WO2007135457A2 - Unités de commande d'alimentation en puissance à mode de commutation - Google Patents

Unités de commande d'alimentation en puissance à mode de commutation Download PDF

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Publication number
WO2007135457A2
WO2007135457A2 PCT/GB2007/050260 GB2007050260W WO2007135457A2 WO 2007135457 A2 WO2007135457 A2 WO 2007135457A2 GB 2007050260 W GB2007050260 W GB 2007050260W WO 2007135457 A2 WO2007135457 A2 WO 2007135457A2
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WO
WIPO (PCT)
Prior art keywords
smps
output
signal
reference level
feedback signal
Prior art date
Application number
PCT/GB2007/050260
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English (en)
Other versions
WO2007135457A3 (fr
Inventor
David M. Garner
David Robert Coulson
Devarahandi Indika Mahesh De Silva
Jayaraman Kumar
Vinod A Lalithambika
Original Assignee
Cambridge Semiconductor Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB0610210A external-priority patent/GB2438464A/en
Application filed by Cambridge Semiconductor Limited filed Critical Cambridge Semiconductor Limited
Publication of WO2007135457A2 publication Critical patent/WO2007135457A2/fr
Publication of WO2007135457A3 publication Critical patent/WO2007135457A3/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters

Definitions

  • This invention generally relates to switch mode power supply (SMPS) controllers and to related methods, and more particularly to SMPS controllers employing primary side sensing to detect a point of zero magnetic flux, at which the output voltage of the SMPS may be sampled accurately on the primary side.
  • SMPS switch mode power supply
  • a magnetic energy storage device such as a transformer or inductor is used to transfer power from an input side to an output side of the SMPS.
  • a power switch switches power to the primary side of the energy storage device, during which period the current and magnetic field builds up linearly. When the switch is opened the magnetic field (and secondary side current) decreases substantially linearly as power is drawn by the load on the output side.
  • An SMPS may operate in either a discontinuous conduction mode (DCM) or in continuous conduction mode (CCM) or at the boundary of the two in a critical conduction mode.
  • DCM discontinuous conduction mode
  • CCM continuous conduction mode
  • a critical conduction mode we are particularly concerned with DCM operating modes in which, when the switching device is turned off, the output voltage steadily, but gradually, declines until a point is reached on the knee of the output curve at which substantially zero output current flows an the inductor or transformer begins to ring, entering a so-called oscillatory phase.
  • the period of the ringing is determined by the inductance and parasitic capacitance of the circuit.
  • DCM includes so-called critical (discontinuous conduction) mode (CRM) operation in which the power switch is turned on again at the first trough of the oscillatory phase (sometimes referred to as the flyback oscillation).
  • CRM critical (discontinuous conduction) mode
  • Operation in CRM can be particularly efficient by reducing losses associated with the power switch turn-off transition.
  • an SMPS is regulated by sensing circuitry on the output side, coupled back to the input side of the SMPS by means of an opto-isolator.
  • some improved techniques employ primary side sensing or, more generally, sensing employing an auxiliary winding on the magnetic energy storage device, or in some related circuits an auxiliary winding of an output filter inductor.
  • FIG. 1 shows an example of a switch mode power supply circuit with primary side sensing.
  • the power supply comprises an AC mains input coupled to a bridge rectifier 14 to provide a DC supply to the input side of the power supply.
  • This DC supply is switched across a primary winding 16 of a transformer 18 by means of a power switch 20, in this example an insulated gate bipolar transistor (IGBT).
  • IGBT insulated gate bipolar transistor
  • a secondary winding 22 of transformer 18 provides an AC output voltage which is rectified to provide a DC output 24, and an auxiliary winding 26 provides a feedback signal voltage proportionally to the voltage on secondary winding 22.
  • This feedback signal provides an input to a control system 28, powered by the rectified mains.
  • the control system provides a drive output 30 to the power switching device 20, modulating pulse width and/or pulse frequency to regulate the transfer of power through transformer 18, and hence the voltage of DC output 24.
  • the power switch 20 and controller 28 may be combined on a single power integrated circuit.
  • the primary side controlled SMPS of Figure 1 derives feedback information from the primary side of the transformer, using an auxiliary winding to avoid high voltage signals, the voltage being stepped down by the turns ratio of the transformer.
  • auxiliary winding it is not necessary to employ a separate auxiliary winding although this may be convenient if such a winding is already contemplated to provide a low voltage supply to the controller.
  • a voltage of the primary winding may be sensed, preferably capacitor coupled so that it can be referenced to the ground of the controller, and stepped down using a potential divider.
  • An example circuit for this is shown inset in Figure 1 , with a dashed connection to the primary winding 16.
  • an auxiliary winding is not necessary to provide a dc supply for the controller as this may be derived from the high voltage dc supply on the primary side of the SMPS or in a number of other ways, for example using a capacitor charge pump driven via a diode from the switched voltage on the power switch. In some preferred implementations, therefore, the auxiliary winding is omitted.
  • a switch mode power supply (SMPS) controller for regulating the output voltage of an SMPS is response to a feedback signal from a winding of a magnetic energy storage device forming part of an output circuit of the SMPS, the SMPS controller comprising: a reference level input to receive an output reference level signal; an input to receive said feedback signal, said feedback signal being responsive to a voltage on said magnetic energy storage device winding; an integrator to integrate a difference between said feedback signal and a first fixed reference level signal; a first comparator to compare an output of said integrator with a second fixed reference level signal and to provide an output responsive to said comparison for regulating said SMPS output voltage.
  • SMPS switch mode power supply
  • the controller includes a second comparator to compare a signal derived from the feedback signal with a third reference level signal derived from the output voltage reference level signal, at a time when the first comparator indicates that the integrator output is substantially equal to said second fixed reference level signal.
  • the controller may have an (internal) output coupled to an output of said second comparator to provide a regulation signal for controlling the SMPS to regulate the SMPS output voltage, for example by controlling the frequency and/or duration of pulses from a pulse generator driving a power switch of the SMPS.
  • the second comparator includes a sample-hold circuit to sample and hold the output of the first comparator at the time when the first comparator indicates that the integrator output is substantially equal to the second fixed reference level signal.
  • the first and second fixed reference level signals are essentially equal to one another, in embodiments both substantially equal to zero. More generally the first and second reference level signals are preferably configured such that the sample and hold time indicates a time when a magnetic flux in the energy storage device is exactly zero.
  • the third reference level signal which is compared by the second comparator with the feedback signal or a scaled version thereof may be equal to the output voltage reference level signal.
  • the implementation can be simplified by using a drive signal for the switching device of the power supply to control the integrator to begin integrating, for example by re-setting the integrator, in particular when the switching device is switched on (power being provided to the magnetic energy storage device).
  • This is particularly useful in operating modes where the flux in the magnetic energy storage device will generally have fallen to a relatively low level before the power switching device is once again activated for the next switching cycle.
  • the sensing signal waveform has a first, approximately linearly decaying portion during which power is supplied by said magnetic device to said SMPS output and a second, oscillatory or "resonant" portion during which substantially no power is supplied by the magnetic device to the SMPS output.
  • the feedback signal is integrated from a point of known, substantially zero flux found by the first integration (that is, the knee point in the feedback signal waveform), until a later point in time, for example a zero-crossing of the feedback signal waveform.
  • This integration indirectly determines the amplitude of the feedback signal at the knee point, since the value of the integration depends upon this amplitude. For example, when integrating to the first zero-crossing point - in Figure 3, from point A to halfway between points A and B - the output of the integration is substantially equal to the area under a quarter of a cycle of a sine wave, which depends on (in embodiments, is equal to) the amplitude of this sine wave.
  • the magnetic energy storage device comprises a transformer and the sensing winding comprises an auxiliary winding of the transformer, although a primary winding may alternatively be employed.
  • the invention provides a method of regulating the output voltage of an SMPS in response to a feedback signal from a winding of a magnetic energy storage device forming part of an output circuit of the SMPS, the method comprising: receiving an output reference level signal; receiving a feedback signal, said feedback signal being responsive to a voltage on said magnetic energy storage device winding; integrating a difference between said feedback signal and a first fixed reference level signal; comparing an output of said integration with a second fixed reference level signal and providing an output responsive to said comparison; and regulating the SMPS using the output of the comparing.
  • the method further comprises comparing a signal derived from the feedback signal with a third reference level signal derived from the output voltage reference level signal at a time when the comparing of the integration output and the second fixed reference level signal indicates that the integrator output is substantially equal to the second fixed reference level signal; and regulating the SMPS output voltage responsive to the comparing of the signals derived from the feedback signal and the third reference level signal.
  • the feedback signal waveform may be integrated, beginning at a time determined by the output of the second fixed reference level signal comparing (for example by resetting the integrator at this point), to determine a control signal for regulating the SMPS.
  • the comparing of the output of the integrator is performed at a time when the magnetic flux in the magnetic energy storage device is exactly zero.
  • the signal difference integration may be controlled by the drive signal, in particular beginning when primary side power is supplied to the magnetic energy storage device.
  • the invention provides a method of regulating the output of an SMPS operating in a discontinuous conduction mode, the SMPS including a magnetic energy storage device having at least one winding, the method comprising: integrating a feedback signal from said at least one winding of said SMPS from a first point in time of known, substantially zero magnetic flux in the said magnetic energy storage device to determine a second time at which said magnetic flux is again substantially zero; and determining an error signal by integrating a waveform of said feedback signal from said second time to a third later time; and using said error signal to regulate said SMPS.
  • the invention still further provides an SMPS controller for regulating the output of an SMPS operating in a discontinuous conduction mode, the SMPS including a magnetic energy storage device having at least one winding, the system comprising: a first integrator to integrate a feedback signal from said at least one winding of said SMPS from a first point in time of known, substantially zero magnetic flux in the said magnetic energy storage device to determine a second time at which said magnetic flux is again substantially zero; and a second integrator to integrate a waveform of said feedback signal from said second time to a third later time and to output an error signal for controlling said SMPS.
  • the error signal comprises an analogue error signal, as this facilitates stabilising the control loop of the SMPS.
  • the integration may integrate a difference between the sensing signal (waveform) and an expected value for the integration (such as the amplitude of the sensing signal at the knee point), for example in order to generate a digital signal representing whether the output voltage of the SMPS is above or below a target value.
  • the magnetic energy storage device comprises a transformer with primary, secondary, and auxiliary windings but in other implementations an auxiliary winding may be provided on another inductor of the SMPS. In still other implementations an auxiliary winding may be omitted and the sensing signal derived from a primary winding, for example as described above with reference to Figure 1.
  • the invention provides a switch mode power supply including an SMPS controller as described above.
  • an SMPS controller as described above is implemented mainly or entirely using analogue circuitry, in particular for the integration, differentiation, and comparison operations.
  • the SMPS controller may be implemented partially or wholly using digital circuitry.
  • the invention further provides a carrier medium carrying processor control code such as rtl or SystemC defining hardware to implements such circuitry.
  • Figure 1 shows an example of an SMPS incorporating primary side sensing.
  • FIG. 2 shows a switch mode power supply (SMPS) including an SMPS controller according to an embodiment of the invention
  • Figure 3 shows waveforms illustrating the operation of the SMPS of figure 2.
  • Figure 4 shows an integrator which may be employed in embodiments of the invention.
  • a method of integrating the voltage on a primary or auxiliary winding of a magnetic energy storage device such as a transformer in order to determine an optimum point of sampling the primary or auxiliary winding voltage to infer an output voltage of the SMPS.
  • embodiments of the technique integrate the sensed voltage from a point of known zero transformer flux to accurately determine a next point of zero transformer flux. This corresponds to an ideal time at which to sample the voltage on the primary or auxilliary winding in order to obtain an accurate measure of the SMPS output voltage.
  • the known point of zero transformer flux is preferably determined using a peak detector to find the peaks and troughs of the auxilliary winding voltage waveform.
  • a differentiator may be employed to find the peaks and troughs of this voltage waveform.
  • the controller then, in embodiments, produces an analogue, that is non-quantised, error signal for regulating the output of a primary-side sensing SMPS system.
  • the use of an analogue error signal allows the loop gain to be predicted accurately, allowing easier loop compensation.
  • embodiments do not require a clocked digital system and may thus be free of clock quantisation errors. Further embodiments of the technique allow the supply current for the controller to be small.
  • Embodiments of the SMPS controller we describe can be implemented more simply than controllers described in the prior art and, in embodiments provide more accurate output control by sensing exactly at a point of zero transformer flux.
  • FIG 2 shows a circuit diagram of an implementation of an embodiment of an SMPS controller according to the invention. As illustrated the controller is operating in the context of a flyback SMPS converter, but the skilled person will understand that the techniques we describe are also applicable to other forms of SMPS converters.
  • the flyback converter shown in figure 2 comprises a flyback transformer (1) having a primary winding (2), a secondary winding (3) and an auxilliary winding (4).
  • the secondary winding is connected to a rectifier and smoothing capacitor to provide the output voltage; the auxilliary winding is similarly connected to a rectifier and smoothing capacitor and is used to provide the power to the control circuitry.
  • the secondary winding is usually physically isolated from the primary and auxilliary windings and their associated components to meet legislative requirements.
  • the secondary voltage may be sensed with a voltage reference and error amplifier on the secondary side with the error signal being sent to the primary side using an isolating optocoupler device.
  • PPS primary-side sensing'
  • the ideal point at which to sample the waveform on the auxilliary winding is the point at which the current in the secondary winding (I s ) has just dropped to zero. This is time 'A' in the waveforms shown in figure 3.
  • the reason for this is that, when the secondary current has just dropped to zero, there is no voltage drop across the secondary rectifier diode or its and the transformer's series resistance; thus, the voltage across the secondary winding is exactly equal to the output voltage. Because the voltage across the auxilliary winding is equal to the voltage across the secondary winding multiplied by the (known) turns ratio between the two windings, the secondary voltage can thus be inferred by measuring the voltage across the auxilliary winding at this point.
  • C is an unknown constant of integration and in this case represents the current (or flux) in the transformer at the beginning of the integration.
  • Points of known zero transformer flux correspond to peaks and troughs on the auxilliary winding waveform (time points B, C, and D in figure 2), hence, to ensure that the auxilliary winding waveforms is integrated from a point of known zero flux, the integrator is reset at each of these peaks and troughs.
  • the peaks and troughs are detected using a peak detector (11) which may take the form of a differentiator circuit or a diode-capacitor circuit (well know to those skilled in the art).
  • the integrator is always reset at a point of known zero flux immediately before the DRIVE signal goes high, and hence the switching cycle, begins. Note that the peak detector should ignore peaks and troughs when the DRIVE signal is high, and during the flyback pulse immediately following the DRIVE signal: this can be achieved using simple combinational logic.
  • the output of the comparator hence goes high at the optimum time for sampling the auxilliary winding waveform, and this sampling is achieved by a simple a sample-and- hold circuit formed by the switch (12) and capacitor (13).
  • the switch implemented by a transistor; however, a number of alternative sample-and-hold topologies may also be employed.
  • the output of the sample-and-hold circuit is thus proportional to the SMPS output voltage, and this is compared to the desired output voltage (V re ⁇ ) by an error amplifier 8. Loop compensation may be achieved by choosing suitable values for the impedances Z 1 and Z 2 , in a manner well understood by those skilled in the art of SMPS design.
  • the error signal V error is used to drive a pulse generator (9) which varies the duty cycle of switching transistor (5) by adjusting the timing of the ON and OFF pulses outputted to gate driver (10).
  • Figure 4 shows an integrator which may be employed in "area correlation" based embodiments of the invention.
  • the integrator is reset by the output of comparator 7 of Figure 2 so that it begins integrating at the knee of the Vaux curve (point A in Figure 3).
  • the output of the integrator may be sampled at the zero-crossing between points A and B in Figure 3, to provide an error signal proportional to the difference between the actual SMPS output voltage and a target.
  • the input to the integrator is (optionally) scaled by a potential divider comprising a pair of resistors R, Rl chosen such that when Vaux defines a quarter cycle of a sine wave the integral of the difference between scaled Vaux and VREF3 is zero.
  • a comparator may be configured to compare Vaux with zero to determine the zero-crossing times.
  • the integrator 6 is reset at points of known zero flux at the peaks and troughs of the auxilliary winding voltage waveform
  • the accuracy of the auxilliary waveform sampling point may be sufficient if the integrator is simply reset at the start of the DRIVE pulse (time point E in figure 2), especially if the duty cycle is small or the transformer has a high damping factor such that the flux remaining the transformer is close to zero at this point.
  • This may be implemented by using the ON signal which is outputted by pulse generator (9) to reset the integrator.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

La présente invention concerne des unités de commande SMPS qui utilisent la détection du côté primaire pour détecter un point de flux magnétique zéro, au niveau duquel la tension de sortie du SMPS peut être échantillonnée avec exactitude sur le côté primaire. On décrit une unité de commande d'alimentation en puissance à mode de commutation (SMPS) qui régule la tension de sortie d'une SMPS en réponse à un signal de rétroaction provenant d'un enroulement auxiliaire d'un dispositif de stockage d'énergie magnétique faisant partie d'un circuit de sortie de SMPS, l'unité de commande SMPS comprenant: une entrée de niveau de référence qui reçoit un signal de niveau de référence de sortie; une entrée qui reçoit le signal de rétroaction, le signal de rétroaction répondant à une tension sur ledit enroulement auxiliaire du dispositif de stockage d'énergie magnétique; un intégrateur qui intègre une différence entre le signal de rétroaction et un premier signal de niveau de référence fixe; un premier comparateur qui compare une sortie dudit intégrateur à un deuxième signal de niveau de référence fixe et qui produit une sortie en réponse à ladite comparaison pour réguler la tension de sortie de SMPS.
PCT/GB2007/050260 2006-05-23 2007-05-14 Unités de commande d'alimentation en puissance à mode de commutation WO2007135457A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0610210.7 2006-05-23
GB0610210A GB2438464A (en) 2006-05-23 2006-05-23 Regulating the output of a switch mode power supply
US11/445,482 US7447049B2 (en) 2006-05-23 2006-06-01 Single ended flyback power supply controllers with integrator to integrate the difference between feedback signal a reference signal
US11/445,482 2006-06-01

Publications (2)

Publication Number Publication Date
WO2007135457A2 true WO2007135457A2 (fr) 2007-11-29
WO2007135457A3 WO2007135457A3 (fr) 2008-06-19

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105486910A (zh) * 2016-01-20 2016-04-13 连云港杰瑞电子有限公司 一种直流高压隔离检测方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985004059A1 (fr) * 1984-03-06 1985-09-12 Hughes Aircraft Company Regulateur de commutation de retour
US4858094A (en) * 1988-10-18 1989-08-15 Allied-Signal Inc. Switched mode power supply with improved load regulation

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985004059A1 (fr) * 1984-03-06 1985-09-12 Hughes Aircraft Company Regulateur de commutation de retour
US4858094A (en) * 1988-10-18 1989-08-15 Allied-Signal Inc. Switched mode power supply with improved load regulation

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105486910A (zh) * 2016-01-20 2016-04-13 连云港杰瑞电子有限公司 一种直流高压隔离检测方法
CN105486910B (zh) * 2016-01-20 2018-09-07 连云港杰瑞电子有限公司 一种直流高压隔离检测方法

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