Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2000-04-19
2001-04-24
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S364000, C315S370000
Reexamination Certificate
active
06222329
ABSTRACT:
TECHNICAL FIELD
This invention relates to a horizontal deflection circuit used for television image receiver or display unit, etc. using cathode ray tube (CRT).
BACKGROUND ART
Horizontal deflection circuit used in television image receiver essentially serves to deliver sawtooth shaped current to horizontal deflection yoke. Generally, flyback transformer is connected as load equivalently in parallel with the horizontal deflection yoke. In addition, it is known that, in order to correct distortion of picture image known as pin cushion distortion, there is provided, as shown in
FIG. 1
, at the horizontal deflection circuit, a diode modulation circuit comprising a pin cushion distortion correction output transistor
151
, a diode
152
, a coil
153
, a diode
154
, a capacitor
155
and a pulse modulation transformer
156
, etc.
The fundamental operation of horizontal deflection will be described below by taking the example of horizontal deflection circuit using transistor as switching element for horizontal output as shown in FIG.
1
.
In
FIG. 1
, when, at the latter half of horizontal scanning time period, horizontal driver pulse of positive polarity is applied to base of a horizontal output transistor
131
so that the horizontal output transistor
131
is turned ON, collector current flows while linearly increasing through a primary coil
136
a
of a flyback transformer
136
from power source (supply terminal). Moreover, simultaneously therewith, positive deflection current flows in a horizontal deflection yoke
134
from sigmoid (S-shaped) distortion characteristic correction capacitors (hereinafter referred to as sigmoid correction capacitor as occasion may demand)
135
a
,
135
b
serving as power source (supply). Further, when the horizontal output transistor
131
is turned OFF at horizontal flyback (retrace) time period, collector current becomes equal to zero (0). In this case, while synthetic inductance of primary coil
136
a
of the flyback transformer
136
and the horizontal deflection yoke
134
and a resonance capacitor
133
resonate, charge current flows into resonance capacitor
133
from the horizontal deflection yoke
134
and the flyback transformer
136
, and then discharge current for discharging it flows into the horizontal deflection yoke
134
and the flyback transformer
116
. However, since a damper diode
132
is connected to the horizontal deflection yoke
134
and the flyback transformer
136
, this resonant phenomenon stops at this stage. As a result, backward current from the horizontal deflection yoke
134
and the flyback transformer
136
does not flow in (through) the resonance capacitor
133
, but flows in the damper diode
132
. At this time, retrace pulse is generated in a secondary coil
136
b
of the flyback transformer
136
. By rectifying this retrace pulse by rectifier circuit (not shown), high voltage can be obtained.
In addition, the pin cushion distortion correction output transistor
151
is caused to be turned ON at a predetermined timing corresponding to quantity of correction in synchronism with horizontal scanning to modulate current flowing in the horizontal deflection yoke
134
by waveform of a predetermined vertical period, thus making it possible to correct pin cushion distortion.
The above-described deflection operation is numerically indicated below. In this case, when maximum amplitude ((peak to peak) value which will be referred to as PP value hereinafter) of horizontal deflection current I flowing in the horizontal deflection yoke
134
is Ipp, maximum voltage of voltages V across both ends of the horizontal deflection yoke
134
is Vp, inductance of the horizontal deflection yoke
134
is L and horizontal flyback (hereinafter referred to as retrace) time period is Tre, voltage V is expressed as below.
V=L
(
dI/dt
) (1)
In the case where the retrace pulse can be approximated by sine wave curve, the maximum voltage Vp is expressed as below.
Vp=
(&pgr;/2)
LIpp/Tre
(2)
On the other hand, when CRT and horizontal deflection yoke
134
which are used are determined, energy of deflection magnetic field necessary for scanning electron beams by that horizontal deflection yoke
134
is univocally determined by shape of CRT and/or high voltage condition, etc. Since magnetic energy that current I flowing in indactance L has is expressed as (½)LI
2
, LIpp
2
represents deflection efficiency of this horizontal deflection yoke
134
. When this deflection efficiency is W, the following formula holds.
LIpp
2
=W
(3)
From the formulas (2), (3), the following relational expression is given.
IppVp
=(&pgr;/2)
W/Tre
(4)
When W and Tre are constant in the above-mentioned formula (4), horizontal deflection current Ipp is inversely proportional to retrace pulse voltage Vp across the both ends of the horizontal deflection yoke
134
.
Since Vp of the retrace time period is necessarily smaller than voltage across the both ends of the switching element in the horizontal deflection circuit conventionally used as shown in
FIG. 1
, Vp is restricted by the withstand voltage performance of the switching element. Accordingly, in the case where horizontal deflection frequency is twice grater than that of ordinary case, such as, for example, flicker free television image receiver, since Tre is caused to be ½. Therefore, if Vp is unchanged when viewed from withstand voltage performance of the switching element, Ipp becomes double. As a result, there increases power loss in respective elements of the circuit by the above-mentioned fact. By this countermeasure, there inevitably results increase in the cost of circuit including respective elements.
DISCLOSURE OF THE INVENTION
This invention has been made in order to solve problems as described above and its object is to provide a horizontal deflection circuit in which retrace pulse voltage applied to the horizontal deflection yoke is caused to be large and deflection current is caused to be small, thus making it possible to easily carry out picture size adjustment in horizontal direction and distortion correction.
In order to solve the above-described problems, a horizontal deflection circuit according to this invention comprises: a first parallel circuit in which a first switching element, a first damper diode and a first resonance capacitor are connected in parallel, one end of the first parallel circuit being grounded, the first parallel circuit being operative to generate a first pulse; a second parallel circuit in which a second switching element, a second damper diode and a second resonance capacitor are connected in parallel, one end of the second parallel circuit being connected to the other end of the first parallel circuit, the second parallel circuit being operative to generate a second pulse; a horizontal deflection yoke having one end connected to the other end of the second parallel circuit and the other end connected to one end of a sigmoid (S-shaped) distortion characteristic correction capacitor; and a flyback transformer having one end connected to a DC power source (supply) and operative to deliver operation current to the first and second switching elements thus to synthesize the first pulse from the first parallel circuit and the second pulse from the second parallel circuit to generate deflection current for driving the horizontal deflection yoke, the horizontal deflection circuit comprising: an integration circuit for integrating horizontal drive signal inputted thereto; a first comparison•latch circuit for comparing signal from the integration circuit with first level to latch comparison result; a second comparison•latch circuit for comparing signal from the integration circuit with second level to latch comparison result; a first drive circuit for driving the first switching element in accordance with an output of the first comparison•latch circuit; a second drive circuit for driving the second switching element in accordance with an output of the second comparison•latch
Honji Hidetaka
Kikuchi Ken
Otaki Susumu
Watanabe Junzo
Lee Wilson
Maioli Jay H.
Sony Corporation
Wong Don
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