FI59497B - REGLERINGSSYSTEM FOER HOEGSPAENNING - Google Patents

Description

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England-England (GB) 36089, 22.03.76 USA (US) 668967 (71) RCA Corporation, 30 Rockefeller Plaza, New York 22, NY, USA (US) (72) Willem den Hollander, Schlieren, Switzerland-Schveiz (CH ) (71 *) Oy Kolster Ab (5 * 0 High Voltage Control System - Regleringssystem för högspänning The present invention relates to a high voltage control circuit as set out in the preamble of claim 1.

It is common practice to provide an extreme anode voltage to a cathode ray tube, such as a television picture tube, with a rectifier with horizontal return pulses obtained from the deflection system associated with the picture tube. It is known that an increase in the voltage at the extreme anode can be caused by an increase in the mains voltage which supplies the television receiver or a decrease in the jet current of the picture tube, the latter often being referred to as a decrease in beam power. Excessive voltage may cause an arc inside the image tube which may destroy the tube or related components or may cause harmful X-rays from the tube. The supply of direct current to the deflection system is adjustable to substantially overcome the increase in the high voltage caused by variations in the beam current or mains voltage.

One type of controller that is useful in deflection systems is a switching controller, where the operating cycle of the switch, 2 59497 located between the power supply source and the deflection system, is adjustable to effect the actual control. This switching controller may be transformer-connected to the deflection system, this transformer providing a separation, thus allowing the controller to be connected to the incoming power grid, while the actual deflection system may be disconnected from the power grid. Such a switching controller is disclosed in another co-pending patent application, U.S. Pat. Serial No. 607,512, filed August 25, 1975, entitled "Synchronized and Controlled Power Supply" (RCA 69,816). The present application discloses an arrangement in which a pulse transformer of an oxidizer is coupled to this controller to synchronize the operation of the power supply at a horizontal deflection frequency in order to minimize the visible phenomena of the power supply connection. The function of this transformer is to isolate the oscillator from the power supply. The amplitude of the pulse then represents variations in the direct current of the deflection system, which variations are caused by variations in the power grid. With this arrangement, the number of connections between the separated and untaken portions in the receiver is reduced. It would be desirable to further control such an arrangement by preventing the variations in high voltage caused by the jet current and further keeping the number of connections between the disconnected and non-intake body to a minimum.

This is solved in the control circuit according to the invention in that the transistor stage is supplied with a rectified mains voltage and controlled via a differentiation circuit and derives width-modulated pulses in addition to amplitude-modulated changes in the supply voltage for the control signal power supply.

Fig. 1 is a block diagram and schematic diagram of a deflection system using a high voltage control circuit according to the present invention.

Figures 2 and 3 illustrate in more detail the power supplies that can be used in the system of Figure 1.

In Figure 1, the power supply and controller 10 convert the output voltage to a regulated DC voltage available from output terminals B and C. Switch terminal C is connected to a horizontal deflection system similar to the type of two bidirectional switches using controlled silicon rectifiers (SCR) such as 59 is disclosed in U.S. Pat in 3,452,244.

The direct current from the switch terminal C is connected via the input reactant 11 to the commutation switch 12, which is made open by the gate switch to conduct during the commutation portion of each offset period through the communication coil 13a. The drawing switch 14, which is controlled by the gate operating signals obtained from a voltage divider including a resistor 21, a capacitor 22, and a capacitor 23 connected across a commutation switch 12 and a waveform circuit including a resistor 24 and an inductance 25 allow the sweep current through. The horizontal frequency current also passes through the primary winding 17a and the switching capacitor 18, energizing the transformer 17 during each horizontal deflection period. The tertiary winding 17b from the horizontal output and high voltage transformer supplies horizontal return pulses to the high voltage multiplier and the rectifier apparatus 19 so as to generate a direct current type high voltage suitable for use with a television picture tube end anode switch.

Since the voltage at the end anode of the picture tube is generated in the horizontal deflection circuit, it is desirable to control the high voltage with respect to the variations caused by the variations in the jet current of the picture tube as a result of the modulation of the video signal. The controlled DC type high voltage substantially eliminates the possibility of damage to the components of the television receiver or a possible excessive amount of X-rays, which is sometimes associated with an excessive voltage applied to the picture tube. The remainder of the circuit of Figure 1 and the illustrative embodiments of the power supply and controller 10 of Figures 2 and 3 allow B + the supply of Figure 1 to be controlled at switch terminal C, resulting in a controlled high voltage of the DC type.

The periodic voltage waveform 26 provided by the secondary winding 17c is rectified and filtered by a diode 27 and a capacitor 28. This positive voltage is connected via a blocking diode 29 to the junction of the resistor 30 and the zener diode 31. The series combination of the bias resistor 33, the zener diode 31 and the resistor 30 provides a quiescent current through the transformer 32 from which its main current path is connected to the supply source B + from the switch terminal D through the resistors 34 and 35. Zener diode 31 smooths the change in voltage across capacitor 28 to the appropriate operating level for transistor 32. The increase in the amount of positive voltage passed through the diode 29 as a result of the increase in voltage waveforms in the shaper 17 is combined through the zener diode 31 and results in a decrease in the conductivity of the transistor 32, the effect of which will be explained later.

The horizontal oscillator 20 provides horizontal frequency synchronous pulses 38 which are connected via a resistor 37 and a capacitor 36 to the junction of the collector electrode of the transistor 32 and the base electrode of the transistor 40. The resistor 35, also connected to the collector of the transistor 32 together with the capacitor 36, forms part of a differentiating circuit which differentiates the voltage waveform 38 as illustrated by the voltage waveform 39. The transistor 40 forms an emitter follower phase with high input impedance. from the capacitor 36 and the resistor 35. The collector of the transistor 32 is also connected to the differentiating circuit, but since the impedance of the collector of the transistor is high, this also does not load the diffuser. Thus, the shape of the pulses 39 does not change as the conductivity of transistor 32 varies, but the DC level changes. The width of the pulses 75 depends on the time that the transistor 43 is conductive, such as when the voltage at the base of the transistor 40 exceeds the value of the sum of the base emitter voltage of the transistor 40, the base emitter voltage of the transistor 43 and the conductive voltage of the diode 44. Thus, when the DC level of the pulses 39 is changed by changing the conductivity of the transistor 32, the conductivity time of the transistor 43 also changes. The width of the pulses 75 increases as the High voltage decreases. The amplitude of the pulses 75 is the voltage B + of the switching terminal D minus the saturation voltage of the transistor 43 and the directional voltage of the diode 44. The amplitude is thus a representative value of any B + variation due to voltage changes in the input power grid. The diode 47 on the primary side of the transformer 46 protects the transistor 43 from overvoltage. Pulses 75 appear on the secondary side of the transformer but the average becomes zero. Although the peak-to-peak value does not change now, the peak-to-zero amplitude depends on the duty cycle. Thus, since the stem 75 has a constant repetition rate, the amplitude depends from peak to zero on the pulse width.

The pulses 75 are connected through the transformer 46 and all transient pulses, i.e. the spikes, are attenuated by a resistor 49. These pulses can be obtained as a pulse 53 at the terminal F. These pulses are used to synchronize the switching of the power supply 10 of the switching controller. Diode 50, capacitor 51 and resistor 52 form a peak detector circuit which generates a constant analog voltage within terminal B of terminal B and controller 10, representing changes in the DC high voltage current and DC voltage at terminal D.

In Figure 1 the pulses 75 is connected through a transformer 46 which implements the secondary side of the transformer 17, the difference between the input voltage. This difference is desirable so that any direct current obtained from the extra winding of the transformer 17 used to power other portions of the television receiver is comparable to the voltage in the body of the receiver. This eliminates the relatively expensive power transformer that would otherwise be necessary to make the difference between the network and the television body. With this isolation arrangement, the feedback for smoothing and detector circuits takes place via switch terminal A in the power supply 10.

Figure 2 illustrates a switched mode power supply similar to that described in British Provisional Patent Application No. 24,861/75, filed June 10, 1975 (RCA 69,816), and which may be used in block 10 of Figure 1 to perform discrete operation of the receiver. The input conductor is connected to a bridge rectifier 60 and the positive DC current is connected to a switching transistor 61 which energizes the primary side of the switching controller converter 62. The secondary side of the transformer 62 is connected via a diode 63 which rectifies the connected square waveform and provides direct current to the switch terminal C to operate the horizontal deflection circuit. Using the arrangement of Fig. 2, the input reactance 11 of Fig. 1 can be eliminated and the switch terminal C connected directly to the compression winding 13a, as illustrated in Fig. 2, and the secondary winding of the transformer 62 effectively acts as a stored energy supply, eliminating the need for input reactance 11. The side output on the secondary side of the transformer 62 is connected via a diode 64 and a filter capacitor 65 so that a smaller amount of B + voltage can be obtained to power the portion indicating the voltage at the switch terminal D from the controller of Figure 1. It can be seen that the function of the transformer 62 of the switching controller is also the operation of the isolation transformer, its secondary winding being connected to the ground of the body, whereby the entire deflection circuit can be separated from the input conductor. The conductivity and inhibit states of the switching transistor 61 are controlled by a suitable switching control circuit 66, the input signal of which is an analog control voltage of the switching terminal B and the synchronous pulse information of the switching terminal F. Thus, the switching is synchronized at the horizontal deflection frequency to eliminate the interference source of video signal reproduction, and the switching intervals of each control period are controlled by an analog voltage connected to switch terminal B. the conductivity state and thus the B + level provided at the terminals C and D.

Figure 3 illustrates another general type of controller that may also use the analog control signals obtained from the circuit of Figure 1. The AC type mains voltage is rectified by a bridge rectifier 60 and the pulsating DC is leveled by a filter circuit including a choke 67 and a capacitor 68. The direct current is then applied through a diode 69 to a switch terminal C to energize the horizontal deflection circuit of Figure 1. Resistors 71 and 72, combined over a power supply source, provide a lower B + level at their connection point, which is connected to switch terminal D to power the detector circuit of Figure 1. The synchronization pulses 53 are connected from the switch terminal F to the switch controller 73 and the analog control voltage is connected via the switch terminal B to the switch control.

In the arrangement of Fig. 3, the thyristor 70 is turned on at a suitable time determined by the detector pulse 53 to the connected switch terminal F for a time determined by the analog voltage connected to the switch terminal B. Thus, the control switch 73 provides a phase control for the conductivity of the thyristor 70. As is known, directing the thyristor 70 to the commutation circuits 13 and 13a allows the energy stored in Figure 1 to be discharged through the thyristor 70 back to the power supply to maintain the desired energy limit in the deflection circuit to provide a controlled high voltage of 59497 to this television receiver. The embodiment of Figure 3 does not allow the use of a shielded body. However, if desired, the isolating power transformer can be included in the AC mains before the bridge rectifier 60 so that the entire frame can be separated.