NASA Technical Reports Server (NTRS) 19930009089: Cascaded transformerless DC-DC voltage amplifier with optically isolated switching devices

6 Pages·0.43 MB·English

by  NASA Technical Reports Server (NTRS)

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US005 179289A
United States Patent 1191 [I I] Patent Number: 5,179,289
Sridharan [45] Date of Patent: Jan. 12, 1993
[54] CASCADED TRANSFORMERLESS DC-DC Primary Examiner-William H. Beha, Jr.
VOLTAGE AMPLIFIER WITH OPTICALLY Attorney, Agenf, or Firm-John H. Kusmiss; Thomas H.
ISOLATED SWITCHING DEVICES Jones; Guy M. Miller
[75] Inventor: Govind Sridharan, Bangalore, India
[571 ABSTRAn
[73] Assignee: The United States of America as
A very high voltage amplifier in which plural cascaded
represented by the Administrator of
banks of capacitors are switched by optically isolated
the National Aeronautics and Space
control switches so as to be charged in parallel from the
Administration, Washington, D.C.
preceding stage or capacitor bank and to discharge in
[21] Appl. No.: 791,759 series to the succeeding stage or capacitor bank in alter-
[22] Filed: Oct. 22, 1991 nating control cycles. The optically isolated control
switches are controlled by a logic controller whose
[51] Int. (3.5 .............................................. H02M 3/07 power supply is virtually immune to interference from
[52] U.S. C1. ....................................... 307/110; 363/60 the very high voltage output of the amplifier by the
[58] Field of Search ..................... 307A 10; 363/60, 62 optical isolation provided by the switches, so that a
[561 References Cited very high voltage amplification ratio may be attained
using many capacitor banks in cascade.
U.S. PATENT DOCUMENTS
2,631,249 3/1953 Smith .
4.900,947 2/1990 Weiner et al. ...................... 307/110 3 Claims, 2 Drawing Sheets
El
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12J CONTROL SIGNALS
107
S TO T’S AND S’S
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US,P atent 5,179,289
Jan. 12, 1993 Sheet 1 of 2
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U.S. Patent 5,179,289
Jan. 12, 1993 Sheet 2 of 2
CONTROL
INPUT TO
r ;'s
0 2 4 6 8 10 t (ms)
FIG. 2a
CONTROL
INPUT TO
I 1 I I I I I I I +
CONTROL SIGNAL TIMING DIAGRAM
FIG. 2 b
IN
FIG. 3
5.179,289
1 2
invention to achieve the foregoing without undue leak-
CASCADED TRANSFORMERLESS DC-DC age of the high voltage back to the power supply
VOLTAGE AMPLIFIER WITH OPTICALLY through the switching network. It is a further object of
ISOLATED SWITCHING DEVICES the invention to achieve a large voltage gain ratio in
5 such a device without a corresponding increase in the
BACKGROUND OF THE INVENTION number of capacitors required to be switched.
1. Technical Field
DISCLOSURE OF THE INVENTION
The invention is related to transformerless DC-DC
power converters and in particular to transformerless In the invention, two or more independently charged
DC-DC voltage amplifiers having a large voltage gain 10 plural banks of capacitors are controlled by optoelec-
ratio. tronic or optically isolated switching devices, rather
2. Background Art than conventional switching devices such as field affect
DC-DC power converters are well-known in the art. transistors or the iike. The first bank of capacitors are
Typically, in order to raise a voltage level of a power connected in parallel by the optoelectronic switching
supply, a bank of capacitors are each charged in parallel 15 devices to an input voltage for a predetermined period
with the supply voltage and are then discharged in of time. The optoelectronic switching devices then
series to a load. This technique is disclosed in U.S. Pat. connect the first bank of capacitors in series to the sec-
No. 4,654,769, for example. Such a device operates in ond bank of capacitors. The second bank of capacitors
two phases, a first phase during which all the capacitors is controlled by its own set of optoelectronic switching
are charged in parallel while being connected to the 20 devices, which at this time connect each of the capaci-
supply voltage, and a second phase in which the capaci- tors in the second bank in parallel across the boosted
tors are disconnected from the supply voltage and are voltage provided by the now series-connected capaci-
connected together in series across the load. The volt- tors of the first bank. After a predetermined amount of
age increase ratio is equal to the number of capacitors. time, the capacitors in the second bank have been
The foregoing concept is also disclosed in U.S. Pat. 25 charged to the boosted voltage level provided by the
No.’s 3,818,309; 4,460,952; 4,321,661; and 4,047,091. In first bank of capacitors. The optoelectronic switching
one variation of this technique, several banks of capaci-
device controlling the second bank of capacitors then
tors are charged separately and then all of the capaci-
disconnects these capacitors from the first bank and
tors are discharged across the load simultaneously, as
connects them in series across an output load or a suc-
disclosed in US.P at. No. 3,579,074. All of the forego- 30
cessive bank of capacitors which is operated in similar
ing disclose multiplying the voltage by a factor N equal
fashion.
to the number of capacitors.
The voltage gain ratio achieved in the invention is
A voltage divider may be constructed in a similar
equal to the product of the number of capacitors in the
manner by reversing the operation, or in other words
first bank and the number of capacitors in the second
charging the capacitors in parallel across the supply and 35
bank. In a tested embodiment of the invention, the first
discharging them in series across the load, as disclosed
bank had 5 capacitors and the second bank had 8 capaci-
in U.S. Pat. No. 3,505,586. As another example of a
tors, and the overall voltage gain was a factor of 40.
voltage divider circuit, the dividing ratio is increased by
In this tested embodiment, the output of a 90 volt
cascading successive stages of capacitor pairs. Each
radio battery was boosted to 3,600 volts dc. The opto-
capacitor pair is charged in series by the preceding 40
electronic control switches were controlled by a 5 volt
stage of a capacitor pair and then is discharged in paral-
lel to the succeeding stage of a capacitor pair, as dis- power supply. Such a large boosted output voltage
closed in U.S. Pat. No. 3,863,135. In this technique, N (several kilovolts) would not be possible using conven-
stages of capacitor pairs provides a voltage reduction of tional integrated circuit components because of the
2.v. 45 tendency of such a large voltage to couple through the
The present invention is concerned with problems in conventional switching elements to the control power
high voltage amplification in a DC-DC power con- supply, making it impossible to operate the switches
verter. The problem with the prior art technique of properly so that the device would work. However, in
increasing a voltage using a bank of capacitors is that accordance with the present invention, a voltage multi-
the voltage gain is necessarily limited by a tendency of 50 plication is achieved without harmful affects from high
high voltages to couple through and thereby paralyze voltage leakage back to the control circuit power sup-
the secondary control switching network which regu- ply, thereby permitting a large voltage multiplication
lates the operation of the capacitor bank. Accordingly, ratic to be achieved.
devices which increase the voltage by charging the Another advantage of the invention is that the volt-
capacitors in parallel and discharging them in series 55 age multiplication ratio does not require a correspond-
across the load necessarily were limited in the ratio by ing number of capacitors. Because each bank of capaci-
which the voltage could be raised. Thus, a single bank tors charges a successive bank, the ratio is the product
of capacitors of limited size sufficed to perform a neces- of the numbers of capacitors in the successive banks of
sarily limited voltage increase function. Because of the capacitors, a significant advantage.
tendency of a voltage which has been boosted by sev- 60
DESCRIPTION OF THE DRAWINGS
eral factors of ten to leak or couple through the switch-
ing network controlling the capacitors to the supply, it FIG. 1 is a simplified schematic diagram of a DC-DC
does not seem possible to achieve a large vc!tage gain power converter embodying the invention.
and a DC-DC power converter. FIG.’s 20 and 2b are contemporaneous timing dia-
Accordingly, it is the object of the present invention 65 grams of the control signals employed in the embodi-
to provide a DC-DC power converter which amplifies ment of FIG. 1.
the voltage with far higher gains than heretofore ac- FIG. 3 is a block diagram illustrating the embodiment
complished in the prior art. It is a further object of the of the invention employing several stages.
5.179,289
3 4
gate of a field effect transistor controlling the conduc-
MODES FOR CARRYING OUT THE
tance between the electrical terminals of the optoelec-
INVENTION
tronic switch. As illustrated in FIG.’s 2a and 26, the
Referring to FIG. 1, the voltage amplifier of the control signals generated on the controller outputs S
invention includes a first bank of capacitors C1 through 5 and R swing between 0 volts and 5 volts dc. Each con-
C5 and a second bank of capacitors C6 through C13. A trol signal is a series of square waves of period 8 ms and
set of optically isolated or optoelectronic switches si duration 3 ms. The square wave outputs R and S of the
~
through si0 connects respective ones of the capacitors controller 10 are 180 degrees out of phase. As a result,
C1 through C5 in the first bank in parallel to two input during a first control cycle of the controller 10, each of
terminals at an input voltage V;. Another set of optically 10 the optoelectronic switching devices si through si9 is
isolated or optoelectronic switching devices rl through rendered conductive between its two electrical termi-
r4 connects the capacitors C1 through C5 of the first nals while each of the optoelectronic switching devices ~
bank in series to two intermediate terminals at an inter- rl through r1g is rendered nonconductive between its
mediate voltage V’;. two electrical terminals. Accordingly, the first bank of
Optically isolated or optoelectronic switches r5 15 capacitors C1 through C5 are each connected in parallel
through r20 connect the capacitors c6t hrough C13 in across the input voltage V; while the second bank of
parallel across the two intermediate terminals at the capacitors c6 through C13 are disconnected from the
intermediate voltage V’;. Optically isolated or optoelec- first bank and are connected in series together across
tronic switches si 1 through si9 connect the capacitors the output Vo. During the other control cycle of the
c6t hrough C13 of the second bank in series across an 20 controller 10, the optoelectronic switches si through
output terminal pair at an output voltage Vo. si9 are nonconductive across their electrical terminals
An optoelectronic switch controller 10 changes each while the optoelectronic switches rl through r19 are
of the optoelectronic switches s1 through s19 and rl conductive across their electrical terminals. Accord-
through r19 between ON and OFF states. Each of the ingly, the first bank of capacitors C1 through C5 are
optoelectronic switches is a three terminal device, two 25 connected in series across the intermediate port V’,
of the terminals comprising electrical current paths while the second bank of capacitors c.5 through c13 are
connected to corresponding ones of the capacitors C1 each connected in parallel across the intermediate ter-
through C13 and a third terminal comprising control minals at the intermediate voltage V‘i. At the same time,
input connected to an output of the controller 10. The S the first bank of capacitors is disconnected from its
output of the controller 10 is connected to the control 30 input terminal pair at the input voltage VI, while the
inputs of all of the optoelectronic switches s1 through second bank of capacitors is disconnected from the
S19 by a conductor network 12. The R output of the output terminal pair at the output voltage Vo.
controller 10 is connected to the control inputs of each In operation, during the first control cycle, the first
of the optoelectronic switches rl through r19 by a con- bank of capacitors C1 through C5 are each charged to
ductor network 14. 35 the input voltage VI, while the second bank of capaci-
While the embodiment of FIG. 1 has been described tors c6 through C13 are discharged in series across the
in connection with the controller which outputs electri- output terminal pair at the output voltage Vo. During
cal control signals to optoelectronic switches which the other control cycle, the first bank of capacitors C1
convert these electrical control signals internally to through C5 discharge in series across the intermediate
optical signals which are then reconverted back inter- 40 terminal pair at the intermediate voltage V’;, so that the
nally andapplied as electrical signals to the gates of intermediate voltage V’j is equal to five times the input
field effect transistors, the invention instead may use voltage VI. Simultaneously, each of the capacitors in
different optoelectronic devices whose control inputs the second bank c6 through C13 is charged to the inter-
are optical rather than electrical. In this alternative mediate voltage V‘; = 5 Vi. Then, during the next con-
embodiment, the conductor networks 12 and 14 are 45 trol cycle, the original configuration is repeated, so that
fiber optic networks, and the controller 10 generates the capacitors in the second bank C6 through C13 are
optical signals at its outputs R and S rather than electri- discharged in series across the output terminal pair to
cal signals, the optical signals having the same wave produce the output voltage Vo. The output voltage is
forms as those illustrated in FIG.’s 20 and 2b. VO=8 XV’j=8 X 5 XVi.
Each of the optoelectronic switches s1 through S19 50 One important feature of the invention is that the
and rl through r19 is of the type commercially available optoelectronic switches r5 and r6 (between the first and
through a large number of well-known suppliers. Each second banks of capacitors) are required to have five
of these switches has attributes which are well-known times the voltage capacity of the switches si and s2
in the prior art, need not be described in further detail connecting the first bank of capacitors to the input
herein. 55 voltage V,. Likewise, the optoelectronic switches s1g
The controller 10 receives its power from a 5 volt and si9 at the output Vo must have eight times the volt-
logic power supply 16. The controller 10 is of the type age capacity of the switches r5 and r6, or forty times the
well-known in the art and generates the control signals voltage capacity of the switches s1 and s2. Thus, the
on its outputs R and S illustrated in FIG.% 20 and 2b, switches in each of the stages are required to have pro-
respectively. The control signal on the R output of the 60 gressively higher voltage capacities or isolation capabil-
controller 10 is applied to the control inputs of each of ity.
the optoelectronic switching devices rl through rig, While the embodiment of FIG. 2 is disclosed as hav-
while the control signal on the S output of the control- ing five capacitors in the first bank and eight capacitors
ler 10 is applied to the control input of each of the in the second bank, actually any number of capacitors
optoelectronic switching devices si through S19. 65 could be used in each of the two banks, depending upon
Within each optoelectronic switching device rl the optical electrical isolation capability of the switches
through r19, the control input (as indicated by an incom- employed. Moreover, more than two cascaded banks of
ing arrow head in FIG. 1) is optically coupled to the capacitors may be employed. For example, referring to
5,179,289
5 6
FIG. 3, a succession of many capacitor banks identical switches, whereby during said first control cycle
to the two capacitor banks illustrated in FIG. 1 may be said first bank of capacitors are connected in paral-
connected in cascade as illustrated in FIG. 3. The con- lel across said pair of input terminals and said sec-
troller 10 generates the same control signals S and R as ond bank of capacitors are connected in series
discussed above. In the embodiment of FIG. 3, the 5 across said pair of output terminals and during said
optoelectronic switches employed in the “downstream” second control cycle said first bank of capacitors
stages must have proportionately higher voltage isola- are connected in series across each of said capaci-
tion capacities than those employed in the beginning tors of said second bank, wherein at least some of
stages, as discussed above. the optically isolating switches of said first and
While the invention has been described in detail by lo second sets of optically isolating switches which
specific reference to preferred embodiments thereof,
are connected to the capacitors in said first bank
variations and modifications may be made without de-
are characterized by a voltage isolation capacity
parting from the true spirit in scope of the invention.
corresponding at least to a voltage present at said
What is claimed is:
pair of input terminals multiplied by the number of
1. A DC-DC voltage amplifier, comprising: l5 capacitors in said first bank of capacitors, and
first and second banks of capacitors;
wherein at least some of said optically isolating
a first set of optically isolating switches, each of said
switches in said first and second sets of optically
first set of optically isolating switches comprising a
isolating switches which are connected to the ca-
pair of electrical terminals and a control terminal
pacitors in said second bank of capacitors are char-
optically isolated from said electrical terminals, 2o
acterized by a voltage isolation capacity corre-
said first set of optically isolating switches compris-
sponding at least to the voltage of said pair of input
ing means for connecting the capacitors of said first
terminals multiplied by the number of capacitors in
bank of capacitors in parallel across a pair of input
said first bank of capacitors multiplied by the num-
terminals and for connecting the capacitors in said
ber of capacitors in said second bank of capacitors.
second bank of capacitors in series across a pair of 25
2. The apparatus of claim 1 further comprising a third
output terminals;
bank of capacitors, wherein said first set of optically
a second set of optically isolating switches, each of
isolating switches comprises means for connecting the
said second set of optically isolating switches com-
capacitors in said third bank of capacitors in parallel
prising a pair of electrical terminals and a control
terminal optically isolated from said electrical ter- 3o across said pair of output terminals and said second set
of optically isolating switches comprises means for con-
minals, said second set of optically isolating
switches comprising means for connecting said necting said capacitors in said third bank of capacitors
capacitors of said first bank of capacitors in series in series across a pair of second output terminals,
across a pair of intermediate terminals and for con- whereby to generate a voltage at said second pair of
necting the capacitors in said second bank of capac- 35 output terminals equal to the voltage of said pair of
itors in parallel across said intermediate pair of input terminals multiplied by the number of capacitors
terminals: and in said first bank multiplied by the number of capacitors
a controller having first and second controller out- in said second bank multiplied by the number of capaci-
puts and comprising means for transmitting first tors of said third bank.
and second control signals on said first and second 40 3. The apparatus of claim 1 wherein said means for
control outputs respectively, said first and second connecting said control outputs to the control inputs of
control signals defining first and second control said optically isolating switching devices comprise first
cycles of said controller, said first controller output and second fiber optic networks corresponding to said
being connected to the control inputs of said first first and second sets of optically isolating switching
set of optically isolating switches and said second 45 devices, and wherein said control signals generated by
control output being connected to the control in- said controller comprise optical signals.
* * * * *
puts of said second set of optically isolating
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