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

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.

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.

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.