JPH0667189B2 - Switching Regulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a switching regulator, and more particularly to a switching regulator that uses a transformer having multiple output windings to obtain a stabilized multiple output DC voltage.

Prior Art This type of conventional multi-output switching regulator is the third
There is a configuration as shown in the figure. In the figure, a transformer 2 having multiple output windings across an unregulated DC input voltage
The temporary winding N1 and the main switching transistor 1 are connected in series with each other. By controlling the conduction angle of the main switching transistor 1 by the control output of the control circuit b, the voltage of the primary winding N1 of the transformer 2 is turned on / off and the on / off voltage is transmitted to the secondary windings N2 and N3, respectively. It has become.

The output from the secondary winding N2 of the transformer 2 is rectified by the diode 3 and smoothed via the smoothing circuit a to become the main DC output V01. The main DC output V01 is supplied to the control circuit b, and a feedback loop is formed so that the conduction angle of the main switching transistor 1 is controlled according to the level of the main DC output voltage V01. As a result, the main DC output V01 is stabilized.

On the other hand, the output from the secondary winding N3 of the transformer 2 is rectified by the diode 4, and the pulse width of the rectified output by the diode 4 is controlled by controlling the conduction angle of the sub-switching transistor 5. The output whose pulse width is controlled is smoothed by a smoothing circuit composed of the diode 9, the choke coil 10 and the capacitor 11 to become the sub DC output V02.

A control circuit c that receives the sub DC output V02 is provided, and the control circuit c generates a control signal according to the level of the input sub DC output V02. The control signal controls ON / OFF of the control transistor 20, and ON / OFF of the sub-switching transistor 5 is controlled via the pulse transformer 19 provided in the collector of the control transistor 20. The resistors 8 and 18 are for supplying the respective base currents of the transistors 20 and 5, and the power source of these transistors 20 and 5 is supplied by the auxiliary power source Vcc.

In such a conventional circuit configuration, the pulse transformer 19 is used to drive the sub switching transistor 5 that controls the sub DC output V02, which is not a good measure in terms of cost and structure. Further, since the auxiliary independent DC power supply Vcc is used for the driving energy of the sub switching transistor 5, the auxiliary power supply circuit is also expensive.

OBJECTS OF THE INVENTION Therefore, the present invention has been made to solve the above-mentioned drawbacks of the conventional ones, and the object thereof is to:
It is to provide a multi-output switching regulator without using an expensive pulse transformer and without using an expensive auxiliary power supply.

According to the present invention, a main switching transistor and a transformer having first and second secondary windings in addition to the primary winding connected in series to the main switching transistor,
First control means for controlling the conduction angle of the main switching transistor according to the main DC voltage obtained from the output from the first secondary winding of the transformer to maintain the main DC voltage constant; A sub-switching transistor for controlling the conduction angle of the rectified output of the second secondary winding of the transformer, and a conduction angle of the sub-switching transistor according to the sub-DC voltage obtained from the output of the sub-switching transistor. A switching regulator having a second control circuit, wherein the second control means controls a base current of the sub-switching transistor to be turned on and off, and a control transistor connected between the base and the emitter of the sub-switching transistor. , A control circuit for controlling on / off of the control transistor according to the sub DC voltage. It has the door, switching regulator, characterized in that the base current of the auxiliary switching transistors to be supplied by the main DC voltage.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same portions as those in FIG. 3 are designated by the same reference numerals. In the figure, a transistor 1 is for main control, and a transformer 2 is a primary winding N.
1. Secondary windings N2 and N3 are provided. The diodes 3 and 4 are for rectifying the power pulses from the respective secondary windings N2 and N3, and the smoothing circuit a is for converting the power pulses from the secondary winding N2 into direct current. The control circuit b is for detecting the first DC output V01, controlling the conduction angle of the transistor 1 in accordance with this, and keeping the DC output V01 constant.

The transistor 5 is a sub-switching transistor that makes the power pulse from the secondary winding N3 conductive or non-conductive,
The transistor 6 is a complementary control transistor for turning on / off the transistor 5. The control circuit c is the second
Is detected to control the conduction angle of the power pulse from the secondary winding N3. The diode 9, the choke coil 10 and the capacitor 11 are provided for rectifying and smoothing the power pulse obtained through the transistor 5 from the secondary winding N3 and converting it to DC. The resistors 7 and 8 are for supplying current to the bases of the transistors 5 and 6, respectively.

Next, the operation of the circuit shown in FIG. 1 will be described. The control circuit b detects the output V01, changes the conduction angle of the pulse driving the base of the transistor 5 according to the output voltage V01, and changes the width of the power pulse appearing in the secondary winding N2. After all, the pulse thus obtained is rectified and smoothed by the diode 3 and the smoothing circuit a, and the DC output V02 obtained is kept constant. That is, if the output voltage V01 becomes higher than the reference, the drive pulse width of the transistor 5 is narrowed to V01.
If the output voltage V01 becomes lower than the reference, the operation is reversed.

Here, a power pulse having the same pulse width as that of the winding N2 appears in the winding N3. Even if the number of turns of the winding N3 is properly selected, it is not possible to obtain a constant and stabilized output as the DC output V02 only by rectifying and smoothing the power pulse from the winding N3. This is due to the load of the DC outputs V01 and V02 and the variation in the voltage drop of each circuit element. Therefore, winding N3
The power pulse voltage is increased, and the conduction angle is controlled by the transistor 5 to keep the DC output V02 constant.

The control circuit c detects the DC output V02 and operates so that the conduction angle of the power pulse width from the winding N3 becomes large if this voltage is higher than the reference, and vice versa if the voltage is lower than the reference.

Now consider only the period when a positive power pulse appears at the cathode of diode 4. At this time, the control circuit c
When the output of is at high level, the transistor 6 turns on,
Since no current flows from the output V01 through the resistor 7 to the base of the transistor 5, the transistor 5 is turned off, the power pulse is blocked and does not appear on the output side. When the output of the control circuit is low level, the transistor 6 is turned off and the output V
A current flows from 01 to the base of the transistor 5 through the resistor 7, the transistor 5 is turned on, and the power pulse appears on the output side. Thus, the DC output V02 can be controlled by controlling the width of the output pulse of the control circuit c in synchronization with the power pulse.
The controlled power pulse is rectified and smoothed by the diode 9, the choke coil 10 and the capacitor 11 to become the DC output V02.

Here, the base drive current of the transistor 5 is the DC output V
It is supplied from 01, and the current flowing through the resistor 8 is only the base current of the transistor 6, so that it is generally very small.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.
The same parts as those in the figure are denoted by the same reference numerals. In this embodiment, the first DC output V01 is a negative output and the second DC output is a positive output, which is the reverse of the embodiment shown in FIG. Therefore, the transistor 5 is changed from NPN to PNP, and the base of the transistor 6 has a constant voltage diode 16,
Except that the capacitor 17 is added, it is exactly the same as the example of FIG.

The constant voltage diode 16 is for level shifting so that the transistor 6 is not turned on when the output of the control circuit c is low level. The capacitor 17 is a speed-up capacitor for shortening the base accumulation time of the transistor 6 when the transistor 6 is off. The operation is the same as in FIG. 1 and will not be described.

In this way, the base drive power supply of the sub switching transistor 5 for stabilizing the sub DC output V02 is supplied from the main DC output V01, and the control transistor 6 is connected between the base and emitter of the sub switching transistor 5, Since the on / off of the transistor 6 is controlled according to the sub DC output V02, a pulse transformer for turning on / off the sub switching transistor 5 and a power source for driving the base are not required.

As described above, according to the present invention, the on / off control of the switching transistor for controlling the sub DC output is directly performed by the control transistor which is ON / OFF controlled according to the sub DC output. Since the base drive current of the switching transistor is configured to be supplied from the main DC power supply, there is no need to use a pulse transformer,
In addition, the power consumption of the auxiliary power source is small.

[Brief description of drawings]

1 and 2 are circuit diagrams showing respective embodiments of the present invention,
FIG. 3 is a diagram showing an example of a conventional switching circuit. Description of symbols of main parts 1 ... Main switching transistor 2 ... Transformer 5 ... Sub switching transistor 6 ... Control transistor

Claims (1)

[Claims] 1. A transformer having a main switching transistor, a primary winding connected in series to the main switching transistor, and first and second secondary windings, and a first secondary winding of the transformer. First control means for maintaining the main DC voltage constant by controlling the conduction angle of the main switching transistor according to the main DC voltage obtained from the output from the line; and the second secondary winding of the transformer. And a second control circuit for controlling the conduction angle of the sub-switching transistor according to the sub-DC voltage obtained from the output of the sub-switching transistor. A regulator, wherein the second control means is
A control transistor connected between the base and the emitter of the sub switching transistor to control the base current of the sub switching transistor on and off, and a control circuit for controlling the on / off of the control transistor according to the sub DC voltage. A switching regulator characterized in that the base current of the sub-switching transistor is supplied by the main DC voltage.