CONFIGURATION

TECHNICAL FIELD

The present invention relates generally to the field of

power supplies. More particularly, the present invention relates to a battery power supply circuit that supplies correct power

polarity to a load device irrespective of the orientation of the battery and a corresponding mounting configuration therefor.

BACKGROUND

Devices which use batteries as a source of power are well known. Such devices include, but are not limited to, portable radios, portable communications devices, and medical devices such as hearing aids.

Most devices that use batteries as a power source provide an access panel or the like which allows the user to install or replace the batteries. Such access by the user increases the possibility for human errors. One type of human error that is frequently encountered is a battery polarity error. A battery polarity error occurs when the user inserts the battery in the device with a reversed polarity. As a result of the error, the

positive terminal of the battery is connected to the negative power terminal of the device and the negative terminal of the battery is connected to the positive terminal of the device. With the battery connected to the device with a reversed polarity, the device will generally not work or, in some instances, may be damaged. Even in the absence of permanent damage, a polarity error can be a source of frustration to the user, particularly when the battery is a disc-type battery, such as the type used in a hearing aid, since it is often difficult for the ordinary user to discern between the positive and negative terminals on such

batteries. As such, it may be difficult for the user to perform the initial installation correctly and to subsequently diagnose the polarity insertion error. Additionally, mechanical damage to a hearing aid may be caused by reverse insertion of the battery resulting in the return of the hearing aid to the manufacturer for repair.

SUMMARY OF THE INVENTION

A power supply circuit is set forth which overcomes the problems associated with incorrect battery insertion. The power supply circuit includes first and second battery terminals for electrical- connection to the battery. The first and second battery terminals are connected to a first transistor switching circuit. The first transistor switching circuit is responsive to power from the battery to through-connect a negative polarity power signal therethrough irrespective of the polarity orientation of the battery. The first and second battery terminals are also connected to a second transistor switching circuit. The second switching circuit is responsive to power from the battery to through-connect a positive polarity power signal therethrough irrespective of polarity orientation of the battery. The negative

and positive polarity power signals are available for connection to a load device, such as a hearing aid. The device is thereby

provided with proper power polarity irrespective of the way in which the battery is inserted between the first and second

battery terminals. In accordance with one embodiment, the power supply

circuit is provided in an efficient and compact mounting configuration. A chip capacitor is utilized in the configuration.

The chip capacitor has a planar side and further includes first

and second capacitor terminals formed from first and second

metallized portions on the planar side. The power supply circuit is formed as a planar monolithic circuit having first and second

terminals for receiving DC power and third and fourth terminals

for supplying DC power of a constant polarity irrespective of

polarity of the DC power received at the first and second

terminals. The power supply circuit is mounted to the planar

side of the chip capacitor and the first and second terminals of

the power supply circuit are respectively connected to the first

and second metallized portions on the planar side of the chip

capacitor. Third and fourth metallized portions may be disposed

on the planar side of the chip capacitor and connected to the third and fourth terminals of the power supply circuit.

In accordance with further features of the mounting configuration, the chip capacitor further comprises a further

planar side disposed generally parallel to the planar side. The

first, second, third, and fourth metallized portions extend to the

further planar side. The first and second metallized portions are

formed as visual indicia indicating that power supply

connections thereto are not polarity sensitive while the third and

fourth metallized portions are formed as visual indicia

respectively indicating which power polarity is available thereat.

Other objects and advantages of the present invention will become apparent upon reference to the accompanying detailed

description when taken in conjunction with the following

drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of a

power supply circuit for use in supplying power of constant

polarity from a battery to a load irrespective of the polarity

orientation of the battery .

FIG. 2 is a schematic diagram of the circuit of FIG.1 illustrating current flow through the circuit when the battery is

in a polarity orientation differing from the one shown in FIG. 1 .

FIG. 3 is an exemplary graph of output voltage versus

battery input voltage at the battery input terminals for the circuit

of FIG.1 .

FIG. 4 is a schematic block diagram of a hearing aid

employing the circuit of FIG.1 .

FIG. 5 is a schematic diagram of the power supply circuit

of FIG. 1 with a voltage divider circuit that may assist in ensuring proper start-up operation.

FIGs. 6 - 8 are perspective views of the power supply

circuit mounted to a chip capacitor where the power supply

circuit is implemented as a monolithic integrated circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A power supply circuit 10 constructed in accordance with

one embodiment of the present invention is illustrated in FIG. 1 .

As illustrated, the power supply circuit 10 includes a first

terminal 1 5 and a second terminal 20 that are connected to a

battery 25. Terminals 1 5 and 20 supply battery power to a first

transistor switching circuit 30 and a second transistor switching

circuit 35.

The first transistor switching circuit 30 includes first and

second n-channel MOSFETs 40 and 45, each having a gate terminal 50, 55, a source terminal 60, 65, and a drain terminal

70, 75 respectively, and which operate, for example, in

enhancement mode. The gate terminal 50 of first n-channel

MOSFET 40 is connected to the second battery terminal 20. The

drain terminal 70 of first n-channel MOSFET 40 is connected to

the first battery terminal 1 5. The gate terminal 55 of the

second n-channel MOSFET 45 is connected to the first battery

terminal 15 while the drain terminal 75 is connected to the

second battery terminal 20. The sources 60 and 65 of the first

and second n-channel MOSFETS 40, 45 are connected together

and supply a negative polarity power signal at line 80.

The second transistor switching circuit 35 includes first

and second p-channel MOSFETs 90 and 95, each having a gate

terminal 100, 105, a source terminal 1 10, 1 1 5, and a drain

terminal 1 20, 1 25, respectively, and which operate, for

example, in enhancement mode. The gate terminal 100 of first

p-channel MOSFET 90 is connected to the second battery

terminal 20. The drain terminal 1 20 of first p-channel MOSFET

90 is connected to the first battery terminal 1 5. The gate

terminal 105 of the second p-channel MOSFET 95 is connected

to the first battery terminal 1 5 while the drain terminal 1 25 is

connected to the second battery terminal 20. The sources 1 10

and 1 1 5 of the first and second p-channel MOSFET 90, 95 are

connected together and supply a positive polarity power signal

at line 130.

In operation, the first transistor switching circuit through-

connects the negative polarity terminal of the battery 25 to terminal 80 for supply to a load 1 35 irrespective of the polarity

of the battery 25 between battery terminals 1 5 and 20.

Similarly, the second transistor switching circuit 35 through-

connects the positive polarity terminal of the battery 25 to

terminal 130 for supply to the load 135 irrespective of the

polarity of the battery 25 between terminals 1 5 and 20.

Operation of the circuit 10 can be illustrated with

reference to FIGs. 1 and 2 which show connection of the

battery to terminals 1 5 and 20 with two different polarity

orientations. In FIG. 1 , the battery 25 has its positive terminal 140 connected to the first battery terminal 15 and its negative

battery terminal 145 connected to the second battery terminal 20. In this orientation, the battery supplies control voltages to the gate terminals 50, 55, 100 and 105 of the MOSFETs 40, 45, 90, and 95. The control voltages cause first p-channel MOSFET 90 and second n-channel MOSFET 45 to go to a conductive state while causing second p-channel MOSFET 95 and first n-channel MOSFET 40 to go to a non-conductive state. As such, MOSFET 90 through-connects the power at the positive terminal 140 of the battery 25 to line 130 to supply the positive polarity power signal at line 130 to the load 135.

Similarly, MOSFET 45 through-connects the power at negative terminal 145 of the battery 25 to line 80 to supply the negative

polarity power signal at line 80 to the load 135. The MOSFETs 45 and 90 thus provide a current path therethrough illustrated by arrow 150.

In FIG. 2, the battery 25 has its positive terminal 140 connected to the second battery terminal 20 and its negative battery terminal 145 connected to the first battery terminal 15. In this orientation, the battery 25 supplies control voltages to the gate terminals 50, 55, 100 and 105 of the MOSFETs 40,

45, 90, and 95 which are opposite those supplied in connection

with the battery orientation illustrated in FIG. 1 . The control

voltages supplied in FIG. 2 cause second p-channel MOSFET 95 and first n-channel MOSFET 40 to go to a conductive state

while causing first p-channel MOSFET 90 and second n-channel

MOSFET 45 to go to a non-conductive state. As such, MOSFET

95 through-connects the power at the positive terminal 140 of

the battery 25 to line 1 30 to supply the positive polarity power

signal to the load 135. Similarly, MOSFET 40 through-connects

the power at negative terminal 145 of the battery 25 to line 80

to supply the negative polarity power signal to the load 135. The MOSFETs 40 and 95 thus provide a current path

therethrough illustrated by arrow 1 60. FIG. 3 is a graph illustrating the voltage at output lines

130 and 80 versus the battery voltage supplied across battery terminals 1 5 and 20. As illustrated, the output voltage,

illustrated by line 170, generally tracks the magnitude of the battery voltage for battery voltages below a first threshold

voltage VTHL The output voltage, however, is of opposite

polarity for battery voltages below VTHI . The circuit 10 does not

conduct battery power to the output lines 1 30 and 80 for

voltages between the first threshold voltage VTHI and a second

threshold voltage VTH2. For voltages greater than VTH2, the

output voltage generally tracks both the polarity and magnitude

of the battery voltage. The non-conductive range between VTHI

and VTH2 can be minimized by employing MOSFETs having very

low threshold voltages. Additionally, the output voltage will

more closely track the input voltage from the battery where MOSFETs having low source to drain resistances are employed. As can be recognized by those skilled in the art, the power supply circuit 10 can function as a transistor rectifier circuit which is relatively lossless compared to diode rectifier circuits, particularly when the threshold voltages of the

MOSFETs and the source to drain resistances of the MOSFETs are made to be very low.

FIG. 4 illustrates one embodiment of a hearing aid 200 employing the power supply circuit 10. The power supply circuit 10 is particularly well suited for use in the hearing aid since most hearing aids receive their power from low-voltage (about 1 .3 VDC) disc-type batteries. Hearing aid users often find it difficult to properly orient the battery with the correct polarity in the hearing aid 200. Therefore, the hearing aid user benefits from the hearing aid 200 being operable irrespective of the battery polarity orientation. Additionally, the power supply circuit 10, being constructed from FETs having limited drain to source resistances as well as requiring minimal control current

and gate voltages, is relatively lossless making it particularly well suited to the low voltage operation of the hearing aid 200.

As illustrated, the hearing aid 200 includes a microphone 205, an amplifier 210, a receiver 215, a battery 25 and the

power supply circuit 10. The microphone 205 operates to

- 12 -

transduce sound waves to electrical signals which are

subsequently amplified by the amplifier 210. The amplifier

output is supplied to the receiver 21 5 which transduces the electrical signals output from the amplifier 210 to sound waves

which may be heard by the user. The amplifier 210 receives

power from the battery 25 through an on/off switch 220 and

the power supply circuit 10. The microphone 205 may receive power from the amplifier. As will be readily recognized by those

skilled in the art, the amplifier 210 may include various filter and

amplification circuitry which tailors the amplifier response output

to the particular hearing loss of the user.

FIG. 5 illustrates a further embodiment of the power

supply circuit 10 which includes a voltage divider circuit 230

that may assist in ensuring proper start-up operation. The

voltage divider circuit 230 is connected between terminals 1 5

and 20 and includes resistors 235 and 240. The resistors 235

and 240 may, for example, each have a resistance of 100K.

The voltage divider circuit 230 includes a central node 245 that

is connected to the negative power polarity signal at line 80.

Alternatively, node 245 may be connected to the positive power

polarity signal at line 130.

Although the MOSFETs 40, 45, 90, 95 of the circuit 10

are illustrated as operating in enhancement mode, a similar

configuration can be implemented using depletion mode

MOSFETs. In such instance, the cut-off voltages of the depletion mode MOSFETs should be greater than the minimum battery voltage at which the load device must operate.

As previously noted, the power supply circuit 10 may be

easily implemented in a monolithic integrated circuit format.

When the power supply circuit 10 is implemented in this fashion, it may be mounted in the manner shown in FIGs. 6 and 7. As illustrated, a circuit, shown generally at 300, includes the power supply integrated circuit 310 and a chip capacitor 320. The chip capacitor 320 may be constructed, for example, in the manner set forth in U.S. Patent No. 5,367,430, and which is commercially available from Presidio Components, Inc. of

California. The chip capacitor 320 includes a first planar side 325 and a second planar side 330. A plurality of metallized

portions 335, 340, 345, and 350 are disposed on the first planar side 325 and extend around the edges of the capacitor 320 to the second planar side 330.

The power supply integrated circuit 310 may be constructed by implementing the circuit of FIG. 1 in a monolithic format using known fabrication techniques. The integrated circuit includes metallized pads 360 and 365 corresponding to battery supply inputs 15 and 20, and metallized pads 370 and 375 corresponding to output lines 80 and 130, respectively.

Metallized pads 360, 365, 370, and 375 are connected

respectively to the first, second, third, and fourth metallized portions 335, 340, 345, and 350 by respective wires 380 using , for example, known wire bonding techniques. A known non¬ conducting adhesive may further be used to assure mechanical stability of the mounting between the power supply integrated circuit 310 and the chip capacitor.

FIG. 7 illustrates the metallization on the second planar side 330 of the chip capacitor 320. As shown, metallized

portions 335 and 350 that are electrically connected to the battery inputs 15 and 20 of the circuit of FIG. 1 have rounded end terminals 400. The round end terminals 400 provide the assembler with a visual indication that there is no particular polarity associated with these outputs. Similarly, metallized portions 340 and 350 that are connected to the outputs 80 and 130 provide the assembler with a visual indication of the power polarity available thereat. Here, metallized portion 350 carries

the positive power polarity output as indicated by the Aplus sign@ shape of the metallization while metallized portion 340 carries the negative power polarity output as indicated by the Anegative sign© shape of the metallization. Metallization layers

335 and 345 also provide electrical connection to the chip capacitor 320 that may, for example, have a capacitance value of 2.2 uF. Capacitor 320 is non-polar in the illustrated

embodiment.

FIG. 8 is a further embodiment of a circuit which uses an

alternative connection technology to the wire bonding of the

embodiment of FIG. 6. In the embodiment of FIG. 8, the power

supply integrated circuit 310 is mounted, connection side down,

to the planar side 325 of the chip capacitor 320. Connections between the pads 360, 365, 370, and 375 (not shown in FIG.

8 since the connections are on the side of the circuit adjacent

planar surface 325) and the corresponding metallized portions

may be made using, for example, the C ⁴ ™ technology used by IBM Corporation. A known non-conducting adhesive may

further be used to assure mechanical stability of the mounting

between the power supply integrated circuit 310 and the chip

capacitor.

When the power supply circuit 10 is utilized in a hearing

aid, it is often necessary to provide a capacitor across the

battery terminal inputs to reduce noise spikes caused by class

D amplifiers typically used in such devices. The embodiments of FIGs. 6 - 8 are particularly advantageous for such devices

since the embodiments provide both the power supply circuit 10

and the requisite capacitor in a single circuit unit which requires

a minimal amount of space

Although the present invention has been described with

reference to a specific embodiment, those of skill in the art will

recognize that changes may be made thereto without departing

from the scope and spirit of the invention as set forth in the appended claims.