Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-06-25
2003-01-21
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C307S402000, C363S089000
Reexamination Certificate
active
06510062
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to isolation-providing voltage converters having isolated input and output grounds, and more particularly to such voltage converters with isolated input and output grounds that employ an output-side pulse width modulator controller.
BACKGROUND OF THE INVENTION
Voltage converters receive an input voltage (Vin) that is AC in an AC:DC power converter, or DC in a DC:DC power supply, and generate one or more output voltages (Vo
1
, Vo
2
) therefrom. The output voltages may be greater than Vin or less than Vin, and may be AC or DC although commonly the converter output voltage Vo
1
, Vo
2
will be rectified. However, as used herein, in the broadest sense “voltage converter” can include an AC:AC converter, an AC:DC converter, a DC:DC converter, or a DC:AC converter, wherein each of the converter types provides isolation between input-side ground and output-side ground, and may be implemented using different topologies.
FIG. 1A
depicts a prior art isolation-providing voltage converter, here a DC:DC power converter
10
that converts an input voltage (Vin) to a rectified DC output voltage Vo
1
. A load (not shown) will be coupled between Vo
1
and output ground. Although
FIG. 1A
actually depicts generation of a single output Vo
1
, it is understood that more than one output voltage could be generated, and that each such output voltage could be of a different magnitude. System
10
could be an AC:DC power converter, in which case Vin would represent an input AC voltage after it has been rectified for presentation to converter
10
. System
10
could also be an AC:AC power converter or a DC:AC converter, in which case the output side lowpass filtering components may be omitted.
Converter
10
provides isolation in that there is an input side ground and an output side ground, with isolation between the two grounds. Converter
10
may thus be said to have a primary or input side
20
that receives operating potential Vin relative to an input-side ground. Converter
10
also has a secondary or output side
30
that outputs potential Vo
1
relative to a secondary-side ground.
In the exemplary topology of
FIG. 1A
, isolation between input side
20
and output side
30
is maintained by transformer T
1
and by an isolation mechanism I
1
. Transformer T
1
typically comprises at least one primary winding W
1
and at least one secondary winding W
2
, etc. from which raw output voltage is provided. Isolation mechanism I
1
may include optical transmitter-receiver pairs, sampled signal, transformed-coupled circuits and the like.
The input side of converter
10
includes a switch Q
1
coupled in series between an end of a primary transformer winding and input-side ground (or other input-side reference potential). While
FIG. 1A
depicts switch Q
1
coupled in series between W
1
and ground, it is understood that the roles of Vin and ground could be reversed, e.g., Q
1
could instead be coupled between the Vin node and winding W
1
. If additional primary side windings are present, each such winding will have a switch such as Q
1
, also coupled between an end of the winding and input side ground (or other input-side reference potential, perhaps Vin).
In a fashion well known to those skilled in the relevant art, each switch Q
1
opens and closes in response to a drive signal from a drive circuit
50
. Drive circuit
50
functions in response to input from a pulse width modulator (PWM) circuit
60
, which itself operates preferably in response to feedback
70
from the generated output-side voltage(s), here Vo
1
. Typically the output side of system
10
will compare Vo
1
to a stable reference voltage derived from Vo
1
and generate a correction signal to PWM
60
, which correction signal is represented by feedback loop
70
. When circuit
50
outputs a drive signal causing Q
1
to turn-on, Q
1
closes and Vin is impressed across the input or primary transformer winding W
1
, and essentially Vin is sampled or chopped. The resultant chopped signal is inductively coupled via transformer T
1
to the secondary transformer winding W
2
.
With the specific topology shown in
FIG. 1A
, on the output side, diode D
1
and lowpass filter L
1
-C
1
rectify and filter the signal to yield an output DC voltage, Vo
1
. (Of course other output side topologies and/or rectification configurations could instead be used.)
The magnitude of Vo
1
may be altered by changing duty cycle of the drive signal provided by circuit
50
to switch Q
1
, which is to say by pulse width modulating the drive signal output from circuit
50
. In the configuration shown, drive signal PWM changes are responsive to a signal or signals from PWM
60
in response to a feedback signal via feedback path
70
. As a result, circuit
50
can make compensating changes in the drive signal delivered to the input of switch Q
1
. For example, if the load or other factors cause Vo
1
to decrease, feedback via path
70
can cause PWM circuit
60
to drive circuit
50
to increase duty cycle of the drive signal to switch Q
1
to increase magnitude of Vo
1
.
In
FIG. 1A
, driver circuit
50
and PWM circuit
60
are referenced to the input side of converter
10
, which is to say these circuits are directly coupled to input-side ground. A practical consideration for circuit
50
and PWM circuit
60
is establishing a bias operating potential, Vbias, to ensure that these circuits can operate as soon as Vin is provided to converter
10
. For the input side configuration shown in
FIG. 1A
, providing bias voltage is straightforward. Among other techniques, Vbias may be directly derived from Vin, for example using a circuit
40
comprising Zener diode Vz, current-limiting resistor R
1
, and filter capacitor C
1
. Another approach is to obtain a bias potential from a primary winding on T
1
, which Vbias approach is suggested by a phantom line in FIG.
1
A. Generating input-side Vbias is relatively straightforward for the topology of
FIG. 1
because Vin, drive circuit
50
, and PWM
60
are each referenced to input-side ground.
But although providing an input-side referenced control circuit
50
and PWM circuit
60
enables a simplified Vbias biasing circuit to be used, it is necessary to include an isolation mechanism I
1
to isolate the output-side ground signals from the input-side grounded PWM circuit
60
. In addition to adding implementation cost and bulk to system
10
, isolation components (e.g., optical transmitter-receiver pairs, transformed-coupled circuits and the like) tend to reduce useful feedback bandwidth. By way of example, optical transmitter-receiver pairs used for I
1
tend to limit feedback bandwidth of loop
70
to perhaps 5 KHz. Understandably large feedback bandwidth is desired to ensure a more rapid correction of Vo
1
, preferably at least 20 KHz.
System
10
in
FIG. 1B
is somewhat similar to what was shown in
FIG. 1A
except that pulse width modulation circuit
60
is now referenced to the output-side of voltage converter
10
. In this configuration, advantageously no isolation components are required between Vo
1
and the input to PWM circuit
60
as the PWM circuit is also now referenced to output-side ground. The absence of isolating elements between Vo
1
, and PWM
60
can maintain a high feedback bandwidth. Unfortunately, however, it is now necessary to provide isolation I
1
, I
2
between the output of PWM circuit
60
and the input to drive circuit
50
, since the input components are referenced to input-side ground. As a result, providing Vbias to PWM circuit
60
is complicated by the necessity to include isolation, shown here as I
2
. Isolation I
2
typically is implemented with a chopper switch (indicated as Q
2
) and an AC-coupled isolating transformer and output-side rectifier. Isolation I
1
may be similarly implemented, or may instead use optical isolating devices. A practical consideration in implementing I
2
is the necessity to comply with U.L. isolation requirements, as I
2
spans between the input-side ground and the output-side ground portions of v
Cartier Steven
Goder Dimitry
Dorsey & Whitney LLP
Patel Rajnikant B.
Switch Power, Inc.
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