Electricity: power supply or regulation systems – Output level responsive – Using a transformer or inductor as the final control device
Reexamination Certificate
2000-11-02
2002-10-29
Vu, Bao Q. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a transformer or inductor as the final control device
C323S261000, C323S232000, C363S056010
Reexamination Certificate
active
06472852
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a resonant buck-type voltage converter which employs a swinging inductance to achieve zero-current switching.
BACKGROUND OF THE INVENTION
A basic buck-type converter configuration is shown in FIG.
1
A and is designated by the general reference character
100
. The input source
122
is the primary supply with its positive terminal connected to node
102
and its negative terminal connected to the common ground reference node
120
. Switch
104
is connected between node
102
and Phase node
106
. The anode of diode
110
is connected to the common ground node
120
and its cathode is connected to Phase node
106
. Output filter
108
is comprised of inductor
116
and capacitor
118
. The output filter
108
input node is the inductor
116
first terminal and it also is connected to Phase node
106
. The output filter
108
output node is connected to the buck converter
100
output terminal
112
and also to the first terminal of capacitor
118
and to the second terminal of inductor
116
. The second terminal of capacitor
118
is connected to the common ground node
120
. The load circuit
114
is connected between the output terminal
112
and the common ground node
120
. Note that, for consistency and clarity, the same identification numbers are generally used throughout this description where the same elements are used in different embodiments.
The basic buck-type converter operates to transfer energy from the input source
122
to the output load
114
based on the state of switch
104
.
FIG. 1B
shows the basic operation of the converter configuration of
FIG. 1A
with the voltage at the Phase node, VPhase, shown as waveform
130
. When switch
104
is closed, i.e., in the on-state, VPhase is equal to Vin as energy is drawn from input source
122
. When switch
104
is open, i.e., in the off-state, the current draw from the input source
122
is stopped, but the load
114
may continue to draw current from the Phase node
106
through the output filter
108
and the diode
110
. This is shown in
FIG. 1B
as the high-to-low portion of waveform
130
. The output voltage, Vout, is the average value, as indicated.
The switch
104
on-state time versus its off-state time is controlled by a Pulse Width Modulation (PWM) circuit that is not shown in
FIG. 1A
, but is common and well known in the art. The duty cycle of the PWM waveform, as shown and indicated in
FIG. 1B
, is close to 50%. This duty cycle is actually a function of the ratio of the output voltage, Vout, versus the input voltage, Vin. Where this ratio is relatively high, indicating that Vout is relatively close to Vin, the PWM waveform must have a relatively high duty cycle so that the switch
104
on-state time is greater than its off-state time. This allows more time for energy transfer from the input source. Where this ratio is relatively low, indicating that Vout is much less than Vin, the PWM waveform must have a relatively low duty cycle so that the switch
104
on-state time is much less than its off-state time. In this case, commutation losses can become significant—up to about 30% of the power flowing through the converter. Next generation microprocessors and highly integrated circuitry will operate at 1.3 volts or less and at currents of 45 amperes or more. In order to avoid having these extremely large currents on the backplanes of computer systems, primary power supply voltages will be larger than 1.3 volts, such as 5 volts or 12 volts, or possibly more in the future. Thus, the application trends are to supply lower output voltages from higher primary supplies, further exacerbating this potential commutation loss problem.
The commutation losses at such relatively high voltages lead to relatively large losses in electrical efficiency. Designers, at the same time, want to be able to operate the voltage converters at higher frequencies, e.g., 1 or 2 megahertz or more instead of 200 or 300 KHz as is presently the case. Increasing the number of commutations taking place within a given period of time like this will inevitably lead to higher losses. The desire, therefore, is to eliminate the commutation losses. This can be done by using resonant techniques to force the commutation to occur at a zero current point. With this realized, the efficiency can be raised to the 90% level, resulting in roughly ⅓ of the previous losses. Consequently, less power is thermally lost and the physical size of the voltage converter can therefore be made smaller. The voltage converters can then operate at higher frequencies without any thermal loss/efficiency penalty.
FIG. 2A
shows a schematic diagram of a buck-type converter designated by the general reference character
150
and intended to take advantage of the resonant techniques discussed above. It is a modification of the circuit shown in FIG.
1
A and the differences will be discussed herein. A resonant capacitor
156
is added with its first terminal connected to Phase node
106
and its second terminal connected to the common ground node
120
. This capacitor provides a relatively soft dv/dt on Phase node
106
. Switching element
126
is shown in its more common actual implementation as an n-channel MOS transistor device (NMOS). Any switching element could be used here, such as other types of transistors, including bipolar devices or isolated gate bipolar transistors (IGBTs). The switch
126
includes transistor
160
and parasitic diode
158
. The transistor
160
source terminal is connected to node
152
, its drain terminal is connected to node
102
and its gate terminal is connected to node
124
. Node
124
receives the output of the PWM switch control circuit that is not shown, but is described above. In a series connection with transistor
160
, the first terminal of inductor
154
is connected to node
152
and its second terminal is connected to Phase node
106
. The inductance
154
may, with equal effect, be located on the other side of switch
126
, i.e., between node
102
and switch
126
. While the goal of this circuit is to switch at zero current to minimize the associated commutation losses, the current actually rings back to negative values and charge is sent back to the input source. The waveforms illustrating only one cycle of the cyclical operation of the circuit of
FIG. 2A
are shown in FIG.
3
A. In
FIG. 3A
, waveform
240
shows the Iin current and the waveform is mapped through time point designations t
0
, tr, and t
1
to the waveform
242
that shows the VPhase voltage. The switch-on time is from t
0
through t
1
and tr represents the resonant time point.
One way to block the negative part of the current waveform shown in
FIG. 3A
is to add a diode or a second transistor back-to-back with the switch transistor accepting the PWM signal of the circuit of FIG.
2
A.
FIG. 2B
shows a schematic diagram of a buck-type converter designated by the general reference character
200
where block
210
effectively replaces switch
126
of FIG.
2
A. In block
210
, the switch
222
includes transistor
218
and parasitic diode
220
. The transistor
218
source terminal is connected to node
202
, its drain terminal is connected to node
214
, which is also the positive terminal connection for input source
122
, and its gate terminal is connected to node
212
. Node
212
accepts the PWM signal for energy transfer control, as discussed above. The second element in block
210
, sub-block
208
, primarily performs a diode function to disallow negative current flow, but includes transistor
204
as well as parasitic diode
206
. Of course, any diode, one-way switching element, or appropriate transistor, such as a bipolar transistor or IGBT, could be used here instead of the NMOS transistor including a parasitic diode, as shown. The transistor
204
source terminal is connected to node
202
, its drain terminal is connected to node
216
, and its gate terminal is connected to node
212
to also receive the PWM signal for energy transfer control. The waveforms illustrating only one cycle
Ritchie David B.
Semtech Corporation
Thelen Reid & Priest LLP
Vu Bao Q.
LandOfFree
Resonant buck-type voltage converter using swinging inductance does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resonant buck-type voltage converter using swinging inductance, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resonant buck-type voltage converter using swinging inductance will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2996081