AC-DC Adapter
Welcome to Free Patent Search
AC-DC Adapter Abstract
An AC-DC adapter includes a power transformer to which an
AC voltage is applied, a rectifier circuit for rectifying and smoothing
an AC voltage developed across the secondary side of said power transformer,
and DC voltage stabilizing member for stabilizing a DC voltage outputted
by said the rectifier circuit.
AC-DC Adapter Claims
What is claimed is:
1. An AC-DC adapter comprising:
a power transformer to which an input AC voltage in a predetermined range
is applied, said power transformer transforming said input AC voltage
to a secondary AC voltage having a predetermined voltage less than a voltage
within said predetermined range;
a rectifier circuit for rectifying and smoothing said secondary AC voltage
developed across a secondary side of said power transformer; and
DC voltage stabilizing means for stabilizing a DC voltage outputted by
said rectifier circuit such that said AC-DC adapter is usable with a power
source within said predetermined range without any adjustment necessary
to said AC-DC adapter.
2. The AC-DC adapter as claimed in claim 1, wherein the DC voltage stabilizing
means includes a self-excited constant-voltage circuit.
3. The AC-DC adapter as claimed in claim 1, wherein the DC voltage stabilizing
means includes a self-excited constant-voltage constant-current circuit.
4. The AC-DC adapter as claimed in claim 1, wherein the rectifier circuit
includes a bridge rectifier to which the AC voltage developed across the
secondary side of said power transformer is applied, and a smoothing capacitor
connected to the bridge rectifier.
5. The AC-DC adapter as claimed in claim 2, wherein the DC voltage stabilizing
means includes:
a fuse connected in series to the output line of the rectifier circuit;
a control transistor having an input coupled to said fuse;
a choke coil coupled to said control transistor;
a comparison transistor connected between a base of the control transistor
and ground; and
an amplifier transistor having a base connected through a resistor and
a constant-voltage diode to an output terminal, a collector connected
to a base of the comparison transistor, and an emitter connected to ground,
wherein a secondary side of the choke coil is connected between an emitter
and the base of the control transistor, and the base of the comparison
transistor is connected through a resistor to the emitter of the control
transistor.
6. The AC-DC adapter as claimed in claim 3, wherein the DC voltage stabilizing
means includes:
a control transistor connected to an output of the rectifier circuit;
a choke coil coupled to said control transistor;
a current detecting resistor coupled to said choke coil;
a comparison transistor connected between a base of the control transistor
and ground;
a current detecting transistor for amplifying a voltage developed across
the current detecting resistor;
a constant-voltage diode connected between an output side of the resistor
and a collector of the current detecting transistor; and
an amplifier transistor having a base connected to the collector of the
current detecting transistor and a collector connected to a base of the
comparison transistor,
wherein a secondary side of the choke coil is connected between the base
and an emitter of the control transistor, and the base of the comparison
transistor is connected through a resistor to the emitter of the control
transistor.
7. The AC-DC adapter as claimed in claim 1, wherein the DC voltage stabilizing
means includes a self-excited circuit.
8. The AC-DC adapter as claimed in claim 4, wherein the DC voltage stabilizing
means includes a self-excited circuit.
9. The AC-DC adapter as claimed in claim 2, wherein the rectifier circuit
includes a bridge rectifier to which the AC voltage developed across the
secondary side of said power transformer is applied, and a smoothing capacitor
connected to the bridge rectifier.
10. The AC-DC adapter as claimed in claim 9, wherein the DC voltage stabilizing
means includes:
a fuse connected in series to the output line of the rectifier circuit;
a control transistor having an input coupled to said fuse; and
a choke coil coupled to said control transistor.
11. The AC-DC adapter as claimed in claim 10, wherein the DC voltage stabilizing
means further includes:
a comparison transistor connected between a base of the control transistor
and ground; and
an amplifier transistor having a base connected through a resistor and
a constant-voltage diode to the output terminal, a collector connected
to the base of the comparison transistor, and an emitter connected to
ground.
12. The AC-DC adapter as claimed in claim 11, wherein a secondary side
of the choke coil is connected between an emitter and the base of the
control transistor, and a base of the comparison transistor is connected
through a resistor to the emitter of the control transistor.
13. The AC-DC adapter as claimed in claim 9, wherein the DC voltage stabilizing
means includes:
a control transistor connected to an output of the rectifier circuit;
a choke coil coupled to said control transistor; and
a current detecting resistor coupled to said choke coil.
14. The AC-DC adapter as claimed in claim 13, wherein the DC voltage stabilizing
means further includes:
a comparison transistor connected between a base of the control transistor
and ground;
a current detecting transistor for amplifying a voltage developed across
the current detecting resistor; and
a constant-voltage diode connected between an output side of the resistor
and a collector of the current detecting transistor.
15. The AC-DC adapter as claimed in claim 14, wherein the DC voltage stabilizing
means further includes:
an amplifier transistor having a base connected to the collector of the
current detecting transistor and a collector connected to a base of the
comparison transistor,
wherein a secondary side of the choke coil is connected between the base
and an emitter of the control transistor, and the base of the comparison
transistor is connected through a resistor to the emitter of the control
transistor.
16. The AC-DC adapter as claimed in claim 2, wherein the DC voltage stabilizing
means further includes:
a control transistor connected to an output of the rectifier circuit,
for controlling said self-excited constant-voltage circuit.
17. The AC-DC adapter as claimed in claim 5, further comprising an output
terminal coupled to said self-excited constant voltage circuit,
wherein a current induced in a secondary side of said choke coil is applied
through said resistor to said comparison transistor such that said current
flows between said collector and said base of said comparison transistor,
and
wherein a voltage at said output terminal is applied to said constant-voltage
diode and said resistor as no more than a predetermined voltage, to said
base of the said amplifier circuit,
said comparison transistor receiving output voltages from said choke coil
and said amplifier transistor to switch a state of said control transistor
to thereby control a direct current,
said AC-DC adapter further comprising a second capacitor coupled to said
output of said choke coil and for smoothing said direct current outputted
by said choke coil and for outputting said direct current having been
smoothed to said constant-voltage diode for conversion into a direct current
having a predetermined voltage and for output to said output terminal.
18. The AC-DC adapter as claimed in claim 3, wherein the DC voltage stabilizing
means further includes:
a control transistor connected to an output of the rectifier circuit,
for controlling said self-excited constant-voltage constant-current circuit.
19. The AC-DC adapter as claimed in claim 6, further comprising an output
terminal coupled to said self-excited, constant-voltage constant-current
circuit,
wherein a current induced in a secondary side of said choke coil is applied
through said resistor to said comparison transistor such that said current
flows between said collector and said base of said comparison transistor,
and
wherein a voltage across said resistor is provided to said output terminal
and applied to said constant-voltage diode and said resistor as no more
than a predetermined voltage, to said base of the said amplifier circuit,
and
wherein a portion of the current flowing to the output terminal is applied
through said constant voltage diode to said base of said comparison transistor.
20. The AC-DC adapter as claimed in claim 19, wherein said comparison
transistor receives output voltages from said choke coil, said amplifier
transistor and said resistor, and to switch a state of said control transistor
based on said voltages from said choke coil, said output terminal, and
said resistor to thereby control a direct current at said output terminal
to be constant in voltage and in current.
Patent Information Search Body
AC-DC Adapter Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an alternating current-direct current ("AC-DC")
adapter which converts an alternating current into a direct current having
a predetermined voltage value and further relates to an AC-DC adapter
which converts an alternating current into a direct current having a predetermined
voltage value and a predetermined current value.
2. Related art
A conventional AC-DC adapter of this type is designed so as to convert
a predetermined AC voltage into a predetermined DC voltage. Hence, in
order to use the AC-DC adapter in other countries which use different
commercial power standards and in order to make the AC-DC adapter usable
world-wide, the AC-DC adapter has a change-over switch. For instance,
in the case where it is required to convert an AC voltage into DC 4.5V,
the switch is operated so that a predetermined AC voltage is obtained
from a variety of input AC voltages.
For the same purpose, some of the AC-DC adapters have a switching circuit.
When, for instance, electronic devices equipped with the above-described
AC-DC adapters are shipped to foreign countries which have different commercial
power standards, the AC-DC adapters must be adjusted so as to meet the
commercial power standards in the countries, thus different AC-DC adapters
must be provided for the different countries and a plurality of kinds
of AC-DC adapters must be provided for one kind of electronic device.
This means that a variety of AC-DC adapters are manufactured on a small
scale, and that the AC-DC adapters manufactured have a high manufacturing
cost.
In the case of the AC-DC adapter having a change-over switch, the following
procedure must be taken. In the country where the AC-DC adapter is used,
after confirmation of the voltage of the local commercial power source,
the change-over switch is suitably operated to switch to the appropriate
input voltage. However, the confirmation of the local power source voltage,
and the operation of the switch are troublesome and, therefore, the AC-DC
adapter is difficult to operate.
If the confirmation of the local power source voltage, or the operation
of the switch is incorrect, then an AC voltage different from the rated
value may be inputted. In this case, the transformer in the AC-DC adapter
may be damaged, or the constant-voltage circuit for processing the secondary
voltage of the transformer may be damaged.
Furthermore, the AC-DC adapter with the switching circuit is disadvantageous
in that the switching circuit is intricate and has a large number of components,
and accordingly has a high manufacturing cost.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this invention is to provide an
AC-DC adapter for world-wide use which can be operated without having
to know the input voltage.
The foregoing object of the invention has been achieved by the provision
of an AC-DC adapter which, according to the invention, includes: a power
transformer to which an AC voltage is applied; a rectifier circuit for
rectifying and smoothing the AC voltage that is developed across the secondary
side of the power transformer; and a self-excited constant-voltage constant-current
circuit for stabilizing a DC voltage outputted by the rectifier circuit.
In the AC-DC adapter of the invention, the input AC voltage is converted
into a predetermined AC voltage by the power transformer, the predetermined
AC voltage is converted into a DC voltage by the rectifier circuit, and
the DC voltage is then stabilized by the self-excited constant-voltage
constant-current circuit. Hence, for instance, a stable DC voltage of
4.5V is obtained from an AC input voltage of 90V to 264V. Therefore, even
in foreign countries, the AC-DC adapter can be used without knowing to
the local power source voltage. In other words, the inventive AC-DC adapter
can be used in foreign countries without modification.
Therefore, when electronic devices equipped with the inventive AC-DC adapters
are to be shipped to foreign countries, it is unnecessary to manufacture
different kinds of AC-DC adapters for the different countries. Thus, a
single AC-DC adapter can be used in all countries. This means that the
AC-DC adapters of the invention can be produced on a large scale, thereby
being less expensive to manufacture.
Furthermore, with the inventive AC-DC adapter, the local voltage of the
commercial power source need not be confirmed and the change-over switch
or the like is unnecessary. That is, the inventive AC-DC adapter can be
operated easily.
In addition, the inventive AC-DC adapter does not encounter the problems
and potential damage that occurs when an AC voltage different from the
rated value is erroneously inputted.
The AC-DC adapter of the present invention, unlike the conventional ones
which use a switching circuit, employs the self-excited circuit. Hence,
the inventive AC-DC adapter, has a simple arrangement, and has a reduced
number of components, and accordingly a low manufacturing cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the fundamental arrangement of an AC-DC
adapter according to the invention;
FIG. 2 is a circuit diagram showing a concrete example of an AC-DC adapter,
which constitutes a first embodiment of the invention; and
FIG. 3 is a circuit diagram showing a concrete example of an AC-DC adapter,
which constitutes a second embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of this invention will be described with reference
to the accompanying drawings.
First embodiment
FIG. 1 shows an AC-DC adapter, which constitutes a first embodiment of
the invention. As shown in FIG. 1, the AC-DC adapter 10 comprises: a power
transformer 12 whose primary side is connected to input terminals 11;
a rectifier circuit 13 connected to the secondary side of the transformer
12; a "self-excited constant-voltage circuit" 14 connected to the output
side of the rectifier circuit 13; and output terminals 15 connected to
the output side of the constant voltage circuit 14.
The rectifier circuit 13 and the constant-voltage circuit 14 are shown
more detail in FIG. 2. The rectifier circuit 13 is made up of a bridge
rectifier 21 to which the secondary AC voltage of the power transformer
12 is applied, and a smoothing capacitor 22 connected to the bridge rectifier
21.
The constant-voltage circuit 14 comprises: a fuse 23 connected in series
to the output line of the rectifier circuit 13; a control transistor 24;
a choke coil 25; a comparison transistor 26 connected between the base
of the control transistor 24 and ground; and an amplifier transistor 29.
The base of the transistor 29 is connected through a resistor 28 and a
constant-voltage diode 27 to the output terminal 15, the collector is
connected to the base of the comparison transistor 26, and the emitter
is connected to ground.
The secondary side of the choke coil 25 is connected to the input side
of the control transistor 24 (i.e., the choke coil 25 is connected between
the emitter and the base of the control transistor 24). The base of the
comparison transistor 26 is connected through a resistor 30 to the emitter
of the control transistor 24.
In the AC-DC adapter, an AC voltage applied across the input terminals
11 is converted into a predetermined AC voltage by the power transformer
12, which is converted into a DC voltage by the bridge rectifier 21 and
the smoothing capacitor 22 in the rectifier circuit 13. The DC voltage
is applied to the constant-voltage circuit 14, where it is controlled
by the control transistor 24 (as described below), and then applied through
the choke coil 25 to the output terminal 15.
According to this circuit, the current induced in the secondary side of
the choke coil 25 is applied through the resistor 30 to the comparison
transistor 26, where it flows between the collector and the base.
The voltage at the output terminal 15 is applied through the constant-voltage
diode 27 and the resistor 28, as a predetermined voltage or lower, to
the base of the amplifier transistor 29 and is amplified by the amplifier
transistor 29, and applied to the base of the comparison transistor 26.
Thus, the comparison transistor 26 operates (based on the voltages from
the choke coil 25 and the amplifier transistor 29) to switch the state
of the control transistor 24, thereby to allow the control transistor
24 to control the direct current. The direct current is then smoothed
by the capacitor 31, and converted by the constant-voltage diode 32 into
a direct current having a predetermined voltage value, which is provided
at the output terminal 15.
Second embodiment
A second embodiment of the invention will be described with reference
to FIG. 3. The fundamental arrangement of the second embodiment is similar
to that of the first embodiment.
In the second embodiment, a rectifier circuit 113 and a constant-voltage,
constant-current circuit 114 are formed as shown in FIG. 3. The rectifier
circuit 113 comprises: a bridge rectifier 121 to which the secondary AC
voltage of the power transformer 112 is applied; and a smoothing capacitor
122 connected to the bridge rectifier 121.
The constant-voltage, constant-current circuit 114 includes: a control
transistor 123 connected to the output line of the rectifier circuit 113;
a choke coil 124; a current detecting resistor 125; a comparison transistor
126 connected between the base of the control transistor 123 and ground;
and a current detecting transistor 127 for amplifying a voltage developed
across the current detecting resistor 125; a constant-voltage diode 128
connected between the output side of the resistor 125 and the collector
of the transistor 127; and an amplifier transistor 129. The base of the
amplifier transistor 129 is connected to the collector of the current
detecting transistor 127, and the collector of the amplifier transistor
129 is connected to the base of the comparison transistor 126.
The secondary side of the choke coil 124 is connected to the input side
of the control transistor 123 (i.e., the choke coil 124 is connected between
the base and emitter of the control transistor 123). The base of the comparison
transistor 126 is connected through a resistor 130 to the emitter of the
transistor 123.
In the AC-DC adapter 110, an AC voltage applied across the input terminals
111 is converted into a predetermined AC voltage by the power transformer
112, which is converted into a DC voltage by the bridge circuit 121 and
the smoothing capacitor 122. The DC voltage is applied to the constant-voltage,
constant-current circuit 114, where it is controlled by the control transistor
123 (as described below), and then is applied through the choke coil 124
and the resistor 125 to the output terminal 115.
In this operation, the current induced in the secondary side of the choke
coil 124 is applied through the resistor 130 to the comparison transistor
126, where it flows between the collector and the base.
The current flowing in the resistor 125 develops a voltage across the
resistor 125 and is amplified by the transistor 127. The voltage thus
amplified, after being limited to a predetermined value or lower by the
constant-voltage diode 128, is applied to the base of the amplifier transistor
129. The amplifier transistor 129 amplifies the voltage, which is then
applied to the base of the comparison transistor 126.
Part of the current flowing to the output terminal 115 is applied through
the diode 131 to the base of the comparison transistor 126.
Thus, the comparison transistor 126 switches the state of the control
transistor 123 according to the voltage and current provided through the
choke coil 124, the current detecting resistor 125 and the output terminal
115 so that the direct current at the output terminal 115 is constant
both in voltage and in current.
With the AC-DC adapter 10, for instance, an input AC voltage of 90V to
264V is changed into an AC voltage of 5V to 30V by the power transformer
12, and a DC voltage of 4.5V is provided at the output terminal 15 with
the aid of the rectifier circuit 13 and the constant-voltage circuit 14
(or the constant-voltage, constant-current circuit 114). Hence, the AC-DC
adapter 10 can be applied to different commercial power sources in many
countries without switching the input AC voltage. Since the input AC voltage
is lowered by the power transformer 12, the rectifier circuit 13 and the
constant-voltage circuit 14 (or the constant-voltage, constant-current
circuit 114) the inventive circuit includes circuit elements which are
small and have a low isolation voltage, and are readily available. This
simplifies and miniaturizes the design of the AC-DC adapter. The above
described AC-DC adapter may be utilized, for instance, for an electric
charger.
As described above, the AC-DC adapter can be used without having to know
to the input voltages and therefore, can be used all over the world. Thus,
the inventive AC-DC adapter has many practical uses.
AC-DC Adapter
About
Us Contact
Us Crazy
Patents
A B
C D
E F
G H
I J
K L
M N
O P
Q R
S T
U V
W X-Y-Z
Copyright 2005-2025 Free-Patent-Search.net, Dental Loupes
|