JPS6361873B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC-DC converter, and more particularly to a DC-DC converter that reduces loss in a circuit that absorbs conductive noise caused by switching operations.

In conventional push-pull type DC-DC converters, a DC-DC converter of the type shown in FIG. 1 is usually used as an externally driven type. In the figure, a DC voltage is input from terminal 51 with the polarity shown in the figure, and terminal 55
-1 is excited by an externally _driven pulse voltage v ₁ and the transistor Q ₁ as a switching element becomes conductive, the current i ₁ flows through the winding T ₁ (A ) and transistor _Q1 to flow into the negative side of the DC input power supply. At this point, the winding inside the primary winding of transformer _T1
Due to the electromotive force induced in T ₁ (B), the transistor
The voltage V ₂ applied between the collector and emitter of Q ₂ is
The voltage is approximately twice the DC input voltage Ei. When the pulse voltage v ₁ ends, the current i ₁ flowing through the transistor Q ₁ becomes zero, but the time it takes for the excitation current of the primary winding of _the transformer T ₁ to become zero, ₁ (B), the voltage V ₁ applied between the collector and emitter of transistor Q ₁ is
increases from zero to a value of approximately 2Ei, and the transistor Q ₂
The voltage V ₂ applied between the collector and emitter of is 2Ei
decreases from to zero. In this state, the transistor
The energization time of Q ₁ is continued for a certain period of time, which is slightly shorter than the energization time of Q 1, and then the initial state, that is, the above-mentioned V ₁ and V _{2 is} restored.
returns to a state equal to the DC input voltage Ei. Next, when the terminal 55-2 is excited by an externally driven pulse voltage v ₂ and the transistor Q ₂ as a switching element becomes conductive, the current increases as in the case where the transistor Q ₁ becomes conductive. i ₂ energizes the winding T ₁ (B) of the primary winding of the transformer T ₁ and the transistor Q ₂ to flow into the negative side of the DC input power supply. At this point, the transformer
Due to the electromotive force induced in the winding T ₁ (A) in the primary winding of T ₁ , the voltage V ₁ between the collector and emitter of the transistor Q ₁ rises from Ei to approximately 2Ei, and the transistor The voltage V ₂ between the collector and emitter of Q ₂ becomes zero. When the externally driven pulse voltage v ₂ ends, the current i ₂ flowing through the transistor Q ₂ becomes zero, but during the time until the excitation current of the primary winding of the transformer _{T 1} becomes zero, ) and T(B)
Due to the induced emf at , the voltage V ₂ between the collector and emitter of transistor Q ₂ increases from approximately
It rises to a value of 2Ei, and the voltage V ₁ between the collector and emitter of the transistor Q ₁ decreases from 2Ei to zero.
This state lasts for a certain time as described above, after which the initial state is restored, ie, the state where V ₁ and V ₂ are equal to Ei. Below externally driven pulse voltage V ₁
and v ₂ connect terminals 55-1 and 5, respectively.
5-2 are excited alternately, and the above-described operating sequence is repeated. In this course of operation, the externally driven pulse voltages v ₁ and v ₂ , the currents i ₁ and i ₂ flowing through the transistors Q ₁ and Q ₂ , the voltages V ₁ and between the collectors and emitters of the transistors Q ₁ and Q ₂
The operating waveform diagram of V ₂ etc. is shown in Fig. 3. FIG. 3 is a waveform diagram when the duty ratios of currents i ₁ and i ₂ flowing through transistors Q ₁ and Q ₂ are both 50% or less, but externally driven pulse voltages v ₁ and v ₂
When the duty ratio of approaches 50%, V ₁ and
The voltage waveform of V ₂ is a rectangular voltage waveform with an amplitude Ei centered at the level of the DC input voltage Ei.

In the waveform diagram of Fig. 3, looking at the voltage V ₁ between the collector and emitter of transistor Q ₁ ,
At the time when i ₁ ends and when i ₂ starts, a spike voltage that exceeds the voltage 2Ei is produced in V ₁ . This spike voltage is caused by the transformer T ₁
This is due to conductive noise generated during switching due to the leakage inductance of T ₁ (A) and T ₁ (B) of the primary winding, and the level of this conductive noise is extremely large compared to the voltage Ei, making it difficult to use as a switching element. There is a risk of voltage damage to transistor _Q1 . To prevent this, a series element of a resistor R ₁ and a capacitor C ₁ is usually connected in parallel to the transistor Q ₁ as a circuit for absorbing the conduction noise, as shown in FIG. The spike-like voltage shown in the waveform diagram of V ₁ in FIG. 3d is a residual voltage generated as a result of suppressing the conduction noise using the absorption circuit. A pulse current corresponding to the switching operation flows into the resistor R ₁ and the capacitor C ₁ forming the conductive noise absorption circuit, causing heat loss in the resistor R ₁ . When the power capacity of the DC-DC converter is large, the specific weight of loss in this absorption circuit increases, significantly degrading the efficiency of the DC-DC converter. This also applies to the operation of transistor Q ₂ , resulting in similar heat losses in the absorption circuit formed by resistor R ₂ and capacitor C ₂ . Note that transistors Q ₁ and Q ₂
As is well known, an alternating current voltage is generated through the transformer T ₁ by the switching operation, and a direct current output voltage is output from the rectifier circuit 1 through the terminal 52 .

In other words, in conventional push-pull type DC-DC converters, an absorption circuit including a resistor and a capacitor is used to prevent voltage breakdown of the switching element due to conductive noise generated during switching operation, so the loss in the absorption circuit increases. ,
It has the disadvantage of degrading the efficiency of the DC-DC converter.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and provide a conductive noise absorption function that basically does not include a resistive element.
Prevents voltage breakdown of switching elements and improves efficiency
The purpose is to provide a DC-DC converter.

The converter of the present invention is a push-pull type DC-DC converter with a large power capacity, and has one terminal connected to the positive side of the DC input voltage and a first terminal connected to the other terminal.
a first primary winding connected to a switching element, and one terminal connected to the negative side of the DC input voltage,
a second primary winding having a second switching element connected to the other terminal;
and a capacitor of a predetermined capacity connected between two connection points between the second primary winding and the first and second switching elements.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention. As shown in the figure, this embodiment includes a transformer T ₂ including a first primary winding T ₂ (A), a second primary winding T ₂ (B), and a transistor acting as a first switching element. Q ₃ , a transistor Q ₄ acting as a second switching element, and a capacitor
C ₃ , diodes D ₃ and D ₄ , and a rectifier circuit 2 .

Next, the operation of this embodiment will be explained. terminal 5
DC voltage Ei is input from 3 to 56-1 with the polarity shown in the figure, and terminal 56-1 is externally driven pulse voltage V ₃
When _transistor Q ₃ as a _switching element becomes conductive due _{to excitation} by Flows into the negative side of the input power supply. At this point, due to the electromotive force induced in the winding T ₂ (B) in the primary winding of the transformer T ₂ , the voltage V ₄ applied between the collector and emitter of the transistor Q ₄ is approximately twice the Ei. The voltage will be . When the pulse voltage v ₃ ends, the current i ₃ flowing through the transistor Q ₃ becomes zero, but the current i 3 flowing through the transistor T ₂
The time it takes for the excitation current of the primary winding to become zero, the winding
Due to the induced electromotive force at T ₂ (A) and T ₂ (B), the voltage V ₃ applied between the collector and emitter of transistor Q 3 increases from zero to a value of approximately 2Ei, and the voltage V ₃ applied between the collector and emitter of transistor Q ₄ increases from zero to a value of approximately 2Ei. Applied voltage V ₄
decreases from 2Ei to zero. After this state continues for a certain period of time, the initial state, i.e., V ₁ and V ₂
Return to a state equal to Ei. Next, when the terminal 56-2 is excited by an externally driven pulse voltage v ₄ and the transistor Q ₄ as a switching element becomes conductive, the current i ₄ flowing through the transistor Q ₄ flows through the primary winding of the transformer T _2. It flows into the negative side of the DC input power supply via T ₂ (B). At this point, the voltage V ₃ between the collector and emitter of transistor Q ₃ increases from Ei to approximately 2Ei due to the electromotive force induced in the primary winding T ₂ (A) of transformer T ₂ The voltage between the collector and emitter of ₄ becomes zero. The external drive pulse voltage V ₄
When , the current i ₄ flowing through the transistor Q ₄ becomes zero, but the time it takes for the excitation current flowing through the primary winding of the transformer T ₂ to become zero, the windings T ₂ (A) and T ₂ ( Due to the induced electromotive force in B), the voltage V ₄ between the collector and emitter of transistor Q ₄ increases from zero to a value of approximately 2Ei, and the voltage V ₃ between the collector and emitter of transistor Q ₃ decreases from 2Ei to zero. . This state lasts for a certain period of time as mentioned above,
Thereafter, the initial state is restored, ie, the state where V ₃ and V ₄ are equal to Ei. Thereafter, the terminals 56-1 and 56-2 are alternately excited by the externally driven pulse voltages _v3 and _v4 , respectively, and the above-described operation process is repeated. Externally driven pulse voltages v ₃ and v ₄ in such an operating course, transistor Q ₃
and the currents i ₃ and i _{4 flowing through Q 4 ,} transistors
FIG _. 4 shows an operating waveform diagram of the voltages V ₃ and _{V 4 between} the collector and emitter of Q 3 and Q 4. In this waveform diagram, when looking at the voltage V ₃ between the collector and emitter of transistor Q ₃ , conduction noise occurs at the point when current i ₃ ends and when current i ₄ starts, as in the case of the conventional example. There are conditions to do so. However, in the embodiment of the invention shown in FIG. 4, the junction of the primary winding T ₂ (A) and the collector of the transistor Q ₃ and _the
A capacitor _C3 of a predetermined capacity is connected between the connection point between the transistor Q4 and the emitter of the transistor _Q4 , and this capacitor _C3 absorbs all the conductive noise generated during the switching operation.
As shown in FIG. 4, no voltage spikes occur. Moreover, since the absorption circuit consisting of the capacitor _C3 does not include a resistive element, there is no resistance loss as seen in the conventional DC-DC converter. This means that the transistor
At Q ₄ , the point at which current i ₄ ends and current i ₃
The same goes for the case where V ₄ increases from zero to 2Ei at the time the engine starts. As mentioned above, due to the switching operation by the external drive pulse voltage on the primary side, an AC voltage is generated on the secondary side via the transformer _T2 , and a predetermined DC voltage is outputted by the rectifier circuit 2 via the terminal 54. This is the same as in the conventional example.

As explained in detail above, the present invention completely absorbs the conductive noise, which is more than twice the supply DC voltage generated through the switching operation on the primary side, without using a resistor terminal, thereby preventing voltage breakdown of the switching element. In addition, there is an effect that the loss in the conductive noise absorption circuit can be completely eliminated and the conversion efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional push-pull type DC-DC converter, FIG. 2 is a block diagram of an embodiment of the present invention, and FIGS. 3 and 4 are a block diagram of a conventional example and an embodiment of the present invention, respectively. FIG. 3 is a waveform diagram for explaining operation. In the figure, 1, 2... rectifier circuit, 51~54, 55-1~
2,56-1~2...terminals.

Claims (1)

[Claims] 1. In a push-pull DC-DC converter with a large power capacity, first and second primary windings and a second
a transformer having a secondary winding; a rectifying means connected in parallel with the secondary winding; a first switching means having one end connected to one end of the first primary winding; a second switching means having one end connected to one end of the second primary winding; one end of the first switching means and the second switching means;
a first DC voltage supply terminal connected to the other end of the first primary winding and the other end of the second switching means; and a second DC voltage supply terminal connected to the other end of the primary winding and the other end of the first switching means.