Battery charger with battery detection circuit

• US 5,422,560 A
• Filed: 03/18/1993
• Issued: 06/06/1995
• Est. Priority Date: 09/30/1991
• Status: Expired due to Fees

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: TelCom Semiconductor, Inc. (Microchip Technology Incorporated)
• Inventors: Yan, Raymond C.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/034,175
• Time in Patent Office: 810 Days
• Field of Search: 320/15, 320/22-24, 320/35, 320/36, 320/31
• US Class Current: 320/160
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A battery charger including a battery detector at a node at which a battery is connectable. When a battery is not present, a voltage at the node fluctuates, but when a battery is present, the battery holds the voltage substantially constant. A level shifter shifts the voltage at the node. If no battery is present, the shifted voltage will fall below a predetermined threshold, but if a battery is present, the shifted voltage will remain above the predetermined threshold. A ground sense comparator detects whether or not the shifted voltage is below the predetermined threshold, and provides a battery detection signal accordingly. A controllable charge driver couples power from a power supply through to a battery, to charge the battery. An integrated circuit provides logic functions of the apparatus, including logic functioning as a charge controller. The charge controller is responsive to the battery detection signal to provide a charge drive signal to turn on the controllable charge driver only if a battery is present. The battery charger is capable of fast charging a wide variety of batteries according to a user-selectable charge rate.

Claims

1. An apparatus for detecting the presence or absence of a battery which has a terminal electrically connectable to and removable from the apparatus, the apparatus comprising:

a battery detection node (14) at which the terminal of the battery is electrically connectable to the apparatus, wherein when the battery is not present, a voltage (VN) at the battery detection node fluctuates, and wherein when the battery is present, the battery holds the voltage at the battery detection node substantially constant; and

a battery detector (12), coupled to the battery detection node, for detecting whether the voltage is fluctuating or is substantially constant, and thereby sensing whether the battery is or is not connected to the apparatus;

wherein the battery detector further comprises;

a ground sense input node (24); and

a level shifter (18), coupled to the battery detection node and the ground sense input node, for shifting the voltage at the battery detection node into a shifted voltage (VL) at the ground sense input node.

2. The apparatus of claim 1, wherein the level shifter comprises:

a capacitor (20) coupled between the battery detection node and the ground sense input node; and

a zener diode (22) coupled to the ground sense input node.

3. The apparatus of claim 1, wherein:

when the battery is present, the shifted voltage remains above a predetermined threshold (VT₃); and

when the battery is not present, the shifted voltage goes below the predetermined threshold.

4. The apparatus of claim 3, wherein the means for sensing further comprises:

a ground sense comparator (26), coupled to the ground sense input node, for detecting whether the shifted voltage is below the predetermined threshold, and for providing a battery detection signal (BATT) indicating whether the shifted voltage is below the predetermined threshold.

5. The apparatus of claim 4, wherein the ground sense comparator further comprises:

an integrated circuit in which logic functions of the ground sense comparator are embodied.

6. The apparatus of claim 4, wherein:

the battery detector further comprises a latch system (48), coupled to the ground sense comparator and to receive a sampling signal (SAMPLE), for providing a latched battery detection signal (LATCHED BATT) according to the battery detection signal and in response to the sampling signal.

7. The apparatus of claim 4 wherein the ground sense comparator further comprises:

first, second, third, and fourth transistors (30, 32, 34,

     36) each having a first power terminal coupled to receive a power signal (V_DD), and each having a second power terminal, and each having a control terminal, the control terminals of the first, second, third, and fourth transistors being coupled together and to the second power terminal of the first transistor;

a fifth transistor (38) having a first power terminal coupled to the second power terminal of the first transistor, and having a second power terminal coupled to receive a power reference (ground), and having a control terminal coupled to receive a bias reference signal (V_BIAS);

sixth and seventh transistors (40,

     42), each having a first power terminal coupled to the second power terminal of the third and fourth transistors, respectively, and each having a second power terminal, and each having a control terminal, the control terminals of the sixth and seventh transistors being coupled together and to the second power terminal of the fourth transistor; and

eighth and ninth transistors (44,

     46), each having a first power terminal coupled to the second power terminals of the sixth and seventh transistors, respectively, and each having a second power terminal coupled to receive the power reference, and each having a control terminal coupled to the ground sense input node and to ground, respectively;

wherein

the ground sense comparator receives the shifted voltage at the control terminal of the eighth transistor, and provides the battery detection signal at the second power terminal of the third transistor.

8. The apparatus of claim 7, wherein the level shifter comprises:

a capacitor (20) coupled between the battery detection node and the ground sense input node; and

a zener diode (22) coupled to the ground sense input node.

9. The apparatus of claim 7, wherein the battery detector further comprises:

a latch system (48), coupled to the second power terminal of the third transistor to receive the battery detection signal, for providing a latched battery detection signal (LATCHED BATT) according to the battery detection signal and in response to a sampling signal.

10. An apparatus for detecting, before a significant charging current is delivered for charging a battery, the presence or absence of said battery, where said battery has a terminal electrically connectable to and removable from the apparatus, the apparatus comprising:

current-limiting means for delivering a current-limited probe signal having an AC component to a battery detection node at which the terminal of the battery is electrically connectable to the apparatus, wherein when the battery is not present, a fluctuating voltage develops at the battery detection node due to the probe signal, and wherein when the battery is present, the battery holds the voltage at the battery detection node substantially constant; and

a battery detector, coupled to the battery detection node, for detecting, independently of the absolute Dc voltage of a potentially present battery and before a significant amount of charge is delivered for charging the potentially present battery, whether the voltage at the battery detection node is fluctuating or is substantially constant, and thereby sensing whether the battery is or is not connected to the apparatus, said battery detector including DC blocking means, coupled to the battery detection node, for blocking a DC component of the voltage while passing through, for purposes of said detection of the fluctuating or nonfluctuating attribute of said voltage, an AC component of the voltage;

wherein the battery detector further comprises;

first, second, third, and fourth transistors (30, 32, 34,

     36) each having a first power terminal coupled to receive a power signal (VDD), and each having a second power terminal, and each having a control terminal, the control terminals of the first, second, third, and fourth transistors being coupled together and to the second power terminal of the first transistor;

a fifth transistor (38) having a first power terminal coupled to the second power terminal of the first transistor, and having a second power terminal coupled to receive a power reference (ground), and having a control terminal coupled to receive a bias reference signal (V_BIAS);

sixth and seventh transistors (40,

     42), each having a first power terminal coupled to the second power terminal of the third and fourth transistors, respectively, and each having a second power terminal, and each having a control terminal, the control terminals of the sixth and seventh transistors being coupled together and to the second power terminal of the fourth transistor; and

eighth and ninth transistors (44,

     46), each having a first power terminal coupled to the second power terminals of the sixth and seventh transistors, respectively, and each having a second power terminal coupled to receive the power reference, and each having a control terminal, the control terminal of the eighth transistor being coupled to the battery detection node, and the control terminal of the ninth transistor being coupled to ground.

11. An apparatus for charging a battery, the apparatus comprising:

means (12) for detecting and indicating whether the battery is coupled to the apparatus independently of absolute battery voltage; and

charging means (104,

     108), responsive to the means for detecting and indicating, for providing a charging signal to the battery when the battery is indicated to be coupled to the apparatus;

wherein the battery to-be-charged includes a battery diode, and the apparatus further comprises;

compensating means (120), couplable to the to-be-charged battery, for compensating for the voltage drop of the battery diode such that the means for detecting and indicating will not sense a fluctuating voltage drop across the battery diode during charging operations of the apparatus.

12. A battery charger for charging a battery which is connectable thereto, the charger comprising:

first and second battery nodes connectable to said battery;

charge supply means for supplying a charging signal to at least one of the first and second battery nodes, where the charging signal includes a DC component and an AC component, and where the AC component is substantially absorbed by the battery when the battery is connected to the first and second battery nodes; and

battery detecting means, coupled to the least one of the first and second battery nodes receiving the charging signal, for separating the AC component of the charging signal from the DC component, comparing the magnitude of the separated AC component against a predefined threshold level, and generating a battery-absent signal when the magnitude of the separated AC component exceeds the predefined threshold level;

wherein the battery detecting means includes;

comparison means for producing a comparison signal indicating the relation between the magnitude of the separated AC component and the predefined threshold level; and

gating means, coupled to the comparison means, for gating the comparison signal during a time span when the AC component is at or near its maximum magnitude, and for producing a gated comparison signal indicating the relation between the magnitude of the separated AC component and the predefined threshold level when the AC component is at or near its maximum magnitude.

13. A battery charger according to claim 12 wherein the battery detecting means further includes:

latching means, coupled to the gating means, for latching the gated comparison signal and producing therefrom a latched battery-absent signal that indicates whether the battery is or is not connected to the first and second battery nodes.

14. A battery charger according to claim 13 wherein the charge supply means receives and responds to the latched battery-absent signal by refraining from supplying the charging signal when the latched battery-absent signal indicates that the battery is not connected to the first and second battery nodes.

15. A battery charger for charging a battery which is connectable thereto, the charger comprising:

first and second battery nodes connectable to said battery;

charge supply means for supplying a charging signal to at least one of the first and second battery nodes, where the charging signal includes a DC component and an AC component, and where the AC component is substantially absorbed by the battery when the battery is connected to the first and second battery nodes; and

battery detecting means, coupled to the least one of the first and second battery nodes receiving the charging signal, for separating the AC component of the charging signal from the DC component, comparing the magnitude of the separated AC component against a predefined threshold level, and generating a battery-absent signal when the magnitude of the separated AC component exceeds the predefined threshold level;

wherein the battery detecting means includes;

clamping and level-shifting means for shifting and clamping the separated AC component of the charging signal to produce therefrom a clamped signal having predefined minimum and maximum magnitudes; and

comparison means, receiving the clamped signal, for producing therefrom a comparison signal indicating the relation between the magnitude of the clamped signal and a predefined threshold magnitude.

16. A method for detecting the presence of a battery wherein the battery, if present, substantially absorbs a low-level AC signal presented to it, said method comprising the steps of, prior to charging the battery:

supplying an absorbable AC signal to a battery connecting post;

separating an AC component of a voltage developed at the battery connecting post from any DC component simultaneously developed thereat; and

determining whether the separated AC component is of substantial or insubstantial magnitude, the latter indicating the battery is present while the former indicates the battery is absent;

wherein the battery optionally includes an internal diode, the method further comprising the step of supplying a forward biasing current to the battery for keeping the internal battery diode, if present, in a forward biased state.