JP2003111412A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a DC-DC converter capable of reducing loss caused by a leakage inductance, and high conversion efficiency. SOLUTION: In this DC-DC converter, there are provided a plurality of basic units M1 (M1 to M4) which comprise a first circuit for converting an input DC signal into a high frequency signal by a switching device Q1 which is ON- OFF drive-controlled by a first pulse signal PWM (A), and filters and outputs the signal obtained by boosting the converted high frequency signal at the transformer T1; and a second circuit which converts the input DC signal into the high frequency signal by a switching device Q2 which is ON-OFF drive- controlled by a second pulse signal PWM (B) of the phase different 180 deg. from the first pulse signal PWM (A), and filters and outputs the signal obtained by boosting the converted high frequency signal at the transformer T2. The input sides of the plurality of basic units M1 to M4 are connected in parallel and the output sides thereof are connected in series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation type DC / DC converter using a transformer, and particularly to a high efficiency DC
/ DC converter.

[0002]

2. Description of the Related Art An example of a conventional insulation type DC / DC converter of this type is shown in FIG. Insulated type DC /
In a DC converter (forward converter) circuit, an input DC voltage is input to a series circuit of a snubber and a switch element Q201 via a capacitor C201, and the switch element Q201 is turned on by a pulse train signal applied to its input side (base), The OFF drive control is performed, and the snubber is connected in parallel to the primary side of the insulating transformer T201 and the diode D201.

The conventional insulation type DC / DC converter has such a structure and transfers energy from the input side to the output side through the operation of the transformer T201. Energy is directly transferred to the output while the switch element Q201 is on. When the switch element Q201 is turned on, the secondary side of the transformer becomes positive and current is supplied to the load through the diode D201. When the switch element Q201 is turned off, the output winding becomes negative and the diode D2
A commutation current flows through 02.

The snubber in the figure protects the switching element Q201 and the diode D201 from an overvoltage spike generated by the leakage inductance of the transformer.

The above-mentioned conventional insulation type DC / DC converter (forward converter) controls ON / OFF driving of the switching element Q201 by a high frequency pulse.
The input DC voltage is boosted on the secondary side through the insulating transformer T201, and the boosted voltage is rectified by the diode D201.
Further, the smoothing capacitor C202 smoothes it to obtain a high voltage output.

[0006]

However, such a conventional DC / DC converter has the following problems. For example, considering the case where an output of 360V is obtained from an input of 30V, the switch element Q201 is turned on. When the duty of the pulse for OFF drive control is 45%, the primary and secondary winding ratio N of the transformer T201 is about 27.

The first problem is that the coupling ratio of the transformer T201 is extremely deteriorated and the leakage inductance is increased when the winding ratio is increased.

The second problem is that the current on the primary side has a winding ratio N
Since it is proportional to
A large switching current flows through 01. Therefore,
A switch element corresponding to a large current must be used, which causes a cost increase.

The third problem is that the increasing leakage inductance stores energy proportional to the square of the switching current, but this energy must be consumed by an additional circuit such as a snubber circuit. That is, high conversion efficiency cannot be expected.

The fourth problem is that when the voltage on the secondary side of the transformer T201 increases, the rectifying diode D20 on the secondary side
1. A high breakdown voltage product is required for each of the commutation diodes D202. Generally, a diode having a high breakdown voltage has a poor reverse recovery characteristic, and thus consumes energy during the reverse recovery period, which is one of the factors that hinder high conversion efficiency.

The fifth problem is that the current flowing during the reverse recovery time returns to the primary side through the transformer T201 and becomes a through current of the switch element Q201, which also causes a reduction in conversion efficiency. ing.

Therefore, an object of the present invention is to provide a DC / DC converter which not only can reduce loss due to leakage inductance but also have high conversion efficiency.

[0013]

In order to solve the above-mentioned problems, the DC / DC converter according to the present invention adopts the following characteristic structure.

(1) An input DC signal is converted into a high frequency signal by a switch element which is ON / OFF driven by a first pulse signal, and the converted high frequency signal is boosted by a transformer to smooth the signal obtained. The input first DC signal is converted into a high frequency signal by a switch element that is ON / OFF driven and controlled by a second pulse signal whose phase is 180 degrees different from that of the first circuit for outputting and the first pulse signal. A plurality of basic units each having a second circuit for smoothing and outputting a signal obtained by boosting a high frequency signal by a transformer are provided, and the input sides of the plurality of basic units are connected in parallel and the plurality of basic units are connected. A DC / DC converter in which the output side of the basic unit is connected in series.

(2) A first pulse signal is used to convert an input DC signal into a high-frequency signal by a switch element that is ON / OFF-driven and output a signal obtained by boosting the converted high-frequency signal with a transformer. Having a plurality of circuits of 1,
The first unit group in which the output side of each first circuit is sequentially connected in series and the second pulse signal whose phase is 180 degrees different from that of the first pulse signal are input by a switch element which is ON / OFF driven and controlled. Converts DC signals to high frequency signals,
A second unit group having a plurality of second circuits for outputting a signal obtained by boosting the converted high-frequency signal with a transformer, and a second unit group in which the output sides of the respective second circuits are sequentially connected in series; The input DC signal is input in parallel to the input sides of the first unit group and the second unit group, and the outputs of the first unit group and the second unit group are rectified and combined to output DC / DC. converter.

(3) The switching element is a PWM generated by comparison with a reference signal by a PWM comparator.
The DC / DC converter according to (1) or (2), which is drive-controlled by a signal and changes the output of the DC / DC converter by changing the reference signal.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a DC / DC converter according to the present invention will be described below with reference to the accompanying drawings.

In the present invention, the rectified outputs of the converters whose switching phases are different by 180 degrees are combined, and this is used as a basic block to accumulate the voltage to obtain a high voltage.
Alternatively, two sets of switching circuits in which the secondary side of the transformer is connected in series and high-frequency voltage is accumulated are prepared, and each set is controlled to be driven by 180 degrees different phases, and the output of each set is added after rectification to obtain a high voltage. Is getting

FIG. 1 is a simplified circuit diagram showing a first embodiment of a DC / DC converter of the present invention. In this embodiment, a signal obtained by a switch element that is ON / OFF driven by a pulse is boosted by a transformer.
Two circuits are provided, and the switch elements of these two circuits are driven and controlled by pulses whose phases are different from each other by 180 degrees. A basic unit (M1 to M4) is a combination of two circuits after being rectified on the secondary side of the transformer, and a plurality of these basic units (four in this example) are used to build up the required high voltage. It adopts the configuration to obtain. The inputs of the basic units are connected in parallel and the outputs are connected in series. As a result, a DC voltage Vo corresponding to the number of stacked stages of the input voltage Vi can be obtained at the output with high conversion efficiency.

First, the operation of the basic unit will be described below with reference to FIG. In the following description, the basic unit M1 will be described as an example, but the same applies to the other basic units M2 to M4. In the first or second circuit (the forward converter A and the forward converter B, respectively) forming the basic unit M1, the input DC voltage Vi is connected to the input side of the transformer T1 or T2 via the capacitor C1 or C2. The basic unit M1 is configured to combine the outputs with the rectified outputs on the secondary side of the transformers T1 and T2 of the forward converter A and the forward converter B.

More specifically, an input capacitor C1 is connected in parallel to the input of the forward converter A, and a series circuit of a transformer T1 and a switch element Q1 is connected in parallel with this capacitor C1. A pulse train signal PWM (A) output from the pulse generator P1, for example, is applied to the input terminal (base terminal in the case of a transistor) of the switch element Q1, and the switch element Q1 switches according to this pulse train. Operate. A rectifier diode D1 is connected to the secondary side of the transformer T1, and a commutation diode D3 and a smoothing choke L1 are connected to the output of this diode D1. A smoothing capacitor C3 is connected to the output of the smoothing choke L1, and smoothed direct current is obtained at both ends of this capacitor C3.

The operation of the forward converter B is the same as that of the above-mentioned forward converter A, but as shown in FIG. 2, the PWM modulation pulse train PWM (B) output from the pulse generator P2 is generated by the pulse generation of the forward converter A. PWM modulation pulse train PWM output from device P1
It is different from the phase of (A) by 180 degrees.

An input capacitor C2 is connected in parallel to the input of the forward converter B, and a series circuit of a transformer T2 and a switch element Q2 is connected in parallel with this capacitor C2. The input terminal (or the base terminal if it is a transistor) of the switch element Q2 is, for example, a pulse train PWM that is output from the pulse generator P2 and has undergone PWM
(B) is applied.

As described above, this pulse train PWM (B)
Is 180 degrees out of phase with the pulse train PWM (A) of the forward converter A. The switch element Q2 performs a switching operation according to this pulse train. A rectifying diode D2 is connected to the secondary side of the transformer T2, and the output of the diode D2 is connected to the commutation diode D3 described in the forward converter A. That is, the outputs of the forward converter A and the forward converter B are combined so that the commutation diode D3 is shared.

A smoothing choke L1 is connected to the composite point of the forward converter A and the forward converter B,
A smoothing capacitor C3 is connected to the output of the smoothing choke L1, and smoothed DC is obtained from both ends of this capacitor C3.

As described above, the switch elements Q1 and Q2 are driven by the PWM-modulated pulse train signal PWM (B) having a phase difference of 180 degrees, and the duty of each pulse train is 50% or less.

In the embodiment shown in FIG. 1, a plurality of basic units (M1 to M4) are prepared, and the inputs of each unit are connected in parallel, while the outputs of each unit are connected in series so as to correspond to the number of units. The high voltage DC output of is obtained. In the case of this embodiment, the input DC voltage is 30V and the final DC output voltage is 360V, and each basic unit is in charge of the output voltage of 90V, and these are stacked in four stages.

The first embodiment of the present invention has been described above. As in the present embodiment, the phase is set to 1 in the basic unit.
By adopting the two-converter method with a shift of 80 degrees, the turns ratio of the transformer can be halved compared to the one-converter method. For example, taking the above-mentioned DC input voltage 30V, DC output voltage 360V, and duty of 45% as an example,
In the case of the 1-converter method of the conventional example, the winding ratio N is N = wherein the input voltage is Vi, the output voltage is Vo, and the duty is D.
Since it is Vo / (Vi × D), it is 1:27, but in the case of the two-converter method according to the present embodiment, the turns ratio of each transformer can be reduced to 1: 13.5, which is half.

Further, the transformer T used in the basic unit by stacking and using the basic units in a plurality of stages.
The winding ratio of 1 and T2 is 1 / the number of stacked layers. In the present embodiment, since there are four stages, 1/4, that is, 1: 3.37.
And can be brought closer to the ideal 1: 1.

As described above, the turn ratio of the transformer is 1:27 in the case of one stage, but according to the present embodiment, it is 1: 3.3.
It is possible to drastically reduce the ratio of 7 to the number of turns to 1/8. Therefore, the leakage inductance that adversely affects the operation of the converter is reduced.

The switching current on the primary side can be reduced by a small amount of primary current in each basic unit due to the current distribution effect of the configuration of a plurality of stages. For example, considering the case where the secondary side output is 1A, the primary side current is 27A in the conventional forward converter, and attention must be paid to the selection of switching elements and the like. On the other hand, in the case of the present embodiment, the primary side current is only 1/8, which is 3.37 A, and there is an advantage that it is not necessary to use a special switching element or the like.

Further, the energy stored in the leakage inductance is proportional to the square of the current, but in this embodiment, the current on the primary side of each transformer is 1 as compared with the conventional type. Since it is reduced to / 8, the stored energy of the leakage inductance of each transformer is 1/64.

Furthermore, since eight transformers are used in the whole inverter of this embodiment, 8 times 1/64.
That is, the total inverter becomes 1/8. As a result, the leakage inductance is 1/8 that of the conventional one-stage forward converter, and the loss due to the leakage inductance can be reduced accordingly.

Further, since the output voltage of the conventional forward converter is as high as 360 V, the reverse withstand voltage corresponding to the voltage is also required for the rectification and commutation diodes. When the reverse breakdown voltage is Vr, the output voltage is Vo, and the duty is D, Vr = Vo / D, and D is 45
%, Vr = 800V, and a reverse breakdown voltage of 800V was required. On the other hand, according to the present embodiment, 1
Since a reverse withstand voltage of / 8 of 100 V is sufficient, an inexpensive diode with a withstand voltage of 200 V having a low loss and a short reverse recovery time can be used, and the short-circuit current flowing through the switch element can be significantly reduced.

Due to the synergistic effect of the improvements described above, according to the present embodiment, the conversion efficiency (= output power / input power) is 97.
We achieved a high efficiency of%.

In the above example, the output voltage of the basic unit is the same, but this may be different in each unit.

FIG. 3 is a DC showing a second embodiment of the present invention.
It is the circuit diagram which simplified the / DC converter. In this embodiment, in order to reduce the number of components, the voltages are accumulated before the secondary side of the transformer is connected in series and rectified.
(In the first embodiment, the voltage is piled up after rectification.) Block of transformer T101, transformer T102
The blocks of are driven alternately by PWM signals whose phases are different by 180 degrees.

In FIG. 3, a first unit group consisting of units A101 to A104 surrounded by an alternate long and short dash line and B1
Each unit of the second unit group consisting of 01 to B104 has the same circuit configuration, but the phase of the pulse train applied to the switch elements in the first unit group and the second unit group is different by 180 degrees from each other. Is.

Explaining the unit A101, the input DC voltage Vi is the same as the capacitor C101 and the transformer T1.
01 and the switch element Q101 in series.
The switch element Q101 performs a switching operation according to the PWM pulse train output from the pulse generator PA applied to the input side, and generates a high frequency signal on the primary side of the transformer T101. The high frequency signal input to the primary side is
It is transmitted to the secondary side of the transformer T101. Unit A1
With units other than 01, the same operation as transformer 2
High frequency output (switching waveform) is generated on the secondary side. Since the high frequency outputs generated on the secondary side of the transformer have the same phase, added high frequency outputs are generated on both ends of the hot side of the unit A101 and the ground side of the unit A104.

By the same operation, the units B101 to B are
A high frequency output is obtained from the output of 104 by the same operation.

The first unit group and the second unit group thus obtained
The high frequency output on the secondary side of each transformer of the unit group is rectified by the diodes D101 and D102 and smoothed by the smoothing choke L101 and the smoothing capacitor C103 to obtain the DC output voltage Vo.

In the above example, the output voltages of the basic units are the same, but this may be different in each basic unit as long as the added high frequency outputs are equal in both unit groups.

The switch elements Q101 and Q102 are alternately on / off driven and controlled by a PWM pulse train having a phase shift of 180 degrees and a duty of 50% or less. Therefore, the output duty can be close to 100%, and the turns ratio of the transformer can be brought close to the ideal 1: 1. Further, the inductance of the smoothing choke L101 can be reduced.

Similar to the first embodiment, the second embodiment also has an advantage that the transformer winding ratio and the leakage inductance can be reduced as compared with the conventional forward converter. The reverse withstand voltage of the rectification and commutation diode is 400V which is 1/2 of 800V of the conventional forward converter in the second embodiment.
For this reason, a 200V breakdown voltage diode with low loss and fast reverse recovery time cannot be used, but since the number of diodes, smoothing chokes, and smoothing capacitors can be 1/4 each, cost reduction can be achieved by significantly reducing the number of parts. realizable. There is also an advantage that the forward voltage drops (Vf) of the diodes do not overlap by four.

The switching control in the first and second embodiments is performed by the PWM control method. This PW
In the M control method, the error signal obtained by comparing the output of the DC / DC converter with the reference voltage is given to the other terminal of the PWM comparator to which the triangular wave (carrier signal) is applied to one terminal, and the control signal of the switch element is supplied. It has occurred. By changing the reference signal, the output voltage of the DC / DC converter can be changed in synchronization with the external signal.

The configuration and operation of the preferred embodiment of the DC / DC converter according to the present invention have been described above in detail. But,
Such an embodiment is merely an example of the present invention and does not limit the present invention in any way. Those skilled in the art can easily understand that various modifications and changes can be made according to a specific application without departing from the gist of the present invention.

[0047]

As described above, the DC / DC according to the present invention
In the DC converter, the turns ratio of the transformer can be made close to 1: 1, loss due to leakage inductance can be reduced, and a DC / DC converter with high conversion efficiency can be realized.

[Brief description of drawings]

FIG. 1 is a simplified circuit diagram showing a first embodiment of a DC / DC converter according to the present invention.

FIG. 2 is a timing diagram of PWM waveforms in the present embodiment.

FIG. 3 is a simplified circuit diagram showing a second embodiment of a DC / DC converter according to the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional DC / DC converter.

[Explanation of symbols]

C1, C2, C101, C102, C201 Input capacitors C3, C103, C202 Smoothing capacitors D1, D2, D101, D102, D201 Rectifying diodes D3, D103, D202 Commutation diodes L1, L101, L201 Smoothing chokes Q1, Q2, Q101 , Q102, Q201 Switch elements P1, P2, PA, PB Pulse generator

Claims (3)

[Claims] 1. An input DC signal is converted into a high frequency signal by a switch element which is ON / OFF driven controlled by a first pulse signal, and the converted high frequency signal is boosted by a transformer and a signal obtained is smoothed and output. And a first circuit for
A signal obtained by converting an input DC signal into a high frequency signal by a switching element that is ON / OFF driven and controlled by a second pulse signal whose phase is 180 degrees different from that of the pulse signal, and boosting the converted high frequency signal with a transformer. A plurality of basic units each having a second circuit for smoothing and outputting the input signal, the input sides of the plurality of basic units being connected in parallel, and the output sides of the plurality of basic units being connected in series. A DC / DC converter characterized by: 2. A first pulse signal which is converted into a high frequency signal by a switching element which is ON / OFF driven by a first pulse signal and which outputs a signal obtained by boosting the converted high frequency signal with a transformer. A plurality of circuits, each of which is
The first unit group in which the output sides of the circuits are sequentially connected in series, and the input DC signal by the switch element whose ON / OFF drive is controlled by the second pulse signal whose phase is 180 degrees different from the first pulse signal. A second unit having a plurality of second circuits for converting into a high-frequency signal and outputting a signal obtained by boosting the converted high-frequency signal with a transformer, wherein the output sides of the respective second circuits are sequentially connected in series. The input DC signal is input in parallel to the input sides of the first unit group and the second unit group, and the outputs of the first unit group and the second unit group are combined after rectification and combined. A DC / DC converter characterized by outputting as an output. 3. The switching element is drive-controlled by a PWM signal generated by comparison with a reference signal by a PWM comparator, and the output of a DC / DC converter is changed by changing the reference signal. The DC / DC converter according to claim 1 or 2.