JPS5921279A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To prevent the voltage breakdown of a switching element and to improve the conversion efficiency of a DC/DC converter by completely absorbing a conduction noise produced through the switching operation at the primary side by a capacitor. CONSTITUTION:A DC/DC converter has a transformer T2 containing the first and second primary coils T2(A), T2(B), transistors Q3, Q4 which operate as the first and second switching elements, a capacitor C3, diodes D3, D4, and a rectifier 2. A conduction noise generated at the switching time is all absorbed by the capacitor C3 which is connected between the connecting point of the primary coil T2(A) and the collector of the transistor Q3 and the connecting point of the primary coil T2(B) and the emitter of the transistor Q4.

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 L) C-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 the terminal 51 with the polarity shown in the figure, and the terminal 55-1 is an externally driven pulse voltage V! When the transistor Q1 as a switching element becomes conductive due to p excitation, the current i! The winding TI(A) of the primary winding of the transformer T1 and the transistors Q and 1f are energized and flow into the negative side of the DC input power source. At this point, a voltage V2 is applied between the collector and emitter of the transistor Q2 due to the electromotive force induced in the winding T1(B) in the primary winding of the transformer T1.
is approximately twice the DC input voltage Ei. When the pulse voltage v1 ends, the transistor Ql? The flowing current 11 becomes zero, but the time it takes for the excitation current of the primary winding of the transformer T1 to become zero, the windings Tl(A) and T! (
B) Depending on the attraction force at Ic, the voltage Vl applied between the collector and emitter of transistor Q1 is from zero to approximately 2E.
The voltage V2 applied between the collector and emitter of transistor Q2 decreases from 2Ei to zero.

This state continues for a certain period of time, which is slightly less than the total conduction time of the transistor Q1, and then returns to the initial state, ie, the state where V1 and v2 are equal to the DC input voltage E1. Next, the terminal 55-2 is excited by the pulse voltage v2 of the external 1 drive.

When the transistor Q2 as a switching element becomes conductive, the current 12 flows through the transformer T!, similar to the case where the transistor Ql described above becomes conductive. The winding T 1 (B+ and transistor Qze in the primary winding is energized and flows into the negative side of the DC input power supply. At this point, the winding TI (A)K in the primary winding of the transformer T Due to the induced electromotive force, the voltage V1 between the collector and emitter of the transistor Ql increases from Ei to approximately 2Ei, and the voltage between the collector and emitter of the transistor Qi becomes zero. Externally driven pulse voltage v2
When the current 12 flowing through the transistor Q2 becomes zero, the voltage V2 between the excitation e1 capacitor and the emitter of the primary winding of the transformer TI increases from zero to approximately 2EiO value, and the voltage V2 between the collector and emitter of the transistor Q1 increases from zero to approximately 2EiO value. Voltage between ■
1 decreases from zEi to zero.

This state continues for a certain period of time as described above, and then the initial state, i.e., the above ■1 and ■! returns to a state equal to Ei. Thereafter, the terminals 55-1 and 55-2 are alternately excited by the externally driven pulse voltages v1 and v2, respectively, and the above-described operation process is repeated. The external drive pulses No. v1 and '2e in this operation process
The operating waveform diagram of currents 11 and 12 flowing through transistors Q1 and (h', voltages V1 and Vz between the collectors and emitters of transistors Q1 and Q2, etc.) is shown in Figure 3. This is a waveform diagram when the duty ratios of 11 and i2 are both 50 or less, but when the duty ratios of externally driven pulse voltages v1 and 2 approach 50%,
The voltage waveforms of V% and Vz are rectangular waveforms of amplitude Ei centered on the level gold of the DC input voltage Ei.

Looking at the voltage VIK between the collector and emitter of the transistor Q1 in the waveform diagram of FIG. occurs. This spike voltage is caused by Tl(
This is due to the conductive noise generated during one switching due to the leakage inductance of A) and Tt(B).The level of this conductive noise is extremely large compared to the voltage El, and there is a risk of voltage breakdown of the transistor Qt- as a switching element. There is. As a preventive measure, as a conduction noise absorption circuit, a series element of a resistor R1 and a capacitor C1 is usually connected to a transistor QI as shown in FIG.
Connect VC in parallel. The spike-like voltage shown in the waveform diagram of Vl in FIG. 3(d) is a residual voltage generated as a result of suppressing the conduction noise using the absorption circuit. A resistor 1t1 that forms this conductive noise absorption circuit
A pulse current corresponding to the switching operation flows into the capacitor C1, causing heat loss at the resistance ratio l. D
C-1) When the power capacity of the C converter is large, the specific weight of loss in this absorption circuit increases, and 1) C-
Significantly degrades the efficiency of the DC converter. About this.

The same applies to the operation of transistor Q2, resulting in similar heat losses in the resistance ratio and the absorption circuit formed by capacitor C2. Note that transistors Ql and Q
Due to the switching operation by zK, a full alternating current voltage is generated through the transformer Tlk.

As is well known, the rectifier circuit IVc outputs a DC voltage 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 switching elements due to conductive noise generated during switching operation. This has the disadvantage of increasing losses and deteriorating the efficiency of the DC-DC converter.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, provide a conductive noise absorption function that is not required by a resistive element, prevent voltage breakdown of a switching element, and provide an efficient DC-DC: +7/(-p). It is in.

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

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

FIG. 2 is a block diagram showing a second embodiment of the present invention. As shown in the figure, in this embodiment, the first primary winding Tz(A
)% second primary winding T z (B)/(T
, acting as a first switching element); y transistor Q3, a transistor Q4 acting as a second switching element, and a capacitor ! ? -c3, diodes D3 and D4, and a rectifier circuit 2.

Next, the operation of this embodiment will be explained. When the DC voltage Ei is inputted from the terminal 53 with the polarity shown in the figure and the terminal 56-1 is excited by the externally driven pulse voltage v3 and the transistor Q3 as a switching element becomes conductive, the current i3 is the winding Tz (A>'!f, - of the primary winding of the transformer T2 and the transistor Qs
'Th conducts and flows into the negative side of the DC input power supply. At this point, Trance T! Winding T z in the primary winding of
Due to the electromotive force induced in (B), the transistor Q4
The voltage V4 applied between the collector and emitter of Ei is
The voltage is approximately twice that of . When the pulse voltage v3 ends, the current 13 flowing through the transistor Q3 becomes zero, but during the time until the excitation current of the primary winding of the transformer T2 becomes zero, the induced induction in the winding Tz (~ and Tz (Bl) By power 1, the collector and emitter of transistor Q.

The voltage v3 applied between the two transistors increases from zero to approximately 2EiO, and the voltage V4 applied between the collector and emitter of the transistor Q4 decreases from 2Ei to zero.

After this state continues for a specific period of time, the initial state, ie, the state in which (1) and (2) earthquakes are equal to Ei, is restored. Next, when the terminal 56-2 is excited by the externally driven pulse voltage v4 and the transistor Q4 as a switching element becomes conductive, the current i4 flowing through the transistor Q4 is the transformer T.

It flows into the negative side of the DC input power supply via the second winding T x (B) k. At this point, i of transformer T,
The electromotive force induced in the next winding Tz (A) The voltage between the collector and emitter of transistor Q3 ■3 is F t
The voltage increases from approximately 2Ei to approximately 2Ei, and the voltage between the collector and emitter of transistor Q4 becomes zero. When the externally driven pulse voltage y4 ends, the current i4 flowing through the transistor Q4e becomes zero, but the winding Tt(A
L due to the induced emf at J and T, 03)
The voltage 4 between the collector and emitter of the transistor Q4 increases from zero to approximately 2E iO value, and the voltage 3 between the collector and emitter of the transistor Q3 decreases from 2Ei to zero.

This state continues for a certain period of time as described above, and then returns to the initial state, ie, the state where 1 and V4 are equal to Ei. Thereafter, the terminals 56-1 and 56-2 are mutually excited by the externally driven pulse voltages Y3 and v4, and the above-described operation process is repeated. In this operation process, the external drive pulse voltage v3 and "4,
Currents i3 and 1 flowing through transistors Q3 and Q4
4. Collector and emitter of transistors Q3 and Q4.

FIG. 4 shows an operating waveform diagram of the voltages 3 and V4 between the two. In this waveform diagram, when looking at the voltage V3 between the collector and emitter of the transistor Q3, the conditions under which conductive noise occurs at the time when the current i3 ends and the time when the current i4 starts, as in the case of the conventional example described above. intervenes. However, in the embodiment of the invention shown in FIG. A capacitor C3 of a predetermined capacity is connected between the points, and this capacitor C3 absorbs all the conductive noise generated during the switching operation, and no spike voltage is generated as shown in Figure 4. . Moreover, since the absorption circuit consisting of capacitor C3 does not include a resistive element, D
There are no resistive losses as seen in CDC converters.

This means that in the transistor Q4, at the time point when the fourth current i4 ends and the time point when the current i3 starts,
(2) The same applies to the case where 4 increases from zero to 2Ei. As mentioned above, due to the switching operation by the external drive pulse voltage on the primary side, the transformer T! As in the conventional example, an alternating current voltage is generated on the secondary side via the rectifier circuit 2, and a predetermined direct current voltage is outputted from the rectifier circuit 2 via the terminal 54.

As explained in detail above, the present invention completely absorbs the conductive noise, which is more than twice the supply DC voltage generated throughout the entire switching operation on the primary side, without using any resistor elements, thereby reducing the voltage breakdown of the switching element. This has the effect of completely eliminating the loss in the conductive noise absorbing circuit and improving the conversion efficiency.

[Brief explanation of drawings]

The first figure is a block diagram of a conventional push-pull type DC-DC converter, the second figure is a block diagram of an embodiment of the present invention, and the third and fourth figures are a conventional example and an embodiment of the present invention, respectively. FIG. 2 is a waveform diagram for explaining the operation of FIG. In the figure, 1.2... Rectifier circuit, 51-54.55-1-2.5
6-1~2...terminals. Part 1 Zusei 7kyu

Claims (1)

[Claims] High power capacity push-pull type DC (C-1) In a C converter, one terminal is connected to the positive side of the DC input voltage, and the first switching element is fully connected to the other terminal.
a transformer having a primary winding and a second primary winding having one terminal connected to the negative side of the DC input voltage and a second switching element connected to the other terminal; and the first and second primary windings. A DC-DC converter comprising a capacitor of a predetermined capacity connected between a winding and two connection points of the first and second switching elements.