Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-10-04
2001-11-27
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06324079
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to the field of power conversion and, more particularly, to switching power supplies with feedback control.
BACKGROUND
Compact and efficient power supplies are an increasing concern to users and manufacturers of electronics. Switching power supplies with pulse width modulated (“PWM”) controllers offer both compactness and efficiency in a number of different topologies. Boost and buck switching power supply topologies are efficient, but do not isolate the power input from the power output. Other topologies, such as the flyback, do isolate the power input from the power output by using a transformer. In such topologies, feedback from the secondary (power output) side of the transformer is needed to adjust the pulse width modulation duty cycle of the power switch. PWM control for a switching power supply may be provided from a single integrated circuit chip or package having some number of external connection pins or terminals. As with many other types of integrated circuit chips or packages, limiting the number of external connection terminals of a power supply package can be advantageous.
For example, U.S. Pat. No. 5,313,381 to Balakrishnan (the “'381 patent”), which is fully incorporated by reference, discloses a three-terminal switching power supply control chip for use with a flyback converter.
FIG. 1
illustrates a flyback converter
20
according to the '381 patent. The converter
20
employs a three-pin control chip
22
to supply current from a rectified DC source (V
bb
)
28
across an isolating transformer
24
to supply power for a load
26
. The power supply chip
22
includes a first terminal
30
coupled to a primary winding
32
of the transformer
24
, a second (“ground”) terminal
36
coupled to a primary side ground reference, and a third terminal
40
for accepting a combined feedback control signal (I
FB
) and a bias supply voltage (V
cc
) to operate the control chip
22
.
Within the power supply chip
22
, the first terminal
30
is alternately coupled to the ground terminal
36
by a power transistor switch
42
. PWM control circuitry
44
drives the power switch
42
at a variable duty cycle. When the power switch
42
is ON, current flows through the primary winding
32
and energy is stored in the magnetic core
45
of the transformer
24
. When the switch
42
is OFF, a secondary diode
46
is forward biased and the stored energy in the transformer core
45
is released through a secondary winding
48
to a filter/storage capacitor
47
and the load
26
. After the transformer
24
is reset, the ON/OFF cycle is repeated.
An error amplifier
50
compares the output voltage V
out
across the load
26
with a reference voltage to generate the feedback control signal I
FB
. The bias supply voltage V
cc
is supplied from an auxiliary secondary winding
52
of the transformer
24
. The bias supply voltage V
cc
is modulated with the feedback control signal I
FB
in an opto-isolator
54
to create the combined bias voltage, feedback signal V
cc
/I
FB
. A feedback extraction circuit (not shown) in the chip
22
separates the feedback signal I
FB
from the bias voltage V
cc
by sensing the excess current flowing through a shunt regulator. The extracted feedback signal I
FB
is used to control the output of the PWM circuitry
44
to constantly adjust the duty cycle of the power switch
42
so as to transfer greater or lesser current to the secondary.
While the flyback converter taught by the '381 patent provides certain advantages, it would be desirable to provide minimal terminal power supply packages for other types of converter topologies, including multi-switch controlled power converter topologies.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a power converter comprising a transformer having forward-biased and flyback-biased secondary windings is operated by a three terminal, PWM-controlled power supply package.
In a preferred embodiment, the power supply package has a first terminal coupled to a main primary winding of a transformer, a second terminal coupled to a ground reference and a third terminal connected to a combined source of operating power and feedback signal. The power supply package includes a power switch having an input coupled to the first terminal, an output coupled to the second terminal, and an activation gate. The package further includes PWM control circuitry responsive to the feedback signal and coupled to the power switch activation gate. A second primary winding is provided for resetting the transformer core.
In accordance with a further aspect of the invention, a four terminal, PWM-controlled power supply package for operating a power converter is provided.
In a preferred embodiment, the power supply package includes a first terminal for coupling to a primary winding of a transformer, a second terminal for coupling to an activation gate of an external power switch, a third terminal for coupling to a ground reference, and a fourth terminal for coupling to a combined source of operating power and feedback signal. The package includes an internal power switch having an input coupled to the first terminal, an output coupled to the third terminal, and an activation gate. The package further includes PWM control circuitry responsive to the feedback signal, the control circuitry including gate drive circuitry having a first output coupled to the internal switch activation gate and a second output coupled to the second terminal.
In an alternate preferred embodiment, the four terminal power supply package further includes a second internal power switch having an input coupled to the second terminal, an output coupled to the third terminal, and a second switch activation gate. In this embodiment, the gate drive circuitry has a first output coupled to the first internal switch activation gate and a second output coupled to the second internal switch activation gate.
In accordance with a still further aspect of the invention, a five terminal, PWM-controlled power supply package for operating a power converter is provided.
In a preferred embodiment, the power supply package includes a first terminal for coupling to a primary winding of a transformer, a second terminal for coupling to an activation gate of an external power switch, a third terminal for coupling to a ground reference, a fourth terminal for coupling to a source of operating power, and a fifth terminal for coupling to a feedback signal. The package includes an internal power switch having an input coupled to the first terminal, an output coupled to the third terminal, and an activation gate. The package further includes PWM control circuitry responsive to the feedback signal, the control circuitry including gate drive circuitry having a first output coupled to the internal power switch activation gate and a second output coupled to the second terminal.
In an alternate preferred embodiment, the five terminal power supply package further includes a second internal power switch having an input coupled to the second terminal, an output coupled to the third terminal, and a second switch activation gate. In this embodiment, the gate drive circuitry has a first output coupled to the first switch activation gate and a second output coupled to the second switch activation gate.
Other objects and features of the present inventions will become apparent hereinafter.
REFERENCES:
patent: 5014178 (1991-05-01), Balakrishnan
patent: 5313381 (1994-05-01), Balakrishnan
patent: 5973945 (1999-10-01), Balakrishnan et al.
patent: 6147883 (2000-11-01), Balakrishnan et al.
patent: 6169444 (2001-01-01), Thuber, Jr.
Collmeyer Arthur J.
Telefus Mark D.
Iwatt
Lyon & Lyon LLP
Nguyen Matthew
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