Electricity: battery or capacitor charging or discharging – Battery or cell charging – Pulsed
Reexamination Certificate
2000-10-16
2001-12-04
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
Pulsed
Reexamination Certificate
active
06326771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery power supply system, and, more particularly, to a buffered battery charger circuit capable of controlling the power supplied to an active system and to a rechargeable battery, and including circuitry for self-adjusting allocation of total power supply ensuring that an active system gets priority of power while maintaining a charge current for the rechargeable battery. Particular utility of the present invention is in a power supply system for portable electronic units; although other utilities are contemplated herein.
2. Description of Related Art
FIG. 1
is a simplified block schematic of a typical prior art power supply topology
20
for a portable electronic system
24
. The active system
24
gets power, conditioned by the system DC/DC converter
22
, either from the battery
18
or from the external input power adapter
10
. The input power adapter
10
gets the power from an external primary power source, such as an AC outlet or a DC source, and provides the power directly to both the system DC/DC converter
22
, through the separating diode
12
, and to the battery charger
14
. The battery
18
is connected and provides power to the system DC/DC converter
22
through the separating diode
16
, as long as the primary power source is not available. When the primary power source is available, the battery is isolated from the power input of the system DC/DC converter
22
by the reversed polarized (reversed biased) diode
16
. In addition, the battery
18
is charged when power is supplied by the primary power source, through the charger
14
. This topology in
FIG. 1
has the disadvantage of big and fast voltage transients at the node
25
, which is the input of the system DC/DC converter
22
.
FIG. 2
shows a simplified block diagram of a buffer battery power supply
20
′ topology. The battery pack
18
is permanently connected to the input of the system DC/DC converter
22
and provides the requested power. The external input power adapter
10
powers the battery charger
14
when an external primary power source is available. The external input power adapter
10
is intended to adapt the parameters of the primary source to the charger input requirements. The battery charger
14
powers in parallel both the system DC/DC converter
22
and the battery
18
to charge it or to maintain the voltage of the fully charged battery at the optimal level. This “buffer battery topology” limits the voltage variations at the system DC/DC converter input (node
25
) to normal battery pack voltage variations and does not allow fast voltage transients at this input. Furthermore, when the power requested by the system
24
temporarily exceeds the capability of the input power adapter
10
, both the input power adapter
10
and the battery
18
will deliver in parallel the power to the system
24
through the converter
22
. Disadvantageously, however, the circuit
20
′ shown in
FIG. 2
provides no mechanism by which the power supplied by the battery charger can be reduced or increase based on preset limits or demand from the battery, the system, or both.
Similarly, U.S. Pat. No. 5,698,964 issued to Kates et al. Provides a battery charging circuit topology. This circuit monitors the current from an AC adapter (i.e., I
in
) and adaptively utilizes all available current to charge the batteries. The system DC/DC converter is powered directly by the AC adapter after its connection; the battery is disconnected from the system. Thus the voltage at the input of the system DC/DC converter abides a heavy transient, from the low voltage of a discharged battery to the AC adapter voltage, every time higher than the maximum charged battery voltage. Furthermore, as the AC adapter output voltage could vary, no real control is provided for the power delivered by the AC adapter to both the system (e.g. portable electronic device) and the battery. A similar topology is provided in U.S. Pat. No. 5,723,970 issued to Bell, which suffers similar and/or additional drawbacks mentioned above.
The approach in the prior art to provide battery charge circuitry and a path to an active system is typically accomplished using separate paths between a power source and a rechargeable battery, and a power source an a load. In the case of the present invention, the source, battery and load (system) are all in parallel thus, the conventional charging/discharging approaches would be inadequate, since the voltage conditions on the battery must be accounted for when providing power to the system.
Thus, there exists a need to provide a buffered battery power supply system that can control both the total output power and the power delivered to the battery. Moreover, there exists a need to provide a system that will significantly reduce the voltage transients that may appear at the electronic device, the battery, or both. Also, there exists a need to provide a buffer topology (where the battery and system are in parallel with a source) that permits charging of the battery when the battery is deeply discharged, and that permits a variety of choices for the source voltage in addition to conventional PWM-type source voltages.
SUMMARY OF THE INVENTION
Accordingly, the present invention solves the aforementioned drawbacks by providing a buffer battery power supply system that includes feedback control of both the total output current delivered by the battery charger circuit and the voltage delivered to the battery. Feedback control is provided based on the total output power (total output current x total output voltage) delivered by the battery charger circuit. To permit charging of a deeply discharged battery while also supplying power to a system (or a DC/DC converter), the present invention also includes a battery switch circuit that selectively decouples the battery from a load (system) when the battery is in a deeply discharged state, yet still provides a path for a trickle charge (low current) to charge the battery sufficiently to begin regular charging.
In one embodiment of the present invention, a power supply system is provided that includes a charger circuit for generating a duty cycle for delivering power to an active system and a battery. A first feedback loop is provided to sense the total output current generated by the charger circuit and a second feedback loop is provided to sense the current delivered to said battery by the charger circuit. The first and second feedback loops including error circuits for generating an error signal to the charger circuit. The charger circuit adjust the duty cycle so thereby controlling the total output current delivered to the active system and the battery based on the value of the error signal. Also, a battery switch circuit is provided that decouples said battery from said active system when said battery voltage is less than the minimum voltage required to power said active system, and couples said battery to said charger circuit to receive a charging current.
In another embodiment of the present invention, a power supply system is provided that includes an input power source, and a charger circuit for generating a duty cycle for controlling the input power source to deliver controlled power to an active system and a battery. A first feedback loop is provided to sense the total output current generated by the charger circuit, the first feedback loop generating a first error signal based on the total output current and a preset threshold total output current signal. A second feedback loop is provided to sense the current delivered to the battery by the charger circuit, the second feedback loop generating a second error signal based on the current delivered to the battery and a preset threshold battery current signal. A third feedback loop is provided for sensing the total output power generated by the charger circuit, the third feedback loop generating a third error signal based on the total output power and a preset threshold total output power signal. Using the first, secon
02 Micro International Limited
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
Tibbits Pia
Wong Peter S.
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