DE1041612B - Circuit arrangement for generating a saw tooth current through an inductance - Google Patents

Description

GERMAN

The invention relates to a circuit arrangement for generating a sawtooth current by an inductance, d. H. on sawtooth generator circuits, time base circuits and the like.

Such circuits can be used, among other things, to generate sawtooth currents for magnetic Beam deflection in a cathode ray tube, e.g. B. in television, find application. Known circuits of this kind act in such a way that a practically constant voltage is applied to an inductor is coupled to the deflection coils or consists of the deflection coils, so that a linear Increase in current in the inductance occurs during the trailing edge of the tooth tooth. During the return the current in the inductor is blocked by a high vacuum or "hard" tube interrupted, which acts as a switch in series with the inductance.

The current in the tube thus has a zero value at the beginning of the trace and reaches a maximum value at its end. The tube is sharply blocked while this maximum current flows, so that the return flow is initiated. This leads to a reversal of the current in the inductance up to a maximum value opposite sign, whereupon the next outward run begins. Usually this can Reverse current or a correspondingly transformed current flow through an auxiliary diode.

The interrupter must lock sharply, and in this regard a hard tube, e.g. B. a pentode tube, well usable. Switching means, such as transistors and thyratron tubes, could indeed have the necessary Allow currents to pass through, but these cannot suddenly be blocked while a current is flowing unless another current path is available. Such switching means can, however Conducted faster than blocked, and they can with a very low voltage drop let through strong initial currents.

The invention relates to a circuit arrangement in which the relatively rapid conduction is used by switching means that can be made conductive faster than blocked. This can be done by such an effect of the switch can be achieved that the switch is conductive and during the return is blocked during the forward movement of the sawtooth.

Such a type of circuit has already been described in German patent specification 876 730, where a thyratron tube is used as a switch.

It is also known from US Pat. No. 2,512,400 to apply a current pulse by means of a gas discharge tube to send through an auxiliary transformer and thereby cause a voltage pulse, through the one-winding transformer circuit arrangement

to generate a sawtooth current

through an inductor

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Great Britain June 21, 1955

Derek Robert Skoyles, London,
has been named as the inventor

mators and inductance connected in series with the battery caused a sharp increase in current will. The drop in the current during the sawtooth tracking is thereby caused by the parallel connection of a Diode linearized in series with an i? C element.

Such an arrangement, however, means a considerable effort and a often disruptive strong one Load on the supply source while the current is flowing through the auxiliary transformer.

In a circuit arrangement for generating a current through an inductance, in which during the Kickback is forced a maximum value of the current in the inductance by applying a high voltage becomes and during the run a low voltage of opposite polarity. preferably via a diode connected to the inductance, in such a way that the current flows during the outgoing flow decreases to a minimum, these disadvantages are avoided and a large ratio is obtained the amplitude of the sawtooth voltage to the voltage of the supply source and a simple structure as well as good linearity if, according to the invention, a capacitor is used during the trace is charged, which is parallel during the kickback via a controlled switch of the inductance is laid.

By using a capacitor that is gradually charged during the run, the voltage source itself becomes pretty even

809659/338

3 4

and little burdened; in particular the influence as well as for the capacitor is in the meaning of

their somewhat noticeable internal resistance to the transfer of energy to or from one of these

Current pulse switched off, so that a very fast reactance is used.

Setback with a significant increase in current generated The means of creating a practically constant

can be. 5 Voltage to the inductance during its development

A transistor is expediently used as a switch;

in the case of the current preferably via its emitter-col- battery connected in series with a rectifier

lektor-stretch, which is known to exist, which rectifier a discharge of the

has very low resistance. Capacitor across the battery. Which he-

In a circuit according to the invention the span io mentioned means can also consist of one with one Voltage source preferably such a rectifier connected in series to a capacitor resistor Capacitance connected that he stand while standing, which is parallel to a storage capacitor The sawtooth runs through this voltage source, which is large enough to be practically charged on is and is during the return and stanten, with the during the scan at the Induküber the switching element due to the inductance in reactivity matching voltage sonanz discharges, the discharge circuit being kept charged in such a way. Furthermore, the is to create the means from a transformer coupling mentioned after the end of the discharge of the capacitor and during the trace between the inductance and the high-voltage endurance Current passes through the inductance, feed points of the charging circuit exist, so that the where he has a practically constant counter voltage at 20 linearly decreasing, back to the supply source Applies inductance. guided current a constant direct current flow

Such a circuit made peak voltage and through inductance possible. In the latter case

Current characteristics compared to the usual direction has the advantage that during the

Circuits have the following deviations: Outgoing energy as a result of a downstream of the supply source

When a peak voltage and a peak current 25 of the recirculated current are recovered; each-

are required for a known time base, but a rectifier is required to

Peak voltage during the current reversal to avoid that during the kickback when the

put the switch, and a current up to the peak value increases rapidly through the inductance, current-

increasing sawtooth current must be taken from the high-voltage supply source during a pulse

Part of the sampling or tracking period (between the 30th

half and full period depending on the execution

tion) flow through the switch. work properly but charging occurs

In circuits according to the present invention of the capacitor preferably in resonance via a

there will be peak voltages on the switch during the charging reactor with which this capacitor

Sampling or trace period built up and cause 35 is tuned to such a frequency that a

therefore high voltages on the switch for a long time. half period corresponds approximately to the stroke.

Furthermore, the peak current for the same peak span is the circuit for the magnetic deflection

voltage twice as large, but only takes a lot of the beam from a cathode ray tube, e.g. B. for

shorter time (if the circuit is used for the same television line deflection, the

Peak current is set up like a known switching 40 main inductance, if desired only from the output

tion, the peak voltage is twice as great). Steering coil or consist of the deflection coils.

The energy loss in the switch is proportional to the fact that the sawtooth current in the inductance is always

Resistance of the switch, and in this regard is of the same sign, requires centering

a transistor much more suitable than a thyratron tube, the scanning on the screen in addition z. B.

since its minimum internal resistance is much smaller. 45 a transformer or capacitor coupling

In addition, losses due to the accumulation of holes in between the inductance and the deflection coil,

a transistor in circuits according to the invention in the case of application for television purposes

can be easily reduced, since the collector electrode or the like can be used in the switch by synchronizing pulses

current is interrupted at a point in time in which are actuated or also by a sawtooth oscilloscope

it has a low value. In fact, if the invention is used in an equalization

Conducting the current from the inductance to the current transformer or voltage converter

another current path after the switch is turned back.

Impact period when a current passes through the low The invention will be explained in more detail with reference to the drawing

Value and with only a slight increase in the explained.

applied voltage are blocked in contrast to the 55 In Fig. 1, a simple and general practice of blocking at peak current in an eye guidance form of the circuit has a capacitor CI ₃ view faster increase in voltage. during the forward run of the sawtooth by means of

The switch can e.g. B. consist of a transistor or a high voltage source via a charge from a thyratron tube, as it is charged in post-impedance Z, and an inductance will be explained in more detail below. 60 LI _{3 over} which the capacitor C1 resonates

The capacitor can be charged in parallel to the series circuit if a switch SW during the reverse

the inductance and the switch. Stroke can also be closed. During the run,

the switch parallel to the series connection of a cond. H. discharges while the switch is open

capacitors and an inductance (the latter is the inductance L 1 over means V ₃ the during

are hereinafter referred to as the "main capacitor" and 65 of the continuous current through the inductance

"Main inductance" denotes where a confusion represents a discharge path. Furthermore, the means V

by adding auxiliary or other reactances, a practically constant voltage of the inductance

can occur). L 1 to. A rectifier D 1 is in series with the

Where appropriate, the terms “up” are used to mean V ₃ to avoid C 1 going directly over

charge "and" discharge "both for the inductance 7 ° which discharges means V instead of via L 1.

If the charging of Cl has to take place in resonance, the impedance Z consists of a charging choke coil with which the capacitor C1 is tuned to a frequency such that half a period corresponds approximately to the trace.

Fig. 2 shows a circuit in which the switch SW is parallel to the series connection of the capacitor C1 and the inductance L 1 instead of in series with the inductance mentioned.

In the two circuits according to FIGS. 1 and 2, the means V can consist of a battery or of a resistor bridged by a capacitor of very high value. The latter solution is applied in FIG. 3, which shows a circuit similar to that of FIG. 1, in which the switch SW consists of a pnp junction transistor T. FIG. An electrolytic capacitor C 2 is bridged by a resistor R , which represents a current path without which the discharge of the current from the inductance L 1 would be prevented, since the capacitor C 2 is charged to the peak voltage that occurs at Ll. In addition to avoiding a direct discharge of Cl via R, the rectifier D1 also prevents the capacitor C 2 from being discharged by resonance with a choke coil L 2.

The capacitor C 1 is charged in resonance for half a period via the charging choke coil L 2 and possibly via a rectifier D 2. The latter is only required if the oscillation frequency of L2-C1 is such that half the period is shorter than the trace otherwise Cl would discharge back into L 2.

The mode of operation of the circuit according to FIG. 3 will now be described with reference to the curves of FIG.

It is assumed that at the end of a run-out, at time i ₀ , no energy remains in L1, while Cl is already charged twice with the high voltage (curve α of FIG. 4) via L 2 in resonance to a voltage Vl. If the transistor T is opened at the moment t _Q , this capacitor voltage V _Cl starts with a negative peak value equal to 2 HT and decreases sinusoidally during the kickback t _o -t ₁ , as the capacitor Cl discharges via the inductance L1 (L 2 is in reality parallel, but is large compared to Ll; its influence is therefore neglected).

The voltage remains sinusoidal until it just becomes positive with a value ν (Fig. 4, curve α); however, Dl then conducts current and allows the current through inductance L1 (L _Ll , curve d) to follow another path via resistor R and capacitor C 2 (means V) instead of the path via switch T. After time t _x the current flows through the inductance L1 via the means V and decreases linearly because a practically constant voltage ν is applied to this inductance through the means V. As a result of the linearity of this decrease, the current through the inductance L1 can cause a sampling during the entire trace, from the moment J ₁ to the next moment t ₀ .

As a result of the presence of the other path via i? -C2, the transistor T can be blocked without interrupting the inductive current, so that the energy loss through the accumulation of holes in the transistor is reduced to a minimum. The transistor T must be conductive during the entire setback and can remain open during an initial part of the trace, but in this state it will have a tendency to interfere with the recharging of the capacitor C1, and it is therefore desirable that the transistor T so soon as possible after the end of the setback.

While the inductance L 1 delivers its energy to the means V , the capacitor C1 is charged again in resonance to a value 2 HT (as shown in the curve α), in a time determined by L2 and Cl.

In addition to the above-mentioned curves α and d , curve b shows the changes in voltage V _Ll across inductance L 1, curve c shows voltage Vj across switch T , and curve e shows current I _Dl through rectifier D1. Furthermore, the curve f shows the emitter-collector current I _{T of} the transistor, approximately equal to the difference between the currents I _Ll and Id _{1 of} the curves d and c.

When the current through inductance L approaches zero _{at an instant i 0} (curve d), switch T is closed again and the cycle is repeated.

The transistor T is opened by the leading edges of negative pulses which are applied to a pulse input point P and blocked by the trailing edges of the same. In 405-line television applications of the circuit according to FIG. 3, these pulses have a duration of 12 to 14 \\. Se.c with a duration of the trace of about 85 μβεα

The one between the collector electrode and the emitter electrode of the transistor during kickback or at the beginning of the same applied voltage difference preferably has a value that at least at the beginning of the setback period is sufficient to cause an avalanche replication of the Bring about charge carriers by collision in the exhaustion layer of the collector electrode. The opening process is thus accelerated, with the current through the transistor building up more quickly and its voltage drops faster, so that a power transistor to act much faster can be brought about than without using the "avalanche" effect.

Furthermore, one can determine the voltage between the collector electrode and the emitter electrode of the transistor by switching a capacitor of z. B. a few thousand pF between the electrodes mentioned can be reduced practically to zero. Such a capacitor is used to store a sufficient amount Number of charge carriers to maintain the discharge across the transistor until whose voltage has decreased to the desired low value.

5 shows a circuit in which the means V contain a transformer coupling which is arranged between the inductance and the high-voltage supply points of the charging circuit, so that the linearly decreasing current fed back to the supply source brings about a constant DC voltage across the inductance L1. In such a device, as mentioned above, energy is recovered during the run by means of a current which is fed back to the supply source, but a rectifier D 3 is required to avoid that during the kickback period when the current through the inductance L1 increases rapidly, current pulses are taken from the high-voltage supply source.

FIG. 6 shows a circuit similar to that of FIG. 3, in which the p-ni-p interface transistor is replaced by a thyratron tube, the sign of the high voltage being reversed accordingly

will. The grid of the thyratron tube is controlled by means of positive pulses which are applied to point P instead of the negative pulses required for the base electrode control in FIG.

If the circuit is used to record a scan on a cathode ray tube, centering the scan on the screen can e.g. B. by means of a transformer coupling between the inductor L1 and the deflection coils or by an AC coupling via a large capacitor C 3, as shown in Fig. 7, where the coils are labeled Ld.

So far, the operating conditions of the transistor T have not been examined in detail, and preferred conditions for television applications in the case of a boundary layer transistor such as the transistor T of FIG. 3 are now being considered.

If the base electrode of a boundary layer transistor is kept somewhat positive, a much higher voltage than the normal reverse voltage (e.g. about ten times the normal operating voltage for a 2 W transistor) can be applied to the collector-emitter electrode path. without much electricity flowing. If a current, even if a very small current, is sent through the base electrode, the collector current and the energy loss of the collector electrode would become too great if the collector electrode voltage could not drop to a value that is significantly lower than the voltage originally applied . In the present case, the voltage across the transistor T decreases as a result of the voltage drop across the inductance L1 connected in series with the transistor. As a result, the gain of the transistor T is increased to a very high value in this limited range of base electrode currents and voltages. This fact enables a very high rate of voltage decrease across T, which is again favorable for the use of the circuit in television time base circuits for magnetic line deflection. In order to achieve maximum efficiency, not only a small current is sent through the base electrode, but this electrode is controlled very negatively in order to ensure that the transistor works in the "knee" or "saturation" state, which is achieved by means of a regenerative feedback or by means of an external generator.

Claims (7)

Patent claims: 1. Circuit arrangement for generating a sawtooth-shaped current through an inductance, in which a maximum value of the current in the inductance is enforced during the kickback by applying a high voltage and in which a low voltage of opposite polarity, preferably via a diode, on the during the trace Inductance lies in such a way that the current decreases to a minimum value during the outward run, characterized in that a capacitor (Cl) is charged during the outward run which is activated during the return via a controlled switch (SW) of the inductance (L 1 ) is laid in parallel. 2. Circuit arrangement according to claim 1, characterized in that a transistor is used as the switch serves. 3. Circuit arrangement according to claim 1 or 2, characterized in that the emitter-collector path of a transistor is used as the controlled switch, which is controlled at the base by pulses. 4. Circuit arrangement according to claim 1 to 3, characterized in that the capacitor (Cl) and the inductance (Ll) are dimensioned so that that the period of their natural oscillation is about four times the kickback time of the sawtooth current amounts to. 5. Circuit arrangement according to one of the preceding claims, characterized in that A charging choke (L 2) is switched on in the charging circuit of the capacitor (Cl) and is dimensioned in this way is that the resonance between the inductor (L2) and the capacitor (C 1) at one frequency whose half period corresponds approximately to the trace duration. 6. Circuit arrangement according to one of the preceding claims, characterized in that in the charging circuit of the capacitor (V 1) a choke is switched on in series with a rectifier permeable to the charging current and that preferably the resonance between the choke (L 2) and the capacitor ( Cl) is at a frequency whose half period is less than the trace duration. 7. Circuit arrangement according to one of the preceding claims, characterized in that the inductance (Ll) is coupled to an up transforming winding (LS) which is in series with a diode (D 3) on the supply source (HT) , such that the supply voltage also serves to linearize the trace (Fig. 5). Considered publications:
U.S. Patent No. 2,512,400. 1 sheet of drawings 809 659/338 10. 5S