JPH02213280A - Auxiliary power supply circuit for high voltage transformer - Google Patents

Abstract

PURPOSE:To shorten a carrier storage time and to improve responsiveness to a control signal by providing a diode for reverse current and making a current, which flows from the upstream side of a transistor for control to a downstream side, flow through this diode for reverse current. CONSTITUTION:When an output end T4 of a coil 102 for auxiliary voltage generation goes to be -several hundreds V, the current flows from a voltage doubler circuit 106 through a diode 202 for reverse current to the coil 102 for auxiliary voltage generation. Accordingly, the current from a base 104b to a collector 104c of a transistor 104 for control is not generated. Thus, a carrier is not replenished in the collector area of the transistor 104 for control and the carrier storage time can be widely shortened. When the control signal is turned off in a transformer 108 for control, the transistor 104 for control can be speedily turned off.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an auxiliary power supply circuit for a high-voltage transformer for maintaining a constant output voltage of a high-voltage transformer that supplies high voltage to the anode of a CRT (cathode ray tube), etc. .

[Prior Art] High voltage transformers such as flyback transformers have been widely used to generate high voltages of several tens of kV. For example, such a high-voltage transformer is essential for supplying high voltage to the anode of a CRT, and as computer equipment develops, CRTs are used as display devices.
In response to the increasing demand for high voltage transformers, the importance of high voltage transformers is also increasing.

Here, an example of a circuit using such a high voltage transformer will be explained based on FIG. 5. High voltage transformer 10
A DC power supply PB is connected to one end of the primary coil N1, and a drive circuit 30 is connected to the other end. on the other hand,
One end of the secondary side of the high voltage transformer 10 is connected to a reference line ABL (automatic brightness limiter),
The other end is connected to the anode 34 of the CRT 32. Further, the input terminal 30a of the drive circuit 30 receives a horizontal drive signal from a horizontal oscillation circuit (not shown).

The CRT 32 has a cathode 36 and a deflection yoke 38 at its rear.

In such a circuit, when the drive circuit 30 is turned on and off by a horizontal drive signal received from the input terminal 30a, the primary coil N1 of the high voltage transformer 10 receives a signal depending on the frequency of the pulse input from the input terminal 30a. A flyback pulse is generated. The high voltage (usually 30k) induced in the secondary coil NH of the high voltage transformer
V) is applied to the anode 34 through the diode DH6. When such a high voltage is applied to the anode 34, a high voltage of about 30 kV is applied between the cathode 36 receiving the video signal and the anode 34 in the CRT 32. The electrons emitted from the cathode 30 then fly toward the anode 34. and,
The electrons emitted from the cathode 36 are transferred to the deflection yoke 38.
The light is scanned in a predetermined direction and collides with the fluorescent surface on the front surface of the CRT 32 to produce a predetermined display.

Here, in such a CRT, it is desirable that the high voltage applied to the anode be constant.

That is, the speed of electrons emitted from the cathode 36 is determined by the electric field strength generated by the potential difference between the anode 34 and the cathode 36. Therefore, the higher the voltage applied to the anode 34, the faster the electrons emitted from the cathode 36. Since the amount of deflection of the electrons deflected by the deflection yoke 38 changes depending on the speed of the electrons passing through the deflection yoke 38, the larger the voltage at the anode 34, the less the electrons are bent and the image becomes relatively C.
This is because if the voltage at the anode 34 becomes smaller as the electrons move closer to the center of the front surface of the RT 32, the electrons will be bent significantly and the image will be relatively spread out.

On the other hand, if the screen of a CRT is white (bright), many electrons need to collide with the fluorescent screen on the front of the CRT. Therefore, when the screen is white, the amount of current is large, and when the screen is black (dark), the amount of current is small.

For example, in a normal CRT 32, its anode 36
The current IH flows when the screen is completely black, and when the screen is completely white, a current of about 1 mA to 2 mA flows. here,
As mentioned above, a high voltage of about 30 kV is applied to the anode 36, but the secondary coil NH of the high voltage transformer 10
The current supply capability of the circuit to the anode 36, which is the output of the circuit, is not very large. Therefore, when the current IH to the anode 36 changes, the voltage on the output side of the high voltage transformer 10 changes accordingly.

For example, when the screen is black, the voltage changes to 30 kV, and when the screen is pure white, the voltage changes to about 26 kV. If the voltage of the anode 36 changes in this way, CR
A problem arises in that the position of the image changes on the screen appearing on T32.

Therefore, in order to solve this problem, it has been desired to keep the anode voltage constant.

In order to solve these problems, the applicant proposed an auxiliary power supply circuit for a high voltage transformer as shown in FIG. This high voltage transformer auxiliary power supply circuit 100 changes the voltage at the input end T1 of the secondary coil NH of the high voltage transformer 10, and controls the voltage to the anode of the CRT to be constant.

That is, when the screen on the CRT is white and the voltage at the anode decreases, the voltage at the input end T1 of the secondary coil NH is increased, and when the voltage at the anode increases, the voltage at the input end T1 is decreased. control so that

For this purpose, the high-voltage transformer auxiliary power supply circuit 100 includes an auxiliary voltage generation coil 102 as a coil for generating auxiliary voltage. This auxiliary voltage generation coil 102 is wound and formed as a secondary coil of the high voltage transformer 10.

Then, the input side end T of this auxiliary voltage generation coil 102
3 is connected to ABL, and the output side end T4 is connected to the collector 104C of the control transistor 104.

Also, the emitter 104 of this control transistor 104
e is connected to the input side end T1 of the secondary coil NH via the voltage doubler circuit 106.

On the other hand, the secondary coil 108a of the control transformer 108 is connected between the emitter 104e and the base 104b of the control transistor 104.
A predetermined control pulse is input to the primary coil 108b of No. 8.

That is, the primary coil 108 of the control transformer 108
One end of b is connected to ground via a resistor 110 and a DC power supply 112, and the other end is connected to ground via a transistor 116.

The connection between the resistor 110 and the DC power supply 112 and the collector of the transistor 116 are connected to a snubber diode 118.
connected by.

Therefore, if a predetermined pulse-like control signal is input to the base 116b of the transistor 116, the current from the DC power supply 112 will flow through the resistor 110 and the coil 108b1.
It flows through transistor 116 to ground. Therefore, the control signal can be transmitted to the secondary coil 108a. Note that the diode 118 is the transistor 11
This is to prevent excessive current from occurring between the collector and emitter of the transistor 116 when the control signal input to the base 116b of the transistor 6 is turned off.

In such an auxiliary power supply circuit 100 for a high voltage transformer, the auxiliary voltage generating coil 102 is wound around the secondary side of the high voltage transformer 10, so in this auxiliary voltage generating coil 102, as shown in FIG. As shown in FIG. 2, a pulsed voltage similar to that generated in the secondary coil NH of a high-voltage transformer is obtained. Normally, the voltage generated in this auxiliary voltage generating coil 102 is set to about 2 kV.

The primary coil 108b of the control transformer 108
As shown in FIG. 7(B), a pulsed control signal is applied as necessary. When this control signal is applied to the primary coil 108b of the control transformer 108, a similar pulse-like signal is induced in the secondary coil 108a according to this control signal, and this pulse-like signal is applied to the control transistor 108.
It will be applied to the base 104b of.

The control transistor 104 is an NPN type transistor, and when a control signal as shown in FIG. 104e will be electrically connected. Therefore, this control transistor 10
The voltage at the emitter 104e, which is the output of the auxiliary voltage generating coil 102, is transmitted to the auxiliary voltage generating coil 102 only when a control signal is input as shown in FIG. 7(C).

If the output as shown in FIG. 7(C) is applied to the low-voltage input terminal T1 of the secondary coil NH of the high-voltage transformer 10, the voltage at T2, which is the output terminal of the secondary coil NH, will be , the voltage is increased by the voltage according to <C> in FIG.

Therefore, if the CRT screen is white, a control signal is sent to the transistor 104, and if the screen is black, the control signal is stopped, and the voltage applied to the anode of the CRT can be held approximately constant.

Furthermore, if the width of the control pulse in FIG. 7(B) is made smaller, the pulse width of the output voltage in FIG. 2(C) becomes smaller accordingly. The voltage supplied to the CRT is a DC voltage, and the increase in voltage generated in the high-voltage transformer auxiliary power supply circuit 100 changes depending on the area of the pulse voltage input to the input terminal T1, so the pulse width of the control signal is By controlling it, the amount of increase in height can be adjusted.

Note that this control can be achieved by detecting the voltage at the anode of the CRT and controlling the control signal supplied to the base of the transistor 116 in accordance with this detected voltage.

In this way, the base voltage can be increased by about 2 kV in the high voltage transformer auxiliary power supply circuit 100, but as mentioned above, the voltage supplied to the CRT anode generally fluctuates by about 4 kV when considering transient high voltage changes. need to be corrected. Therefore, in this example, the voltage is doubled by the voltage doubler circuit 106 so that a voltage of up to 4 kV can be input to the input terminal T1.

Note that the voltage generated here can be adjusted by changing the number of turns of the auxiliary voltage generating coil 102, but since the upper limit of the withstand voltage of commercially available transistors is approximately 2 kV, the on/off is controlled by the control transistor 104. It is also necessary to control the voltage to about 2 kV. Therefore, in this example, the output voltage is doubled by the voltage doubler circuit 106.

Therefore, the voltage doubler circuit 106 will be explained next.

The voltage doubler circuit 106 includes a diode 1 connected in series to an emitter 104e on the output side of the control transistor 104.
20, 122, 124, and this diode 1
24 is the secondary coil N of the high voltage transformer 10
It is connected to the input terminal T1 of H. A connection portion between the cathode of the diode 120 and the anode of the diode 122 is connected to ground through a diode 126 and a capacitor 128. Further, a connection portion between the cathode of the diode 122 and the anode of the diode 124 and the anode side of the diode 120 are connected by a capacitor 130.

In such a circuit, when the output of the control transistor 104 as shown in FIG. 7(C) is applied, a part of the current is used as the current 11 to charge the capacitor 128. The capacitor 128 is charged until the voltage reaches the input voltage of 2 kV. On the other hand, when the emitter 104e of the control transistor 104 reaches 100 V, the current I2 flows toward the capacitor 130.
flows, and the capacitor 130 is charged. and,
When the capacitor 128 is charged with 2kV, the potentials on the anode side and the cathode side of the diode 122 are equal, so the potential on the cathode side of the diode 122 is also 2kV.
It must be V. Therefore, capacitor 1
2kV charging will be performed on the 30th.

Then, in a state where such charging is completed, the seventh
If a 2kV pulse-like output as shown in FIG.
The pulsed voltage of 4 kV obtained by adding 2 kV of 30 is input to the input terminal T1 of the high voltage transformer 10. In this way, the voltage doubler circuit 106 receives a pulsed voltage of 2 kV, doubles it to 4 kV, and outputs the same. Therefore, correction for the voltage change JkV at the anode of the CRT can be achieved in the high voltage transformer auxiliary power supply circuit 100.

[Problems to be Solved by the Invention] In the conventional example shown in FIG. 5, the voltage at the anode 34 of the CRT 32 fluctuates depending on the brightness of the display screen, resulting in a change in the size of the image. was there.

On the other hand, even when an auxiliary power supply circuit for a high voltage transformer as shown in FIG. 6 is used, there is a problem in that the response is poor and sufficient control of the anode potential cannot be achieved.

That is, when a control signal as shown in FIG. 7(B) is inputted to the control transformer 108, the control transistor 104 must originally obtain an output as shown in FIG. 7(C). However, when we conducted an experiment using the high-voltage transformer auxiliary power supply circuit 100 shown in FIG. 6, we found that the pulsed voltage output from the transistor 104 did not immediately become zero, as shown in FIG. 7(D). There is a problem in that it takes a considerable amount of time for this to become zero. As a result of detailed research on this matter, it has been found that the reason why it takes time to turn off the output of the transistor 104 is as follows.

That is, the fact that current flows through the transistor 104 even though the base potential is at a low level is considered to be because carriers remain inside the transistor 104. That is, as a characteristic of a transistor, in order to turn the transistor off, when the carriers existing inside the transistor disappear, the collector-emitter region becomes completely off. However, in this example,
The emitter 104e and the base 104b are the control transformer 1
08 secondary coil 108a.

Therefore, when the voltage on the collector side of the transistor 104 is several hundred V, a current flows from the base 104b of the control transistor 104 toward the collector 104c.

When a current flows in this direction, electrons, which are carriers, are replenished in the collector region of the control transistor 104. Therefore, when the next 2 kV pulse comes to the transistor 104 in which electrons exist in the collector region, a voltage will be output from the control transistor 104 according to the amount of carriers.

By repeating this process, the control transistor 104 outputs a pulsed voltage for a certain period of time.

In this way, in the high-voltage transformer auxiliary power supply circuit proposed earlier, the control transistor 1 remains active even after the control signal is turned off.
Voltage will be output from 04, and the auxiliary power supply circuit 1
The time it takes to stop outputting the auxiliary voltage from 00 becomes longer,
There was a problem in that the controllability of the voltage supplied to the anode of the CRT was poor.

The present invention was made with the aim of solving the above-mentioned problems, and an object of the present invention is to provide an auxiliary power supply circuit for a high-voltage transformer that has good response to control signals and good controllability of output voltage. .

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for controlling the secondary coil of a high-voltage transformer, in which a high-frequency pulse is input to the primary coil and a high voltage is generated at the output end of the secondary coil. In the auxiliary power supply circuit connected to the input terminal and for controlling the voltage at the high voltage output terminal, an auxiliary voltage generation coil arranged on the secondary side of the high voltage transformer and an auxiliary voltage generation coil arranged on the output side of this auxiliary voltage generation coil are connected to the input terminal and are connected to the high voltage output terminal. A control signal input transformer in which a secondary coil is connected between a connected control transistor and the base and emitter of the control transistor, and a control signal for turning on and off the control transistor is input to the primary coil. and a voltage doubler circuit connected downstream of the control transistor and including at least a voltage holding capacitor, and a bypass connection between the emitter and collector of the control transistor,
It has a reverse current diode that allows current to flow from the downstream side to the upstream side, and is characterized by improving responsiveness when the control transistor is turned off and effectively controlling the output voltage of the high voltage transformer.

[Function] The auxiliary power supply circuit for a high voltage transformer according to the present invention has the above-described configuration, and inputs the voltage generated in the auxiliary voltage generating coil to the high voltage transformer via the control transistor. Therefore, by turning on and off the control transistor 104, the input voltage to the high voltage transformer can be controlled, and a desired high voltage can be output from the high voltage transformer.

In the present invention, a reverse current diode is disposed between the emitter and collector of the control transistor to allow current to flow from the downstream side to the upstream side of the control transistor. Therefore, when the output voltage of the auxiliary voltage generating coil 102 is 100 V, the current flows from the upstream side to the downstream side of the control transistor via the reverse current diode. Therefore, as described above, carriers are not replenished in the collector region of the control transistor, and carriers can be annihilated more quickly, thereby improving responsiveness to control signals.

[Example] Hereinafter, an auxiliary power supply circuit for a high voltage transformer according to the present invention will be explained based on the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same members as those in the circuit shown in FIG. 6 are designated by the same reference numerals, and their explanations will be omitted.

A characteristic feature of the high-voltage transformer auxiliary power supply circuit 200 according to this embodiment is that it includes diodes 202 and 204. That is, the control transistor 1
A diode 204 is placed between the emitter 104e of 04 and the voltage doubler circuit 106, and this diode 204
and the collector 1 of the control transistor 104
04c, a backflow diode 202 is arranged.

The auxiliary voltage generating coil 102 has a 2k voltage similar to the conventional example.
A pulse-like voltage of about V is generated. This voltage is then increased to about 4 kV by the voltage doubler circuit 106 and then supplied to the secondary coil NH of the high voltage transformer 110. Here, the diode 204 is the control transistor 1
04 side is used as an anode, and the voltage doubler circuit 106 side is used as a cathode, and the reverse current diode 202 is configured so that current flows from the downstream side to the upstream side.
When the current from the control transistor 104 is passed, there is no difference in operation from the conventional example.

However, when the output terminal T4 of the auxiliary voltage generating coil 102 becomes 100 V, the current from the voltage doubler circuit 106 flows toward the auxiliary voltage generating coil 102 through the reverse diode 202.

Therefore, the base 104 of the control transistor 104
No current flows from b to collector 104c. Therefore, carriers in the collector region of the control transistor 104 are not replenished, and the carrier accumulation time can be significantly shortened. Therefore, when the control signal in the control transformer 108 is turned off, the control transistor 104 can be quickly turned off.

That is, as shown in FIG.
When the input signal to the control transistor 104 is as shown in FIG. 2(A) and the control signal input to the control transformer 108 is as shown in FIG. 2(B), the output of the control transistor 104 is as shown in FIG. 2(C). become that way. As is clear from this, when the control signal is turned off, the output of the control transistor 104 is immediately turned off. Therefore, it is possible to obtain an output of the control transistor 104 that almost accurately responds to the control signal.

Note that the diode 204 is provided to prevent the current flowing toward the auxiliary voltage generation coil 102 from the voltage doubler circuit 106 from flowing into the base 104b of the control transistor 104 via the secondary coil 108a of the control transformer 108. be. Therefore, the forward voltage drop of the diode 202 is lower than the voltage drop across the collector 10 of the control transistor 104.
4b and the base 104b, the current flows through the reverse current diode 202, so the diode 204 can be omitted.

However, since the diode 202 generally requires a large reverse breakdown voltage of 2 kV, its voltage drop is larger than the voltage drop between the collector and base of the transistor 104. For this reason, the diode 204 is often required.

FIG. 3 shows a modification of the voltage doubler circuit 106, which is a triple voltage circuit 160 that triples the input voltage. That is, in this triple voltage circuit 160, the voltage doubler circuit 1
06, two diodes 162, 164 and two capacitors 166° and 168 are added. Therefore, the positive side of the capacitor 166 has a voltage of 4 kV, and together with the 2 kV of the capacitor 168, an output of 6 kV can be obtained.

Furthermore, FIGS. 4(A) and 4(B) show another embodiment of the present invention, in which a DC power supply 220 is connected in series with the reverse current diode 202 instead of the diode 204. It is placed. According to this embodiment, the forward voltage drop in the diode 202 can be compensated by the DC power supply 220, and even if the diode 204 is omitted, the current flowing from the voltage doubler circuit 106 to the auxiliary voltage generation coil 102 can be passed through the backflow diode 202.

[Effects of the Invention] As explained above, according to the auxiliary power supply circuit for a high voltage transformer according to the present invention, since the backflow diode is provided,
A current can flow from the upstream side to the downstream side of the control transistor via this reverse current diode. Therefore, the collector region of the control transistor is not replenished with carriers, the carrier accumulation time can be shortened, and the responsiveness to control signals can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of an auxiliary power supply circuit for a high voltage transformer according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing voltage characteristics in the same embodiment, and Fig. 3 is the configuration of a triple voltage circuit. Circuit diagram showing Figure 4 (A)
, (B) is a circuit diagram showing the main part of another embodiment, FIG. 5 is a circuit diagram showing an example of a circuit using a high-voltage transformer, and FIG. 6 is a circuit showing the configuration of the auxiliary power supply circuit proposed earlier. FIG. 7 is a characteristic diagram for explaining the operation of the auxiliary power supply circuit shown in FIG. 10... High voltage transformer 102... Auxiliary voltage generation coil 104...
Control transistor 108 ... Control signal input transformer 106 ...
・Voltage doubler circuit 202 ・・・ Backflow diode

Claims (1)

[Claims] (1) A high-frequency pulse is input to the primary coil and a high voltage is generated at the output end of the secondary coil.Auxiliary power supply connected to the input end of the secondary coil of a high voltage transformer and used to control the voltage at the high voltage output end. In the circuit, an auxiliary voltage generation coil disposed on the secondary side of the high voltage transformer, a control transistor connected to the output side of this auxiliary voltage generation coil, and a base and an emitter of this control transistor. A control signal input transformer with a secondary coil connected in between, and a control signal input transformer in which a control signal for turning on and off the control transistor is input to the primary coil, and a capacitor connected downstream of the control transistor for at least voltage holding. A voltage doubler circuit that includes a voltage doubler circuit, and a reverse current diode that bypass-connects the emitter-collector of the control transistor and causes current to flow from the downstream side to the upstream side, and improves responsiveness when the control transistor is turned off. death,
A high-voltage transformer auxiliary power supply circuit characterized by effectively controlling the output voltage in a high-voltage transformer.