DK165036B - Circuit arrangement for the power supply for a television receiver - Google Patents

Abstract

A combinatorial circuit component for television sets with an overload protection circuit on the primary side and a secondary-side regulating circuit and starting circuit with final disconnection of the mains section. The protective circuit, which comes into play in the event of anomalies on the primary side, causes a jump in the negative voltage on the secondary side. This is compared with a secondary (standby) voltage, created independently of the combinatorial circuit, in a comparator, which supplies a control voltage to which the secondary protection circuit responds thus interrupting the excitation of the switch in the mains section.

Description

in

DK 165036 B

The present invention relates to a circuit device for supplying a television receiver with a line frequency synchronized switching power supply.

For devices in communication technology, such as a television receiver, it is known to produce the operating voltages required for each stage with a switching power supply from the mains voltage. (Funkschau 1975, booklet 5, pages 40-43). A switching netting enables the galvanic separation 10 of the receiver circuit from the grid to be advantageous for the connection of external appliances and for the protective insulation measures. Since a switching power supply operates at a high frequency relative to the mains frequency, the separating transformer serving for the galvanic separation can be designed considerably smaller and lighter than a 50 Hz mains transformer. By means of several windings or winding outlets and connected rectifiers, operating voltages of various sizes and polarity can be generated on the secondary side of the transformer of the switching grid.

In the case of a synchronized switching power supply, the control circuit may be located on the secondary side and the control circuit and the protective circuit on the primary side. Such a power part requires a net-insulated coupling element, such as e.g. an optocoupler, so that e.g. the regulatory information in compliance with the grid separation is transferred to the primary page. This is e.g. important when the supply voltage to the deflection is to be kept stable and which would vary without regulation due to the modulation of the audio output stage. This initially disadvantageous disadvantage is offset by the fact that a synchronized switchgear is substantially simpler to make noise-free as the switching frequency of the unsynchronized switchgear changes with the load, while the switching frequency of the synchronized switchgear remains constant, e.g. .

30 works with line frequency or its harmonic.

There is an integrated circuit (TEA 2026) for controlling the switchgear, which contains a protective circuit that disables the device in the event of a malfunction. This protection circuit acts on a pulse width modulator which supplies the control pulses 35 for the switch located on the primary side over an optocoupler. A starting circuit located in the integrated circuit again releases the pulse width module at the aftermath of the disturbance so that it causes a soft coupling of the coupling grid part by emitting the control pulses starting with a pulse of small width, 2

DK 165036 B

which control pulses are still growing. In addition to this protection circuit, there is on the primary side an additional overload fuse which, when exceeding a limit value for the current flowing through the coupling transistor, interrupts the control of the coupling transistor. It is now difficult to bring the information about the elevated collector current to the secondary side of the switchgear, since the protection circuit for the final switch-off is located on this side. This information can, e.g. transmitted by a separator transformer or by means of an additional optocoupler.

10 However, this means an additional cost.

US-A 4,330,816 discloses a circuit device for a switching power supply, in which a comparator circuit is used, to which one input is fed a secondary voltage produced by the switching power supply and to whose other input a reference voltage is applied. Here, the comparator circuit serves to control, by voltage comparison, the pulse width modulator, so that the secondary voltages produced remain constant by changing the width of the pulses controlling the switch in the switchgear. However, disturbances on the primary side are not detected by the 20 comparator circuit.

The object of the present invention is to find a solution which, while avoiding an additional network location, transmits noise in the information to the secondary side of the switching network part, and further prevents the transmission of disturbances that arise on the primary side. This is achieved by the invention as claimed in claim 1.

The invention will then be explained in more detail with reference to the drawing, which shows an embodiment of the circuit device according to the invention.

In the drawing, 1 denotes the transformer in the switchgear, which transformer has a primary winding 2, which is connected at one end to the rectifier UB of a mains rectifier 3 and smoothed by a capacitor 4 and at its other end over a transistor 5 and a current target. resistor 6 is connected to the negative pole of the grid rectifier 3. The transistor 5 is controlled over a further winding 7 in the transformer 1, with which winding which is connected in parallel with a pulse 8 which is modulated in their width, switch 8. is non-conductive, transistor 5 is always conductive or vice versa. At the alternating opening and closing 3

DK 165036 B

with the pulse frequency, the induced voltage is transmitted to the secondary side of the transformer 1, so that on secondary windings 9, 10 and 11 over rectifiers 12 and 13 and 14, secondary DC voltages U1, U2 and U3 are generated on capacitors 15,16 and 17. pulses are generated by a control circuit 18 and are passed over an optocoupler 19 to the control electrode of the switch 8. The pulses are produced in a known manner by a pulse width module ator 20, which is produced on the side separated from the grid by the unscheduled oscillator. line frequency 10 saw-shaped voltage 21 is compared to a voltage produced by the switchgear, e.g. U3. This voltage is made adjustable by a voltage divider 22. The pulses amplified in an amplifier 23 are then fed to the optocoupler 19. In the control circuit 18 there is a further starting circuit 24 which, at startup of the switching power supply, ensures that the pulses starting with a minimum value of the pulse width slowly grows up to a regulated value. The control circuit 18 has a protective circuit 25 which can be influenced by several noise sizes occurring on the secondary side. Thus, it reacts e.g. on bi11 cane estimates, 20 surges or high currents, etc. These inputs are symbolically indicated by 26.

In the event of a disturbance, the pulse width module ator 20 is switched off. Thereafter, the start circuit 24 is switched on again after a forced pause dependent on a timing link 27, so that the switchgear part starts soft again. On the web side of the switchgear, whose mains separation is symbolically indicated by line 28, an overload protection is built-in. The current is measured using the transistor 5.

When a limit value is exceeded, a voltage drop is generated on the resistor 6 which, over a diode 29, builds up a voltage 30 on the capacitor 30 which makes the switch 8 conductive, so that the transistor 5 immediately becomes powerless. This condition as a criterion for an overload must now be transmitted to the side separated from the mains by the switchgear, so that the protective circuit 25 located in the control circuit 18 reacts and can provide a soft connection of the switchgear. In order to transmit the noise information to the side separate from the grid, it is utilized that all secondary voltages in the event of a disturbance undergo a negative voltage jump. One of the secondary voltages produced, e.g.

Ul, therefore, over a capacitor 31 is coupled to one input

DK 165036 B

on a comparator 32. At the second input of the comparator there is a constant voltage. This tension on e.g. 5 volts can be taken out of a separate transformer 33 which holds the steps for a remote control in operation by a television receiver.

This rectified voltage, filtered by a rectifier 34 and filtered by means of a capacitor 35, which is held stable over a resistor 36 by means of a zener diode 37, is applied as a reference voltage to the second input of the comparator 32. As soon as the capacitor 31 comes a negative voltage jump which is 10 below the reference voltage, the comparator outputs a pulse which engages the protection circuit 25 above the threshold value switch 38. The switchgear is then switched off.

In the starting circuit 24 a counter may be built in, which counts the successive switch-ins after a switch-off.

15 At a certain number of these processes, the control of the mains part can be permanently switched off to protect the device provided and to exclude a fire hazard caused by components overload.

List of reference notes for T -PA-531 20 1 Transformer 20 Pulse width modulator 2 Primary winding 21 Sawtooth voltage 3 Power supply 22 Voltage parts 4 Capacitor 23 Amplifier 25 5 Transistor 24 Start circuit 6 Resistance 25 Protection circuit 7 Primary winding 28 Secondary winding 8 Switching 27 Switching input 8 Switch 27 29 Rectifier 11 Secondary winding 30 Capacitor 12 Rectifier 31 Capacitor 13 Rectifier 32 Comparator 14 Rectifier 33 Transformer 35 15 Capacitor 34 Power Rectifier 16 Capacitor 35 Capacitor 17 Capacitor 36 Resistor 18 Control unit 37 Zener diode 19 Optocoupler 38 Threshold value switch

Claims (2)

5 DK 165036 B Patent claims. 1. A circuit device for supplying a television receiver with a line-frequency synchronized switching network for mains disc 11 or view of the receiver with an overload protection circuit located on the primary side and with a control circuit (18) on the secondary side for load-dependent impedance depending on load a switching transistor arranged on the primary side over a mains separating coupling element 10 (19), and with a comparator circuit (32), to which one input coupled to a secondary voltage produced by the coupling network part and to the other input coupled to a reference voltage, characterized in that the comparator circuit (32), upon the reaction of the primary side (6,29,30,8) applied by lowering the generated secondary voltage to the comparator input, provides a signal on the comparator output of the secondary circuit (25) arranged as over control circuit 24) to p turing of the switchgear part again, the pulse width module engages the motor after a forced pause. Circuit arrangement according to claim 1, characterized in that the voltage independent of the coupling network part as a reference voltage for the comparator circuit (32) is taken from a mains part to produce the standby voltage. 25 30 35