JPS604672B2 - switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator using a transistor chopper circuit.

Conventional switching regulators of this type generally have a first
The configuration is as shown in the figure.

That is, a rectifier circuit 2 is connected to the alternating current 1, a pulsating output is obtained by full-wave rectification of the alternating current, and this is converted to a flat direct current output via a smoothing capacitor 3. A series circuit of an NPN transistor 4, a diode 7, and an output capacitor 6 is connected in parallel with this smoothing capacitor 3. An inductance 5 is connected between the emitter of the transistor 4 and one terminal of the smoothing capacitor 3. Load 8 is connected in parallel with output capacitor 6. On the other hand, the control circuit for the switching transistor 4 consists of a constant frequency oscillator 11, a voltage detector 9 for the capacitor 6, and a driver circuit 13 for driving the transistor.The ON signal for the transistor 4 is given from the constant frequency oscillator 11, and the OFF signal is given from the constant frequency oscillator 11. The signal is supplied from the detector 9. When the transistor 4 is turned on, current flows from the smoothing capacitor 3 to the inductance 5, and its value gradually increases. Then, when the transistor 4 is turned off, the inductance 5 tries to continue flowing current, so that from now on, current flows through the closed circuit of the inductance 5, the capacitor 6, and the diode 7, charging the output capacitor 6 with the polarity shown in the figure. Then, this current becomes almost zero and the diode 7
After turning off, the next on signal is prepared from the constant frequency oscillator 11, the transistor 4 is turned on again, and the same operation as before is repeated. The on time of transistor 4 is the capacitor 6.
The voltage of the capacitor 6 is kept approximately constant by changing the voltage of the capacitor 6 according to fluctuations in the voltage of the capacitor 6. However, with such a configuration, the input current becomes a pulsed current with a large high frequency component because the DC conversion circuit consisting of the rectifier circuit 2 and the smoothing capacitor 3 usually uses a simple capacitor input type. , the input power factor deteriorates significantly.

If inductance is used to improve this power factor, the inductance becomes very large, which not only increases the size of the device but also disadvantages it in terms of cost. Therefore, if the smoothing capacitor 3 is omitted and the pulsating output of the rectifier circuit 2 is directly applied to the chopper circuit, the input power factor is improved.

In this case, in a circuit in which the transistor 4 operates at a constant frequency as shown in Fig. 1, in a phase where the instantaneous value of the voltage of the power supply 1 is high, the current flowing through the inductance 5 when the transistor 4 conducts can be made sufficiently large. Therefore, the voltage of the capacitor 6 can be maintained at a constant value, but since the operating frequency of the transistor 4 is constant in the phase where the voltage of the power supply 1 is low, it is not possible to make the on time sufficiently long, and the voltage flows through the inductance 5. Since the current is not sufficiently large, the voltage across the capacitor 6 drops. In order to prevent this, it is necessary to make the value of the inductance 5 sufficiently small so that a sufficient current flows through the inductance 6 even in the low phase of the power supply voltage. Then, even if the on-time of transistor 4 is shortened in the high voltage phase, a pulse-like current with a steep rise will flow through transistor 4 and inductance 5.
requires a device with a large current capacity. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a switching regulator that can omit the smoothing circuit, improve the input power factor, and further reduce the size of the entire device.

The circuit configuration of the present invention will be explained below with reference to FIG.

Parts that are the same as in FIG. 1 are designated by the same numbers. In FIG. 2, a pulsating current obtained by full-wave rectification of an AC power supply 1 by a rectifier circuit 2 is applied to a chopper circuit. The control circuit for the transistor 4 consists of an inductance detector 24 with an inductance 5, a voltage detector 21 with an output capacitor 6, a detector 22 with the instantaneous value of the output voltage of the rectifier circuit 2, and a drive circuit 26 that drives the transistor. , the transistor 4 is turned on by the magnetic velocity detector 24 when the magnetic flux of the inductor sos 5 becomes almost zero, and the on time is determined by the voltage detector 21 of the output capacitor 6 and the output voltage detector 22 of the rectifier circuit 2. It looks like this. The time it is on is load 8.
When the voltage of the capacitor 6 decreases depending on the state of , the length increases, and when the instantaneous value of the rectifier circuit 2 is low, the length increases. Therefore, the voltage of the capacitor 6 becomes a stable voltage with little fluctuation. Furthermore, when the magnetic flux of the inductance 5 becomes almost zero, the inductance 4 is turned on and accumulates electromagnetic energy for the next charging of the capacitor 6, so the utilization rate of the electromagnetic energy of the inductance 5 is reduced. This is extremely high, and the shape of the inductance 5 can also be made smaller. An embodiment of the present invention is shown in FIG.

The voltage detector 21 of the capacitor 6 consists of resistors 33 and 34 and divides the voltage between the positive reference voltage VREP and the negative side of the capacitor 6.

The detected voltage (slightly positive) is then intensified by an intensifier 31 and applied to the inverting input of a comparator 32. The instantaneous value detection circuit 22 of the pulsating output of the rectifier circuit 2 consists of a series circuit of a resistor 39 and a capacitor 40 connected in parallel with the rectifier circuit 2. Then, the connection point between the resistor 39 and the capacitor 40 is applied to the non-inverting input of the comparator 32. The magnetic flux detector 24 of the inductance 5 includes a saturable reactor 37 connected in series with the inductance 5, and a small capacitor 2.
Consists of 6. The voltage of saturable reactor 37 is applied to the base of NPN transistor 35 via resistor 38. The collector and emitter of the transistor 35 are capacitors 40
Connect in parallel with In this case, the saturable reactor 37 has a small shape so that the magnetic flux is saturated with a small amount of current. The driver circuit 26 of the transistor 4 is made up of a series circuit of a PNP transistor 42 and a drive transformer 43, and the output of the comparator 32 is applied to the base of the transistor 42 via a resistor 41. The secondary side of the transformer 43 is connected between the base and emitter of the transistor 4. Next, the operation of the circuit shown in FIG. 3 will be explained according to FIG. 4. FIG.

The opening in FIG. 4 shows the voltage waveform of the inductance 5. During the time T, the current gradually increases and the voltage becomes equal to the output voltage of the rectifier circuit 2. During the T2 period, the diode 7 conducts and the current gradually decreases because the capacitor 6 is charged, and the voltage becomes equal to the voltage of the capacitor 6. During the period L, when the current in the inductance 5 decreases and reaches zero at time ta, the diode 7 is turned off. When the diode 7 is turned off, a negative current flows due to the voltage of the capacitor 36 (the P side is negative and the q side is positive in FIG. 3), and a negative pulse-like voltage is generated in the saturable reactor 37. Then, the voltage of the capacitor 36 is reversed and reaches its maximum value at time tb, with the P side being positive and the Q side being negative. At this time, the negative current becomes zero, and then the capacitor 36
A raw current begins to flow due to the voltage. At this time, a positive pulse voltage is generated in the saturable reactor 37. The voltage waveform of the saturable reactor 37 is shown in FIG. 4C. At time tb, the magnetic flux of the inductance 5 is almost zero.

On the other hand, the voltage of the capacitor 40 is charged through the resistor 39 by the output voltage of the rectifier circuit 2.

When a positive pulse voltage is generated in the saturable reactor 37 at time tb, the transistor 35 becomes conductive for an instant, the capacitor 40 is discharged, and the voltage becomes zero. Thereafter, the transistor 35 is turned off and the capacitor 401 is charged again. This pattern is shown by waveform x in FIG. Next, the output voltage of the multiplier 31 is a positive DC voltage.
This waveform is indicated by 2 y. And when x>y, comparator 3
The output of 2 is 1E x<y 〃 ○, which is shown in the tree in Figure 4 (1E is the DC power supply voltage of the comparator). Therefore, when x>y, transistor 42 is turned off, so transistor 4 is turned off. , x<y, the transistor 42 is turned on, so the transistor 4 is turned on.

In other words, it is the saturable reactor 37 that provides the ON signal for the transistor 4. When the voltage of the capacitor 6 decreases due to fluctuations in the load 8, the output voltage of the multiplier 31 increases, and the value of y increases, so the on-time T, of the transistor 4 becomes longer. As the voltage increases, the value of y becomes smaller and the on-time T, becomes shorter. Next, in a phase where the instantaneous value of the output voltage of the rectifier circuit 2 is low, the charging time of the capacitor 40 is long, so the rise of the waveform x is gradual, and the on-time of the transistor 4 is T.
, will be made longer. Conversely, in a phase where the voltage of the rectifier circuit 2 is high, the rise of the capacitor 40 becomes rapid, shortening the on-time T.

In this way, the on-time of the transistor 4 is changed in response to changes in the voltage of the capacitor 6 due to load fluctuations and changes in the instantaneous value of the output voltage of the rectifier circuit 2, so the capacitor 6 provides a stable constant voltage. Since the transistor 4 is turned on when the magnetic flux of the inductance 5 becomes almost zero, the electromagnetic energy of the inductance 5 is utilized to the maximum to charge the capacitor 6, and the shape of the inductance 5 is can be made smaller.

As described above, according to the present invention, it is possible to improve the input power factor by omitting the smoothing circuit, and it is possible to provide a small and lightweight switching regulator.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications without changing the gist.

For example, FIGS. 5 and 6 show the above-described control circuit 50 applied to a chopper circuit configured as shown in the figures.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an example of a conventional switching regulator, FIG. 2 is a circuit configuration diagram of a switching regulator according to the present invention, FIG. 3 is an embodiment of the present invention, and FIG.
The diagram shows the waveforms of each part to explain the operation of the circuit in Figure 3, and Figure 5.
FIG. 6 shows different embodiments of the present invention. 1... AC power supply, 2... Rectifier circuit, 4
...Transistor, 5...Inductance, 6
...Output capacitor, 7""" diode. Next 1 figure next 2 figure next 3 figure next 4 figure 5 figure

Claims (1)

[Claims] 1 In a switching regulator consisting of an AC power supply, a rectifier circuit whose input end is connected to the above power supply, and a transistor chopper circuit that is supplied with the unsmoothed output of this rectifier circuit, the chopper circuit is a chopper circuit. A chopper transistor and an inductance are connected in series, a series circuit of a diode and an output capacitor is connected in parallel with the inductance, and a control circuit for controlling the chopper transistor is provided. It consists of a voltage detection circuit, an instantaneous value detection circuit for the output voltage of the rectifier circuit, and a drive circuit that turns on and off the chopper transistor.When the magnetic flux of the inductance becomes almost zero, the chopper transistor is turned on and the chopper transistor is turned on. The time is controlled by inputting the output voltages of the voltage detection circuit of the output capacitor and the instantaneous value detection circuit of the rectifier circuit to a comparator, and using the output voltage signal of the comparator;
A switching regulator characterized in that it is repeatedly turned on and off within each cycle of the pulsating output of a rectifier circuit.