U.S. patent application number 10/266338 was filed with the patent office on 2004-04-08 for solarswitch.
Invention is credited to Reynolds, Robert L..
Application Number | 20040066173 10/266338 |
Document ID | / |
Family ID | 31993598 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040066173 |
Kind Code |
A1 |
Reynolds, Robert L. |
April 8, 2004 |
SOLARSWITCH
Abstract
An active switch for electrically connecting and disconnecting a
power source such as a solar array to a charge storage device is
disclosed. The active switch allows a minimal amount of reverse
back current flow from the charge storage device to the power
source having a low on-resistance.
Inventors: |
Reynolds, Robert L.;
(Newbury Park, CA) |
Correspondence
Address: |
Philip T. Virga
Suite 105
1525 Aviation Blvd.
Redondo Beach
CA
90278
US
|
Family ID: |
31993598 |
Appl. No.: |
10/266338 |
Filed: |
October 7, 2002 |
Current U.S.
Class: |
320/141 |
Current CPC
Class: |
H02J 7/35 20130101; H01M
10/465 20130101; Y02E 10/56 20130101; Y02E 60/10 20130101; H01M
14/005 20130101 |
Class at
Publication: |
320/141 |
International
Class: |
H02J 007/04 |
Claims
What is claimed is:
1. An active switch charging system, comprising: an intermittent
current limited power source; a device for storing charge; and an
active switch for electrically connecting and disconnecting the
power source to the device wherein when disconnecting the power
source from the device the active switch allows a minimal amount of
reverse back current flow from the device to the power source.
2. The active switch charging system according to claim 1, wherein
the active switch further comprises: a field effect transistor
operated by logic control.
3. The active switch charging system according to claim 2, wherein
the logic control further comprises: a reverse current
detector.
4. The active switch charging system according to claim 3, wherein
the reverse current detector further comprises: an differential
amplifier.
5. The active switch charging system according to claim 2, wherein
the logic control further comprises: a voltage threshold
detector.
6. The active switch charging system according to claim 5, wherein
the voltage threshold detector further comprises a comparitor.
7. The active switch charging system according to claim 5, wherein
the voltage threshold detector further comprises: an operational
amplifier.
8. The active switch charging system according to claim 5, wherein
the voltage threshold detector further comprises: a battery
protection circuit.
9. The active switch charging system according to claim 5, wherein
the voltage threshold detector further comprises: a battery
regulation circuit.
10. The active switch charging system according to claim 2, wherein
the logic control further comprises: a light source detector.
11. The active switch charging system according to claim 2, wherein
the logic control further comprises: a power detector.
12. The active switch charging system according to claim 3, wherein
the logic control further comprises: a "loss less" current flow
detector.
13. An active switch charging system, comprising: an intermittent
current limited power source; a device for storing charge; and a
field effect transistor operated by logic control for electrically
connecting and disconnecting the power source to the device wherein
when disconnecting the power source from the device the active
switch allows a minimal amount of reverse back current flow from
the device to the power source.
14. The active switch charging system according to claim 13,
wherein the logic control further comprises: a reverse current
detector.
15. The active switch charging system according to claim 14,
wherein the reverse current detector further comprises: an
differential amplifier.
16. The active switch charging system according to claim 13,
wherein the logic control further comprises: a voltage threshold
detector.
17. The active switch charging system according to claim 16,
wherein the voltage threshold detector further comprises: a
comparitor.
18. The active switch charging system according to claim 17,
wherein the voltage threshold detector further comprises a battery
protection circuit.
19. The active switch charging system according to claim 17,
wherein the voltage threshold detector further comprises a battery
regulation circuit.
20. A solar switch comprising a field effect transistor operated by
an operational amplifier for electrically connecting and
disconnecting a solar source to a device whereby when disconnecting
the solar source from the device a minimal amount of reverse back
current flow from the device to the solar source is allowed.
Description
[0001] Conventional solar battery charging systems employ a "back
flow" or reverse current diode to prevent battery current from
flowing back through a solar array in the absence of solar energy.
Typically, a Schottky diode is used for this reverse current
protection due to a low forward voltage drop required for Schottky
diode operation. The forward voltage drop has a direct impact on
charge efficiency such that the less power that is dissipated
across the diode, the more charge power is delivered to the
battery. The charge efficiency has been acceptable when dealing
with macro solar charging systems since the battery charge voltages
have been typically "high" in ratio to the Schottky diode forward
voltage drop. However, this is not desirable in micro solar
charging systems where the charge voltages are not high in ratio to
the Schottky diode forward voltage drop. Therefore it would be
desirable to provide a circuit that prevents battery back flow
current having less forward voltage drop than a Schottky diode.
SUMMARY OF THE INVENTION
[0002] An active switch for electrically connecting and
disconnecting a power source such as a solar array to a charge
storage device is provided. The active switch allows a minimal
amount of reverse back current flow from the charge storage device
to the power source and has a low on-resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a graph illustrating the battery charge efficiency
versus battery voltage characteristics of a diode compared to an
active switch;
[0004] FIG. 2 shows a simplified circuit diagram incorporating an
active switch circuit in a micro solar charging system;
[0005] FIG. 3 shows a detailed circuit diagram implementing the
active switch circuit of FIG. 2 with commercially available
components;
[0006] FIG. 4 shows a simplified circuit diagram incorporating an
active switch circuit utilizing external logic input;
[0007] FIG. 5 shows a simplified circuit diagram incorporating an
active switch circuit utilizing a battery charge regulator;
[0008] FIG. 6 shows a simplified circuit diagram incorporating an
active switch circuit utilizing a photo transistor;
[0009] FIG. 7 shows a simplified circuit diagram incorporating an
active switch circuit as an internal battery protection circuit;
and
[0010] FIG. 8 shows a simplified circuit diagram incorporating an
active switch circuit utilizing an impedance matching DC to DC
convertor circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] Micro solar devices and micro solar charging systems
typically operate at voltages that are "low" in ratio to a Schottky
diode forward voltage drop. This results in more power being
dissipated in the diode and less charge power being delivered to a
device or charge storage device. Referring to FIG. 1 there is shown
a graph 20 illustrating battery charge efficiency 22 versus battery
voltage 24 characteristics of a diode compared to an active switch.
FIG. 1 shows the reduction in battery charge efficiency 22 as a
function of battery voltage 24 due to the "series" back flow
components. As shown by the solid line 26 the efficiency reduction,
caused by a 0.23 volt drop of a Schottky diode, becomes more
significant as the battery charge voltage decreases. A
microelectronic device (not shown) such as a cellular phone will
typically operate with a battery of 4.2 volts 30 or less. Other
micro electronics devices operate at battery voltages down to 0.8
volts 32. As can be seen in FIG. 1, the solar charging efficiency
will substantially degrade due to the power loss across the
Schottky diode.
[0012] Turning once again to FIG. 1, the dashed trace 28 shows the
"improved" solar charge efficiency of a "low loss" active switch
serving the same function of back flow or reverse current
protection. The active switch consists of a low voltage metal oxide
semiconductor field effect transistor (hereinafter referred to as a
MOSFET) with a very low source to drain resistance that is suitable
for use in microelectronic devices such as a cellular phone or
pocket charger. The active switch charge efficiency is based on a
series "resistance" and not a "voltage drop" therefore the charge
efficiency will increase further with less series current. The
current used to simulate trace 28 is 200 ma which would typically
be the high end of micro solar battery charging for a device such
as a cellular phone.
[0013] FIG. 2 below shows a simplified circuit diagram 36 of an
intermittent current limited power source such as a solar array 34
connected to a device for storing charge such as a battery 38
through an active switch circuit 40. The active switch circuit 40
substantially reduces the power that is lost by conventional
reverse current diodes normally associated with solar charging
devices. Referring once again to FIG. 2, the active switch circuit
40 consists of a reverse current detector IC-1 44 and a low loss
N-channel enhancement mode MOSFET switch Q1 46 having an internal
diode D1 50. In operation, incident solar energy generated by solar
array 34 causes a counter clockwise current flow to occur as shown
by "I-on" 48 in FIG. 2. The solar array 34 electromotive force
(EMF) forward biases D1 50 and current begins to flow. The reverse
current detector IC-1 44, which in this embodiment is shown as an
differential amplifier detects the positive difference voltage
across D1 50 at the non inverting input which causes Q1 46 to turn
on. Q1 46 acts a low loss switch with a very low source to drain
resistance overcoming the power loss associated with conventional
diodes. The absence of solar energy incident upon the solar array
34 causes the current flow described above to stop and current from
the battery attempts to flow in the reverse direction as indicated
by "I-OFF" 52 in FIG. 2. The reverse current detector IC-1 44
detects a negative differential voltage at the non inverting input
and causes Q1 46 to turn off.
[0014] More specifically, D1 50 and Q1 46 provide a voltage drop
such that IC-1 46 is able to detect current flow without the
addition of a series resistor that is normally present in current
sensing applications. Thus the directional current sense detector
is able to determine current flow without the usual power losses
associated with series resistors. In this manner, it is a "loss
less" current detection device since it adds no further power
losses to the system. It should be understood that D1 50
additionally would not conduct current in the I-Off direction
52.
[0015] FIG. 3 illustrates one example of a detailed circuit diagram
for implementing the active switch circuit 40 of FIG. 2 with
commercially available components. A solar array 34 having
sufficient voltage for charging a 4.2 lithium ion battery 38 having
an internal battery protection circuit and charge regulator 42 is
shown in FIG. 3. The solar array 34 connects to the battery 38
through the battery regulator 42 and the active switch circuit 40.
The active switch circuit 40 consists of a Burr-Brown operational
amplifier (part number OPA349) IC-1 44 and a low loss Siliconix
N-channel MOSFET (part number Si2302DS) switch Q1 46 having the
internal diode D1 50. As described above, the solar array 34
electromotive force (EMF) forward biases D1 50 and current begins
to flow. The Burr-Brown operational amplifier IC-1 44 detects the
positive difference voltage across D1 50 at the non inverting input
which causes Q1 46 to turn on and current begins to flow. The
absence of solar energy causes the current flow described above to
stop and current from the battery 38 attempts to flow in the
reverse direction wherein the Burr-Brown operational amplifier IC-1
44 detects a negative differential voltage at the non inverting
input and causes Q1 46 to turn off. The off-state current flow of
IC-1 46 Is approximately 6 micro amp.
[0016] FIG. 4 shows a simplified circuit diagram incorporating the
active switch circuit 40 wherein the operational amplifier 44 opens
and closes the MOSFET 46 by an external logic control line 60,
which by way of example only, may be an output control signal
generated from a computer algorithm or microelectronic device. The
embodiment shown in FIG. 4 may have less than 6 micro amps of
reverse current. Referring now to FIG. 5, there is shown another
embodiment wherein the active switch circuit 40 can be controlled
by a logic input 62 to the battery charge regulator 44 (which by
way of example only is a Maxim 1736 chip regulator). FIG. 5 allows
a small amount of back flow current to exist. Maximum back flow
current to the solar array 34 from the battery 38 is approximately
160 mirco amps through the battery regulator 44. This is a
tolerable situation since with a minimal amount of full sun
exposure, forward charging will compensate for the small amount of
charge lost due to the back flow current.
[0017] Referring now to FIG. 6, there is shown an active switch
circuit 40 operating as a battery protector circuit. In this
configuration comparitor IC 1 66 compares the divided battery
voltage from voltage divider R1 68 and R2 70 to the voltage at the
reference diode D1 72. If the divided voltage is higher than the
reference voltage, the active low loss switch remains on and passes
current. If the divided voltage is lower than the reference
voltage, the active low loss switch turns off and passes no current
thus protecting the battery 38 from over discharge. R1 68 and R2 70
are set to keep the battery 38 from going below a predetermined
safe battery voltage. The circuit shown in FIG. 6 allows a small
amount of back flow current to exist. Maximum back flow current to
the solar array 34 is approximately 180 mirco amps through the
battery regulator 44. This is a tolerable situation since with a
very small amount of full sun exposure on the solar array 34, the
forward charging will compensate for the small amount of charge
lost due to the back flow current. Complete drain of the battery 38
is prevented by the "battery low voltage cutoff" active switch.
More specifically, complete drain of the battery is prevented by
the "active switch" of the battery protector circuit that prevents
current flow in an "under voltage" condition of the battery i.e.:
approximately 2 volts for a 4.2 Lithium ion battery.
[0018] In yet another embodiment, FIG. 7 shows using a
phototransistor 64 as the logic input to control the MOSFET Q1 46
in an active switch configuration. Exposing the photo transistor to
light causes its internal resistance to lower which causes current
to flow in R1 and turn on the MOSFET active switch Q1. In still yet
another embodiment, FIG. 8 shows using an impedance matching
circuit and a DC-DC converter circuit 70 to control the active
switch. A logic pin-out port 76 from the DC-DC converter circuit 70
is used with a VISHAY 2N4858A MOSFET 74 as the logic input to
control the MOSFET Q1 46 in an active switch configuration. There
is less than 1 micro amps of reverse current in this
configuration.
[0019] It should further be noted that numerous changes in details
of construction, combination, and arrangement of elements may be
resorted to without departing from the true spirit and scope of the
invention as hereinafter claimed.
* * * * *