JP2855746B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC-DC converter, in particular, a drive-side circuit and an output-side circuit which are DC-isolated and can be isolated from one input to multiple outputs between outputs. DC- using piezoelectric coupler
Related to DC converter.

[Prior Art] In recent years, electronic devices have tended to become smaller and thinner, and circuits made up of discrete components have been made into hybrid ICs and peripheral circuits made into LSIs. In addition, these miniaturizations are also being promoted with power supplies required to operate electronic devices.In this example, there is a DC-DC converter that has a downsized transformer by increasing the switching frequency. It has become 1-2cm.

 A conventional example will be described with reference to the drawings.

 FIG. 7 is a circuit diagram of a conventional DC-DC converter.

The DC voltage VI applied to the input terminal 71 is converted into AC by switching with a switching element 2 such as a transistor, and the voltage is stepped down or stepped up using a transformer 73 and rectified by a rectifier diode 74 to be converted into a DC voltage again. Error detection circuit so that this voltage becomes a desired voltage.
The difference is detected at 75 and returned to the control circuit 77 using the photocoupler 76 or the like, the switching time ratio is controlled, and the like is taken out as the output voltage VO. Therefore, the power supply connected to the input terminal 71 and the voltage VO taken out as the output voltage
Is isolated by a transformer, so that a ground loop is not formed in the electronic device, and malfunction due to noise can be prevented.

For this reason, DC-DC converters have been installed in large packages of communication equipment for each package, and the demand has been increasing with the miniaturization of DC-DC converters. ing.

In such a DC-DC converter, a winding transformer is used as a coupler that couples an input side and an output side, and performs isolation while also performing step-down or step-up. Further, in order to feed back a voltage obtained as an output to a switching circuit on the input side, the voltage is coupled by a photocoupler or the like through Vf conversion (voltage-frequency conversion).

In the DC-DC converter as described above, a coupler is used as a functional element for isolating an input and an output, and one of them is a winding transformer which is a main part for performing step-down or step-up. There is a photocoupler for feeding back the error of the output voltage to the control system of the switching circuit.

Among them, the former winding transformer has primary and secondary windings on a magnetic core (core), and the winding ratio is the ratio of step-down or step-up of input and output, and the number of secondary windings is plural. By doing so, one-input multiple-output can be configured. The latter photocoupler receives light from a light emitting element such as an LED by a phototransistor, and is formed by integrally molding the LED and the phototransistor.

As described above, the conventional DC-DC converter performs voltage conversion (step-up or step-down) using a winding transformer. If the switching frequency is increased, the number of windings can be reduced, and the core of the transformer can be reduced to a small one.

Therefore, in order to reduce the size, the switching frequency is increased. At present, the switching frequency of 1 MHz has come to be marketed.

Also, as the switching frequency increases, the loss of the semiconductor, which is the switching element, increases.Therefore, resonance type converters that perform switching at a place where the voltage or current is almost zero are becoming popular. It is a type converter. Further, recent DC-DC converters have been marketed in which a large-capacity multilayer ceramic capacitor is molded in one case without using an aluminum electrolytic capacitor in order to enhance reliability.

Such DC-DC converters have been reduced in size by increasing the switching frequency, but have an efficiency of 60 to 65%.
Therefore, increasing this efficiency has been a major issue for DC-DC converters. In addition, in a system configuration in which a DC-DC converter is mounted for each package in a large communication device,
Conventionally, power supplies such as ± 12 V and 48 V were made in each package using 5 V power supply (main power supply of the device was set to 5 V and supplied to each package via a power supply line). In recent years, it has become a trend to produce a low voltage such as 5 V in a package with 48 V power supply because of the size reduction, and it is important to reduce the loss from this point as well.

[Problems to be solved by the invention]

In the conventional DC-DC converter described above, the step-down or step-up of the voltage creates a desired voltage by controlling the turns ratio of the winding transformer and the current flowing through the transformer by time division or the like. It can be. However, even in a state where no output is taken out (no load), current must flow through the primary side of the transformer.
It is consumed as heat loss of the switching transistor. For this reason, the efficiency as a power supply becomes worse as the output current becomes smaller, and drops to about 50% in a small current region, and the current does not become zero at no load. Also,
The downsizing due to the increase in the frequency becomes inefficient due to the effects of the reverse recovery time of the rectifying diode and the switching time of the switching transistor, and this amount is consumed as heat loss inside the power supply. In addition, these winding transformers and switching transistors basically use a large-capacity capacitor or choke coil in the output stage to convert DC to AC, step up / down, and return to DC again. However, there is a drawback in that a conventional filter must be constructed, which becomes a major bottleneck in miniaturization.

[Means for solving the problem]

In the DC-DC converter of the present invention, at least two piezoelectric elements having at least one pair of opposed electrodes are mechanically connected via an insulating layer, and the two or more piezoelectric elements are supported by a support frame. Fixed, at least one of these
One is a drive-side element, and at least one is a piezoelectric coupler, a switching transistor, and a capacitor, which are output-side elements.

[Action]

The present invention provides a DC-DC converter in which a coupler is composed of two piezoelectric elements, the FET is directly controlled by the coupler to operate as a switch element, and a voltage charged in a capacitor is obtained by combining a plurality of the switch elements. To produce an output voltage by performing the serial-parallel conversion of

Generally, a piezoelectric element is distorted (displaced) by applying an electric field.
This is an element which can generate a voltage by applying pressure (external strain). For this reason, the piezoelectric coupler used in the present invention is a device in which two or more piezoelectric elements are mechanically connected and fixed in one support frame to drive an FET (field effect transistor).
When an electric field is applied to one of the piezoelectric elements, the element expands, and pressure is applied to the other fixed piezoelectric element. At this time, a voltage is necessarily generated from the piezoelectric element.

Therefore, the piezoelectric element that applies an electric field is the drive side,
If the voltage generation side is the output side element, this is a coupler whose output voltage changes according to the input signal. If the voltage applied to the drive side is pulsed, the output voltage will also be pulsed (a very long time). FET is driven on the output side to operate as a switch element.

〔Example〕

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

FIG. 1 is a circuit diagram of a step-up DC-DC converter according to an embodiment of the present invention. The piezoelectric coupler 11 has one drive and six outputs and the piezoelectric coupler 12 has one drive and four outputs (the piezoelectric coupler will be described later). And a drive circuit 1 that operates these two piezoelectric couplers in a 180-degree timing relationship.
By operating the input side and output side piezoelectric couplers with the signals of Φ1 and Φ2 from the drive circuit 13, the switches (FETs of the piezocoupler) are operated, and the input applied to the capacitors C1, C2, C3. The voltage at the terminal is obtained at the output terminal as a triple output voltage.

Here, the configuration and operation of the piezoelectric coupler will be described.

FIG. 2 shows a configuration of an element showing one embodiment of a piezoelectric coupler used in the DC-DC converter of the present invention. The first piezoelectric element 22 having a counter electrode 21 therein and the second The piezoelectric element 24 is mechanically connected with an adhesive 26 via an insulator 25, and the two piezoelectric elements 22 and 24 are bonded and fixed inside a support frame 27.

Further, the support frame 27 has a drive terminal 28 and an output terminal 29 for connection to an external circuit, and a lead wire 30 drawn from the first piezoelectric element 22 and the second piezoelectric element 24 is connected thereto. . Further, the support frame 27 is provided with a screw fixing hole 31 for mounting the device.

In the piezoelectric coupler configured as described above, since the two piezoelectric elements are completely fixed by the support frame, when an electric field is applied to the drive terminal 28, the first piezoelectric element 22 expands in the fixed axis direction.

Then, a pressure is applied to the second piezoelectric element 24 by an amount corresponding to the extension, and at this time, a voltage is generated from the second piezoelectric element 24.

Therefore, an output voltage is generated at the output terminal according to the change in the driven voltage.

However, this voltage is only output when the drive voltage changes (when the pressure changes) and is not output continuously.

For this reason, if a pulse-like voltage is applied to the drive terminal 28, the coupler changes its output according to this change.

In a piezoelectric coupler obtained by such a configuration, an output voltage is obtained from a piezoelectric element on an output side by a signal given to a piezoelectric element on a drive side, and this output voltage usually needs to be received by a high impedance element. For FE
Configure by adding T.

FIG. 3 shows that the LET array 33 is mounted on the support frame 32 and this FET is
The output from the secondary side piezoelectric element 34 which is the output side to the array 33 is divided into five electrode pairs 35, 36, 37, 38, and 39 (individually forming the insulating layer 40), and these are respectively connected to the source gate of the FET. It is connected between.

With this configuration, if the piezoelectric element of the drive element 41 on the primary side is driven with a pulse voltage, a pulse-like pressure is applied to the secondary-side piezoelectric element according to the pulse voltage, and the divided secondary side piezoelectric element is driven. Electrode pairs of piezoelectric elements 35, 36, 3
Voltages are output from 7, 38, and 39.

As a result, between the source and the drain of the FET to which this output is connected, the switch operates as five switch elements as shown in FIG. 4, and the switch elements are obtained in a completely isolated state. Therefore, the step-up DC-DC converter shown in FIG. 1 is configured by using two pairs of such isolated switch elements.

Next, the operation of the DC-DC converter shown in FIG. 1 will be described.

Here, the timing of Φ1 and the timing of Φ2 are 18
0 degrees different, when the input-side switch element (FET) is on, the output-side switch element is off, and when the output-side switch element is on, the input-side switch element is off. Shall be.

First, when the input side switch is turned on at the timing of Φ1, the voltage VI applied to the input terminal is
1, C2 and C3 are applied in parallel and charged. Next, at the timing of Φ2, the switch on the input side is turned off and the switch on the output side is turned on. At this time, the voltages charged in C1, C2, and C3 are connected in series. As a result, the output voltage VO is obtained as a voltage three times the input terminal voltage VI.
By repeating the timing 2 in a constant cycle, a constant voltage is obtained at the output terminal.

In practice, a smoothing capacitor and a choke coil are additionally used at the output end, and a stable output voltage can be obtained by the smoothing circuit.

As is clear from the above description, the piezoelectric coupler used in the present invention has at least two piezoelectric elements mechanically connected and fixed in a support frame. A voltage can be taken out as an output element, and the number of piezoelectric elements on the output side is not limited to one due to the element configuration, but the required number of circuits (the number of switches)
Thus, not only the triple voltage shown in FIG. 1 but also a voltage of an arbitrary magnification can be generated.

In the embodiment of the present invention, the step-up type DC-DC converter is described. However, a step-down type converter, a ± bipolar converter, and the like can be freely created by a group of isolated switches obtained by a piezoelectric coupler. .

FIG. 5 shows the configuration of a step-down DC-DC converter according to another embodiment of the present invention.
It is the reverse of the figure.

In this case, when the switch on the input side is turned on at the timing of Φ1, the capacitors C1, C2, and C3 are connected in series, so that if these capacitors have the same capacity, 1/3 of the input voltage is applied to each capacitor. In addition, it is charged.

Next, when the switch on the output side is turned on at the timing of Φ2, the capacitors C1, C2, and C3 are connected in parallel, and a voltage of 1/3 of the input charged in each capacitor is obtained at the output terminal.

FIG. 6 shows a configuration of a DC-DC converter showing an embodiment for generating a voltage of ± polarity using one input voltage. In this case, too, the timings of the input side and output side switches are adjusted. It can be created by the timing of Φ1 and Φ2.

As is clear from the above description, the DC-DC converter of the present invention uses two pairs of piezoelectric couplers to obtain isolated switch groups, respectively. Any voltage, such as a type and a polarity inversion type, can be created.

〔The invention's effect〕

Since the DC-DC converter of the present invention obtains the voltage conversion by combining the switch element and the capacitor isolated by the piezoelectric coupler, no charge is discharged from the capacitor in the no-load state. Therefore, the current flowing from the voltage source applied to the input terminal becomes zero. Therefore, if the output is not taken out, the power consumed as the input becomes zero, and the efficiency of the output does not decrease due to the state of the output. In addition, since no polar parts such as a transformer are used, a compact device can be constructed, and there is no need to forcibly increase the switching frequency as in the past.
Sufficient operation characteristics can be obtained at a frequency of several tens of kHz. As a result, the switching loss of the switching element (here, FET) is only generated by the ON resistance alone, and the conversion efficiency of the entire converter is high.

Further, since the DC-DC converter of the present invention performs direct DC conversion without converting to AC, ripples are reduced, and there is no need to use a capacitor or a choke coil having a large capacity as a filter element. There is.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a schematic diagram showing a shape of a piezoelectric coupler used in a DC-DC converter of the present invention, and FIG. FIG. 4 is a schematic diagram of a piezoelectric coupler showing an embodiment, FIG. 4 is an equivalent circuit diagram of an output side circuit when the piezoelectric coupler having the FET shown in FIG. 3 is driven by a pulse voltage, and FIG. 5 is another embodiment of the present invention. FIG. 6 is a circuit diagram of a step-down DC-DC converter using a piezoelectric coupler showing an example. FIG. 6 is a circuit diagram of a bipolar output type DC-DC converter using a piezoelectric coupler showing another embodiment of the present invention. FIG. 1 is a circuit diagram showing an example of the related art. 1 ... input end, 2 ... output end, 11 ... input side piezoelectric coupler, 12 ... output side piezoelectric coupler, 13 ... drive circuit.

Claims (1)

(57) [Claims] At least two piezoelectric elements having at least one pair of opposed electrodes are mechanically connected via an insulating layer, and at least two piezoelectric elements are fixed by a support frame. Wherein at least one of the DC-DC converters is a drive-side element, and at least one is a piezoelectric-coupler, a switching transistor, and a capacitor, which are output-side elements.