Dual range power supply and adapter for use with same

A dual range power supply 200 is operable with either an AC line input, or a DC input. To facilitate use with an AC input the power supply is provided with a pair of AC prongs, connected to a rectifier bridge. The power supply is also provided with a positive DC receptacle. In using the power supply with a DC source, the power supply is connected to an adapter. The adapter has receptacle slots for receiving the AC prongs of the power supply, and a positive DC prong which mates with the positive DC receptacle of the power supply. Positive DC power is applied to the power supply through the positive DC receptacle while the DC return is through the rectifier bridge and at least one of the AC prongs.

TECHNICAL FIELD 
The invention relates in general to power supplies, and particularly to 
power supplies operable at both line AC levels and vehicular DC levels. 
BACKGROUND OF THE INVENTION 
Many electrical and electronic devices require a power supply for 
converting electrical voltage and current at given levels to levels usable 
by the device. One of the most common types of power supply is the so 
called wall mount transformer, which comprises a transformer circuit for 
converting an alternating current (AC) voltage at a commercial level, such 
as 120 volts AC, to a direct current (DC) level usable by the device. 
Indeed, such supplies are sold by the millions worldwide for devices that 
can work efficiently at a single output DC level. Typically these types of 
supplies use a simple step down transformer, appropriately designed, with 
a rectifier circuit on the output. Other types of devices, such as, for 
example, battery chargers and mobile computer power supplies, require 
output levels that may change during use, or that may be of such magnitude 
that the step down transformer approach results in a power supply that is 
too bulky for mobile applications. 
In recent years there has been a drive towards mobility for electronic 
devices. This is especially true for communications devices such as 
cellular radio-telephones, and computing equipment such as laptop 
computers. In many instances the use of such equipment is desirable in 
automobiles, and as such, there are numerous accessories available that 
permit the use of a vehicular cigarette lighter socket to power these 
types of devices. However, in order to use both an AC source, and a DC 
source, the user of the device typically must purchase separate power 
supplies; one for use with an AC source, and one for use with a DC source. 
It would therefore be desirable to have a power supply that can operate 
from both AC and DC sources, thus relieving the burden of having to 
purchase and keep two different power supplies. Although a dual range 
power supply would be fairly simple to realize, to date there has not been 
a strong presence of such a power supply in the marketplace. 
One reason that may account for the virtual absence of a dual range power 
supply for mobile equipment is a safety concern. Connectors for AC and DC 
power inputs are typically dissimilar, and therefore two connectors are 
used, one for each type of input. However, when operating the power supply 
from an AC source, it may be possible through some sort of equipment 
malfunction that the AC power becomes evident at a DC connector, and may 
pose a shock hazard. Furthermore, a hazard potential may exist if the user 
were able to provide both types of power simultaneously. That is, 
connecting to AC and a DC sources at the same time. 
Therefore there exists a need for a dual range power supply operable from 
either an AC source or a DC source in a manner such that the simultaneous 
interconnection of the two different types of input is barred. In 
addition, the device must accommodate two very different types of 
electrical receptacles in order to be successfully utilized in both AC 
line powered and DC vehicular powered applications. Such a power supply 
would offer ease of use, mobility, and eliminate the safety concerns 
described above.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
While the specification concludes with claims defining the features of the 
invention that are regarded as novel, it is believed that the invention 
will be better understood from a consideration of the following 
description in conjunction with the drawing figures, in which like 
reference numerals are carried forward. 
The invention solves the problem of having one power connector accessible 
while using a second by providing a conventional type AC dual blade or 
prong type connector, and an adapter, which also uses the AC connector, 
for use with a DC source. Referring now to FIG. 1, there is shown an 
electrical schematic diagram 100 of a power supply circuit for a dual 
range power supply in accordance with the invention. The dual range power 
supply is operable from either an AC source or a DC source. Briefly, the 
diagram shows an input section comprising a rectifier bridge 102 and a 
bulk filter capacitor 109, as is conventional. AC voltage is supplied to 
the input section by first and second AC prongs 106 and 108, used for 
connecting the dual range power supply to an AC source, and which are 
electrically coupled to the rectifier bridge in a conventional manner. 
Voltage from the input section is fed to a first primary winding 110 of a 
transformer 112. A secondary winding 114 provides voltage to a secondary 
rectifier circuit 116 comprising a diode 118 and a filter capacitor 120, 
and provides an output level between points 122 and 124. A feedback 
circuit 126 samples the output level, and provides a signal to a 
controller 128, in a conventional manner. The controller operates a switch 
circuit 130, to which the first primary winding is coupled, to generate an 
appropriate signal across the first primary winding. The controller 
samples the current through the switch circuit by use of a sense resistor 
network 132 disposed between the switch circuit and a reference line 134, 
which is connected to the first and second AC prongs through the rectifier 
bridge. Thus far the elements described are typically part of a 
conventional commercial AC level fed power supply. 
For operating the power supply with a DC source, a positive DC connector, 
such as a positive DC receptacle 136 is provided, and is coupled to a 
second primary winding 138 via a DC power line 140. The second primary 
winding is for use when the power supply is operated from a DC source. The 
controller 128 is coupled to the DC power line 140, and voltage on the DC 
power line is filtered by a power capacitor 142. The positive DC connector 
is coupled to the DC power line. Power is directly applied to the DC power 
line either when a positive DC voltage level is applied to the positive DC 
connector which is connected to a power source, or through a bootstrap 
resistor 144 when the dual range power supply is connected to an AC 
source. However, rather than provide a negative DC connector, the DC 
return from the reference line 134 is through the AC prongs. That is, DC 
power is supplied through the positive DC connector, through the power 
supply to the reference line, through the rectifier bridge, and finally 
through the AC prongs. Since the AC prongs are used as the DC return, they 
are not left exposed when the power supply is operated from a DC source. 
A better appreciation of how the power supply functions can be gained from 
a perusal of FIGS. 2-5 and the following description. Referring now to 
FIGS. 2 and 3, there is shown a front view and a side view, respectively, 
of a dual mode power supply 200 in accordance with the invention. The 
power supply comprises a body 201, preferably fabricated of an 
electrically insulative material, first and second AC prongs 106 and 108, 
and a positive DC receptacle 136. The first and second AC prongs and the 
positive DC receptacle may be disposed on a common face 202 of the power 
supply body. Mounted within the body is a power supply circuit in 
accordance with that shown and described in FIG. 1. The power supply 
provides a DC output to an associated device through, for example, a cable 
204. However, since AC prongs are not suitable for use with a DC source, 
particularly a vehicular cigarette lighter socket, an adapter is 
necessary. 
Referring now to FIGS. 4 and 5, there is shown a side view and a top view, 
respectively, of an adapter 400 for use with a dual mode power supply in 
accordance with one embodiment of the invention. The dual range power 
supply and adapter together comprise a dual range power supply system. In 
the preferred embodiment, the adapter comprises a cylindrical body 401, 
having a bottom 402, and a top 404, a positive electrode 406 disposed at 
the bottom, and a negative electrode 408 disposed on the side 409 of the 
cylindrical body. The positive and negative electrode function to make 
electrical contact with a DC source. 
In the preferred embodiment, the cylindrical body is sized for insertion 
into a vehicular cigarette lighter socket, as is conventional. A pair of 
receptacles 410 are disposed on the top, and are sized and spaced for 
receiving the AC prongs of a power supply in accordance with that shown in 
FIGS. 2 and 3. The negative electrode is coupled to at least one of the AC 
receptacles. Furthermore, there is provided a positive DC prong 412, 
corresponding with the positive DC receptacle 136. The AC prongs and AC 
receptacles and positive DC prong and receptacle are oriented in a common 
direction so that the positive DC prong is received in the positive DC 
socket when the AC prongs are inserted into the AC receptacles, or in 
other words, when the power supply is plugged into the adapter. Thus, in 
practicing the invention, when operation from an AC source is used, the 
power supply is used in a conventional manner with the AC source; the AC 
prongs are sized and spaced conventionally to fit a commercial AC outlet. 
When the power supply is to be used with a DC voltage source, such as a 
vehicular cigarette socket, an adapter such as that shown in FIGS. 4 and 5 
is used to connect to the DC source, and the power supply plugs into the 
adapter to make the DC connection necessary to operate the power supply. 
The adapter further comprises circuitry to realize the DC connection, as is 
shown in FIG. 6, an electrical diagram 600 of an adapter circuit in 
accordance with the invention. The positive electrode 406 is coupled to 
the positive DC prong 412, and, in the preferred embodiment, comprises a 
fuse 602 in line between the electrodes and the power supply, a transient 
zener 604 coupled in parallel with the electrodes, an electromagnetic 
interference (EMI) filter 606 coupled in parallel with the electrodes, and 
output capacitor 608 disposed across the positive DC connector and the AC 
receptacles. When the power supply is connected to the adapter, the DC 
return from the reference line 134 goes through the rectifier bridge, the 
AC prongs, and to the negative electrode of the adapter. 
Thus, the invention solves the problem of having a device, such as a laptop 
computer, powered by a single power supply operable with either an AC 
source, or a DC source. Furthermore, the invention avoids the safety 
concern of having a connector for a first type of power source available 
while connected to the second by commonly orienting connectors for both, 
and preferably on a common face of the power supply, so as to make the 
connectors inaccessible when connected to either an AC source or a DC 
source. 
To further enhance the safety of the adapter, an alternative embodiment is 
contemplated that prevents the electrification of the positive DC prong 
412 until the AC prongs of the power supply are inserted into the AC 
receptacle slots. Referring now to FIG. 7, there is shown an electrical 
schematic diagram 700 of an alternative embodiment of an adapter for use 
with a dual range power supply, in accordance with the invention. The 
safety and filter elements shown in FIG. 6 may be present, but have been 
removed here for clarity. In the alternative embodiment, the adapter uses 
one of the AC prongs of the power supply to complete an electrical 
circuit, connecting the positive DC prong 412 to the positive electrode 
406. The other AC prong still gets connected to the negative electrode 408 
through a second receptacle slot 410. The first receptacle slot 702 is 
modified, and comprises a first side 704 and a second side 706, both of 
which are electrically conductive. The first side is electrically 
connected to the positive electrode 406, and the second side is 
electrically connected to the positive DC prong 412. When the power supply 
200 is connected to the adapter, a first AC prong becomes inserted into 
the first receptacle slot 702, and makes contact with both the first and 
second sides of the receptacle slot, and thus, being electrically 
conductive, provides an electrical path between the positive electrode 406 
and the positive DC prong 412. At the same time, a second AC prong becomes 
inserted into the second receptacle slot 410, thus connecting the second 
AC prong to the DC return of negative electrode 408. 
To illustrate how the power supply and adapter function electrically, an 
electrical schematic diagram of an adapter connected to a dual range power 
supply in accordance with this alternative embodiment of the invention is 
shown. Referring now to FIG. 8, there is shown the input portion of the 
same circuit illustrated in FIG. 1, and specifically the rectifier bridge 
102. The rectifier bridge is conventional, and includes a first rectifier 
800 and a second rectifier 802. The first AC prong 106 is connected across 
the first rectifier 800, and the second AC prong 108 is connected across 
the second rectifier 802. In this diagram the adapter 400 is shown 
connected to the power supply module 200. The second AC prong 108 mates 
with the second receptacle slot 410 of the adapter, thus providing a 
return path from reference line 134, through the second rectifier and the 
second AC prong to the negative electrode 408. Positive DC power is 
supplied from the positive electrode 406 through the electrical connection 
formed between the first AC prong 106 and the first and second sides, 704 
and 706 respectively, of the receptacle slot 702, to the positive DC prong 
412 which is connected to the positive DC receptacle 136, supplying power 
to the DC power line 140. Power does not flow into the input of the power 
supply module because, by virtue of applying a positive DC voltage level 
to the first AC prong 106, the first rectifier 800 becomes reverse biased. 
Thus, this alternative embodiment provides the adapter with a circuit so 
that the positive DC prong is energized only when the power supply module 
is plugged into the adapter. 
This alternative embodiment is especially important if the adapter is 
designed for use with a vehicular cigarette lighter socket since, if the 
adapter is mounted in the socket, and the power supply is not connected to 
the adapter, without this alternative embodiment, the positive DC prong is 
energized and exposed, possibly posing a hazard. This alternative 
embodiment eliminates this hazard by disconnecting the positive DC prong 
from the positive electrode until such time as the power supply is 
connected to the adapter. Additionally, as the preferred embodiment is an 
adapter for use in a vehicular cigarette lighter socket, it would be 
convenient if the adapter were able to be semi-permanently mounted in the 
socket. Otherwise every time the power supply is removed from the adapter, 
the potential exists for such an action to also inadvertently remove the 
adapter from the socket. Therefore it is contemplated that the adapter may 
be provided with a cam mechanism, movable by, for example, inserting a 
screwdriver into an opening provided on the top of the adapter and turn 
the cam mechanism to engage the wall of the socket. 
While the preferred embodiments of the invention have been illustrated and 
described, it will be clear that the invention is not so limited. Numerous 
modifications, changes, variations, substitutions and equivalents will 
occur to those skilled in the art without departing from the spirit and 
scope of the present invention as defined by the appended claims.