DE2711020A1 - CIRCUIT FOR DELAYED SWITCHING ON OF OPERATING VOLTAGE IN A BROADCAST RECEIVER - Google Patents

Description

Licentia Patent-Verwaltungs-GmbH Theodor-Stern-Kai 1

6000 Frankfurt / Main 70

Hanover, March 2nd, 1977 PT-Wp / rs H 77/11

Circuit for the delayed activation of an operating voltage in a radio receiver .

The task of providing an operating voltage often occurs in a radio receiver for a power level to be connected to the level with a certain delay when the device is switched on, in order to avoid the destruction of semiconductors due to undefined conditions during the start-up process.

This measure is particularly important when connecting the operating voltage for the line output stage in a television receiver. If after switching on the receiver or switching from standby mode to normal mode, the control the line end stage does not yet have its correct value, i.e. the line end stage is driven undefined ^ and the full Operating voltage is already available, so the line output transistor be destroyed by these undefined relationships.

Such a delayed activation of an operating voltage can be achieved, for example, with an electronic switch in the form of a Achieve transistor, which is controlled to conduct later on at its base via a time constant element. This requires but an additional circuit complexity.

809838/0084

H 77/11

The invention is based on the task of utilizing already existing components and with little additional circuitry the delayed connection of the operating voltage to ensure.

This object is achieved by the invention described in claim 1. Advantageous further developments of the invention are described in the subclaims.

In the invention, the ability of an existing protective circuit to switch off the operating voltage in an emergency, It is also used to switch on this operating voltage with a delay after switching on the device. The protection circuit is therefore in its triggered state immediately after switching on the device, as if it were there There is a fault in the device and the operating voltage is initially switched off in the desired manner. The protection circuit is so independent of the fault voltage occurring during the fault and secondly due to a voltage occurring when switching on triggered in the sense of a shutdown of the operating voltage.

The invention can be used particularly advantageously in a television receiver with a switched-mode power supply and with standby mode. With such a switched-mode power supply, the operating voltages are obtained by rectifying the output voltage at the secondary winding of the isolating transformer. The delayed switch aer operating voltage can take place in the desired manner on the secondary side of the switching power supply. This has the advantage that no intervention in the primary side is necessary and the desired absolute galvanic separation between the primary side and the secondary side of the switched-mode power supply is guaranteed.

The invention is based on the drawing using the example of a television receiver explained with a switched power supply, standby mode and remote control. Show in it

809838/0084

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S-

Figure 1 shows a circuit example and Figure 2 curves to explain the mode of operation.

FIG. 1 shows a switched-mode power supply 1 with an isolating transformer 2, which is fed by the mains voltage, of a television receiver the primary winding 3 and the secondary winding 4. The secondary winding 4 supplies four operating voltages U ^, υ-, U, and U- via rectifier 5,6,7,8. U ^ is the operating voltage for the line output stage 9, which is from the line oscillator 10 via the Driver stage 11 is controlled. The line output stage 9 feeds the line deflection coils 12 for the picture tube 13. An ultrasonic remote control receiver 14 with a microphone is also provided 15, an electronic switch 16, a protection circuit 17 with a relay winding A and a switch 18, a filter element 19 and a threshold value circuit 20.

The mode of operation is explained with reference to FIG. In the switch position shown, the television receiver works in standby mode. The operating voltage U ^ for the line output stage 9 and the operating voltages U ₂ , U ₃ for the other stages such as the video output stage, the vertical deflection, the individual amplifiers and the sound section are switched off by the relay contacts a ^, a2 »a ₃ . The operating voltage U> is not switched off and keeps the remote control receiver 14 ready to receive. If necessary, the picture tube 13 is additionally preheated by the secondary winding 4 via a further rectifier circuit or by the operating voltage U ^ which is always present. The line oscillator 10 also receives no operating voltage. The driver stage 11 receives the operating voltage U ₄ , but does not carry any current because of the lack of control from the line oscillator 10.

Ia time t ^ the microphone 15 receives an ultrasonic remote control signal 21 for switching the receiver on to normal operation. The remote control receiver 14 then generates the switching voltage U ₅ , which closes the switch 16. The desk 16 is preferably used as a programmable stabilization circuit

809838/0084

- H 77/11

educated. The line oscillator 10 is now supplied with the operating voltage U- and supplies the control voltage for the line output stage 9 via the driver stage 11. However, the action of the filter element 9 causes the voltage Ur at the output of this filter element to rise slowly, so that the switch 18 in the protective circuit 17 is not initially closed. When the threshold value U is reached at the point in time t2, the threshold value circuit 20 supplies the voltage U _ß at the terminal 22, which actuates the switch 18. As a result, the winding A _{is supplied with current by the voltage U 4} , so that the relay contacts aj, a ₂ , aß are closed. At time t ₂ , the receiver is completely switched on. It can be seen that the voltages U ^, Up, U3 appear with a time delay from tj to t ₂ of about one second. During this time, the correct control of the line output stage 9 is ensured, so that the line output stage transistor is not endangered.

The primary purpose of the protective circuit 17 is to switch off the operating voltages U ^ _1, U ₂ , U3 in the event of a fault in the circuit by opening the contacts aj to ag. This takes place with an error voltage U _p at the terminal 23. This is preferably derived from the magnitude of the current through the flyback transistor or the magnitude of the voltage of the kickback pulses. If this current or the voltage exceeds a certain value, the error voltage Up opens the switch 18, so that the contacts a ^ to a ^ are opened. Such a protective circuit is described in more detail in DT-PS 15 91 712. This capability of the protective circuit 17 is also used by the control at terminal 22 through the voltage Ug for the delayed activation of the operating voltage U ₁ for the line output stage 9.

The relay contacts a are only used to switch between standby mode and normal mode. With the complete Switching off the receiver, the mains voltage on the primary side of the isolating transformer 2 in the switched-mode power supply 1 completely shut down. - 5 -

809838/0084

Claims (8)

H 77/11 Claims I ₉ J Circuit for the delayed activation of an operating voltage in a radio receiver, in particular for the line output stage in a television receiver, with a protective circuit which is triggered in the event of an error and switches off the operating voltage, characterized in that the protective circuit (17) in addition to the delayed activation of the Operating voltage (U ^) is used. 2. A circuit according to claim 1, characterized in that a switching voltage (Ug) occurring when the receiver is switched on is applied via a delay stage (19) to a control terminal (22) of the protective circuit (17) in such a way that it is initially triggered. 3. A circuit according to claim 1, characterized in that the protective circuit (17) acts on the excitation winding (A) of a relay, of which a contact (a ^) is in the path of the operating voltage (U ₁ ). 4. A circuit according to claim 3, characterized in that in a receiver with a switched-mode power supply (1) with an isolating transformer (2) from whose secondary winding (4) the operating voltage (U-) is obtained via a rectifier (5), the relay contact (a ^) is behind the rectifier (5) in the path of the operating voltage (U ^). 5. A circuit according to claim 3 or 4, characterized in that in a receiver with standby mode, in which when switching to normal operation operating voltages (U ^, U_, U ₃ ) with relay contacts (a ^ - aj) switched on v / earth, the Relay contacts are controlled by the protective circuit. 809838/0084 ^OR 'QINAL INSPECTED / H 77/11 • 3. 6. A circuit according to claim 2 and 5, characterized in that an operating auxiliary voltage (U ₄ ) which is constantly present in standby mode is applied to the input of the delay stage (19) when switching to normal operation (switch 16). 7. A circuit according to claim 6, characterized in that in a television receiver when switching to normal operation, _{the auxiliary operating voltage (U 4} ) is applied simultaneously to the line oscillator (10) and the input of the delay stage (19) (switch 16). 8. A circuit according to claim 1, characterized in that the delay (t ^ to t ^) is about 1 s. 809838/0084