WO1986007214A1 - Protection circuit for a supply unit - Google Patents

Protection circuit for a supply unit Download PDF

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Publication number
WO1986007214A1
WO1986007214A1 PCT/EP1986/000276 EP8600276W WO8607214A1 WO 1986007214 A1 WO1986007214 A1 WO 1986007214A1 EP 8600276 W EP8600276 W EP 8600276W WO 8607214 A1 WO8607214 A1 WO 8607214A1
Authority
WO
WIPO (PCT)
Prior art keywords
power supply
electronic switch
transformer
control circuit
during
Prior art date
Application number
PCT/EP1986/000276
Other languages
German (de)
French (fr)
Inventor
Erich Geiger
Uwe Hartmann
Original Assignee
Deutsche Thomson-Brandt Gmbh
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
Application filed by Deutsche Thomson-Brandt Gmbh filed Critical Deutsche Thomson-Brandt Gmbh
Publication of WO1986007214A1 publication Critical patent/WO1986007214A1/en

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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/1213—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC converters
    • 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

  • the invention is based on a protective circuit for a switched-mode power supply unit, which works as a flyback converter, for supplying electronic devices with a transformer, the primary winding of which is dependent on the load of a driver stage and is controlled by an electronic switch, whose width is modulated by pulses, during a charging phase to an unregulated DC voltage can be connected, a control circuit controlling the driver stage being provided, which changes the duty cycle of the pulses depending on the load on the switching power supply and the unregulated voltage and blocks the electronic switch during a discharge phase.
  • a protective circuit in which, in conjunction with a horizontal deflection circuit with a line transformer in a television receiver, a winding of the line transformer taps an information voltage which is compared in a threshold switch with a reference voltage, when exceeded a monostable Flip-flop is switched on.
  • the flip-flop switches off the driver stage, which blocks the final transistor which supplies the deflection current, so that the latter is protected from excessive current. (DE-PS 27 50 213). After that by the monostable
  • the flip-flop predetermined time constant, the horizontal deflection circuit comes back into operation and is switched off again when the fault information is still present. This process is repeated intermittently until the entire television receiver is switched off after a number of switch-offs.
  • switching power supplies for the power supply of electronic devices, in particular for the power supply of television receiving devices.
  • These work as flyback converters i.e. when the electronic switch, which is usually controlled with line-frequency pulses and is switched on in the manner described in the preamble of the claim, the energy is transmitted to the secondary side of the transformer.
  • Switching power supplies constructed in this way are also provided with a protective circuit which, in the event of excessive current in the electronic switch, is switched off in the manner described above.
  • the requirements are particularly high when switching power supplies are used in television receivers. They should initially have the highest possible control range, ie they should regulate mains voltages from 90V to 264V. The regulation is carried out by changing the duty cycle of the line-frequency control pulses. These switching power supplies are exposed to large load fluctuations, which are caused by the large beam current fluctuations and depending on the delivered low-frequency power. Future use in connection with cameras, screen text decoders and other peripheral devices will result in additional loads on the switching power supply.
  • both the peak value of the charging current flowing through the switched-on electronic switch and through the primary winding of the transformer and the discharge time during which the stored energy is released to the secondary side of the transformer are proportional ⁇ nal of the withdrawn power.
  • the charging time depends on the applied unregulated operating voltage and the power drawn.
  • the transformer should be dimensioned so that the discharge time and the charging time of the switching power supply are the same at maximum power and minimum voltage and thus the highest possible control is achieved and that the discharge phase and the charging phase do not overlap with this power. With the minimum power removed and the maximum unregulated operating voltage, the smallest possible charging time should not be. result in greater charge than discharge.
  • the load fluctuations in a television receiver can be very large due to the strong beam current fluctuations, especially since the contrast-c is set very high in the case of large-format picture tubes.
  • the jet current can be exceeded six to seven times for a short duration, for example for the duration of one or more fields.
  • Both the line amplifier and the power supply must be able to handle this overload without suffering damage.
  • This overload is greater the smaller the internal resistance of the line output stage.
  • This additional power to be applied affects the power supply unit and this would have to be overdimensioned for protection against these brief overloads.
  • the invention has for its object to provide in addition to the static protection circuit, a dynamic protection circuit which also protects the switching power supply of the type specified in the preamble of the claim against short-term overloads. This object is achieved by the invention specified in the patent claim.
  • the invention is described below using an exemplary embodiment of a switching power supply.
  • Figure 1 shows a switching power supply with the notified circuit measure
  • FIG. 2 shows diagrams to explain the mode of operation of the circuit according to FIG. 1.
  • FIG. 1 shows a known flyback switching power supply which generates the stable operating voltages U1 to Un for the television receiver from the unregulated DC voltage UB rectified from the mains voltage UN with the aid of the rectifier 1.
  • the switching power supply consists of a transformer 2 whose primary winding 3 is in series with the electronic switch 4, which is driven with i pulse-width-modulated pulses via the transistor 5 and the push-pull driver stage 6. At the secondary windings 7, the operating voltages Ul to Un are removed.
  • a control circuit 8 ensures a change in the duty cycle of the control pulses.
  • FIG. 2a shows the case of normal operation under extreme conditions for the switching power supply, ie for the case of the lowest unstabilized operating voltage ÜB with maximum power Pmax.
  • the overload case occurs at the time to.
  • the discharge time ie by reducing the di / dt
  • the charging current IL is already switched on again at the time t1, so that after a sustained overload the setpoint voltage US is exceeded after a few cycles and the electronic switch 4 becomes saturated and can be destroyed. Only after the overload has been removed at time t2 does the charging and discharging process return to normal values (FIG. 2b). However, if the overload is longer, it is easy to see that the electronic switch will be destroyed.
  • the registered circuit measure now inevitably prevents a charging process by the charging current IL as long as a discharge current IE is still flowing, ie in the extreme case described, the electronic switch 4 cannot be switched on again until the discharge current IE disappears.
  • This information reaches the transistor 5 via the diodes 10 and 11 and the resistor 12, which also receives the control pulses UT, which are thus partially effective, despite the control with the pulses UT (FIG. 2d) during the time ⁇ no charging current can occur, but the transformer is first completely discharged, which is indicated in FIG. 2c by the broken line.
  • the switched-mode power supply is not completely switched off here, only the regulation to the constant output voltage is deactivated for the duration of the overload. As long as about the 4 "is present, the information resistor 12 ', the electronic switch is" necessarily locked and can not be switched. The final value of the charging current IL is then not reached, so that the target voltage US is not reached and drops somewhat during the overload, but a brief drop in this no longer regulated target voltage is not discernible to the user of the television set. It is achieved with the circuit measure that the switching power supply does not have to be oversized for protection against short-term overload.

Abstract

In a protection circuit of the supply unit for electronic apparatuses, the switch transistor (4) is necessarily maintained in the closed state by a control circuit (10, 11, 12) till the transformer (2) of the supply unit is completely discharged.

Description

Patentanmeldung Patent application
Schutzschaltung für ein SchaltnetzteilProtection circuit for a switching power supply
Die Erfindung geht aus von einer Schutzschaltung für ein als Sperrwandler arbeitendes Schaltnetzteil zur Speisung elektronischer Geräte mit einem Transformator, dessen Pri¬ märwicklung von einer Treiberstufe lastabhängig durch einen in ihrer Breite modulierte Impulse gesteuerten elektro¬ nischen Schalter während einer Ladephase an eine unge¬ regelte Gleichspannung anschaltbar ist, wobei eine die Treiberstufe ansteuernde Regelschaltung vorgesehen ist, die in Abhängigkeit von der Belastung des Schaltnetzteils und der ungeregelten Spannung das Tastverhälnis der Impulse ändert und den elektronischen Schalter während einer Ent¬ ladephase sperrt.The invention is based on a protective circuit for a switched-mode power supply unit, which works as a flyback converter, for supplying electronic devices with a transformer, the primary winding of which is dependent on the load of a driver stage and is controlled by an electronic switch, whose width is modulated by pulses, during a charging phase to an unregulated DC voltage can be connected, a control circuit controlling the driver stage being provided, which changes the duty cycle of the pulses depending on the load on the switching power supply and the unregulated voltage and blocks the electronic switch during a discharge phase.
Es ist eine Schutzschaltung bekannt, bei welcher in Ver¬ bindung mit einer Horizontalablenkschaltung mit einem Zeilentransformator in einem Fernsehempfangsgerät von einer Wicklung des Zeilentransformators eine Informa¬ tionsspannung abgegriffen wird, die in einem Schwellwert¬ schalter mit einer Referenzspannung verglichen wird, bei deren Überschreiten eine monostabile Kippstufe eingeschal¬ tet wird. Die Kippstufe schaltet die Treiberstufe ab, die άan den Ablenkstrom liefernden Endtransistor sperrt, so daß dieser vor zu großem Strom gescnützt wird. (DE-PS 27 50 213). Nach der durch die monostabile Kippstufe vorgegebenen Zeitkonstante tritt die Horizontal¬ ablenkschaltung wieder in Funktion und wird wieder abge¬ schaltet, wenn die Störinformation noch vorhanden ist. Dieser Vorgang wiederholt sich intermittierend bis nach einer Anzahl von Abschaltungen das gesamte Fernsehemp¬ fangsgerät abgeschaltet wird.A protective circuit is known in which, in conjunction with a horizontal deflection circuit with a line transformer in a television receiver, a winding of the line transformer taps an information voltage which is compared in a threshold switch with a reference voltage, when exceeded a monostable Flip-flop is switched on. The flip-flop switches off the driver stage, which blocks the final transistor which supplies the deflection current, so that the latter is protected from excessive current. (DE-PS 27 50 213). After that by the monostable The flip-flop predetermined time constant, the horizontal deflection circuit comes back into operation and is switched off again when the fault information is still present. This process is repeated intermittently until the entire television receiver is switched off after a number of switch-offs.
Es ist auch bekannt, für die Stromversorgung von elektro¬ nischen Geräten, insbesondere für die Stromversorgung von Fernsehempfangsgeräten Schaltnetzteile zu verwenden. Diese arbeiten als Sperrwandler, d.h. bei gesperrtem zumeist mit zeilenfrequenten Impulsen angesteuerten elektronischen Schalter, der in der im Oberbegriff des Patentanspruchs bezeichneten Art eingeschaltet ist, wird die Energie auf die Sekundärseite des Transformators übertragen. Auch derartig aufgebaute Schaltnetzteile sind mit einer Schutz¬ schaltung versehen, die bei zu großem Strom im elektro¬ nischen Schalter in der zuvor beschriebenen V/eise abge¬ schaltet werden..It is also known to use switching power supplies for the power supply of electronic devices, in particular for the power supply of television receiving devices. These work as flyback converters, i.e. when the electronic switch, which is usually controlled with line-frequency pulses and is switched on in the manner described in the preamble of the claim, the energy is transmitted to the secondary side of the transformer. Switching power supplies constructed in this way are also provided with a protective circuit which, in the event of excessive current in the electronic switch, is switched off in the manner described above.
Bei der Anwendung von Schaltnetzteilen in Fensehempfangs- geräten sind die Anforderungen besonders hoch. Sie sollen zunächst einen möglichst hohen Regelbereich besitzen, d.h. sie sollen Netzspannungen von 90V bis 264V ausregeln. Die Regelung erfolgt durch Änderung des Tastverhältnisses der zeilenfrequenten Ansteuerimpulse. Diese Schaltnetzteile sind großen LastSchwankungen ausgesetzt, die durch die großen Strahlstromschwankungen und in Abhängigkeit von der abgegebenen niederfrequenten Leistung hervorgerufen werden. Bei der zukünftigen Anwendung in Verbindung mit Kameras, Bildschirmtextdecodern und anderen Peripheriegeräten ergeben sich zusätzliche Belastungen des Schaltnetzteils. Bei einem Schaltnetzteil nach dem Sperrwandlerprinzip ist sowohl der Scheitelwert des Ladestroms, der durch den ein¬ geschalteten elektronischen Schalter und durch die Primärwicklung des Transformators fliesst sowie die Ent- ladezeit, v/ährend der die gespeicherte Energie an die Sekundärseite des Transformators abgegeben wird, proportio¬ nal der entnommenen Leistung. Die Ladezeit dagegen ist abhängig von der angelegten ungeregelten Betriebsspannung und der entnommenen Leistung. Der Transformator soll dabei so dimensioniert sein, daß bei maximal abgenommener Leistung und minimaler Spannung die Entladezeit und die Ladezeit des Schaltnetzteils gleich groß sind und damit eine höchstmögliche Aussteuerung erreicht wird und daß sich bei dieser Leistung die Entladephase und die Aufladephase zeitlich gerade nicht überschneiden. Bei minimaler entnommer Leistung und maximaler ungeregelter Betriebsspannung soll die kleinstmögliche Ladezeit keine . größere Ladung als Entladung zur Folge haben. Bei einem Fernsehgerät sind diese Forderungen sehr schwer zu erfüllen. Die LastSchwankungen können bei einem Fernseh¬ empfänger durch die starken StrahlStromschwankungen sehr groß sein, zumal bei großformatigen Bildröhren der Kontras-c sehr hoch eingestellt wird. Trotz Vorkehrungen gegen zu hohe Strahlströme mit Hilfe von Schaltungen zur Strahlstrombegrenzung kann der Strahlstrom für kurze Dauer z.B. für die Dauer eines oder mehrerer Halbbilder um das Sechs- bis Siebenfache überschritten werden. Sowohl die Zeilenendstufe als auch das Netzteil müssen diese Überlast ohne Schaden zu erleiden verarbeiten können. Diese Überlast ist umso größer, je kleiner der Innenwider¬ stand der Zeilenendstufe ist. Diese zusätzliche aufzu¬ bringende Leistung wirkt auf das Netzteil zurück und dieses müßte für die Absicherung gegen diese kurzzeitigen Über¬ lastungen überdimensioniert werden. Der Erfindung liegt die Aufgabe zugrunde, neben der statischen Schutzschaltung zusätzlich eine dynamische Schutzschaltung vorzusehen, die das Schaltnetzteil der im Oberbegriff des Patentanspruchs angegebenen Art auch gegen kurzzeitige Überlastungen schützt. Diese Aufgabe wird durch die im Patentanspruch angegebene Erfindung gelöst.The requirements are particularly high when switching power supplies are used in television receivers. They should initially have the highest possible control range, ie they should regulate mains voltages from 90V to 264V. The regulation is carried out by changing the duty cycle of the line-frequency control pulses. These switching power supplies are exposed to large load fluctuations, which are caused by the large beam current fluctuations and depending on the delivered low-frequency power. Future use in connection with cameras, screen text decoders and other peripheral devices will result in additional loads on the switching power supply. In the case of a switched-mode power supply based on the flyback converter principle, both the peak value of the charging current flowing through the switched-on electronic switch and through the primary winding of the transformer and the discharge time during which the stored energy is released to the secondary side of the transformer are proportional ¬ nal of the withdrawn power. The charging time, however, depends on the applied unregulated operating voltage and the power drawn. The transformer should be dimensioned so that the discharge time and the charging time of the switching power supply are the same at maximum power and minimum voltage and thus the highest possible control is achieved and that the discharge phase and the charging phase do not overlap with this power. With the minimum power removed and the maximum unregulated operating voltage, the smallest possible charging time should not be. result in greater charge than discharge. With a television set, these requirements are very difficult to meet. The load fluctuations in a television receiver can be very large due to the strong beam current fluctuations, especially since the contrast-c is set very high in the case of large-format picture tubes. Despite precautions against excessive jet currents with the aid of circuits for limiting the jet current, the jet current can be exceeded six to seven times for a short duration, for example for the duration of one or more fields. Both the line amplifier and the power supply must be able to handle this overload without suffering damage. This overload is greater the smaller the internal resistance of the line output stage. This additional power to be applied affects the power supply unit and this would have to be overdimensioned for protection against these brief overloads. The invention has for its object to provide in addition to the static protection circuit, a dynamic protection circuit which also protects the switching power supply of the type specified in the preamble of the claim against short-term overloads. This object is achieved by the invention specified in the patent claim.
Nachstehend wird die Erfindung an einem Ausführungsbei - spiel eines Schaltnetzteil beschrieben.The invention is described below using an exemplary embodiment of a switching power supply.
Figur 1 zeigt ein Schaltnetztzeil mit der angemeldeten Schaltungsmaßnahme;Figure 1 shows a switching power supply with the notified circuit measure;
Figur 2 zeigt Diagramme zur Erläuterung der Wirkungsweise der Schaltung nach Figur 1.FIG. 2 shows diagrams to explain the mode of operation of the circuit according to FIG. 1.
In Figur 1 ist ein bekanntes Sperrwandlerschaltnetzteil dargestellt, welches aus der mit Hilfe des Gleichrichters 1 aus der Netzspannung UN gleichgerichteten ungeregelten Gleichspannung ÜB die stabilen Betriebsspannungen Ul bis Un für den Fernsehempfänger erzeugt. Das Schaltnetz¬ teil besteht aus einem Transformator 2 dessen Primär¬ wicklung 3 in Serie zum elektronischen Schalter 4 liegt, der mit i pulsbreiten-modulierten Impulsen über den Transistor 5 und die Gegentakttreiberstufe 6 ange¬ steuert wird. An den Sekundärv/icklungen 7 werden die Be¬ triebsspannungen Ul bis Un abgenommen. In Abhängigkeit von der Belastung des Schaltnetzteils sorgt eine Regelschaltung 8 für eine Änderung des Tastverhältnisses der Ansteuer- impulse. Zum Schutz vor Dauerüberlastung wird am Emitter des elektronischen Schalters 4 eine Spannung abgenommen, die eine mono≤tabile Kippschaltung 9 derart umschaltet, daß die Ansteuerimpulse für eine gewisse Zeit abgeschalter •Λerden. Wie oben bereits erwähnt, ist die Entladezeit des Transformators allein von der Belastung des Schaltnetz¬ teils abhängig und vergrößert sich mit dieser. Wird die Entladezeit bei Überlastung so groß, daß der elektronische Schalter 4 durch die Regelschaltung 8 vor Abklingen des Entladestroms IE bereits wieder eingeschaltet wird, startet der Ladestrom IL nicht mit dem Wert Null sondern besitzt schon einen Anfangswert. Dies is in Figur 2b dargestellt. Figur 2a zeigt den Fall des Normalbetriebes bei extremert Bedingungen für das Schaltnetzteil, d.h. für den Fall der niedrigsten unstabilisierten Betriebsspannung ÜB bei maxi¬ mal entnommener Leistung Pmax. In Figur 2b tritt zum Zeit- punkt to der Überlastfall ein. Durch die Verlängerung der Entladezeit, d.h. durch die Verkleinerung des di/dt wird der Ladestrom IL zum Zeitpunkt tl bereits wieder einge¬ schaltet, so daß nach fortdauernder Überlast nach einigen Zyklen die Sollspannung US überschritten wird und der elektronische Schalter 4 in die Sättigung kommt und zerstört werden kann. Erst nach Entfernen der Überlast zum Zeitpunkt t2 pendelt sich der Lade- und Entladevorgang wieder auf normale Werte ein (Figur 2b). Ist die Überlast jedoch von längerer Dauer, ist leicht einzusehen, daß der elektronische Schalter dadurch zerstört wird.FIG. 1 shows a known flyback switching power supply which generates the stable operating voltages U1 to Un for the television receiver from the unregulated DC voltage UB rectified from the mains voltage UN with the aid of the rectifier 1. The switching power supply consists of a transformer 2 whose primary winding 3 is in series with the electronic switch 4, which is driven with i pulse-width-modulated pulses via the transistor 5 and the push-pull driver stage 6. At the secondary windings 7, the operating voltages Ul to Un are removed. Depending on the load on the switching power supply, a control circuit 8 ensures a change in the duty cycle of the control pulses. To protect against continuous overload at the emitter of the electronic switch 4, a voltage is decreased, which switches a flip-flop mono≤tabile 9 so that the drive pulses for a certain time abgeschalter • Λerden. As already mentioned above, the discharge time of the transformer depends solely on the load on the switching power supply and increases with it. If the discharge time when overloaded is so great that the electronic switch 4 is already switched on again by the control circuit 8 before the discharge current IE has decayed, the charge current IL does not start with the value zero but already has an initial value. This is shown in Figure 2b. FIG. 2a shows the case of normal operation under extreme conditions for the switching power supply, ie for the case of the lowest unstabilized operating voltage ÜB with maximum power Pmax. In FIG. 2b the overload case occurs at the time to. By extending the discharge time, ie by reducing the di / dt, the charging current IL is already switched on again at the time t1, so that after a sustained overload the setpoint voltage US is exceeded after a few cycles and the electronic switch 4 becomes saturated and can be destroyed. Only after the overload has been removed at time t2 does the charging and discharging process return to normal values (FIG. 2b). However, if the overload is longer, it is easy to see that the electronic switch will be destroyed.
Die angemeldete Schaltungsmaßnahme verhindert nun einen Ladevorgang durch den Ladestrom IL zwangsläufig solange noch ein Entladestrom IE fließt, d.h. im geschilderten Extremfall wird der elektronische Schalter 4 nicht eher wieder einschaltbar, bis der Entladestrom IE verschwindet. Dazu wird die Tatsache ausgenutzt, daß, solange der Entladestrom IE fließt, an einem Ende einer Primärwicklung des Transformators ein positives Potential vorhanden ist. Diese Information gelangt über die Dioden 10 und 11 und den Widerstand 12 an den Transistor 5, der auch die An- steuerimpulse UT erhält, die damit teilweise umwirksam v/erden, indem trotz Ansteuerung mit den Impulsen UT (Figur 2d) während der Zeit Δ kein Aufladestrom fHessen kann, sondern der Transformator erst vollkommen entladen wird, was in Figur 2c mit der unterbrochenen Linie ange¬ deutet ist.The registered circuit measure now inevitably prevents a charging process by the charging current IL as long as a discharge current IE is still flowing, ie in the extreme case described, the electronic switch 4 cannot be switched on again until the discharge current IE disappears. The fact that, as long as the Discharge current IE flows, there is a positive potential at one end of a primary winding of the transformer. This information reaches the transistor 5 via the diodes 10 and 11 and the resistor 12, which also receives the control pulses UT, which are thus partially effective, despite the control with the pulses UT (FIG. 2d) during the time Δ no charging current can occur, but the transformer is first completely discharged, which is indicated in FIG. 2c by the broken line.
Es wird hier das Schaltnetzteil nicht vollkommen abge¬ schaltet, sondern es wird nur die Regelung auf die konstante Ausgangsspannung für die Dauer der Überlastung außer Funktion gebracht. Solange über den" Widerstand 12 die Information' anliegt, ist der elektronische Schalter" 4 zwangsläufig gesperrt und nicht einschaltbar. Es wird dann zwar nicht der Endwert des • Ladestroms IL erreicht, so daß während der Überlast die Sollspannung US nicht er¬ reicht wird und etwas zurückgeht, jedoch ist für den Be¬ nutzer des Fernsehgerätes ein kurzzeitiges Absinken dieser nicht mehr geregelten Sollspannung nicht erkennbar. Es wird mit der Schaltungsmaßnahme erreicht, daß für die Absicherung gegen kurzzeitige Überlastung das Schalt¬ netzteil nicht überdimensioniert zu werden braucht. The switched-mode power supply is not completely switched off here, only the regulation to the constant output voltage is deactivated for the duration of the overload. As long as about the 4 "is present, the information resistor 12 ', the electronic switch is" necessarily locked and can not be switched. The final value of the charging current IL is then not reached, so that the target voltage US is not reached and drops somewhat during the overload, but a brief drop in this no longer regulated target voltage is not discernible to the user of the television set. It is achieved with the circuit measure that the switching power supply does not have to be oversized for protection against short-term overload.
BezugszeichenlisteReference list
Gleichrichter Transformator Primärwicklung elektronischer Schalter Transistor Gegentakttreiberstufe Sekundärwicklungen Regelschaltung monostabile Kippstufe Diode Diode Widerstand Rectifier transformer primary winding electronic switch transistor push-pull driver stage secondary windings control circuit monostable multivibrator diode diode diode resistor

Claims

PatentansprücheClaims
Schutzschaltung für ein als Sperrv/andler arbeitendes Schaltnetzteil zur Speisung elektronischer Geräte mit einem Transformator, dessen Primärwicklung von einer Trei¬ berstufe last- und spannungsabhängig über einen durch in ihrer Breite modulierte Impulse gesteuerten elektronischen Schalter während einer Ladephase an eine ungeregelte Gleichspannung anschaltbar ist, wobei eine die Treiber¬ stufe ansteuernde Regelschaltung vorgesehen ist, die in Abhängigkeit von der Belastung des Schaltnetzteils und ungeregelter Spannung das Tastverhältnis der Impulse ändert und den elektronischen Schalter während einer Ent¬ ladephase sperrt, d a d u r c h g e k e n n z e i c h ¬ n e t, daß ein S-teuerkreis vorgesehen ist, der während der Entladephase des Sperrwandlernetzteils den elektro¬ nischen Schalter zwangsläufig unabhängig von dem von der Regelschaltung erzeugten Signal in gesperrtem Zustand hält.Protective circuit for a switching power supply unit working as a blocking transformer for supplying electronic devices with a transformer, the primary winding of which can be connected to an unregulated DC voltage during a charging phase by a driver stage depending on the load and voltage via an electronic switch controlled by width-modulated pulses, whereby a control circuit which controls the driver stage is provided, which changes the pulse duty factor of the pulses as a function of the load on the switched-mode power supply and unregulated voltage and blocks the electronic switch during a discharge phase, characterized in that an S control circuit is provided which during the discharge phase of the flyback converter power supply, the electronic switch inevitably holds in the blocked state independently of the signal generated by the control circuit.
Schutzschaltung nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, daß der Steuerkreis an das Ende einer Wicklung des Transformators des Schaltnetzteils angeschlossen ist, die während der Ent¬ ladephase eine positive Spannung über eine Diode und einen Widersrand an die Treiberschaltung liefert, die den den Basisstrom für den elektronischen Schalter liefernden Transistor soerrt. Protective circuit according to claim 1, characterized in that the control circuit is connected to the end of a winding of the transformer of the switching power supply which, during the discharge phase, supplies a positive voltage via a diode and an opposing edge to the driver circuit which provides the base current for the electronic switch supplying transistor.
PCT/EP1986/000276 1985-05-21 1986-05-10 Protection circuit for a supply unit WO1986007214A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19853518195 DE3518195A1 (en) 1985-05-21 1985-05-21 PROTECTIVE CIRCUIT FOR A SWITCHING POWER SUPPLY
DEP3518195.8 1985-05-21

Publications (1)

Publication Number Publication Date
WO1986007214A1 true WO1986007214A1 (en) 1986-12-04

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Application Number Title Priority Date Filing Date
PCT/EP1986/000276 WO1986007214A1 (en) 1985-05-21 1986-05-10 Protection circuit for a supply unit

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EP (1) EP0221974A1 (en)
DE (1) DE3518195A1 (en)
WO (1) WO1986007214A1 (en)

Cited By (3)

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Publication number Priority date Publication date Assignee Title
FR2626419A1 (en) * 1988-01-21 1989-07-28 Sgs Thomson Microelectronics DEMAGNETIZATION MONITORING DEVICE FOR PRIMARY AND SECONDARY REGULATED CUTTING FEEDING
DE3844210A1 (en) * 1988-12-29 1990-07-05 Electronic Werke Deutschland Switched-mode power supply having overload protection
EP0385544A1 (en) * 1989-03-02 1990-09-05 Koninklijke Philips Electronics N.V. Switched-mode power supply circuit

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DE3733474A1 (en) * 1987-09-30 1989-04-20 Thomson Brandt Gmbh SWITCHING POWER SUPPLY
DE4117891A1 (en) * 1991-05-31 1992-12-03 Thomson Brandt Gmbh Switching network adaptor for TV receiver or video recorder - has capacitor second electrode coupled to current source in integrated circuit
DE4431783A1 (en) * 1994-09-07 1996-03-14 Thomson Brandt Gmbh Switched-mode power supply circuit with reduced switching losses

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DE2430481A1 (en) * 1973-06-28 1975-01-16 Honeywell Inc Electronic flash gun charging arrangement - with some magnetic energy retained in the transformer core, decreased time to charge storage capacitor
DE2434688A1 (en) * 1973-07-26 1975-02-13 Sits Soc It Telecom Siemens Regulated direct current converter - with built in over-current protection
FR2259473A1 (en) * 1974-01-28 1975-08-22 Radiotechnique Compelec Ringing-choke power supply - has fast response output regulation and is for computer memory supplies
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DE3227174A1 (en) * 1982-07-21 1984-01-26 Trilux-Lenze Gmbh + Co Kg, 5760 Arnsberg Circuit arrangement for generating a DC voltage

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2626419A1 (en) * 1988-01-21 1989-07-28 Sgs Thomson Microelectronics DEMAGNETIZATION MONITORING DEVICE FOR PRIMARY AND SECONDARY REGULATED CUTTING FEEDING
EP0329571A1 (en) * 1988-01-21 1989-08-23 STMicroelectronics S.A. Demagnetization control device for a switch-mode supply with primary and secondary regulation
US4885673A (en) * 1988-01-21 1989-12-05 Sgs-Thomson Microelectronics S.A. Demagnetization monitoring device for a switching power supply with a primary and a secondary regulation
DE3844210A1 (en) * 1988-12-29 1990-07-05 Electronic Werke Deutschland Switched-mode power supply having overload protection
EP0385544A1 (en) * 1989-03-02 1990-09-05 Koninklijke Philips Electronics N.V. Switched-mode power supply circuit
US5032967A (en) * 1989-03-02 1991-07-16 U.S. Philips Corporation SMPS apparatus having a demagnetization circuit

Also Published As

Publication number Publication date
EP0221974A1 (en) 1987-05-20
DE3518195A1 (en) 1986-11-27

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