JPH05207742A - Converter controller - Google Patents

Abstract

PURPOSE:To eliminate a secondary winding of a choke coil of a converter controller and to avoid an increase in insulating positions between windings. CONSTITUTION:A controller comprises a main transformer 2 connected with a DC power source 1, a switching Tr 10, diodes 3, 4 connected to a secondary side of the transformer 2, a choke coil 5, a capacitor 6, and a load resistor 7. A DC feedback circuit has an error amplifier 8, an adder 13 and a comparator 11, and a triangular wave generator 12 is connected to the comparator 11. An output of the comparator 11 is connected to the Tr 10, and a feedback signal is supplied to the Tr 10. An AC feedback circuit has a first capacitor 20 connected at its one end to a drain of the Tr 10, a first resistor 21 connected in series with the capacitor 20, an operational amplifier 23 connected to a capacitor 25 through a second resistor 22, and a third resistor 24, a second capacitor 25 connected between an input terminal and an output terminal of the amplifier 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter control device, and more particularly to a double feedback type converter control device for adding direct current and alternating current and feeding back.

[0002]

2. Description of the Related Art As one type of control system for switching power supplies, a double feedback system in which direct current and alternating current components are added and fed back is known. For example, a technical document "Switching Power Supply System" issued in February 1991 is known. An example is given in "Symposium" (published by the Japan Management Association).
The circuit diagram shown in FIG. 4 is an application of the double feedback control similar to that shown in this technical document to a forward converter.

The double feedback control shown in the figure has a normal DC feedback circuit and an AC feedback circuit for improving the characteristics, and increases the phase margin in the vicinity of several 10 KHZ to improve the stability. ..

The converter shown in FIG. 3 includes a main transformer 2 having a DC power supply 1 connected to one end of a primary coil, and a switching transistor (hereinafter abbreviated as switching Tr) 10 connected to the other end of the primary coil. , A rectifier circuit composed of diodes 3 and 4 connected to the secondary side of the main transformer 2, an LC filter circuit composed of a choke coil 5 and a capacitor 6, and a load resistor 7. ..

The DC feedback circuit has an error amplifier 8 whose + side input terminal is connected to the load resistor 7 and whose − side input terminal is connected to a reference power source 9. The output of this error amplifier 8 is an adder. 13 is input. The output side of the adder 13 is connected to the-side input terminal of the comparator 11, and the triangular wave generator 12 is connected to the + side input terminal of the comparator 11. The output of the comparator 11 is connected to the switching Tr10 and supplies a feedback signal to the switching Tr10.

On the other hand, the AC feedback circuit includes resistors 14, 15,
The input signal is received from the secondary winding of the choke coil 5, and the output signal is sent from the output side of the operational amplifier 18 to the adder 13.

Next, the circuit operation of the above configuration will be described with reference to FIGS. 4 and 5, but for ease of understanding, the converter portion excluding the AC feedback circuit described above will be described first. Note that FIG. 5 shows voltage waveforms at points A to E in FIG. In the converter part, DC power supply 1
When is turned on, the converter output is zero, so that the outputs of the error amplifier 8 and the adder 13 have the minimum possible values.

Therefore, by appropriately selecting the potential relationship with the output (D) of the triangular wave generator 12, as shown in FIG. 5, the duty ratio of the output (E) of the comparator 11 is set to a large value. Will be possible. When the switching Tr 10 is interrupted by the output (E) of the comparator 11, the converter output voltage (A) smoothed by the LC filter including the choke coil 5 and the capacitor 6 gradually rises.

When the converter output voltage (A) rises,
The output (B) of the error amplifier 8 and the output (C) of the adder 13 increase, the conduction period of the switching Tr 10 decreases due to the action of the comparator 11, and when the converter output voltage becomes equal to the reference voltage, A constant duty ratio is achieved and constant voltage control is achieved. From such an operation, it can be said that it is a DC amplifier in which the output voltage is negatively fed back to the + side input terminal of the error amplifier 8 so as to prevent fluctuation of the output voltage and maintain a constant voltage.

By the way, in order to obtain good characteristics with respect to changes in input voltage and output current, it is necessary not only to increase the loop gain as a negative feedback amplifier, but also to have a certain degree of gain near several tens KHz. .. However, it is difficult to achieve this requirement while maintaining the stability of the circuit only by the DC feedback control.

The reason is that in the converter circuit, the LC filter must be used in order to convert the DC power into a pulse and return it to the DC again. However, since the LC filter is also a resonance circuit, the resonance frequency A sudden phase delay occurs due to a secondary delay from this side. As a result, the loop characteristic also causes a sudden phase delay near the resonance frequency of the filter,
This is because the phase margin is insufficient, an abnormal oscillation phenomenon occurs, and it becomes unstable easily.

Therefore, in order to solve such a problem, a double feedback control has been devised in which an AC feedback circuit is provided in addition to the DC feedback circuit. In the double feedback control, the DC feedback circuit feeds back a signal with a large phase delay that has passed through the LC filter circuit of the converter, while the AC feedback circuit outputs the switching output from the secondary winding of the choke coil 5. Is taken out and integrated by the operational amplifier 18, and the output signal thereof is added to the adder 13, so that there is no DC gain,
Negative feedback can be applied only to a specific frequency band.

In this case, the feedback signal of the AC feedback circuit is L
Instead of the C filter, it is smoothed by the CR filter including the resistor 16 and the capacitor 17, and the phase delay is small. Therefore, if this frequency band and the resonance frequency of the LC filter are matched, the gain near the resonance frequency is lowered in the overall characteristics, and the phase is an intermediate value in the case where the DC feedback circuit and the AC feedback circuit are independent. Therefore, the phase delay is reduced, the phase margin is increased, and it becomes stable.

However, such a conventional double feedback control has the following technical problems.

[0015]

That is, in the above-mentioned conventional double feedback control converter, since the secondary winding of the choke coil 5 is required at the input portion of the AC feedback circuit, the choke coil 5 can be miniaturized. However, it is difficult to reduce the cost and there is a problem that the number of insulating points between the primary and secondary windings of the coil 5 increases.

The present invention has been made in view of such conventional problems, and an object of the present invention is to reduce the size and cost of the choke coil and to increase the number of insulating portions. It is to provide a converter control device that can be avoided.

[0017]

In order to achieve the above object, a first invention is a main transformer to which a DC power source is supplied,
A switching transistor connected to the primary side of the main transformer, a rectifying circuit and an LC filter circuit connected to the secondary side of the main transformer, and an adder for adding the outputs of the DC and AC feedback circuits, In a converter for feeding back a feedback signal to the switching transistor via a comparator connected to the output side of the adder, the AC feedback circuit inputs an AC component from which a DC component is removed from a drain portion of the switching transistor as an input signal. The input signal is integrated and output to the adder.

In this case, as an AC feedback circuit, a first capacitor whose one end is connected to the drain of the switching transistor, and a first resistor whose one end is connected in series to this capacitor and whose other end is grounded, Connected between an operational amplifier in which one input terminal is connected to the other end side of the first capacitor via a second resistor and the other terminal is grounded, and one input terminal and output terminal of the operational amplifier And a feedback element, and the feedback element can be configured by a third resistor and a second capacitor connected in parallel.

As a second invention, a main transformer to which a DC power is supplied, a switching transistor connected to the primary side of the main transformer, a rectifier circuit and an LC filter connected to the secondary side of the main transformer. A converter for adding a circuit and an adder for adding the outputs of a direct current and an alternating current feedback circuit, wherein a feedback signal is fed back to the switching transistor via a comparator connected to the output side of the adder. Is characterized in that an alternating current component obtained by removing a direct current component from the feedback signal of the comparator is used as an input signal, and an integrated value of the input signal is inverted and output to the adder.

In this case, as an AC feedback circuit, a first capacitor, one end of which is connected to the output side of the comparator, and a first resistor, one end of which is connected in series and the other end of which is grounded, Connected between an operational amplifier in which one input terminal is connected to the other end side of the first capacitor via a second resistor and the other terminal is grounded, and one input terminal and output terminal of the operational amplifier The feedback element and an inverting amplifier connected to the output side of the operational amplifier are provided, and the feedback element can be configured by a third resistor and a second capacitor connected in parallel.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, the same or corresponding parts as those of the conventional circuit described above are designated by the same reference numerals. FIG. 1 shows an embodiment of a converter control device according to the present invention. The control device shown in the figure includes a DC power supply 1, a main transformer 2, and a switching Tr.
10, a rectifier circuit composed of rectifier diodes 3 and 4, an L composed of a choke coil 5 and a capacitor 6.
It has a C filter circuit and a load resistor 7.

The positive side of the DC power supply 1 is connected to the hot end on the primary side of the main transformer 2, and the negative side of the power supply 1 is grounded. The secondary hot end of the main transformer 2 is connected to the anode of the rectifier diode 3, and the cathode thereof is connected to the cathode of the rectifier diode 4 and one end of the choke coil 5. The other end side of the choke coil 5 is connected to the + side input terminal of the error amplifier 8. The cold end on the secondary side of the main transformer 2 and the anode of the rectifier diode 4 are grounded.

The + input terminal of the error amplifier 8 is connected to the load resistor 7 and the capacitor 6 whose one end is grounded. The positive side of the reference power supply 9 is connected to the-side input terminal of the error amplifier 8, and the negative side of the reference power supply 9 is grounded. The drain of the switching Tr 10 is connected to the cold end on the primary side of the main transformer 2. The output side of the error amplifier 8 is connected to one input terminal of the adder 13.

The output of the adder 13 is connected to the minus side input terminal of the comparator 11, and the plus side input terminal of the comparator 11 is connected to the output side of the triangular wave generator 12. Comparator 11
The output of is connected to the gate of the switching Tr10. The source of the switching Tr10 is grounded. In the above configuration, the error amplifier 8 is a DC feedback circuit, and the path from the error amplifier 8 to the adder 13, the comparator 11, and the switching Tr 10 is a DC feedback path.

On the other hand, the AC feedback circuit includes a first capacitor 20 having one end connected to the drain of the switching Tr 10, and a first resistor 21 having one end connected in series to the capacitor 20 and the other end grounded. , The first capacitor 2
An operational amplifier 23 in which the − side input terminal is connected to the other end side of 0 through the second resistor 22 and the + side input terminal is grounded.
And a feedback element connected between the negative input terminal and the output terminal of the operational amplifier 23. The feedback element is
Specifically, the third resistor 24 and the second capacitor 26 are connected in parallel, and the output side of the operational amplifier 23 is connected to the other input terminal of the adder 13.

In the control device constructed as described above, the operation of the DC feedback path is the same as that of the conventional example described above, so the description thereof will be omitted and the operation of the AC feedback circuit will be described with reference to FIG. .. Note that FIG. 2 shows voltage waveforms at points E and G in FIG. 1 and point F in FIG.

In the control device of this embodiment, since the input signal of the AC feedback circuit is taken into the operational amplifier 23 via the capacitor 20 and the resistor 22, the switching Tr is switched.
It is applied to the-side input terminal of the operational amplifier 23 in a state in which the DC part is removed from the drain voltage of 10.

The drain voltage of the switching Tr10 at this time has a waveform shown by G in FIG. 2, but since the integrated output by the operational amplifier 23 is a demodulation component of this PWM signal, it is involved in the shape of the waveform. do not do. On the other hand, in the above-described conventional AC feedback circuit, the waveform indicated by F in FIG. 2 is integrated by the operational amplifier 18, but the polarities of both digital signals are the same, and the gain of the operational amplifier 23 is appropriately selected. , It is possible to obtain the same integrated output, and it can be said that both are equivalent as an AC feedback circuit.

Therefore, also in the converter control device shown in FIG. 1, the phase delay is reduced and the phase margin is increased to be stable. In this case, especially in this embodiment,
There is no need to provide a secondary winding on the choke coil 5 as in the conventional double feedback control, an increase in the number of insulation points is avoided, and at the same time, the structure of the choke coil 5 is simplified, and the size and cost are reduced. Can be achieved.

FIG. 3 shows another embodiment of the present invention, and only the characteristic points will be described below. In the embodiment shown in the figure, the output voltage of the comparator 11 is used as the input signal of the AC feedback circuit instead of the drain voltage of the switching Tr 10, and this output voltage is applied to the operational amplifier 23 via the DC voltage removing capacitor 20. ing. In this embodiment, the integrated output of the operational amplifier 18 is inverted by the inverting amplifier 20 and input to the adder 13.

Also in the converter control device thus constructed, the same operation and effect as in the above embodiment can be obtained.

[0032]

As described in detail in the above embodiments,
According to the converter control device of the present invention, the secondary winding of the choke coil is not required, and the insulating parts of the primary and secondary side circuits can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a converter control device according to the present invention.

FIG. 2 is a voltage waveform diagram at points E and G in FIG.

FIG. 3 is a circuit diagram showing another embodiment of the converter control device according to the present invention.

FIG. 4 is a circuit diagram showing a conventional converter control device.

5 is a voltage waveform diagram of points A to E in FIG.

[Explanation of symbols]

 1 DC Power Supply 2 Main Transformer 3,4 Diode 5 Choke Coil 8 Error Amplifier 10 Switching Tr 11 Comparator 13 Adder 20 First Capacitor 21 First Resistor 22 Second Resistor 23 Op Amp 24 Third Resistor 25 Second Capacitors

Claims (4)

[Claims] 1. A main transformer to which a DC power is supplied, a switching transistor connected to a primary side of the main transformer, a rectifier circuit and an LC filter circuit connected to a secondary side of the main transformer, a DC and A converter that adds an output of an AC feedback circuit and feeds a feedback signal back to the switching transistor via a comparator connected to the output side of the adder, wherein the AC feedback circuit is the switching transistor. The converter control device is characterized in that an alternating current component from which a direct current component has been removed from the drain portion of is used as an input signal, and the input signal is integrated and output to the adder. 2. The alternating current feedback circuit includes a first capacitor whose one end is connected to the drain of the switching transistor, and a first resistor whose one end is connected in series and whose other end is grounded. Connected between an operational amplifier in which one input terminal is connected to the other end side of the first capacitor through a second resistor and the other terminal is grounded, and one input terminal and output terminal of the operational amplifier 2. The converter control device according to claim 1, further comprising: a third resistor and a second capacitor connected in parallel, the feedback control element being provided with a third resistor and a second capacitor. 3. A main transformer to which a DC power is supplied, a switching transistor connected to the primary side of the main transformer, a rectifying circuit and an LC filter circuit connected to the secondary side of the main transformer, a DC and A converter that adds an output of an AC feedback circuit and feeds a feedback signal back to the switching transistor via a comparator connected to the output side of the adder, wherein the AC feedback circuit is the comparator. The converter control device is characterized in that an alternating current component obtained by removing a direct current component from the feedback signal is used as an input signal, and an integrated value of the input signal is inverted and output to the adder. 4. The AC feedback circuit includes a first capacitor whose one end is connected to the output side of the comparator, and a first resistor whose one end is connected in series and whose other end is grounded. Connected between an operational amplifier in which one input terminal is connected to the other end side of the first capacitor through a second resistor and the other terminal is grounded, and one input terminal and output terminal of the operational amplifier 2. A feedback element which is connected to the output side of the operational amplifier, and an inverting amplifier connected to the output side of the operational amplifier, wherein the feedback element comprises a third resistor and a second capacitor which are connected in parallel. Converter control device.