Electric power conversion systems – Current conversion – With means to connect the input to diverse power sources
Reexamination Certificate
2002-11-04
2004-05-18
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
With means to connect the input to diverse power sources
C363S052000
Reexamination Certificate
active
06738277
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to circuits and, more specifically, the present invention relates to circuits including series stacked capacitors.
2. Background Information
One function of a power converter is to convert rectified alternating current (AC) power into a regulated direct current (DC) output.
FIG. 1
shows elements included at an input
103
to a power converter
101
. Diode bridge BR
1
105
rectifies AC input. Series stacked capacitors C
1
107
and C
2
109
are coupled across diode bridge BR
1
105
to smooth the output voltage of diode bridge BR
1
105
. Series stacked capacitors are common in power supplies that can be configured to operate using multiple different input voltages such as for example either 115 VAC or 230 VAC. As shown, switch SW
1
111
is coupled between diode bridge BR
1
105
and the connection point
113
between series stacked capacitors C
1
107
and C
2
109
. When operating for example at 230 VAC, switch SW
1
111
is opened. When operating for example at 115 VAC, switch SW
1
111
is closed.
Resistors R
1
115
and R
2
117
are coupled across series stacked capacitors C
1
107
and C
2
109
as shown to maintain roughly equal voltages across C
1
107
and C
2
109
and provide the necessary bleed current needed to balance the voltage across series stacked capacitors C
1
107
and C
2
109
when the supply is configured for 230 VAC input. During 115 VAC operation, the two series stacked capacitors C
1
107
and C
2
109
function as part of an input voltage doubler circuit. When configured for 230 VAC, however, the two series stacked capacitors C
1
107
and C
2
109
have no DC connection to a center point voltage other than that which is provided by resistors R
1
115
and R
2
117
. Without resistors R
1
115
and R
2
117
, the center point voltage of the two series stacked capacitors C
1
107
and C
2
109
can deviate from the ideal ½ DC input due to capacitor leakage current, which can cause one capacitor to have more voltage stress than the other capacitor. In fact, it is possible that one of the capacitors can be over-voltage stressed and become damaged.
Resistors R
1
115
and R
2
117
therefore provide a solution to the balance problem by providing bleed current. The resistance values of R
1
115
and R
2
117
must be low enough to establish a bleed current that is several times higher than the worst case leakage current imbalance between the series stacked capacitors C
1
107
and C
2
109
in order to be effective. This requires the resistors to dissipate much more power than the actual power dissipated as a result the difference current between the two capacitors. Consequently, resistors R
1
115
and R
2
117
result in significant input power consumption with respect to many standby or output no-load requirements of a power supply converter coupled to receive the rectified AC power.
SUMMARY OF THE INVENTION
An active circuit that substantially reduces the bleed current required for balancing leakage current in series stacked capacitors is disclosed. This active circuit can also be designed to disconnect any bleed current when capacitors are configured for voltage doubler operation as bleed current is not necessary in this configuration. In one embodiment, the circuit is switched across a capacitor to provide bleed current as required to balance the leakage current. In one embodiment, the voltage at the connection point between two capacitors is bounded within a few volts of two reference voltages. In one embodiment, the bleed current is substantially equal to the difference in leakage current between two series stacked capacitors. In one embodiment, the active circuit includes a sink-source follower circuit. In one embodiment, a sink-source follower circuit includes inputs where each are referenced to voltages that are offset by a fraction of the voltage applied across the series stacked capacitors and the outputs of the sink-source follower circuits are coupled to the connection point between two series stacked capacitors. In one embodiment the offset is limited to a very low value and can be substantially zero. In one embodiment, the sink follower circuit includes a PNP bipolar transistor coupled to a source follower circuit, which includes an NPN bipolar transistor. In one embodiment, resistors are connected in series with the collector of each of the bipolar transistors to limit the peak current conducted by the bipolar transistors. In one embodiment, the active circuit is used in a power supply circuit
In another embodiment, a method of substantially reducing the bleed current required for balancing leakage current in series stacked capacitors utilizing an active circuit is disclosed. In one embodiment, the bleed current required is switched in as required to balance leakage current from the series stacked capacitors. In one embodiment, the bleed current from the active circuit is switched off and is substantially equal to zero when series stacked capacitors are configured for doubler operation. In one embodiment, the bleed current is substantially equal to a difference in leakage currents between two capacitors. In one embodiment, the active circuit includes a means to maintain an output voltage, connected to the connection point between two series stacked capacitors, relative to an input reference voltage. In one embodiment, the disclosed method is applied in a power supply circuit. Additional features and benefits of the present invention will become apparent from the detailed description and figures set forth below.
REFERENCES:
patent: 4783729 (1988-11-01), Konopka
patent: 5099407 (1992-03-01), Thorne
Blarkely,Sokoloff, Taylor & Zafman, LLP
Power Integrations, Inc.
Riley Shawn
LandOfFree
Method and apparatus for balancing active capacitor leakage... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for balancing active capacitor leakage..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for balancing active capacitor leakage... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3248152