GB2071449A

GB2071449A - Horizontal deflection circuit

Info

Publication number: GB2071449A
Application number: GB8105204A
Authority: GB
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1980-03-05
Filing date: 1981-02-19
Publication date: 1981-09-16
Also published as: DE3026466A1; FR2477813A2; DE3026466C2

Abstract

A transistorised horizontal deflection circuit comprising an input regulator switch (T1), an input inductance, a deflection coil (L2), a recovery capacitor (C2), a retrace capacitor (C1) and a switching transistor (T2). The input switch (T1) is switched on under the control of a regulation circuit (2) for a period which depends on the amplitude of a supply voltage applied to terminals (1) from an unregulated source. The input inductance is provided by the leakage inductance existing between an additional primary winding (L%1) and a secondary winding (L%3) of a high voltage transformer (TRHT), which windings may be wound on opposite legs of a magnetic core. Hence the deflection circuit and high voltage outputs are d.c. isolated from the input. <IMAGE>

Description

SPECIFICATION Horizontal deflection circuit This invention refers to a transistorized horizontal deflection circuit, for television receivers, comprising, connectible in series with an unregulated source of supply voltage, an input switch, an input inductance, a deflection coil and a recovery capacitor and, in parallel with the deflection coil and recovery capacitor, on the one hand a retrace capacitor and on the other hand the collector-emitter path of a switching transistor, with the input switch being switched on under the control of a regulation circuit for a period which depends upon the amplitude of the supply voltage.

Such a circuit is described in French Patent Application No. 77 28765 published on 20th April 1 979. The main advantages of such a horizontal deflection circuit are very low cost, low losses and therefore excellent efficiency. This is achieved by injecting just the required energy into the horizontal deflection circuit and eliminating supply voltage variations by varying the time during which this voltage is applied to the said deflection circuit.

However, it may be desirable to isolate most of the horizontal deflection circuit components from the mains supply. One possible solution, of course, would be the use of a power transformer, but that is an expensive solution. Another solution has been proposed in the case of a conventional horizontal deflection circuit containing an input inductance and a switching inductance in series with the power supply. This consists in designing these two inductances in the form of a transformer. Apart from the fact that this solution is applicable only to this type of conventional deflection circuit, once again an extra transformer must be provided.

An object of the present invention is to avoid these problems while obtaining isolation with respect to the mains supply.

A further object of the present invention is to provide a horizontal deflection circuit isolated from the mains supply, which is inexpensive and without the use of an extra transformer.

According to the present invention, there is provided a transistorized horizontal deflection circuit comprising connectible in series with an unregulated source of supply voltage, an input switch, an input inductance, a deflection coil and a recovery capacitor and, in parallel with the deflection coil and the recovery transistor, on the one hand a retrace capacitor and on the other hand the collector-emitter path of a switching transistor, and the circuit further comprising a regulation circuit, wherein the input switch is switched on in use of the circuit under the control of the regulation circuit for a period which depends on the amplitude of the supply voltage, wherein the circuit includes a high voltage transformer having a first primary winding, an additional primary winding connectible in series with the source and the input switch and secondary winding connected in parallel with the deflection coil and the recovery capacitor, the input inductance being comprised by the leakage inductance between the additional primary winding and the secondary winding, energy being supplied to the rest of the deflection circuit via the transformer and its leakage inductance.

If the high voltage transformer is a conventional high voltage transformer in which all the windings are located on the same leg of the magnetic core, the winding, which usually serves as the primary, can remain connected in the same way with a capacitor in parallel with the deflection coil and recovery capacitor in series, and the additional primary winding can be placed on the opposite leg of the said magnetic core.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic drawing of an embodiment of horizontal deflection circuit according to the present invention, and Fig. 2 shows the arrangement of the windings on the high voltage transformer of the circuit of Fig. 1.

Fig. 1 is a schematic diagram showing a horizontal deflection circuit according to the present invention which is derived directly frcm the circuit described in the French Patent Application No. 77 28765. For this reason, we have retained the same reference numerals as those used in that application for identical components.

It can be seen that an unregulated power source from the mains supply voltage at terminals 1 is used. This voltage is rectified by diode D1 and filtered by capactior C3 before being applied to input switch T1, consisting of transistor T3 and diode D3 connected in parallel head to tail. The input switch T1 is connected in series with a primary winding L' 1 of a high voltage transformer TRHT between the terminals of the power source.

Winding L'2 of the transformer TRHT supplies in the usual way, after rectification, the very high voltage HT required by the picture tube (not shown).

Winding L'3 which, as it will be seen later, can be the primary winding used in a conventional horizontal deflection circuit, is connected in series with capacitor C4, in parallel with the series connected deflection coil L2 and recovery capacitor C2, as well as in parallel with the retrace capacitor C1 and the collector-emitter circuit of switching transistor T2, the latter being driven by a transformer TR1 whose primary receives the control pulses at the sweep frequency furnished by an oscillator (not shown).

A regulation circuit 2, in accordance with the French Patent Application, controls the input switch T1 by means of a small transformer TR2 and receives information indicating whether the conduction period of the input switch T1 is correct and permitting this period to be regulated. This information is obtained at the junction point of winding L'3 and capacitor C4, but could just as well be obtained at the junction point between L2 and C2 as in the French Patent Application or else at the collector of transistor T2.

Lastly, a conventional starting circuit has also been shown using, as usual, a starting transformer TR3 supplying, at switching on, a voltage rectified by diode D2 used to start the circuits not yet supplied by the horizontal deflection circuit and more especially from a secondary winding (not shown) of the high voltage transformer TRHT. In addition, a circuit 3 is provided to protect switch T1 against voltage surges and it contains an additional winding L'4 which returns the unconsumed energy to the source in case of failure (failure of transistor T2, for example).

Basically, the present invention comprises replacing the input inductance which, in the circuit of the French Patent Application, was connected between the input switch T1 and the collector of switching transistor T2 by the leakage inductance of transformer TRHT, with the designed selfinductance of winding L' 1 being very high. Thus, when switch T1 is closed, energy is stored in the space of transformer TRHT. The operation of the horizontal deflection circuit according to the invention is exactly the same as that described in the present patent application.

As can be seen, only the components, located inside the largest box formed of dashed lines, are not isolated from the mains supply. All the rest of the circuit is isolated without the need for an additional transformer.

In a conventional high voltage transformer, the primary and secondary windings are all wound on the same leg of the magnetic core. According to the present invention, the only modification needed to such a transformer is the addition of an extra primary winding L'1 wound on the opposite leg of the magnetic core (Fig. 2).In this case, the ex-primary winding L'3 remains connected in exactly the same way to the deflection circuit, L2, C2, C1, TR2. The fact that the extra primary winding is wound on the opposite leg of the magnetic core, on the one hand, permits safety standards concerning insulation to be very easily satisfied, due to the distance between L' 1 and the other windings, and, on the other hand, due to the low coupling between L' 1 and the other windings, provides a low coupling capacity and therefore very little radiation towards the mains supply.

In addition, the technological configuration can be designed so that all components, not isolated from the mains supply, are not located on the main printed circuit CI (Fig. 2) which, then, contains only the isolated part of the circuit. Thus, for example, the outputs of windings L'2, L'3 . ..

can be oriented towards the bottom towards the printed circuit Cl, whereas the outputs of winding L'1 are insulated wires oriented towards the top.

Since there is no direct current flowing through the secondary circuit L'3, no premagnetization occurs and no harmonic tuning is required.

Furthermore, it will be noted that the system is self-compensated concerning the effects of output variations on picture size due to the concomitant variation on the very high voltage and the sweep amplitude.

It is very easy to select component ratings for those parts located on the primary side (L' 1, T3, etc.) to make the system operate very efficiently on a 12-volt or 24-volt d-c supply. A converter is then not required.

Lastly, it can also be noted that the regulation circuit can, in addition to its main function, provide perfect protection in case of secondary short circuits, including the high voltage section. It also guarantees good operation for systems with various frequencies (625/819 lines, for example).

Claims

1. A transistorized horizontal deflection circuit comprising connectible in series with an unregulated source of supply voltage, an input switch, an input inductance, a deflection coil and a recovery capacitor and, in parallel with the deflection coil and the recovery transistor, on the one hand a retrace capacitor and on the other hand the collector-emitter path of a switching transistor, and the circuit further comprising a regulation circuit, wherein the input switch is switched on in use of the circuit under the control of the regulation circuit for a period which depends on the amplitude of the supply voltage, wherein the circuit includes a high voltage transformer having a first primary winding, an additional primary winding connectible in series with the source and the input switch and a secondary winding connected in parallel with the deflection coil and the recovery capacitor, the input inductance being comprised by the leakage inductance between the additional primary winding and the secondary winding, energy being supplied to the rest of the deflection circuit via the transformer and its leakage inductance.

2. A horizontal deflection circuit as claimed in claim 1, wherein the high voltage transformer is comprised by a conventional high voltage transformer having a primary winding arranged in parallel with the series connection of the deflection coil and the recovery transistor and acting as the secondary winding of the first mentioned high voltage transformer, and having secondary windings which provide low voltages and the high voltage required for a television picture tube, wherein the windings of the conventional high voltage transformer are coated on the same leg of a magnetic core, wherein the said primary winding of the conventional high voltage transformer is connected in series with a further capacitor and wherein the additional primary winding is located on the opposite leg of the magnetic core.

3. A horizontal deflection circuit as claimed in claim 1 or claim 2, wherein the high voltage transformer is mounted on a printed circuit board containing components of the deflection circuit wnerein those components of the sad defle-t ^ circuit which are not isolated from the supply voltage source are not located on the said printed circuit board, the output leads of the additional primary winding being insulated wires directed away from the said printed circuit board.

4. A horizontal deflection circuit according to any one of claims 1 to 3, including an additional secondary winding capable of restoring unconsumed energy to the source, and connected in series with the voltage source in use of the circuit via a diode.

5. A horizontal deflection circuit substantially as herein described with reference to and as illustrated in the accompanying drawings.

6. A T.V. receiver incorporating a circuit as claimed in any preceding claim.