GB1589832A

GB1589832A - Tv receivers power supply

Info

Publication number: GB1589832A
Application number: GB3976677A
Authority: GB
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1977-09-23
Filing date: 1977-09-23
Publication date: 1981-05-20

Description

(54) TV RECEIVERS POWER SUPPLY (71) We INTERNATIONAL STANDARD ELECTRIC CORPORATION a Corporation organised under the laws of the State of Delaware, USA, of 320 Park Avenue, New York 22, State of New York, USA do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a power supply unit, comprising a switching transistor, a control and regulating circuit, containing a pulse-width modulation stage and an overload protection circuit for either restricting the current to, or periodically switching-off, the switching transistor when a predetermined storage current is exceeded, and a transformer whose primary side is connected with the switching transistor and the control and regulatory circuit, for supplying a television receiver with one or more stabilized supply voltages obtained from the secondary slde of the transformer when the switching transistor is nonconducting, and for generating a supply voltage for operating a remote control circuit.

Power supply units of this kind have already been used with television receivers for some years (see Funkschau 1972, No.

10, pp 339 to 341). These power supply units are characterised by a high efficiency and a good stabilization of the output voltage with respect to mains voltage variations and load variations. Moreover, the overload protection circuit has considerably reduced the danger of setting fire to component parts owing to defects in the circuit.

To a continuously increasing extent, television receivers are being equipped with remote control units. Quite a number of these remotely controllable receivers are also provided with an on/off switching facility for controlling the television stage. The remote control circuit provided for in television receivers is supplied, in known types of circuits, from a power supply unit of its own.

The on/off switching of the television stage is effected with the aid of a bipolar relay which has to be designed in accordance with the high switch-on current (current pulse into the charging capacitor) of more than 50 A. In order to avoid this expensive component part which is also critical as regards its service life, it is known to let the switching transistor be permanently blocked in the power supply unit during the stand-by phase, so that no output voltages are being provided by the power supply unit. For this purpose, only a small current is required to flow from the remote control circuit to the control and regulating circuit.

According to another proposal (prospec tus of Siemens AG "Spannungsversorgung eines Fernsteuermpfangers und Analogspeichers wahrend des Stand-bv (SB) Betriebes mit dem Sperrwandlernetzteil AZB 5000" of January 1975) the stabilized output voltage of the power supply unit is also utilized for supplying the remote control circuit. For turning off the television receiver, the supply voltage as applied from the power supply unit to the largest load of the television stage, is interrupted by the action of a transistor circuit. One disadvantage of this circuit resides in that the output voltages have to be provided with load resistors, because otherwise the output voltages run up to the peak voltages of the cut-off edge.

A further disadvantage of the circuit is to be seen in the full supply voltages being continuously applied throughout weeks and months of stand-by operation to the circuit parts, such as the video output stages, the vertical amplifier, the sound amplifier, and the tuner stabilizing circuit. Also, the full inverse voltage as during normal operation, is applied to the switching transistor in the power supply unit.

It is also known to control the horizontal final stage not by a special driver stage, but by the transducer/transformer. In that case, however, a high current has to be interrupted.

According to the present invention there is provided a power supply network for a T.V. receiver to which power may be applied to provide either a stand-by operation state or a normal operation state, which network comprises a switching transistor, a control and regulating circuit containing a pulse-width modulation stage, and a transformer whose primary side is connected with the switching transistor and the control and regulatorry circuit wherein at least one stabilized supply voltage for normal operation of the television is produced by the network on the secondary side of the transformer during the periods when the switching transistor is non-conductive, wherein a further supply voltage is obtained for a remote control circuit of the T.V. receiver by rectifying a voltage on the secondary side of the transformer during the conducting periods of the switching transistor, and wherein during the stand-by operation state of the T.V. receiver there is performed a step-down adjustment of said at least one supply voltage simultaneously with the provision of the remote control circuit supply voltage.

The invention provides the possibility to stcp down the output voltages of the power supply unit as stabilized by a pulse-width control, in such a way by the switch-off command from the remote control device for the time of the stand-by phase, that all functions of the television receiver will be turned off. This does not affect the output voltage during the "on" period of the power supply unit, because the keying ratio has no influence thereon. The remote control circuit itself, however, is further being supplied by the power supply unit, and thus remains ready to operate.

Considerable advantages of this circuit layout reside in that during the stand-by phase of the television receiver, the switching transistor in the power supply unit is operated by approximately half the peak voltage than during normal operation of the receiver, and in that, moreover, the supply voltage of the television stage drops down to a fraction of its normal value.

Also, a controlling of the horizontal final stage by the power supply unit remains poss ible now as before (according to the Siemens proposal, a driving ac of approximatcly 2 A would have to be interrupted if the horizontal output stage, as the greatest load, were to be turned off).

During practical operation, in the case of a colour television receiver with a switched off television stage, there will result losses amounting to about 10 W. A further reduction of the losses can be achieved by the so-called pulsating operation of the switching power supply unit. For this purpose, according to one embodiment of the invention, for effecting the switching of the television receiver from the normal operating state into the stand-by state, the supply vol tagc used for supplying the television receiver, is substantially reduced. i.e. by switching the overload protection circuit from the normal operating state to a periodic permanent releasing (tripping) operation. Another embodiment provides for a separate control generator for the switching transistor in the transducer stage, in such a way that for switching the television receiver from the operating state into the stand-by state, the supply voltage serving to supply the television receiver, is substantially reduced, by an electronic switching off by remote control of the control and regulating circuit (first control and regulating circuit) used for the normal operation of the television receiver, and by switching-on simultaneously a further control circuit which produces control pulses for the switching transistor which are narrow with respect to those of the first control circuit, steadily given by the circuit and nonvariable pulse width, and which periodically disconnects these control pulses.

Switching from normal operation to stand-by operation is achieved by changing the response sensitivity of the overload protection circuit. The rhythmical on-off switching by the overload protection circuit only permlts a restricted number of control pulses to reach the switching transistor; this is followed by an interval which is determined by the hold-in time constant of the overload protection circuit. In the case of a pulse/space ratio of e.g. 1:5 in a colour television receiver, the losses in the power supply unit, resulting in a practically embodied circuit, have amounted to less than 2 W.

This is still less than the power loss in a conventional power supply unit employing a 50 Hz-mains transformer. As regards an uninterrupted stand-by operation, this is of considerable advantage.

Examples of embodiment of the invention will now be described in greater detail with reference to the accompanying drawings, in which: Figure 1 shows a conventional power supply circuit for comparison with the power supply circuits according to embodi mcnt of the invention and as shown in Figures 2 and 3.

Figure 1 shows the power supply of a television receiver comprising a switching network, and the power supply of a remote control circuit. By the switch 1 the television receiver is switched to stand-by operation.

The supply voltage for the remote control unit is generated by the mains transformer 2, the rectifier 3, the charging capacitor 4 and the stabilizing circuit 5. A switch-on command signal transmitted by the remote control transmitter is prepared in the remote control receiving circuit 6, and fed to the relay 7. The make contacts of this relay are closed upon receiving the switch-on command signal, and the primary supply voltage for the switching network is generated by the components: resistor 8, rectifier 9 and charging capacitor 10 in the usual way. The control circuit 13 first starts to control the switching transistor 16 with short pulses. The de voltage is stored in the winding 17 (inductance) and controlling must start with short pulses in order to avoid an excessively great storage current which is caused by the charging current in the capacitances 21, 23. The reference numeral 25 indicates a storage sensor or current sensing device for the storage process. During the blocked or non-conducting phase of the switching transistor, the stored energy flows via the windings 18 and 19, the diodes 20 and 22 into the charging capacitors 21 and 23. The now rising supply voltage UB2 effects in the control and regulating circuit, via the input 15, and by means of the time constant elements as provided for in the control circuit 13, an enlargement of the switch-on pulses for the switching transistor, thus causing a higher energy storage in the switching network partial inductance 24.

The supply voltages UBI and UB2 for the television receiver continue to rise during the blocking phase until the actual-value voltage at the input 15 has reached the nominal-value voltage at the input 14 (nominal-to-actual value comparator). The nominal-value voltage is generated with the aid of the zener diode 11 and fed to the input 14 of the control and regulating circuit.

A further widening of the control pulses Is thus avoided by the pulse-width modulation stage. In case the primary supply voltage drops, wider control pulses are transmitted by the pulse-width modulation stage, whereas narrower control pulses are transmitted in the case of a rising primary supply voltage. Accordingly, the control and regulating circuit takes care that the energy as flowing off the secondary windings 18, T9, is stored in the primary winding (inductance) 17 at the same level including the losses.

With the exception of the supply voltage generation for the remote control circuit and the relay circuit 7, the circuit according to the invention as shown in Figure 2 is iden tical to the circuit shown in Figure 1.

Whereas the supply voltages UB1 and UB2 are likewise obtained during the blocking phase of the power supply unit (network), this does not apply to the supply voltage generation UB3 for the remote control circuit 6. As is shown in Figure 2, the sense of winding of the coil winding 26 is reversed by 1800 with respect to the coil windings 17, 18 and 19. This means to imply that the voltage at the anode of diode 27 becomes positive when the switching transistor 16 is switched to the conducting state. Independently of the switch-on period of the switching transistor 16 and the load at the coil winding 26, the voltage transformation from the primary-side coil winding 17 to the secondary-side coil winding 26 during the "on?' period, is exclusively subject to transformation laws. In distinction thereto, via the diodes 20, 22, energy is only taken off during the blocking time of the switching transistor 16 (blocking transformer principle), with the different storage time regulating both the energy pick-up and release. In this way it is now possible to reduce the stabilized output voltage UBI and UB2 by the control circuit 13 for the time of the stand b operation without affecting the voltage B3 at the charging capacitor 28. This voltage UB3 is not stabilized and changes in proportion to the primary voltage at the capacitor 10. In case the remote control circuit 6, however, requires additionally a stabilized voltage, it is possible to insert in the usual way a series of parallel control for the stabilizing circuit 5. The switching between the receiver functions "on" and "stand-by" is achieved by a positive or negative control current flowing from the remote control circuit 6 to the control and regulating circuit 13.

One alternative resides in that for the switching off or the switching of the receiver from the normal operation condition to the stand-by operating condition respectively, caused by the remote control, a negative control current flowing via a line 30, will effect e.g. the stepping down of the nominal-voltage value in the control circuit, which will have the consequence that the pulse-width control circuit will reduce the storage time as given by the switching transistor 16, until the output voltage UB2 will correspond to the reduced nominal-voltage value and thus drops below the normal supply voltage value.

A similar effect can be achieved by a positive control current from the remote control circuit, when this current in a resistance network in the pulse width modulation stage 13 is being added to the actual-value current. A further possibility of reducing the output voltage UB2 and UBI resides in making the overload protection circuit, which forms part of the control circuit 13, so sensitive as to achieve a periodic permanent release (tripping) state.

As already described hereinbefore, the control circuit, during its starting moment, provides narrow control pulses for the operation in which the switching transistor 16 is driven into saturation, thus keeping the voltages UBI and UB2 at a low level. By correspondingly dimensioning the time constants of the RC-sections in the overload protection circuit, the control pulses are either switched off or applied to chassis ground, before a widening can take place.

As pulse transition periods there may be used e.g. 1 ms to 2 ms by providing for intervals ranging between 5 and 20 ms.

Accordingly, the control pulses are transmitted in pulse groups, with the control pulses simultaneously being made narrow.

Figure 3 shows a block diagram relating to one example of embodiment in which, instead of carrying out a modification of the overload protection circuit, there are used two control circuits. By the remote control command signal "stand-by", the first control and regulating circuit 13 is completely disconnected (switched off) electronicaly via the line 30 from the remote control receiving circuit 6, and a second control circuit 29 is switched on. This second control circuit delivers stcady and invariable predetermined narrow pulses of a different for example, lower frequency to that of the first control circuit 13. This second control circuit may be provided with the necessary supply voltage from the UB3 which is independent of UBI and UB2.

WHAT WE CLAIM IS: 1. A power supply network for a T.V.

receiver to which power may be applied to provide either a stand-by operation state or a normal operation state, which network comprises a switching transistor, a control and regulating circuit containing a pulsewidth modulation stage, and a transformer whose primary side is connected with the switching transistor and the control and regulatory circuit, wherein at least one stabilized supply voltage for normal operation of the television is produced by the network on the secondary side of the transformer during the periods when the switching transistor is non-conducting, wherein a further supply voltage is obtained for a remote control circuit of the T.V. receiver by rectifying a voltage on the secondary side of the transformer during the conducting periods of the switching transistor, and wherein during the stand-by operation state of the T.V. receiver there is performed a step down adjustment of said at least one supply voltage simultaneously with the provision of the remote control circuit supply voltage.

2. A power supply network according to claim 1, comprising a resistance matrix in the pulse-width modulation stage, wherein for the purpose of switching the television receiver from the normal operation state to the stand-by operation state, said at least one supply voltage is substantially reduced by reducing a respective nominal-value voltage provided for the pulse-width modulation stage with the aid of the resistance matrix and by means of a negative current flowing from the resistance matrix to the remote control circuit.

3. A power supply network according to claim 1, comprising a resistance matrix in the pulse width modulation stage, wherein for switching the television receiver from the normal operation state to the stand-by operation state, said at least one supply voltage is substantially reduced by stepping up the actual value thereof with the aid of the resistance matrix and by means of a positive current flowing from the remote control circuit to the resistance matrix.

4. A power supply network according to claim 1, comprising an overload protection circuit for restricting the current supplied to the switching transistor, or periodically switching off the switching transistor, when a predetermined storage current is exceeded, and wherein for switching the television receiver from normal operation state to the stand-by operation state, said at least one supply voltage is substantially reduced, by switching over the overload protection circuit from "normal operation" to a periodic permanent release (tripping) operation.

5. A power supply network according to claim 1, wherein for switching the television receiver from the normal operation state to the stand-by operation state, said at least one supply voltage is substantially reduced by an electronic remote control switchingoff of the control and regulating circuit used for the normal operation of the television receiver, and by simultaneously connecting a further control circuit which, compared to the first control circuit, generates narrow control pulses for the switching transistor which are steadily given by the circuit and of non-variable pulse width, said further control circuit periodically switching off these control pulses.

6. A power supply network according to claim 5, wherein the control pulses are transmitted at an operating frequency which is lower than the normal operating frequency, with the control pulses simultaneously being made narrow.

7. A power supply network for a remote-control T.V. receiver, substantially as hereinbefore described with reference to Fig. 2 or Fig. 3 of the accompanying drawings.

8. A remote control T.V. receiver having a power supply network according to any preceeding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. used e.g. 1 ms to 2 ms by providing for intervals ranging between 5 and 20 ms. Accordingly, the control pulses are transmitted in pulse groups, with the control pulses simultaneously being made narrow. Figure 3 shows a block diagram relating to one example of embodiment in which, instead of carrying out a modification of the overload protection circuit, there are used two control circuits. By the remote control command signal "stand-by", the first control and regulating circuit 13 is completely disconnected (switched off) electronicaly via the line 30 from the remote control receiving circuit 6, and a second control circuit 29 is switched on. This second control circuit delivers stcady and invariable predetermined narrow pulses of a different for example, lower frequency to that of the first control circuit 13. This second control circuit may be provided with the necessary supply voltage from the UB3 which is independent of UBI and UB2. WHAT WE CLAIM IS:

1. A power supply network for a T.V.