JPH0247195B2 - CHOKURYUUCHOKURYUHENKANKI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a DC-DC converter that performs on-off control of a transistor to control a DC voltage or convert a level, and more specifically to a DC-DC converter that controls a DC voltage or converts a level by controlling on/off of a transistor. The present invention relates to a DC-DC converter having a circuit for controlling inrush current of a smoothing capacitor.

Prior Art In FIG. 1 showing a self-excited on-off type DC-DC converter having a conventional inrush current prevention circuit, a pair of DC currents on the output side of a full-wave rectifier circuit 1 for rectifying commercial AC of 50 Hz to DC, for example, is shown. power line 2
An input smoothing electrolytic capacitor 3 is connected between a and 2b. In a circuit having the capacitor 3 as described above, when a power switch (not shown) provided on the power supply side of the capacitor 3 is turned on, a rush current tends to flow through the capacitor 3. Therefore, in order to prevent this inrush current, a thyristor 4 with a triac configuration, which functions as a semiconductor switch, is installed on the power supply line 2b on the power supply side of the capacitor 3.
A parallel circuit of the inrush current limiting resistor 5 and the inrush current limiting resistor 5 is connected. A switching transistor 6 is connected in series to the power supply line 2b. 7 is an output transformer, which has a primary winding 8, a secondary winding 9, a tertiary winding 10, and a quaternary winding 1.
1, and the primary winding 8 is connected between the power supply line 2a and the transistor 6. Reference numeral 12 denotes an output rectifying and smoothing circuit, which is constructed by connecting a capacitor 14 to the secondary winding 9 via a rectifying diode 13, and supplies power to a load 15. The tertiary winding 10 is a base drive winding, one end of which is connected to the base of the switching transistor 6 via a base current limiting resistor 16, and the other end connected to the emitter. Reference numeral 17 denotes a constant voltage control circuit, which includes a constant voltage control capacitor 18, a rectifier diode 19 for charging the capacitor, and a Zener diode 20 as a constant voltage diode. One end of a capacitor 18 in this constant voltage control circuit 17 is connected to the lower end of the tertiary winding 10, and the other end is connected to the upper end of the tertiary winding 10 via a rectifier diode 19. The rectifier diode 19 has a tertiary winding 10 oriented to reverse bias the transistor 6.
The capacitor 18 is charged with the voltage of the tertiary winding 10 during the off-period of the transistor 6, that is, the regulated voltage. A Zener diode 20 as a constant voltage diode is connected between the other end of the capacitor 18 and the base of the transistor 6. Note that the Zener diode 20 is connected in such a direction that it breaks down to a constant voltage when the transistor 6 is forward biased. 21 is a starting resistor, and a switching transistor 6
and the power line 2a. The quaternary winding 11 of the transformer 7 is provided to provide a gate signal to the thyristor 4. A capacitor 22 connected to this quaternary winding 11 via a rectifier diode 23 is filled with the polarity shown in the figure during the off period of the switching transistor 6, and supplies a DC gate signal to the thyristor 4 via a resistor 24. .

Next, the operation of the circuit shown in FIG. 1 will be explained. When the power is turned on, a charging current flows to the capacitor 3 through the resistor 5, and rush current is suppressed. Of course, the thyristor 4 is kept off during this startup.
When the capacitor 3 is charged, the base current of the switching transistor 6 flows through the starting resistor 21, and the transistor 6 is turned on. During the ON period of the switching transistor 6, the power supply voltage is applied to the primary winding 8, and a voltage is also obtained in the tertiary winding 10 in response to this, and as shown in FIG. Base current I _B
is supplied. As a result, the conduction of the transistor 6 is maintained, and the collector current I _C gradually increases as shown in FIG. At this time, a voltage is generated in the secondary winding 9 that turns off the diode 13, and the release of energy is prevented. After that, h _FE・I _B
(where h _FE is the current amplification factor of transistor 6), and when transistor 6 becomes saturated, it becomes impossible to increase the collector current I _C and transistor 6 shifts to an unsaturated state. As a result, the voltage across the primary winding 8 decreases, the base current also decreases, and the transistor 6 suddenly turns off. The energy stored in the transformer 7 during the on period ( _t1 to _t2 ) of the transistor 6 is released through the rectifier diode 13 during the off period ( _t2 to _t3 ) of the transistor 6. While the energy of the transformer 7 is being released, a voltage that reverse biases the transistor 6 is generated in the tertiary winding 10, so the transistor 6 does not turn on, but when the energy release ends,
The transistor 6 is turned on again due to ringing caused by the leakage inductance of the transformer 7.

When oscillation starts as described above, the capacitor 22 is charged at a predetermined time constant by the voltage of the quaternary winding 11 during the off period of the switching transistor 6.
A gate signal is supplied to the thyristor 4 having a triax configuration, and the thyristor 4 is turned on. As a result, the resistor 5 is short-circuited by the thyristor 4, and power is supplied without power loss due to the resistor 5.

Note that in the constant voltage control circuit 17, the capacitor 18 is charged with the voltage of the tertiary winding 10 during the off period of the transistor 6. The voltage of the tertiary winding 10 during this off period is the output voltage of the rectifier and smoothing circuit 12 V ₀
Therefore, the capacitor 18 is charged with a voltage corresponding to the fluctuation of the output voltage V ₀ .
A series circuit of a Zener diode 20 and a capacitor 18 is connected in parallel to the emitter-base junction of the transistor 6, and the Zener diode 20 has a directionality that breaks down at the voltage when the transistor 6 is turned on. The base bias or base current of the transistor 6 is controlled by the voltage difference between the constant voltage or reference voltage obtained across the transistor 20 and the charging voltage of the capacitor 18.
Constant voltage characteristics can be obtained. If the output voltage increases now, the capacitor 18 is charged to a high voltage via the diode 19 during the off period. As a result, when the base current is supplied to the transistor 6 using the voltage generated in the tertiary winding 10 during the ON period of the transistor 6, the current flowing through the Zener diode 20 increases and the base current flowing to the transistor 6 decreases. As a result, the peak of collector current I _C determined by h _FE I _B can be suppressed low,
The stored energy of the transformer 7 becomes smaller, and the output voltage V ₀ is returned to the reference voltage. When the output voltage V ₀ is lower than the reference value, the operation is opposite to the above.

By configuring the DC-DC converter as described above, a constant DC output voltage can be obtained relatively easily, and the rush current of the capacitor 3 can be suppressed. However, in order to control the thyristor 4 of the inrush current prevention circuit, it is necessary to provide a power supply circuit for gate current supply consisting of a quaternary winding 11, a capacitor 22, a diode 23, and a resistor 24, which increases the number of components and This also led to a decrease in efficiency due to power loss in this circuit.

OBJECTS OF THE INVENTION Therefore, an object of the present invention is to provide a DC-DC converter that can simplify a capacitor inrush current prevention circuit and improve efficiency.

Structure of the Invention The present invention to achieve the above object includes: a smoothing capacitor connected between a pair of DC power lines; a switching transistor connected in series to the power line on the load side of the capacitor; It has at least a pair of main electrodes and a control electrode, is connected in series to the power supply line on the electrode side of the capacitor, is connected in series to the switching transistor, and is connected between the base and emitter of the switching transistor. a semiconductor switch connected in parallel with the semiconductor switch so that at least a part of the current flowing through the main electrode flows between one of the pair of main electrodes and the control electrode to turn on the semiconductor switch; The present invention relates to a DC-DC converter comprising an inrush current limiting resistor and a drive signal supply circuit connected to the base of the switching transistor and supplying a base current for turning on and off the switching transistor. .

Effects of the Invention According to the above invention, since the circuit that supplies the base current of the switching transistor and the circuit that supplies the current that turns on the semiconductor switch are configured in common, the circuit configuration can be simplified and the cost can be reduced. It is possible to reduce this amount and improve efficiency.

Embodiment Next, a DC-DC converter according to an embodiment of the present invention will be described with reference to FIGS. 3 to 11.
However, in Figures 3 to 11, the numbers 1 to 1
0, and 12 to 20 are substantially the same as those indicated by the same reference numerals in FIG. 1, so their explanation will be omitted. In addition, the same reference numerals are given to the parts that are common to each other in FIGS. 3 to 11, and the common parts will be explained in the embodiment in which the reference numerals are used first, and the explanation thereof will be omitted in the later embodiments. .

First Embodiment In the DC-DC converter according to the first embodiment shown in FIG.
The primary winding 25 of the current transformer 25 is connected in series with
One end of the secondary winding 27 of the current transformer 25 is connected to the base of the switching transistor 6 via a reverse blocking rectifier diode 28, and the other end of the secondary winding 27 is connected to the control electrode of the thyristor 4. There is. The thyristor 4 has a triax configuration as shown in Fig. 1, and has a pair of main electrodes and a control electrode (gate).
and one of the pair of main electrodes is a transistor 6
and the other end is connected to the rectifier circuit 1. Note that the turns ratio of the current transformer 25 is 1:
h is set to _FE . Tertiary winding 1 of transformer 7
0 and the base of the transistor 6 is set so that the base current supplied from the tertiary winding 10 is significantly limited compared to the circuit of FIG.

When the power is turned on in this circuit, the capacitor 3 is charged through the resistor 5. Thereafter, by the action of the starting resistor 21 and the tertiary winding 10 of the transformer 7, the converter is started in the same way as the converter shown in FIG. During the ON period of transistor 6, the composite current I _B of currents I _B1 and I _B2 shown in FIG. 4 becomes the base current of transistor 6, and the collector current has a slope as shown by I _C in FIG. 4. and increase. Note that I _B1 is a constant base current supplied from the tertiary winding 10 of the transformer 7, and I _B2 is the constant base current supplied from the secondary winding 27 of the current transformer 25.
The base current is supplied based on current feedback from the current _IB1 , and the current IB1 is set smaller than the maximum value of the current _IB2 . The current in the current transformer secondary winding 27 is
The current flows through a closed circuit consisting of the secondary winding 27, the diode 28, the base and emitter of the transistor 6, and the main electrode and control electrode of the thyristor 4.
It serves as the base current of the transistor 6, and
It acts as a gate current for the thyristor 4, and when the transistor 6 is turned on, the thyristor 4 is also turned on. Therefore, when oscillation starts, the resistor 5 is short-circuited by the thyristor 4, and power is supplied through the thyristor 4. Note that the input smoothing capacitor 3 is charged and discharged at the cycle of the full-wave rectified output of the 50 Hz commercial AC power supply. On the other hand, the switching transistor 6 and the thyristor 4 are, for example, two to
Continue at a high repetition frequency such as 10kHz. Therefore, the thyristor 4 enters an on state equivalent to when a DC gate signal is continuously supplied.

The constant voltage control operation in this circuit is the same as that shown in FIG. The current I _B flowing into the base decreases, and the output voltage decreases.

This embodiment has the following advantages.

(A) The current in the current transformer secondary winding 27 is transferred to the transistor 6.
In addition to being used as the base current of the thyristor 4, it is also used as the gate current of the thyristor 4, so there is no need to provide a special base control circuit for the thyristor 4, making it possible to simplify the circuit configuration and improve efficiency.

(B) Since the base of the switching transistor 6 is controlled by current feedback by the current transformer 25 and also by voltage feedback by the tertiary winding 10 of the transformer 7, a highly efficient self-excited DC-DC converter is provided. You can.

(C) Since the collector current I _C of the switching transistor 6 is positively fed back to the base by the current transformer 25, the base current I _B increases as the collector current I _C increases. Therefore, supply of excessive base current is suppressed and efficiency is improved.

(D) Based on the tertiary winding 10 of the transformer 7, the current I _B1 is supplied by voltage feedback when the transistor 6 starts to turn on, so that self-oscillation can be stably continued.

(F) Even if the input voltage increases and the current I _B1 in the transformer tertiary winding 10 increases accordingly, the ratio of I _B1 to the total base current I _B is small, so the switching loss due to overdrive is reduced. The increase is small.

Second Embodiment The converter of the second embodiment shown in FIG. 5 is a modification of the constant voltage control circuit 17 shown in FIG. It has a control transistor 29.
An error amplifier 30 outputs a voltage corresponding to the difference between the DC output voltage of the rectifying and smoothing circuit 12 and the reference voltage of the reference power supply 31, and controls the control transistor 29 via the photocoupler 32. Even in a circuit obtained by modifying the constant voltage control circuit in this way, it is possible to obtain the same effects as those shown in FIG. 3.

Third Embodiment A converter according to a third embodiment shown in FIG. 6 has a differentiating circuit consisting of a capacitor 33 and a resistor 34 connected in place of the base current limiting resistor 16 of the converter shown in FIG. A diode 35 is connected between the base and emitter of the transistor 6 to form a discharge circuit for the capacitor 33. In this converter, the base current I _B2 of I _C /h _FE flows as shown in FIG. 7 by current feedback by the current transformer 25, and at the same time,
In Fig. 7 when transistor 6 is on and off
A differential current indicated by I _B1 flows through the capacitor 33. In other words, the current in Figure 7 that combines I _B1 and I _B2
I _B becomes the base current of transistor 6. To explain further, when the energy release of the transformer 7 is completed and a voltage is generated in the tertiary winding 10 that forward biases the transistor 6, a differential current I _B1 based on this voltage flows into the transistor 6, turns on quickly and reliably. Furthermore, when the collector current I _C reaches h _FE · I _B and the transistor 6 is turned off, the voltage of the capacitor 33 is discharged through the diode 35, a reverse bias voltage is applied to the transistor 6, and the transistor 6 is rapidly turned off. It turns off. In addition, I _C , I _B1 , I _B2 , I _B in Figure 7
The solid line indicates the maximum input voltage, and the dotted line indicates the minimum input voltage. In this example, 3
Since no current is supplied from the next winding 10 during the entire on period of the transistor 6, it is possible to further improve the efficiency.

Fourth Embodiment The converter of the fourth embodiment shown in FIG. A control circuit 37 for separate excitation is connected to. Control circuit 3
7 is configured to control on/off of the transistor 6, and further configured to control the conduction time (duty ratio) of the transistor 6. Even in the circuit configured in this way, the current positively fed back by the current transformer 25 flows through the transistor 6 and the thyristor 4, so that both can be controlled to be turned on.

Fifth Embodiment The converter of the fifth embodiment shown in FIG. 9 is a modification of the circuit shown in FIG. A load 15 is connected via 38. This circuit operates substantially the same as the circuit of FIG.

Sixth Embodiment The sixth embodiment of the converter shown in FIG.
This is a modification of the base control circuit shown in the figure, and instead of forming the base control signal based on the output transformer 7, an independent base control circuit 39 is provided, and the transistor 6 is connected via the transformer 40, resistor 34, and capacitor 33. The base control signal is configured to provide a base control signal.

Seventh Embodiment The converter of the seventh embodiment shown in FIG. 11 does not have a current transformer. Therefore, the base current of the transistor 6 and the gate signal of the thyristor 4 are supplied from the tertiary winding 10 of the transformer 7.

Modifications The present invention is not limited to the embodiments described above, and the following modifications are possible, for example.

(A) It is also applicable when connecting another load circuit to the output stage or input stage of the capacitor 3.

(B) The constant voltage control circuit can be replaced with various circuits other than those in the embodiment. For example, in FIG. 5, the control transistor 29 may be controlled without using the photocoupler 32.

(C) SCR without using thyristor 4 as a tryout,
It may also be a semiconductor switch such as a transistor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional DC-DC converter, FIG. 2 is a waveform diagram of each part of FIG. 1, and FIG. 3 is a circuit diagram of a DC-DC converter according to the first embodiment of the present invention. 4 is a waveform diagram of each part of FIG. 3, FIG. 5 is a circuit diagram of a DC-DC converter according to a second embodiment of the present invention, and FIG. 6 is a circuit diagram of a DC-DC converter according to a third embodiment of the present invention. A circuit diagram of a DC-DC converter, FIG. 7 is a waveform diagram of each part of FIG. 6, and FIGS. , and a circuit diagram showing a DC-DC converter of a seventh embodiment, respectively. DESCRIPTION OF SYMBOLS 1... Rectifier circuit, 2a, 2b... DC power supply line, 3... Input smoothing capacitor, 4... Thyristor (semiconductor switch), 5... Rush current limiting resistor, 6... Switching transistor, 7... Output transformer, 25... current transformer, 26... primary winding, 27... secondary winding.

Claims (1)

[Claims] 1. A smoothing capacitor connected between a pair of DC power supply lines, a switching transistor connected in series to the power supply line on the load side of the capacitor, at least one pair of main electrodes, and a control circuit. an electrode, is connected in series to the power supply line on the power supply side of the capacitor, is connected in series to the switching transistor, and at least part of the current that flows between the base and emitter of the switching transistor. a semiconductor switch connected to be turned on by flowing between one of the pair of main electrodes and the control electrode; an inrush current limiting resistor connected in parallel to the semiconductor switch; connected to the base of the switching transistor and turned on to the switching transistor;
A DC-DC converter comprising: a drive signal supply circuit that supplies a base current for off-drive; and a DC-DC converter. 2. The drive signal supply circuit connects a current transformer primary winding connected in series to the switching transistor, and supplies a current corresponding to the current of the current transformer primary winding to the base and emitter terminals of the switching transistor. 2. The DC-DC converter according to claim 1, further comprising a current transformer secondary winding that allows current to flow between the control electrode and the main electrode of the semiconductor switch.