JPH05276742A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To provide a DC-DC converter of less switching loss by shortening time needed for turning off a switching transistor, connected in series to a DC source. CONSTITUTION:A third transistor Q3 is provided on the high-potential side of a DC source E for causing turn-off time stored carriers of a first transistor Q1 connected to a main current path via a power line 1 to flow. Furthermore, the third transistor Q5 is turned on quickly by an approximate sum voltage of the voltage of a capacitor C1 charged during on-time of the first transistor Q1 and the voltage of the power line 1 via a second resistor R2. Consequently, the stored carriers flow in the third transistor Q3 quickly and it becomes possible to shorten time needed for turning the first transistor Q1 off. Accordingly, it becomes possible to lessen the switching loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter in which switching loss is reduced by shortening the time required to turn off a switching transistor.

[0002]

2. Description of the Related Art D for converting a DC voltage into a desired DC voltage
The C-DC converter is configured to obtain a DC voltage by rectifying or smoothing the output of a switching transistor connected in series with a DC source. Rectification and smoothing may be performed directly on the output of the switching transistor, or may be performed on the secondary side in addition to the primary side of the transformer. When performing rectification and smoothing via a transformer, the switching transistor is connected in series to the primary winding of the transformer.

FIG. 4 is a circuit diagram of a conventional DC-DC converter. The high potential side of the DC source E is connected to the input terminal 1A, the low potential side is connected to the input terminal 1B, and the high potential side input terminal 1A is connected.
The first transistor Q1, which is a switching transistor, and the choke coil L1 are connected between the output terminal 2A and the output terminal 2A, and the resistor R is provided between the base and emitter of the transistor Q1.
10 are connected.

Further, the base has a second resistor via a resistor R11.
Is connected to the collector of the transistor Q2, and the emitter of the transistor Q2 is connected to the input terminal 1B. A flywheel diode D1 and a smoothing capacitor C2 are connected to both sides of the choke coil L1. Reference numeral 10 is a control circuit for the transistor Q2.

In this DC-DC converter, the transistor Q1 is switched as the transistor Q2 is turned on and off, and the transistor Q2 drives the transistor Q1. Then, a desired DC voltage is obtained between the output terminals 2A and 2B. The resistor R10 plays a role of causing carriers accumulated when the transistor Q1 is turned off to turn on.

However, it takes a long time for the carrier to flow through the resistor R10, and the time for the transistor Q1 to turn off, that is, the time from turning on to turning off at the time of turn-off becomes long, so that there is a drawback that switching loss becomes large.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to shorten the turn-off time of a switching transistor connected in series with a DC source to reduce switching loss.

[0008]

According to the first aspect of the present invention, a main current path is connected in series to a high potential side of a DC source via a power supply line.
And a second transistor for driving the first transistor to turn on and off, and a desired DC voltage is obtained from the output of the first transistor. In the DC-DC converter, the first transistor stores its accumulation at turn-off. A third transistor that carries carriers is connected,
The third transistor is driven by a series circuit of a first resistor and a capacitor, and one end of the first resistor of the series circuit is connected to the power supply line and one end of the capacitor is connected to the power supply line through a second resistor. By connecting the connection point of the first resistor and the capacitor to the third transistor, the third transistor is turned on by the voltage of the power supply line passing through the second resistor and the voltage of the capacitor being substantially superposed. It is characterized by

[0009]

1 is a circuit diagram showing an embodiment of a DC-DC converter of the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals. Figure 1
In the power source line 1 connected to the input terminal 1A on the high potential side, the collector and the emitter, which are the main current paths of the PNP type first transistor Q1, are connected, and the collector is connected to the output terminal 2A via the choke coil L1. Connecting.

The base of the transistor Q1 is a PNP type fourth transistor Q4 via a current limiting resistor R3.
Of the transistor Q4, and the collector of the transistor Q4 is connected to the input terminal 1B on the low potential side via the power supply line 2. The power line 2 is normally grounded. A collector and an emitter of an NPN-type third transistor Q3 are connected between the emitter and the base of the transistor Q1, and a diode D2 is connected between the emitter and the base.

The connection point P of the series circuit composed of the first resistor R1 and the capacitor C1 is connected to the base of the transistor Q3. One end of the resistor R1 is connected to the power supply line 1, one end of the capacitor C1 is connected to the collector of the second transistor Q2, is connected to the power supply line 1 via the second resistor R2, and is further connected to the base of the transistor Q4. Connecting. This series circuit constitutes a drive circuit for the transistor Q3.

The emitter of the second transistor Q2 is connected to the power supply line 2, and its collector is connected to the base of the transistor Q4. The diode D2 connected between the emitter and the base of the transistor Q3 protects the transistor Q3 from the reverse voltage applied between the base and the emitter of the transistor Q3 at the moment when the transistor Q2 is turned on, and the connection point P of the series circuit is connected. A resistor R4 connected between one end of the capacitor C1 and the capacitor C1 has a role of accelerating the discharge of the capacitor C1.

A flywheel diode D1 and a smoothing capacitor C2 are connected between the choke coil L1 and the power supply line 2 on both sides. DC-D configured in this way
In the C converter, the on / off operation of the second transistor Q2 is controlled by the control circuit 10, and the first transistor Q1 is driven by the second transistor Q2 via the transistor Q4.
In the meantime, the desired DC voltage is obtained.

Next, the operation peculiar to the DC-DC converter of the present invention will be described with reference to the current and voltage waveform diagrams of FIG. In FIG. 3, the output voltage V ₁ of the first transistor Q1, the output current I ₁ , the current I ₂ flowing through the third transistor Q3, the current I ₃ flowing through the capacitor C1 and the base voltage V 3 of the third transistor Q3 are shown. _{The two} waveforms are shown in order from the top. The horizontal axis is a common time axis, and the current is indicated by (+) in the arrow direction.

From time t ₁ when the first transistor Q1 is on to time t ₂ , the third transistor Q3 is off. This is because when the transistor Q1 is on, the base of the transistor Q3 is connected to the power supply line 2 on the low potential side via the capacitor C1 and the transistor Q2, while the emitter is the resistor R3 and the transistor Q4.
Since it is connected to the power supply line 2 via
This is because the base and emitter of No. 3 are reverse biased. The capacitor C1 is charged by the current I ₃ flowing from the first resistor R1 during this time.

At time t ₂ , the second transistor Q2 and the fourth transistor Q2
When the transistor Q4 of 1 is turned off, the first transistor Q1 also tries to be turned off. At this time, the base of the transistor Q3 is applied with a voltage V _{2 which} is a superposition of the charging voltage of the capacitor C1 and the voltage of the power supply line 1 passing through the second resistor R2, and the transistor Q3 is rapidly turned on.

Then, the accumulated carriers of the transistor Q1 flow as the current I ₂ , and the transistor Q1 turns off in a short time between the time t ₃ and the time t ₄ . The charged electric charge of the capacitor C1 is discharged as a current of the resistor R4 and a base current of the transistor Q3. In this way, the third carrier Q1 is used to flow the accumulated carriers.
Since the transistor Q3 is connected and the transistor Q3 is rapidly turned on at the high voltage V ₂ as described above, the turn-off time of the transistor Q1 from the time t ₃ to the time t ₄ is shortened and the switching loss is reduced. it can.

The voltage V ₂ that turns on the transistor Q3 is immediately clamped to the base-emitter voltage V _BE as shown in FIG. Therefore, the high voltage V ₂ shown by the dotted line does not appear at the base of the transistor Q3. FIG. 2 is a circuit diagram showing another embodiment of the DC-DC converter of the present invention. The DC-DC converter of FIG. 2 is configured to invert the polarity of the output voltage with respect to the input voltage, and a (-) voltage is obtained at the output terminal 3A with reference to the output terminal 3B.

A choke coil L2 is connected between the collector of the first transistor Q1 and the power supply line 2 connected to the low potential side of the DC source E, and a rectifying diode D3 is connected between the output terminal 3A and the collector of the transistor Q1. ing. A smoothing capacitor C3 is connected between the output terminals 3A and 3B. Further, the first transistor Q1 is driven only by the second transistor Q2, and one end of the capacitor C1 of the drive circuit for the third transistor Q3 has a resistor R3 for current limiting.
Is connected to the power supply line 1 via the first transistor Q1. Further, the diode D2 and the resistor R4 are omitted from the circuit.

This is different from FIG. 1 in that the third transistor Q3 has a voltage of the capacitor C1 and a resistor R3,
It is turned on by the superimposed voltage of the power supply line 1 via the base-emitter of the transistor Q1. That is, the current limiting resistor R3 also serves as a second resistor that connects one end of the capacitor C1 to the power supply line 1.

Even in such a DC-DC converter, the accumulated carriers of the first transistor Q1 flow through the third transistor Q3, and further, the third transistor Q3.
Is turned on in the same manner as in the first embodiment, the time from turning on of the first transistor Q1 to turning off of the first transistor Q1 is shortened as compared with the case of using a conventional resistor.

Although a bipolar transistor is used as the transistor in any of the embodiments, a field effect transistor can also be used. In the embodiment, the first
Although the output of the transistor Q1 is directly smoothed to obtain the DC voltage, the present invention can be applied to a configuration in which the input side and the output side of the DC-DC converter are rectified and smoothed via a transformer. Needless to say.

[0023]

As described above, in the DC-DC converter of the present invention, the stored carriers at the time of turn-off of the first transistor whose main current path is connected in series via the power supply line to the high potential side of the direct current source flows. The third transistor is connected.

Then, the third transistor is suddenly turned on by a voltage in which the voltage of the capacitor charged when the first transistor is turned on and the voltage of the power supply line on the high potential side that has passed through the second resistor are substantially overlapped. Is configured. Therefore, since the accumulated carriers of the first transistor are quickly removed, the time required for turn-off can be shortened and the switching loss can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a DC-DC converter of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the DC-DC converter of the present invention.

FIG. 3 is a waveform diagram of current and voltage of FIG.

FIG. 4 is a circuit diagram of a conventional DC-DC converter.

[Explanation of symbols]

 1 Power Supply Line Q1 First Transistor Q2 Second Transistor Q3 Third Transistor

Claims (1)

[Claims] 1. A first transistor having a main current path connected in series to a high potential side of a direct current source via a power supply line, and a second transistor for turning on and off the first transistor, the first transistor comprising: In a DC-DC converter that obtains a desired DC voltage from the output of a transistor, a first transistor is connected to a third transistor that allows the stored carriers to flow at turn-off, and the third transistor is the first transistor.
Driven by a series circuit of a resistor and a capacitor, one end of the first resistor of the series circuit is connected to the power supply line, and one end of the capacitor is connected to the power supply line via a second resistor, and the first resistance and the capacitor are connected. Is connected to a third transistor, the third transistor is turned on by a voltage obtained by substantially superimposing the voltage of the capacitor on the voltage of the power supply line passing through the second resistor. DC converter.