Short circuit protection for a portable device powered by a battery pack having undervoltage protection

Patent metadata

Field	Value
Publication number	US-9543772-B2
Application number	US-201414465045-A
Country	US
Kind code	B2
Filing date	Aug 21, 2014
Priority date	Aug 21, 2014
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

A portable device includes set of charger contacts and a set of battery contacts. The battery contacts mate with corresponding contacts of a battery pack used to power the portable device, and the charger contacts allow charging of the battery pack while connected to the portable device. The battery pack includes an undervoltage protection circuit that opens when an undervoltage condition occurs across the battery pack contacts. The portable device further includes short circuit protection element connected between corresponding contacts of the set of battery contacts and the set of charger contacts that, upon a short circuit condition occurring at the charger contacts, prevents the undervoltage protection circuit from tripping and opening.

First claim

We claim:

1. A portable device, comprising:
a set of battery contacts including a positive battery contact and a negative battery contact;
a set of charger contacts including a positive charger contact corresponding to the positive battery contact and defining a first pair of corresponding contacts, a negative charger contact corresponding to the negative battery contact and defining a second pair of corresponding contacts; and
a short circuit protection element comprising a transistor switch circuit electrically coupled between a charger contact and a battery contact in at least one pair of the first and second pairs of corresponding contacts, wherein the transistor switch circuit comprises:
a transistor coupled between the at least one pair of the first and second pairs of corresponding contacts;
a diode and a resistor each disposed in parallel with the transistor; and
a comparator circuit that turns the transistor on when the portable device is coupled to a charger based on voltage applied by the charger across the positive and negative charging contacts and maintains the transistor turned off otherwise.

2. The portable device of claim 1 , wherein the set of battery contacts are disposed in a battery compartment of the portable device.

3. The portable device of claim 1 , wherein the each contact of the set of charger contacts are disposed on an external surface of the portable device.

4. The portable device of claim 3 , wherein each contact of the set of charger contacts comprises a flat surface that is coplanar to the external surface of the portable device.

5. The portable device of claim 1 , further comprising device circuitry coupled between the positive and negative battery contacts.

6. A portable device system, comprising:
a portable device having a battery interface including a set of battery contacts having a positive battery contact and a negative battery contact, a set of charger contacts having a positive charger contact corresponding to the positive battery contact and defining a first pair of corresponding contacts, a negative charger contact corresponding to the negative battery contact and defining a second pair of corresponding contacts, and a short circuit protection element comprising a polymeric positive temperature coefficient device electrically coupled between a charger contact and a battery contact in at least one pair of the first and second pairs of corresponding contacts; and
a battery pack configured to be coupled to the battery contacts of the portable device including at least one battery cell and an undervoltage protection circuit which opens a switch in series with the at least one battery cell in response to a load that would cause a voltage of the at least one battery cell to fall below an undervoltage threshold, and wherein
the short circuit protection element comprising the polymeric positive temperature coefficient device of the portable device has an activation time that is less than an activation time of the undervoltage protection circuit of the battery pack.

7. A portable device system, comprising:
a portable device having a battery interface including a set of battery contacts having a positive battery contact and a negative battery contact, a set of charger contacts having a positive charger contact corresponding to the positive battery contact and defining a first pair of corresponding contacts, a negative charger contact corresponding to the negative battery contact and defining a second pair of corresponding contacts, and a short circuit protection element comprising a transistor switch electrically coupled between a charger contact and a battery contact in at least one pair of the first and second pairs of corresponding contacts; and
a battery pack configured to be coupled to the battery contacts of the portable device including at least one battery cell and an undervoltage protection circuit which opens a switch in series with the at least one battery cell in response to a load that would cause a voltage of the at least one battery cell to fall below an undervoltage threshold; and
wherein the short circuit protection element comprising the transistor switch circuit comprises:
a transistor coupled between the at least one pair of the first and second pairs of corresponding contacts;
a diode and a resistor each disposed in parallel with the transistor; and
a comparator circuit that turns the transistor on when the portable device is coupled to a charger based on voltage applied by the charger across the positive and negative charger contacts and maintains the transistor turned off otherwise.

8. The portable device system of claim 7 , wherein the each contact of the set of charger contacts are disposed on an external surface of the portable device.

9. A portable two-way radio device, comprising:
a battery compartment configured to accept a battery pack having an undervoltage protection circuit;
a set of battery contacts in the battery compartment having a positive battery contact and a negative battery contact;
a set of charger contacts disposed on an external surface of the portable two-way radio device and having a positive charger contact corresponding to the positive battery contact and defining a first pair of corresponding contacts, a negative charger contact corresponding to the negative battery contact and defining a second pair of corresponding contacts; and
a short circuit protection element electrically coupled between a charger contact and a battery contact in at least one pair of the first and second pairs of corresponding contacts, wherein the short circuit protection element prevents the undervoltage protection circuit in the battery pack from opening in the event of a short circuit condition between the positive charger contact and the negative charger contact.

10. The portable two-way radio device of claim 9 , wherein the short circuit protection element is a polymeric positive temperature coefficient device.

11. The portable two-way radio device of claim 9 , wherein the short circuit protection element is disposed between the positive charger contact and the positive battery contact.

Assignees

• Motorola Solutions Inc
• Motorola Solutions Inc

Inventors

• Henry David
• Avanic Branko L
• Phang Wayne M

Classifications

• H02J7/731 Primary

  specially adapted for holding portable devices containing batteries (H02J7/751 takes precedence) · CPC title

• H02J7/0044 Primary

  Electricity · mapped topic

• H02H7/18 Primary

  for batteries; for accumulators · CPC title