All parts of the receiver are fitted on one board exept the TUNER and the POWER SUPPLY TRANSFORMER which are on the bottom of the cabinet.
The CHASSIS TECHNOLOGY is based on ASIC'S which are:TCA511 TBA311A17 TBA120SQ TAA611B12 and lots of discretes. Power supply is delivered after rectifiing via Transistor stabiliser. The set can be power supplyed via a 12Volt source in a socket on the rear of the lid.
Power supply is realized with mains transformer and Linear transistorized power supply stabilizer, A DC power supply apparatus includes a rectifier circuit which rectifies an input commercial AC voltage. The rectifier output voltage is smoothed in a smoothing capacitor. Voltage stabilization is provided in the stabilizing circuits by the use of Zener diode circuits to provide biasing to control the collector-emitter paths of respective transistors.A linear regulator circuit according to an embodiment of the present invention has an input node receiving an unregulated voltage and an output node providing a regulated voltage. The linear regulator circuit includes a voltage regulator, a bias circuit, and a current control device.
In one embodiment, the current control device is implemented as an NPN bipolar junction transistor (BJT) having a collector electrode forming the input node of the linear regulator circuit, an emitter electrode coupled to the input of the voltage regulator, and a base electrode coupled to the second terminal of the bias circuit. A first capacitor may be coupled between the input and reference terminals of the voltage regulator and a second capacitor may be coupled between the output and reference terminals of the voltage regulator. The voltage regulator may be implemented as known to those skilled in the art, such as an LDO or non-LDO 3-terminal regulator or the like.
The bias circuit may include a bias device and a current source. The bias device has a first terminal coupled to the output terminal of the voltage regulator and a second terminal coupled to the control electrode of the current control device. The current source has an input coupled to the first current electrode of the current control device and an output coupled to the second terminal of the bias device. A capacitor may be coupled between the first and second terminals of the bias device.
In the bias device and current source embodiment, the bias device may be implemented as a Zener diode, one or more diodes coupled in series, at least one light emitting diode, or any other bias device which develops sufficient voltage while receiving current from the current source. The current source may be implemented with a PNP BJT having its collector electrode coupled to the second terminal of the bias device, at least one first resistor having a first end coupled to the emitter electrode of the PNP BJT and a second end, a Zener diode and a second resistor. The Zener diode has an anode coupled to the base electrode of the PNP BJT and a cathode coupled to the second end of the first resistor. The second resistor has a first end coupled to the anode of the Zener diode and a second end coupled to the reference terminal of the voltage regulator. A second Zener diode may be included having an anode coupled to the cathode of the first Zener diode and a cathode coupled to the first current electrode of the current control device.
A circuit is disclosed for improving operation of a linear regulator, having an input terminal, an output terminal, and a reference terminal. The circuit includes an input node, a transistor, a bias circuit, and first and second capacitors. The transistor has a first current electrode coupled to the input node, a second current electrode for coupling to the input terminal of the linear regulator, and a control electrode. The bias circuit has a first terminal for coupling to the output terminal of the linear regulator and a second terminal coupled to the control electrode of the transistor. The first capacitor is for coupling between the input and reference terminals of the linear regulator, and the second capacitor is for coupling between the output and reference terminals of the linear regulator. The bias circuit develops a voltage sufficient to drive the control terminal of the transistor and to operate the linear regulator. The bias circuit may be a battery, a bias device and a current source, a floating power supply, a charge pump, or any combination thereof. The transistor may be implemented as a BJT or FET or any other suitable current controlled device.
The TCA 511 is a silicon monolithic integrated circuit in a 16—lead dual in—line plastic
package. It incorporates the following functions: high stability horizontal oscillator,
horizontal APC circuit with high noise immunity and large pull—in range, high stability
vertical oscillator and sawtooth generator.
lt is intended for driving TV horizontal and vertical transistorized output stages.
The circuit can work with stabilized supply voltage having a value from 9 to 15 V.
A dropping resistor and a filter capacitor may be used to obtain the suipply from higher
voltages; however, the voltage on pins 3 and 4 must never exceed the maximum
Pins 2 and 6 can be DC driven if the reference level of the synchronization pulses is
less than 1 V. With reference levels greater than this value, a coupling capacitor must
be inserted in series with the input, and pins 2
and 6 must be connected to ground
via a resistor.
The capacitor connected to pin 1 must be selected with regard to the frequency
tolerance, to the thermal stability and to the capacitor's ageing.
The width of the output pulse, to be chosen according to the needs of the output
stages, is defined by the resistor connected between pin 1 and pin 16.
The vertical output is taken from pin 14, which is a buffered output of the sawtooth
voltage generated at pin 15.
The output current from pin 14 is defined by an internal resistor in the integrated
circuit. if a greater current is needed, a resistor may be connected between pin 14
and pin 3.
The oscillator output pulse is available at pin 15 if the capacitor C9 is not connected. _
This configuration is used for driving output stages in which the sawtooth is generated
by Miller effect.
The capacitor connected between pin 10 and ground must be selected with regard
to the frequency tolerance, 1:0 the thermal stability and to the capacit0r’s ageing.
In multistandard receivers, the oscillation frequency may be changed by switching the
value of the capacitor connected to pin 10.
TBA 311 TV SIGNAL PROCESSING CIRCUIT
The TBA 311 is a monolithic integrated circuit in a 16-lead clual in-line or quad in—Iine
plastic package. It is intended for use as signal processing circuit for black and
white and colour television sets.
The circuit is designed for receivers equipped with tubes or transistors in the deflection
and video output stages, and with PNP or NPN transistors in the tuner and NPN in
the IF amplifier.
Only signals with the negative modulation can be handled by the circuit. The circuit
is protected against short circuit between video output and GND. The TBA 311 includes:
0 VIDEO PREAMPLIFIER with EIMITTER FOLLOWER OUTPUT
0 GATED AGC for VIDEO» IF AMPLIFIER and TUNER
0 NOISE INVERTER CIRCUIT for GATING AGC and SYNC. PULSE SEPARATOR
o HORIZONTAL SYNC. PIULSE SEPARATOR
0 VERTICAL SYNC. PULSE SEPARATOR
0 BLANKING FACILITY for the VIDEO AMPLIFIER.
All circuits were made by:
SGS is Società Generale Semiconduttori - Aquila Tubi E Semiconduttori (SGS-ATES, "Semiconductor General Society - Tubes and Semiconductors Aquila"), later SGS Microelettronica, a former Italian company now merged into STMicroelectronics
- ATES (Aquila Tubi e Semiconduttori), a vacuum tube and semiconductor maker headquartered in the Abruzzese city of l'Aquila, who in 1961 changed its name into Azienda Tecnica ed Elettronica del Sud and relocated its manufacturing plant in the outskirts of the Sicilian city of Catania
- Società Generale Semiconduttori (founded in 1957 by Adriano Olivetti).
Category: Germanium Transistor, PNP Transistor, Transistor
MHz: <1 MHz
Ge PNP Power BJT
I(C) Abs.(A) Collector Current=10
Absolute Max. Power Diss. (W)=30
I(CBO) Max. (A)=100u
h(FE) Min. Static Current Gain=20
h(FE) Max. Current gain.=90
@I(C) (A) (Test Condition)=1.0
@V(CE) (V) (Test Condition)=2.0
- The EHT Output is realized with a selenium rectifier.
The EHT selenium rectifier which is a Specially designed selenium rectifiers were once widely used as EHT rectifiers in television sets and photocopiers. A layer of selenium was applied to a sheet of soft iron foil, and thousands of tiny discs (typically 2mm diameter) were punched out of this and assembled as "stacks" inside ceramic tubes. Rectifiers capable of supplying tens of thousands of volts could be made this way. Their internal resistance was extremely high, but most EHT applications only required a few hundred microamps at most, so this was not normally an issue. With the development of inexpensive high voltage silicon rectifiers, this technology has fallen into disuse.
PLANET Mod:730 CHASSIS A40-73 Tuning unit with bandswitch for high frequency receivers
1. Tuning unit with bandswitch for high frequency receivers having potentiometer means for the control of capacity diodes composed of a plurality of parallelly disposed resistance paths on which wipers are moved by means of screw tuning spindle means mounted beside one another in a common housing of insulating material, bandswitch means formed of metal wires associated with each tuning spindle means, said tuning spindle means being joined for rotation with sleeve means simultaneously forming operating knobs which are borne in apertures in the front plate and each sleeve means having an axial flange surface engaging the back side of the front plate about one aperture therein, said flange surface being slightly larger than the cross section of the apertures and tapering conically away from the back side of the front plate.
2. Tuning unit of claim 1 wherein the sleeve means are joined telescopically and coaxially with the tuning spindle means, and the flange surface engages the back side of the front plate when the sleeve means are in the state wherein they are pulled out of the front plate.
3. Tuning unit of claim 1 wherein the ends of the tuning spindle means which are opposite the front plate have each an annular groove into which a spring bracket engages whose bent end is supported against the housing and which has two diametrically disposed spring arms having opposite spring curvature, the said spring arms in each case contacting the opposite axial walls of the groove.
4. Tuning unit of claim 3 wherein the spring bracket rests with its bent end against the housing and the spring arms additionally engage a bracket formed on the housing or an intermediate bracket formed in one piece with the connection soldering lugs.
5. Tuning unit of claim 3 wherein the spring bracket is formed in one piece with the connection soldering lugs and has spring arms curved both in the same direction which engage an axial wall of the annular groove in the spindle and the opposite axial wall rests against a housing wall.
6. Tuning unit of claim 1 wherein the pointers associated with each potentiometer means lie on the one hand in windows associated with each tuning spindle means in the front plate, and on the other hand are rotatably mounted with their ends opposite the front plate in pivot pins on the housing, and the guiding pin of the spindle nuts carried in a longitudinally displaceable manner on each tuning spindle is provided with a slit disposed parallel to the longitudinal axis of the tuning spindle and slides with its peripheral surface resiliently within the slide tract of the pointer.
7. Tuning unit of claim 1 wherein the bandswitches are formed each of a displaceable metal rod which is in working engagement with stationary metal rods common to all bandswitches of a tuning unit, contacting each of them individually.
8. Tuning unit of claim 7 wherein the metal rods are metal wires.
9. Tuning unit of claim 7 wherein the metal rods are stamped metal parts.
10. Tuning unit of claim 7 wherein levers of insulating material are placed on the front ends of the displaceable metal rods and extend through windows which are provided with detents and which are associated with each tuning spindle in the housing front plate, while the opposite ends are held fixedly in the rearward end of the housing, and the displaceable metal rods individually make contact with contact cams on the stationary metal rods, these cams being in an offset array corresponding to the detents in the windows, the corresponding rods extending parallel to the front plate and parallel to one another behind the front plate.
11. Tuning unit of claim 7 wherein insulating material bridges or insulating material slide pieces are inserted between the contact cams of two adjacent, stationary metal rods and within the free space between two such parallel metal rods.
12. Tuning unit of claim 7 wherein the displaceable metal rods have, in the vicinity of their mountings on the housing, an articulation in the form of a vertically disposed flat portion.
The invention relates to a tuning unit with bandswitch for high frequency receivers, especially radio and television receivers, having a potentiometer system for the control of capacity diodes, the said potentiometer system consisting of a plurality of parallel resistance paths along which wiper contacts can be driven by means of screw spindles disposed adjacent one another in a common insulating material housing in which a bandswitch formed of metal rods is associated with each tuning spindle.
In these tuning units, the working voltages of the capacity diodes in the tuning circuits are recorded once a precise tuning to the desired frequency has been performed. A potentiometer tuning system has great advantages over the formerly used channel selectors operating with mechanically adjustable capacitors (tuning condensers) or mechanically adjustable inductances (variometers), mainly because it is not required to have such great precision in its tuning mechanism.
Tuning units with bandswitches formed of variable resistances and combined with interlocking pushbuttons controlling the supply of recorded working voltages to capacity diodes are known. Channel selection is accomplished by depressing the knobs, and the tuning or fine tuning are performed by turning the knobs. The resistances serving as voltage dividers in these tuning units are combined into a component unit such that they are in the form of a ladderlike pattern on a common insulating plate forming the cover of the housing in which the tuning spindles and wiper contacts corresponding to the variable resistances are housed. The number of resistances corresponds to the number of channels or frequencies which are to be recorded. The wiper contact picks up a voltage which, when applied to the capacity diodes determines their capacitance and hence the frequency of the corresponding oscillating circuit. The adjustment of the wipers is performed by turning the tuning spindle coupled to the tuning knob. By the depression of a button the electrical connection between a contact rod and a tuning spindle is brought about and thus the selected voltage is applied to the capacity diodes. Since the push buttons release one another, it is possible simply by depressing another button to tune to a different receiving frequency or a different channel, as the case may be.
To permit the switching of a number of channels in a certain tuning range, bandswitches for a plurality of tuning ranges, such as UHF and VHF for example, are often provided in the tuning units described above. In the pushbutton tuning unit of the above-named type, the bandswitch consists of a printed circuit board which is fastened on the housing of the tuning unit, and a switch lever which is preset by means of the pushbutton by turning, and is operated by depressing the pushbutton while at the same time selecting the channel.
Where this combination of knobs and pushbuttons is not possible, the selection of the range is accomplished by means of an additional lever which can be set over to select the range.
However, since such tuning units require too many riveting operations when they are assembled, tuning units were later created in which the individual parts in the voltage divider and pushbutton housing were loosely inserted and/or held in place by projections, lugs, hooks or tabs of resilient plastic. In spite of these initial improvements, the bandswitch, especially the one associated with the tuning units, was still technically intricate and very expensive.
It is the object of the invention, therefore, to create an additionally improved and simplified tuning unit containing a bandswitch of simple, space-saving and reliably operating design.
In accordance with the invention, this object is accomplished in a tuning unit with bandswitch of the kind described in the beginning by joining the tuning spindles for rotation with sleeves simultaneously forming the control knobs, which are mounted in apertures in the front plate of the housing and have each a flange engaging the back of the front plate around the aperture, the said flange being slightly larger than the aperture and tapering conically away from the back of the front plate.
In further development, the sleeves can be joined telescopically for rotation with the tuning spindles, and the flange is able to engage the back side of the front plate when the sleeve is in the position in which it is drawn out of the front plate. The sleeves constructed in this manner, whose portions projecting from the apertures in the front plate form the control knobs for the tuning spindles, permit easy assembly of the tuning unit and at the same time assure positive co-rotation of sleeves and spindles. The sleeves can be pushed from the front side of the front plate through the apertures onto the clutch surfaces of the spindles, this inward pushing being easily accomplished on account of the taper, and the dropping out of the sleeve being prevented by the flange engaging the back of the front plate. If the control knobs project only slightly out of the front plate, they can be operated from the outside by inserting a tool into them. With the telescoping type of coupling, however, it is possible to draw the sleeves or control knobs further outwardly so that they can be rotated by hand without the use of tools.
To provide constant assurance of the axial fixation of the tuning spindles, the tuning spindle ends farthest from the front plate can each be provided with an annular groove engaged by a spring bracket whose one leg is supported against the housing and whose other leg is forked to form two spring arms, each bent in the opposite direction and each engaging one of the two opposite walls of the annular groove. The tuning spindles are secured against axial displacement by this construction of the invention alone, without the need for further measures. This facilitates the joining of the sleeves or control knobs to the tuning spindle, because in this case there is no need for precise axial fixation and extreme dimensional accuracy.
Furthermore, the indicators associated with each potentiometer can be mounted in windows in the front plate which are associated with each tuning spindle or tuning knob for visual indication at the front, the other extremities farthest from the front plate being mounted for pivoting on pins set in the housing; the guiding pin on the spindle nut that is driven longitudinally on each tuning spindle can be provided with a slit disposed parallel to the long axis of the tuning spindles and can slide within the indicator slide lever slot, with its surface resiliently engaging the walls of said slot.
In an especially advantageous embodiment, the tuning unit can have bandswitches each formed of a displaceable metal rod which is in contacting engagement individually with stationary metal rods which are common to all of the bandswitches of a tuning unit. It contrast to the bandswitches known hitherto, which as a rule consist of a printed circuit board with switchable contacts thereon, this frequency bandswitch of the invention is of great simplicity, can be manufactured simply and inexpensively, and at the same time is very reliable in operation.
The displaceable and stationary metal rods of the bandswitches can be formed of metal wires or they can be of stamped sheet metal. Also, in further expansion of the concept of the invention, the stationary metal rods thus formed can be all entirely alike and merely offset from one another, thereby further simplifying the manufacture and stocking thereof.
To permit connection also to audiovisual apparatus, one or more of the stationary metal rods can be divided electrically into at least two parts each.
In a special development of this concept, lugs of insulating material can be mounted on the front ends of the displaceable metal wires, these lugs extending through windows in the front plate of the housing which are associated with each tuning spindle and are provided with detents, while the opposite ends can be held fixedly at the rear end of the housing, and the displaceable metal wires can make contact with contact humps on the stationary metal wires, the humps being offset from one another to correspond to the detents in the windows, and the stationary metal wires extending in back of the front plate, parallel to the latter and parallel to one another.
To increase switching reliability, bridges or sliding pieces made of insulating material can be inserted between the contact humps of adjacent stationary wires within the free space between two such parallel lying metal wires.
To achieve easy displacement of the displaceable metal wires despite the fixed end mounting on the housing, the displaceable metal wires, in further embodiment of the invention, can have each an articulation adjacent their end mountings, in the form of a vertically disposed flattened portion. This flat permits the metal wires to be deflected horizontally against a weak spring bias.
DESCRIPTION OF THE DRAWING
As an example of the embodiment of the invention, there is represented in the drawings a tuning unit with bandswitch for television receivers. In these drawings,
FIG. 1 is a front elevational view of a tuning unit with bandswitch,
FIG. 2 is a plan view showing the bandswitch of the tuning unit of FIG. 1,
FIG. 3 is a side elevational, cross-sectional view of the tuning unit of FIG. 1,
FIG. 4 is a rear elevational view of the tuning unit of FIG. 1,
FIG. 5 is a plan view showing the indicator means of the tuning unit of FIG. 1,
FIG. 6 shows the sleeve with the operating knob and tuning spindle,
FIG. 7 shows the telescoping manner in which the sleeve is joined to the tuning spindle,
FIG. 8 is a fragmentary view of the bandswitch,
FIG. 9 is another fragmentary view of the bandswitch, and
FIG. 10 shows how the tuning spindle is fixed in position.
The method of representation used in the drawings is greatly simplified, for the purpose of better delineating the features of the invention. The tuning unit with bandswitch consists of an insulating material housing 1 with a front plate 2, which is closed by a cover plate 3 accommodating the resistance paths. The housing 1 is divided by parallel sidewalls 4 into chambers in which the tuning spindles 5 are disposed.
The embodiments is an 8-fold tuning unit having eight bandswitches assocated with each tuning spindle, and eight indicators.
Accordingly, there are eight apertures 6 in a central row, through which the operating knobs 7 of the sleeves 8 coupled with the tuning spindles 5 are passed. The operating knobs 7 have recessed surfaces 9 for turning with a turning tool. In a row extending parallel above the row of the apertures 6 there are eight windows 10, whose upper edge is provided with notches 11. Lugs 12 of insulating material extend through the windows 10 and engage the upper notches 11 and are joined behind the front plate to displaceable metal wires 13 of the bandswitch. In a row located beneath the row of apertures 6 another eight windows 14 are provided, through which the ends of the pointers of the indicators 15 protrude.
Now, the bandswitch consists in each case of a displaceable metal wire 13 which can be brought into working engagement with stationary metal wires 16, which are all of the same construction and are only disposed offset from one another. While the displaceable metal wire 13 extends substantially parallel to the longitudinal axis and thus at right angles to the front plate 2, the stationary, parallelly disposed metal wires 16 are parallel to the front plate 2 and are thus inserted at a right angle to the displaceable metal wire. A departure from parallelism or from the right angle, as the case may be, takes place substantially only when the displaceable metal wire 13 is deflected to the two outer notches. The rearward end 18 of the displaceable metal wire, which forms a vertical loop, is tightly inserted into a receiver 17. Just ahead of the loop 18, the metal wire 13 is provided with a vertically disposed portion 19 by a flattening on the metal wire 13. The movement, when the metal wire 13 is deflected into the desired notches or detents, takes place horizontally by the flexing of these portions 19. The stationary metal wires 16 are held tightly in their positions in projections 20 on the housing, or by lugs or the like. Since three switch actions are provided, that is, three ranges, for each tuning spindle, a bandswitch consists of one displaceable metal wire and three stationary metal wires 16, which are used for all switches.
To permit each bandswitch to have exactly three switching actions, each of the three stationary metal wires 16 has one contact hump 21 corresponding to one of the detents 11 in the windows 10 of the front plate 2. The contact humps 21 are thus located one next to the other as seen from the front plate 2. So that the displaceable metal wire 13 will always come into mechanical and electrical contact only with the desired contact hump, and prevent short circuits, insulating bridges 22 are installed between the adjacent metal wires 16, said insulating bridges being stationary.
If more or less than three switching actions are desired, all that need be done in the case of the bandswitch of the invention is to change the number of stationary metal rods or wires accordingly.
The sleeves 8 with the operating knob 7 have a flange 23 engaging the back of the front plate 2 and tapering back to the point where it joins the tuning spindle. This enables the sleeves to be pushed in, in the case of a housing that has already been manufactured with the tuning spindle installed, without creating the possibility that the sleeves 8 might escape after they have been inserted. The sleeves 8 are connected to the tuning spindles 5 usually by means of driving surfaces. If manual operation without tools is to be possible, rather than requiring a tool for the operation of the sleeves, the coupling of the sleeve 8 to the tuning spindle will be a telescoping coupling (see FIG. 7).
The actual firm axial fixation of the tuning spindle 5 is located on the rear end of the housing. Here the tuning spindle 5 has an annular groove 24 which is engaged by a spring by means of two diametrically disposed spring arms 25 and 26. The spring arms 25 and 26 have oppositely curved lugs and are supported on the housing at their terminal and marginal surfaces and their lugs engage opposite axial walls 27 and 28 of the annular groove 24.
Additional support is provided by the common, bent foot 29 of the spring arms 25 and 26 against the cover plate of the housing.
The indicator means of the tuning unit with bandswitch consists of a pointer 15 which is movable within the window 14, and a cam 30 which is a prolongation of the pointer 15. At its rearward end, the pointer is mounted rotatably in the housing on pin 31. Within the cam 30 slides a guiding pin 32 which is attached to the spindle nut or carriage 40. Upon the rotation of the tuning spindle, the spindle nut is longitudinally displaceable therewith. In order to achieve good guidance and hence precise indication, the guiding pin has a slit 33 extending parallel to the longitudinal axis of the tuning spindle 5, so that it will resiliently engage the cam 30 within the slot thereof.
The necessary soldering lugs are indicated at 34.
On the basis of the design of the tuning unit with bandswitch in accordance with the invention, a desired frequency range--UHF, for example--can be selected by deflecting a displaceable metal wire 13 into one of the detents 11 by means of the lug 12 mounted thereon. Within this range, a transmitter or channel can then be selected by turning the tuning spindle 5. The transmitter preselected in this manner can then be tuned in by means of a keyboard or by electronic recall from a keyboard which is not shown. The fine tuning of this tuned-in transmitter, as well as the selection of a different transmitter within the same frequency range, is accomplished by turning the tuning spindle 5.
All of the details explained in the above description and represented in the drawings are important to the invention.
PLANET Mod:730 CHASSIS A40-73 B-W TELEVISION DIAGRAM AND DEFLECTION CIRCUIT:
A unidirectional conductive device is coupled from a base terminal to a collector terminal of a horizontal deflection output transistor in a television receiver and poled in a direction to prevent the transistor from saturating when it is driven into its conductive state during a portion of each deflection cycle. Biasing means is coupled to the diode to preselect the desired operating voltage of the transistor during its conduction period.
In present day transistor deflection circuits, for example, those used in the horizontal output stage of a television receiver; the output transistor is normally operated in a switching mode, that is, the transistor is driven into saturation during a trace interval of each deflection cycle and driven out of conduction during the retrace portion of each deflection cycle. By operating the transistor in its saturation region, average power losses are minimized. With saturated operation, however, the accumulation of minority carriers in the base region will effect a continuation in the flow of collector current after the trace interval during the initial portion of the retrace interval while the transistor is being driven into its non-conducting state. In addition to causing this undesirable delay time in turning off the transistor, losses occurring during this period may be localized in small areas commonly referred to as "hot spots." These losses are characterized in being regenerative and tend to cause second breakdown of the device. This effect is explained in greater detail in a paper authored by the present inventor and entitled "Thermal Regeneration in Power Dissipating Elements" which appeared in "The Electronic Engineer" publication in the January 1967 issue. Although operating the horizontal output transistor in its saturated region may reduce the average power dissipated in this device during its conduction interval, it increases the possibility of second breakdown during the turn-off time. With the advent of high voltage (1,500 volts) transistors, it is possible to develop the necessary output energy utilizing one of these transistors which can be operated in a non-saturated mode. The circuit of the present invention insures that the deflection output transistor will not be driven into saturation.
Certain low power transistor switching circuits, such as employed in computer applications, have utilized diodes in conjunction with resistive biasing means coupled between the base and collector terminals to prevent the transistor from saturating and thereby increase the maximum switching frequency of the circuit by reducing the turn-off time of the device.
In the solid state deflection art, however, it is desirable to reduce the turn-off time of the device not to increase the frequency of operation of the circuit, but rather to prevent second breakdown of the device as the relatively large inductive voltage pulse appears during the initial portion of the flyback interval, when current flowing through the deflection winding is interrupted to initiate the retrace portion of each deflection cycle.
The non-saturated operation of the deflection output transistor is achieved in circuits embodying the present invention by automatically holding the collector voltage above the saturation level by shunting excess base drive from the base to emitter junction into the collector circuit. Prior transistor deflection systems employ only the saturated operation of the deflection output device.
Circuits embodying the present invention include a deflection output transistor having a diode coupled between its base and collector terminals and poled to prevent the transistor from being driven into saturation during its conduction period of each deflection cycle.
The invention can be more fully understood by referring to the drawings together with the description below and the accompanying claims.
In the drawings:
FIG. 1 illustrates in block and schematic diagram form, a television receiver including a solid state deflection output stage embodying the present invention;
FIG. 2a is a waveform diagram of the voltage present at the collector terminal 55c of transistor 55 in FIG. 1;
FIG. 2b shows the drive current to terminal A in FIG. 1;
FIG. 2c is a waveform diagram of the current in diode 56 in FIG. 1;
FIG. 2d is a waveform diagram of the base current flowing in transistor 55 of FIG. 1;
FIG. 3 is a schematic diagram of an alternative embodiment of the present invention;
FIG. 4a is a waveform diagram of the voltage appearing at the terminal 366 in FIG. 3;
FIG. 4b is a waveform diagram of the drive current to terminal A in FIG. 3;
FIG. 4c is a waveform diagram of the current in diode 356 in FIG. 3; and
FIG. 4d is a waveform diagram of the base drive current to transistor 355 in FIG. 3.
Referring specifically to FIG. 1, an antenna 10 receives television signals and couples these signals to a tuner 12 which selects the desired radio frequency signals of a predetermined broadcast channel, amplifies these signals, and converts the amplified radio frequency signals to a lower intermediate frequency (I.F.). The tuner 12 is coupled to an I.F. amplifier 14 which amplifies the intermediate frequency signals. The I.F. amplifier 14 is coupled to a video detector 16 which derives video information from the I.F. signals. The video detector 16 is coupled to a video driver stage 18 which amplifies the video signals. The video driver stage 18 is coupled to a video output stage 20, an automatic gain control stage 25 and a synchronizing separator stage 42. An output signal from video driver stage 18 may also be coupled to a sound channel (not shown) to reproduce the audio portion of the transmitted television program. The video output stage 20 couples amplified video information to a control element, such as a cathode 28, of a kinescope 30.
The automatic gain control stage 25 operates in a conventional manner to provide gain control signals which are applied to a radio frequency amplifier included in tuner 12 and to the I.F. amplifier 14. Sync separator 42 separates the synchronization information from the video information and also separates the horizontal synchronizing information for the vertical synchronizing information. The vertical synchronizing pulses derived from sync separator 42 are applied to the vertical deflection system 44 which provides the required deflection current to a vertical deflection winding 43 associated with kinescope 30 by means of the interconnection Y--Y. The horizontal synchronizing pulses from sync separator 42 are applied to an automatic frequency control detector 45 which serves to synchronize a horizontal oscillator 46 with the horizontal synchronizing pulses. The horizontal oscillator stage 46 is coupled to a horizontal driver stage 48 which develops the required drive signal and may be coupled by means of an output transformer in stage 48 (not shown) to a transistorized horizontal output stage 50. The transformer secondary, coupled to terminal A, provides a direct current path for the drive current.
The horizontal output stage 50 includes an output transistor 55 having a base, a collector and an emitter terminal 55b, 55c and 55e, respectively. A resistor 52 and a capacitor 53 are coupled in parallel between the horizontal driver stage 48 and the base terminal 55b of transistor 55.
The output stage includes a unidirectional conductive device such as a diode 56 coupled between the base and collector terminals 55b and 55c of transistor 55. Stage 50 also includes a damper diode 57 coupled across transistor 55, a retrace capacitor 58 coupled across transistor 55 and the series combination of a horizontal deflection winding 59 and an S-shaping capacitor 60 also coupled across transistor 55. Output stage 50 also includes a flyback transformer 61 with a primary winding 61p coupled from a source of operating potential (B+) to the collector terminal 55c of transistor 55. A secondary winding 61s on transformer 61 develops high voltage pulses which are coupled to a high voltage rectifier 63 to provide the ultor voltage for application to a terminal 32 on kinescope 30. Flyback transformer 61 may also include additional windings (not shown) for providing, for example, keying pulses to the AGC stage 25.
The output stage 50 in FIG. 1 is a conventional shunt fed trace driven circuit with the exception of the diode 56 and the bias network including resistor 52 and capacitor 53. Beginning at the center of the trace interval of the deflection cycle, the yoke current is zero and capacitor 60 has a maximum charge. The drive signal applied to the base terminal 55b of transistor 55 turns this device on, thereby completing the conduction path for yoke current which includes capacitor 60, yoke 59 and the collector to emitter current path through transistor 55. During this portion of scan the yoke current is supplied by the charge on capacitor 60 and increases to a maximum value in one direction at which time scan retrace is initiated by driving transistor 55 out of conduction by applying an appropriate signal from the driver stage 48 to the base 55b of transistor 55. During the latter portion of the trace interval when the magnitude of the yoke current is increasing, the output transistor of prior circuits is normally driven into saturation and is in this conduction state at the instant retrace is initiated. During the first portion of retrace, the yoke current is at a maximum and resonates with the retrace capacitor 58 by charging capacitor 58 in a polarity to reverse bias the damper diode 57. As the yoke current decreases to zero, capacitor 58 has a maximum charge impressed upon it; and during the second portion of retrace, the capacitor (58) drives current through the yoke in a reverse direction until it is discharged and the voltage across it reverses sufficiently to forward bias damper diode 57. Diode 57 then conducts during this first portion of trace to complete the current path for yoke current which is, at this instant, at a maximum value in a direction in yoke 59 to charge capacitor 60 and is increasing toward zero. At the mid-point of trace the yoke current has reached zero and the cycle is completed by driving transistor 55 into conduction once again.
Turning now to the operation of the circuitry of FIG. 1 including the present invention, reference is made to the waveform diagrams of FIG. 2. The initial portion of trace is represented in FIG. 2 by the time period between t 0 and t 1 in the figure. It is recalled that during this period damper diode 57 is conducting. The voltage at collector terminal 55c of transistor 55 is represented by the voltage waveform (V c ) in FIG. 2a and is equal to the forward voltage drop across diode 57 which is of the order of -0.7 volts. At some non-critical time before t 1 , the horizontal driver 48 provides a drive current (I A ), as is shown in FIG. 2b. This current flows through diode 56 as is illustrated in FIG. 2c, since the diode is forward biased. [The cathode of diode 56 is at the same voltage as collector terminal 55c (-0.07 volts) and the drive current produces a positive voltage at point A which is at the anode of diode 56.] As time t 1 (the center of trace) is reached, damper diode 57 turns off allowing the collector voltage on transistor 55 to increase as shown in FIG. 2a. At the same time, a portion of the drive current flowing into terminal A is conducted by the now forward biased base to emitter junction of transistor 55 as is illustrated by the waveform of FIG. 2d. Transistor 55 is now conducting the increasing yoke current during the latter portion of scan represented by the period from t 1 to t 2 in FIG. 2. As the magnitude of the yoke current increases during the t 1 to t 2 interval, the base current in transistor 55 increases as shown in FIG. 2d. Diode 56 conducts as illustrated in FIG. 2c to shunt the remaining portion of the applied drive current at terminal A. It is noted that the sum of the currents shown in FIGS. 2c and 2d will equal the current shown in FIG. 2b. The values of resistor 52 and capacitor 53 can be selected to hold the transistor collector voltage at a preselected value sufficient to prevent saturation of the transistor 55. If, for example, the voltage across capacitor 53 is 5.3 volts, the voltage at terminal A with respect to ground will be approximately 6 volts (5.3 volts plus the forward voltage drop across the base-emitter junction of transistor 55). The collector voltage will then be approximately equal to the voltage at terminal A less the forward voltage drop across diode 56. It is desirable to choose values of resistor 52 and capacitor 53 to operate transistor 55 near but not into the saturation region of conduction during the latter portion of each trace interval.
At time t 2 retrace is initiated by applying a relatively large negative drive signal as shown in FIG. 2b to the base terminal of transistor 55. During the retrace interval (t 2 to t 0 in FIG. 2), the collector voltage increases in a typical manner as illustrated in FIG. 2a. At time t 0 the cycle is again repeated.
The circuit modification illustrated in FIG. 3 is another embodiment of the invention which reduces the change in voltage applied to the yoke 59 of FIG. 1 at time t 1 . As shown in FIG. 2a, when diode 57 turns off and transistor 55 conducts, the voltage at the collector terminal 55c of transistor 55 changes by as much, for example, as 6 volts. This voltage change, which is coupled to the yoke 59, will vary the rate of change of yoke current during the center of trace and may, in certain circuits, cause an undesirable non-linearity in the scanning rate. As FIG. 4a illustrates, the circuit of FIG. 3 reduces this change in voltage at the mid-point of trace (t 1 ).
Referring to FIG. 3, the circuit elements which correspond to those of FIG. 1 are prefaced by the numeral 3. In explaining FIG. 3, it is helpful to refer to the waveform diagrams of FIG. 4. Transformer 364 in FIG. 3 is a tightly coupled auto-transformer wherein the tap point 365 may be, for example, at the 5 percent point on the transformer. That is, the segment between terminals 365 and 366 contain 5 percent of the total number of windings on transformer 364. Transformer 364 may also include a secondary winding such as the high voltage winding which is not shown in the figure. In operation, as drive current is applied at sometime prior to t 1 as is shown in FIG. 4b, damper diode 357 is conducting and the voltage at terminal 366 is therefore at approximately -0.7 volts. Drive current flowing into terminal A as represented in FIG. 4b will be conducted by diode 356 during this interval as indicated by the diode current waveform in FIG. 4c. At the middle portion of trace (t 1 ), the damper diode turns off and voltage at terminal 366 is thereby allowed to go slightly positive (less than 0.7 volts). The collector voltage of transistor 355 is held at a value of approximately 5 volts (assuming, for example, the B+ voltage is equal to 100 volts and the collector is coupled to the tap 365 on transformer 364 at a 5 percent point). At this instant, the base to emitter junction will be forward biased and transistor 355 conducts. It is seen that the anode voltage of diode 356 is at approximately +0.7 volts and its cathode which is coupled to terminal 366 is at a less positive voltage. Diode 356 begins to conduct during the latter portion of trace as illustrated by the current waveform diagram shown in FIG. 4c.
During the latter portion of trace, the transistor tends to saturate and the collector voltage at terminal 355c tends to decrease. As this occurs, more current will flow from the B+ terminal through the upper portion of transformer 364. Due to the relatively tight coupling of the segments of transformer 364, terminal 366 experiences a decrease in voltage which controls the forward bias applied to diode 356 to shunt sufficient drive current to hold the transistor 355 out of saturation. The collector voltage of transistor 355 is thus held at some preselected value depending on the location of tap point 365 on transformer 364. Since transformer 364 is utilized, terminal 366 will remain at a low voltage during the latter portion of trace as shown in FIG. 4a, and diode 356 will be forward biased during the application of a positive drive signal to terminal A. As before, the base drive current will increase and diode 356 conduction will decrease generally as shown in FIGS. 4c and 4d during the latter portion of trace. At time t 2 in FIG. 4, a negative drive pulse is applied to the circuit which initiates the retrace interval of the deflection cycle.
Although the specific embodiments of the invention are illustrated in the horizontal deflection output stage of a black and white television receiver, the invention has equal applicability to other deflection systems and may be utilized in a color television receiver.