U.S. patent application number 10/922074 was filed with the patent office on 2006-02-23 for apparatus and method for selectively coupling a system with a first power supply or a second power supply.
Invention is credited to Jose Antonio Vieira Formenti, Mark Allen Hamlett.
Application Number | 20060038449 10/922074 |
Document ID | / |
Family ID | 35908974 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060038449 |
Kind Code |
A1 |
Formenti; Jose Antonio Vieira ;
et al. |
February 23, 2006 |
Apparatus and method for selectively coupling a system with a first
power supply or a second power supply
Abstract
An apparatus for selectively coupling a system with a first
power supply or a second power supply includes: (a) a first switch
for effecting a first coupling of the system with the first power
supply; (b) a second switch for effecting a second coupling of the
system with the second power supply; (c) a first switch control
unit coupled for controlling the first switch; (d) a second switch
control unit coupled for controlling the second switch; (e) a
connection director unit coupled with the first and second switch
control units for providing control signals to effect the first and
second coupling; at least one of the first and second coupling
being effected as an initial coupling establishing a generally
time-dependent increasing current between the system and one power
supply and a continuing coupling establishing a substantially
constant operating current between the system and the one power
supply.
Inventors: |
Formenti; Jose Antonio Vieira;
(Allen, TX) ; Hamlett; Mark Allen; (Richardson,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
35908974 |
Appl. No.: |
10/922074 |
Filed: |
August 19, 2004 |
Current U.S.
Class: |
307/131 |
Current CPC
Class: |
H02J 7/0068
20130101 |
Class at
Publication: |
307/131 |
International
Class: |
H01H 83/14 20060101
H01H083/14 |
Claims
1. An apparatus for selecting a power supply in a dual supply
system; the apparatus comprising: (a) a connection director unit;
said connection director unit presenting a plurality of actuating
signals; (b) a first switching unit coupled with said connection
director unit, coupled with a first power supply and coupled with
said system; said first switching unit generating a first
indicating signal to indicate whether said first switch is closed;
(c) a second switching unit coupled with said connection director
unit, coupled with a second power supply and coupled with said
system; said second switching unit generating a second indicating
signal to indicate whether said second switch is closed; (d) said
first switching unit being coupled with said second switching unit;
said first switching unit responding to a first signal combination
of said second indicating signal and at least one first actuating
signal of said plurality of actuating signals for effecting a first
coupling between said system and said first power supply; and (e)
said second switching unit being coupled with said first switching
unit; said second switching unit responding to a second signal
combination of said first indicating signal and at least one second
actuating signal of said plurality of actuating signals for
effecting a second coupling between said system and a second power
supply; said at least one second actuating signal including an
initiating signal and an operating signal; said second switching
unit responding to said initiating signal to establish a generally
time-dependent increasing current between said system and said
second power supply; said second switching unit responding to said
operating signal to establish a substantially constant operating
current between said system and said second power supply.
2. An apparatus for selecting a power supply in a dual supply
system as recited in claim 1 wherein said first switching unit
responds to said second predetermined signal combination to
interrupt said first coupling and wherein said second switching
unit responds to said first predetermined signal combination to
interrupt said second coupling.
3. An apparatus for selecting a power supply in a dual supply
system as recited in claim 1 wherein said first switching unit
includes a break-before-make circuit; said break-before-make
circuit ensuring that said first switching unit interrupts said
first coupling before said second switching unit effects said
second coupling when said connection director unit presents said
second predetermined signal combination.
4. An apparatus for selecting a power supply in a dual supply
system as recited in claim 1 wherein said first switching unit
includes a timer unit coupled for receiving said at least one first
actuating signal; said timer unit operating to assure said
substantially constant operating current between said system and
said second power supply occurs no more than a predetermined time
interval after said connection director unit presents said second
predetermined signal combination.
5. An apparatus for selecting a power supply in a dual supply
system as recited in claim 2 wherein said first switching unit
includes a break-before-make circuit; said break-before-make
circuit ensuring that said first switching unit interrupts said
first coupling before said second switching unit effects said
second coupling when said connection director unit presents said
second predetermined signal combination.
6. An apparatus for selecting a power supply in a dual supply
system as recited in claim 2 wherein said first switching unit
includes a timer unit coupled for receiving said at least one first
actuating signal; said timer unit operating to assure said
substantially constant operating current between said system and
said second power supply occurs no more than a predetermined time
interval after said connection director unit presents said second
predetermined signal combination.
7. An apparatus for selecting a power supply in a dual supply
system as recited in claim 3 wherein said first switching unit
includes a timer unit coupled for receiving said at least one first
actuating signal; said timer unit operating to assure said
substantially constant operating current between said system and
said second power supply occurs no more than a predetermined time
interval after said connection director unit presents said second
predetermined signal combination.
8. An apparatus for selectively coupling a system with a first
power supply or a second power supply; the apparatus comprising:
(a) a first switch for switchingly effecting a first coupling of
said system with said first power supply; (b) a second switch for
switchingly effecting a second coupling of said system with said
second power supply; (c) a first switch control unit coupled with
said first switch for controlling said first switch; (d) a second
switch control unit coupled with said second switch for controlling
said second switch; (e) a connection director unit coupled with
said first switch control unit and coupled with said second switch
control unit; said connection director unit providing a first
plurality of control signals to effect said first coupling; said
connection director unit providing a second plurality of control
signals to effect said second coupling; at least one of said first
coupling and said second coupling being effected as an initial
coupling and a subsequent continuing coupling; said initial
coupling establishing a generally time-dependent increasing current
between said system and one power supply of said first power supply
and said second power supply; said continuity coupling establishing
a substantially constant operating current between said system and
said one power supply.
9. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 8 wherein
said first switch control unit and said second switch control unit
cooperate to interrupt said coupling of said system with one power
supply of said first power supply and said second power supply when
the other power supply of said first power supply and said second
power supply is coupled with said system.
10. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 8 wherein
at least one switch control unit of said first switch control unit
and said second switch control unit includes a break-before-make
circuit coupled with the other switch control unit of said first
switch control unit and said second switch control unit; said
break-before-make circuit ensuring that at least one of said first
switch and said second switch interrupts said first coupling before
effecting said second coupling and interrupts said second coupling
before effecting said first coupling.
11. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 8 wherein
at least one switch control unit of said first switch control unit
and said second switch control unit includes a timer unit coupled
with the other switch control unit of said first switch control
unit and said second switch control unit; said timer unit operating
to ensure said continuity coupling is effected by said other switch
control unit no more than a predetermined time interval after said
initial coupling is established by said other switch control
unit.
12. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 8 wherein
at least one switch control unit of said first switch control unit
and said second switch control unit includes a break-before-make
circuit coupled with the other switch control unit of said first
switch control unit and said second switch control unit; said
break-before-make circuit ensuring that at least one of said first
switch and said second switch interrupts said first coupling before
effecting said second coupling and interrupts said second coupling
before effecting said first coupling.
13. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 9 wherein
at least one switch control unit of said first switch control unit
and said second switch control unit includes a timer unit coupled
with the other switch control unit of said first switch control
unit and said second switch control unit; said timer unit operating
to ensure said continuity coupling is effected by said other switch
control unit no more than a predetermined time interval after said
initial coupling is established by said other switch control
unit.
14. An apparatus for selectively coupling a system with a first
power supply or a second power supply as recited in claim 10
wherein at least one switch control unit of said first switch
control unit and said second switch control unit includes a timer
unit coupled with the other switch control unit of said first
switch control unit and said second switch control unit; said timer
unit operating to ensure said continuity coupling is effected by
said other switch control unit no more than a predetermined time
interval after said initial coupling is established by said other
switch control unit.
15. A method for selectively coupling a system with a first power
supply or a second power supply; the method comprising the steps
of: (a) in no particular order: (1) providing a first switch
connected for switchingly effecting a first coupling of said system
with said first power supply; (2) providing a second switch
connected for switchingly effecting a second coupling of said
system with said second power supply; (3) providing a first switch
control unit coupled with said first switch for controlling said
first switch; (4) providing a second switch control unit coupled
with said second switch for controlling said second switch; and (5)
providing a connection director unit coupled with said first switch
control unit and coupled with said second switch control unit; (b)
operating said connection director unit to provide a first
plurality of control signals and to provide a second plurality of
control signals; (c) operating said first switch control unit and
said second switch control unit to respond to said first plurality
of control signals and said second plurality of control signals to
selectively effect said first coupling and said second coupling;
and (d) effecting at least one of said first coupling and said
second coupling as an initial coupling and a subsequent continuing
coupling; said initial coupling establishing a generally
time-dependent increasing current between said system and one power
supply of said first power supply and said second power supply;
said continuing coupling establishing a substantially constant
operating current between said system and said one power
supply.
16. A method for selectively coupling a system with a first power
supply or a second power supply as recited in claim 15 wherein said
first switch control unit and said second switch control unit
cooperate to interrupt said coupling of said system with one power
supply of said first power supply and said second power supply when
the other power supply of said first power supply and said second
power supply is coupled with said system.
17. A method for selectively coupling a system with a first power
supply or a second power supply as recited in claim 15 wherein at
least one switch control unit of said first switch control unit and
said second switch control unit includes a break-before-make
circuit coupled with the other switch control unit of said first
switch control unit and said second switch control unit; said
break-before-make circuit ensuring that at least one of said first
switch and said second switch interrupts said first coupling before
effecting said second coupling and interrupts said second coupling
before effecting said first coupling.
18. A method for selectively coupling a system with a first power
supply or a second power supply as recited in claim 15 wherein at
least one switch control unit of said first switch control unit and
said second switch control unit includes a timer unit coupled with
the other switch control unit of said first switch control unit and
said second switch control unit; said timer unit operating to
ensure said continuity coupling is effected by said other switch
control unit no more than a predetermined time interval after said
initial coupling is established by said other switch control
unit.
19. A method for selectively coupling a system with a first power
supply or a second power supply as recited in claim 15 wherein at
least one switch control unit of said first switch control unit and
said second switch control unit includes a break-before-make
circuit coupled with the other switch control unit of said first
switch control unit and said second switch control unit; said
break-before-make circuit ensuring that at least one of said first
switch and said second switch interrupts said first coupling before
effecting said second coupling and interrupts said second coupling
before effecting said first coupling.
20. A method for selectively coupling a system with a first power
supply or a second power supply as recited in claim 16 wherein at
least one switch control unit of said first switch control unit and
said second switch control unit includes a timer unit coupled with
the other switch control unit of said first switch control unit and
said second switch control unit; said timer unit operating to
ensure said continuity coupling is effected by said other switch
control unit no more than a predetermined time interval after said
initial coupling is established by said other switch control unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to systems having a
plurality of power supplies. A preferred embodiment of the present
invention is directed to systems that have a battery power supply
and an alternating current power supply.
[0002] Two problems may occur when switching power supplies such
as, by way of example and not by way of limitation, when switching
between battery power supply and a dc power supply such as would be
derived from an AC adapter for a notebook computer or a handheld
computing or communication device. First, when powering up the
system using an AC adapter power supply, high peak currents (e.g.,
in excess of 70 Amps) may occur. Such a condition may cause
reliability problems and usually adds to the cost of the system
because of increased robustness of components required to withstand
the rigors of high inrush current such as, by way of example and
not by way of limitation, increased robustness of protection
components and switches. Second, there can be reliability issues
relating to switching between power supplies that have voltages
higher than the ratings for commercially available PMOS (P-channel
Metal Oxide Semiconductor) power switches (i.e., approximately 20
volts). Circuit designers commonly have added protection circuits
to overcome this reliability issue. However, the protection
circuitry may sometimes effect a lock up condition when switching
between power supplies at high voltage.
[0003] There is a need for an apparatus and method that can effect
switching between power supplies that limits current inrush when
powering up a system using an AC adapter-derived power supply.
[0004] There is a need for an apparatus and method that can effect
switching between power supplies that avoids a lock up condition
when switching between power supplies.
SUMMARY OF THE INVENTION
[0005] An apparatus for selectively coupling a system with a first
power supply or a second power supply includes: (a) a first switch
for effecting a first coupling of the system with the first power
supply; (b) a second switch for effecting a second coupling of the
system with the second power supply; (c) a first switch control
unit coupled for controlling the first switch; (d) a second switch
control unit coupled for controlling the second switch; (e) a
connection director unit coupled with the first and second switch
control units for providing control signals to effect the first and
second coupling; at least one of the first and second coupling
being effected as an initial coupling establishing a generally
time-dependent increasing current between the system and one power
supply and a continuing coupling establishing a substantially
constant operating current between the system and the one power
supply.
[0006] A method for selectively coupling a system with a first
power supply or a second power supply includes the steps of: (a) in
no particular order: (1) providing a first switch connected for
switchingly effecting a first coupling of the system with the first
power supply; (2) providing a second switch connected for
switchingly effecting a second coupling of the system with the
second power supply; (3) providing a first switch control unit
coupled with the first switch for controlling the first switch; (4)
providing a second switch control unit coupled with the second
switch for controlling the second switch; and (5) providing a
connection director unit coupled with the first switch control unit
and coupled with the second switch control unit; (b) operating the
connection director unit to provide a first plurality of control
signals and to provide a second plurality of control signals; (c)
operating the first switch control unit and the second switch
control unit to respond to the first plurality of control signals
and the second plurality of control signals to selectively effect
the first coupling and the second coupling; and (d) effecting at
least one of the first coupling and the second coupling as an
initial coupling and a subsequent continuing coupling; the initial
coupling establishing a generally time-dependent increasing current
between the system and one power supply of the first power supply
and the second power supply; the continuing coupling establishing a
substantially constant operating current between the system and the
one power supply.
[0007] It is, therefore, an object of the present invention to
provide an apparatus and method that can effect switching between
power supplies that limits current inrush when powering up a system
using an AC adapter power supply.
[0008] It is another object of the present invention to provide an
apparatus and method that can effect switching between power
supplies that avoids a lock up condition when switching between
power supplies.
[0009] Further objects and features of the present invention will
be apparent from the following specification and claims when
considered in connection with the accompanying drawings, in which
like elements are labeled using like reference numerals in the
various figures, illustrating the preferred embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an electrical schematic diagram illustrating a
prior art apparatus for selectively coupling a system with a first
power supply or a second power supply.
[0011] FIG. 2 is an electrical schematic diagram illustrating an
apparatus for selectively coupling a system with a first power
supply or a second power supply configured according to the present
invention.
[0012] FIG. 3 is an electrical schematic diagram illustrating an
alternate embodiment for the timer unit of the apparatus of the
present invention.
[0013] FIG. 4 is a flow diagram illustrating the method of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] FIG. 1 is an electrical schematic diagram illustrating a
prior art apparatus for selectively coupling a system with a first
power supply or a second power supply. In FIG. 1, an apparatus 10
is configured for selecting a power supply for a dual supply system
(not shown in FIG. 1) coupled with a system connection locus 18.
Apparatus 10 includes a connection director unit 12 coupled with
switching units 14, 16.
[0015] Switching unit 14 includes a switch control unit 20 coupled
with a PMOS switch 22. Switch control unit 20 includes an AND gate
24 and an "inverter" 26 ("inverter" 26 is a level shifter which
translates a digital control signal to a level-shifted digital
signal, ACDRV, the new level-shifted signal having a high voltage
of V.sub.CC, for example, and a low voltage of V.sub.CC-V.sub.NEG).
V.sub.NEG is a predetermined lower supply voltage established at a
level below supply voltage V.sub.CC. The level-shifting inverter 26
will hereafter be called simply an inverter. AND gate 24 receives a
first input 30 (signal ACON; AC adapter voltage connection on) from
connection director unit 12 and receives a second input 32 from
switching unit 16. When signal ACON received at first input 30 is a
"1" and the signal received from switching unit 16 at second input
32 is a "1", AND gate 24 provides a "1" signal to inverter 26. When
inverter 26 receives a "1" from AND gate 24, inverter 26 presents a
signal ACDRV as a "0" (V.sub.CC-V.sub.NEG) to PMOS switch 22,
thereby turning on PMOS switch 22 and coupling system connection
locus 18 with an AC adapter power supply (not shown in FIG. 1)
coupled at an AC adapter power input locus 36. Signal ACDRV is also
provided to a comparator 40. Comparator 40 receives a voltage of
(V.sub.CC-V.sub.REF; V.sub.REF is a reference voltage) at an
inverting input locus 42. When signal ACDRV is "0", comparator 40
presents a "0" at an output locus 46. When signal ACDRV is "1"
(i.e., at voltage level V.sub.CC), comparator 40 presents a "1" at
output locus 46.
[0016] Switching unit 16 includes a switch control unit 50 coupled
with a PMOS switch 52. Switch control unit 50 includes an AND gate
54 and an inverter 56. AND gate 54 receives a first input 60
(signal BATON; battery connected to system) from connection
director unit 12 and receives a second input 62 from switching unit
14. When signal BATON received at first input 60 is a "1" and the
signal received from switching unit 14 at second input 62 is a "1",
AND gate 54 provides a "1" signal to level-shifting inverter 56.
Level-shifting inverter 56 will hereafter be called simply an
inverter. When inverter 56 receives a "1" from AND gate 54,
inverter 56 presents a signal BATDRV as a "0" to PMOS switch 52,
thereby turning on PMOS switch 22 and coupling system connection
locus 18 with a PACK (i.e., battery pack) power supply (not shown
in FIG. 1) coupled at a PACK power input locus 66. Signal BATDRV
signal is also provided to a comparator 70. Comparator 70 receives
a reference voltage, V.sub.CC-V.sub.REF, at an inverting input
locus 72. When signal BATDRV is "0", comparator 70 presents a "0"
at an output locus 76. When signal BATDRV is "1", comparator 70
presents a "1" at output locus 76.
[0017] Output 46 is coupled with input locus 62 of AND gate 54 so
that a "1" cannot be provided to inverter 56 whenever signal ACDRV
is a "0". By this arrangement signal BAT DRV cannot close PMOS
switch 52 when PMOS switch 22 is closed. Output 76 is coupled with
input locus 32 of AND gate 34 so that a "1" cannot be provided to
inverter 36 whenever signal BATDRV is a "0". By this arrangement
signal ACDRV cannot close PMOS switch 22 when PMOS switch 52 is
closed.
[0018] Switching unit 16 also includes a protection circuit 80 that
includes Zener diodes 82, 84 opposingly coupled between source 53
and gate 55 of PMOS switch 52. Protection circuit 80 keeps V.sub.GS
(gate-to-source voltage) of PMOS switch 52 from exceeding a
predetermined value such as, by way of example and not by way of
limitation, 20 volts, absolute (i.e., .+-.20 volts).
[0019] Using apparatus 10, when either PACK power input locus 66 or
AC adapter power input locus 36 is switched to couple with system
connection locus 18 in response to signals ACON, BATON from
connection directing unit 12, comparators 40, 70 operate as
"break-before-make" systems. Comparator 70 controls operation of
AND gate 24 to ensure that signal BATDRV no longer turns on PMOS
switch 52 before signal ACDRV can turn on PMOS switch 22.
Comparator 40 controls operation of AND gate 54 to ensure that
signal ACDRV no longer turns on PMOS switch 22 before signal BATDRV
can turn on PMOS switch 52.
[0020] During power up conditions using an AC adapter power supply
unit (not shown in FIG. 1) connected with AC adapter power input
locus 36 with no battery pack present (or with battery pack
present), the secondary circuit of the AC adapter unit (not shown
in FIG. 1) can provide very high current to connection locus 18 for
short periods of time. Because the AC adapter is already on with
power at locus 36, very high current peaks are often present in
PMOS switch 22. It is difficult to control how fast the (internal
or external) PMOS switch 22 connects the AC adapter. By way of
example and not by way of limitation, with notebook computers
having a 5 amp standard AC adapter unit coupled, peak currents from
the AC adapter unit to the notebook computer (i.e., the system
coupled with system connection locus 18) can reach 70 Amps for
several hundred microseconds until protection circuitry internal to
the AC adapter unit is activated. Such potential for a high current
gives rise to reliability considerations in designing systems
because of power dissipation (and associated heat) and excessive
current through PMOS switch 22. Decreasing rise times at gate 25 of
PMOS switch 22 reduces the undesirable current peak but at the
expense of additional power dissipation and heat, and is therefore
not an effective solution to this current inrush problem.
[0021] Another drawback with apparatus 10 is that PMOS 52 must
always be turned off using the higher voltage applied at system
connection locus 18. Many external switching FET (Field Effect
Transistor) devices having a rated V.sub.GS at 20 volts. This high
voltage requires using protection circuit 80 (described above) to
clamp gate 55 of PMOS switch 52 during turn-off transients. For
systems operating with voltages higher than the clamping voltage of
protection circuit 80, a lockup condition will occur when a command
to switch to AC adapter power is issued by connection directing
unit 12 and BATDRV locus 55 exceeds the system voltage at system
connection locus 18 by more than a predetermined amount, such as 20
volts. That is, when connection directing unit 12 changes signal
ACON from "0" to "1" and changes signal BATON from "1" to "0" and
voltage at BATDRV input locus 55 exceeds voltage at system
connection locus 18 by 20 volts or more (for example), Zener diodes
82, 84 (gate clamp diodes) will break down when signal BATDRV
increases (BATDRV "1" is typically set to voltage V.sub.CC. Voltage
at system, locus 18, can initially be as low as 0 V). Under such
conditions, the threshold voltage at noninverting input locus 74 of
amplifier 70 will never be reached, amplifier 70 will not fulfill
its break-before-make function, PMOS switch 52 will be off while
PMOS switch 22 will also be left off indefinitely, thereby leaving
the system locus 18 unpowered indefinitely, even though power is
desired from the AC adapter.
[0022] FIG. 2 is an electrical schematic diagram illustrating an
apparatus for selectively coupling a system with a first power
supply or a second power supply configured according to the present
invention. In FIG. 2, an apparatus 110 is configured for selecting
a power supply for a dual supply system (not shown in FIG. 2)
coupled with a system connection locus 118. Apparatus 110 includes
a connection director unit 112 coupled with switching units 114,
116.
[0023] Switching unit 114 includes a switch control unit 120
coupled with a PMOS switch 122. Switch control unit 120 includes an
AND gate 124 and an inverting level-shifter (hereafter referred to
as an inverter) 126. AND gate 124 receives a first input 130
(signal ACON; AC adapter-to-system on) and a second signal SOFT
(soft start) from connection director unit 112. AND gate 124
receives a second input 132 from switching unit 116.
[0024] Preferably, AC adapter power is initiated for apparatus 110
using signal SOFT for a predetermined time to initiate a soft start
for apparatus 110. To initiate a soft start, signal SOFT is set to
a "1". When the signal received from switching unit 116 at input
132 is also a "1" (at the same time signal SOFT is set to a "1")
inverter 126 is set to a HIGH Z state in which output signals from
inverter 126 do not seek to drive toward a maximum value or toward
a minimum value. In this HIGH Z orientation, a soft start circuit
190 is actuated and serves to establish a generally time-dependent
increasing current through a PMOS transistor 122. Signal SOFT turns
on an NMOS (N channel Metal Oxide Semiconductor) switch 191 to
complete a circuit through an RC (Resistor-Capacitor) circuit
including a resistor 192 coupled between a V.sub.NEG voltage node
127 and a locus 193 in common with a gate 125 of PMOS transistor
122. Soft start circuit 190 also includes a capacitor 194 coupled
between locus 193 and drain 123 of PMOS transistor 122, which is in
common with a system connection locus 118 to which the system to be
powered is coupled (the system is not shown in FIG. 2). Applying
signal SOFT to soft start circuit 190 permits a relatively gradual
increase of gate current applied at gate 125, thereby establishing
a generally time-dependent increasing current between system
connection locus 118 and an AC power input locus 136 to which an AC
power supply (not shown in FIG. 2) is coupled. High levels of
inrush current are thereby avoided. After a time, signal SOFT is
set to "0", turning off NMOS transistor 191, and setting signal
ACON at first input 130 to "1". When signal ACON is a "1" and the
signal received from switching unit 116 at second input 132 is a
"1", AND gate 124 provides a "1" signal to inverter 126. When
inverter 126 receives a "1" from AND gate 124, inverter 126
presents a signal ACDRV as a "0" to PMOS switch 122, thereby
turning on PMOS switch 122 and maintaining coupling between system
connection locus 118 and an AC adapter power supply (not shown in
FIG. 2) coupled at AC adapter power input locus 136. Signal ACDRV
is also provided to a comparator 140. Comparator 140 receives a
reference voltage, V.sub.CC-V.sub.REF, at an inverting input locus
142. When signal ACDRV is "0", comparator 140 presents a "0" at an
output locus 146. When signal ACDRV is "1", comparator 140 presents
a "1" at output locus 146.
[0025] Switching unit 116 includes a switch control unit 150
coupled with a PMOS switch 152. Switch control unit 150 includes an
AND gate 154 and an inverter 156. AND gate 154 receives a first
input 160 (signal BATON; battery switch 152 on) from connection
director unit 112 and receives a second input 162 from switching
unit 114. When signal BATON received at first input 160 is a "1"
and the signal received from switching unit 114 at second input 162
is a "1", AND gate 154 provides a "1" signal to inverting
level-shifter (hereafter referred to as an inverter) 156. When
inverter 156 receives a "1" from AND gate 154, inverter 156
presents a signal BATDRV as a "0" to PMOS switch 152, thereby
turning on PMOS switch 152 and coupling system connection locus 118
with a PACK (i.e., battery pack) power supply (not shown in FIG. 2)
coupled at a PACK power input locus 166. Signal BATDRV is also
provided to comparator 170. Comparator 170 receives a reference
voltage of V.sub.CC-V.sub.REF at an inverting input locus 172. When
signal BATDRV is "0", comparator 170 presents a "0" at an output
locus 176. When signal BATDRV is "1", comparator 170 presents a "1"
at output locus 176.
[0026] Output 146 is coupled with input locus 162 of AND gate 154
so that a "1" cannot be provided to inverter 156 whenever signal
ACDRV is a "0". By this arrangement signal BATDRV cannot close PMOS
switch 152 when PMOS switch 122 is closed.
[0027] Switching unit 116 also includes a protection circuit 180
that includes Zener diodes 182, 184 opposingly coupled between
source 153 and gate 155 of PMOS switch 152. Protection circuit 180
keeps V.sub.GS (gate-to-source voltage) of PMOS switch 152 from
exceeding a predetermined value such as, by way of example and not
by way of limitation, 20 volts.
[0028] Output 176 is coupled with a reset node 204 of a timer unit
200. Timer unit 200 receives signal BATON at an inverting set node
202. Timer 200 presents output signals at an output node 206. An OR
gate 208 has a first input 210 coupled with output 176 and a second
input 212 coupled with timer output node 206.
[0029] When signal BATON goes to "0" (and signal ACON goes to "1")
indicating an order from connection director unit to disconnect
system locus 118 from PACK power input locus 136 and to connect
system connection locus 118 with AC power input locus 136, signal
BATON is applied at inverting set node 202, thereby setting timer
unit 200. If voltage at BATDRV input locus 155 exceeds voltage at
system connection locus 118 by 20 volts or more, Zener diodes 182,
184 (gate clamp diodes) will break down when signal BATDRV
increases, as described earlier herein in connection with FIG. 1.
However, OR gate 208 will apply a "1" signal if either of its input
loci 210, 212 experiences a "1" signal. That is, if amplifier 170
reaches sufficient threshold voltage to present a "1" signal at
output 176, OR gate 208 will present a "1" to AND gate 124 on line
132, thereby permitting AND gate 124 to respond to signal ACON
going to a "1" value by presenting a "1" to inverter 126 and gating
PMOS transistor 122 to complete a circuit between system connection
locus 118 and AC power input locus 136. A "1" signal on line 176
will also be applied to reset node 204 of timer unit 200 and reset
timer unit 200. This is a normal shift from battery power to AC
power.
[0030] If a lock up condition occurs with amplifier 170 (as
described earlier herein with in connection with FIG. 1), then
timer unit 200 will ensure that a "1" signal is presented from
output node 206 to input 212 of OR gate 208 after a predetermined
time has elapsed, so that PMOS switch 122 will be turned on by
switch control unit 120 substantially as described when output 176
is a "1". This use of timer unit 200 precludes there being an
indefinite period for a lock up condition being experienced by
break-before-make circuit (embodied in amplifier 170). Breakdown of
Zener diodes 182, 184 and therefore possible indefinite turn off of
both PMOS transistor 152 and PMOS transistor 122 is thereby avoided
(an indefinite state where there is no system power for an
indefinitely long time is avoided). The make-before-break
configuration ensures that PMOS switch 152 is turned off before
signal ACON can effect turning on of PMOS switch 122. It is
preferable that apparatus 110 effect initial powering up using AC
adapter power and effect any change to AC adapter power from
battery power (or from no initial system power) using an initial
condition with signal SOFT at a "1" followed by a continuing
condition in which signal ACON is at a "1".
[0031] FIG. 3 is an electrical schematic diagram illustrating an
alternate embodiment for the timer unit of the apparatus of the
present invention. In FIG. 3, line 376 from a break-before-make
circuit embodied in a comparator (not shown in FIG. 3) is coupled
with a reset node 404 of a timer unit 400. Timer unit 400 receives
signal BATON at an inverting set node 402. Timer unit 400 presents
output signals at an output node 406. An OR gate 408 has a first
input 410 coupled with output 376 and a second input 412 coupled
with timer output node 406.
[0032] When signal BATON goes to "0" (and signal ACON goes to "1")
indicating an order from a connection director unit (not shown in
FIG. 3) to disconnect a system (not shown in FIG. 3) from battery
power and to connect the system with AC power, signal BATON is
applied at inverting set node 402, thereby setting timer unit 400.
If BATDRV voltage with respect to system voltage is sufficiently
high, protection circuits protecting transistor switching units
will break down, as described earlier herein in connection with
FIGS. 1 and 2. OR gate 408 will apply a "1" signal if either of its
input loci 410, 412 experiences a "1" signal. If sufficient
threshold voltage is present to support normal operations, line 376
will present a "1" at input 410 and OR gate 408 will present a "1"
to AND gate 324 on line 332, thereby permitting AND gate 324 to
respond to signal SOFT going to a "1" value by presenting a "1" to
inverting level-shifter (hereafter referred to simply as inverter)
326 to set inverter 326 in a HIGH Z mode. Only when signal SOFT is
"1" and output from OR gate 408 is "1" and signal ACON is "1" can
inverter 326 turn on PMOS transistor 122 to complete a circuit
between a system and AC power.
[0033] If a lock up condition occurs because of not achieving a
threshold voltage (as described earlier herein with in connection
with FIGS. 1 and 2), then timer unit 400 will ensure that a "1"
signal is presented from output node 406 to input 412 of OR gate
408 after a predetermined time has elapsed, so that PMOS switch 322
will be turned on substantially as described when output 376 is a
"1". This use of timer 400 precludes there being an indefinite
period for a lock up condition being experienced by
break-before-make circuit (embodied in comparator 370; not shown).
Breakdown of protective circuits and damage to PMOS switches are
thereby avoided. The make-before-break configuration of the timer
unit configuration illustrated in FIG. 3 ensures that a PMOS switch
connecting a system with battery power is turned off before either
signal SOFT or signal ACON can effect connecting a system with AC
power.
[0034] FIG. 4 is a flow diagram illustrating the method of the
present invention. In FIG. 4, a method 500 for selectively coupling
a system with a first power supply or a second power supply begins
at a START locus 502. Method 500 continues with the step of, in no
particular order, (1) providing a first switch connected for
switchingly effecting a first coupling of the system with the first
power supply, as indicated by a block 504; (2) providing a second
switch connected for switchingly effecting a second coupling of the
system with the second power supply, as indicated by a block 506;
(3) providing a first switch control unit coupled with the first
switch for controlling the first switch, as indicated by a block
508; (4) providing a second switch control unit coupled with the
second switch for controlling the second switch, as indicated by a
block 510; and (5) providing a connection director unit coupled
with the first switch control unit and coupled with the second
switch control unit, as indicated by a block 512.
[0035] Method 500 continues with the step of operating the
connection director unit to provide a first plurality of control
signals and to provide a second plurality of control signals, as
indicated by a block 514. Method 500 continues with the step of
operating the first switch control unit and the second switch
control unit to respond to the first plurality of control signals
and the second plurality of control signals to selectively effect
the first coupling and the second coupling, as indicated by a block
516.
[0036] Method 500 continues with the step of effecting at least one
of the first coupling and the second coupling as an initial
coupling and a subsequent continuing coupling; the initial coupling
establishing a generally time-dependent increasing current between
the system and one power supply of the first power supply and the
second power supply; the continuing coupling establishing a
substantially constant operating current between the system and the
one power supply, as indicated by a block 518. Method 500
terminates at an end locus 520.
[0037] It is to be understood that, while the detailed drawings and
specific examples given describe preferred embodiments of the
invention, they are for the purpose of illustration only, that the
apparatus and method of the invention are not limited to the
precise details and conditions disclosed and that various changes
may be made therein without departing from the spirit of the
invention which is defined by the following claims:
* * * * *