Safety circuit for charging devices

• US 8,803,472 B2
• Filed: 07/28/2007
• Issued: 08/12/2014
• Est. Priority Date: 07/28/2007
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Adelman, Lonnie W., King, Clarence R. III, Regan, Patrick, Ramirez, Jose De Jesus
• Primary Examiner(s): Tso, Edward H
• Assistant Examiner(s): PIGGUSH, AARON C
• Application Number:
  US11/829,904
• Publication Number:
  US 20090027003A1
• Time in Patent Office: 2,572 Days
• Field of Search: 320/106, 320/162, 320/165, 320/167
• US Class Current: 320/106
• CPC Class Codes: H02J 7/0029 with safety or protection devices or circuits

Abstract

Systems and methods for implementing a safety circuit in charging devices are disclosed. In an exemplary embodiment, a method may include closing a latch to stop delivery of a charging current to a battery when voltage produced by the battery indicates that the battery is non-rechargeable. The method may also include dropping a threshold from an initial value for the voltage produced by the battery to a baseline value so that the latch remains closed even if the voltage produced by the non-rechargeable battery drops below the initial value of the threshold. The method may also include resetting the latch each time a battery is connected to the charging device.

Claims

1. A method comprising:

a closing a latch to stop delivery of a charging current to a battery when voltage produced by the battery indicates that the battery is non-rechargeable;

dropping a threshold from an initial value for the voltage produced by the battery to a baseline value so that the latch remains closed even if the voltage produced by the non-rechargeable battery drops below the initial value of the threshold;

resetting the latch each time a battery is connected to the charging device; and

providing a non-charging current to a device including the battery to keep the device powered on even after charge cutoff, the non-charging current is less than a level of current that vents a non-rechargeable battery.

2. The method of claim 1, further comprising resetting the threshold to the initial value each time a battery is connected to the charging device.

3. The method of claim 2, wherein resetting the threshold is in response to a signal from an electronic device holding the battery.

4. The method of claim 3, wherein the signal is delivered from the electronic device when the electronic device is connected to the charging device.

5. The method of claim 3, wherein the signal from a signal that accords with a Universal Serial Bus specification.

6. The method of claim 1, wherein the baseline value is substantially lower than the initial value for the voltage produced by the battery.

7. The method of claim 3, wherein the baseline value is about 0 volts.

8. The method of claim 1, wherein power is supplied to charge the battery only after a device containing the battery is enumerated.

9. A safety circuit for a charging device comprising:

a first comparator configured to compare voltage produced by a battery to a threshold, output from the first comparator indicating if a battery is a rechargeable battery or a non-rechargeable battery;

a second comparator receiving the output from the first comparator, the second comparator latching closed to stop delivery of a charging current to the battery if the battery is non-rechargeable;

an FET connected to the first comparator, if the battery is a non-rechargeable battery, the FET turning on to drop the threshold from an initial value to a baseline value to latch the first comparator in a high state, and the second comparator in a low state, even if voltage produced by the battery drops below the initial value; and

a reset circuit coupled to the first comparator and the second comparator, the reset circuit issuing a reset signal to the first comparator and the second comparator each time a battery is connected to the charging device.

10. The safety circuit of claim 9, wherein the battery is a non-rechargeable battery if voltage produced by the battery exceeds the threshold.

11. The safety circuit of claim 9, wherein the baseline value is substantially lower than the initial value.

12. The safety circuit of claim 11, wherein the baseline value is substantially 0 volts.

13. The safety circuit of claim 9, further comprising a noise filter operatively associated with the reset circuit so that noise is not confused as the reset signal.

14. The safety circuit of claim 9, wherein the reset circuit issues the reset signal in response to a connect signal received from an electronic device holding the battery.

15. The safety circuit of claim 14, wherein the connect signal is a signal that accords with a Universal Serial Bus specification.

16. The safety circuit of claim 9, further comprising negative voltage circuit coupled to input on the first comparator, the negative voltage circuit providing protection against a backwards-installed battery.