JP3016570B2 - Voltage resonance type high voltage generation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high voltage generating circuit for obtaining an anode voltage of a cathode ray tube, and more particularly to a voltage resonance type high voltage generating circuit independent of a horizontal deflection circuit.

BACKGROUND ART Conventionally, a circuit shown in FIG. 6 is known as this kind of circuit. In the figure, a flyback transformer FBT, a resonance capacitor C ₁ , a damper diode D ₁ and an output transistor Q ₁ constitute a voltage resonance type switching circuit 1. Fly back end of the primary winding of the transformer FBT is, AC power supply voltage is rectified by the rectifier circuit 2 and the capacitor C ₂ menstrual stable power supply circuit 3 by stabilized DC voltage capacitor C ₃ obtained by the And high pressure regulator 4. In the switching circuit 1, a high voltage is generated in the secondary side of the flyback transformer FBT by the flyback transformer FBT output transistor Q ₁ the primary winding as a load inductance is switched in synchronism with the horizontal scanning frequency.

High voltage generated in the secondary side of the flyback transformer FBT is output is rectified by a high voltage rectifying diode D ₂ as the anode voltage of the cathode ray tube (not shown). In order to stabilize the high voltage, the high voltage is detected by the bleeder resistors R ₁ and R ₂ , and the detection output is fed back to the high voltage regulator 4. The high voltage regulator 4 is configured to control the level of the DC voltage supplied to the flyback transformer FBT according to the fluctuation of the high voltage.

In the conventional voltage resonance type high voltage generating circuit configured as described above, since the stabilized power supply circuit 3 suppresses the fluctuation of the AC input voltage, the stabilized power supply circuit 3 is indispensable. Thus, there is a disadvantage that the entire circuit configuration becomes large-scale and the cost increases.

SUMMARY OF THE INVENTION [Object of the Invention] Accordingly, an object of the present invention is to provide a voltage resonance type high voltage generation circuit capable of suppressing fluctuation of high voltage due to fluctuation of high voltage and fluctuation of AC input voltage with a simple circuit configuration. Aim.

[Constitution of the Invention] A voltage resonance type high voltage generating circuit according to the present invention includes a flyback transformer and a first switch circuit connected to one end of a primary winding of the flyback transformer and switched at a predetermined frequency. A switching circuit, a power supply circuit for generating a predetermined DC voltage, and connected between an output terminal of the power supply circuit and the other end of the primary winding of the flyback transformer to selectively conduct the DC voltage. A second switch circuit for supplying the other end of the primary winding of the flyback transformer, detecting means for detecting a high voltage generated in a secondary winding of the flyback transformer, and Control means for switching at a frequency, the first switch circuit being connected to the other end of the primary winding of the flyback transformer and the second
Resonance control means for absorbing resonance when the switch circuit is not conducting, wherein the control means conducts simultaneously with the first switch circuit of the second switch circuit in accordance with a detection output of the detection means. It is characterized by controlling the conduction time.

According to the voltage resonance type high voltage generating circuit of the present invention, switching is performed at the same frequency as the switching frequency of the first switch circuit in the voltage resonance type switching circuit, and the output terminal of the DC power supply circuit and the flyback transformer In the second switch circuit connected between the other end of the primary winding of
The DC voltage conduction time, which is conducted simultaneously with the first switch circuit to the other end of the primary winding of the flyback transformer, is controlled according to the high voltage detection output, and the first switch circuit is conducted and the second switch is conducted. Resonance when the circuit is not conducting is absorbed by the resonance absorbing means.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which parts identical to those in FIG. 6 are denoted by the same reference numerals. Here, the transistor Q ₁ is responsible for the switching means of the first switch circuit. In the figure, a transistor Q ₂ as a switch means in a second switch circuit is connected between a positive output terminal of a rectifier circuit 2 and one end of a primary winding of a flyback transformer FBT.
There are connected, the transistor Q ₂ diodes
D ₄ is connected in parallel with reverse polarity. A flywheel diode is provided for the voltage resonance type switching circuit 1.
D ₃ is connected in parallel. The base of the transistor Q ₂ is, phase control circuit 5 for controlling the conducting (ON) time of the transistor Q ₂ in accordance with the detected output of the high voltage by bleeder resistors R _1, R ₂ are connected.

Phase control circuit 5, for example as shown in FIG. 2, the sawtooth wave generating circuit 21, bleeder resistor R _1, a reference voltage generating a voltage value according to the detection output of the R ₂ to generate a variable reference voltages V ₁ a circuit 22, and a comparator 23 for comparing the sawtooth wave and the reference voltage V _1. The reference voltage V ₁ is resistance
It supports detection output by R ₁ and R ₂ , so that the reference voltage V
It will be referred to as ₁ and the detection voltages V ₁ to. Thus, control pulses sawtooth wave is pulse width modulated by the detection voltage V ₁ (PWM), i.e. the pulse width so that the control pulse that varies in response to variations in the high voltage is obtained. Then, it is the conduction of the transistor Q ₂ (ON) time is controlled by this control pulse.

Next, the circuit operation of such a configuration will be described with reference to the waveform diagram of FIG. In the third diagram, (a) represents the current flowing through the flyback transformer FBT, (b) a flyback pulse, (c) the operating state of the transistor Q _1,
(D) shows the operating state of the transistor Q _2, respectively.

When transistor Q ₂ is turned on at time t _1, capacitor C ₂
DC voltage is applied to the flyback transformer FBT through the transistor Q _2. At this time, the transistor Q ₁ is already on. Between t _{1 and} t ₂ , C ₂ → Q ₂ → FBT → Q ₁ → C ₂
A current flows through the flyback transformer FBT through the path of. When at time t ₂ transistor Q ₁ is turned off, the flyback transformer FBT and the resonant circuit due to resonance capacitor C ₁ is formed, in between t ₂ -t _3, the route of _{FBT → C 1 → C 2 →} Q 2 → FBT resonant current flows, t ₃ in between _{-t 4, C 1 → FBT →} D 4 → C 2 → discharge current flows in a path C _1. Flyback pulse (b) occurs in a period of the t ₂ -t _4. Between t _{4 and} t ₅ , FBT → D ₄ → C
Current flows through the path of ₂ → D ₁ → FBT.

In the state shown by the solid line in FIG. 3, the high voltage decreases, also the detection voltages V ₁ decreases accordingly. Detection voltage V ₁
When but decreases, the phase control circuit 5 generates a control pulse which acts to advance the conduction angle of the transistor Q _2. As a result, the transistor Q ₂ is an early point in time t ₁ than the point in time t ₁ '
Turns on. That transistor Q ₁ and the transistor
By the time the Q ₂ is on at the same time becomes long, the current flowing through the flyback transformer FBT (a) increases as indicated by a dotted line in Figure 3. As a result, as the flyback pulse (b) rises as shown by the dotted line in FIG. 3, the high voltage rises and is stabilized. Note that the flywheel diode D ₃ acts to absorb resonance of the point A due to the fact that the transistor Q ₃ is on and the transistor Q ₂ is off in the period T.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a coil L ₁ connected between the positive side output terminal and the collector of the transistor Q ₂ of the rectifier circuit 2, which is connected in parallel between the negative side output terminal and the collector of the transistor Q ₂ except that the voltage regulating circuit 6 comprising a capacitor C ₄ and the transistor Q ₃ is newly added is the same as the embodiment of Figure 1. This voltage adjusting circuit 6 includes a transistor Q ₂
And acts as impedance means for generating a DC voltage which gradually rises in synchronism with turning on (conduction).
The base of the transistor Q ₃ are the control pulse of the reverse phase is applied to a control pulse applied to the base of the transistor Q _2.

Next, the circuit operation of such a configuration will be described with reference to the waveform diagram of FIG. Note that in FIG. 5, (a) shows the current flowing through the flyback transformer FBT, (b) a flyback pulse, (c) the operating state of the transistor Q _1,
(D) shows the operating state of the transistor Q _2, respectively.

When the transistor Q ₂ is turned on at time t _1, the transistor
Q ₃ is opposite to the turned off, the charging of the capacitor C ₄ is started. When the transistor Q ₃ is shifted from the ON state to the OFF state, the DC voltage from capacitor C ₂ to the capacitor C ₄ is gradually charged, for example sinusoidally through the coil L _1. As a result, the voltage applied to the flyback transformer FBT through the transistor Q ₂ rises sinusoidally. At this time, the transistor Q ₁ is already on. Between t _{1 and} t ₂ , a current flows through the flyback transformer FBT through the path of C ₄ → Q ₂ → FBT → Q ₁ → C ₄ . When the transistor Q ₁ is turned off at time t _2, the flyback transformer FB
T and the resonant circuit of the resonance capacitor C ₁ is constituted, t ₂
Between −t ₃ , the resonance current flows through the path of FBT → C ₁ → C ₄ → Q ₂ → FBT, and between t _{3 and} t ₄ , the path of C ₁ → FBT → D ₄ → C ₄ → C ₁ A discharge current flows. Flyback pulse (b) occurs in a period of the t ₂ -t _4. t ₄ In between _{-t 5, FBT → D 4 →} C 4 → D 1
→ Current flows through the FBT path.

As a result, as in the embodiment of Figure 1, the high voltage decreases, since also detected voltages V ₁ decreases accordingly, so that the phase control circuit 5 to advance the conduction angle of the transistor Q ₂ , The flyback pulse (b) rises, so that the high voltage rises and is stabilized.

Also, since the cause rise the voltage to be applied in synchronism with the ON of the transistor Q ₂ in the flyback transformer FBT sinusoidally, so that it is possible to reduce the occurrence of spike voltage during the on transistor Q _2. The spike voltage, since the winding of the flyback transformer FBT contains the leakage inductance, the steep DC voltage at the moment of turning on the transistor Q ₂ is applied to the flyback transformer FBT caused by the influence of the leakage inductance Is what you do.

In the present embodiment, the coil L ₁ of the high-voltage adjustment circuit 6 as an impedance means is constituted by the capacitor C ₄ and the transistor Q _3, is not limited to this, short, on of the transistor Q ₂ Any configuration may be used as long as the DC voltage applied to the flyback transformer FBT is gradually raised so as not to generate a spike voltage in synchronization with.

Effect of the Invention As described above, in the voltage resonance type high voltage generation circuit according to the present invention, switching is performed at the same frequency as the switching frequency of the first switch circuit in the voltage resonance type switching circuit, and the output terminal of the DC power supply circuit is connected to the output terminal. In a second switch circuit connected between the other end of the primary winding of the flyback transformer,
Since the DC voltage conduction time, which is conducted simultaneously with the first switch circuit to the other end of the next winding, is controlled in accordance with the high voltage detection output, there is no need to use a stabilized power supply circuit as in the prior art, which is simple. With the circuit configuration, the fluctuation of the high voltage due to the fluctuation of the high voltage and the fluctuation of the AC input voltage can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a circuit diagram showing a specific example of the phase control circuit shown in FIG. 3, FIG. 3 is a waveform diagram of each part for explaining the circuit operation of FIG. 1, and FIG. 4 is a circuit showing another embodiment of the present invention. FIG. 5 is FIG.
FIG. 6 is a circuit diagram showing a conventional example, and FIG. 6 is a circuit diagram showing a conventional example. Explanation of Signs of Main Parts 1 ... Voltage Resonant Switching Circuit 5 ... Phase Control Circuit, 6 ... Voltage Adjustment Circuit FBT ... Flyback Transformer

Claims (2)

(57) [Claims] 1. A voltage resonance type switching circuit including a flyback transformer, a first switch circuit connected to one end of a primary winding of the flyback transformer and switching at a predetermined frequency, and generating a predetermined DC voltage. A power supply circuit, an output terminal of the power supply circuit, and one of the flyback transformers.
A second switch circuit connected between the other end of the flyback transformer and selectively supplied with the DC voltage to supply the other end of the primary winding of the flyback transformer; Detecting means for detecting a high voltage generated in the winding; control means for switching the second switch circuit at the predetermined frequency; and the first switch connected to the other end of the primary winding of the flyback transformer And a resonance absorbing means for absorbing resonance when the circuit is conductive and the second switch circuit is not conductive, wherein the control means controls the second switch circuit of the second switch circuit in accordance with a detection output of the detection means. A voltage resonance type high voltage generating circuit for controlling a conduction time of conducting simultaneously with one switch circuit. 2. The voltage according to claim 1, wherein the power supply circuit has impedance means for generating a DC voltage that gradually rises in synchronization with the conduction of the second switch circuit as the DC voltage. Resonant high voltage generation circuit.