CN1829041A - Switching control device for primary side control output current of power supply - Google Patents

Abstract

The present invention provides switching type controller, used in power supply delivery unit primary side for controlling current output. It includes waveform detector, discharge time detector, oscillator, integrator, error amplifier pulsewidth comparer. The current output of power supply delivery unit can be stable adjusted on primary side.

Description

The switching control device of power supply unit primary side control output current

Technical field

The present invention is a kind of switching control device, is meant a kind of switching control device that is applied to power supply unit especially.

Background technology

Can provide the stable voltage and the power supply unit of electric current to be widely used in various electronic installations at present.Based on the demand that meets safety (safety), the power supply unit of an off-line type (off-linepower converter) must it primary side and secondary side between electrical isolation (galvanicisolation) is provided.In the relevant application of many chargers, very high with requirement cheaply for the constant current curve.With the technology of present announcement, can't very accurately control the output current of power supply unit at the set switching controller of the primary side of power supply unit, thereby can't reach constant current curve with linear characteristic.Moreover, in order to reach aforesaid constant current curve, can reach constant current control just must increase current circuit at the secondary side of power supply unit, thus, must pay the cost that raises the cost again.Therefore, output current how accurately to control power supply unit is considerable problem with reducing cost.

Summary of the invention

In order to reach above-mentioned purpose, the present invention proposes a kind of switching control device, is applied to a transformer primary side of a power supply unit, in order to the output current of control power supply unit.This switching control device comprises a switching controller, and switching controller can produce one and switch signal, and this switching signal can be switched a transformer and the stable output of adjusting power supply unit.This switching controller comprises the error amplifier that an operational amplifier and a reference voltage are formed, and controls in order to output current; One comparator is controlled the pulse duration of this switching signal in conjunction with a pulse-width modulator according to the output of this error amplifier.

This switching control device comprises an oscillator again, and this oscillator produces an oscillator signal in order to determine the switching frequency of this switching signal; One waveshape detector is by once sampling side switch current signal, in order to produce a current waveform signal; One discharge time detector be connected to this transformer, in order to detect a discharge time of secondary side switch current; One integrator is by integration one average current signal and this discharge time, in order to produce an integrated signal.This average current signal is the mean value of this current waveform signal, and the directly proportional pass of the switching cycle of the time constant of this integrator and this switching signal, so this integrated signal is proportional to the output current of power supply unit.This integrated signal is connected to the input of this error amplifier, and switching controller can be adjusted output current according to this integrated signal.

Technical scheme of the present invention is to realize like this.

A kind of switching control device is applied to a transformer primary side of a power supply unit, in order to control an output current, it is characterized in that including: a waveshape detector, detect element by an electric current, this transformer primary side switch current of sampling is in order to produce a current waveform signal; One discharge time detector, be connected to this transformer, in order to detect a discharge time of this Circuit Fault on Secondary Transformer switch current; One integrator, be connected in this waveshape detector and this discharge time detector, obtain this discharge time and this current waveform signal, in order to produce an integrated signal; And a pulse-width controller, connect this integrator, receive this integrated signal, switch signal in order to produce one; This switching signal is in order to switching this transformer, and stablizes the output current of adjusting this power supply unit according to this reference voltage.

Wherein, this pulse-width controller includes: an operational amplifier, connect this integrator, and receive this integrated signal and a reference voltage, in order to amplify this integrated signal; An and comparator, be connected in this operational amplifier and a pulse width modulation circuit, according to the integrated signal of this amplification, in order to controlling the pulse duration of this switching signal, and stablize this output current of adjusting this power supply unit according to this reference voltage by this pulse width modulation circuit.Wherein, further include an oscillator and connect this waveshape detector, integrator and this pulse-width controller, in order to produce an oscillator signal, to determine the switching frequency of this switching signal.Wherein, the directly proportional relation of a switching cycle of a time constant of this integrator and this switching signal.

Wherein, this waveshape detector comprises: one first comparator, obtain this transformer primary side switch current signal by its anode, and its negative terminal is connected to one first electric capacity, in order to keep the peak value of this transformer primary side switch current signal, and in its output output control one first switch conduction or end, the numerical value of this transformer primary side switch current signal is proportional to the numerical value of this primary side switch current; One first constant current source charges to this first electric capacity by this first switch; One the first transistor, this first electric capacity that is connected in parallel is in order to discharge to this first electric capacity; One second electric capacity is obtained this transformer primary side switch current signal by a second switch, and keeps the initial value of this transformer primary side switch current signal; This second switch carries out conducting according to a storage assembly or ends; One transistor seconds, this second electric capacity that is connected in parallel is in order to discharge to this second electric capacity; One the 3rd electric capacity is by the voltage of one the 3rd switch periods ground sampling across this first electric capacity, in order to produce a slope current waveform signal; And one the 4th electric capacity, by the voltage of one the 4th switch periods ground sampling, in order to produce a drift current waveform signal across this second electric capacity.

Wherein, this integrator comprises: one first voltage changes current converter, according to this drift current waveform signal of this waveshape detector output, can plan charging current in order to produce one first; One second voltage changes current converter, according to this slope current waveform signal of this waveshape detector output, can plan charging current in order to produce one second; One timing electric capacity is obtained this by one the 5th switch and first can be planned that charging current and this second can plan the average current signal that the charging current addition is produced, to charge; One the 3rd transistor, this timing electric capacity that is connected in parallel is used for this timing electric capacity is discharged; One output capacitance is by the voltage of one the 6th switch periods ground sampling across this timing electric capacity, in order to produce this integrated signal.

Wherein, this oscillator includes: a tertiary voltage changes current converter, has vibration operational amplifier, an oscillation resistance and an oscillistor, and wherein this tertiary voltage commentaries on classics current converter produces a reference current; One first oscillating current mirror has one first oscillistor, one second oscillistor and one the 3rd oscillistor, and wherein the 3rd oscillistor produces a vibration charging current; One second oscillating current mirror has one the 4th oscillistor and one the 5th oscillistor, and wherein the 5th oscillistor produces an oscillating discharge electric current; One oscillating capacitance is connected to the drain electrode of the 3rd oscillistor by one first oscillation switch, with the drain electrode that is connected to the 5th oscillistor by one second oscillation switch; One vibration comparator, its anode is connected to this oscillating capacitance, produces an oscillator signal in order to this second oscillation switch is carried out conducting or end; One the 3rd oscillation switch, one first end is connected to a high critical voltage, and one second end is connected to the negative terminal of this vibration comparator; One the 4th oscillation switch, one first end are connected to a low critical voltage, and one second end is connected to the negative terminal of this vibration comparator, is controlled by this oscillator signal; One vibration inverter, one input end is connected to the output of this vibration comparator, produces an inverse oscillation signal, in order to this first oscillation switch and the 3rd oscillation switch are carried out conducting or end; One first inverter, one second inverter, one the 3rd inverter and one the 4th inverter are connected in series, and wherein the input of this first inverter is provided by this oscillator signal; And one with the door, in order to produce a clear signal, wherein should be connected to the output of the 4th inverter with the first input end of door, wherein should be connected to the output of this first inverter with second input of door, wherein this clear signal is in order to carry out conducting to this first transistor, this transistor seconds and the 3rd transistor or to end.

Wherein, this, detector included discharge time: a delay circuit, drop edge for this switching signal provides a transmission delay, and wherein the time of this transmission delay is determined by the electric current of the first zero detection constant current source of inside and the capacitance that a first zero detects electric capacity; One single triggering signal generator, be connected in this delay circuit, in order to produce a voltage sampling signal, electric current and one second capacitance that detects electric capacity zero point that the pulse duration of this voltage sampling signal detects constant current source zero point by one second of its inside are determined according to this transmission delay; One zero point the detection calculations amplifier, what its anode was connected to this transformer should auxiliary winding, in order to detect a reflected voltage; One sampling capacitance is connected to the output of detection calculations amplifier at this by a sampling switch at zero point, according to the conducting of this sampling switch or by in order to this reflected voltage of sampling; One zero point detection comparator, its anode connects this sampling capacitance, negative terminal then is connected to the negative terminal and the output of detection calculations amplifier at this at zero point by a reference voltage critical value; Detect inverter one the 4th zero point, has an input and supplied by this switching signal; Detect inverter one the 5th zero point, has an input and supplied by this voltage sampling signal; Detect for one the 3rd zero point and door, have the output that a first input end is connected to detection comparator at this at zero point; Detect for one the 4th zero point and door, in order to produce a discharge time signal, wherein detection at the 4th zero point is connected to the output that detects inverter the 4th zero point with the first input end of door; One the one SR D-flip flop, one output are connected to second input of detection at the 4th zero point and door, and one sets end is connected to the output that detects inverter the 4th zero point, and a replacement is held and is connected to the output that detects for the 3rd zero point with door; And one the 2nd SR D-flip flop, one is set end and is connected to the output that detects inverter the 5th zero point, and a replacement termination is received this switching signal, and an output is connected to second input that detects for the 3rd zero point with door.

Utilize the present invention, the output current that can accurately control power supply unit with reduce cost

Above general introduction and ensuing detailed description are all exemplary in nature, are in order to further specify claims of the present invention.And about other purpose of the present invention and advantage, will be set forth in follow-up explanation and accompanying drawing.

Description of drawings

Fig. 1 is arranged at the power supply unit schematic diagram for switching control device of the present invention;

Fig. 2 is that the power supply unit of Fig. 1 operates in the each point signal waveforms under the DCM;

Fig. 3 is that the power supply unit of Fig. 1 operates in the each point signal waveforms under the continuous conduction mode;

Fig. 4 is the switching control device schematic diagram of preferred embodiment of the present invention;

Fig. 5 is an output voltage V _OWith output current I _OThe curve synoptic diagram that closes of correspondence;

Fig. 6 is the waveshape detector schematic diagram of preferred embodiment of the present invention;

Fig. 7 is the integrator schematic diagram of preferred embodiment of the present invention;

Fig. 8 is the oscillator schematic diagram of preferred embodiment of the present invention; And

Fig. 9 is detector schematic diagram discharge time of preferred embodiment of the present invention.

Wherein, description of reference numerals is as follows:

10 transformers

20,122,125,250,251,252,253,254,255,308,309,353,363,512,519,532,534,535,536,537,538,539,560 transistors

30 current sense resistors

40 rectifiers

50,210,511,531 resistance

60 rectifiers

65,112,121,124,215,354,570,571 electric capacity

70 switching control devices

71 operational amplifiers

75,105,205,310 comparators

91,92,114,119,155,156,270,355,365 and the door

93,115,116,150,151,152,260,261,262,263,264,351,361,366 inverters

95 D flip-flops

100 discharge time detector:

106 reference voltages

117,118 SR D-flip flops

200 oscillators

101,201 operational amplifiers

300 waveshape detector

120,123,124,305,352,362 constant current sources

109,230,231,232,233,311,312,314,315,550,551 switches

321,322,324,325,364 electric capacity

400 pulse width modulation circuits

500 integrators:

510 first timing amplifiers

Embodiment

With reference to figure 1, it is arranged at the power supply unit schematic diagram for switching control device of the present invention.Power supply unit comprises a transformer 10, and transformer 10 has auxiliary winding N _A, first side winding N _P, with secondary side winding N _SFor the stable output voltage V of adjusting power supply unit _OWith output current I _O, a switching controller 70 produces switching signal V _PWMBe used for this transformer 10 is carried out change action by switching transistor 20.

Wherein this switching controller 70 comprises feed end VCC, voltage detecting end VDET, earth terminal GND, electric current and detects end VS and output VPWM.This output VPWM exports this switching signal V _PWMThis voltage detecting end VDET is connected to auxiliary winding N by resistance 50 _A, in order to detection of reflected voltage V _AUX, this reflected voltage V _AUXThen further electric capacity 65 is charged, in order to provide energy to this switching controller 70 by rectifier 60.This electric current detects end VS and is connected to current sense resistor 30, and this current sense resistor 30 connects source electrode from this transistor 20 to ground connection, in order to primary side switch current I _PBe converted into primary side switch current signal V _IP

Cooperate Fig. 1, please refer to Fig. 2, for the power supply unit of Fig. 1 operates in each point signal waveforms under the DCM.Above-mentioned DCM is meant that before next switching cycle began, the energy storage of transformer discharged fully.As switching signal V _PWMWhen changing high potential into, produce primary side switch current I immediately _PThis primary side switch current I _PPeak I _PACan be expressed as:

$I_{\mathrm{PA}}=\frac{V_{\mathrm{IN}}}{L_P}\×T_{\mathrm{ON}}---\left(1\right)$

V wherein _INInput voltage for transformer 10; L _PFirst side winding N for transformer 10 _PInductance value; T _OMThen be switching signal V _PWMON time.

As switching signal V _PWMWhen dropping to electronegative potential, the energy that is stored in transformer 10 will be discharged into the secondary side of transformer 10, and transfer energy to the output of power supply unit by a rectifier 40.Secondary side switch current I _SPeak I _SACan be expressed as:

$I_{\mathrm{SA}}=\frac{(V_O+V_F)}{L_S}\×T_{\mathrm{DSD}}---\left(2\right)$

V wherein _OOutput voltage for power supply unit; V _FBe forward pressure drop across rectifier 40; L _SThen be the secondary side winding N of transformer 10 _SInductance value; T _DSDThen be under the DCM, secondary side switch current I _SDischarge time.

As switching signal V _PWMWhen dropping to electronegative potential, the auxiliary winding N of transformer 10 _ATo produce reflected voltage V _AUXThis reflected voltage V _AUXCan be expressed as:

$V_{\mathrm{AUX}}=\frac{T_{\mathrm{NA}}}{T_{\mathrm{NS}}}\×(V_O+V_F)---\left(3\right)$

T wherein _NAWith T _NSRepresent the auxiliary winding N of transformer 10 respectively _AWith secondary side winding N _SUmber of turn.

In sum, as secondary side switch current I _SWhen dropping to zero, reflected voltage V _AUXTo begin to reduce, the energy storage of transformer 10 will discharge fully this moment.And T discharge time of equation (2) _DSDCan adaptive switched signal V _PWMThe drop edge to reflected voltage V _AUXDrop point measure.

Cooperate Fig. 1, please refer to Fig. 3, for the power supply unit of Fig. 1 operates in each point signal waveforms under the continuous conduction mode.Above-mentioned continuous conduction mode is meant that before next switching cycle began, the energy storage of transformer did not discharge fully.When power supply unit operates under the continuous conduction mode, primary side switch current I _PPeak I _{P (PEAK)}For:

I _P(PEAK)＝I _PA+I _PB---------------------------------(4)

$I_{\mathrm{PA}}=\frac{V_{\mathrm{IN}}}{L_P}\×T_{\mathrm{ON}}---\left(5\right)$

I wherein _PBBe expressed as the energy that is stored in the transformer 10.

As switching signal V _PWMWhen dropping to electronegative potential, the energy storage of transformer 10 will be delivered to the secondary side of transformer 10.Therefore, by primary side switch current I _PCan determine secondary side switch current I with the umber of turn of transformer 10 _SThis secondary side switch current I _SPeak I _{S (PEAK)}Can be expressed as:

$I_{S\left(\mathrm{PEAK}\right)}=\frac{T_{\mathrm{NP}}}{T_{\mathrm{NS}}}\×I_{P\left(\mathrm{PEAK}\right)}=\frac{T_{\mathrm{NP}}}{T_{\mathrm{NS}}}\×(I_{\mathrm{PA}}+I_{\mathrm{PB}})---\left(6\right)$

T wherein _NPFirst side winding N for transformer 10 _PThe number of turn.

With reference to figure 4, be the preferred embodiment of switching control device of the present invention.One waveshape detector 300 is by once sampling side switch current signal V _IPIn order to produce current waveform signal V _AWith V _BThe auxiliary winding N of detector 100 discharge time by transformer 10 _AIn order to detect secondary side switch current I _ST discharge time _DSD/ T _DSCOscillator 200 produces oscillator signal PLS, with deciding switching signal V _PWMSwitching frequency.Integrator 500 is by integral mean current signal I _AVGWith T discharge time _DSD/ T _DSCBe used for producing integrated signal V _XOwing to consider two kinds of situations of DCM and continuous conduction mode simultaneously, according to this current waveform signal V _AWith V _BIn order to produce this average current signal I _AVGThe time constant of integrator 500 and switching signal V _PWMThe directly proportional pass of switching cycle T, this integrated signal V _XBe proportional to the output current I of power supply unit _O

Pulse-width controller comprises operational amplifier 71 and reference voltage V _REF1The error amplifier of being formed is in order to reach output current control.Comparator 75 is in conjunction with pulse width modulation circuit 400, according to the output of this error amplifier in order to control switching signal V _PWMPulse duration.This error amplifier amplifies this integrated signal V _X, and provide loop gain to control in order to output current.By detecting this primary side switch current I _PTo this switching signal of modulation V _PWMThis paths of pulse duration form a current control loop.This current control loop is according to reference voltage V _REF1In order to control primary side switch current I _PAmplitude.And secondary side switch current I _SWith primary side switch current I _PRelation on proportional is shown in equation (6).Please in the lump with reference to figure 2 and the shown oscillogram of Fig. 3, the output current I of power supply unit _OBe secondary side switch current I _SMean value.Therefore, the output current I of power supply unit _OCan be expressed as:

$I_O=(I_{\mathrm{SB}}\×\frac{T_{\mathrm{DS}}}{T})+(I_{\mathrm{SA}}\×\frac{T_{\mathrm{DS}}}{2T})---\left(7\right)$

T wherein _DSBe expressed as the T under the DCM _DSDOr the T under the continuous conduction mode _DSCTherefore, the output current I of power supply unit _OCan obtain stable the adjustment.

Primary side switch current I _PConvert primary side switch current signal V to by current sense resistor 30 _IP Waveshape detector 300 detects primary side switch current signal V _IPAnd generation current waveform signal V _AWith V _BIntegrated signal V _XCan design by the equation (7) shown in following:

$V_X=(V_B+\frac{V_A-V_B}{2})\×\frac{T_{\mathrm{DS}}}{T_I}---\left(8\right)$

Wherein

$V_A=\frac{T_{\mathrm{NS}}}{T_{\mathrm{NP}}}\×R_S\×(I_{\mathrm{SA}}+I_{\mathrm{SB}})---\left(9\right)$

$V_B=\frac{T_{\mathrm{NS}}}{T_{\mathrm{NP}}}\×R_S\×I_{\mathrm{SB}}---\left(10\right)$

T wherein _ITime constant for integrator 500.

With reference to equation (7)-(10), integrated signal V _XCan be integrated into:

$V_X=\frac{T}{T_I}\×\frac{T_{\mathrm{NS}}}{T_{\mathrm{NP}}}\×R_S\×I_O---\left(11\right)$

Can learn integrated signal V thus _XBe proportional to the output current I of power supply unit _OAs output current I _ODuring increase, integrated signal V _XIncrease.Yet, by the stable adjustment of current control loop, integrated signal V _XMaximum be subjected to reference voltage V _REF1Limit.Under the FEEDBACK CONTROL of current control loop, maximum output current I _{O (MAX)}Be expressed as:

$I_{O\left(\mathrm{MAX}\right)}=\frac{T_{\mathrm{NP}}}{T_{\mathrm{NS}}}\×\frac{G_A\×G_{\mathrm{SW}}\×V_{R1}}{1+(G_A\×G_{\mathrm{SW}}\×\frac{R_S}{K})}---\left(12\right)$

Wherein K is that constant equals T _I/ T; V _R1Be reference voltage V _REF1Magnitude of voltage; G _AGain for error amplifier; G _SWIt then is the gain of commutation circuit.

If the very high (G of the loop gain of current control loop _A* G _SW＞＞1), maximum output current I _{O (MAX)}Can be expressed as:

$I_{O\left(\mathrm{MAX}\right)}=K\×\frac{T_{\mathrm{NP}}}{T_{\mathrm{NS}}}\×\frac{V_{R1}}{R_S}---\left(13\right)$

The maximum output current I of power supply unit _{O (MAX)}Will be according to reference voltage V _REF1Size and be stabilized to adjust and become solid constant current.Output voltage V _OWith output current I _OCorresponding relation, can learn by curve synoptic diagram shown in Figure 5.

In the preferred embodiment of the present invention in order to produce switching signal V _PWMPulse-width modulator 400 comprise D flip-flop 95, inverter 93, with door 91 with door 92.The input of D flip-flop 95 (D) is by supply voltage V _CCInstitute provides.Oscillator signal PLS sets D flip-flop 95 by inverter 93.And the output of D flip-flop 95 (Q) is connected to and the first input end of door 92.Then be connected to the output of inverter 93 with second input of door 92.With the output of door 92 also be to produce this switching signal V simultaneously _PWMThe output of pulse-width modulator 400.D flip-flop 95 is reset according to bringing in the output of door 91.Receive voltage circuit signal S with the first input end of door 91 _V, this voltage circuit signal S _VGenerated by voltage control loop, this voltage control loop is used for stablizing the output voltage V of adjusting power supply unit _OCurrent circuit signal S _IGenerate by comparator 75 outputs, export to simultaneously and door 91 second input, in order to reach output current control.Wherein the anode of comparator 75 is connected to the output of operational amplifier 71, and the negative terminal of this comparator 75 is connected to oscillator 200, and RMP is provided by ramp signal.This voltage circuit signal S _VWith this current circuit signal S _IThe D flip-flop 95 of can resetting, in order to restriction with adjust switching signal V _PWMPulse duration, also reach simultaneously the stable output voltage V of adjusting _OWith output current I _O

With reference to figure 6, be the waveshape detector schematic diagram of preferred embodiment of the present invention.The anode of first comparator 310 is connected to electric current and detects end VS, is proportional to transformer primary side switch current I in order to reception _PPrimary side switch current signal V _IP, its negative terminal is connected to first electric capacity 321, and this first electric capacity 321 can be kept primary side switch current signal V _IPPeak value.First constant current source 305 charges for first electric capacity 321.First switch 311 is connected between first constant current source 305 and first electric capacity 321.The output of first comparator 310 is in order to carry out conducting to this first switch 311 or to end.When these first switch, 311 conductings, first constant current source 305 is in order to charge to this first electric capacity 321, and obtain peak voltage signal V across first electric capacity, 321 two ends this moment _SPCooperate Fig. 3, this peak voltage signal V _SPBe proportional to I _PAAdd I _PBSummed current.The first transistor 308 is in parallel with first electric capacity 321, is used for first electric capacity 321 is discharged.Switch 312 is in order to periodically to sample from the peak voltage signal V of first electric capacity, 321 to the 3rd electric capacity 322 _SPThen, obtain slope current waveform signal V across the 3rd electric capacity 322 two ends _A

Second switch 314 is connected to electric current and detects between the end VS and second electric capacity 324.Second electric capacity 324 is used for keeping primary side switch current signal V _IPInitial value.Across second electric capacity 324 thereby obtain voltage signal V _SICooperate Fig. 3, initial value voltage signal V _SIBe proportional to electric current I _PBCurrent value.Transistor seconds 309 is in parallel with second electric capacity 324, is used for second electric capacity 324 is discharged.Switch 315 is in order to periodically to sample from the initial value voltage signal V of second electric capacity, 324 to the 4th electric capacity 325 _SIThen, obtain drift current waveform signal V across the 4th electric capacity 325 two ends _B

With reference to figure 6, inverter 351, current source 352, transistor 353, electric capacity 354 with form very first time delay circuits with door 355.Inverter 361, current source 362, transistor 363, electric capacity 364, form the first single triggering signal generator with door 365 and inverter 366, be used for exporting storage assembly STR, this storage assembly STR is the single triggering signal.The input of very first time delay circuit is by switching signal V _PWMInstitute provides.The electric current I of current source 352 ₃₅₂With the time of delay of the capacitance of electric capacity 354 decision very first time delay circuit.The output of this very first time delay circuit is connected to the input of the first single triggering signal generator.The electric current I of current source 362 ₃₆₂Pulse duration with the capacitance of electric capacity 364 decision storage assembly STR.Storage assembly STR control second switch 314 is used for once sampling side switch current signal V _IPInitial value.Therefore, postpone the rising edge of switching signal in order to produce storage assembly STR according to one.After this time of delay, according to switching signal V _PWMThe rising edge in order to produce to postpone switching signal.Adding time of delay is the interference of switching surging for fear of coming from.

With reference to figure 7, be the integrator schematic diagram of preferred embodiment of the present invention.The first timing operational amplifier 510, the first timing resistance 511 and the first timing transistor 512 are formed first voltage is changeed current converter, according to drift current waveform signal V _BCan plan electric current I in order to produce first ₅₁₂Transistor 514,515 and 519 is formed first current mirror, can plan electric current I by shining upon first ₅₁₂In order to produce electric current I ₅₁₅With electric current I ₅₁₉Transistor 516 and 517 is formed second current mirror, by the mapping electric current I ₅₁₅In order to produce electric current I ₅₁₇The second timing operational amplifier 530, the second timing resistance 531 and the second timing transistor 532 are formed second voltage is changeed current converter, according to slope current waveform signal V _ACan plan electric current I in order to produce second ₅₃₂Transistor 534 and 535 is formed the 3rd current mirror, can plan electric current I by shining upon second ₅₃₂In order to produce electric current I ₅₃₅Transistor 536 and 537 is formed the 4th current mirror, according to electric current I ₅₃₅With electric current I ₅₁₇In order to produce electric current I ₅₃₇Electric current I ₅₃₇Can be expressed as:

I ₅₃₇＝I ₅₃₅-I ₅₁₇

The geometric size of transistor 536 is the twice of transistor 537.Therefore, electric current I ₅₃₆Size of current be electric current I ₅₃₇Twice.Transistor 538 and 539 is formed the 5th current mirror, by the mapping electric current I ₅₃₇In order to produce electric current I ₅₃₉The drain electrode of transistor 519 and transistor 539 are connected to each other, by adding up electric current I ₅₁₉With electric current I ₅₃₉In order to produce average current signal I _AVGAverage current signal I _AVGCan be expressed as:

$I_{\mathrm{AVG}}=\frac{V_B}{R_{511}}+\frac{(\frac{V_A}{R_{531}}-\frac{V_B}{R_{511}})}{2}---\left(14\right)$

The time constant of the first timing resistance 511, the second timing resistance 531 and timing electric capacity 570 decision integrators 500, the second timing resistance 531 and the first timing resistance 511 are the directly proportional relation.When the resistance value of setting the second timing resistance 531 equals the resistance value of the first timing resistance 511, equation (14) can be write as again:

$I_{\mathrm{AVG}}=\frac{1}{R_{511}}\×(V_B+\frac{V_A-V_B}{2})---\left(15\right)$

The 5th switch 550 is connected between the drain electrode and timing electric capacity 570 of transistor 519.The conducting of switch 550 is only at secondary side switch current I _ST discharge time _DSThis section cycle.The 3rd transistor 560 is in parallel with timing electric capacity 570, is used for timing electric capacity 570 is discharged.The 6th switch switch 551 is used to provide the voltage of periodically sampling across timing electric capacity 570 to output capacitance 571.Across output capacitance 571 two ends thereby produce integrated signal V _X

$V_X=\frac{1}{R_{511}{C}_{570}}\×(V_B+\frac{V_A-V_B}{2})\×T_{\mathrm{DS}}---\left(16\right)$

With reference to figure 8, be the oscillator schematic diagram of preferred embodiment of the present invention.Vibration operational amplifier 201, oscillation resistance 210 are formed tertiary voltage commentaries on classics current converter with oscillistor 250.This tertiary voltage changes current converter according to reference voltage V _REF2In order to produce reference current I ₂₅₀Several oscillistors 251,252,253,254 and 255 are formed current mirror, according to reference current I ₂₅₀In order to produce vibration charging current I ₂₅₃With the oscillating discharge electric current I ₂₅₅The drain electrode of transistor 253 produces vibration charging current I ₂₅₃, the drain electrode of transistor 255 produces the oscillating discharge electric current I ₂₅₅First oscillation switch 230 is connected between the drain electrode and oscillating capacitance 215 of transistor 253.Second oscillation switch 231 is connected between the drain electrode and oscillating capacitance 215 of transistor 255, obtains ramp signal RMP across oscillating capacitance 215 two ends.The anode of vibration comparator 205 is connected to oscillating capacitance 215, and the output of vibration comparator 205 produces oscillator signal PLS, and this oscillator signal PLS determines switching frequency, but and conducting or cutoff switch 312,315 and the 6th switch 551.First end of the 3rd oscillation switch 232 is by a high critical voltage V _HInstitute provides, and first end of the 4th oscillation switch 233 is by low critical voltage V _LInstitute provides.Second end of second end of the 3rd oscillation switch 232 and the 4th oscillation switch 233 is connected to the negative terminal of vibration comparator 205 jointly.The input of vibration inverter 260 is connected to the output of vibration comparator 205, in order to produce inverse oscillation signal/PLS.Oscillator signal PLS is in order to conducting or by second oscillation switch 231 and the 4th oscillation switch 233.Inverse oscillation signal/PLS is in order to conducting or by first oscillation switch 230 and the 3rd oscillation switch 232.Inverter 261,262,263 and 264 is one another in series and is connected.The input of first inverter 261 is provided by oscillator signal PLS.Produce clear signal CLR with the output of door 270, its first input end is connected to the output of inverter 264, and its second input is connected to the output of first inverter 261.Clear signal CLR is in order to conducting or by the first transistor 308, transistor seconds 309 and the 3rd transistor 560.The resistance value R of oscillation resistance 210 ₂₁₀Capacitance decision switching signal V with oscillating capacitance 215 _PWMSwitching cycle T.

$T=\frac{{\mathrm{<figure-callout\; id="215"\; label="C"\; filenames="A20051005417100232.png"\; state="\{\{state\}\}">C</figure-callout>}}_{215}\&times;V_{\mathrm{OSC}}}{V_{\mathrm{REF}2}/{\mathrm{<figure-callout\; id="210"\; label="R"\; filenames="A20051005417100232.png"\; state="\{\{state\}\}">R</figure-callout>}}_{210}}={\mathrm{<figure-callout\; id="210"\; label="R"\; filenames="A20051005417100232.png"\; state="\{\{state\}\}">R</figure-callout>}}_{210}\&times;{\mathrm{<figure-callout\; id="215"\; label="C"\; filenames="A20051005417100232.png"\; state="\{\{state\}\}">C</figure-callout>}}_{215}\&times;\frac{V_{\mathrm{OSC}}}{V_{\mathrm{REF}2}}---\left(17\right)$

V wherein _OSC=V _H-V _L, C ₂₁₅Capacitance for oscillating capacitance 215.

With reference to figure 9, be detector schematic diagram discharge time of preferred embodiment of the present invention.The first zero detects inverter 150, transistor 122, first zero detection constant current source 120, first zero detection electric capacity 121 and a first zero detection and 155 compositions, second time delay circuit, and the input of this second time delay circuit is by switching signal V _PWMInstitute provides.This second time delay circuit is for switching signal V _PWMThe drop edge one transmission delay is provided.The first zero detects the electric current I of constant current source 120 ₁₂₀Detect time of the capacitance decision transmission delay of electric capacity 121 with the first zero.Detect constant current source 123, second zero point at inverter 151, inverter 152, transistor 125, second zero point and detect electric capacity 124 and detect for second zero point with door 156 and form second a single triggering signal generator, in order to produce voltage sampling signal SMP.The input of this second single triggering signal generator is connected to the output of second time delay circuit, and this also is the output of first zero detection and door 155.Detect the electric current I of constant current source 123 second zero point ₁₂₃Pulse duration with the capacitance decision voltage sampling signal SMP that detects electric capacity 124 second zero point.

Detection calculations amplifier 101 action at zero point is as buffer amplifier, and its negative terminal and output are connected to each other, and its anode also is the input of buffer amplifier, is connected to voltage detecting end VDET.This voltage detecting end VDET is connected to the auxiliary winding N of transformer 10 by resistance 50 _A, in order to detection of reflected voltage V _AUXSampling switch 109 is connected between the output and sampling capacitance 112 of buffer amplifier.Control the conducting of sampling switch 109 or end by voltage sampling signal SMP.Therefore, reflected voltage V _AUXSampling action as voltage V _DETTo keep voltage V across sampling capacitance 112 two ends _DETOne zero point detection comparator 105 be used for detection of reflected voltage V _AUXReduction.Zero point, detection comparator 105 anode was connected to sampling capacitance 112.One reference voltage critical value 106 be connected to zero point detection comparator 105 negative terminal and the output of buffer amplifier between, be used to provide a critical value in order to detection of reflected voltage V _AUXReduction.Therefore, as reflected voltage V _AUXDecrement during greater than reference voltage critical value 106, detection comparator 105 will produce high potential at zero point.The input that detects inverter 115 the 4th zero point is by switching signal V _PWMInstitute provides.The input that detects inverter 116 the 5th zero point is provided by voltage sampling signal SMP.Detect first input end with door 119 the 3rd zero point and be connected to detection comparator 105 output at zero point.

The one SR D-flip flop 117 and the 2nd SR D-flip flop 118 have a rising edge respectively and trigger set input and high potential triggering replacement input.The setting end (S) of the 2nd SR D-flip flop 118 is connected to the output that detects inverter 116 the 5th zero point, and its end (R) of resetting is by switching signal V _PWMInstitute provides, and its output (Q) is connected to second input that detects for the 3rd zero point with door 119.The output of the one SR D-flip flop 117 (Q) is connected to the first input end that detects for the 4th zero point with door 114.Detection at the 4th zero point is connected to the output that detects inverter 115 the 4th zero point with second input of door 114.Detect output generation discharge time signal S the 4th zero point with door 114 _DSThe setting end (S) of the one SR D-flip flop 117 also is connected to the output that detects inverter 115 the 4th zero point, and its end (R) of resetting is connected to the output that detects for the 3rd zero point with door 119.Discharge time signal S _DSIn order to conducting or cutoff switch 550.Discharge time signal S _DSPulse duration and secondary side switch current I _ST discharge time _DSDirectly proportional relation.

Complex chart 4, Fig. 6 and Fig. 8, integrated signal V _XWith secondary side switch current I _SOutput current I with power supply unit _ODirectly proportional relation.Therefore, equation (11) can be write as again:

$V_X=m\&times;\frac{T_{\mathrm{NS}}}{T_{\mathrm{NP}}}\&times;R_S\&times;I_O---\left(18\right)$

Wherein m is a constant, can be expressed as:

$m=\frac{{\mathrm{<figure-callout\; id="210"\; label="R"\; filenames="A20051005417100232.png"\; state="\{\{state\}\}">R</figure-callout>}}_{210}\&times;C_{215}}{R_{511}\&times;C_{570}}\&times;\frac{V_{\mathrm{OSC}}}{V_{\mathrm{REF}2}}---\left(19\right)$

The resistance value R of the first timing resistance 511 ₅₁₁Resistance value R with oscillation resistance 210 ₂₁₀Directly proportional relation.The capacitance C of timing electric capacity 570 ₅₇₀Capacitance C with oscillating capacitance 215 ₂₁₅Directly proportional relation.Therefore, integrated signal V _XBe proportional to the output current I of power supply unit _O

The above only is the present invention's preferred embodiment wherein, is not to be used for limiting practical range of the present invention; Be that all equalizations of doing according to claims of the present invention change and modification, be all claim of the present invention and contain.

Claims (8)

1. switching control device is applied to a transformer primary side of a power supply unit, in order to control an output current, it is characterized in that including:

One waveshape detector detects element by an electric current, and this transformer primary side switch current of sampling is in order to produce a current waveform signal;

One discharge time detector, be connected to this transformer, in order to detect a discharge time of this Circuit Fault on Secondary Transformer switch current;

One integrator, be connected in this waveshape detector and this discharge time detector, obtain this discharge time and this current waveform signal, in order to produce an integrated signal; And

One pulse-width controller connects this integrator, receives this integrated signal, switches signal in order to produce one; This switching signal is in order to switching this transformer, and stablizes the output current of adjusting this power supply unit according to this reference voltage.

2. switching control device as claimed in claim 1, wherein, this pulse-width controller includes:

One operational amplifier connects this integrator, receives this integrated signal and a reference voltage, in order to amplify this integrated signal; And

One comparator, be connected in this operational amplifier and a pulse width modulation circuit, according to the integrated signal of this amplification, in order to controlling the pulse duration of this switching signal, and stablize this output current of adjusting this power supply unit according to this reference voltage by this pulse width modulation circuit.

3. switching control device as claimed in claim 1 wherein, further includes an oscillator and connects this waveshape detector, integrator and this pulse-width controller, in order to produce an oscillator signal, to determine the switching frequency of this switching signal.

4. switching control device as claimed in claim 1, wherein, the directly proportional relation of a switching cycle of a time constant of this integrator and this switching signal.

5. switching control device as claimed in claim 1, wherein, this waveshape detector comprises:

One first comparator, obtain this transformer primary side switch current signal by its anode, and its negative terminal is connected to one first electric capacity, in order to keep the peak value of this transformer primary side switch current signal, and in its output output control one first switch conduction or end, the numerical value of this transformer primary side switch current signal is proportional to the numerical value of this primary side switch current;

One first constant current source charges to this first electric capacity by this first switch;

One the first transistor, this first electric capacity that is connected in parallel is in order to discharge to this first electric capacity;

One second electric capacity is obtained this transformer primary side switch current signal by a second switch, and keeps the initial value of this transformer primary side switch current signal; This second switch carries out conducting according to a storage assembly or ends;

One transistor seconds, this second electric capacity that is connected in parallel is in order to discharge to this second electric capacity;

One the 3rd electric capacity is by the voltage of one the 3rd switch periods ground sampling across this first electric capacity, in order to produce a slope current waveform signal; And

One the 4th electric capacity is by the voltage of one the 4th switch periods ground sampling across this second electric capacity, in order to produce a drift current waveform signal.

6. switching control device as claimed in claim 1, wherein, this integrator comprises:

One first voltage changes current converter, according to this drift current waveform signal of this waveshape detector output, can plan charging current in order to produce one first;

One second voltage changes current converter, according to this slope current waveform signal of this waveshape detector output, can plan charging current in order to produce one second;

One timing electric capacity is obtained this by one the 5th switch and first can be planned that charging current and this second can plan the average current signal that the charging current addition is produced, to charge;

One the 3rd transistor, this timing electric capacity that is connected in parallel is used for this timing electric capacity is discharged;

One output capacitance is by the voltage of one the 6th switch periods ground sampling across this timing electric capacity, in order to produce this integrated signal.

7. switching control device as claimed in claim 3, wherein, this oscillator includes:

One tertiary voltage changes current converter, has vibration operational amplifier, an oscillation resistance and an oscillistor, and wherein this tertiary voltage commentaries on classics current converter produces a reference current;

One first oscillating current mirror has one first oscillistor, one second oscillistor and one the 3rd oscillistor, and wherein the 3rd oscillistor produces a vibration charging current;

One second oscillating current mirror has one the 4th oscillistor and one the 5th oscillistor, and wherein the 5th oscillistor produces an oscillating discharge electric current;

One oscillating capacitance is connected to the drain electrode of the 3rd oscillistor by one first oscillation switch, with the drain electrode that is connected to the 5th oscillistor by one second oscillation switch;

One vibration comparator, its anode is connected to this oscillating capacitance, produces an oscillator signal in order to this second oscillation switch is carried out conducting or end;

One the 3rd oscillation switch, one first end is connected to a high critical voltage, and one second end is connected to the negative terminal of this vibration comparator;

One the 4th oscillation switch, one first end are connected to a low critical voltage, and one second end is connected to the negative terminal of this vibration comparator, is controlled by this oscillator signal;

One vibration inverter, one input end is connected to the output of this vibration comparator, produces an inverse oscillation signal, in order to this first oscillation switch and the 3rd oscillation switch are carried out conducting or end;

One first inverter, one second inverter, one the 3rd inverter and one the 4th inverter are connected in series, and wherein the input of this first inverter is provided by this oscillator signal; And

One with the door, in order to produce a clear signal, wherein should be connected to the output of the 4th inverter with the first input end of door, wherein should be connected to the output of this first inverter with second input of door, wherein this clear signal is in order to carry out conducting to this first transistor, this transistor seconds and the 3rd transistor or to end.

8. switching control device as claimed in claim 1, wherein, this, detector included discharge time:

One delay circuit provides a transmission delay for the drop edge of this switching signal, and wherein the time of this transmission delay electric current that detected constant current source by the first zero of inside is determined with the capacitance of first zero detection electric capacity;

One single triggering signal generator, be connected in this delay circuit, in order to produce a voltage sampling signal, electric current and one second capacitance that detects electric capacity zero point that the pulse duration of this voltage sampling signal detects constant current source zero point by one second of its inside are determined according to this transmission delay;

One zero point the detection calculations amplifier, what its anode was connected to this transformer should auxiliary winding, in order to detect a reflected voltage;

One sampling capacitance is connected to the output of detection calculations amplifier at this by a sampling switch at zero point, according to the conducting of this sampling switch or by in order to this reflected voltage of sampling;

One zero point detection comparator, its anode connects this sampling capacitance, negative terminal then is connected to the negative terminal and the output of detection calculations amplifier at this at zero point by a reference voltage critical value;

Detect inverter one the 4th zero point, has an input and supplied by this switching signal;

Detect inverter one the 5th zero point, has an input and supplied by this voltage sampling signal;

Detect for one the 3rd zero point and door, have the output that a first input end is connected to detection comparator at this at zero point:

Detect for one the 4th zero point and door, in order to produce a discharge time signal, wherein detection at the 4th zero point is connected to the output that detects inverter the 4th zero point with the first input end of door;

One the one SR D-flip flop, one output are connected to second input of detection at the 4th zero point and door, and one sets end is connected to the output that detects inverter the 4th zero point, and a replacement is held and is connected to the output that detects for the 3rd zero point with door; And

One the 2nd SR D-flip flop, one is set end and is connected to the output that detects inverter the 5th zero point, and a replacement termination is received this switching signal, and an output is connected to second input that detects for the 3rd zero point with door.

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