WO2007135452A1 - 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
WO2007135452A1
WO2007135452A1 PCT/GB2007/050231 GB2007050231W WO2007135452A1 WO 2007135452 A1 WO2007135452 A1 WO 2007135452A1 GB 2007050231 W GB2007050231 W GB 2007050231W WO 2007135452 A1 WO2007135452 A1 WO 2007135452A1
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WO
WIPO (PCT)
Prior art keywords
smps
sensing signal
signal
waveform
output
Prior art date
Application number
PCT/GB2007/050231
Other languages
English (en)
Inventor
David Robert Coulson
Johan Piper
David M. Garner
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 GB0610211A external-priority patent/GB2438465B/en
Application filed by Cambridge Semiconductor Limited filed Critical Cambridge Semiconductor Limited
Priority to CN200780026587.1A priority Critical patent/CN101490940B/zh
Publication of WO2007135452A1 publication Critical patent/WO2007135452A1/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
    • H02M3/33523—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 with galvanic isolation between input and output of both the power stage and the feedback loop

Definitions

  • This invention generally relates to a switch mode power supply (SMPS) controllers and to related methods. More particularly it relates to SMPS controllers employing primary side sensing to detect in a sensing waveform, at which point the output voltage of the SMPS may be sampled 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.
  • the magnetic field (and secondary side current) decreases substantially linearly (on average) 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
  • 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). Operation in CRM can be particularly efficient by reducing losses associated with the power switch turn-off transition.
  • CCM continuous conduction mode
  • the power switch is turned on to "recharge” the flux in the inductor or transformer for a subsequent cycle before the flux, and hence output current, has fallen to zero (so that the inductor or transformer is substantially always “on”).
  • 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 proportional to the voltage on secondary winding 22.
  • This feedback signal provides an input to a control system 28, powered by the rectified mains.
  • the secondary winding is usually physically isolated from the primary winding (and auxiliary winding, if present) and their associated components to meet legislative requirements.
  • 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.
  • transformer voltage waveform to generate feedback information for regulating an SMPS. These facilitate operation across a wide range of input and output conditions and, in embodiments, provide lower cost, inaudible operation and improved output regulation.
  • a system for sensing an output voltage of a switch mode power supply including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding
  • the system comprising; an input to receive a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power is supplied by said magnetic device to said SMPS output; a signal follower coupled to said input to generate a decay signal approximating said decaying portion of said sensing signal waveform; a comparator to compare said decay signal with said sensing signal waveform to identify when said sensing signal waveform decays faster than said decay signal; and a sampler to sample said sensing signal responsive to said comparator to provide an output signal sensing said output voltage of said SMPS.
  • SMPS switch mode power supply
  • the above described sensing system may be employed in an SMPS controller operating in either DCM/CRM mode or in CCM mode.
  • DCM/CRM mode the second portion of the feedback signal waveform comprises an oscillatory portion of the waveform (although not necessarily with a complete cycle of oscillation); in CCM mode the second portion of the waveform comprises a portion of the waveform during which input power is switched to the magnetic energy storage device.
  • the system may be employed to detect a point of substantially zero magnetic flux by detecting a knee in this sensing waveform between the decaying and oscillatory portions of the waveform.
  • the output voltage of the SMPS may be sampled accurately on the primary side since, because the secondary side current is substantially zero, there is substantially no voltage drop across the secondary side components, typically a diode and some series resistance.
  • the system can be used to determine when a power switching device switching input power to the magnetic energy storage device turns on.
  • a power switching device comprises a bipolar or MOSFET switch which often has a small switching delay.
  • the sensing signal waveform By monitoring the sensing signal waveform the actual switching time of such a device can be established.
  • a CCM mode SMPS controller it is desirable for a CCM mode SMPS controller to be able to control an SMPS in a DCM mode so that this mode can be employed at low load levels.
  • Embodiments of the above described sensing system can be used in both DCM and CCM modes and thus a single, common sensing system can be used for an SMPS controller rather than having to switch between different sensing systems depending upon the operating mode of the SMPS.
  • Embodiments of the sensing system provide such dual mode operation (triple mode, if CRJVl is considered as a separate mode).
  • the system also includes an enable input to receive an enable signal for disabling the operation of the sampler during the oscillatory portion of the sensing signal.
  • the enable signal may disable the signal follower and/or comparator and/or may gate the comparator output; it may be derived from the sensing signal waveform or, for example, from a drive signal driving a power switching device of the SMPS.
  • the signal follower comprises a decaying peak detector, to detect peaks of the sensing signal and to hold these with a decaying characteristic.
  • the decaying peak detector comprises a rectifier coupled to capacitor, with a discharge circuit, such as a current generator, coupled across the capacitor.
  • the comparator may have an offset built in to offset a voltage drop across the rectifier.
  • the sampler to sample the sensing signal responsive to the comparator may comprise a sample-hold circuit to sample and hold the sensing signal when the sensing signal waveform decays faster than the decay signal.
  • the sensing signal may be sensed either directly or indirectly, for example by sensing the decay (the output of the decaying peak detector) which, until the sampling point, tracks the sensing signal.
  • the sampler comprises an integrator to sample the sensing signal by integrating the sensing signal waveform from the point when the sensing signal waveform decays faster than the decay signal, to a later point on the sensing signal waveform, for example a zero-crossing of the sensing signal waveform.
  • the invention further provides an SMPS controller including a sensing system as described above and, in preferred embodiments, a comparator to compare the output signal with a reference and to provide a control output for controlling a switch mode power supply in response to the comparison.
  • the comparator in embodiments, may comprise an error amplifier to provide an analogue error signal (albeit in embodiments this may be represented in a digital form, though with multiple rather than just two binary levels). Use of an analogue control signal facilitates stabilising the control loop of the SMPS.
  • the invention provides an SMPS controller for controlling the output of an SMPS, the SMPS including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding, the controller comprising: a sense input to receive a sense signal waveform from said magnetic device; a decaying peak detector coupled to said sense input to detect when said sense signal waveform has a falling slope of greater than a threshold value and to generate a first timing signal: an output to provide an SMPS control signal responsive to a value of said sense signal waveform at a time indicated by said first timing signal.
  • the SMPS control signal is used to regulate an output voltage of the SMPS, for example by controlling a pulse width and/or frequency of an oscillator driving a power switch switching power to the magnetic energy storage device.
  • the controller includes a timing signal input so that the SMPS control signal output does not detect large negative slopes at peaks in a resonant, oscillatory portion of the sense signal waveform.
  • the controller includes a sample-hold module to sample and hold the sense signal waveform in response to the first timing signal.
  • the sample-hold module may, in embodiments, sample peaks of this superimposed "noise", holding the last sample before the second timing signal indicates that substantially no power is being supplied by the SMPS, that is the last sample before the sampling is disabled by the second timing signal.
  • an integration-based or "area correlation” sampling technique may be employed.
  • the invention provides a method of sensing an output voltage of a switch mode power supply (SMPS), the SMPS including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding, the method comprising: inputting a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power is supplied by said magnetic device to said SMPS output; identifying a knee point said sensing signal waveform between said decaying portion and said second portion of said waveform; and using a value of said sensing signal at said knee point to sense said SMPS output voltage; and wherein said identifying of said knee point comprises fitting an approximate tangent to said decaying portion of said sensing signal waveform; and identifying departure of said sensing signal waveform from said approximate tangent to identify said knee point.
  • SMPS switch mode power supply
  • the knee point on the sensing signal waveform corresponds to a point at which the secondary current has just dropped to substantially zero (at which point the voltage across a secondary winding may substantially equal an output voltage of the SMPS).
  • the sensing signal will in general provide a signal which is proportional to the SMPS output voltage, for example as determined by a primary: secondary or auxiliary: secondary turns ratio of a transformer of the SMPS, rather than voltage which is exactly equal to the SMPS output voltage.
  • Some embodiments of the method may directly determine when the sensing signal waveform departs from the approximate tangent, by more than a threshold different in slope, to identify the knee point. However in some preferred embodiments when the method is operating (enabled) each departure of the sensing signal waveform, by greater than a threshold level, from the approximate tangent is detected and used trigger a sample (and hold) of the sensing signal (or a signal derived therefrom) until the second portion of the sensing signal waveform is reached, at which point the last detected departure, which was sampled (and held) provides a value of the sensing signal (or a signal derived therefrom) at the knee point.
  • an area integration method as indicated above may be employed, using the value of the sensing signal at the knee point by integrating the sensing signal waveform from the knee point to a later point to (indirectly) sense the SMPS output voltage.
  • the invention provides a method of sensing an output voltage of a switch mode power supply (SMPS), the SMPS including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding, the method comprising: inputting a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power is supplied by said magnetic device to said SMPS output; identifying a knee point on said sensing signal waveform between said decaying portion and said second portion of said waveform; and using a value of said sensing signal at said knee point to sense said SMPS output voltage; and wherein said identifying of said knee point comprises detecting a point of greater than a threshold negative slope in said sensing signal wavefo ⁇ n.
  • SMPS switch mode power supply
  • the regulating may, in embodiments, comprise comparing the sensed output voltage with a reference level to provide an error signal substantially proportional to the difference between the two, and using the error signal to control the SMPS.
  • the invention provides a system for sensing an output voltage of an SMPS, the SMPS including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding, the system comprising: means for inputting a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power; means for identifying a knee point on said sensing signal waveform between said decaying portion and said second portion of said waveform; and means for using a value of said sensing signal at said knee point to sense said SMPS output voltage; and wherein said means for said identifying of said knee point comprises: means for fitting an approximate tangent to said decaying portion of said sensing signal waveform; and means for identifying departure of said sensing signal waveform from said approximate tangent to identify said knee point.
  • the invention still further provides a system for sensing an output voltage of an SMPS, the SMPS including a switched magnetic energy storage device for conveying power from an input to an output of said SMPS, said magnetic device having at least one winding, the system comprising: means for inputting a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power is transferred; means for identifying a knee point on said sensing signal waveform between said decaying portion and said second portion of said waveform; and means for using a value of said sensing signal at said knee point to sense said SMPS output voltage; and wherein said means for said identifying of said knee point comprises: means for detecting a point of greater than a threshold negative slope in said sensing signal waveform.
  • 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.
  • a system or SMPS controller as described above is implemented mainly or entirely using analogue circuitry. This is because clocked digital systems can introduce higher costs, audible noise problems and output inaccuracies due to the time-quantisation effects of the digital sampling process.
  • system or 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
  • FIG. 3 shows details of the voltage sensing block of the controller of Figure 2;
  • Figure 4 shows an example decaying peak detector for the voltage sensing block of Figure 3;
  • Figure 5 shows an example sample/hold module for the voltage sensing block of Figure
  • Figure 6 shows an example error amplifier for the voltage sensing block of Figure 3
  • Figure 7 shows waveforms illustrating the principle of operation of an SMPS controller according to an embodiment of the invention.
  • Figure 8 shows example waveforms illustrating the operation of the SMPS controller of Figure 3.
  • a winding on the power transformer such as a primary or auxiliary winding, provides a waveform to a peak detector with defined decay characteristic.
  • the peak detector voltage thus forms a tangent to a selected portion of the auxiliary winding waveform.
  • a status signal from the peak detector indicates the time(s) when the tangent coincides with (and departs from) the auxiliary winding waveform, thus in DCM/CRM providing an estimated instant when the transformer secondary winding current has dropped to zero.
  • the status signal controls a sample/hold circuit, which at that instant captures a voltage reflecting a secondary voltage of the transformer, such as a voltage from the primary or an auxiliary winding of the transformer.
  • a sample/hold circuit which at that instant captures a voltage reflecting a secondary voltage of the transformer, such as a voltage from the primary or an auxiliary winding of the transformer.
  • CCM essentially the same technique may be employed to determine when the (primary side) power switching device has turned on.
  • an error amplifier compares the captured voltage against a reference to determine an error signal, preferably an analogue error signal, which may be used to regulate the power converter output voltage.
  • an analogue error signal allows the loop gain to be predicted accurately, facilitating loop compensation. Further analogue embodiments of the technique facilitate implementation of a controller with a low power consumption.
  • the voltage across, say, the auxiliary winding is equal to the voltage across the secondary winding multiplied by the (known) turns ratio between the two windings, and the secondary voltage can thus be inferred by measuring the voltage across (say) the auxiliary winding at this point.
  • the secondary voltage can be sensed via a primary or auxiliary winding in a similar way to DCM mode except that the secondary voltage is sampled at a nonzero secondary side current.
  • This non-zero (although sometimes small) current introduces a non-zero voltage drop across the secondary side components, which may comprise for example a diode and some output resistance.
  • some compensation is made for the voltage drop from the secondary side winding to the SMPS output across these components. This compensation can be made, for example, based upon an approximate knowledge of the secondary side current, which can be inferred from the current in the primary side switch.
  • FIG 2 shows a block diagram of a flyback single-switch SMPS 200 incorporating an embodiment of an SMPS controller according to the invention.
  • 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.
  • a DC source 100 is connected to the primary winding of a transformer in series with a primary side switch 106.
  • the secondary winding of the transformer is connected to an output diode 101 in series with a capacitor 102.
  • a load, represented by a resistor 103 is connected across the output capacitor 102.
  • One end of an auxiliary winding on the transformer 104 is connected between the negative terminal of the DC supply 100 and the other end "VAUX" is connected to an Oscillator and Timing Block 105 and to a Voltage Sense Block 107.
  • the Voltage Sense Block 107 generates a signal (or value) VCTL representing the required level of output power, from signals VAUX and Tl.
  • the VCTL signal is fed back to the Oscillator and Timing Block which generates a DRIVE pulse for switch 106 at an appropriate frequency and duration.
  • the timing signal Tl is derived from the VAUX signal, providing the timing control for the Voltage Sense Block 107.
  • Tl is driven active shortly after VAUX goes positive (allowing time for the initial overshoot waveform artefacts to decay), for example based on a comparison of VAUX with zero or on the DRIVE signal.
  • Tl may be driven inactive when VAUX goes negative again. For example, a comparator may be employed to identify a negative-going zero-crossing of VAUX to drive Tl inactive.
  • Timing signal Tl may be generated either by oscillator block 105 or within voltage sensing block 107.
  • the Oscillator and Timing Block 105 uses the input VCTL to control the frequency and pulse duration applied to the DRIVE output, which controls the main primary switch 106.
  • the Oscillator and Timing Block 105 may be implemented in many different ways; examples of some particularly advantageous techniques are described in the Applicant's patent applications US 60/698808 (0513772.4) and PCT/GB2005/050244, hereby incorporated by reference.
  • the VAUX (sensing) signal from the primary or auxiliary winding of the power transformer typically appears as shown.
  • This is a transform of the secondary winding, generally with superimposed artefacts generated by winding leakage inductance, stray capacitance, and the like.
  • the tangent method works by fitting a tangent with a negative slope to the flyback portion of the VAUX waveform. The tangent slope is chosen to optimise the accuracy of identifying the knee point and to ensure that the waveform artefacts have minimal influence.
  • the VAUX signal is then sampled at the knee point and compared to a voltage reference to determine the output error voltage. A preferred practical implementation, as described below.
  • FIG. 3 shows the main functional blocks of the Voltage Sensing circuit 107, which together comprise a decaying peak detector block 109, a sample/hold block 110 and an error amplifier block 111, generating the output signal VCTL (output voltage control).
  • Typical waveforms are shown in Figure 8.
  • the output VPD (voltage peak detect) from the decaying peak detector block 109 is not used in some embodiments; in others it may be used to sense or sample a value of VAUX since it approximately tracks VAUX during its approximately linearly decaying portion and is substantially equal to VAUX at the knee point.
  • Figure 4 shows an implementation of the decaying peak detector (DPD) block 109 of Figure 3.
  • DPD decaying peak detector
  • the VAUX is fed into the input (IN) of the DPD block as shown.
  • timing signal Tl is inactive (low in Figure 8) the DPD is reset, forcing the output voltage VPD to 0 volts.
  • Tl is active, and therefore switch Sl is closed and switch S2 is open so that the DPD is not reset.
  • the circuit works as a peak detector, providing output VPD which decays at a predetermined rate.
  • the peak detector may be free-running, in which case the EN signal may be gated by Tl .
  • VPD follows the VAUX waveform except when the slope of VAUX exceeds a certain (negative) value, at which point the VAUX and VPD waveforms separate from one another.
  • the STATUS signal from the DPD is active when the DPD is updating (increasing) the VPD signal.
  • a diode Dl and a capacitor Cl together comprise a peak detector; this is enabled when switch S 1 is closed and S2 is open.
  • a current sink Il discharges the voltage on Cl, thus defining the slope of the tangent.
  • a comparator COMPl compares the tangent approximating voltage on Cl with the VAUX input.
  • a voltage source Vl adds a small DC offset compensating for the forward voltage drop of Dl.
  • comparator COMPl will issue a STATUS active if VAUX is greater than or equal to the (decaying) voltage on Cl.
  • the DPD effectively detects when VAUX has greater than a threshold downwards or negative slope.
  • the peak detector is re-initialised by the RST signal, closing switch S2 and opening switch S 1 , thereby discharging the voltage on capacitor Cl.
  • the rate of discharge of Cl is set by II, which is chosen according to the implementation so that, in embodiments, the voltage on Cl follows the approximately linear descent of VAUX, that is so that it follows an approximate tangent to VAUX prior to its oscillatory or resonant portion.
  • FIG. 5 An example implementation for the sample/hold module 110 is illustrated in Figure 5.
  • Buffer BUFl, capacitor C2 and switch S3 together comprise a sample/hold circuit, which samples the VAUX input when EN is active and holds the sampled value when EN is inactive.
  • the voltage output VSENSE holds the instantaneous value of VAUX when STATUS is driven inactive (at various points in the flyback phase and finally at the knee point), as shown in Figure 8.
  • Amplifier OPl, capacitor Cl and resistor Rl form a simple integrator, enabled by switch S4. While input EN is active, switch S4 is closed, enabling the amplifier OPl to integrate the difference between VSENSE and VREF.
  • the time constant is preferably at least several cycles of oscillator 105, for example around 10 cycles. In this way the accumulated error over many switching cycles may be used by the Oscillator and Timing Block to modify the delivered power and thereby regulate the output voltage.
  • the resistor and capacitor shown may be replaced by a variety of different impedance networks, for example in order to compensate the control loop using, say, pole-cancellation techniques.
  • the waveform to which the tangent-detection technique we have described is applied is relatively clean, and thus a modicum of filtering may be applied.
  • the waveform may be "qualified" to disable the operation of the tangent detection except in the vicinity of the knee point, for example by disabling the peak detector until a point close to the knee point is reached. This may be implemented, for example, by modelling the flux in the transformer by integrating the voltage on a primary or auxiliary winding of the transformer, more particularly by integrating the sensing signal, from a point of known zero transformer flux to determine a next point of zero transformer flux.
  • This latter point corresponds to the knee on the primary or auxiliary winding sensing signal and hence the timing of this point may be used to define a window within which the tangent method should look at the sensing signal waveform, for example by enabling the peak detector over this time window.
  • Points of known zero-transformer flux correspond to peaks and troughs on the oscillatory portion of the sensing signal waveform and thus, for example, the integrator may be reset at each of these peaks and troughs so that it is always reset at a point of known zero flux before the power switching device is switched on and the switching cycle begins.
  • the peaks and troughs may conveniently be detected using a peak detector, which may take the form of, for example, a differentiator circuit or a diode capacitor circuit.
  • the circuit which defines a time window for example, the aforementioned integrator together with a comparator to determine when the integrator once again reaches its reset value, is arranged so that the window is "opened" just before when the knee point is expected.
  • This can be arranged, for example, by comparing the output of the integrator to its reset value, say zero, modified by a small offset.
  • this technique is implemented using a decaying peak detector, providing a timing signal indicating detection of the knee point.
  • Sample/hold and error amplifier circuits may be employed to achieve output voltage regulation.

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  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

La présente invention concerne des unités de commande pour des alimentations en puissance à mode de commutation (SMPS) qui utilisent la détection côté primaire. L'invention porte sur un système qui permet d'identifier un point nommé coude dans une forme d'onde de détection au niveau duquel la tension de sortie du SMPS peut être échantillonnée avec exactitude sur le côté primaire. Le système identifie le coude en établissant une tangente sur une partie d'une forme d'onde de la tension d'un transformateur de puissance et échantillonne la forme d'onde de tension au niveau du coude pour déterminer la tension de sortie du SMPS. Dans des modes de réalisation préférés, cette technique est mise en oeuvre au moyen d'un détecteur de pics décroissants, qui utilise un signal d'horloge indiquant la détection du coude. Des circuits d'échantillonnage/maintien et des circuits d'amplificateur d'erreur peuvent être utilisés pour assurer la régulation de la tension de sortie.
PCT/GB2007/050231 2006-05-23 2007-05-02 Unités de commande d'alimentation en puissance à mode de commutation WO2007135452A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN200780026587.1A CN101490940B (zh) 2006-05-23 2007-05-02 开关式电源控制器

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0610211A GB2438465B (en) 2006-05-23 2006-05-23 Switch mode power supply controllers
GB0610211.5 2006-05-23
US11/445,473 US7567445B2 (en) 2006-05-23 2006-06-01 Switch mode power supply controllers
US11/445,473 2006-06-01

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2051360A1 (fr) * 2007-10-17 2009-04-22 Power Systems Technologies GmbH Circuit de commande pour un bloc à découpage à commande primaire avec précision améliorée du réglage de la tension ainsi que bloc à découpage à commande primaire
US8199538B2 (en) 2008-05-23 2012-06-12 Cambridge Semiconductor Limited Switched mode power supply with improved current sensing
WO2020260681A1 (fr) * 2019-06-27 2020-12-30 Tridonic Gmbh & Co Kg Convertisseur indirect synchrone pour entraîner des charges de del

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EP2051360A1 (fr) * 2007-10-17 2009-04-22 Power Systems Technologies GmbH Circuit de commande pour un bloc à découpage à commande primaire avec précision améliorée du réglage de la tension ainsi que bloc à découpage à commande primaire
WO2009049849A1 (fr) * 2007-10-17 2009-04-23 Power Systems Technologies Gmbh Circuit de commande pour alimentation à découpage commandée côté primaire présentant une précision accrue de régulation de tension et alimentation à découpage commandée côté primaire
US8199538B2 (en) 2008-05-23 2012-06-12 Cambridge Semiconductor Limited Switched mode power supply with improved current sensing
WO2020260681A1 (fr) * 2019-06-27 2020-12-30 Tridonic Gmbh & Co Kg Convertisseur indirect synchrone pour entraîner des charges de del
US11758631B2 (en) 2019-06-27 2023-09-12 Tridonic Gmbh & Co Kg Synchronous flyback converter for driving LED loads

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