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COURS MULTIVIBRATEUR ASTABLE PDF

Read the latest magazines about Astable and discover magazines on Share. Astable Timer – Electron Electronics LES MULTIVIBRATEURS ASTABLES. Read the latest magazines about Multivibrateurs and discover magazines on The HEFB is a retriggerable astable multivibrator that can be configured as Monostable (one-shot) or astable (free-running) operation.

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Country of ref document: Date of ref document: Kind code of ref document: Year of fee payment: The present invention relates to a feed device regulated by combined cutting line scanning circuit horizontal of a television receiver that supplies DC voltage.

It concerns, more particularly, of the DC voltage supply devices of the type ensuring the increase in output of the device, the level of an input DC voltage multivibratur regulate this level through a recurring cutting aatable voltage input, switching being synchronous with the line frequency horizontal of the television receiver supplied with the aid of this device.

Level increase feeders and control by cutting this type are known including publications US-A3 or 3,and they are similar to power supply devices by cutting or-DC converters continuous accumulation type called “flyback Englishuninsulated, in which the collector-emitter path of a bipolar switching transistor is connected in series with a switching inductance between the terminals of a source providing a voltage input and a rectifier diode is connected between the junction of the inductance with the transistor and one of the plates of a filtering capacitor in parallel with the load such that the current stored in the inductor during the transistor of the conduction interval is used for charging the capacitor and supply the load through the diode during the consecutive blanking interval thereof.

The use of a cutting feeding device of this type in television receivers for feeding, in particular, the scanning-line circuit thereof has been described, for example, in two articles respectively Van Schaik entitled “An Introduction to Power Supplies Switched-More in TV Receivers and” Control Circuits for SMPS in TV Receivers “, published respectively on pages 93 to of the No. Since no cutting feed devices described in these articles, isolated or not the network, they use a “series” converter or “direct” said “forward” in English or a “parallel” converter or ” accumulation ” ” flyback “does not provide at its DC voltage output for supplying the scanning-line circuit before the switching transistor has been released saturated or conductor one or more times, the of this transistor control circuit should include self relaxation oscillator and must be supplied by the same DC input voltage voltage of the AC network, rectified and filtered and the switching circuit comprising the inductor and the series transistor.

This synchronization with the scanning of the cutting line, advantageous to reduce or eliminate visible interference on the screen, which are generated by high-frequency energy radiation due to switching steep transitions, especially when blocking of the switching transistor is generally carried out using a signal comprising pulses of line return, taken at the terminals of an auxiliary secondary winding of the transformer-line whose primary winding is usually connected between the output of the feeder by and cutting one of the terminals of the scanning-line switch which equips the output stage.

It is also possible to use for this purpose the signal from the oscillator-line see, for example, the publication FR-A When this threshold amplitude has been exceeded, the switching back of the rocker is controlled by the pulses of line return, here a negative polarity which supplant starting pulses.

Such an arrangement is equivalent to a rocker of the astable multivibrator type during the startup period, which becomes a flip-flop triggered by the pulses of line return and whose quasi-stable state has a variable duration, depending on the magnitude of these pulses in order to obtain regulation by the duty cycle. The pulse which controls the closure of the switch the saturation of the switching transistor begins here with the leading edge of the return pulse line and its duration or length is adjusted according to the current supplied by the load and the variation of the rectified and filtered voltage, so that its end controlling the opening of the switch the blocking of the transistor of cutting occurs during the horizontal scanning go.

Thus one can see that this power supply by cutting, as most of those known, performs the regulation of the output voltage by varying the duty cycle inversely with the level thereof. As the high-frequency radiation is precisely the most intense during sudden transitions of current in the inductor cutting and voltage at the terminals thereof, it can be seen the occurrence of one or more vertical lines clear or dark in the direction of the modulation of the carrier contrasting with the normal content of the image, whose location on the screen depends on the duration of the pulse controlling the chopper transistor.

The present invention allows, on one hand, to avoid or at least substantially reduce visible interference on the screen by controlling the blocking of the chopper transistor in synchronism with the leading edge of the return pulse line and, secondly, to ensure the start of the scanning-line circuit having a simple drive circuit without particular oscillator, and an effective protection, especially of the switching transistor which is blocked when the circuit balayage- line does not work. This is made possible by the use of a feeder to increase the level and cutting regulation called “boost” or “switching regulator in English of the type described in the publication US and which control circuit comprises according to the invention, the sweep circuit, and in particular its output stage, it feeds.

In other words, in the feed device by cutting object of the invention, the scanning-line circuit forms part of the control circuit of the switching transistor, since it is this circuit that determines, upon its startup by setting turn on the device, the recurrence period of the rectangular signal with variable duty cycle, provided by the modulator pulse width.

One of the other stage feeding the inputs of attack directly receives a first voltage waveform whose positive alternations comprise constant voltage plateaus and whose negative alternations comprise pulses retbur line polarity negative, supplied by a first secondary winding of the line transformer, in order to control the blocking of the chopper transistor substantially simultaneously with the scanning transistor.

The invention will be better understood and its other objects, features, and advantages will be apparent from the following description and the accompanying drawings relating thereto, given by way of example, in which: Figure 1 shows the stages of the block diagram of power supply device and the scanning-line circuit of the television receiver, feeding and synoptically in the form of blocks the respective circuits which control them.

The input DC voltage VE which is not regulated, is provided by a bridge rectifier R to four diodes, powered at its input by the secondary winding of an isolation step-down transformer TS buck, whose primary winding is powered by the AC mains. The output terminals of the rectifier bridge R are connected respectively to the armatures of a first smoothing capacitor C1 which is imposed between the input voltage VE.

The positive pole P of the input voltage VE source is connected to one terminal of an inductor L energy storage, while its negative terminal N is connected to the ground G of the receiver, which is isolated from the network. The other terminal of the inductor L is connected on the one hand, to the collector of a first bipolar switching transistor T1 of the NPN type, whose emitter is connected to ground G, and on the other hand, the anode of a first diode D1 whose cathode is connected to the positive plate of a second filter capacitor C2.

The negative plate of the second capacitor C2 being connected to ground G, the output voltage VS supplying the load is imposed between the terminals. Such a feeding device BS to increase the “step-up or” boost in English and regulating the level of its output voltage, that the first switching transistor T1 and the first diode D1 are connected such respectively conduct currents flowing through the ir the juctance L in the same direction, provides at its output constituted by the terminals of the second capacitor C2, an initial DC voltage VSI from the connection to the primary winding network of the transformer TS isolation.

This initial voltage VSI which is equal to the input voltage VE less the forward voltage VD1 of waste through the first diode D1, is then supplied to the load to the initiation of the control circuit SC which output 6 is connected to the base of the first transistor T1 in order to make alternately saturated and blocked. When the first transistor T1 becomes saturated by biasing positively the base-emitter junction, its collector-emitter path meets the junction of the inductor L with the anode of the first diode D1 to ground G.

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Diode D1 then being polarized upside down, it ceases to conduct, and the inductor L together by the first transistor T1 between the positive and negative poles P N of the source providing the DC input voltage VE non- regulated, then conducts a current IL increasing linearly so as to store energy which increases with the square of the duration of conduction of the first transistor T1, until the locking thereof. At the blocking time of the first transistor T1 obtained after the control circuit SC has reduced its base-emitter voltage to zero or below, the voltage across the inductor L reverses so that at its junction with the collector of transistor T1 and the anode of the diode D1, appears a VM voltage higher than the input voltage VE, which has the effect of polarizing the direct diode D1.

Therefore, the diode D1 conducts from the moment of blocking of the transistor T1 a linearly decreasing current until the disappearance of the energy stored in the form of current IL in the inductor, which charges the second capacitor C2 to a VS output voltage higher than the input voltage VE.

Regulating astsble level of the output voltage VS is performed here in a conventional manner, by varying the duty cycle, that is to say the ratio quotient of the length of the conduction interval of astablf T1 and the sum of the respective lengths of two of astaable conduction intervals and successive locking, depending on the desired output voltage VS determined by comparison with a stable reference voltage.

The scanning-line circuit SH which comprises in cascade the oscillator-line or horizontal OH whose circuit loop to phase lock with separate line-synchronizing signal from the composite video signal has not been shown here, the HD drive stage controlled by the oscillator on line OH and controlling the output stage OS of the scanning line, is entirely powered by the power supply device described above.

Indeed, the input positive supply U of the scanning circuit SH is connected by means of a fuse FS to the junction of the cathode of the first diode D1 with the positive plate of the second capacitor C2, which constitutes the terminal SP positive output of BS feeder.

This U feed inlet is multivibrateut joined to that of the HD driver circuit, preferably via a conventional voltage regulator VR to Zener diode or series ballast transistor to that of oscillateur- line OH, which are multivibrateu connected to the isolated ground G.

The power supply Multiviibrateur of the scanning-line circuit SH input is connected, in addition, one terminal of the primary winding of the line B1-transformer TL, AB whose other terminal is connected, in parallel, to the collector of another TH switching transistor of NPN type, said scan transistor, the cathode of a second diode DR, called astaboe recovery, one plate of another capacitor CR, said capacitor return line, and one of the plates of an additional capacitor CS, said effect capacitor “S or go, which supplies the horizontal deflection coil LH, one terminal is connected to the other frame, while the intervals go scanning.

The emitter of transistor TH scans, the anode of the recovery diode “shunt DR, the other plate of capacitor CR return and the other terminal of the horizontal deflection coil LH are connected to ground G. This assembly thus connected elements constitutes the output stage OS of the scan line whose operation is well known and does. As mentioned above, since the cour of the primary winding of the step-down isolation transformer Multivubrateur on the network, the rectifier R fed to the first astab,e capacitor C1 to provide between its terminals P and N a low DC voltage VE unregulated.

The first transistor T1 then being blocked, this input voltage is applied across the sstable L and the first diode D1, the second capacitor C2 to obtain between the SP terminal and ground G an initial output voltage VSI substantially equal to VE-VD1 which is approximately equal to 60 percent of the output voltage VS.

This provides on its output connected to the input of the HD driver pulses to an autonomous frequency close to the frequency-line.

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In response to these pulses, the HD drive circuit also fed by the BS device provides to the base of transistor TH scanning of controlling pulses. During the return sweep, the transistor TH and the diode DR is blocked, the accumulated energy in the form of current in the deflector LH inductances respectively and the primary winding B1 of TL-line transformer which are then, from the point of view of the alternating current, connected in parallel, flow of oscillatory manner through the CR feedback capacitor which forms with them a multlvibrateur resonant circuit whose resonant period determines the duration of the flyback interval.

It then appears periodically about the points AB and the ground G a voltage ccours VTH of almost half sine wave, which has been shown in diagram A of Figure 2. This means that the first secondary winding Astablee provides a voltage waveform – VTL which, between two successive pulses of line return, comprises a positive plate whose level is equal to the mean value of these multivibratur is used, according to the invention for controlling the blocking of the first transistor T1 so that interference that would otherwise be visible, occur only during the erasing line intervals or delete said “blanking English comprising multivibrwteur back-line.

One terminal of each secondary windings B2, B3 is connected to the ground G, while their other astablf are respectively connected to two inputs 1 and 2 of the control circuit SC. A third input 3 thereof is connected to the output SP of the BS power device and a fourth input 4 is connected to the positive pole P of the source of input voltage VE. A fifth terminal 5 SC control circuit is connected to the astablle G N pole or negative and its output 6 is connected to the base wstable the first transistor T1.

This control circuit SC causes as a result of the initiation of the scanning-line circuit SH, a first setting saturation of the first transistor Multivibrateut to a time determined by a modulator of pulse width by operating the vector comparison of a waveform of sawtooth voltage whose production is controlled by a first pulse return-line, a voltage regulation, depending on the output voltage VS.

During this interval of saturation of the transistor T1 which extends to the leading edge of the next flyback pulse, the energy is stored in inductance L.

From the blocking instant of the transistor Vours, diode D1 transfers this energy stored in the second capacitor C2, across which it causes an increase of the voltage VS with respect to its initial value, until the cancellation of the current in which the diode D1 becomes reverse biased. Le diagramme C de la figure 2 montre la forme d’onde correspondante du courant IL parcourant l’inductance L.

The diagram C of Figure 2 shows the corresponding waveform of the current IL running through the inductor L. When the base of the first transistor T1 receives the output 6 of the control circuit SC, a rectangular signal which causes its release saturation at the time multivibdateur, its collector-emitter voltage VCE diagram B becomes close to multivlbrateur V CEsat and the inductor L is passed through a current IL diagram C increases linearly from the time t1 until time t2 relocking of the transistor T1, which is controlled by the leading edge of the flyback pulse VTH diagram A.

The collector current of transistor T1 is canceled after the lapse of time of storage of minority carriers in the base, the voltage across the inductor L reverses its polarity so as to astablr to the input voltage VE such that the emitter-collector voltage VCE diagram B then reaches a level greater than VM VS and VE so as to apply a forward bias to the first diode D1, which becomes conductive of current IL in the inductance L.

This current IL becomes from time t2 where it reaches its maximum value IM, decreasing linearly and passes through the first diode D1 in astablw forward direction for charging the second capacitor C2 and supplied, inter alia, the scanning circuit SH. When the current IL passing through the first diode D1 becomes zero at time t3, the collector-emitter voltage VCE of the first transistor T1 becomes equal to the unregulated input voltage VE to the next release time of the transistor T1, and the first diode D1 remains reverse biased until time of subsequent relocking thereof.

From the foregoing, it can readily be seen that the main advantage of this combined muptivibrateur lies in the fact that a single oscillator OH belonging to the scanning circuit SH is sufficient to control the two switching transistors T1 and TH. On the other hand, couds overload in the circuits of the television, such as for example a short multivibrzteur of the scan transistor TH, resulting in an overcurrent in the diode D and the inductor L.

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The first transistor T1 it will not undergo this current and it is protected. To protect the rest of the television receiver atable the inductor L and the first diode D1 multivibrateut be set in series on the supply line from the second capacitor C2 a fuse FS.

This fuse FS can also be inserted between the pole P and inductance L. We also know that it is difficult to achieve switching power supplies for proper operation when it is not fully charged to power, for example, a remote control receiver in the standby state. Here the problem does not arise, since when the power is on, there is always a minimum load established by the scanning-line circuit.

When this circuit does not work, the feed does not work either, but it xstable a VSI output voltage value lower than the nominal voltage VS which can not produce damage, and which may, for example, make it possible to powering a watch receiver for television receivers equipped with a remote control.

Finally the control circuit SC makes it possible to block the transistor T1 at the beginning of each intervaile return line, where the suppression circuit or erasing turned off or the spots on the cathode ray tube.

Thus, whatever stray radiation that could excite the receiving circuits, parasites and products will result in no visible effect on the tube screen cathode ray. The variation in current or the control voltage is used to vary the moment when the instantaneous amplitude of a waveform of sawtooth voltage which is either in slope and amplitude substantially constant, reaches the level of this control voltage or variable slope as a function of control current which adds a capacitor charging current reaches the predetermined level of a reference voltage threshold fixed relative to the beginning or the end of the saw tooth.

Thus, a rectangular two-level signal and constant periodicity defined by the pulses of line return, whose duty cycle varies in function of the current or voltage regulation.

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If it is arranged, which is possible, for a reduction in the output voltage VS with respect astabls its nominal value defined by the reference voltage, increases the duty cycle and an increase of VS has the opposite effect, a control is obtained of the output voltage VS which stabilizes at this nominal value.

The output 14 of the modulator 10 supplies a first input 21 of the driver stage 20 of the first switching transistor T1, a second input receives the pulses 22 of flyback negative polarity – VTL w nance of rove- first secondary winding B2 of TL-line transformer. Figures 4 and 5 illustrate two different embodiments of the driver stage 20 of Figure 3, providing effective blocking of the first transistor T1. In Figure 4, the driver stage 20A cornp makes a third supply inlet 23, e connected to the positive pole P of the source of input voltage VE Unregulated and one of terminals of a first resistor R1 1.

Cous second e cokrs these diodes D3 has its cathode connected to the multivibrateir of a third transistor T2 of the NPN type and the one terminal of a second jultivibrateur R2 ohms. The emitter of the third transistor T2 is connected to the other multivibratfur of the second resistor R2 and to the output 24 of stage 20A, which is connected via the output 6 of the control circuit SC at the base of first transistor Sstable.

The base of the first transistor T1 is held in its transmitter and to ground G, by means multivibarteur a fourth resistor R4 ohms. The third transistor T2 is connected in common collector. When the set 14 of the modulator 10 Figure 3 which is connected to the input 21 of stage 20A provides a low state, that is to say, a near zero voltage, the positively biased diode D2 becomes conductive so that its anode is at a voltage of several tenths of a volt 0.

Under these conditions and if at the same time, the voltage waveform – VTL applied to the transistor T3 of the manifold has its constant positive level, coinciding with the time of the going scan line, the transistors T1 and T2 become saturated simultaneously with the effect described above with regard to the BS feeder of Figure 1.

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The third transistor T2 then operates on its saturation characteristic symmetrical, that is to say, it is reversed so that its collector and emitter becomes vice-versa. The capacitor C3 serves to accelerate the blocking promoting transmission to the base of T1 steep transitions negative flyback pulses.

FIG 6 is a diagram, in schematic section, a possible embodiment of the modulator of the pulse width 10 of the control circuit SC of Fig 3. When the waveform VI applied to the inverting input – of the comparator A2 is greater than the regulation voltage VR, which is the case dins the interval between t9 and t1, its output connected to the output 14 the modulator 10A FORMIT a low state. This high stall persists until time t4 after time t2 of the beginning of the next pulse of Return- licne whose control before the front bbcage the first transistor T1, when the waveform VI becomes greater than the voltage VR control.

When the VR control voltage is negative as in the diagram E of Figure 7a predetermined fraction of the output voltage VS is higher than the reference voltage, and the duration of the positive pulse t2 – t1 is less than half the interval of the scanning range from RT.

Changing this time t2 – t1 and therefore the duty ratio is performed in the opposite direction of the variation of the output voltage VS in order to stabilize at a previously set level, with respect to this reference voltage. One can also apply the waveform – VTL to the input 11 of the modulator 10A.

In this case, it is also necessary to invert the inputs of comparator A2. Suitable for operating limits, particularly in view of the value of the inductance L, the cyclic ratio of the durations t2-t1 is varied between 0, where the input voltage VE is equal to the output voltage nominal VS, and about two-thirds, where the maximum power is supplied for a minimum voltage at the input.

It also requires that the ratio of the parasitic AC voltage output and the AC voltage input, allowing to obtain an image that is not disrupted for the eye. A less than or equal to one hundredth to this report gives satisfactory results.

This inlet 11 feeds a passive shaping circuit, providing negative sawtooth decreasing during the intervals of the scanning range from RT. The other terminal of the ninth resistor R9 is connected to the base of a fourth NPN type transistor T3, which is the stage voltage comparator, whose emitter is connected to ground and whose collector open which constitutes the output 14 of the modulator 10B, is connected to the input 21 of the driver stage 20A Figure 4 or 20B FIG 5constituted by the cathode of the second diode D2.

The value of capacitor C6 is selected to limit the maximum negative voltage applied to the base-emitter junction of the transistor T3 to a value less than its breakdown voltage avalanche effect Zener. The transistor T3 becomes conductive when its base current IB consists of the sum of currents 11 and 12 becomes positive. When the instantaneous amplitude of the negative current 11 becomes equal to the positive current 12 shown by another arrow in Figure 8 and by means of a constant level inverted – 12 indicated by dashed lines in Figure 7, which occurs at time t1, the base current of the transistor T3 becomes zero and it becomes blocked.

The stream 12 is due in major part to the IR control current supplied by the output of the regulator stage 30 in Figure 3 and proportional to the error voltage, the duration of the OFF state t4 – tl the transistor T3 and, therefore, that t2 – t1 of the saturated state of the first transistor T1 and the duty ratio will vary inversely to the variation of this current Mulfivibrateur.