Horizontal deflection apparatus

Disclosed is an apparatus for controlling a drive transistor of a horizontal deflection apparatus which comprises a comparator; a switching controller which compares a reference voltage coupled to a non-inverting terminal with a signal provided externally through an inverting terminal and removes noise; a switch including a first switch coupled to a constant voltage and a grounded second switch, either the first or second switch being operated according to an output of the switching controller; a diode; a capacitor; a resistor; and a base current supplier. When the constant current, generated by the constant voltage, is provided through the first switch, the constant current is provided to the base terminal of the transistor through the diode, the transistor is turned on, and the capacitor is charged to as much as a forward voltage drop of the diode, and when the first switch is turned off and the grounded second switch is turned on, the transistor is turned off to discharge the capacitor. The present invention supplies a uniform current to the base terminal or discontinues the supply of the uniform current so as to reduce switching loss of the transistor.

BACKGROUND OF THE INVENTION
 (a) Field of the Invention p The present invention relates to a horizontal
 deflection apparatus. More specifically, the present invention relates to
 an apparatus for controlling a drive transistor of a horizontal deflection
 apparatus to reduce switching loss of the drive transistor.
 (b) Description of the Related Art
 A horizontal deflection apparatus uses horizontal synchronization signals
 and synchronization to generate sawtooth waves of 15.75 KHz, and provides
 the sawtooth waves to a horizontal deflection coil in order to scan
 electron beams of television cathode ray tubes (CRT) or computer monitors
 in the horizontal direction.
 FIG. 1 is a circuit diagram illustrating a conventional horizontal
 deflection apparatus, and FIG. 2 is a waveform diagram of an equivalent
 circuit of a controller of a drive transistor. A controller 100 of the
 drive transistor Q2 is an equivalent circuit of a pulse transformer for
 providing a base current for the drive transistor Q2.
 As shown in FIG. 1, a drive signal to operate a switch Q1 is provided to
 the switch Q1 from an internal microprocessor. When the switch Q1 is
 turned on, an inductor current i.sub.LB is increased with the passage of
 time at a slope of V.sub.B /L.sub.B as shown in FIG. 2 since this circuit
 adopts a forward converter method. Since carriers in the base layer move
 in the negative direction, the drive transistor Q2 is turned off according
 to a base current i.sub.B2 of the drive transistor Q2, and energy is
 stored in an inductor L.sub.B. At this time, when the carriers in the base
 layer are removed, the base current i.sub.B2 of the drive transistor Q2
 goes into a completely off state, and the base current i.sub.B2 of the
 drive transistor Q2 becomes zero.
 When the switch Q1 is turned off, the inductor current i.sub.LB flows
 through the base of the drive transistor Q2 in a state decreasing with the
 passage of time (i.e., at a negative slope) because of the time delay of
 the inductor L.sub.B. Therefore, the drive transistor is turned on. At
 this time, after the base current i.sub.B2 of the drive transistor Q2 is
 provided at a maximum value, the base current i.sub.B2 is then gradually
 reduced but continuously maintained in an on state.
 When the controller 100 of the drive transistor is operated as above, a
 resonance switch 110 of the horizontal deflection apparatus operates in
 four operation modes in an equivalent circuit such as that shown in FIG.
 3. Waveforms in the four operation modes are shown in FIG. 4.
 FIG. 3(a) shows a first operation mode of the resonance switch 110.
 In the first operation mode, the drive transistor Q2 is turned on so that a
 resonance is not generated, and an inductor current i.sub.Ly of a yoke
 coil L.sub.y is increased from a point t0 to a point t2 in FIG. 4. It is
 assumed that the current i.sub.Ly flowing through the yoke coil L.sub.y
 flows through a diode D2 coupled to the drive transistor Q2 in parallel,
 and that the drive transistor Q2 is turned off.
 As shown in FIG. 4, when the diode D2 is turned on at the point t0 and a
 diode current i.sub.D2 flows, a voltage between a collector and emitter of
 the drive transistor Q2 becomes zero, and a capacitor Cx in FIG. 1 is
 charged to generate a capacitor voltage Vx. Therefore, when the drive
 transistor Q2 is turned on at a zero voltage point t1 (i.e., when the
 switch Q1 is turned off), a switching loss of the drive transistor Q2 is
 very low because the switching operation is performed in a zero voltage
 state.
 FIG. 3(b) shows a second operation mode of the resonance switch 110.
 As shown, the second operation mode of the resonance switch 110 is
 performed between the interval t2 and t3. Since the capacitor voltage Vx
 is provided, the diode D2 is turned off and the current i.sub.Ly of the
 yoke inductor L.sub.y is increased from a negative direction to a positive
 direction, and a collector current i.sub.C2 starts to gradually flow
 through the drive transistor Q2.
 At this time, as shown in FIG. 4, a base current i.sub.B2 of the drive
 transistor Q2 is reduced from a very high value to a very low value in a
 zero voltage switching state because of a time delay of the inductor
 L.sub.B in FIG. 1. On the other hand, a collector current i.sub.C2 of the
 drive transistor Q2 is gradually increased because of the yoke inductor
 L.sub.y. In the waveform of the base current i.sub.B2 of FIG. 4, a current
 I.sub.BF represents a forward bias current to drive the drive transistor
 Q2, and a current I.sub.BR represents a reverse bias current to stop the
 drive transistor Q2.
 The collector circuit i.sub.C2 gradually increases up to a maximum value
 I.sub.CP, and when the current I.sub.Ly flowing to the yoke coil L.sub.y
 reaches a maximum value I.sub.LP, the second operation mode stops.
 FIG. 3(c) shows a third operation mode of the resonance switch 110.
 As shown, the third operation mode of the resonance switch 110, which is
 performed between an interval t3 and t4 of FIG. 4, starts when the switch
 Q1 is turned on, that is, when the drive transistor Q2 is turned off. When
 the drive transistor Q2 is turned off, the collector current i.sub.C2
 flowing through the drive transistor Q2 is reduced, and the yoke coil
 current i.sub.Ly flows through a capacitor Cy coupled to the drive
 transistor Q2 in parallel.
 Therefore, as the capacitor Cy is charged, the voltage at the capacitor Cy
 steeply increases in a sine wave form, the voltage V.sub.CE2 also
 increases as a sine wave, and the collector current i.sub.C2 flowing
 through the drive transistor Q2 steeply reduces. When a drive status is
 not maximized in this state, that is, if even a small collector current
 i.sub.C2 flows, subsequent switching loss occurs.
 The capacitor Cy is discharged by a serial resonance of the yoke coil Ly
 and the capacitor Cy, and the voltage at the capacitor Cy reduces in a
 sine wave form.
 FIG. 3(d) shows a fourth operation mode of the resonance switch 110.
 As shown, the fourth operation mode of the resonance switch 110 is
 performed after an interval t4 of FIG. 4. When the current is discharged
 from the capacitor Cy and the voltage at the capacitor Cy becomes
 negative, the diode D2 coupled to the capacitor Cy in parallel is turned
 on to complete the fourth operation mode, and the yoke coil current
 i.sub.Ly flows through the diode D2, after which the mode returns to the
 first operation mode.
 Characteristics of the switching loss in the vicinity of the point t3 will
 now be described in detail.
 FIG. 5(a) is a diagram illustrating a switching loss under first base
 driving conditions during operation of a conventional horizontal
 deflection device, in which a horizontal deflection frequency is not
 changed but a magnitude of a base current is changed. Here, the solid
 lines represent reference base driving conditions, and the dotted lines
 represent the first base driving conditions.
 As shown, when the base current i.sub.B2 is reduced from the forward bias
 base current I.sub.BF to the reverse bias base current I.sub.BR under the
 reference base driving conditions of the drive transistor Q2, a voltage
 V.sub.CE2 between the collector and emitter, and the collector voltage
 i.sub.C2 of the drive transistor Q2 are represented by the solid lines
 around and after the point t3.
 When the reverse bias current I.sub.BR is not sufficiently small after the
 point t3, an off switching operation of the drive transistor Q2 is not
 performed quickly so that the collector current i.sub.C2 continues to
 flow. At this time, since the voltage VCE2 steeply increases at the point
 t3, switching loss of the drive transistor Q2 occurs.
 To prevent this energy loss, when the forward bias base current I'.sub.BF
 and the reverse bias base current I'.sub.BR are reduced according to the
 first base driving conditions as shown by dotted lines in FIG. 5(a), the
 voltage V'.sub.CE2 is increased since the forward bias base current
 I'.sub.BF for turning on the drive transistor Q2 is small. At this time,
 the collector current I'C2 is increased to a maximum value before the
 point t3, thereby resulting in the generation of switching loss.
 FIG. 5(b) is a diagram illustrating switching loss under second base
 driving conditions during operation of a conventional horizontal
 deflection apparatus. As in FIG. 5(a), the horizontal deflection frequency
 is not charged but the magnitude of the base current is changed. Here, the
 solid lines represent reference base driving conditions, and the dotted
 lines represent the second base driving conditions.
 Assuming that, under the second base driving conditions, the forward bias
 base current I'.sub.BF is greater than I.sub.BF, and the reverse bias base
 current I'.sub.BR is less than I.sub.BR, since the forward bias base
 current I'.sub.BF is sufficient to turn on the drive transistor Q2, the
 voltage V'.sub.CE2 between the collector and emitter is reduced to nearly
 zero. However, since the base current I'.sub.B2 is greatly reduced before
 the point t3, the voltage V'.sub.CE2 between the collector and emitter is
 substantially increased. Therefore, since the collector current I'.sub.C2
 in the vicinity of the point t3 is at a maximum, the switching loss is
 increased.
 Therefore, the reverse bias base current I.sub.BR of the controller 100 of
 the drive transistor Q2 is optimized to suit the characteristics of
 television sets or monitors. However, since the horizontal deflection
 frequency of the monitors must be modified to adjust the resolution of the
 monitors, optimization is very difficult.
 FIG. 6(a) is a waveform of the reverse bias base current when the
 horizontal deflection frequency is changed to a higher frequency.
 As shown, when changes in the resolution of the monitor increases the
 horizontal deflection frequency to therefore change the point where the
 base current i.sub.B becomes zero (i.e., from the point t3 to t'3), the
 reverse bias base current I.sub.BR at the point t3 increases to I'.sub.BR
 at the point t'3.
 Therefore, when the reverse bias base current increases over that required
 to turn off the drive transistor Q2, the drive transistor Q2 is not
 completely turned off, and switching loss occurs at the point t'3 as a
 result of the maximum collector current and also the voltage between the
 collector and emitter.
 FIG. 6(b) is a waveform of the forward bias base current when the
 horizontal deflection frequency is changed to a smaller frequency.
 As shown, when changes in the resolution of the monitor decreases the
 horizontal deflection frequency to therefore change the point where the
 base current i.sub.B becomes zero (i.e., from the point t3 to t'3), the
 reverse bias base current I.sub.BR at the point t3 decreases to I'.sub.BR
 at the point t'3.
 Therefore, when the reverse bias base current decreases below that required
 to turn off the drive transistor Q2, the moment at which the drive
 transistor Q2 is turned off becomes point t3, which is earlier than the
 point t'3 at which the base current becomes completely zero. Accordingly,
 the voltage between the collector and emitter increases before the point
 t'3 so that switching loss occurs.
 Hence, the drive transistor Q2 experiences almost no switching loss through
 use of zero voltage switching. However, when the drive transistor Q2 is
 turned off, very heavy switching loss repeatedly occurs. This is
 particularly the case when the horizontal deflection frequency is changed
 to adjust the resolution of the monitor.
 In case of controlling the drive transistor of the horizontal deflection
 apparatus such that the horizontal deflection frequency of a color
 television is uniform or the horizontal deflection frequency of a computer
 monitor is varied, much heat is generated in the power switching elements
 when using the conventional methods. To solve this problem, elements
 having greater current and voltage capacities, or a heat sink are used.
 However, both of these methods increase overall costs, particularly the
 use of the heat sink. Also, reliability is not ensured with the use of the
 heat sink.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a horizontal deflection
 apparatus to reduce switching loss and product costs.
 In one aspect of the present invention, in a horizontal deflection
 apparatus using a horizontal synchronization signal and generating a
 signal of a predetermined frequency then supplying the signal to a
 horizontal deflection coil by switching a drive transistor to horizontally
 scan electron beams of a cathode ray tube (CRT), a method for controlling
 the drive transistor comprises the steps of: (a) supplying a constant
 current to the drive transistor to turn on the drive transistor when a
 first signal is provided; and (b) discontinuing the supply of the constant
 current to the drive transistor to turn off the drive transistor when a
 second signal is provided.
 The step (a) is characterized in that, when the constant current is
 supplied, a capacitor coupled to a base terminal of the drive transistor
 is charged.
 The step (b) is characterized in that resulting from the discontinued
 supply of the constant current, charges charged in a capacitor, which is
 coupled to a base terminal of the drive transistor, are discharged to
 thereby control the drive transistor to off.
 In another aspect of the present invention, an apparatus for controlling a
 drive transistor comprises a switching controller comparing a reference
 voltage with a signal provided externally, and removing noise; a switch
 comprising a first switch coupled to a constant voltage and a second
 switch having a first terminal coupled to a first terminal of the first
 switch and having a second terminal grounded, either the first or second
 switch being turned on according to an output of the switch controller;
 and a base current supplier comprising diodes and a capacitor, the base
 current supplier supplying, when the first switch is turned on and a
 constant current is supplied from the constant voltage, the constant
 current to a base terminal of the drive transistor through the diodes so
 that the drive transistor is turned on and the capacitor is simultaneously
 charged as much as a forward voltage drop of the diodes, and discharging,
 when the second switch is turned on, the capacitor and turning off the
 drive transistor.
 The base current supplier is characterized in that an anode of one or the
 diodes is coupled to the first and second switches, a cathode is coupled
 to the base terminal of the drive transistor, and the capacitor is coupled
 to the diodes in parallel.
 A cathode of one diode is coupled to an anode of a next diode in series in
 a predetermined n number of diodes of the base current supplier.
 In a further aspect of the present invention, a horizontal deflection
 apparatus comprises a resonance switch comprising a drive transistor which
 receives a horizontal synchronization signal to horizontally scan electron
 beams of a cathode ray tube (CRT) and performs a switching operation; a
 first diode having a cathode coupled to a collector terminal of the drive
 transistor and having a grounded anode; a first capacitor having a first
 terminal coupled to the cathode of the first diode and having a second
 terminal which is grounded; an inductor having a first terminal coupled to
 one terminal of the capacitor; and a second capacitor having a first
 terminal coupled to a second terminal of the inductor and having a second
 terminal which is grounded, and, performing a zero voltage switching
 operation according to an output of the drive transistor when the drive
 transistor is turned on; a controller of the drive transistor supplying a
 constant current to a base terminal of the drive transistor while a first
 signal is provided, and discontinuing the supply of the constant current
 when a second signal is provided; and a horizontal deflection output
 terminal comprising a transformer having a primary coupled to the
 collector of the drive transistor, the horizontal deflection output
 terminal being coupled to the resonance switch to supply energy to a
 secondary of the transformer.
 The controller of the drive transistor comprises a switching controller
 comparing a reference voltage with a signal externally provided, and
 removing noise; a switch comprising a first switch having a first terminal
 coupled to a constant current and a second switch having a first terminal
 coupled to a second terminal of the first switch and having a second
 terminal which is grounded, and either the first or second switch being
 turned on according to an output of the switching controller; and a base
 current supplier comprising a second diode and a third capacitor, and
 supplying, when the first switch is turned on and a constant current is
 supplied from the constant voltage, the constant current to a base
 terminal of the drive transistor through the second diode so that the
 drive transistor is turned on and the third capacitor is simultaneously
 charged as much as a forward voltage drop of the second diode, and
 discharging, when the second switch is turned on, the third capacitor and
 turning off the drive transistor.
 The base current supplier is characterized in that an anode of the second
 diode is coupled to the first and second switches, a cathode is coupled to
 the base terminal of the drive transistor, and the third capacitor is
 coupled to the second diode in parallel.
 The second diode of the base current supplier can be replaced with a
 predetermined number of diodes in which a cathode of one diode is coupled
 to an anode of a next diode in series.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 In the following detailed description, only the preferred embodiment of the
 invention has been shown and described, simply by way of illustration of
 the best mode contemplated by the inventor(s) of carrying out the
 invention. As will be realized, the invention is capable of modification
 in various obvious respects, all without departing from the invention.
 Accordingly, the drawings and description are to be regarded as
 illustrative in nature, and not restrictive.
 FIG. 7 is a horizontal deflection apparatus according to a preferred
 embodiment of the present invention.
 As shown, the horizontal deflection apparatus comprises a controller 100 of
 a drive transistor Q2, a resonance switch 110, and a horizontal deflection
 output terminal 120.
 The controller 100 of the drive transistor Q2 supplies constant current to
 a base terminal of the drive transistor Q2 while the drive transistor Q2
 is turned on, and turns off the drive transistor Q2 by discontinuing the
 constant current. The controller 100 comprises a switching controller 710,
 a switch 720, and a base current supplier 730.
 The switching controller 710, comprising a comparator, compares a reference
 voltage Vref provided through a non-inverting terminal with an external
 signal provided through an inverting terminal, and removes noise below a
 predetermined level and provided externally. The switching controller 710
 then controls a switching operation of the switch 720 using a signal that
 is over an optimum level.
 The switch 720 comprises switches Q.sub.A and Q.sub.B. Either switch
 Q.sub.A or Q.sub.B is operated according to an output of the switching
 controller 710. The base current supplies 730 comprises diodes Da and Db,
 and a capacitor C. A cathode of the diode Da is coupled to an anode of the
 diode Db, an anode of the diode Da is coupled to one terminal of the
 capacitor C, and a cathode of the diode Db is coupled to another terminal
 of the capacitor C, thereby forming a parallel structure.
 Therefore, if a base current i.sub.B is received through the switch 720,
 the diodes Da and Db are turned on, and the capacitor C is charged with a
 charge corresponding to a forward voltage drop of the diodes Da and Db.
 Here, the magnitude of the base current I.sub.B is a uniform value of
 Vcc/Rx.
 When there is no signal provided from the switch 720, the capacitor C is
 rapidly discharged and the counter-directional base current i.sub.B is
 generated such that the drive transistor Q2 is swiftly turned off.
 Operation of the controller 100 of the drive transistor Q2 will now be
 described.
 When a high status signal is provided to the inverting terminal of the
 switching controller 710, the switching controller 710 compares the
 provided signal with the reference voltage Vref supplied through the
 non-inverting terminal, and when the switching controller 710 determines
 the compared signal to be a high status signal over a predetermined level,
 the switching controller 710 turns on the switch Q.sub.A and turns off the
 switch Q.sub.B so as to distinguish a signal from noise.
 Therefore, when the current supplied from the voltage Vcc passes through
 the resistor Rx coupled to the voltage Vcc in series, the switch QA of the
 switch 720, and the diodes Da and Db of the base current supplier 730, the
 current charges the capacitor C coupled to the diodes Da and Db in
 parallel as much as the forward voltage drop provided to the diodes Da and
 Db, and the current then flows to the base of the drive transistor Q2 to
 turn on the drive transistor Q2.
 At this time, the magnitude of the base current i.sub.B to turn on the
 drive transistor Q2 can be adjusted by the voltage Vcc and the resistor
 Rx. The base current i.sub.B then maintains a uniform magnitude during the
 period in which the drive transistor Q2 is turned on. That is, a uniform
 current i.sub.B flows starting from when the drive transistor Q2 starts to
 drive to just before the drive transistor Q2 is stopped.
 When a low status signal is provided through the inverting terminal of the
 switching controller 710, the switching controller 710 turns on the switch
 Q.sub.B of the switch 720 and turns off the switch Q.sub.A, thereby
 discharging the capacitor C as much as the forward voltage drop provided
 to the diodes.
 The base current i.sub.B flowing in a direction opposite that indicated by
 the arrow of FIG. 7 passes from the drive transistor Q2 to the capacitor C
 and switch Q.sub.B by the charges discharged from the capacitor C, and the
 base current i.sub.B initially turns off the drive transistor Q2 when
 flowing in the negative direction, and becomes zero when the carriers on
 the base layer are removed.
 Therefore, since the switch 720 is operated in the switch mode, switching
 loss is minimized and the switch can be packaged within a very small IC.
 FIG. 8 is a waveform diagram of the base current used to operate the drive
 apparatus according to a preferred embodiment of the present invention. As
 shown, the initial base current to turn on the drive transistor Q2
 maintains a uniform value during on intervals, and the controller 100
 supplies to the resonance switch 110 the base current which is obtained by
 dividing the maximum collector current just before being turned off with a
 current amplification ratio.
 Therefore, when a user changes the resolution of the computer monitor,
 although the horizontal deflection frequency is changed, since the
 magnitude of the base current i.sub.B is uniform during the on interval of
 the drive transistor Q2, switching loss can be minimized in case of
 changes of the resolution of the computer monitor.
 The resonance switch 110 comprises the drive transistor Q2 having a base
 terminal coupled to an output terminal of the controller 100 of the drive
 transistor Q2 and having a grounded emitter; the diode D2 having a cathode
 coupled to a collector terminal of the drive transistor Q2 and having an
 anode terminal which is grounded; the first capacitor Cy having one
 terminal coupled to the cathode terminal of the diode D2 and having
 another terminal which is grounded; the inductor Ly having one terminal
 coupled to one terminal of the capacitor Cy; and the second capacitor Cx
 having one terminal coupled to another terminal of the inductor Ly and
 having another terminal which is grounded. When the drive transistor Q2 is
 turned on, a zero voltage switching operation is performed according to
 the output of the controller 100 of the drive transistor Q2.
 The horizontal deflection output terminal 120, comprising a transformer T
 having a primary coupled to the collector terminal of the drive terminal
 Q2, is coupled to the resonance switch 110 and provides energy to a load
 coupled to a secondary of the transformer T.
 Therefore, a uniform current is supplied to the base terminal of the drive
 transistor Q2 while the drive transistor is turned on so that switching
 loss of the drive transistor Q2 is minimized.
 The drive apparatus according to the preferred embodiment of the present
 invention does not use a pulse transformer and instead controls a
 transistor by a switch mode so as to supply a uniform base current. As a
 result, the size of a heat sink can be minimized by reducing switching
 loss, thereby reducing the size of the horizontal deflection apparatus,
 increasing reliability, and reducing product costs.
 While this invention has been described in connection with what is
 presently considered to be the most practical and preferred embodiment, it
 is to be understood that the invention is not limited to the disclosed
 embodiments, but, on the contrary, is intended to cover various
 modifications and equivalent arrangements included within the spirit and
 scope of the appended claims.