JPS63167671A - Multioutput flyback converter - Google Patents

Abstract

PURPOSE:To enhance the reliability and the efficiency and to reduce the cost of a multioutput flyback converter by stabilizing the output voltage of the side to which the converter is not fed back, by a saturable coil. CONSTITUTION:A multioutput flyback converter is divided to two sections, the section regarding the output 1 of the first section is stabilized at its output voltage by a pulse-width control, and the section regarding the output 2 of the second section is stabilized at the secondary side output voltage of a main transformer 12 by a saturable reactor 16. Thus, the section of the output 1 is composed of a switching transistor 2, a pulse width converter 4, and an error amplifier 5, etc., while the section of the output 2 is composed of a satura ble coil 16, a transistor 18, an error amplifier 20, etc. Thus, the converter corrects the variation in the load current of the output by the coil 16 and an output variation due to an input voltage, thereby stabilizing the output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-output flyback converter, and particularly to a multi-output flyback converter characterized in that the voltage on the secondary side is stabilized using a saturable reactor. Connect to buck converter.

[Prior Art] FIGS. 4 and 5 are circuit diagrams of a conventional multi-output flyback converter. Both have two outputs 1 and 2 for one human power. Further, changes in the output voltage of the output l are fed back to the input terminal.

In the multi-output flyback converter shown in FIG. 4, output 2 is not fed back. For this reason, diode 1
3 and the capacitor 14, the secondary side output of the main transformer 12 is rectified and smoothed, and then the 3-terminal regulator 24
was used to stabilize the output voltage.

In the multi-output flyback converter shown in Fig. 5, the fourth
In place of the three-terminal regulator 240 shown in the figure, a switching transistor 25, a diode 28, a choke coil 29, and a capacitor 30 constitute a converter. Then, using this chopper converter, rectification is performed by diode 13 and capacitor 14,
The smoothed output voltage of the main transformer 12 was stabilized, resulting in high efficiency and high constant voltage accuracy.

[Problems to be Solved] The conventional multi-output flyback converter described above has a problem in that when a three-terminal regulator is used to stabilize the output voltage, the loss of the three-terminal regulator is large and the efficiency is reduced. was there. Further, the output voltage and stability are determined by the three-terminal regulator, and there is a problem in that the output voltage and constant voltage accuracy cannot be set arbitrarily.

On the other hand, when a chopper converter is used, there are problems in that the number of parts is large, resulting in decreased reliability and increased cost.

The present invention was made in view of the above problems, and by stabilizing the output voltage on the non-feedback side using a saturable coil, the number of parts and loss are reduced, and high reliability and The objective is to provide a multi-output flypack converter that enables high efficiency, low cost, and high constant voltage accuracy.

[Means for Solving Problems] In order to achieve the above object, the multi-output flyback converter of the present invention includes a saturable reactor connected in series with the secondary winding of the main transformer, and an output current flowing through the saturable reactor. This configuration includes output current feedback means for feeding back and resetting a part of the current.

[Embodiment] The present invention will be described in detail below based on the drawings. Note that parts common to or corresponding to those of the conventional example are denoted by the same reference numerals.

FIG. 1 is a circuit diagram of a multi-output flyback converter according to an embodiment of the present invention.

The multi-output flyback converter shown in the figure is characterized by having a saturable reactor on the output 2 side, and is mainly divided into two parts.

The first part, which is mainly connected to the output l, is a flyback converter that stabilizes the output voltage through pulse width control. Further, the second portion is a portion between the output 2 and the portion where the secondary output voltage of the main transformer is stabilized by a saturable reactor.

In the portion between the output 1, 1 is a capacitor, 2 is a switching transistor, 3 is a drive transformer, 4 is a pulse width conversion circuit, and 5 is an error amplifier. In addition, 6 is a reference voltage power supply, 7 and 8 are voltage detection resistors, 9 is a filter, 10 is a capacitor, 11 is a diode, and 1
2 is the main transformer.

The capacitor 10 and the diode 11 are connected to the main transformer 1
This constitutes a rectifying and smoothing circuit that rectifies and smoothes the secondary side output of 2. This output is connected to a filter 9, and is also connected to an error amplifier 5 via a voltage detection resistor 7.8.
is man-powered. A reference voltage power supply 6 is connected to the other input terminal of the error amplifier 5, and an output obtained by amplifying the error of these two input terminals is connected to the pulse width conversion circuit 4.

Furthermore, the output of the pulse width conversion circuit 4 is connected to the primary side of the drive transformer 3, and the secondary side output of the drive transformer 3 is connected to the switching transistor 2.

Next, in the part between the output 2, 16 is a saturable coil, 17 is a diode, 18 is a transistor, and 19 is a resistor. Further, 20 is an error amplifier, 21 is a reference voltage power supply, and 22 and 23 are voltage detection resistors.
' In this part, the diode 13 and the capacitor 14 constitute a rectifying and smoothing circuit, and this rectifying and smoothing circuit and the main transformer 12
A saturable coil 16 is connected between the secondary winding and the secondary winding. Further, the output of this rectifying and smoothing circuit is connected to the filter 15 and to voltage detection resistors 22 and 23, and the error amplifier 20 amplifies the error with respect to the reference voltage power supply 21. In general, the output of the error amplifier 20 is connected as a control input of the transistor 18.

Further, the output of the rectifying and smoothing circuit is connected to the saturable coil 16 via a resistor 19, a transistor 18, and a diode 17.
It is connected to the.

With the above configuration, the multi-output flyback converter using the saturable reactor of the present invention corrects output voltage fluctuations caused by changes in the output load current or changes in the input voltage using the saturable coil, Output voltage can be stabilized.

Below, saturable coil 1 for changes in load current of output 2
The operation of the multi-output flyback converter shown in FIG. 1 will be explained in detail, focusing on the operation No. 6.

In addition, FIG. 2 is a diagram showing the B-H curve of the saturable coil 16, FIG. 3(a) is a diagram of the voltage waveform at both ends of the saturable coil 16, and FIG. It is a diagram.

(2) When the load current of the output 2 is small When the transistor 2 is on, a voltage is applied to the diode 13 in the opposite direction, and no current flows.

Therefore, the capacitor 1 is connected to the saturable coil 16 through a resistor 19, a transistor 18, and a diode 17.
4 discharge current flows. That is, the saturable coil 16 is reset.

When the load current is small, feedback is applied so that a large amount of current flows through the saturable coil 16. Therefore, the saturable coil 16 is deeply reset (point B), as shown by the solid line in FIG.

Next, when transistor 2 is turned off, main transformer 12
The secondary side voltage of is reversed, and a current is about to flow through the diode 13. However, immediately after reversal, it is blocked by the saturable coil 16, and all the secondary voltage is applied to the saturable coil 16 (FIG. 3(a)). Therefore, no current flows through the diode 13 as shown in FIG. 3(b). Eventually, when the saturable coil 16 becomes saturated (point A), the saturable coil 16 becomes in the same state as an air-core coil, and no voltage is applied to the saturable coil 16 as shown in the third [3J(a)]. It disappears. Therefore, a current flows through the diode 13 as shown in FIG. 3(b).

At this time, since the saturable coil 16 is deeply reset, it takes longer to reach saturation than when the load current is large. That is, when the load current is small, the time required for blocking by the saturable coil 16 becomes longer than when the load current is large.

Therefore, the period during which current flows through the diode 13 becomes shorter. As a result, the increase in output voltage can be suppressed.

(2) When the load current of output 2 is large In this case, the situation is opposite to the above case. That is, when the transistor 2 is on, feedback is applied to the saturable coil 16 so that the discharge current of the capacitor 14 is reduced. Therefore, the time during which the current is blocked by the saturable coil 16 becomes shorter, and the period during which the current flows through the diode 13 becomes longer.

As a result, a drop in output voltage can be suppressed.

As described above, when the load current is small, it works as in the case (2), and when the load current is large, it works as in the case (2), so the output voltage can be stabilized against changes in the load current.

It is clear that a similar effect can be expected when the transistor 2 is a FET and the output voltage is negative.

[Effects of the Invention] As explained above, the present invention stabilizes fluctuations in output voltage due to changes in load current and changes in input voltage by changing the blocking time of the saturable reactor. The present invention has the advantage that it is possible to obtain a multi-output flyback converter with a small number of parts, high precision stabilization, high efficiency, high reliability, low cost, and high constant voltage precision.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a multi-output flyback converter according to an embodiment of the present invention, Fig. 2 is a diagram showing a B-H curve of a saturable coil, and Fig. 3(a) is a diagram showing a B-H curve of a saturable coil. FIG. 3(b) is a voltage waveform diagram, FIG. 3(b) is a current waveform diagram of a diode in a rectifying and smoothing circuit, and FIGS. 4 and 5 are circuit diagrams of a conventional multi-output flyback converter. 12: Main transformer 16: Saturable coil 17: Diode 18: Transistor 19: Resistor 20
:Error amplifier 21:Reference voltage power supply 22.23:Voltage detection resistor

Claims (1)

[Claims] The multi-output flyback converter includes a saturable reactor connected in series with the secondary winding of the main transformer, and output current feedback means for feeding back a part of the output current to the saturable reactor and resetting it. A multi-output flyback converter characterized by: