON time, and promptly the frequency jitter scope of said Switching Power Supply is by the excursion of said former limit ON time and the excursion decision of secondary ON time at this moment, and said interrupting time can be ignored to the influence of the switching frequency of Switching Power Supply.Said technical scheme to change the former limit peak current of said former limit peak current detection comparator, shakes the switching frequency of said Switching Power Supply through changing the reference voltage of said former limit peak current detection comparator.Control the excursion of said former limit peak current through the excursion of setting said reference voltage; And then can control the frequency jitter scope of said Switching Power Supply; Make and adopt the said switching frequency of trembling the Switching Power Supply of frequency circuit that controllable periodic jitter takes place, thereby make said Switching Power Supply have Electro Magnetic Compatibility preferably.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art; To do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below; Obviously, the accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills; Under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.

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

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 invention tremble frequency circuit;

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

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

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

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

Embodiment

Said as the background technology part, thus the variation of existing Switching Power Supply through interrupting time realizes that the variation of switch periods realizes the shake of its frequency.But interrupting time is the charging voltage decision by the charge pump of the sampled value of the output voltage of Switching Power Supply and said Switching Power Supply.And the charging voltage of said charge pump is wayward, thereby causes the variation of switch periods of said Switching Power Supply wayward, and promptly the frequency jitter scope of said Switching Power Supply is wayward, causes its Electro Magnetic Compatibility relatively poor.Simultaneously; If the intersection point of horizontal line and staircase curve is at the transition point of two steps among Fig. 3; The only corresponding interrupting time of output voltage this moment; The cycle of Switching Power Supply does not change, and promptly the switching frequency of said Switching Power Supply can not shaken, and can not reach to optimize the compatible effect of Switching Power Supply electromagnetism.

The inventor discovers that on most of POL, the interrupting time that draws through the charge pump charging curve all is single, and promptly the switch periods of Switching Power Supply can not shaken.And on remaining POL,, realize that the shake of the switch periods of Switching Power Supply also is at random even can shine upon a plurality of interrupting times, uncontrollable.When former limit peak current changes; On whole POLs; The excursion of former limit ON time and the excursion of secondary ON time all are proportionate relationship with the excursion of former limit peak current; All controlled; And this moment, the variation of interrupting time can be ignored, and the excursion of switch periods depends primarily on the excursion of former limit ON time and the excursion of secondary ON time, i.e. the shake of switching frequency 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 current through the excursion of control reference voltage is the excursion of the former limit of may command ON time and the excursion of secondary ON time; Thereby make the frequency of Switching Power Supply that controlled periodic jitter take place, make it have Electro Magnetic Compatibility preferably.

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

The frequency jitter module; Said frequency jitter module is connected with the former limit peak current detection comparator of said Switching Power Supply; Be used to change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

It is said that to tremble the excursion that frequency circuit controls former limit peak current through the excursion of control reference voltage be the excursion of the former limit of may command ON time and the excursion of secondary ON time; Thereby make the frequency of Switching Power Supply that controlled periodic jitter take place, make it have Electro Magnetic Compatibility preferably.

It more than is the application's core concept; To combine the accompanying drawing in the embodiment of the invention below, the technical scheme in the embodiment of the invention carried out clear, intactly description, obviously; Described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills are not making the every other embodiment that is obtained under the creative work prerequisite, all belong to the scope of the present invention's protection.

A lot of details have been set forth in the following description so that make much of the present invention; But the present invention can also adopt other to be different from alternate manner described here and implement; Those skilled in the art can do similar popularization under the situation of intension of the present invention, so the present invention does not receive the restriction of following disclosed specific embodiment.

Secondly, the present invention combines sketch map to be described in detail, when the embodiment of the invention is detailed; For ease of explanation; The profile of indication device spare structure can be disobeyed general ratio and done local the amplification, and said sketch map is example, and it should not limit the scope of the present invention's protection at this.

Embodiment one

Based on above-mentioned thought, the embodiment of the invention provides a kind of frequency circuit of trembling of PFM Switching Power Supply, and the said frequency circuit of trembling comprises:

The frequency jitter module; Said frequency jitter module is connected with the former limit peak current detection comparator of said Switching Power Supply; Be used to change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

Wherein, said frequency jitter module comprises:

Reference voltage provides the unit, and said reference voltage provides the unit to be connected with said former limit peak current detection comparator;

The reference voltage controller; Said reference voltage controller is used to change the output voltage that said reference voltage provides the unit; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

Concrete, it is the voltage source of a plurality of parallel connections that said reference voltage provides the unit, each voltage source through one with it corresponding switch be connected with said former limit peak current detection comparator;

Control the on off state of said switch through said reference voltage controller; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.

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

Said frequency jitter module comprises: reference voltage provides the unit; Said reference voltage provides the unit to comprise: the first voltage source U1 and the second voltage source U2; Wherein, the said first voltage source U1 is connected with the negative input end of said former limit peak current detection comparator through first switch 502; The said second voltage source U2 is connected with the negative input end of said former limit peak current detection comparator through second switch 503.

Said frequency jitter module changes the reference voltage of said former limit peak current detection comparator through the on off state of reference voltage controller 501 said first switches of control and second switch; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.The on off state of said first switch and second switch is controlled in said reference voltage controller 501 controls through control signal jitter.Concrete, said reference voltage controller 501 generates said control signal jitter according to input signal clk.Said control signal jitter control is the said first voltage source U1 of control directly; Said control signal jitter carries out the said second voltage source U2 of high-low level conversion back control through inverter 504, guarantees that said at any time first switch 502 has only a conducting with second switch 503.

When 502 conductings of said first switch of said reference voltage controller 501 controls, and control said second switch 503 by the time, the said first voltage source U1 is that the negative input end of said former limit peak current detection comparator 301 provides the first reference voltage V1; Otherwise, controlling said first switch 502 when said reference voltage controller 501 and end, and control said second switch 503 conductings, the said second voltage source U2 is that the negative input end of said former limit peak current detection comparator 301 provides the second reference voltage V2.Change the reference voltage of negative input end of the former limit peak current detection comparator of Switching Power Supply through the last+mode of stating.Wherein, the first reference voltage V1 and the second reference voltage V2 are two magnitudes of voltage with setting difference.The not shown said first voltage source U1 and the second voltage source U2 among Fig. 4 only show the two output voltage V 1, V2.With reference to figure 5, said voltage controller 501 is a pseudo-noise code generator, is made up of the d type flip flop of 6 series connection, controls said voltage controller 501 through an input signal clk, makes it produce a control signal jitter.Concrete, said input signal clk is to be the square-wave signal of 256us in the cycle, generate one-period through said voltage controller 501 backs this moment is (2^6-1) * 256us control signal jitter (being the square-wave signal of 160128ms).

Control the on off state of said first switch 502 and second switch 503 through said control signal jitter; When said control signal jitter is logic high; 502 conductings of said first switch; Said second switch 503 ends, and the reference voltage of the negative input end of said former limit peak current detection comparator 301 is the first reference voltage U1 that first voltage source V 1 provides; When said control signal jitter is logic low; Said first switch 502 ends; Said second switch 503 conductings; The reference voltage of the negative input end of said former limit peak current detection comparator 301 is the second reference voltage U2 that second voltage source V 2 provides, and changes the reference voltage of the negative input end of said former limit peak current detection comparator 301 through said control signal jitter, thereby changes the size of former limit peak current.

Need to prove; The logic high of said control signal jitter and the occurrence probability of logic low are much at one; Shown in the embodiment of the invention in the circuit structure because d type flip flop is that 010101 this situation can not occur, ' 1 ' number of times appears and than occur ' 0 ' often 1.

With reference to figure 6, Fig. 6 has the said circuit diagram of trembling the PFM controller of frequency circuit of technical scheme of the present invention.Can know with the contrast of existing P FM controller; PFM controller shown in Figure 6 has increased the frequency jitter module 317 (said frequency jitter module circuit diagram is as shown in Figure 4) that is connected with the former limit peak current detection comparator 301 of Switching Power Supply; Said frequency jitter module 317 provides the reference voltage that the cycle changes for the negative input end of said former limit peak current detection comparator 301, and the positive input terminal of said former limit peak current detection comparator 301 is according to the voltage signal Vcs and the current reference voltage output control signal SHUTD control R-S trigger 313 of current sense resistor 203.

When for the negative input end of said former limit peak current detection comparator 301 provides reference voltage U, at this moment, former limit ON time is:

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

The 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, and Ipk=U/Rcs is a former limit peak current, the turn ratio of Nps primary coil 204 and secondary coil 205.Said being directly proportional.

When changing reference voltage U, the switch periods of Switching Power Supply changes, and excursion is mainly by the excursion of former limit ON time Tonp and the excursion decision of secondary ON time Tons.Present embodiment is said to be trembled frequency circuit and has two reference voltages and provide the unit to be used to provide the reference voltage of two settings: the first reference voltage U1, the second reference voltage U2.Through controlling the said first reference voltage U1 and the second reference voltage U2 difference is the excursion in controllable switch cycle, thus the frequency jitter scope of control switching.

Concrete, make the first reference voltage U1=U-△ U, the second reference voltage U2=U+ △ U; U2-U1=2 △ U then, when the control signal jitter of said reference voltage controller 501 outputs is logic high, 502 conductings of said first switch; Second switch 503 ends; When the negative input end of said former limit peak current comparator 301 was imported reference power source U1, at this moment, former limit peak current was:

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

Former limit ON time is:

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

The 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 of said reference voltage controller 501 outputs was logic low, said first switch 502 ended; Second switch 503 conductings; When the reference power source of the negative input end input of said former limit peak current comparator 301 was U2, at this moment, former limit peak current was:

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

Former limit ON time is:

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

The 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 the reference voltage, and eff is a switch power efficiency, and Vo is the output voltage of Switching Power Supply, and Io is the output current of Switching Power Supply.Tremble frequency and do not change the power output of Switching Power Supply, 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, during △ U=0.0225V, bring above-mentioned formula into,

$\frac{\mathrm{\Δf}}{f}=0.05$

Can know by above-mentioned analysis, pass through the frequency jitter module of telling, but ± 5% shake takes place in the switching frequency of Switching Power Supply, thereby optimize the Electro Magnetic Compatibility of Switching Power Supply.Through setting the difference of said first reference voltage and second reference voltage, the jitter range of the switching frequency of controllable switch power supply.

The said frequency circuit of trembling can make Switching Power Supply occurrence frequency shake in the scope of setting when above-mentioned adjusting was illustrated in the constant voltage mode of operation, and output is stable; And under the constant current mode of operation, for a fixing load, because above-mentioned corresponding two the former limit peak currents of mode frequently of trembling promptly have:

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

First current source 304 of Switching Power Supply and the current ratio of second current source 305 are fixed as 1:1, promptly have:

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

When said PFM controller was operated in constant current mode, the average output current of Switching Power Supply was:

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

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

With reference to figure 7, when the former limit peak electricity rheology of Switching Power Supply was big, its average output current will become greatly, and the overweight phenomenon of load may appear in Switching Power Supply, thereby caused the output voltage of Switching Power Supply to descend; When the former limit of Switching Power Supply peak current diminished, the load of Switching Power Supply was crossed reconstructed image and is disappeared, and its output voltage gos up, and back and forth changes in this way.So this moment, the output voltage of Switching Power Supply will present sawtooth waveforms.

So; In order to make Switching Power Supply under the constant current mode of operation; Average output current remains unchanged, and the said frequency circuit of trembling also comprises: the duty ratio adjusting module, when Switching Power Supply is operated in constant current mode; Said duty ratio adjusting module is through adjustment Tons/Tsw size, and the Tons/Tsw average output current that can guarantee Switching Power Supply under the constant current mode of operation that remains unchanged remains unchanged.

With reference to figure 8, Fig. 8 is the circuit diagram that includes the PFM controller of said frequency jitter module of present embodiment and duty ratio adjusting module.Said duty ratio adjusting module comprises: constant current Control current source 318 and constant current control transmission door 319, and said constant current control transmission door 319 is connected with constant current control comparator 309 through first transmission gate 306; Adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods through the on off state of controlling said constant current control transmission door 319, and then guarantee that said Switching Power Supply is operated in that average output current remains unchanged under the constant current mode.

When the U1 value is 0.8775V, the U2 value is 0.9225V, and the current value of current source 318 is 0.11I, and the control signal of transmission gate 319 is output signal jitter of pseudo-noise code generator 501.When jitter is logic high, transmission gate 319 closures; Otherwise break off.When Ipk=0.8775/Rcs, jitter is a logic high, the electric current I of electric capacity 308 chargings _ChargeBe that (I+0.11I) is 1.11I, the electric current I of electric capacity 308 discharges _DischargeBe I, so have

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

Its average output current was when Switching Power Supply was in the constant current mode of operation:

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

When Ipk=0.9225/Rcs, jitter is a logic high, and the capacitor charge and discharge electric current is I, so have:

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

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

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

Can know that by above-mentioned analysis when Ipk changed, Tons/Tsw had made corresponding adjustment, realize that the Switching Power Supply average output current remains unchanged.Guaranteed that promptly Switching Power Supply realizes can guaranteeing the constant of output current in the frequency jitter under the constant current mode of operation.

Can know that through above-mentioned argumentation the said frequency circuit of trembling of technical scheme of the present invention can make the switching frequency of Switching Power Supply that controlled shake takes place, and has guaranteed its Electro Magnetic Compatibility.

Embodiment two

On the basis of the foregoing description; Present embodiment provides a kind of frequency method of trembling of PFM Switching Power Supply; Controllable periodic jitter takes place in the switching frequency to realize said Switching Power Supply on all POLs, thereby makes said Switching Power Supply have Electro Magnetic Compatibility preferably.

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

Can adopt a plurality of controlled voltage sources is that said former limit peak current detection comparator provides periodically variable reference voltage.

Identical with method among the embodiment one; Can adopt two power supplys; First voltage source and second source are that said former limit peak current detection comparator provides reference voltage; Said first voltage source is connected with said former limit peak current detection comparator through first switch; Said second source is connected with said former limit peak current detection comparator through second switch, controls the conducting of said first switch and second switch and ends through a control signal, thereby make the reference voltage generating period of said former limit peak current detection comparator sexually revise; Thereby controllable shake takes place in the switching frequency that can make Switching Power Supply, thereby makes said Switching Power Supply have Electro Magnetic Compatibility preferably.

Said method also comprises: adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods, the average output current when making said Switching Power Supply be operated in constant current mode remains unchanged.

Need to prove; With identical among the embodiment one be; The quantity of the said power supply of present embodiment and for said former limit peak current detection comparator connected mode is not unique, for example can directly adopt a voltage source that periodic square wave signal can be provided is that said former limit peak current detection comparator provides reference voltage or adopts quantity greater than 2 voltage source periodically variable reference voltage to be provided.The core concept of technical scheme of the present invention is to realize the controllable jitter of the switching frequency of Switching Power Supply through changing reference voltage.

Embodiment three

On the basis of the foregoing description; Present embodiment provides a kind of PFM Switching Power Supply; Said PFM Switching Power Supply comprises: transformer, have the input power source that is used to be coupled former limit winding, be used to provide secondary winding and an auxiliary winding of switch power source output voltage; Switching tube, said switching tube are power transistor, with said former limit winding coupled; PFM controller described in the embodiment one is connected and controls the Kai Heguan of said switching tube with said switching tube.

Except that said PFM controller, the connected mode between miscellaneous part and the said miscellaneous part is all identical with Switching Power Supply shown in Fig. 1.But the circuit structure of said Switching Power Supply and the one corresponding description of operation principle reference implementation example are repeated no more at this.

The said Switching Power Supply of present embodiment has PFM controller described in the embodiment one, so controllable periodic jitter can take place the switching frequency of said Switching Power Supply, has Electro Magnetic Compatibility preferably.

Need to prove that three embodiment according to the invention can remark additionally between the three for the difference of technical scheme of the present invention embodies mode each other.To the above-mentioned explanation of the disclosed embodiments, make this area professional and technical personnel can realize or use the present invention.Multiple modification to these embodiment will be conspicuous concerning those skilled in the art, and defined General Principle can realize under the situation that does not break away from the spirit or scope of the present invention in other embodiments among this paper.Therefore, the present invention will can not be restricted to these embodiment shown in this paper, but will meet and principle disclosed herein and features of novelty the wideest corresponding to scope.

Claims (11)

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

   The frequency jitter module; Said frequency jitter module is connected with the former limit peak current detection comparator of said Switching Power Supply; Be used to change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.
2. 2. circuit according to claim 1 is characterized in that, said frequency jitter module comprises:

   Reference voltage provides the unit, and said reference voltage provides the unit to be connected with said former limit peak current detection comparator;

   The reference voltage controller; Said reference voltage controller is used to change the output voltage that said reference voltage provides the unit; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.
3. 3. circuit according to claim 2 is characterized in that, it is the voltage source of a plurality of parallel connections that said reference voltage provides the unit, each voltage source through one with it corresponding switch be connected with said former limit peak current detection comparator;

   Control the on off state of said switch through said reference voltage controller; Thereby change the reference voltage of said former limit peak current detection comparator; To change the former limit peak current of said former limit peak current detection comparator, the switching frequency of said Switching Power Supply is shaken.
4. 4. circuit according to claim 2 is characterized in that, said reference voltage provides the unit to comprise: first voltage source, and said first voltage source is connected with said former limit peak current detection comparator through first switch; Second voltage source; Said second voltage source is connected with said former limit peak current detection comparator through second switch;

   Said reference voltage controller is a pseudo-noise code generator, is used to produce the control signal that one-period changes, and controls the on off state of said first switch and second switch, thereby changes the reference voltage of said former limit peak current detection comparator.
5. 5. circuit according to claim 4 is characterized in that said pseudo-noise code generator is made up of the d type flip flop of 6 series connection.
6. 6. circuit according to claim 1 is characterized in that, also comprises:

   The duty ratio adjusting module, said duty ratio adjusting module is connected with the constant current control comparator of said Switching Power Supply; When said Switching Power Supply was operated in constant current mode, said duty ratio adjusting module was used to adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods, and the average output current of said Switching Power Supply is remained unchanged.
7. 7. circuit according to claim 6 is characterized in that, said duty ratio adjusting module comprises:

   Constant current Control current source, said continuous current source is connected with said constant current control comparator through constant current control transmission door; Adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods through the on off state of controlling said transmission gate.
8. A PFM Switching Power Supply tremble frequency method, it is characterized in that, comprising:

   The reference voltage of the former limit peak current detection comparator through changing said Switching Power Supply changes former limit ON time and secondary ON time, and the switching frequency of said Switching Power Supply is shaken.
9. 9. method according to claim 8 is characterized in that, said method also comprises:

   Adjust the secondary ON time of said Switching Power Supply and the ratio of switch periods, the average output current when making said Switching Power Supply be operated in constant current mode remains unchanged.
10. 10. a PFM Switching Power Supply is characterized in that, comprising:

    Transformer, have the input power source that is used to be coupled former limit winding, be used to provide secondary winding and an auxiliary winding of switch power source output voltage;

    Switching tube is with said former limit winding coupled;

    The PFM controller is connected and controls the Kai Heguan of said switching tube with said switching tube;

    Wherein, said PFM controller comprises each described frequency circuit of trembling of claim 1-7.
11. 11. Switching Power Supply according to claim 8 is characterized in that, said switching tube is a power transistor.

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