Miniaturized high frequency direct current power supply

A power supply is disclosed which is compatible with modern thin film technology which has an overall size compatible with modern miniaturized electronic components. Input power having an oscillating component in the 50/60 Hz 120/220 volt range is immediately switched to high frequency current exceeding 100 KHz and preferably switched with a frequency in the megahertz range. The switched current, otherwise unaltered from its current having an oscillating component, is then transduced in voltage at a thin film transformer, passed through thin film mounted electronic components for rectification and filtering. A regulator circuit modifies the semi-conductor switch duty cycle to control the rectifier output voltage. All transformer, rectifier, and filter components are of thin film variety and mounted to attain efficient heat dissipation together with size reduction comparable to the powered components driven by the power supply.

This invention relates to the miniaturization of power supplies for 
producing direct current. More particularly, a power supply is disclosed 
in which incoming current having an oscillating component in the range of 
50/60 Hz is immediately converted to high frequency switched current in 
the megahertz range and thereafter rectified utilizing electronic 
components of the thin film variety. This approach drastically reduces the 
size of a power supply to a point whereby it can be in the form of a 
plug-in, a card, or an IC chip for use in a computer, cellular telephone, 
and telecommunication industries. 
BACKGROUND OF THE INVENTION 
Electronic components continue to be reduced in size. Unfortunately, direct 
current power supplies for such electronic components have not undergone 
such size reductions. Specifically, it is now common for small portable 
electronic components such as portable computers to have accompanying 
power supplies that are substantial in size and weight comparable to the 
portable computers themselves. 
Conventional power supplies that rectify 50/60 Hertz 120/220 volt 
alternating current into direct current are particularly large. Such 
devices usually include full wave or half wave rectifiers which produce 
direct current still having the "ripple" of the originating alternating 
current. Thereafter, this ripple in the rectified current is substantially 
eliminated by appropriate electronic circuitry, such as a capacitance and 
inductance, to produce the required stable direct current. 
Unfortunately, such conventional power supplies involved low frequencies 
and long wave lengths. These low frequencies and long wave lengths lead to 
high power losses. Almost everyone using such devices is familiar with the 
"warm" feeling that such large rectification devices have after continued 
use. Further, such components have large size. They either occupy a 
substantial volume of the devices which they power or alternatively 
constitute large stand alone components which reside outside of the units 
which they power. 
In an effort to further reduce size, so-called switched mode power supplies 
have been utilized. These devices include a low frequency rectifier and 
relatively crude filter. The total power from this low frequency rectifier 
and filter is then routed to a semiconductor switch. With the 
semiconductor switch, the rectified power is then converted to high 
frequency switched power which is thereafter rectified. 
These switched power supplies generally operate with their switching 
transistors operating in the kilohertz range--typically below 40 KHz. 
While the ultimate rectification that they can produce is superior, and 
the rectifying components of such power supplies are somewhat smaller, 
they frequently are not equivalent in size to the components that they 
serve. For example, the average "notebook computers" single largest 
component is the power supply. It is almost always, external to the 
remainder of the computer and rather bulky relative to that computer. 
SUMMARY OF THE INVENTION 
A power supply is disclosed which is compatible with modern thin film 
technology which has an overall size compatible with modern miniaturized 
electronic components. Input power having an oscillating component in the 
50/60 Hz 120/220 volt range is immediately switched to high frequency 
current exceeding 100 KHz and preferably switched with a frequency in the 
megahertz range. The switched current, otherwise unaltered from its 
current having an oscillating component, is then transduced in voltage at 
a thin film transformer, passed through thin film mounted electronic 
components for rectification and filtering. A regulator circuit modifies 
the semi-conductor switch duty cycle to control the rectifier output 
voltage. All transformer, rectifier, and filter components are of thin 
film variety and mounted to attain efficient heat dissipation together 
with size reduction comparable to the powered components driven by the 
power supply. 
It is to be noted that over the prior art, several distinctions are 
present. 
First, by feeding the 110/220 volt, 60 Hertz supply directly to a 
semiconductor switch section, the bulky low frequency rectifier/filter 
section of prior art power supplies is eliminated. 
Second, by going to the megahertz range of semiconductor switching 
directly--and omitting the initial crude rectification stage common to 
most switching power supplies--the high frequency supply is reduced to 
"card compatible size" as small as a single I.C. chip. For the first time, 
power supplies have a size that is compatible with the components which 
they serve. 
Third, thin film technology can be used for transformer, rectification and 
filtering components of the invention. As a result, required heat 
dissipation of the smaller rectification device is easily accommodated. 
New Material 
As a direct result of experimentation with the circuitry here described, it 
has been discovered that the high frequency semiconductor switch when 
powered directly from the power line, effectively does away with the 60 
Hertz frequency component. Furthermore, an embodiment of the circuit is 
disclosed which does not include the thin film transformer and utilizes a 
regular inductor. Over conventional power supplies, substantial size 
reduction still results. While the previously disclosed embodiment 
including the thin film transformer and the thin film inductor remains 
preferred, the disclosure of the new embodiment (FIG. 4) has been found to 
be operable and to have utility.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a conventional switched power supply of the prior art 
is illustrated. A.C. input 14 provides power to be rectified. This current 
then passes through low frequency rectifier/filter 18 and then to energy 
storage device 20. In the conventional switched power supply of the prior 
art, switching at semi-conductor switch S.sub.p is then provided, usually 
in a range below 40 KHz. Voltage is conventionally transduced at 
transformer 22 to the desired voltage for conventional rectifier 24. 
Rectified current leaves power supply output 34. As is common, the duty 
cycle of semi-conductor switch S.sub.p is controlled through regulator 
circuit 26 which continually monitors the switched power supplies output. 
In the switched power supply, it will be observed that an attempt is first 
made to rectify the current when the current is still in the 50/60 Hz 
range. This initial rectification requires large components because of 
long wave lengths. In what follows, I take the step of immediately 
switching to high frequency--above 100 KHz and preferably in the MHz 
range. This immediate switching to higher frequencies is believed to be in 
the opposite direction of conventional power supplies. However, the high 
frequency produced makes the remainder of the processing possible 
utilizing miniaturized components. 
Referring to FIG. 2, a diagram of the invention herein is set forth. A.C. 
input 14 includes current having a substantial 50/60 Hz oscillating 
component. While it is not necessary that the rectified current of this 
invention have true alternating current format, the invention is designed 
for the power supply to be powered utilizing current having 50/60 Hz 
oscillating component or harmonics of this frequencies. 
Upon entry into the power supply, immediate switching at semi-conductor 
switch S occurs. Such switching takes the current to a switched frequency 
exceeding 100 KHz and preferably to the MHz range. Thereafter, current 
flow includes high frequency voltage transformer 42 and high frequency 
voltage rectifier/filter 44. As will hereafter be developed, these 
circuits because of the high frequencies involved can be quite small. 
Thereafter, power supply output 54 provides current while high frequency 
regulator 46 controls voltage output by controlling semi-conductor switch 
S duty cycle. 
Referring to FIG. 3, semi-conductor switch S is shown with sink 62, gate 
64, and source 60. As can be understood, duty cycle at gate 64 is modified 
through a regulator circuit including differential amplifier 70 and 
reference voltage 72, both of which can be thin film mounted because of 
the high frequencies involved. 
High frequency voltage transformer 42 is schematically shown and is of the 
thin film variety. Such devices are described and set forth in Magnetic 
Thin Film Inductor for Integrated Circuit Applications by myself in IEEE 
Transactions on Magnetics, Vol. Mag. 15, No. 6, Nov. 1979 at pages 
1803-1805. 
Once voltage is transduced, it then passes to high frequency rectifier 
44.sub.R and thereafter to high frequency inductor 44.sub.I, and high 
frequency capacitor 44.sub.C all of which are thin film mounted. 
A word can be added about that power required to drive semi-conductor 
switch S. Specifically, semi-conductor switch S is only given sufficient 
power to drive the switching function. Unlike switches of the prior art, 
input of low frequency rectified current is not utilized to drive the 
switching circuit. I generally prefer feed back rectified power from 
output 54 to drive semi-conductor switch S. Alternately, sufficient 
current to start switching can be provided from either a small direct 
current source such as battery or alternatively from a low level rectifier 
having sufficient current to power switching only. 
Regarding the utility of this invention, some comparisons may be useful. In 
the following table, I give the relative power supply sizes of the prior 
art of FIG. 1 compared to the preferred embodiment of FIG. 3. 
TABLE I 
______________________________________ 
Power Supply Size Comparisons 
Typical or Estimated Volume 
Component Type (in Cubic Inches) 
______________________________________ 
P.C. Computer Power Supply 
215 
Notebook Computer Power 
37 
Supply 
Plugin Power Supply* 
12 
Card Power Supply* 
6 
I.C. Power Supply* 
0.3 
______________________________________ 
*Underlying this invention. 
New Material 
As a direct result of experimentation with the circuitry here described, it 
has been discovered that the high frequency semiconductor switch when 
powered directly from the power line, effectively does away with the 60 
Hertz frequency component. Furthermore, an embodiment of the circuit is 
disclosed which does not include the thin film transformer and utilizes a 
regular inductor. Over conventional power supplies, substantial size 
reduction still results. While the previously disclosed embodiment 
including the thin film transformer and the thin film inductor remains 
preferred, the disclosure of the new embodiment (FIG. 4) has been found to 
be operable and to have utility. 
It is to be understood that the experimental circuit disclosed herein is 
believed to be novel in so far as direct switching of the 60 Hertz input 
voltage occurs. It is not known to applicant that power supplies having 
direct switching above 1 KHz and preferably to the MHz range occurs. 
Referring to FIG. 4, an experimental circuit for the miniaturized power 
supply of this invention is disclosed. Over the circuit previously 
described in FIG. 3, the thin film transformer is omitted. A conventional 
high frequency rectifier 64.sub.R is utilized. Additionally a conventional 
inductance 64.sub.I is utilized. In all other aspects, the circuit is the 
same as that previously illustrated with respect to FIG. 3. 
It was found that semiconductor switch S was effective in eliminating the 
60 Hertz signal of A.C. input 14 and the circuit was operable without the 
presence of the thin film transformer. 
Since thin film transformers and inductors are not currently commercially 
available an inductor-capacitor circuit at the output of the switch was 
utilized to translate the 110 volt power line voltage and provide 
sufficient filtering to obtain several volts DC suitable for typical 
applications. 
The circuit responded to a conventional regulation circuit as indicated in 
FIG. 3. This maintained the output voltage at the desired level. 
Regarding size, the entire circuit as described fits into a space of 3" by 
2" by 1". It is to be noted that this volume is some two or three times 
smaller than commercially available power supplies, such as those used 
with so-called "notebook" computers. 
A power supply with a thin film transformer and inductor still remains 
preferred for further size reduction. For example, a typical size of such 
a thin film transformer in chip form would be 3/4" by 1/4" by 1/8". This 
compares with a conventional transformer of 2" by 11/2" by 11/4". Thus by 
the use of a thin film transformer, reduction over a conventional 
transformer occurs by a factor of 150 times. 
EXPERIMENTAL RESULTS 
Summary of some experimental results are given below: 
(a) Referring to FIG. 3, we have performed an experiment in which we switch 
the semiconductor switch up to a MHz without the use of a bulky 60 Hz 
transformer preceding it. 
(b) Since thin film transformers are not commercially available, we used an 
inductor-capacitor circuit at the output of the switch to translate the 
110 volt power line voltage and filtered it to obtain several volts d.c. 
suitable for typical applications. 
(c) A regulation circuit as indicated in FIG. 3 was constructed and used to 
maintain the output d.c. voltage at a desired level. 
(d) The entire circuit as described above fits into a space of 
3".times.2".times.1". This volume is some two or three times smaller than 
commercially available power supplies for similar applications, such as 
notebook computers. 
(e) With a thin film transformer, the volume mentioned in (d) above will be 
reduced by at least half and the entire circuit can be mounted on a card 
to be placed inside a notebook computer. 
(f) A thin film transformer should be made in chip form. Its size will 
depend on the power level involved but a typical size might be 
3/4".times.1/4".times.1/8". This compares with a conventional transformer 
of 2".times.11/2"11/4". Thus, a thin film transformer can reduce the 
volume over a conventional one by some 150 times.