JP2002125369A - Dc-to-dc converter and motor drive device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive device provided with a DC/DC converter in which miniaturization, high efficiency, cost reduction and improvement in reliability of components are realized. SOLUTION: A plurality of low breakdown voltage diodes 2a, 2b of low loss are connected in series with a snubber circuit 9, and snubber resistors 1a, 1b are connected in parallel with each of the diodes. Thereby balance of divided voltages is maintained, and a reverse voltage applied to the diodes is restrained to be within the level of the breakdown voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter and a motor driving device using the same, particularly to a snubber circuit.

[0002]

2. Description of the Related Art In recent years, A used for industrial equipment and the like has been developed.
A C-input motor drive device is used all over the world. For example, in Europe and China, a three-phase power supply of about 400 VAC is input to the motor drive device.

[0003] The motor driving device is provided with a DC / DC converter that converts an input AC voltage into a DC voltage by a rectifier circuit and generates a voltage required by a motor control circuit.

Normally, a DC / DC converter is several tens of kilos.
Switching is performed at a frequency of about Hz, a DC voltage is applied to the primary winding of the transformer, and a predetermined DC voltage is generated in the secondary winding. A snubber circuit including a capacitor, a diode, and a resistor is provided in parallel with the primary winding in order to suppress the drain-source jump voltage so as not to exceed the withstand voltage of the MOS-FET.

Hereinafter, DC used in a conventional motor driving device will be described.
The following description focuses on the / DC converter.

In FIG. 2, reference numeral 21c denotes a snubber resistor, 2
2c is a snubber diode, 23 is a snubber capacitor, 2
4 is a transformer, 25 is a MOS-FET, 26 is a rectifier circuit, 27 is an oscillation circuit, 28 is a load (motor control circuit),
29 is a snubber circuit.

A DC / DC converter is a MOS-FET
25, the DC voltage charged in the rectifier circuit 26 is applied to the primary winding of the transformer 24,
A predetermined voltage is generated in the next winding.

When the MOS-FET 25 is switched off, the voltage between the drain and the source of the MOS-FET 25 jumps up temporarily, and the snubber resistor 21c, the snubber diode 22c and the snubber capacitor 23 are used to reduce the jumping voltage as much as possible. A snubber circuit is installed.

As the primary voltage becomes higher, the jump voltage and the energy stored in the snubber capacitor also increase, and the heat generated by the loss in the snubber diode and snubber resistor also increases.

[0010]

However, in the above-mentioned conventional configuration, when the input power supply voltage such as 400 VAC input is high, the reverse voltage applied to the snubber diode also increases, so that a diode with a high withstand voltage must be used. However, a diode with a high withstand voltage generally has a large structure and a large loss compared with a diode with a low withstand voltage, and is expensive.

When the input power supply voltage is high, the energy charged in the snubber capacitor also increases,
It was necessary to cope with the heat generated by the snubber diode and the snubber resistor.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a DC / DC converter capable of reducing the size and cost of a device and improving reliability, and reducing the size and cost by using the same. It is an object of the present invention to provide a motor drive device with improved reliability.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a series connection of a capacitor and a plurality of diodes in parallel with a primary winding of a transformer, and a resistor connected in parallel to each of the diodes. DC with integrated snubber circuit
A / DC converter used in a power supply unit of a motor drive device.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a capacitor and a plurality of diodes are connected in series with a primary winding of a transformer,
Since each of the diodes has a snubber circuit in which a resistor is connected in parallel, it is possible to maintain the balance of the divided voltage by the resistor and suppress the reverse voltage applied to the diode within the withstand voltage level, and at the same time disperse the heat generated by the diode and the resistor. By doing so, the reliability of the parts can be improved.

Further, since a low breakdown voltage diode is used for the diode of the snubber circuit, the cost can be reduced.

Further, if the DC / DC converter of the present invention is used for a motor drive having an input of about 400 V AC, the size and cost of the motor drive can be reduced and the reliability can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a motor driving apparatus using a DC / DC converter according to the present invention will be described with reference to the drawings, focusing on the DC / DC converter.

In FIG. 1, 1a and 1b are snubber resistors, 2a and 2b are snubber diodes, 3 is a snubber capacitor, 4 is a transformer, 5 is a MOS-FET, 6 is a rectifier circuit, 7 is an oscillation circuit, and 8 is a load. Is a motor control circuit, and 9 is a snubber circuit.

The motor driving device converts the AC voltage input by the rectifier circuit 6 into a DC voltage, generates a required voltage by the motor control circuit 8, and controls the inverter circuit.

The DC / DC converter is a MOS-FET
Switching is performed by 5 and the DC voltage charged in the rectifier circuit 6 is applied to the primary winding of the transformer 4 to generate a predetermined voltage in the secondary winding.

Further, when the MOS-FET 5 is switched off, the voltage between the drain and the source of the MOS-FET 5 jumps up temporarily, and the snubber circuit 9 of the present invention is provided in order to reduce this jumping voltage as much as possible.

That is, the jump voltage (energy)
Is absorbed by the snubber capacitor 3 through the snubber diodes 2a and 2b, and the energy charged in the snubber capacitor 3 is consumed by the snubber resistors 1a and 1b.

Also, when a high voltage is applied such that the input voltage, that is, the DC voltage applied to the primary winding of the transformer 4 exceeds DC 740 V, the jump voltage also increases, so that the snubber diodes 2a, 2b By installing a plurality of diodes in series, the reverse voltage applied to each diode can be divided, and snubber resistors 1a and 1b connected in parallel with each diode are used (shared) to maintain the divided voltage balance. are doing.

With this configuration, a low-loss diode that is low in cost and relatively inexpensive can be used, and the DC / DC converter and a motor driving device using the same can be downsized.
High efficiency and low cost can be achieved.

Further, as the jump voltage increases, the energy lost in the snubber diode and the snubber resistor also increases, so that the heat generation of each component increases.
By installing a plurality of such as the snubber diodes 2a and 2b and the snubber resistors 1a and 1b of the present invention, the heat generated by each component can be dispersed, and the reliability of the component can be improved.

[0026]

As is apparent from the above embodiment, according to the first aspect of the present invention, the reverse voltage applied to the diode of the snubber circuit can be suppressed within the withstand voltage level, and the voltage for balancing the divided voltage and the charging energy of the snubber capacitor can be reduced. A resistor can be shared for discharging, and the size and cost of the DC / DC converter can be reduced. Further, since the heat generated by the snubber circuit can be dispersed, the reliability of the components can be improved.

According to the second aspect of the present invention, the DC
Since a low breakdown voltage diode can be used for the / DC converter, the cost can be further reduced.

Further, according to the third and fourth aspects of the present invention, by using the DC / DC converter of the present invention,
The size, efficiency and cost of the motor drive device can be reduced. In particular, in the case of AC 400 V input, the effect is enormous, and the heat generation is dispersed, so that the reliability of the motor driving device can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a motor driving device including a DC / DC converter according to the present invention.

FIG. 2 is a circuit diagram of a motor drive device including a conventional DC / DC converter.

[Explanation of symbols]

 1a, 1b Resistor 2a, 2b Diode 3 Capacitor 4 Transformer 9 Snubber circuit

Claims (4)

[Claims] 1. A snubber circuit comprising a snubber circuit in which a capacitor and a plurality of diodes are connected in series with a primary winding of a transformer in parallel, and a resistor is connected in parallel to each of the diodes.
C / DC converter. 2. The DC / DC converter according to claim 1, wherein a low withstand voltage diode is used as the diode. 3. A motor driving device using the DC / DC converter according to claim 1. 4. The motor drive of claim 3 wherein the input is about 400 VAC.