JPH0591737A - Multioutput type switching power source - Google Patents

Abstract

PURPOSE:To conduct complementary control operations of two switching transistors at the same timing by providing a voltage comparator for comparing outputs of first and second output detectors with a reference voltage to control to switch the primary side of a power transformer. CONSTITUTION:When a control transistor 55 is turned OFF by a control signal supplied to a terminal 56 of a power source, a predetermined divided voltage is supplied to turn ON a transistor 53, and a transistor 28 is turned ON to turn ON a power source switch. Accordingly, when the transistor 55 is turned ON, the power source switch is turned OFF. When the transistor 28 is turned ON, the transistor 55 is turned OFF, and hence a second switching transistor 41 is cut OFF. And, a second output voltage detector 40 is in an inhibiting state, but since a predetermined base bias is applied to a switching transistor 31, it is turned ON, and a first output voltage detector 30 is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output type switching power supply device suitable for use in an integrated type composite electronic device incorporating a television receiver and a video tape recorder.

[0002]

2. Description of the Related Art In recent years, electronic devices have been compounded. Among them, a composite electronic device in which a television receiver and a video tape recorder are integrated is known. In such a composite electronic device, it is necessary to obtain a power supply voltage suitable for the electronic device as in the case of using each alone. It is necessary to use a stabilized power supply voltage.

The power supply voltage thus stabilized is
Moreover, as a power supply device that generates a plurality of power supply voltages having different voltage values using the same power supply transformer, it is preferable to use a multi-output type switching power supply device as shown in FIG. FIG. 3 shows a power supply device used in an electronic device in which a television receiver and a video tape recorder are combined, and a power supply device of a ringing choke converter system is shown as a switching system. The types of devices and converter methods are just examples.

In FIG. 3, a power supply terminal 1 to which a DC voltage Ein is supplied is grounded via a primary winding 2P of a converter transformer 2 and a collector-emitter series circuit of an NPN transistor 3 which constitutes a switching element. It In addition, a series circuit of a capacitor 4 and a resistor 5 forming a snubber circuit for absorbing surge is connected in parallel with the collector / emitter of the transistor 3.

The power supply terminal 1 is connected to the base of the transistor 3 through a series circuit of a starting resistor 6 and a parallel circuit 10. The parallel circuit 10 includes a diode 7 and a resistor 8
The capacitor 9 is connected in parallel to the series circuit of. One end of the base winding 2B of the transformer 2 is grounded, and the other end is connected to the connection point of the resistor 6 and the parallel circuit 10.

The connection point between the parallel circuit 10 and the base of the transistor 3 is grounded via the collector / emitter of the NPN transistor 11 for controlling the base current. One end of the secondary winding 2Sa of the transformer 2 is grounded, and the other end is grounded via a series circuit of an anode / cathode of a rectifying diode 12 and a smoothing capacitor 13.
The DC voltage Ea obtained at the connection point of the diode 12 and the capacitor 13 is output to the output terminal 1 via the power switch 28.
4 is derived. This DC voltage Ea is used for television receivers, and therefore its voltage value is 100 tens of volts.

The output terminal 14 is grounded via a series circuit of a resistor 15, a variable resistor 16 and a resistor 17.
The voltage obtained at the mover of the variable resistor 16 is the comparator 1
8 and is compared with the reference voltage Vref. Comparator 1
8 outputs a signal of higher level as the voltage obtained at the mover of the variable resistor 16 becomes higher. Comparator 18
Output signal of the control transistor 11 via the resistor 19
The DC voltage Ea is stabilized by being supplied to the base of the.

The transformer 2 is further wound with another secondary winding 2Sb, and the pulse voltage obtained here is rectified by the diode 21, which is the capacitor 2
It is smoothed by 2. Since the DC voltage obtained here is not completely stabilized, this DC voltage is further supplied to the stabilizing circuit 24 to be stabilized and then led to the output terminal 25.

Since the DC voltage Eb obtained at the output terminal 25 is used as the power supply voltage of the video tape recorder,
Its value is a few tens of volts. A power switch for the video tape recorder is provided further on the load side than the output terminal 25, but this is not shown. The power switch and the power switch 28 described above are controlled by a microcomputer.

Next, the stabilizing operation of FIG. 3 will be described with reference to the signal waveform diagram of FIG. When the DC voltage Ein is supplied to the power supply terminal 1, a starting current is supplied to the base of the transistor 3 via the resistor 6 and the parallel circuit 10. Since the primary winding 2P and the base winding 2B of the transformer 2 are connected so as to have a positive feedback, the oscillation immediately starts, and the amplitude of the voltage VB induced in the base winding 2B becomes large (see FIG. 4H). The transistor 3 is immediately turned on.

When the transistor 3 is turned on, a voltage is applied in the reverse direction to the diode 12 connected to the secondary winding 2Sa of the transformer 2 (the voltage VS induced in the secondary winding 2Sa is shown in FIG. No current flows in the diode 12). Therefore, the load of the transistor 3 is the transformer 2
And the collector current IC increases linearly (A in the same figure).

FIG. 2B shows the collector-emitter voltage VCE of the transistor 3, and FIG. 1C shows the base current IB of the transistor 3. The base current IB is a combination of the current ID1 flowing through the series circuit of the diode 7 and the resistor 8 and the current IC1 flowing through the capacitor 9.
That is, when the transistor 3 is turned on, the forward voltage VB induced in the base winding 2B of the transformer 2 causes the capacitor 9 to have a time constant determined by the capacitance of the capacitor 9 and the resistance of the base winding 2B. Decay current I
C1 flows (D in the figure). When the voltage across the capacitor 9 reaches the forward drop voltage of the diode 7, a current ID1 flows in the series circuit of the diode 7 and the resistor 8 (E in the figure).

As described above, the collector current IC which increases linearly continues to increase during the storage time tstg of the transistor 3 even after increasing to hFE times the base current IB (A in the same figure). When the storage time tstg has elapsed, the current sharply decreases, and at the same time, a reverse voltage VB is generated in the base winding 2B (H in the figure), and the base current IB of the transistor 3 becomes a reverse bias current (C in the figure). ), The transistor 3 is turned off.

Here, the maximum value ICP of the collector current IC will be described. The collector current IC is IC = IB · hFE
Therefore, the base current IB increases linearly at the same time. Maximum value of this collector current IC ICP
Is as follows:

ICP = IBP · hFE + tstg · Ein / LP (1) In this formula, IBP is the maximum value of the base current IB of the transistor 3, and LP is the inductance of the primary winding 2P of the transformer 2. ..

Next, when the transistor 3 is turned off, the energy accumulated in the core of the transformer 2 during the on period of the transistor 3 is discharged because the rate of change of the magnetic flux becomes negative, so that each winding of the transformer 2 is discharged. Generates a voltage with the "." Mark side being negative. At this time, in the primary winding 2P of the transformer 2, a current I that linearly decreases as shown in FIG.
L starts to flow. Similarly, in the diode 12 connected to the secondary winding 2S, a current ID2 that linearly decreases as shown in FIG.

In this state, the release of the energy stored in the core of the transformer 2 is completed and the currents IL and ID
When 2 becomes 0, there is no change in the magnetic flux in the transformer 2, and a voltage in the opposite direction to that in the past is generated in each winding of the transformer 2. Therefore, the voltage VB induced in the base winding 2B of the transformer 2 also becomes a forward voltage, and the base current flows in the direction in which the transistor 3 is turned on. As a result, the transistor 3 is turned on, and the same operation as described above is repeated.

By such a repetitive operation, a rectangular wave voltage VS as shown in FIG. 1I is obtained at the secondary winding 2S of the transformer 2, which is rectified and smoothed and a DC voltage Ea is outputted to the output terminal 14. can get.

Next, the case where the DC voltage Ea fluctuates will be described. When the DC voltage Ea increases, the voltage obtained at the mover of the variable resistor 16 increases and the comparator 18
The output signal level of becomes high. Therefore, the base current of the transistor 11 increases, and at the same time, its collector current also increases. As a result, the base current IB of the transistor 3 decreases, and the collector current IC is reduced from the relation of the above equation (1).
The maximum value I CP of the transistor 3 also decreases, and the ON period of the transistor 3 is shortened (J in the same figure).

When the ON period of the transistor 3 is shortened in this way, the amplitude of the rectangular wave voltage VS obtained in the secondary winding 2S of the transformer 2 in the positive direction becomes small (K in the same figure). Therefore, the DC voltage Ea obtained at the output terminal 14 is controlled to decrease.

On the contrary, when the DC voltage Ea becomes low, the DC voltage Ea obtained at the output terminal 14 is controlled in the opposite manner to the above.
Is controlled to increase. From such an operation, the DC voltage Ea obtained at the output terminal 14 is stabilized.
The value of the DC voltage Ea can be varied by changing the mover position of the variable resistor 16.

The reason why the stabilizing circuit 24 is provided on the side of the other secondary winding 2Sb in the circuit of FIG. 3 is as follows.

When the power switch 28 is turned off, the potential at the point p in FIG. 3 rises, so that the presence of the above-mentioned control loop operates to lower the potential at the point p. Then, the potential at the point q on the side of the other secondary winding 2Sb also decreases accordingly, so that the DC voltage Eb of the output terminal 25 decreases without the stabilization circuit 24, and the stabilized power supply voltage is reduced. It cannot be supplied to the video tape recorder side.
Therefore, a stabilizing circuit 24 is further provided as shown in the figure.

[0024]

By the way, when the stabilizing circuit 24 is provided in this way, it is necessary to consider a heat dissipation measure of the stabilizing circuit 24. Normally, a heat sink is attached, but in order to attach the heat sink, it is necessary to secure a certain space, and it is necessary to use an element with high withstand voltage, which causes problems such as cost increase. Cause.

As one means for solving these problems, the output terminal 25 without the stabilizing circuit 24 is provided.
As a means for stabilizing the obtained DC voltage Eb, the configuration shown in FIG. 5 can be considered.

Although the description of the same components as those in FIG. 3 is omitted, a first output voltage detection circuit 30 is provided on the output terminal 14 side, and a second output voltage is provided on the other output terminal 25 side. A detection circuit 40 is provided.

The first output voltage detection circuit 30 uses the resistors 15, 16 and 17 for voltage division as in the conventional case.
The switching transistor 31 is connected between the connection point r and the resistor 16. The divided voltage at the connection point r is supplied to the voltage comparator 18.

The second output voltage detection circuit 40 is also composed of voltage dividing resistors 42, 43 and 17 and a switching transistor 41 connected in series with these resistors. As the switching transistor 41, a PNP type transistor is used, the emitter of which is connected to the output terminal 25,
The base is connected to the output terminal 14 side through a voltage dividing circuit composed of resistors 44 and 45.

Since the switching transistor 31 is turned off when the power switch 28 is turned off, at this time, the first output voltage detection circuit 30 is also output terminal 1
It is intended to be completely separated from the load connected to No. 4. Otherwise, when the second output voltage detection circuit 40 is used, the resistors 15 and 16 are connected in parallel to the connection point r through the output terminal 14, and the constants in the second output voltage detection circuit 40 become constant. This is because the setting of becomes complicated.

The control operation for stabilization shown in FIG. 5 is as follows. When the power switch 28 is turned on,
Since the second switching transistor 41 is reverse-biased, the second output voltage detection circuit 40 is inoperative, and the first switching transistor 31 is forward-biased, so that the first output voltage detection circuit 30 is in the operating state. Become. When the first output voltage detection circuit 30 operates, the DC voltage Ea obtained at the output terminal 14 is output in a stabilized state by the control loop including the first output voltage detection circuit 30. DC voltage Ea
Is stabilized, the peak value of the output pulse obtained at both ends of the other secondary winding 2Sb becomes constant, so that the output terminal 25
The direct-current voltage Eb obtained in the above step is also stabilized.

On the other hand, when the power switch 28 is turned off, the first switching transistor 31 is cut off, so that the first output voltage detection circuit 30 is disconnected from the control system. Since the second switching transistor 41 becomes forward biased and is turned on, the second output voltage detection circuit 40 is in the operating state.

As a result, the divided voltage at the connection point r determined by the resistors 42, 43 and 17 is compared with the reference voltage Vref, and the conduction angle of the control transistor 11 is controlled so that they match each other. The peak value of the output pulse obtained at the secondary winding 2Sb becomes constant, and thereby a stabilized predetermined DC voltage Eb is obtained at the output terminal 25.

That is, the DC voltages Ea and Eb obtained at the two output terminals 14 and 25 are stabilized by simply adopting the simple circuit configuration shown in FIG.
The drawbacks due to the configuration can be eliminated.

However, the circuit configuration shown in FIG. 5 causes the following new problems. As is clear from the operation described above, the switching transistors 31 and 4
1 must be controlled at the same timing complementarily, but the voltage change characteristics differ because the capacitive and inductive loads connected to the output terminals 14 and 25 are different, which causes the switching transistor 31 and 41
In some cases, it becomes impossible to complementarily control and at the same timing. The explanation will be given below.

FIG. 6 shows changes in the DC voltage Eb with respect to the DC voltage Ea when the power switch 28 is turned on and off. The DC voltage Ea has the rising and falling characteristics as shown in FIG. Show. This characteristic is provided because a capacitive or inductive load is connected to the output terminal 14. Since a capacitive load or an inductive load is also connected to the output terminal 25, the voltage characteristics of the output terminal 25 have the same tendency.

Now, when the rising characteristic when the power switch 28 is turned on is enlarged, it becomes as shown in FIG. Since the rising and falling characteristics of the DC voltages Ea and Eb are different depending on the size of the capacitive and inductive loads connected to the output terminals 14 and 25, the first switching transistor 31 is turned on at time T1. However, the second switching transistor 41 may not yet be turned off. In the figure, the case where the second switching transistor 41 is turned on and inverted for the first time at time T2 is shown.

In this case, both switching transistors 31 and 41 are turned on during the period W1. Then, the divided voltage at the point r applied to the voltage comparator 18 rises, so that a control loop for lowering the DC voltage Ea of the output terminal 14 is formed, and the DC voltage Eb of the output terminal 25 is instantaneously changed. It goes down (Fig. 6C).

Similarly, when the power switch 28 is turned off, the second switching transistor 41 is still in the ON state at time T3 as shown in FIG.
In the case where the first switching transistor 31 is inverted to the off state in 4, both switching transistors 31 and 41 are held in the on state only during the period W2. Also in this case, since the divided voltage at the point r increases, the DC voltage Eb of the output terminal 25 operates so as to decrease,
The voltage fluctuation as shown in FIG.

When such a voltage change occurs, especially when the voltage changes as shown in the figure, the output terminal 2
When a microcomputer or the like is connected to 5, and the DC voltage Eb drops below the operation guaranteed voltage of the microcomputer, the microcomputer is instantly reset.
It's a big problem.

Therefore, the present invention has solved such a conventional problem, and is complementary to the two switching transistors used in the circuit configuration shown in FIG. 5 in order to reduce the number of components. The control operation is performed at the same timing.

[0041]

In order to solve the above-mentioned problems, according to the present invention, a plurality of output voltages having different voltages can be taken, and at least one of the output voltages is regarded as a stabilized voltage. In the multi-output switching power supply device configured as described above, the power switch connected to the output terminal from which the stabilized first output voltage is obtained and the first power switch connected to the load side of the power switch. A first output voltage detection circuit having a switching transistor; a control circuit for the power switch;
Comparing the outputs of the second output voltage detection circuit having the second switching transistor connected to the output terminal from which the second output voltage is obtained and the outputs of the first and second output voltage detection circuits with the reference voltage A primary side of a power transformer, and a voltage comparator configured to perform switching control, and the first and second switching transistors are complementarily controlled at the same timing based on a control signal applied to the control circuit. It was made to be done.

[0042]

In FIG. 1, the transistor 28 functions as a power switch. A control signal (a rectangular wave signal, not shown) is applied to the terminal 56 to control the transistor 55.
When is turned off, a predetermined bias voltage is applied to the control transistor 53 via the pair of resistors 51 and 52, so that the control transistor 53 is turned on and the transistor 28 is brought to the on state.

At the same time, the voltage at the terminal s is applied to both the first and second switching transistors 31 and 41 at the same time, so that the second switching transistor 41 is turned off and the second output voltage detection circuit 40 is turned off. Operation is prohibited. On the other hand, the first switching transistor 31 is conversely controlled to be in the ON state. Therefore, the first
The output voltage detection circuit 30 operates to stabilize the DC voltage Ea. With the stabilization of the DC voltage Ea, the DC voltage Eb
Is also stabilized. Since the first and second switching transistors 31 and 41 are forcibly controlled by the control signal, they are complementarily controlled at the same timing.

When the polarity of the control signal is reversed, the transistor 28 turns off. Then, the first switching transistor 31 is turned off and the second switching transistor 41 is turned on. As a result, the second output voltage detection circuit 40 enters the operating state and the DC voltage Eb
Is stabilized.

In this case as well, since the on / off of the transistor 55 is forcibly controlled by the control signal applied to the transistor 55, the first and second switching transistors 31 and 4 are provided.
1 is turned on and off at the same timing. Therefore, the DC voltage Eb does not fluctuate significantly at any timing when the transistor 28 is turned on and when it is turned off.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an example of a multi-output type switching power supply device according to the present invention will be described in detail with reference to the drawings. For convenience of description, description of the same configurations as those shown in FIGS. 3 and 5 will be omitted.

FIG. 1 shows an example of a multi-output type switching power supply device according to the present invention, in which a DC voltage Ea used in a television receiver is output to a terminal 14 and a video tape to a terminal 25. It is assumed that the DC voltage Eb used in the recorder is output.

Also in this invention, the first output voltage detecting circuit 30 is connected to the output terminal 14 side, and the output terminal 25 is connected.
The second output voltage detection circuit 40 is connected to the side.
The configuration is almost the same as that of the conventional example, but the connection relationship of the switching transistors 31 and 41 provided therein is slightly different. Further, in the present invention, a control circuit 50 for the transistor 28 functioning as a power switch is provided.

A PNP type transistor is used as the transistor 28, the emitter and collector of which are connected in series with the power supply path of the output terminal 14, and the transistor 2 is provided at the base thereof.
A control transistor 53 for controlling the on / off state of the transistor 8 is connected. Further, the voltage of the input stage of the transistor 28 is supplied to the voltage dividing resistors 51 and 52, and the divided voltage obtained at the connection point s thereof is applied to the base of the control transistor 53.

A control transistor 55 is further connected between the connection point s and the ground, and ON / OFF is controlled by a control signal SP (rectangular wave signal) supplied to a terminal 56. The divided voltage obtained at the connection point s is further supplied to the bases of both the first switching transistor 31 and the second switching transistor 41 via resistors 57 and 58. First and second switching transistor 3
Different conductive types are used for 1 and 41.

In the switching power supply device configured as described above, when the control transistor 55 is turned off by the control signal supplied to the terminal 56, a predetermined divided voltage is applied from the connection point s to the control transistor. 5
This transistor 53 turns on because it is supplied to
Along with this, the transistor 28 is turned on. At this time, the power switch is turned on. Therefore, since the control transistor 53 is off when the control transistor 55 is on, the transistor 28 is also off, so the power switch is off.

When the transistor 28 is on, the control transistor 55 is off, so that the base voltage of the second switching transistor 41 becomes higher than the emitter voltage, and the second switching transistor 41 is in the cutoff state. The second output voltage detection circuit 40 is in the operation prohibited state. On the other hand, since a predetermined base bias is applied to the first switching transistor 31, this turns on and the first output voltage detection circuit 30
Becomes the operating state. As a result, the DC voltage Ea obtained at the terminal 14 is stabilized. At the same time, the DC voltage Eb obtained at the terminal 25 is also stabilized.

Since the first and second switching transistors 31 and 41 are compulsorily controlled in common by the control signal SP supplied to the control transistor 55,
Since they are complementarily controlled at the same timing, the ON / OFF timings of them do not shift.

On the other hand, when the control transistor 55 is turned on, the control transistor 53 is turned off.
Is turned off and the power switch is opened. Since the control transistor 55 turns on, the first switching transistor 31 turns off and, conversely, the second switching transistor 41 turns on. as a result,
The first output voltage detection circuit 30 is prohibited, only the second output voltage detection circuit 40 is in the operating state, and the DC voltage Eb obtained at the output terminal 25 is a stabilized voltage.

Even in this control mode, since the on / off states of the first and second switching transistors 31 and 41 are forcibly controlled by the control signal SP supplied to the control transistor 55, one of them is turned off and the other is turned on at the same time. It is controlled so as to turn on at the same timing, and the on / off timing does not shift.

By the way, the configuration shown in FIG.
Since 8 and the base of the transistor 11 are directly connected by a line, the primary side (power supply side) and the secondary side (load side) viewed from the transformer 2 are not completely insulated. Originally, it is preferable to completely electrically separate the two.

FIG. 2 is a block diagram showing an example for achieving this. In this case, the photocoupler 60 is used as shown in FIG. The voltage comparator 18 is composed of the control transistor 18a and the photodiode 62 provided in the photocoupler 60, and the divided voltage is the reference voltage Vre.
When it becomes f or more, the photodiode 62 is excited (turned on). Therefore, the phototransistor 61, which is the light receiving portion, is turned on when the photodiode 62 is excited, and the voltage control similar to that in FIG. 1 is performed.

According to this structure, since the primary side and the secondary side of the transformer 2 are completely separated by the photocoupler 60, the safety measure is perfect.

The ringing choke converter method described above is merely an example. The applicable composite electronic device is also an example.

[0060]

As described above, according to the present invention, the control transistor simultaneously complements the switching transistors provided in the first and second output voltage detection circuits so that the on / off timings of the switching transistors coincide with each other. It is configured to control.

According to this, since the on / off timings of the two switching transistors are completely coincident with each other, the DC voltage obtained at the other output terminal is not instantaneously disturbed when the power switch is turned on / off. Therefore, even if a microcomputer or the like is connected to the other output terminal as a load, there is no possibility that the microcomputer will malfunction.

Therefore, the present invention is extremely suitable when applied to the power supply device of the composite electronic equipment as described above.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a multi-output type switching power supply device according to the present invention.

FIG. 2 is a system diagram showing another example of the multi-output type switching power supply device according to the present invention.

FIG. 3 is a system diagram of a conventional multi-output type switching power supply device.

FIG. 4 is a waveform diagram for explaining the operation.

FIG. 5 is a system diagram showing another example of a conventional multi-output type switching power supply device.

FIG. 6 is a waveform diagram for explaining the operation.

[Explanation of symbols]

 2 Transformers 2Sa, 2Sb Secondary winding 11, 61 Control transistor 14 Output terminal 18 Voltage comparator 25 Output terminal 28 Transistor functioning as power switch 30 First output voltage detection circuit 40 Second output voltage detection circuit 50 Control circuit 31 first switching transistor 42 second switching transistor Ea stabilized DC voltage Eb stabilized DC voltage

Claims (1)

[Claims] 1. A multi-output switching power supply device capable of taking a plurality of output voltages having different voltages, and obtaining at least one of the output voltages as a stabilized voltage. A power switch connected to an output terminal from which the first output voltage is obtained, a first output voltage detection circuit having a first switching transistor connected to the load side of the power switch, and the power switch And a second output voltage detection circuit having a second switching transistor connected to an output terminal from which a second output voltage is obtained, and outputs of the first and second output voltage detection circuits and a reference A voltage comparator that compares the voltages and controls the primary side of the power transformer to perform switching control, and is applied to the control circuit. Based on the control signal
And a second switching transistor are complementarily controlled at the same timing.