482,370

PATENT SPECIFICATION

Application Date: Aug. 27, 1936. No. 23489/36.

Complete Specification Left: July 24, 1937.

Complete Specification Accepted: March 28, 1938.

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PROVISIONAL SPECIFICATION

Improvements in or relating to Oscillatory Electric Circuits

We, ERIC LAWRENCE CASLING WHITE, of 32, The Rise, Hillingdon, Middlesex, and ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, both British Subjects, do hereby declare the nature of this invention to be as follows:-

This invention relates to electric oscillatory circuits of the type employed for providing a time base in connection with cathode ray tubes for the purpose of deflecting the electron beam.

Many forms of circuit for generating voltages of saw tooth wave form for deflecting the electron beam in a cathode ray tube have been proposed and in some firms of such circuit a diode valve is operatively associated with deflecting coils and with an oscillator valve controlled by synchronising signals. An example of such a proposed circuit will be described more in detail hereinafter.

The object to the present invention is to effect economy in power consumed in oscillatory circuits of the type to which the invention relates and to prevent waste of power.

According to the present invention an oscillatory circuit for supplying deflecting wave forms for a cathode ray tube includes a valve in the output circuit of which is connected a winding coupled to deflecting means, a diode valve being connected across a portion of said winding and serving to control the passage of current through said winding. In a particular circuit arrangement embodying the invention the grid of a valve is fed with potentials of saw-tooth waveform by a blocking oscillator circuit and a winding in its anode lead forms the primary winding of a transformer, the secondary winding of which is constituted by the scanning coils of a cathode ray tube. The diode valve is connected in series with a parallel connected resistance and condenser combination across a portion of the said primary winding. The valve employed may be a pentode valve and in order to maintain the shape of the output current wave similar for all amplitudes, the amplitude of the voltage fed to the control grid of the pentode may be varied simultaneously with the voltage applied to the screening grid. A convenient means for effecting such simultaneous variation consists of a variable resistance connected in the common supply to the anode circuit of a blocking oscillator valve feed the pentode valve, and to the screen grid of the pentode.

In order that the nature of the invention may be more clearly understood a form of circuit embodying previous proposals will now be described in greater detail, together with an example of a circuit embodying the invention and reference will be made to the accompanying drawings in which:-

Fig. 1 is an oscillatory circuit showing a diode valve, part of a blocking oscillator circuit and scanning coils of a cathode ray tube arranged in a manner previously proposed.

Fig. 2 shows a voltage wave-form generated by the blocking oscillator circuit in Fig. 1.

Fig. 3 shows current wave-forms generated by the circuit of Fig. 1 and

Fig. 4 is an oscillatory circuit embodying the invention.

Referring to Fig. 1 of the drawing, the valve 1 of which only the envelope and anode are shown diagrammatically, forms part of a blocking oscillator circuit including condenser 2 and a resistance 6. While the valve 1 is non-conducting, the condenser 2 is being charged form a source of high tension voltage 5 through the resistance 6, in the anode lead of the valve 1. The control grid of a valve 7 is connected to the junction between the resistance 4 and condenser 3 and the anode circuit of the valve 7 includes the primary winding 8 of a transformer 9. Scanning coils 11 of a cathode ray tube (not shown in the drawings) are connected to the secondary winding 10 of the transformer 8. The anode of the valve 7 is connected directly with the cathode of a diode valve 12, the anode of which is connected through a resistance 13, shunted by a condenser 14 to the positive terminal of the H.T. source 5.

In the operation of this circuit, the blocking oscillator valve 1 generates a voltage wave form as shown in Fig. 2, the potential of the grid of valve 7 following this wave form. In Fig. 3 the curve A represents the wave form of the current passing through the valve 7, the curve B represents the current through the diode valve 12, and the curve C, the current through the primary winding 8. From the curve C it will be seen that the current through the primary winding builds up to practically the peak value of the current passing through the valve 7 as shown in curve A, and then reverses in a half cycle of the natural frequency of the stray capacities from anode of 7 to earth with the inductance of the scanning coils 11 stepped-up by the transformer 8. The current reversal is however, not complete owing to various losses, and as shown in the drawings the actual reversal may be only of the order of 50%. In the circuit described it is necessary to maintain a considerable potential across the resistance 13, this being determined by the mean current through the diode valve 12, and considerable power is wasted in this resistance. Further, the source of H.T. supply 5 has to be of inconveniently high voltage.

In Fig. 4 the invention is shown applied to a circuit of the general form of Fig. 1, but with additional improvements. Thus, the cathode of the diode 12 is connected to a tapping point in the primary winding 8 of the transformer 9 and the upper end of this primary winding, instead of being connected directly to the H.T. source, is connected to the parallel resistance and condenser combination 13 and 14 which are connected in the anode lead to the diode valve 12 as in Fig. 1. A further alteration is in the connection of the positive terminal of the H.T. source directly to the anode of the diode 12 instead of to the upper end of the resistance and condenser combination.

It will be seen that the diode and resistance/condenser combination are connected across only a portion of the primary winding 8 and it is necessary that the ratio of the number of turns in that portion of the number of turns in the whole primary winding should be equal to or less than the ratio of the mean currents of the diode and pentode valves, so that the diode current, as increased by the turns ratio, is now greater than, or equal to the pentode current. when the currents are equal, the resistance 13 may be of infinite value and no power is consumed in it. Further, the voltage produced across the condenser 14 now adds to that of the source 5 as far as the pentode is concerned.

It is desirable to maintain the shape of the pentode current curve A similar for all amplitudes and accordingly amplitude control is effected by simultaneously varying the potential applied to the screening grid of the pentode valve and the amplitude of the saw tooth potential applied to the control grid of that valve.

This may be done by connecting a variable resistance 16 in series with the resistance 6 and the positive terminal of the H.T. source 5, the screening grid of the pentode valve 7 being connected to the junction between the fixed resistance 6 and variable resistance 16. It will be understood that other methods of effecting simultaneous variation of the values mentioned may be adopted.

Dated this 26th day of August, 1936.

F. W. CACKETT,

Chartered Patent Agent.

COMPLETE SPECIFICATION

Improvements in or relating to Oscillatory Electric Circuits

We, ERIC LAWRENCE CASLING WHITE, of 32, The Rise, Hillingdon, Middlesex, and ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, both British Subjects, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

This invention relates to electric oscillatory circuits of the type employed for providing a time base in connection with cathode ray tubes for the purpose of deflecting the electron beam.

Many forms of circuit for generating voltages of saw tooth wave form for deflecting the electron beam in a cathode ray tube have been proposed and in some forms of such circuit a diode valve is operatively associated with deflecting coils and with an oscillator valve controlled by synchronising signals. An example of such a proposed circuit will be described more in detail hereinafter.

The object of the present invention is to effect economy in the power consumed in oscillator circuits of the type to which the invention relates and to prevent waste of power.

According to the present invention a circuit arrangement for supply a saw-tooth current waveform to an inductive load such as the deflecting coil of a cathode ray tube, includes a valve coupled to a primary winding which is coupled to the load and a diode or equivalent valve having a resistance in series therewith and connected across a portion of said primary winding or across a further winding coupled to said primary winding, the connection of said resistance and the ratio of the turns of that portion of said primary winding or of said further winding to the total turns in said primary winding being such that the average value of the current flowing through the diode during one complete cycle of said saw-tooth current waveform is equal to or greater than the average value of the current flowing through said valve during the same period with the result that the energy dissipated in said resistance is determined by the difference between the current flowing through said valve and the current flowing through said diode. In a particular circuit arrangement embodying the invention the grid of a valve is fed with potentials of saw-tooth waveform by a blocking oscillator circuit and a winding in its anode lead forms the primary winding of a transformer, the secondary winding of which is connected with the scanning coils of a cathode ray tube. The diode valve is connected in series with a parallel connected resistance and condenser combination across a portion of the said primary winding. The valve employed may be a pentode valve and in order to maintain the shape of the output current wave similar for all amplitudes, the amplitude of the voltage fed to the control grid of the pentode may be varied simultaneously with the voltage applied to the screening grid. A convenient means for effecting such simultaneous variation consists of a variable resistance connected in the common supply to the anode circuit of a blocking oscillator valve feeding the pentode valve, and to the screen grid of the pentode.

In order that the nature of the invention may be more clearly understood and readily carried into effect, a form of circuit embodying previous proposals will now be described in greater detail, together with an example of a circuit embodying the invention and reference will be made to the drawings filed with the provisional specification in which:-

Fig. 1 is an oscillatory circuit showing a diode valve, part of a blocking oscillator circuit and scanning coils of a cathode ray tube arranged in a manner previously proposed.

Fig. 2 shows a voltage wave-form generated by the blocking oscillator circuit in Fig. 1.

Fig. 3 shows current wave-forms generated by the circuit of Fig. 1 and

Fig. 4 is an oscillatory circuit embodying the invention.

Referring to Fig. 1 of the drawings, the valve 1 of which only the envelope and anode are shown diagrammatically, forms part of a blocking oscillator circuit including condenser 2 and a resistance 6. While the valve 1 is non-conducting, the condenser 2 is being charged from a source of high tension voltage 5 through the resistance 6, in the anode lead of the valve 1. The control grid of a valve 7 is connected to the junction between the resistance 4 and condenser 3 and the anode circuit of the valve 7 includes the primary winding 8 of a transformer 9. Scanning coils 11 of a cathode ray tube (not shown in the drawings) are connected to the secondary winding 10 of the transformer 8. The anode of the valve 7 is connected directly with the cathode of a diode valve 12, the anode of which is connected through a resistance 13, shunted by a condenser 14 to the positive terminal of the H.T. source 5.

In the operation of the circuit of Fig. 1 the blocking oscillator valve 1 generates a voltage waveform as shown in Fig. 2, the potential of the grid of valve 7 following this waveform. In Fig. 3 the curve A represents the waveform of the current passing through the valve 7, the curve B represents the current though the diode valve 12, due to the voltage drop across the coil 8 which arises as explained later in greater detail, and the curve C, the current through the primary winding 8. From the curve C it will be seen that the current through the primary winding builds up to practically the peak value of the current passing through the valve 7 as shown in curve A and then reverses in a half cycle of the natural frequency of the tuned circuit formed by the effective inductance of the coil 8 which is partly dependent upon the inductance of the scanning coils 11 stepped up by the transformer 9 and associated stray capacities. The current reversal is not however complete owing to various losses and as shown in the drawings the actual reversal may be only of the order of 50%. The curve C is shown rising to a peak value corresponding with the peak value of the saw-tooth voltage waveform of Fig. 2 and represents current flowing in the coil 8 in the direction from the high potential end to the low potential end, this current then falling to below zero, the curve subsequently rising and representing a decreasing current flowing in the reverse direction through the coil 8 and also through the diode 12 until point is reached at which the coil current passes through zero and again increases. The first part of the curve B, therefore, represents current flowing through the coil 8 and the diode 12, the remaining portion of the curve B showing that the diode current at this period does not continue to increase as does the coil current. The form of the curves A and B is repeated in succeeding cycles.

During the slow voltage rise on the grid of valve 7 there is a constant rate of change of current in the scanning coils 11 which represents a constant voltage difference across the primary winding 8. The voltage difference must be supplied from the H.T. battery 5 which must be large enough to provide the necessary high tension potential on the anode of valve 7 as well as the steady voltage difference. During the latter part of the slow voltage rise, energy from the high tension battery 5 via valve 7 is stored through the transformer in the scanning coils. During the first part of the curve B showing the conductive condition of the diode 12, the energy represented by the produce of this diode current and the steady voltage difference across the winding 8 is dissipated in the resistance 13, that is to say, all the energy from the high tension battery 5 which is stored in the coils is lost in the resistance 13 except for such energy as is lost in resistance, eddy current losses and dielectric losses of the coils and transformer. It is the object of this invention to reduce the power required for operating this circuit by reducing the loss in resistance 13.

In Fig. 4 the invention is shown applied to a circuit of the general form of Fig. 1, but with additional improvements. Thus, the cathode of the diode 12 is connected to a tapping point in the primary winding 8 of the transformer 9 and the upper end of this primary winding, instead of being connected directly to the H.T. source, is connected to the parallel resistance and condenser combination 13 and 14 which are connected in the anode lead to the diode valve 12 as in Fig. 1. A further alteration is in the connection of the positive terminal of the H.T. source directly to the anode of the diode 12 instead of to the upper end of the resistance and condenser combination.

It will be seen that the diode and resistance/condenser combination are connected across only a portion of the primary winding 8 and the tapping point on the transformer is adjusted until a point is found at which the ratio of the turns of that portion to the whole of the winding 8 is such that the auto transformer effect, when current flows through the valve 7, is such that the potential at the upper end of that winding is substantially equal to that of the high tension battery with the result that little or no current will flow in the circuit including the upper portion of the winding 8 the resistance 13 and the diode, and the valve current will flow only through the diode 12. When the valve 7 ceases to pass current the current in coil 8 decrease passing through zero in similar manner to that described with reference to Fig. 3, the current on reversal flowing through the diode 12. Thus current flows through the diode during almost the complete cycle of the applied saw-tooth waveform but through the valve during less than a complete cycle with the result that the diode current is at least equal to or is increased compared with, the anode current of the valve 7 so that the average diode current is slightly in excess of the average anode current. thus very little energy is dissipated in resistance 13 and this resistance, instead of carrying the whole diode current now carries the difference between the diode current and the valve current. as the terminal of the battery 5 is connected directly to the anode of the diode 12 instead of through resistance 13, fewer H.T. volts are required and the condenser 14 stores energy which provides power for overcoming the back e.m.f. of part of the winding 8.

The leakage inductance between that portion of the winding 8 across which the diode 12 is connected and the whole of the winding 8, should be kept as low as practicable so that during the forward strokes of the saw-tooth, when the valve 7 is beginning to take current the current reversal in the coil 8 shall be smooth and free from discontinuity due to the leakage inductance referred to.

It is desirable to maintain the shape of the pentode current curve A similar for all amplitudes and accordingly amplitude control is effected by simultaneously varying the potential applied to the screening grid of the pentode valve and the amplitude of the saw tooth potential applied to the control grid of that valve.

This may be done by connecting a variable resistance 16 in series with the resistance 6 and the positive terminal of the H.T. source 5, the screening grid of the pentode valve 7 being connected to the junction between the fixed resistance 6 and variable resistance 16. It will be understood that other methods of effecting simultaneous variation of the values mentioned may be adopted.

While in the arrangement described with reference to Figure 4 the diode 12 is shown connected to a tapping point in the winding 8, the diode may be connected with a separate winding coupled with the winding 8. Thus, the cathode of the diode would in such a case be disconnected from the tapping point in the winding 8 and connected to one end of the separate winding, the other end of the separate winding being connected directly to the lead connecting the upper end of winding 8 to the resistance/condenser combination 13, 14. The number of turns in the separate winding would be chosen to produce the same effect as the selection of the ratio of turns of the winding 8 across which the diode and resistance/condenser combination 13, 14 are connected, to the total turns in the winding 8.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

  1. A circuit arrangement for supplying a saw-tooth current waveform to an inductive load such as the deflecting coil of a cathode ray tube including a valve coupled to a primary winding which is coupled to the load and a diode or equivalent valve having a resistance in series therewith and connected across a portion of said primary winding or across a further winding coupled to said primary winding, the connection of said resistance and the ratio of the turns of said portion of said primary winding or of said further winding to the total turns in said primary winding being such that the average value of the current flowing through the diode during one complete cycle of said saw-tooth current waveform is equal to or greater than the average value of the current flowing through said valve during the same period with the result that the energy dissipated in said resistance is determined by the difference between the current flow though said valve and the current flowing through said diode.
  2. A circuit arrangement according to Claim 1, wherein a condenser is associated with said diode in such a manner that the current from the diode stores energy in the condenser, the energy so stored being used to assist, or to provide some of the energy causing, the flow of anode current in the valve.
  3. A circuit arrangement according to Claim 1 or 2 wherein the input circuit of said valve is coupled with a saw-tooth waveform generating circuit, and said winding constitutes the primary winding of a transformer, the secondary winding of which is connected in circuit with the deflecting coils of a cathode ray tube.
  4. A circuit arrangement according to any one of the preceding claims wherein said valve is of the screen grid or pentode type, and wherein in order to maintain the shape of the output current wave substantially similar for all amplitudes, means are provided for varying simultaneously the amplitude of the voltage fed to the control grid, and the voltage applied to the screening grid.
  5. A circuit arrangement according to Claim 4 wherein a variable resistance is connected I the common supply lead to the anode of a blocking oscillator valve feeding the input circuit of said screen grid or pentode valve and to the screening grid of that valve.
  6. A circuit arrangement for supplying a saw-tooth deflecting waveform substantially as described with reference to Fig.4 of drawings filed with the Provisional Specification.

Dated this 23rd day of July, 1938.

F. W. CACKETT,

Chartered Patent Agent.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. – 1938.