JPS6154875A - Push-pull type dc/dc converter - Google Patents

Abstract

PURPOSE:To improve the conversion efficiency by absorbing the conduction noise generated by switching operation by an absorbing circuit, thereby preventing the voltage breakdown of a switching element. CONSTITUTION:A DC/DC converter has a transformer T1, transistors (Tr)Q3, Q4 operating as the first and second switching elements a capacitor C3, a resistor R3, diodes D3-D5, and a rectifier 2. In this case, a series-parallel circuit of the capacitor C3, the resistor R3 and the diode D5 is connected between the connecting point of the first primary winding A of the transformer T2 and the collector of the TrQ3, and the connecting point of the second primary winding B and the emitter of the TrQ4. Thus, the prescribed output is obtained from the secondary side of the transformer T2 by switching with an external drive pulse, but conduction noise generated at the switching operation time is almost absorbed to the series-parallel circuit to eliminate a spike voltage.

Description

[Detailed description of the invention] [: 5@″Ac7)t!E*fj-'m)
The present invention provides a push-pull type DC that can efficiently absorb conduction noise accompanying switching operations.
-Regarding a DC converter.

[Prior art]

Conventional push-pull type DC-DC converters (= externally driven type are often used. This type of DC-DC converter has abnormal spike-like characteristics at the starting and stopping points of the transistor used as a switching element. This spike-like voltage is due to the conductive noise that occurs during switching (secondary) due to the leakage inductance that exists between the two secondary windings of the transformer. As a measure to prevent this, 1.Normally, a series element consisting of a resistor and a capacitor is connected to the output side of the transistor. Large heat loss occurs within itself.

This has the disadvantage of degrading the efficiency of the DC-DC converter.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned conventional drawbacks.

By adding a conductive noise absorption circuit with low insertion loss, the voltage breakdown of switching elements can be reduced to DC! -DC
The purpose is to provide a converter.

[Structure of the invention]

The Bunyupuru WDC-DC converter according to the present invention has the following features:
A first primary winding of a transformer having one end on the positive side connected to the positive side terminal of a DC input power source, and a first transistor circuit having one end connected to the other end on the opposite side of the first primary winding. , a series circuit consisting of a resistor and a capacitor, one end of which is connected to the other end of the opposite polarity side of the first primary winding, and the resistor (= in parallel, the opposite polarity side of the first primary winding serves as an anode. a second transistor circuit having an emitter connected to the other end of the series circuit, a collector connected to the positive terminal of the DC input power supply, and a cathode connected to one end of the series circuit; a third diode having an anode connected to the other end of the series circuit and a cathode connected to the positive terminal of the DC input power supply;
the anode of the diode (one end of which is connected to the dual pole side, and the other end is connected to the negative terminal of the DC input power supply, the other end of the first transistor circuit, and the anode of the second diode); and a second primary winding.

Margin below [Conventional example] 9. Here, to clarify the difference from the present invention.

A conventional example (two examples will be explained with reference to the circuit diagram in FIG. 3 and the time chart in FIG. 4. First, in FIG. 5,
A DC input voltage is applied from the terminal 51 with the polarity shown in the figure, and an externally driven pulse voltage v is applied to the terminal 55-1.
1 was added.

The circuit is excited. In response to this pulse voltage v1, when the transistor Q1 as a switching element becomes conductive, the current 11 is passed from the winding TI(A) of the primary winding of the transformer T1 to the transistor Q1, and the DC input power source is turned on. Flows into the negative side.

At this point, due to the electromotive force induced in winding T1(B) in the primary winding of transformer T1.

The voltage v2 applied between the collector and emitter of the transistor Q2 is approximately twice the DC input voltage E.

When the pulse voltage v1 ends, the transistor Q1
The current 11 flowing through the transformer T1 becomes zero, but in the time it takes for the excitation current of the primary winding of the transformer T1 to become zero, the first winding TI (A) and TI (B) rises from zero to approximately 2 The voltage V2 applied between the collector and emitter of Q2 drops from 2E to zero. This state is the transistor Q
The energization time continues for a certain period of time, which is slightly below the energization time of 1, and then returns to the initial state, that is, the state where v1 and v2 are equal to the DC input voltage E (2).

Next, the externally driven pulse voltage v2 causes the terminal 55-2 to
When an excitation input is applied to the transistor Q2 as a switching element and the transistor Q2 becomes conductive, the current 12 flows through the winding TI( B) energizes transistor Q2 and flows into the negative side of the DC input power supply.

At this point, due to the electromotive force induced in winding TI(A) in the primary winding of transformer T1.

Voltage between collector and emitter of transistor Q1■1
The voltage increases from E to approximately 2E, and the transistor Q
The voltage v2 between the collector and emitter of 2 becomes zero. When the externally driven pulse voltage v2 ends, the current 12 flowing through the transistor Q2 becomes zero, but the time required for the excitation current of the primary winding of the transformer T1 to become zero is 1 winding TI(A
) and the induced electromotive force at TI(E)l2, the voltage v2 between the collector and emitter of transistor Q2 increases from zero to a value of approximately 2E (==), and the voltage v2 between the collector and emitter of transistor Q1 becomes 2E to zero. This state lasts for a certain period of time, as described above, and then returns to the initial state, ie, the state where V and v2 are equal to E.

Below, by externally driven pulse voltages v1 and V2,
The terminals 55-1 and 55-2 are alternately excited, respectively, and the above-described operating sequence is repeated.

External drive pulse voltages v1 and v2 as described in the above description. Currents 11 and i2 . flowing through transistors Q1 and Q2. The operating waveforms of voltages v1 and v2 between the collectors and emitters of transistors Q1 and Q2 are shown in the time charts from (a) to (f) in FIG. 4, respectively.

This time chart example shows transistors Q1 and Q
The duty ratios of currents 11 and 12 flowing through 2 are both 5.
This shows the case of 0chi or less.

When the duty ratios of the externally driven pulse voltages 1 and v2 approach 50%, the voltage waveforms of 1 and v2 become rectangular voltage waveforms of amplitude E centered around the level of the DC input voltage E.

By the way, the time chart in Figure 4 (at 2.

Voltage V1 between the collector and emitter of transistor Q1
Paying attention to , a spike-like voltage exceeding the voltage 2E is generated at vl at the point when +'l ends and when 12 starts (=).This spike-like voltage is caused by TI( This is caused by the leakage inductance that exists between A) and TI (B), which occurs as conductive noise during switching.The level of this conductive noise is extremely large compared to the voltage E.

There is a possibility that the voltage may destroy the transistor Q1 as a switching element. As a preventive measure.

In order to absorb the above conduction noise, normally, as shown in Figure 3, a series element of resistor R1 and capacitor C1 is connected in parallel to transistor Q1.V in Figure 4(d)
The spike-like voltage shown in the waveform of 1 is the residual voltage generated in this absorption circuit (2) as a result of suppressing the conductive noise (2). A pulse current equivalent to the switching operation flows into fC1, causing heat loss in the resistor R1.When the operating frequency of the DC!-DC converter is high, the specific gravity of the loss in this absorption circuit increases, and the converter's The efficiency is significantly degraded.This also applies to the operation of the transistor Q2, and similar heat loss occurs in the absorption circuit formed by the resistor R2 and the capacitor fC2.The switching operation by the transistors Q1 and Q2 causes the As is already known, an AC voltage is generated through T1 and a DC output voltage generated by the rectifier circuit 1 is outputted through the terminal 52.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described in detail with reference to nine drawings.

FIG. 1 shows a circuit diagram of an embodiment according to the present invention. In this example, the first primary winding T2 (A
) and a second primary winding T2 (B)
, a transistor Q5 acting as a first switching element, a transistor Q4 acting as a second switching element, a capacitor fC3, and a resistor R6.

Diode D3. It includes D4 and D5 and a rectifier circuit 2. To explain the operation of the embodiment constituted by such elements, a DC voltage E1 is applied from the terminal 53 with the polarity shown in the figure. Further, an external drive pulse of voltage v5 is applied from the terminal 56-1 to excite one circuit. Due to this excitation, when the transistor Q3 as a switching element becomes conductive, the current 15 is transferred to the transformer T.
Winding T2 (A) of the two primary windings and transistor Q6 are energized to flow into the negative side of the DC input power source. At this point 1: the winding T2 in the primary winding of the transformer T2
Due to the electromotive force induced in (B), the voltage v4 applied between the collector and emitter of the transistor Q4 becomes approximately twice the voltage of the voltage E. When the pulse voltage v3 ends.

The current i3 flowing through the transistor Q6 becomes zero.

However, during the time it takes for the excitation current in the primary winding of transformer T2 to become zero, the voltage applied between the collector and emitter of transistor Q6 due to the induced electromotive force in windings T2 (A) and T2 (B) increases from zero to a value of approximately 2E. Further, the voltage v4 applied between the collector and emitter of the transistor Q4 decreases from 2E to zero. After this state lasts for a certain time, the initial state, ie.

The voltages v3 and 4 return to a state equal to the voltage E.

Then, when an external driving pulse of voltage v4 is applied to the terminal 56-2 and the transistor Q4 as a switching element becomes conductive, the current 14 flowing through the transistor Q4 increases.
flows into the negative side of the DC input power source via the primary winding T2(B) of the transformer T2. At this point (2), due to the electromotive force induced in the primary winding T2 (A) of the transformer T2.

Voltage v between the collector and emitter of transistor Q3
3 is a voltage increase of approximately 2E from E to approximately 2E.

The voltage between the collector and emitter of transistor Q4 becomes zero. When the externally driven pulse voltage v4 ends, the current i4 flowing through the transistor Q4 becomes zero. However, the time it takes for the excitation current flowing through the primary winding of transformer T2 to become zero.

Due to the electromotive force induced in the windings T2 (A) and T2 (B), the voltage between the collector and emitter of transistor Q4 rises from zero to a value of approximately 2E, and the voltage between the collector and emitter of transistor Q6 increases. The voltage V5 between them drops from 2E to zero.

This state lasts for a certain amount of time as described above.

After that, the initial state, ie, the v3 and V4 are changed to E
It returns to a state equivalent to that of the factory. In this way.

Terminals 56-1 and 56-2 are periodically (double excited) by externally driven pulse voltages v3 and v4, respectively, and
The previously described operating sequence is repeated.

FIG. 2 shows externally driven pulse voltages v5 and v4 in the circuit of FIG. 3 is a time chart showing operating waveforms of currents 13 and i4 flowing through transistors Q3 and Q4, respectively, and voltages 3 and v4 applied between the collectors and emitters of transistors Q6 and Q4, respectively. In this time chart, if we pay attention to the voltage 5 between the collector and emitter of the transistor Q5, at the time when the current i5 ends and the time when the current 14 starts.

As in the case of the conventional example, there are conditions that cause conduction noise to occur. However, in the embodiment shown in FIG. A series-parallel circuit consisting of a capacitor C6 of a predetermined capacity, a resistor R3, and a diode D5 is connected to. This series-parallel circuit absorbs most of the conduction noise generated during switching operation, and no spike voltage is generated as shown in the time chart of FIG. 2. The resistor R3 connected in series with the capacitor C3 and the -order winding T2 (A)
and the leakage inductance that exists between T2(B) and
The capacitor 9-03 and the resistor R act as a damper for the series resonant circuit formed by the DC input power source.
Since the movement of charge in the series circuit consisting of 2 and 2 is determined only by the leakage inductance (2), the value of resistor R3 can be set to a small value according to the circuit characteristics, and therefore the loss in this part is very small.

In this embodiment as well, an alternating current voltage is induced on the secondary side via the transformer T2 by the switching operation by an external drive pulse on the negative side, and a predetermined direct current voltage is generated from the rectifier circuit 2 (2), and the terminal Supplying the output to the load via 54 is similar to the conventional example.

〔Effect of the invention〕

As is clear from the above explanation (2), according to the present invention,
By adding an absorption circuit with low insertion loss to absorb the conductive noise generated by the switching operation on the primary side of the transformer (2) by adding an absorption circuit with low insertion loss, voltage breakdown of the switching element is prevented, and the noise is reduced to the output. This makes it possible to reduce contamination and noise radiation, and is particularly effective in improving conversion efficiency when applied to converters with high operating frequencies due to switching.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment according to the present invention, FIG. 2 is a time chart for explaining the operation of the embodiment of FIG. 1, and FIG. 3 is a configuration of a conventional DC-DC converter. A circuit diagram showing an example. Fig. 4 is a time chart for explaining the operation in the conventional example shown in Fig. 3. In the figure (=, 2 is a rectifier circuit, 53.54 is a terminal. -2 is a terminal for applying an external driving pulse. Q3. Q and 4 are transistors, D3 to D5 are diodes, R3 is a resistor, 03 is a capacitor, and T2 is a transformer.

Claims (1)

[Claims] 1. A first primary winding of a transformer whose one end on the positive side is connected to the positive side terminal of a DC input power supply, and a first transistor whose one end is connected to the other end on the opposite side of the first primary winding. circuit and
a series circuit consisting of a resistor and a capacitor, one end of which is connected to the other end of the opposite pole side of the first primary winding; a second transistor circuit having an emitter connected to the other end of the series circuit and a collector connected to the positive terminal of the DC input power source; and a second transistor circuit having a cathode connected to one end of the series circuit. a third diode having an anode connected to the other end of the series circuit and a cathode connected to the positive terminal of the DC input power supply, and one end of the reverse polarity side connected to the anode of the third diode. and a second primary winding of the transformer, the other end of which is connected to the negative terminal of the DC input power source, the other end of the first transistor circuit, and the anode of the second diode. Push-pull type DC-DC converter.