JPS6040065Y2 - Cathode ray tube heater circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heater circuit for a cathode ray tube in a receiver that receives TV broadcast waves having different horizontal scanning frequencies.

As such a receiver, for example, the horizontal scanning frequency is 20.47.
5KHz (81 scanning lines Hayashi) and 15.625KHz
There is a device that receives two broadcast waves (number of scanning lines: 625).

In such receivers, the boost voltage or power supply voltage of the horizontal deflection circuit is generally switched in accordance with the horizontal scanning frequency in order to compensate for high voltage and changes in deflection caused by differences in horizontal scanning frequency.

That is, when the horizontal scanning frequency changes, the peak value of the pulse generated in the flyback transformer changes, and this changes the high voltage on the secondary side and the horizontal deflection.

To compensate for this, the boost voltage or power supply voltage is changed so that the peak value of the pulse remains constant.

In this case, if the peak value of the pulse is constant, the effective value of the pulse increases in approximately proportion to the higher the horizontal scanning frequency.

On the other hand, some heater circuits for cathode ray tubes in television receivers are ignited by pulses generated in a flyback transformer.

When this heater circuit is used in the above-mentioned television receiver, the effective value of the pulse changes depending on the horizontal scanning frequency, and therefore the electric power supplied to the heater changes, so it cannot be used as is.

For this reason, in the past, the taps of the windings for extracting the heater voltage were switched using a relay or the like, depending on the horizontal scanning frequency.

The present invention provides a heater circuit for a cathode ray tube that can keep the power of the heater constant regardless of the horizontal scanning frequency without using switching means such as relays.

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a flyback transformer, 2 is a horizontal output transistor, 3 is a damper diode, 4 is a resonant capacitor, 5 is a deflection coil, 6 is a correction capacitor,
7 is a boost capacitor, 8 is a boost diode, 9
is when the horizontal scanning frequency is low (e.g. 15.625K)
Hz), it is closed to the a side, and when it is high (e.g. 20
．． 475KHz), the switch is closed to the b side,
10 is a high-voltage rectifier diode, 11 is a winding for taking out heater voltage, and 12 is a heater for a cathode ray tube.

13.14 is the inductance h that constitutes the series resonant circuit
with a coil of and a capacitor of capacitance C8, its resonant frequency f.

is selected to be approximately equal to the lower horizontal scanning frequency.

17 is a current limiting resistor. In the above configuration, when the horizontal scanning frequency is low, the switch 9 is closed to the a side, and as a result, a pulse 15 having a peak value of ■□ appears at the collector of the transistor 2 as shown in FIG. 2A.

Also, when the horizontal scanning frequency is high, the switch 9 is closed to the b side, so that the collector of the transistor 2 has a
A pulse 16 appears as shown in FIG. 2B.

This pulse 16 is boosted up by ΔV from the pulse peak value V2 to Vl shown by the dotted line by its peak value force and the boost voltage generated across the capacitor 7.

This allows the high voltage and horizontal deflection width on the secondary side to match those when the horizontal scanning frequency is low.

Further, since the heater single ignition pulse similar to the pulse 15 or 16 obtained from the winding 11 has a constant peak value, when the frequency is high, the AC effective voltage is larger than when the frequency is low.

Resonant frequency f due to coil 13 and capacitor 14.

is chosen approximately equal to the lower frequency, so when the frequency of the ignition pulse is low, the series resonant circuit exhibits low impedance, and when the frequency of the ignition pulse is high, the series resonant circuit deviates from the resonance point. shows high impedance.

Therefore, for example, as shown in FIG. By changing the sharpness Q by co and appropriately selecting the impedance for high frequencies as 4 or 4..., even if the frequency and AC effective voltage at both ends of the winding 11 change,
Constant power can be supplied to the heater 12.

Note that the resonance frequency f. f does not necessarily have to match the horizontal scanning frequency, but depends on variations in component constants.

The resonance point of LoCo may be chosen to be lower than the lower horizontal scanning frequency in order to reduce the effect of changes in .

The above has described an embodiment in which the present invention is applied to the case where the boost voltage is switched according to the horizontal scanning frequency, but the present invention can also be applied to the case where the power supply voltage of the horizontal deflection circuit is switched according to the horizontal scanning frequency. be able to.

The present invention uses a cathode ray tube in a receiver that receives TV broadcast waves with different horizontal scanning frequencies and selectively connects a boost circuit to the horizontal deflection circuit or switches the power supply voltage depending on the horizontal scanning frequency. The pulse for igniting the heater is supplied to the heater via a series circuit of an inductance and a capacitor that has a resonance frequency near the low horizontal scanning frequency.

Therefore, according to the present invention, the power supplied to the heater can be made constant regardless of the horizontal scanning frequency with a simple circuit configuration without using switching means such as a relay.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of pulses generated in the collector, and FIG. 3 is a frequency characteristic diagram of the heater circuit. In addition, in the symbols used in the drawings, 1...
・Flyback transformer, 7...Boost capacitor, 8...Boost diode, 11...
...Heater voltage extraction winding, 12...
・Cathode ray tube heater 13... Coil, 14
・・・・・・It is a capacitor.

Claims (1)

[Scope of utility model registration request] It is forced to receive a plurality of television broadcast waves each having a different horizontal scanning frequency, and it is also forced to selectively connect a boost circuit to the horizontal deflection circuit or switch the power supply voltage according to the horizontal scanning frequency. In a receiver in which the cathode ray tube heater is ignited by the pulse obtained from the horizontal deflection circuit, a series circuit of an inductance and a capacitor is connected between the output end of the pulse and the heater. A heater circuit for a cathode ray tube, characterized in that the resonance frequency of the series circuit is selected near the lower horizontal scanning frequency of the plurality of horizontal scanning frequencies.