JPS6364151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching circuit, and particularly to one suitable for improving the efficiency of a switching regulator.

BACKGROUND ART In general, batteries are used as a driving power source for various portable or vehicle-mounted electronic devices such as video tape recorders (VTRs) and video cameras. With this type of power supply, there is a risk that the terminal voltage may fluctuate significantly due to sudden changes in the load due to switching of operating modes, etc., and switching is required to suppress such fluctuations and stabilize the operation of electronic equipment. A regulator is used.

FIG. 1 shows a conventional step-down switching regulator. In this switching regulator, the ripple component of the DC input Vi supplied between the input terminals 2A and 2B is removed by the ripple absorption capacitor 4 installed between the input terminals 2A and 2B, and the ripple component is removed from the DC input Vi supplied between the input terminals 2A and 2B. The current is converted into alternating current by a switching transistor 6, and then converted back to direct current by a direct current regeneration circuit 14 comprising a diode 8, a choke coil 10, and a capacitor 12, and then taken out as a stabilized output Vo from output terminals 16A and 16B.

The DC voltage Vo generated between the output terminals 16A and 16B is applied to the inverting input terminal of the comparator 18, and is compared with a reference voltage set at the non-inverting input terminal by the power supply 20, and its fluctuation is detected. The non-inverting terminal of the comparator 18 receives an AC signal from the collector side of the switching transistor 6.
Positive feedback is provided via 2. That is, in this switching regulator, since the comparator 18 constitutes an oscillator together with the error amplifier, it functions as a pulse width modulation circuit to generate a pulse having an ON-OFF duty corresponding to the fluctuation level. There is. The output pulse of the comparator 18 is applied as a control pulse to the base of a driving transistor 24 that supplies a driving current to the switching transistor 6.

In such a switching regulator, the switching operation of the switching transistor 6 has a constant delay time and rise and fall times with respect to the pulse input.
Such a delay in pulse operation is not just a temporal response delay, but the current flowing during that time results in power loss. That is, the value obtained by integrating the current flowing during this period over time becomes the loss. Such losses reduce the conversion efficiency when converting direct current to alternating current, such as in a switching regulator, and in order to improve efficiency, it is necessary to eliminate such switching time delays. is necessary.

In addition, in recent various electronic devices driven by low voltage,
It goes without saying that such a reduction in conversion efficiency shortens the service life of the battery, and therefore there is a need for improvement.

An object of the present invention is to provide a switching circuit that improves efficiency by shortening the switching operation time of a switching transistor.

In this invention, the phase of a pulse formed by a switching transistor is inverted, extracted, differentiated, and superimposed on the input pulse at the base of the switching transistor, thereby shortening the switching time.

Embodiments of the invention will be described in detail with reference to the drawings. FIG. 2 shows a switching regulator implementing the switching circuit of the present invention.
In the figure, the same parts as the circuit shown in FIG. 1 are given the same reference numerals. A switching correction circuit 30 is added to the switching transistor 6, which inverts the polarity of the switch pulse formed by the switching operation, differentiates the pulse, and adds the pulse to a part of the control pulse. There is.
The switching correction circuit 30 of this embodiment includes a transformer 32 that also serves as a choke coil in the DC regeneration circuit 14, and a polarity inversion pulse obtained by the transformer 32 is differentiated by a capacitor 34 and applied to the base of the switching transistor 6. There is. That is,
The transformer 32 has a primary coil 32P and a secondary coil 32S formed on a common iron core so that the polarities are opposite to each other. A chiyoke transformer is used in which one terminal is commonly connected so as to be inverted from the input side. The primary coil 32P is installed as a chiyoke coil in the DC regeneration circuit 14 as in the conventional circuit,
On the other hand, the output terminal of the secondary coil 32P is connected to the base of the switching transistor 6 via a capacitor 34.

Further, between the base of the switching transistor 6 and the output terminal of the DC regeneration circuit 14,
A driving transistor 36 is connected. That is, the transistor 36 is connected between the base and collector of the switching transistor 6, with its collector connected to the base of the switching transistor 6, and its emitter connected to the output side of the DC regeneration circuit 14. A resistor 3 is connected to the base of this transistor 36.
A DC input is applied as a bias via the switching transistor 8, and a switching output from the collector of the switching transistor 6 is fed back via a capacitor 40.

Further, the base of this transistor 36 is connected to the collector of a transistor 42 for controlling its operating current, and the emitter of this transistor 42 is connected to a constant voltage diode 44 for setting a reference voltage. GND) side, and a DC reproduction output is provided via a resistor 46. This transistor 42
A DC output is applied to the base of the transistor 42 from the connection point of the resistors 48 and 50 connected in series between the input terminals 16A and 16B, and this DC output, the forward drop voltage of the voltage regulator diode 44, and the base of the transistor 42・It is designed to be compared with a reference voltage set by the composite value of the emitter voltage.

In the above configuration, the operation is explained as follows.
When the DC output voltage detected at the connection point between the resistors 48 and 50 is lower than the reference voltage, an operating current flows through the transistor 36 according to this potential.
At this time, the transistor 36 is turned on,
A drive current flows to transistor 6 via transistor 36 . Further, when the DC output voltage is higher than the reference voltage, the transistor 42 is activated by the operation of the transistor 36 according to this potential.
It becomes OFF state. As a result of the switching operation being maintained continuously at a constant oscillation frequency in this way, the DC input Vi is converted to AC by the switching operation of the switching transistor 6.
After being converted into DC again by the DC regeneration circuit 14, the stabilized output Vo is output from the output terminals 16A and 16B.
is extracted as. For example, when a fluctuation occurs in the DC input due to a fluctuation in the load, the above-mentioned stabilizing operation is instantaneously performed, and it becomes possible to continuously supply a constant DC output to the load.

In such a switching operation, the collector of the switching transistor 6 has the voltage shown in FIG.
The switching pulse shown in is generated. Since this pulse is applied to the primary coil 32P of the transformer 32, a pulse with reversed polarity as shown in FIG. 3B is generated in the secondary coil 32S. This pulse is superimposed on a constant DC level. Since this pulse is applied to the base of the switching transistor 6 via the capacitor 34, the differential pulse shown in FIG. Ru. Each edge of this differential pulse corresponds to an edge portion of the switching pulse, and since the directions of increase and decrease in potential level are opposite to each other, the switching transistor 6 corresponds to the ON or OFF operation. It functions to support this. As a result, the switching operation time of the switching transistor 6 can be shortened, power loss during this time can be reduced, and conversion efficiency can be improved.

FIG. 3A shows the switching pulse when the switching correction circuit 30 is added, and FIG. 3B shows the switching pulse when it is not added. Each pulse is shown with the time axis expanded, and the time Ta for each pulse to fall from 90% to 10% of the level Vc,
Comparing Tb, when the switching correction circuit 30 is added, it is possible to significantly shorten the time for the pulse to fall (Ta<Tb),
Power loss during this time can be reduced. In particular, this reduction in power loss increases as the switching frequency increases, and conversion efficiency can be improved.

Further, regarding such efficiency improvement, the switching correction circuit 30 has a switching transistor 6
Since the switching pulse formed by the above method is used, there is no energy loss and the switching pulse is extremely efficient. Furthermore, this circuit is constructed by connecting a capacitor 34 in series to a transformer 32 which also serves as a chiyoke coil, and does not require many elements. In particular, as in this embodiment, the transformer 32 is composed of a chiyoke transformer;
It can also be miniaturized and provided at low cost.

Moreover, in this embodiment, since the driving current of the switching transistor 6 is added to the DC reproduction output side by the transistor 36, the conversion efficiency can be improved.According to experiments, in the case of the embodiment, It has been confirmed that the conversion efficiency is as high as 93% due to synergistic effects such as shortening of switching time.

Further, in the embodiments described above, a self-excited switching regulator has been described, but the same effect can be obtained even when the present invention is applied to a separately excited switching regulator as shown in FIG. You can expect it. That is, since the switching regulator of this embodiment is separately excited, the positive feedback capacitor 40 of the previous embodiment is removed, and the base of the driving transistor 36 is provided with a standard such as a sawtooth wave or a triangular wave. Let a reference waveform 54 from function generator 52 be provided with a varying level formed at the collector of transistor 42. As a result, similar pulse width control is possible, but even in such a separately excited switching regulator, the effects obtained by implementing the present invention are exactly the same. Furthermore, when an NPN type transistor is used as the driving transistor 36 as in the embodiment, it is advantageous in that there is no base current outflow, but even if a PNP type transistor is used, the driving current of the switching transistor 6 is It can be added to the output, and the conversion efficiency can be improved as well. Similarly, the transistor 42 is not limited to the NPN type transistor of the embodiment.

In the embodiment, switching pulses are detected using a choke transformer that also serves as the choke of the DC regeneration circuit 14, but an inductor other than such a choke transformer may be used to detect switching pulses. A similar effect can be expected, and the same effect can be obtained even if the inductor is connected to a circuit part other than the DC regeneration circuit that can detect switching pulses.

Further, although the embodiments have been described using a switching regulator as an example, it goes without saying that the present invention can be applied not only to this type of switching regulator but also to various switching circuits.

As explained above, according to the present invention, the switching operation time of the switching transistor can be shortened, the switching efficiency can be improved, and the power loss can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional switching regulator, FIG. 2 is a circuit diagram showing an embodiment of the switching circuit of the present invention, FIGS. 3 and 4 are explanatory diagrams showing its operating waveforms, and FIG. The figure is a circuit diagram showing another embodiment of the invention. 6...Switching transistor, 30...Switching correction circuit, 32...Transformer, 34...Capacitor.

Claims (1)

[Claims] 1. A switching transistor that opens and closes in response to an input pulse, and a pulse formed by the switching transistor whose polarity is inverted, taken out, and differentiated to apply the input pulse to the base of the switching transistor. 1. A switching circuit comprising: a switching correction circuit that applies an electric current in a superimposed manner; 2. A patent claim characterized in that the switching correction circuit is constituted by a choke transformer connected to the switching transistor, and a capacitor that applies a polarity inversion pulse of the choke transformer to the base of the switching transistor. The switching circuit according to the range 1 above.