US2710353A - Blocking oscillator - Google Patents

Description

`Fume 7, 1955 B. DAMMERS ETAL 2,710,353

BLOCKING OSCILLATOR Filed Feb. 18, 1950 if l. :2U-max E BERNHARDUS sam-Anous DAMMERS ABRAHAM SEERTRUDA WILHELMUS UITJ'ENS IN V EN TOR5 2,710,353 Patented June 7, 1955 BLOCKING OSCILLATOR liernhardus Gerhardus Dammers and Abraham Geertruda Wilhelmus Uitjens, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., trustee Application February 18, 1950, Serial No. 144,944

3 Claims. (Cl. Z50-36) The present invention relates to a circuit-arrangement for producing a sawtooth current in a coil connected to the secondary of a transformer, the primary of which is included in the output circuit of a discharge tube, and more particularly to a circuit-arrangement for the production of sawtooth current wherein the voltage occurring across the secondary of the transformer during the sweep portion of the sawtooth current is rectified and the rectified voltage is made operative in the output circuit of the discharge tube.

In circuit-arrangements of this type it has hitherto been customary to supply to the control grid of the discharge tube a sawtooth voltage, or at least a voltage which increases after the unblocking of the tube which unblocking occurs upon exceeding a given threshold Value.

Due to this a very high anode-current is produced in the tube and if the tube is a screen-grid tube, the screengrid dissipation is also excessively high.

The principal object of the present invention is to provide a circuit-arrangement for the production of a sawtooth current wherein a different method of controlling the discharge tube is employed so that maximum anode current is reduced.

Another object of the invention is to provide a circuitarrangement for producing sawtooth current, wherein screen-grid dissipation of the discharge tube is reduced.

Still another object of the present invention is to provide a circuit-arrangement for the production of saw-tooth currents wherein the physical size of the discharge tube may be minimized.

Further objects of the invention will appear from the following description.

According to the invention, a substantially constant voltage unblocking the tube, which voltage is periodically interrupted by pulse voltages cutting ol the tube, is supplied to the control grid of the discharge tube.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing in which:

Figure 1 represents one embodiment of a circuit-arrangement according to the invention,

Figure 2 is a current diagram by means of which the operation of the invention will be explained, and

Figure 3 is a curve showing variation of the controlgrid voltage as a function of time.

Referring now to the drawing, and more particularly to Figure l, there is shown the basic elements of the circuitarrangement according to the invention for producing a saw-tooth current, comprising a pentode 1, the anode circuit of which includes a primary Z of a transformer 3. A coil 5 wherein the sawtooth current is produced, and which may be, for example, the deection coil of a cathode-ray tube is connected to a part of a secondary 4 of transformer 3.

One end of the secondaryv 4 is connected to the positive terminal of a direct current supply (not shown) which supplies a voltage Vb. The other end of secondary coil 4 is connected to the anode of a diode 6. The cathode of diode 6 is connected both to the end of the winding 2 remote from the anode of pentode 1 and, through a condenser 7, to the cathode of pentode 1.

When the tube 1 is made conductive, the primary 2 of the transformer is traversed by a sawtooth' current. During the sweep portion of this current, a voltage having the polarity indicated in the drawing is developed across the winding 4, with the result that the diode 6 becomes conductive and the condenser 7 is charged. This condenser is charged to a voltage approximately equal to the sum of the voltages of the direct current supply Vb and the Voltage occurring across the winding 4 during the sweep portion of the sawtooth current, so as to form a source of direct current supply of considerably higher voltage.

If the control at a control grid 8 of the pentode is effected by means of a sawtooth voltage by which the pentode is unblocked on exceeding a given negative bias, the current curves shown in Fig. 2 occur as a function of time.

The tube 1 is traversed by a current Ia as shown by the curve 9 of Fig. 2. This current has a maximum value Ia (max). The sawtooth current traversing coil 5, shown in curve 15 of Fig. 2, Varies between the Values I1 and +12, the value 114-12 being equal to 2 Imax if Imax represents the amplitude of the sawtooth current.

From Fig. l it appears that the voltage Es across the primary of the transformer is determined by where n represents the transformation ratio of the transformer.

From Fig. 2 it follows that:

2 q=g2=efticiency of coil plus transformer From both expressions it follows that:

Iafmax) X (Vb-Vu) =2ImaxXEsX LEM In order to make the left-hand member of (l) as small as possible:

1. K should be as small as possible which means that le (max) should practically not exceed I2,

2. The eiciency i7 should be made as high as possible by rendering coil 5 and transformer 3 as free as possible of losses.

3. The transformation ratio should approach as closely as possible to unity. To this end the pentode 1 should be controlled in a definite manner.

ince, in the circuit shown in Fig. 1, the two transformer windings are connected in series through the diode 6, and because the average primary and secondary currents should be equal to one another and because a further relation exists between the ampere turns in the two windings in connection with the sawtooth current supplied to coil 5, the transformation ratio in should not be chosen arbitrarily.

From this condition We may deduct the relation a=Q=ratio of the areas shown in Fig. 2 2 in the current diagram and b =%=relative current loss which occurs in 1 the condenser 7 shown in Fig. 1

Ix being the current leaking from condenser 7.

When it is desired that the transformation ratio should approach unity, a should be made as high as possible which means, as appears from Fig. 2, that the pentode should be controlled in such manner that the average anode current Ia approaches as closely as possible the maximum anode current Ia (max).

This is ensured by supplying the control grid of the pentode with a control voltage varying with time as shown in Fig. 3.

During the sweep portion of the sawtooth current traversing coil 5 in Fig. 1, a substantially constant unblocking voltage Vg is available at the control grid 8,

which voltage may, for example, be equal to the cathode potential of the pentode. During the fly-back, the tube 1 is cut of by a pulse voltage.

If the circuit-arrangement shown in Fig. 1 does not self-oscilate but is, for example, controlled by a preceding blocking oscillator, the negative voltage pulses appearing across the anode of the tube of the blocking oscillator may be supplied to the control grid of the pentode 1. The circuit-arrangement shown in Fig. 1 is self-oscillatory. To this end a positive feedback path is provided between a tapping 10 on the secondary of the transformer 3 and the control grid 8 of the pentode 1. This feedback path comprises a blocking condenser 11 and a resistance 12, which is preferably a variable re- BIBIXEI where the factor 1 K 1 -lb -la is determined by the method of controlling the pentode.

In the known method of control, the value of this factor is approximately 0.8 to 0.9, Whereas the use of the circuit-arrangement according to the invention permits a value lower than 0.4 to be attained. Owing to this, a stronger sawtooth current can be obtained with a materially lower pentode load.

VJhile we have described our invention in a speciiic use thereof and in a specic embodiment, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art Without departing from the spirit and scope of the invention.

We claim:

1. A circuit-arrangement for generating a sawtooth current, comprising an electron discharge tube having a cathode, a control grid and an anode, an input circuit intercoupling said cathode and said control grid, an output circuit intercoupling said cathode and said anode, a transformer having a primary and a secondary Winding, said primary winding being included in said output circuit, means to apply a positive potential to one end of said secondary winding, an output coil coupled in parallel with a portion of said secondary winding, means to apply a substantially constant potential to said input circuit to render said tube conductive thereby producing a voltage in said secondary Winding and a current ow in said output coil, a capacitive element interposed in said output circuit between said primary coil and said cathode, a rectiher element coupled to the other end of said secondary winding and to said output circuit between said primary Winding and said capacitive element to rectify said voltage, and apply the rectiiied voltage to said output circuit, and means to apply a pulse voltage to said input circuit periodically to render said tube nonconductive thereby to arrest current flow in said output coil.

2. A circuit arrangement, as set forth in claim l, wherein said means to apply a pulse voltage to said input circuit is constituted by feedback means intercoupling said secondary Winding to said input circuit.

3. A circuit arrangement, as set forth in claim 2, Wherein said feedback means includes a condenser connected in series with a resistor between a point in said secondary winding and said grid.

References Cited in the le of this patent UNITED STATES PATENTS 2,165,815 Rhea July 1l, 1939 2,250,686 Urtel July 29, 1941 2,512,543 Haantjes et al. June 20, 1950

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