Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1997-05-08
1998-12-01
Wong, Peter S.
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363 17, 363 20, 323222, 323282, H02M 3335, G05F 1613
Patent
active
058447865
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a DC--DC converter circuit and an inductive load driver using this DC--DC converter circuit; in particular, it relates to an inductive load driver using a DC--DC converter circuit to ensure a good rise characteristic of the load current by applying a voltage that is stepped up on commencement of drive of the inductive load driver.
BACKGROUND ART
In general, in order to operate an electromagnetic actuator such as a solenoid valve at high speed, it is necessary to achieve rapid rise of the exciting current, overcoming the inductance.
The transfer function G(S) of the exciting current I with respect to the applied voltage E when the internal resistance of the coil is R and its inductance is L is known to be: immediately after application of voltage E in the condition where I=0 is E/L, while the steady current is E/R; it is known that first-order delay of time-constant L/R is produced.
Consequently, in order to achieve fast operation with a rapid rise in current in a coil of fixed R and L, it is necessary to employ a large applied voltage E. However, when the applied voltage is increased, the steady current also becomes larger than necessary, causing heat to be generated in the coil, which tends to cause burn-out or results in increased size of the device or waste of energy. Also, in the case of machines in for example a moving vehicle that are powered by a battery mounted in the vehicle, the voltage that can be applied is limited, so often sufficient voltage is not obtained.
In order to solve this problem, a voltage step-up circuit (e.g. a flyback DC--DC converter) for raising the voltage applied to the coil and a current control circuit for controlling the steady current have been provided, so as to achieve rapid increase of the current by applying high voltage on current rise, and preventing increase of the current by more than is necessary by using the current control circuit to suppress the applied voltage when the current reaches a prescribed value.
FIG. 31 shows an example of a conventional inductive load driver using a DC--DC converter of the flyback type as voltage step-up circuit. In this figure, 1 is a charger circuit comprising a flyback-type DC--DC converter.
One of the problems in using a flyback-type DC--DC converter as a voltage step-up circuit is the problem of efficiency and increased size of the device. Conventionally, a choke coil or transformer were often used as the inductance of the charger circuit in order to accumulate energy, but these suffered from the problem that they increased the size of the device and lowered the efficiency of the circuit.
In particular, in applications in which accumulation and discharge of energy to the coil is repeated at a high rate, as for example in a flyback type DC--DC converter or voltage step-up chopper, a semiconductor switch was employed as the switching means for accumulating the energy in the coil. However, the efficiency of the circuit was adversely affected by losses produced by the voltage drop on closure of this semiconductor switching means and switching losses in the opening/closing process. Furthermore, in addition to the volume of the ancillary devices needed to dissipate the heat generated by the device due to power loss in this semiconductor switching means, and the volume of the coils or transformer for the accumulation of this energy, the device as a whole tended to become larger and more complicated.
Also, in a DC--DC converter circuit as described above such as is currently being used for power supply to electronic devices, the effects on reliability of the device as a whole of ripple of the power source current consumed by the circuit present a problem.
The present invention is characterized in that, in a DC--DC converter circuit using a coil or transformer provided with a magnetic core in which a process is repeated whereby energy is introduced into the core from a power source and once energy has been accumulated in the core, the energy accumulated in the core is discharged to a
REFERENCES:
patent: 3771040 (1973-11-01), Fletcher et al.
patent: 4346340 (1982-08-01), Hackett-Jones
patent: 4675797 (1987-06-01), Vinciarelli
patent: 4720667 (1988-01-01), Lee et al.
International Search Report in PCT/JP95/02309 mailed Mar.5, 1996.
English translation of First Office Action in Peoples Republic of China No. 95196140.3, issued Mar. 26, 1998.
Hagiwara Masao
Kawaji Yasushi
Yoshida Daisuke
Komatsu Ltd.
Patel Rajnikant B.
Wong Peter S.
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