DC-to-DC converter

Details DC-to-DC converter DC-to-DC converter

2002-10-30

2004-08-17

Berhane, Adolf (Department: 2838)

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

C363S097000

Reexamination Certificate

active

06778410

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a power converter. In particular, the present invention relates to a DC-to-DC converter with high efficiency and power density.
2. Description of the Related Art
FIG. 1
shows a resonant reset dual switch forward DC-to-DC converter. In the converter
10
, a switch Q
101
turns on to divide the DC input voltage into square wave voltage according to a predetermined duty ratio. The square wave voltage is then transformed to secondary winding of the transformer T
101
, and is rectified into a DC voltage to output to load by a rectifying device composed of an inductor L
101
and a capacitor C
101
. The converter needs a large input rectifying device and an output rectifying device because the converter has a non-continuous input current and a large output voltage ripple.
Consequently, the size and cost of the converter may increase. In addition, the transformer T
101
is reset by the inductor L
101
and the capacitor C
101
such that the voltage stress of the switch Q
101
is very high, and also has high electromagnetic interference (EMI) because the converter Q
101
usually operates in a hard switching condition.
FIG. 2
shows a DC-to-DC converter
20
with a synchronous rectifying resonant reset forward circuit. The converter
10
shown in
FIG. 1
may have a low power efficiency due to consumption of diodes D
101
and D
102
when the converter
10
is applied to low input voltage, for example below 12 volts. As shown in
FIG. 2
, the diodes D
101
and D
102
of the converter
20
are replaced by synchronous rectifiers Q
102
and Q
103
to increase power efficiency. The synchronous rectifiers Q
102
and Q
103
are driven by the induced voltage across the secondary winding N
102
of the transformer T
101
.
FIG. 3
illustrates the key operating waveform of the converter
20
shown in FIG.
2
. As shown in
FIG. 3
, the first synchronous rectifier Q
102
is always turned on when the switch Q
101
is turned on (t1 to t2), and the synchronous effect is ideal. The second synchronous rectifier Q
103
, however, is not turned on when the switch Q
101
is turned off (t3 to t4), thus the synchronous effect is less than ideal. This problem may affect whole efficiency of the converter
20
when the converter is applied to low output voltage. Although the converter
20
has a simple structure, the synchronous effect is not ideal, and the input current ripple and the output voltage ripple are high. Thus, the converter
20
also needs a large rectifier.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a novel and improved DC-to-DC converter that can overcome the above-mentioned disadvantages of the related art.
In the present invention, the converter has three inductors, two capacitors, a first switch and a second switch, a first rectifier and a second rectifier, and a transformer with a primary winding and a secondary winding.
The first switch and the second switch are turned on alternately according to a controlling signal, and a current may flow through the primary winding of the transformer thereby transferring energy to the second winding. The first rectifier and the second rectifier operate according to the energy transferred from the primary winding to obtain a solid current through the third inductor, and a solid DC output voltage is output to the load.


REFERENCES:
patent: 4025863 (1977-05-01), Higuchi et al.
patent: 4553199 (1985-11-01), Harada et al.
patent: 4823249 (1989-04-01), Garcia, II
patent: 6064580 (2000-05-01), Watanabe et al.
patent: 6426884 (2002-07-01), Sun
patent: 6618274 (2003-09-01), Boylan et al.

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