JPH03267884A - Voltage resonance type high voltage generating circuit - Google Patents

Abstract

PURPOSE:To suppress fluctuation of a high voltage and fluctuation of an AC input voltage with simple circuit constitution by detecting a high voltage generated at a secondary winding of a flyback transformer and controlling a conduction time of a switch means applying a DC voltage selectively to a switching circuit accordingly. CONSTITUTION:The generating circuit is provided with a voltage resonance type switching circuit 1 including a flyback transformer FBT, a power supply circuit 2 generating a prescribed DC voltage, a switch means Q2 applying the DC voltage selectively to the switching circuit 1, a detection means D2 detecting a high voltage generated in a secondary winding of the flyback transformer FBT, and a phase control means 5 controlling the conduction time of the switch means Q2 in response to the detected output by the detection means D2. Thus, a voltage resonance type high voltage generating circuit able to suppress the fluctuation of a high voltage and fluctuation of an AC input voltage with simple circuit constitution is realized.

Description

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

BACKGROUND ART Conventionally, as this type of circuit, the one shown in FIG. 6 is known. In the figure, a voltage resonant switching circuit 1 is formed by a flyback transformer FBT, a resonant capacitor C1, a damper diode D1, and an output transistor Q1.
is configured.

One end of the primary winding of the flyback transformer FBT has A
C power supply voltage is rectified by rectifier circuit 2 and capacitor C2
A DC voltage obtained by being stabilized by the stabilized power supply circuit 3 is supplied via the capacitor C3 and the high voltage regulator 4.

In the switching circuit 1, a high voltage is generated on the secondary side of the flyback transformer FBT by switching the output transistor Q1 in synchronization with the horizontal scanning frequency using the primary winding of the flyback transformer FBT as a load inductance.

The high voltage generated on the secondary side of the flyback transformer FBT is rectified by a high voltage rectifier diode D2 and output as an anode voltage of a cathode ray tube (not shown).

In order to stabilize this high voltage, the high voltage is detected by bleeder resistors R, , R2, and the detected output is fed back to the high voltage regulator 4. The high voltage regulator 4 uses a flyback transformer FBT according to fluctuations in high voltage.
The controller is configured to control the level of DC voltage supplied to the controller.

In the conventional voltage resonance type high voltage generation circuit configured in this way, the stabilized power supply circuit 3 is designed to suppress fluctuations in the AC input voltage, so the stabilized power supply circuit 3 is indispensable. As a result, the overall circuit configuration becomes large-scale, resulting in high costs.

Summary of the Invention [Object of the Invention] Therefore, an object of the present invention is to provide a voltage resonance type high voltage generation circuit that can suppress fluctuations in high voltage and AC input voltage with a simple circuit configuration.

[Configuration of the Invention] A voltage resonant high voltage generation circuit according to the present invention includes a voltage resonant switching circuit including a flyback transformer, a power supply circuit that generates a predetermined DC voltage, and selectively transmits the DC voltage to the switching circuit. A switch means for supplying the power, a detection means for detecting a high voltage generated in a secondary winding of the flyback transformer, and a control means for controlling conduction time of the switch means in accordance with a detection output of the detection means. The structure is as follows.

[Operation of the Invention] In the voltage resonance type high voltage generation circuit according to the present invention 1, the high voltage generated on the secondary side of the flyback transformer is detected, and a direct current is applied to the switching circuit including the flyback transformer in accordance with this detection output. The conduction time of the switch means for selectively supplying the voltage is controlled.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which parts equivalent to those in FIG. 6 are denoted by the same reference numerals. In the figure, a transistor Q2 as a switch means is connected between the positive output terminal of the rectifier circuit 2 and one end of the primary winding of the flyback transformer FBT, and a diode D2 is connected to the transistor Q2 with a diode D2 of opposite polarity. are connected in parallel. Further, a flywheel diode D3 is connected in parallel to the voltage resonance type switching circuit 1.

The base of the transistor Q2 has bleeder resistors R,,R
Transistor Q2 in response to the high voltage detection output by Q2.
A phase control circuit 5 is connected thereto to control the conduction (on) time of the circuit.

The phase control circuit 5 includes, for example, as shown in FIG. 2, a sawtooth wave generation circuit 21 and a reference voltage generation circuit 22 that generates a reference voltage V1 whose voltage value is variable according to the detection output from the bleeder resistor R1°R2. , and a comparator 23 that compares the sawtooth wave with a reference voltage V1. The reference voltage V1 corresponds to the detection output from the resistors R, , R2, and therefore the reference voltage v1 will be referred to as the detection voltage V1. As a result, a control pulse in which a sawtooth wave is pulse width modulated (PWM) by the detection voltage V1, that is, a control pulse whose pulse width changes in accordance with fluctuations in the high voltage is obtained. This control pulse controls the conduction (on) time of transistor Q2.

Next, the circuit operation of such a configuration will be explained with reference to the waveform diagram of FIG. 3. In FIG. 3, (a) shows the current flowing through the flyback transformer FBT, (b) shows the flyback pulse, (C) shows the operating state of the transistor Q1, and (
d) shows the operating states of the transistor Q2.

When transistor Q2 is turned on at time t1, the DC voltage of capacitor C2 is applied to flyback transformer FBT through transistor Q2.

At this time, transistor Q1 is already turned on.

Between tl and t2, a current flows through the flyback transformer FBT along the path C2→Q2→FBT→Q1→C2. When the transistor Q1 turns off at time t2, a resonant circuit is formed by the flyback transformer FBT and the resonant capacitor C1, and between t2t3, FBT→C1→C2→Q
A resonant current flows in the path 2→FBT, and a discharge current flows in the path CI-FBT4D2→C2→C1 between t3 and t4. During this period t2-t4, the flyback pulse (
b) occurs. Between t4 and t5, FBT-D2→C
Current flows through the path 2→D1→FBT.

In the state shown by the solid line in FIG. 3, when the high voltage decreases, the detected voltage vl also decreases accordingly. Detection voltage V
1 decreases, the phase control circuit 5 generates a control pulse which acts to advance the conduction angle of the transistor Q2. As a result, the transistor Q2 turns on at times t and l earlier than the time t1, and the flyback transformer FBT
The current (a) flowing through is as shown by the dotted line in FIG.

As a result, the flyback pulse (b) increases as shown by the dotted line in FIG. 3, so that the high voltage increases and is stabilized. Note that the flywheel diode D3 functions to absorb resonance at the point A due to the transistor Q1 being on and the transistor Q2 being off during the period T.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a coil L1 is connected between the positive output terminal of the rectifier circuit 2 and the collector of the transistor Q2, and a capacitor C4 and a transistor Q3 are connected in parallel between the collector of the transistor Q2 and the negative output terminal. This embodiment is the same as the embodiment shown in FIG. 1, except that a voltage adjustment circuit 6 consisting of the following is newly added. This voltage adjustment circuit 6 acts as an impedance means for generating a DC voltage that gradually rises and changes in synchronization with turning on (conducting) the transistor Q2. The base of transistor Q3 is connected to transistor Q2.
A control pulse having an opposite phase to the control pulse applied to the base of is applied.

Next, the circuit operation of such a configuration will be explained with reference to the waveform diagram of FIG. 5. In FIG. 5, (a) shows the current flowing through the flyback transformer FBT, (b) shows the flyback pulse, (C) shows the operating state of the transistor Q1, and (
d) shows the operating states of the transistor Q2.

When transistor Q2 is turned on at time t1, transistor Q3 is turned off, and charging of capacitor C4 is started. As the transistor Q3 shifts from the on state to the off state, the capacitor C2 is connected to the capacitor C4.
The DC voltage from is gradually charged through the coil L1, for example in a sinusoidal manner. As a result, the voltage applied to the flyback transformer FBT through the transistor Q2 rises in a sinusoidal manner. At this time, transistor Q1 is already turned on. Between t1t2, Ca-
"A current flows through the flyback transformer FBT through the path Qz→FBT-Ql→C4. At time t2, the transistor Q
1 turns off, a resonant circuit is formed by the flyback transformer FBT and the resonant capacitor C1, and t2-t3
Between t3 and t4, a resonant current flows in the path of FBT-CI-CA→Q2-FBT, and between t3 and t4, C+=FBT −=
A discharge current flows through the path of D2-''C4=C+.

A flyback pulse (b) is generated during this period t2-t4. Between t4 and t5, FBT-+D2→Ct-D
Current flows through the 1-FBT path.

As a result, as in the case of the embodiment shown in FIG. 1, when the high voltage decreases, the detected voltage V1 also decreases accordingly, so the phase control circuit 5 controls the conduction angle of the transistor Q2 to advance. As a result, the flyback pulse (b) increases, so that the high voltage increases and is stabilized.

Further, since the voltage applied to the flyback transformer FBT rises in a sinusoidal manner in synchronization with turning on the transistor Q2, it is possible to reduce the generation of spike voltage when the transistor Q2 is turned on. This spike voltage is caused by the fact that the winding of the flyback transformer FBT contains leakage inductance, so the moment transistor Q2 is turned on, a steep DC voltage is generated across the flyback transformer FB.
This occurs due to the influence of leakage inductance when applied to T.

In this embodiment, the voltage adjustment circuit 6 as an impedance means is configured by the coil L1, the capacitor C4, and the transistor Q3, but it is not limited to this. The DC voltage applied to the flyback transformer FBT is
Any configuration that allows the voltage to rise gradually so as not to generate a spike voltage may be used.

As described in detail of the invention, in the voltage resonance type high voltage generation circuit according to the present invention, the high voltage generated on the secondary side of the flyback transformer is detected, and the switching circuit including the flyback transformer is activated according to the detected output. Since the structure is configured to control the conduction time of the switch means that selectively supplies DC voltage to
This means that fluctuations in input voltage can be suppressed.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a waveform diagram of each part to explain the circuit operation of FIG. 1. FIG. 4 is a circuit diagram showing another embodiment of the present invention. Figure 5 is the fourth
FIG. 6 is a waveform diagram of each part for explaining the operation of the circuit shown in the figure, and FIG. 6 is a circuit diagram showing a conventional example. Explanation of symbols of main parts

Claims (2)

[Claims] (1) A voltage resonant switching circuit including a flyback transformer, a power supply circuit that generates a predetermined DC voltage, a switch means for selectively supplying the DC voltage to the switching circuit, and a secondary circuit of the flyback transformer. A voltage resonance type high voltage generation circuit comprising: a detection means for detecting a high voltage generated in a winding; and a control means for controlling conduction time of the switch means in accordance with a detection output of the detection means. (2) The voltage resonance type high voltage generator according to claim 1, wherein the power supply circuit includes impedance means for generating a DC voltage that gradually rises and changes in synchronization with conduction of the switch means as the DC voltage. circuit.