JPS6325555B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-voltage stabilizing circuit used in parallel supply operation of high-voltage power supplies for television picture tubes and other high-voltage power supply circuits.

Conventional configuration and its problems Recently, projection type television receivers using cathode ray tubes have been developed, and in order to increase the luminous flux output, red, blue, and green cathode ray tubes (hereinafter abbreviated as CRT) have been developed.
It is necessary to supply a large amount of power to the type projection tube. In this case, it is often more advantageous in design to use two small flyback transformers and supply them in parallel than to use a large flyback transformer. On the other hand, if two sets of voltage stabilizing circuits are used and their outputs are commonly connected and supplied to a load, an imbalance will occur in the output current, and various balance control means will be required.

Balance control in a conventional example of a high voltage stabilizing circuit will be described below.

FIG. 1 shows an example of a conventional balance control circuit for a high voltage power supply circuit. Reference numeral 1 designates a switching circuit for driving the switching transistor 4, which causes the flyback transformer 2 to perform a switching operation to induce a boost pulse in the secondary winding of the transformer. 3 is a rectifier diode that generates a DC voltage at its output. In this example, the rectifying capacity is
Substituted by CRT capacity. 6 is a current detection resistor connected in series with the secondary winding, and 5 is a capacitor that passes high frequency components.

Another high voltage generation circuit exactly the same as above is provided. 7 is a switching circuit, 8 is a flyback transformer, 9 is a rectifier diode, 10 is a switching transistor, 11 is a capacitor, 12 is a current detection resistor, and the high voltage rectified output is connected to the above-mentioned first high voltage output terminal. , supplies a load current to the anode of the CRT 13. 13 becomes a load
A CRT is shown, and 14 is a cathode circuit that controls the anode current of the CRT 13.

Reference numerals 15 and 16 denote voltage dividing resistors for detecting high voltage output, whose impedances are converted by a transistor 17, and resistors 18 and 20 and a variable resistor 19 constitute a voltage divider for detecting high voltage. 25 is an operational amplifier, the differential input terminal of which is connected to the detection voltage of the current detection circuit described above;
It is connected via a series resistor 28 to the base of a transistor 29 constituting an error amplifier. resistance 2
7 is connected to the variable resistor of the voltage divider and to the base of the transistor 29. 30 is a bias resistor that supplies a bias current to the Zener diode 32; 31 is a bias resistor that supplies a bias current to the Zener diode 32;
This is a temperature compensation diode for temperature compensating the V _BE voltage and the Zener diode voltage. It is connected to the emitter of the transistor 29, and the load resistor 40 is connected to the collector. Its output is the input power supply voltage of the high voltage generation circuit. It is connected to the base of the output control transistor 22 to be controlled. 24 is connected between the emitter of the transistor 22 and ground to bypass the high frequency current flowing through the flyback transformer.

A similar error amplifier is arranged to control the input power supply voltage of the other high voltage generation circuit.
The base of the transistor 38 is connected to a terminal of a variable resistor 19 of a voltage divider via a resistor 33, and is also grounded through a resistor 28. A constant voltage source composed of a resistor 37, a Zener diode 36, and a temperature compensation diode 35 is connected to the emitter of the transistor 38, and a load resistor 39 is connected to the collector.
is connected, and its output is applied to the base of the output control transistor 21 to control the input power supply voltage of the high voltage generation circuit. Capacitor 23 is for high frequency current bypass.

The operation of the conventional high voltage stabilizing circuit configured as described above will be explained. When the output terminals of the first high voltage generation circuit and the second high voltage generation circuit shown in Figure 1 are connected, the load current will be balanced if the output voltages match, but even if there is a slight difference in potential between the output voltages, the load current will be balanced. When this occurs, the lower the internal impedance of the power supply, the more unbalanced the output current will be, and one of the high voltage generating circuits will be overloaded and destroyed. Therefore, based on the current detection voltage detected by the resistors 6 and 12, the transistor 29 is controlled by the operational amplifier 25 so that the difference in current value is eliminated, and the input power source of the second generation circuit of the high voltage circuit is varied. .

For example, if a difference occurs due to some variation in pulse width, etc. in the first high voltage generation output, the output current I ₂ will be larger than the output current I ₂ of the second high voltage output, so the voltage across the detection resistor 6 will be higher. The level increases in the negative direction. Then, the output of the operational amplifier 25 decreases, the base potential of the transistor 29 decreases, and the emitter voltage of the transistor 22, that is, the input power supply voltage Ve ₂ of the second high voltage generation circuit increases a little, and I ₂ becomes larger. controlled in a similar manner.

At this time, generally I ₁ + I ₂ = I _a remains constant and is supplied to the load, but if the high voltage becomes too high, a constant voltage negative feedback circuit using the voltage divider circuit of the high voltage detector will keep the high voltage constant. It is maintained. That is, resistors 27 and 33
Therefore, when the high voltage increases, the output of the error amplifier simultaneously decreases, and the levels of both Ve ₁ and Ve ₂ decrease, working to keep the high voltage output constant.

However, in the above configuration, two error amplifiers are present in the two high voltage circuits, so there are two reference voltage sources. Moreover, since the operating bias currents of the transistors 29 and 38 change greatly, the gain of the error amplifier changes, which causes a change in the loop gain, and the oscillation conditions etc. differ with respect to various changes in the load current. The disadvantage is that it tends to cause unstable phenomena.

Furthermore, considering the temperature drift of high voltage, it is difficult to design temperature compensation for V _BE when the operating currents of transistors 29 and 38 change.
As a method for temperature-compensating V _BE , there is a method in which the error amplifier using the transistors 29 and 38 is replaced with an emitter-coupled differential amplifier, but this increases the number of transistors.

Purpose of the Invention The present invention solves the above-mentioned conventional problems, and provides a circuit that can perform stable control operation of the loop gain unaffected by the operating point of the load current, etc. in a balance control circuit of high voltage generation circuits operating in parallel. The purpose is to provide a simple configuration.

Structure of the Invention The present invention includes a first operational amplifier that detects the load current balance of two high voltage generation circuits, and a second operational amplifier that detects an error in the absolute value of the high voltage. This is a high-voltage stabilization circuit equipped with an emitter-coupled amplifier that simultaneously differentially balances the input power supply voltage of the circuit.It can stabilize the loop gain of current balance control and high-voltage value control, and has good characteristics against temperature drift. It is something that can be obtained.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a circuit diagram of a high voltage generation circuit in an embodiment of the present invention. In the figure, parts having the same functions as the conventional one are designated by the same reference numerals as in FIG. 1, and the explanation thereof will be omitted. In FIG. 2, a transistor 48 and a transistor 49 constitute an emitter-coupled amplifier, emitter resistors 46 and 47 are connected to each, and the collector of a current source transistor 45 is connected to the connection point. However, its emitter is grounded by an emitter resistor 44, and the output of the second operational amplifier 41 is input to its base. A constant voltage source made of a bias resistor 42 and a Zener diode 43 is connected to the inverting input terminal of the second operational amplifier, and the intermediate terminal of the variable resistor 19 of the high voltage detection voltage divider is connected to the non-inverting input terminal. Connecting. A DC bias is applied to the base of the transistor 48 by a voltage divider including resistors 51 and 52 and a capacitor 50. The output of the emitter-coupled amplifier is obtained from load resistors 53 and 54 and applied to the bases of output control transistors 21 and 22, respectively.

The operation of the high voltage stabilizing circuit of this embodiment configured as described above will be explained below. If the high voltage output voltage is unbalanced due to some factor and the output current I ₁ becomes larger, then the first
The output tends to be lowered by the operational amplifier. Therefore, at the same time as the collector of transistor 49 rises, the collector of transistor 48 tends to fall, controlling the bases of transistors 21 and 22 to control the high voltage generation circuit in the direction of lowering Ve ₁ and increasing Ve ₂ . Therefore, the outputs of the two high voltage generating circuits always perform a balanced supply operation.

On the other hand, the absolute value of the high voltage output is stabilized by controlling the current source bias of the emitter-coupled amplifier. For example, when the high voltage output increases for some reason, the base potential of the transistor 45 increases by the second operational amplifier 41, and the current biases of the transistors 48 and 49 simultaneously increase, causing the base potential of the control transistors 21 and 22 to increase. By lowering the potential, Ve ₁ and Ve ₂ are simultaneously lowered and operate to lower the high voltage.

As described above, according to this embodiment, an emitter-coupled amplifier is used as a means for controlling the input power supply voltage of the two high-voltage generating circuits, and the operational amplifier 25 for current balance control is connected to the differential input terminal of the emitter-coupled amplifier. Since the output of the arithmetic amplifier for high voltage detection power is added to the control terminal of the constant current bias circuit, it is possible to always balance the current and stabilize the absolute value of the high voltage. It is possible. Moreover, unlike the conventional example, the transistor 48,
The loop gain of negative feedback control does not change due to the operating current of 49.

That is, the gain from the differential input stage is
On the other hand, the high voltage control loop is determined by the ratio of the load resistance 53 or 54 to the resistance 44 and the load resistance 54 by the current source control circuit.
This is because it is decided by 3 or 54. The loop gain required for current balance and stabilization of the high voltage absolute value can be determined independently by the first operational amplifier and the second operational amplifier, respectively, and the reaction speed is determined by the capacitor 26 or 55. It can be adjusted with Therefore, countermeasures against oscillation can be easily taken by changing to various filters depending on the required gain and response speed of the loop.

In addition, the temperature drift of high voltage is determined by the temperature characteristics of the voltage source applied to the inverting input terminal of the second operational amplifier, so it is very easy to design, and unlike the conventional example, it is necessary to use a temperature compensation diode for V _BE. becomes unnecessary.

The above embodiment has been described in the case of a CRT load, but it goes without saying that balance control is possible with any switching power supply as long as it is a power supply circuit that can control the output voltage by controlling the power supply voltage. do not have. Most operational amplifiers are of the two-package type, which is advantageous for miniaturization because many of them can be of the same size as conventional amplifiers.

Effects of the Invention As described above, according to the high voltage stabilizing circuit of the present invention, the first operational amplifier that detects the balance of the load current and the second operational amplifier that detects the absolute value of the high voltage can be combined. By connecting each error amplification output to the differential input stage of one emitter-coupled amplifier and the control terminal of the constant current source circuit, the temperature characteristics are excellent and the control loop is stabilized. A balance control circuit that is easy to measure can be realized with a simpler configuration, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional high voltage stabilizing circuit, and FIG. 2 is a circuit diagram showing a high voltage stabilizing circuit according to an embodiment of the present invention. 2, 8...First and second flyback transformers, 6, 12...Resistance for output current detection, 1
5, 16... Voltage divider for high pressure detection, 25, 26...
First and second operational amplifiers, 45...transistors for constant current source circuits, 43...Zener diodes, 48, 49...transistors forming emitter-coupled amplifiers.

Claims (1)

[Claims] 1 A parallel supply device is provided in which two high-voltage generation circuits using flyback transformers are connected in common, and an output current detection circuit is provided in each of the high-voltage output circuits, and the two output currents are The output terminal of the detection circuit is added to the first operational amplifier as an error input, a voltage dividing circuit is provided to detect the voltage of the high voltage output, and the output of the voltage dividing circuit and the reference voltage are used as error inputs to perform a second calculation. In addition to the amplifier, an emitter-coupled amplifier is provided to supply a differential output to each of the power supply circuits of the two high voltage generation circuits, and the output of the first operational amplifier is coupled to the emitter-coupled amplifier. A high voltage stabilizing circuit configured to supply at least one of the differential input terminals of the amplifier and to supply the output of the second operational amplifier to the control terminal of the current source circuit of the emitter-coupled amplifier. .