US2185363A - Thermionic valve circuits - Google Patents

Description

Jan. 2, 1940. E. L. c. WHITE 2,185,363

THERMIONIC VALVE CIRCUITS TIME POTE NTI AL INVENTOR EL. C. WHITE TIME A T TOR/VE) Patented Jan. 2, 1940 'rnnamomc VALVE cmourrs Eric Lawrence Casling White, Hillingdon, lingland, assignor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application December 8, 1937, Serial No. 178,640 In Great Britain December 12, 1936 6 Claims.

This invention relates to thermionic valve circuits such as are employed in oscillation generators or the relaxation oscillator type which are frequently employed for the purpose of generat- 6 ing saw-tooth voltage waves or oscillators of the multivibrator type which may be employed for frequency division or frequency multiplication or for counting purposes.

In the usual type of multivibrator circuit, two

10 thermionic valves are provided, the anode of one valve being coupled to the grid of the other and the anode of the latter valve being coupled to the grid of the first valve. The valves are arranged in such a manner that one valve inbeu coming conducting renders the previously conducting valve non-conducting.

These circuits may be employed for discharging periodically a condenser which is connected between the anode and cathode of the first valve, the condenser being charged in a manner dependent upon the particular use of the circuit. When employed for the purpose of generating voltages of saw-tooth wave form, the condenser is usually charged substantially continuously through an impedance connected to a suitable source of current or through a diode or other suitable means, and when employed for frequency division or for counting purposes the condenser is charged in steps under the control of applied pulses.

It is the chief object of the present invention to provide a new or improved circuit suitable for use for the above and other purposes.

According to the invention a thermionic valve circuit comprising a condenser having one plate connected to a point of substantially fixed potential and adapted to be charged or discharged at a desired ratethrough a suitable device, so that the potential relative to ground of the other plate rises at said desired rate, to some value at which it is caused to be respectively discharged or charged through the grid-cathode space of a valve to the grid of which the said other plate is connected, the said valve interacting with a further valve .to produce sudden transitions of the cathode potential of said valve between predetermined upper and lower limits, whereby the charge. on he condenser is rapidly restored to I its initial value and then the circuit restored to w the condition in which the condenser may be charged or discharged at the desired rate.

In carrying out the invention, the thermionic valve circuit which is adapted to discharge or to charge a condenser arranged to be respectively 55 charged or discharged either through an impedance' or in steps under the control of applied pulses, comprises two valves, the anode of one of which is coupled to the control grid of the other and through a resistance or inductance to a source of anode current of which the negative end is earthed, whilst the cathode of the one valve is connected directly to the cathode of the other and through a resistance or inductance to earth, and the condenser, which is adapted to be discharged or charged, is connected between 10 the control grid of the first-mentioned valve and a point of fixed potential such as earth, or alternatively the high voltage line. the arrangement being such that the valves interact so that when one valve is conducting the other is renl5 dered non-conducting.

The valves are chosen and arranged so that the second passes a considerably greater current than the first. The potential of the cathodes thus undergoes transitions between two limits according to which or the valves is conducting and passing its current through the resistance in the common lead of said cathodes. With such an arrangement the condenser is discharged or charged as soon as grid current flows in the grid circuit of the associated valve, i. e., as soon as the cathode potential falls below the grid potential of said valve. The coupling between the anode of the one valve and the grid of the other valve is preferably of the resistance-capacity typ a leak resistance being provided between the grid and cathode of the second-mentioned valve. The particular disposition and manner of charging or discharging of the condenser depends upon the type of circuit to which the invention is applied.

In order that the said invention may be clearly understood and readily carried into effect it will now be described in detail with reference to the accompanying drawing in which- Fig. l is a diagram of a circuit constructed in accordance with the preferred form of the invention,

Fig. 2 is a diagram of a modification of a part of the circuit shown in Fig. 1,

Fig. 3 is a further modification of part of the circuit shown in Fig; 1 and Figs. 4 and 5 are explanatory diagrams. Referring to Fig. 1 the circuit comprises twovalves l and 2, which, in the example shown,

are of the triode type, the anode of the first valve being connected through a resistance 3 to the positive terminal of an associated source of anode current indicated by a battery 4, the anode also being connected through a coupling condenser 5 to the control grid of the valve 2. The anode of the valve 2 is directly connected to the positive terminal of the source of anode current whilst the two cathodes of the valves are directly connected together, a resistance Ii being provided between the point of connection of the two cathodes and earth, as shown. A leak resistance I is provided between the control grid of the valve 2 and the cathodes of the valves. The condenser, which is arranged to be rapidly discharged through the grid circuit of valve I, is indicated at 8, and is connected in the grid circuit of valve I between the control grid and earth.

In the example shown, the condenser 8 is arranged to be charged at a desired rate through a resistance 8, one end of which is connected to the condenser 8, whilst the other end is connected to the positive terminal of the source of anode current 4. During operation of the circuit, the condenser 8 is slowly charged through the resistance 9 and is suddenly discharged, as hereinafter more particularly referred to, producing a voltage of saw-tooth wave form. Instead of charging the condenser 8 through the resistance 9, it may be charged through some other high impedance, such as a saturated diode for producing a more linear saw-tooth wave or a choke coil. The time constant of the condenser 8 and the charging device controls the form of the rising voltage across the condenser 8, whilst the duration of the charging period of the condenser 8, that is to say of the slow rising portion of the saw-tooth wave, depends on the potential to which the cathode of the valve I is raised by the anode current of the valve 2 flowing through the resistance 6.

The operation of the circuit will now be described with reference to Fig. 4.

The line G represents the saw-tooth potential appearing on the grid I8 of valve I to which the condenser 8 is connected. This represents the voltage across the condenser 8, that is between grid I8 and earth. The dotted line C represents the corresponding variation of potential of the cathode II of the valve I, and it will be seen that this makes sudden transitions between limits V1 and V2 corresponding to the respective potential drops across resistance 6 due to the anode current of either valve I or valve 2. A cycle of operations occurs as follows starting at the point 2| in Fig. 4.

At this point the condenser 8 has been discharged down to voltage V1 in, a manner to be described. Valve 2 has just become conducting and so the cathode II of valve I is at a potential V: such that valve I is effectively biased well beyond anode current cut-off. The condenser 8 is then charged up through resistance 9 by the high voltage source 4, as shown by the line 2I22-23. As the potential of grid I8 rises up towards that of the cathode II the effective grid bias of the valve I becomes less negative until at some point such as 22 the valve I starts to pass a little anode current. This results in a fall of potential of the anode I2 which is instantaneously applied via condenser 5 to the grid I3 01' valve 2, resulting in a decrease of anode current through valve 2 and resistor 6 whereby the potential of cathode II falls thus increasing the anode current of valve I and further lowering the potential of its anode I 2. The two valves thus react on each other by this cumulative process until the anode current of valve 2 decreases substantially to zero and the potential of cathode II falls to the value V1 corresponding to the passage through resistor 8 of the anode current of valve I only. It will therefore be seen that the potential of cathode I I undergoes a rapid transition from the value V2 to the value V1, as indicated in Fig. 4 by the line 282324. The potential of grid I8 continues to rise for a short distance beyond the point 22 until it becomes equal to the falling cathode potential at point 23; thereafter the grid tends to be positive with respect to the cathode, so that grid current flows and allows the condenser 8 to be rapidly discharged through the comparatively low resistance of the now conducting grid-cathode space and the resistance 8. In fact, the grid I8 follows the cathodedown to the potential V1 and the condenser is discharged down to V1 as indicated by the line 23-24. However, the nonconducting condition of valve 2 due to the sudden fall of its grid potential is not a stable one, since the condenser 5 charges up through grid-leak resistance 1 and the anode-cathode space of valve I (which is now conducting). The potential of grid I3 therefore starts rising again and valve 2 starts to conduct again, passing current through resistance 8 which raises the potential of cathode II, decreases the. anode current of valve I and causes its anode I2 to rise in potential. This potential rise is instantaneously communicated over condenser 5 to grid I3 of valve 2 causing a further increase of anode current of the said valve 2, which further raises the potential of cathode I I, and so on. This cumulative process causes a second rapid transition back to the original condition in which valve 2 is conducting, and valve I is biased back well beyond anode-current cut-off by the rise of potential of cathode II up to the value V2. The above rise of potential of cathode II is indicated in Fig. 4 by the portion 24--2| of line C and it will be seen that grid-current ceases at the point 24 and the condenser 8 starts charging up once more through resistance 8 as indicated, by the part 2425 of line G.

The cycle of operations just described is automatically repeated so that a train of saw-tooth oscillations of potential appears across condenser 8, between grid I8 and earth.

Figures 2 and 3, as stated above, show a modification of a part of the circuit shown in Figure 1. That part of the circuit shown in Figure l to be found at the left of the broken line may be replaced by Figure 2 or Figure 3, the four conductors shown at the right-hand portion of each of the figures being connected to the four conductors intersected by the broken line shown in Figure 1.

Referring now to Fig. 2, a further example of the invention is illustrated in which the condenser 8 is connected across resistance 9, :Ietween the grid I8 of valve I and the high potential end of the source 4, shown in Figure 1. Apart from this modification the circuit is the same as in Fig. 1. In this case the saw-tooth voltage of Fig. 4 appears between grid I8 and earthas before, while valves I and 2 interact in the same way and the potential of cathode II varies in the same way as shown in Fig. 4. The operation differs from that of Fig. 1, however, in that the condenser 8 is now discharged slowly through resistance 9 during the period that valve I is nonconducting untilthe grid I8 rises to the potential indicated by point 22 in Fig. 4, when the cathode II is suddenly lowered in potential as previously described and condenser 8 is rapidly charged up again by the source 4 through the temporarily 75 a1as,sas

conducting grid circuit of valve I. In this case it will be seen that the potential of grid 10 falls as the condenser it charges and vice versa, in contradistinction to the previous case Fig. 1. The condenser 8 will in this case (Fig. 2) have across it a saw-tooth voltage which is complementary to curve G in Fig. 4;this is indicated at G in Fig. 5.

It will be seen, however, that the circuits of Figs. 1 and 2 have the common features that one plate of the condenser is connected to a point of fixed potential while the other plate has a sawtooth variation of potential. It will be appreciated that the return stroke of the saw-tooth oscillation (23-44 in Fig. 4) will be very fast due to the trigger action of the circuit in lowering the potential of cathode I i.

According to a further feature of the invention for valve I there is chosen a multigrid valve such as a tetrode or pentode and one of the grids such as a screening grid is adapted to serve the purpose of the anode l2 of Fig. 1 or Fig. 2, while the required output wave form is taken from the anode proper which is connected to the source or anode current through some convenient impedance. This is illustrated in Fig. 3, in which the elements are numbered to correspond with those of Fig. 1.

The valve i is shown as a pentode and its screen grid M takes the place of the anode I! of Fig. 1, while an impedance i6 is connected in the circuit of the anode i5, from which the output potentials are taken.

For example impedance It may consist of a resistance and condenser in parallel, adjustment of which controls the amplitude of saw-tooth potentials taken from anode l5.

Where the invention is used forcounting or similar purposes it may be desirable to stabilize the point at which the grid potential of valve I is suddenly reduced by returning the grid-leak I in Fig. 1 to a point of fixed potential, such as a tapping on a potentiometer associated with the high voltage source 4.

Where the circuit is arranged for the purpose of counting pulses or for frequency division or multiplication, controlling pulses may be applied at a suitable point in the circuit and either in the positive or negative sense according to the particular point of application of the pulses.

I claim:

1. A circuit for producing current and voltage variations of saw-tooth wave form comprising a first and a second discharge device each including at least a cathode, a control electrode and an anode, means including a common resistance for connecting said cathodes to the negative terminal of a source of potential, resistance means for connecting the control electrode of said second device to said cathodes, means including a condenser for connecting the anode of said first device to the control electrode of said second device, means for connecting the anode of said second device to said source of potential, means including a resistance for connecting the anode of said first device to said source of potential, a condenser and a resistance connected in series across the source of potential, and means for connecting the control electrode of said first device to the junction of said last named resistance and condenser.

2. A circuit for producing current and voltage variations of saw-tooth wave form comprising a first and a second discharge device each including at least a cathode, a control electrode and an anode, means including a single resistance for connecting said cathodes to the negative terminal of a source of potential, resistance means for connecting the control electrode of said second device to said cathode means including a condenser for connecting the anode of said first device to the control electrode of said second device, means for connecting the anode of said second device to the positive terminal of said source of potential, means including a resistance for connecting the anode of said first device to said source of potential, means including a condenser for connecting the control electrode of said first device to the negative terminal of said source of potential, and means including a resistance for connecting the control electrode of said first device to the positive terminal of said source of potential.

3. A circuit for producing current and voltage variations of saw-tooth wave form comprising a first and a second discharge device each including at least a cathode, a control electrode and an anode, means including a common resistance for connecting said cathodes to the negative terminal of a source of potential, resistance means for connecting the control electrode of said second device to said cathodes, means including a condenser for connecting the anode of said first device to the control electrode of said second device, means for connecting the anode of said second device to said source of potential, means including a resistance for connecting the anode of said first device to said source of potential, and means including a condenser and a resistance for connecting the control electrode of said first device to the positive terminal of said source of potential.

4. A circuit for producing current and voltage variations of saw-tooth wave form comprising a source of potential, series means connected across said source including a first resistor, a condenser and a second and third resistor, a first and a second discharge device each including at least a cathode, a control electrode and an anode, means for connecting said cathodes to the junction of said second and third resistors, means for connecting the control electrode of said second device to the junction of said condenser and said second resistor, means for connecting the anode of said first device to the junction of said first resistor and said condenser, means for connecting the anode of said second device to the positive terminal of said source of potential, and a resistance and condenser one terminal of each of which is connected to the control electrode of said first device and the other terminals being connected to the source of potential.

5. A circuit for producing current and voltage variations of saw-tooth wave form comprising a source of potential, series means connected across said source including a first resistor, a condenser, a second resistor, a third resistor, a first and a second discharge device each including at least a cathode, a control electrode and an anode, means for connecting said cathodes to the junction of said second and third resistor, means for connecting the control electrode of said second device to the junction of said condenser and said second resistor, means for connecting the anode of said first device to the junction of said first resistor and said condenser, means for connecting the anode of said second device to the positive terminal of said source of potential, another condenser and resistor connected in series across said source of current,

and means for connecting the control electrode of said first device to the junction of said last named condenser and resistor.

6. A circuit for producing current and voltage variations of saw-tooth wave form comprising a source of potential, series means connected across said source including a first resistor, a condenser, a second resistor, a third resistor, a first and a second discharge device each including at least a cathode, a control electrode and an anode, means for connecting said cathodes to the Junction of said second and third resistor,

means for connecting the control electrode of said second device to the junction of said condenser and said second resistor, means for connecting the anode of said first device to the junction of said first resistor and said condenser, means for connecting the anode of said second device to the positive terminal-oi said source of potential, and means including a resistor and a condenser for connecting the control electrode of said first device to the said source of potential.

ERIC LAWRENCE CASLING WHITE.

positive terminal of 10

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